Electrical Failure Analysis for fire & incident investigations with over 400 illustrations
Dr. Marcus O. Durham, PE, CFEI, CVFI Dr. Robert A. Durham, PE, CFEI, CVFI Rosemary Durham, CFEI, CVFI Jason Coffin, CFEI, CVFI
THEWAY Corp.
PO Box 33124 Tulsa, OK 74153 918-496-8709 www.ThewayCorp.com
Edition: 110511
©Copyright 2009 - 2011 – All rights reserved.
Electrical Failure Analysis for fire & incident investigations investigations with over 400 illustrations
Contact: THEWAY Corp. P.O. Box 33124 Tulsa, OK 74153 918-496-8709 www.ThewayCorp.com
[email protected]
Editor: Marcus O. Durham Cover Design: Marcus O. Durham Printed in United States of America First printing by Dream Point Publishers, September 20 10
Library of Congress Control Number ISBN:
Copyright 2009 - 2011 by Marcus O. Durham, Theway Corp. All rights reserved under International Copyright Law. Co ntents and/or cover may not be reproduced in whole or in part in any form without the express written consent o f the Publisher.
ABLE OF C ONTENTS ONTENTS T
Table of Contents ................................................................................................. 3 Preface Preface .......................... ........................................ ............................ ............................. ............................. ............................ ............................ ................. ... 9 0.1 Overview Overview ........................... .......................................... ............................ ........................... ............................ ........................... .............9 Chapter 1 - Fundamentals ................................................................................... 11 1.1 Introductio Introduction n ............................ .......................................... ............................ ............................ ............................ .................... ...... 11 1.2 It’s All About 3’s ............................ .......................................... ............................ ............................ ......................... ........... 12 1.3 Measure Measure ........................... ......................................... ............................ ............................ ............................ ........................... ............. 12 1.4 Calculate Calculate ........................... .......................................... ............................ ........................... ............................ ......................... ........... 12 1.5 Impedance Impedance ........................... .......................................... ............................. ............................ ............................ ...................... ........ 13 1.6 Recap ........................... ......................................... ............................ ............................. ............................. ............................ ................ 13 1.7 Wire purpose ........................................................................................ 14 1.8 Source of power ................................................................................... 14 1.9 Nominal voltages ......................... ............... ..................... ..................... ..................... ..................... ..................... .............. ... 15 1.10 Conductors ...................................................................................... 15 1.11 Review ........................... .......................................... ............................. ............................ ............................ ...................... ........ 16 Interlude – Analysis Analysis Team ............................ .......................................... ............................ ............................ ......................... ...........17 Chapter 2 - How it fails – Result of Failure ....................................................... 19 2.1 Introductio Introduction n ............................ .......................................... ............................ ............................ ............................ .................... ...... 19 2.2 Metals........................... ......................................... ............................ ............................. ............................. ............................ ................ 19 2.3 Electrical metal conditions ................................................................... 20 2.4 Failures Failures............................ .......................................... ............................ ............................ ............................ ........................... ............. 20 2.5 Sources of ignition ............................................................................... 21 2.6 Non-contact ignition .................... .......... ..................... ..................... ..................... ..................... ..................... .............. ... 22 2.7 An Illustration Illustration ............................ ........................................... ............................. ............................ ............................ ................ 22 2.8 Debunking arc-mapping myths ............................................................ 23 2.9 Fault Forms ............................ .......................................... ............................ ............................ ............................ .................... ...... 24 2.10 Heat transfer .................................................................................... 24 2.11 Temperature and power ................................................................... 25 2.12 Fire .......................... ........................................ ............................ ............................. ............................. ............................ ................ 25 2.13 Review ........................... .......................................... ............................. ............................ ............................ ...................... ........ 25 2.14 Bibliography – Illustrations ............................................................. 26 Chapter 3 – Why it Fails - Cause of Failure ....................................................... 27 3.1 Introductio Introduction n ............................ .......................................... ............................ ............................ ............................ .................... ...... 27 3.2 Why? Cause of failure .......................................................................... 27 3.3 Process Process ............................ .......................................... ............................ ............................ ............................ ........................... ............. 28 3.4 Physics Physics ............................ .......................................... ............................ ............................ ............................ ........................... ............. 28 3.5 Components of system ......................................................................... 29 3.6 Missteps Missteps ............................ ........................................... ............................ ........................... ............................ ......................... ........... 30 3.7 Deterioratio Deterioration n ............................ .......................................... ............................ ............................ ............................ .................. .... 30 3.8 Probability factors ................................................................................ 30 3.9 Outside influence ................................................................................. 31 3.10 Electrical measure ........................................................................... 31 3.11 Review ........................... .......................................... ............................. ............................ ............................ ...................... ........ 32 3.12 Bibliography - Illustrations ............................................................. 33 Chapter 4 – Heating Devices .............................................................................. 35 4.1 Introductio Introduction n ............................ .......................................... ............................ ............................ ............................ .................... ...... 35 4.2 Thermal cut-offs.................... .......... ..................... ..................... ..................... ..................... ..................... ..................... .......... 35 4.3 Fixed ............................ .......................................... ............................ ............................. ............................. ............................ ................ 36 4.3.1 Source Source ........................... ......................................... ............................ ............................ ............................ .................... ...... 36 4.3.2 Path ............................ ........................................... ............................. ............................ ............................ ...................... ........ 36 4.3.3 HVAC heaters ............................................................................ 37 4.3.4 Cooktop & Ovens ....................................................................... 37 4.3.5 Clothes dryers ............................................................................. 38 4.3.6 Recessed lights ........................................................................... 38 4.3.7 Fluorescent lights........................................................................ 39
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4.3.8 Enclosed lights ........................................................................... 39 4.4 Portable Portable........................... ......................................... ............................ ............................ ............................ ........................... ............. 40 4.4.1 Source & Path ............................................................................ 40 4.4.2 Ceramic and other heaters .......................................................... 40 4.4.3 Lamps ............................ .......................................... ............................ ............................ ............................ .................. .... 40 4.4.4 Kitchen appliances ..................................................................... 41 4.4.5 Microwave Microwave ............................ .......................................... ............................ ............................. ......................... .......... 41 4.4.6 Office appliances ....................................................................... 41 4.5 Handy .......................... ......................................... ............................. ............................ ............................ ............................ ................ 41 4.5.1 Source & Path ............................................................................ 41 4.5.2 Hair dryers ................................................................................. 42 4.5.3 Hair irons ............................ .......................................... ............................ ............................ ........................... ............. 42 4.5.4 Clothes irons .............................................................................. 42 4.5.5 Tools ............................ .......................................... ............................ ............................ ............................ .................... ...... 42 4.5.6 Battery chargers ......................................................................... 43 4.6 Review............................ .......................................... ............................ ............................ ............................ ........................... ............. 43 Chapter 5 – Cooling & Other Devices ............................................................... 47 5.1 Introduction ......................................................................................... 47 5.2 Common risks................. risks............................... ............................ ............................ ............................ ........................... ............. 47 5.3 Cooling ........................... ......................................... ............................ ............................ ............................ ........................... ............. 48 5.4 Fan ........................... ......................................... ............................ ............................ ............................ ............................ .................... ...... 48 5.5 Water ........................... .......................................... ............................. ............................ ............................ ............................ ................ 49 5.6 Class 2 power supplies ........................................................................ 49 5.7 Electronics Electronics .......................... ......................................... ............................. ............................ ............................ ...................... ........ 50 5.8 Review............................ .......................................... ............................ ............................ ............................ ........................... ............. 50 Chapter 6 – Protection Protection ........................... ......................................... ............................ ............................. ............................. ................. ... 53 6.1 Introduction ......................................................................................... 53 6.2 Current Current ............................ .......................................... ............................ ............................ ............................ ........................... ............. 53 6.3 Voltage Voltage ........................... ......................................... ............................ ............................ ............................ ........................... ............. 53 6.4 GFCI............................ ........................................... ............................. ............................ ............................ ............................ ................ 54 6.5 AFCI............................ ........................................... ............................. ............................ ............................ ............................ ................ 54 6.6 Surge Protection Systems .................................................................... 54 6.7 True UPS ............................ ........................................... ............................. ............................ ............................ ...................... ........ 55 6.8 Battery Back-up UPS .......................................................................... 55 6.9 Surge suppressors ................................................................................ 55 6.10 Power strips .......................... ......................................... ............................. ............................ ............................ ................ 56 6.11 Protected power strips ..................................................................... 56 6.12 Caveats - U/L .................................................................................. 56 6.13 Extension cords.............. cords............................ ............................. ............................. ............................ ...................... ........ 56 6.14 Review ........................... .......................................... ............................. ............................ ............................ ...................... ........ 56 Chapter 7 – Grounding Grounding ............................ ........................................... ............................. ............................ ............................ ................ 59 7.1 Introduction ......................................................................................... 59 7.2 Investigator perspective ....................................................................... 59 7.3 3-in-1 3-in-1 ........................... .......................................... ............................. ............................ ............................ ............................ ................ 60 7.4 Grounding system ................................................................................ 60 7.5 Neutral .................... .......... ..................... ..................... ..................... ..................... ..................... ..................... ..................... .............. ... 61 7.6 Stray ............................ ........................................... ............................. ............................ ............................ ............................ ................ 61 7.7 Stray 120/240V .................................................................................... 61 7.8 Ground differences .............................................................................. 62 7.9 Grounding electrode ............................................................................ 62 7.10 Ground values ................................................................................. 62 7.11 Illustration – circulating current ..................................................... 63 7.12 How much is too much? ................................................................. 64 7.13 Measurement .................................................................................. 64 7.14 Grounding & lightning ................................................................... 65 7.15 Sum it up ........................ ....................................... ............................. ............................ ............................ ...................... ........ 65 7.16 Review ........................... .......................................... ............................. ............................ ............................ ...................... ........ 65 7.17 Bibliography - Illustrations .................... ......... ..................... ..................... ..................... ................... ......... 66 Chapter 8 – Codes & Law...................... Law.................................... ............................ ............................. ............................. ................. ... 67 8.1 Introduction ......................................................................................... 67
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8.2 National Electrical Code .................. ..................... .......... ..................... ..................... ..................... .......... 67 8.3 Jurisdiction Jurisdiction .......................... ......................................... ............................. ............................ ............................ ...................... ........ 68 8.4 National Electrical Safety Code ..................... .......... ..................... ..................... ..................... ................. ....... 68 8.5 State Law ............................ ........................................... ............................. ............................ ............................ ...................... ........69 8.6 Importance Importance .......................... ......................................... ............................. ............................ ............................ ...................... ........ 69 8.7 IEEE 142 ........................... .......................................... ............................ ........................... ............................ ......................... ........... 69 8.8 NFPA 780 ............... ..................... ........... ..................... ..................... ..................... ..................... ..................... .............. ... 70 8.9 NFPA 921 ............... ..................... ........... ..................... ..................... ..................... ..................... ..................... .............. ... 70 8.10 Professional responsibility .............................................................. 71 8.11 Review ........................... .......................................... ............................. ............................ ............................ ...................... ........ 71 Chapter 9 – Electric and Communication Utilities ............................................. 73 9.1 Introductio Introduction n ............................ .......................................... ............................ ............................ ............................ .................... ...... 73 9.2 Electric Electric utility....................................... ..................................................... ............................ ............................ .................... ...... 73 9.3 Communications .................................................................................. 74 9.4 Radio & Television .............................................................................. 74 9.5 CATV........................... ......................................... ............................ ............................. ............................. ............................ ................ 75 9.6 Network powered broadband ..................... .......... ...................... ..................... ..................... ..................... .......... 75 9.7 Intersystem Bonding ............................................................................ 76 9.8 Review ............................ .......................................... ............................ ............................ ............................ ........................... ............. 77 Chapter 10 – Lightning........ Lightning...................... ............................. ............................. ............................ ............................ ...................... ........ 79 10.1 Introduction ..................................................................................... 79 10.2 Differential potential ....................................................................... 79 10.3 Lightning transients ......................................................................... 79 10.4 Strokes Strokes............................ ........................................... ............................. ............................ ............................ ...................... ........ 80 10.5 Control Control ........................... .......................................... ............................. ............................ ............................ ...................... ........ 80 10.6 Ground Ground ........................... .......................................... ............................. ............................ ............................ ...................... ........ 81 10.7 Bond ........................... ......................................... ............................ ............................ ............................ ........................... ............. 81 10.8 Errors & omissions .......................................................................... 81 10.8.1 Clear air and end poles........................................................... 81 10.8.2 Poor ground electrode ............................................................ 82 10.8.3 Rebar............................ ........................................... ............................. ............................ ............................ ................ 82 10.8.4 Gas pipe ............................ .......................................... ............................ ............................ ......................... ...........82 10.8.5 Satellite dish & cable ............................................................. 82 10.9 Grounding & lightning .................................................................... 83 10.1 lightning Report .............................................................................. 83 Chapter 11 – Artifact identification .................................................................... 85 11.1 Introduction ..................................................................................... 85 11.2 First ............................ .......................................... ............................ ............................ ............................ ........................... ............. 85 11.3 Sleuth ........................... .......................................... ............................ ........................... ............................ ......................... ........... 85 11.4 Corporate memory........................................................................... 86 11.5 Legwork Legwork ............................ .......................................... ............................ ............................ ............................ .................... ...... 86 11.6 Exemplar Exemplar ........................... ......................................... ............................ ............................ ............................ .................... ...... 86 11.7 Team........................... ......................................... ............................ ............................ ............................ ........................... ............. 86 Chapter 12 – User Warnings .............................................................................. 87 12.1 Introduction ..................................................................................... 87 12.2 Warnings Warnings ........................... ......................................... ............................ ............................ ............................ .................... ...... 87 Chapter 13 – Safety Safety ........................... .......................................... ............................. ............................ ............................ ...................... ........ 89 13.1 Introduction ..................................................................................... 89 13.2 Personal Protection Equipment ....................................................... 89 13.3 Scene evaluation ..................... .......... ..................... .................... ..................... ..................... ..................... ................ ..... 90 13.4 Lockout / tagout .............................................................................. 90 Chapter 14 – Ethics Ethics ........................... .......................................... ............................. ............................ ............................ ...................... ........ 91 14.1 Introduction ..................................................................................... 91 14.2 Morality Morality .......................... ......................................... ............................. ............................ ............................ ...................... ........ 91 14.3 Ethics vs law ................................................................................... 92 14.4 Client ............................ ........................................... ............................ ........................... ............................ ......................... ........... 93 14.5 Predilection Predilection ........................... .......................................... ............................. ............................ ............................ ................ 94 14.6 Support Support ........................... .......................................... ............................. ............................ ............................ ...................... ........ 94 14.7 Public and private ............................................................................ 95
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14.8 Rules ............................ .......................................... ............................ ............................ ............................ ......................... ........... 95 14.9 Resolution Resolution ........................... ......................................... ............................ ............................. ............................. ................. ... 96 14.10 Authors Authors .......................... ......................................... ............................. ............................ ............................ ...................... ........ 96 14.11 Bibliography – illustrations illustrations ............................ .......................................... ............................ .................. .... 96 Chapter 15 – Practices & Procedures ................................................................. 97 15.1 Introduction .................................................................................... 97 15.2 Economics Economics ............................ ........................................... ............................. ............................ ............................ ................ 97 15.3 Scientific method ............................................................................ 98 15.4 Fire departments ............................................................................. 98 15.5 Initial identifier ............................................................................... 99 15.6 Origin & cause .............................................................................. 100 15.7 Engineers Engineers ............................ .......................................... ............................ ............................ ............................ ................ .. 100 15.8 The rest of the story ...................................................................... 101 Chapter 16 – Water Impact .............................................................................. 103 16.1 Introduction .................................................................................. 103 16.2 3-in-1 failure modes ...................................................................... 103 16.3 Conducting..... Conducting................... ............................ ............................ ............................ ............................. ....................... ........ 103 16.4 Corrosion Corrosion ............................ .......................................... ............................ ............................ ............................ ................ .. 103 16.5 Deposition Deposition........................... ......................................... ............................ ............................. ............................. ................ 103 16.6 Manifestation ................................................................................ 104 16.7 Migration Migration ............................ .......................................... ............................ ............................ ............................ ................ .. 104 16.8 Mitigation Mitigation ........................... ......................................... ............................ ............................. ............................. ................ 105 16.9 Machination .................................................................................. 105 16.10 Review ........................... .......................................... ............................. ............................ ............................ .................... ...... 105 Chapter 17 – Petrochemicals ........................................................................... 107 17.1 Introduction .................................................................................. 107 17.1 Units ............................ .......................................... ............................ ............................ ............................ ....................... ......... 107 17.2 Properties Properties ............................ .......................................... ............................ ............................ ............................ ................ .. 107 17.3 Conversions .................................................................................. 108 17.4 UL flammability rating ................................................................. 108 17.5 Electrical fault and flammability .................................................. 109 17.6 Heat release rate ............................................................................ 109 17.7 Codes ........................... ......................................... ............................ ............................ ............................ ....................... ......... 110 17.8 National Fuel Gas Code ..................... .......... ..................... ..................... ..................... ..................... ............. 111 17.9 Regulations Regulations ........................... .......................................... ............................. ............................ ........................... ............. 111 17.10 Analysis Analysis ............................ .......................................... ............................ ............................ ............................ .................. .... 112 Chapter 18 – Energy Analysis - Fire Movement and Energy Transport .......... 113 18.1 Introduction .................................................................................. 113 18.2 Energy.............. Energy............................ ............................. ............................. ............................ ............................ .................... ...... 113 18.3 Units ............................ .......................................... ............................ ............................ ............................ ....................... ......... 114 18.4 .......................................... ............................ ............................ .................. .... 114 It’s All About 3’s ............................ 18.5 Distance sidebar ............................................................................ 114 18.6 Energy - Measure .......................................................................... 115 18.7 Energy - Calculate ........................................................................ 115 18.8 Energy - Review ........................................................................... 115 18.9 Transport - Measure ...................................................................... 116 18.10 Transport - Calculate .................................................................... 116 18.11 Transport - Impedance .................................................................. 117 18.12 Transport - Review ....................................................................... 117 18.1 Temperature .................................................................................. 118 18.2 Ignition temperatures .................................................................... 119 18.3 Plumes ........................... .......................................... ............................. ............................ ............................ .................... ...... 119 18.4 A thing called entropy .................................................................. 119 18.5 Realms of energy .......................................................................... 120 18.6 Review ........................... .......................................... ............................. ............................ ............................ .................... ...... 120 Chapter 19 – Biological Effects ........................................................................ 123 19.1 Introduction .................................................................................. 123 19.2 Routes ............................ ........................................... ............................. ............................ ............................ .................... ...... 123 19.3 Electrical / Biological Research .................................................... 123 19.4 Some Players ................................................................................ 124
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19.5 Effect of Shock .............................................................................. 124 19.6 .......................................... ............................ ............................ ............................ ................ .. 125 It’s Threes............................ 19.7 ......................................... ............................ ......................... ........... 125 What’s the Difference? ........................... 19.8 Code Basis? ................................................................................... 126 19.9 Stray Current ................................................................................. 127 19.10 Electromagnetic Energy ................................................................ 127 19.11 Summary - It’s Just Physics .......................... ........................................ ............................ .................. .... 128 19.12 Bibliography - Illustrations ...................... ........... ..................... ..................... ..................... ............... ..... 128 Chapter 20 – Projects Projects ........................... ......................................... ............................ ............................ ............................ .................. .... 129 20.1 Introduction ................................................................................... 129 Chapter 21 – Plates – electrical failure photos .................................................. 131 21.1 Introduction ................................................................................... 131 Authors Authors ............................ .......................................... ............................ ............................ ............................ ............................ ......................... ........... 145 Dr. Marcus O. Durham, PE, CFEI, CVFI .................................................... 145 Dr. Robert A. Durham, PE, CFEI, CVFI ..................................................... 145 Rosemary Durham, CFEI, CVFI ................................................................. 146 Jason A. Coffin, CFEI, CVFI ...................................................................... 147 Supplementa Supplementall ............................ .......................................... ............................ ............................ ............................ ............................. ................. 149 22.1 Electrical Failure Questions – initial initial ........................... ......................................... ................ .. 149 22.2 Electrical Failure Questions – follow-up .................... ......... ..................... ................. ....... 150 22.3 Electrical Shock Survey ................................................................ 151 22.4 Evaluation Form - electrical failure analysis ................... .............. ........... ... 153 finis........................... ......................................... ............................ ............................ ............................ ............................ ............................ .................. .... 155
REFACE P REFACE 0.1
OVERVIEW
The book is structured for anyone working in the failure analysis industry. The course is particularly designed for individuals that encounter electrical systems in the process of incident investigations. This includes engineers, technicians, investigators, insurance, legal, supervisors, and staff. There is enough technical information that any investigator will benefit from the material, illustrations, and explanations. The book is not intended to make the user an electrical expert, but to broaden the investigator’s insight into electrical systems.
There are over 400 illustarations. The majority are photos of actual incidents we have investigated. Other photos are of events we have created in our research and are used as illustrations and aids. There are numerous diagrams to document the discussion. The book has purposefully limited the use of equations and math to make it more accessible. That does not limit the technical value and discussion. Only one chapter on Energy Transport is heavily structured with math to illustrate the thermodynamic engineering principles. That material can be bypassed by nonengineers. At the completion of the book and short course, the participant will understand the components of and know how to look at failures, particularly as related to electrical. This investigation will will involve considerations of the Codes and Standards. As members of several Standards organizations, we can assure you that issues addressed in these references are only there because someone had a problem. The discussion will further involve the relationship between investigators, engineers, and legal, as well as the role of public and private sector processes. In addition to a book structured for electrical failures, there are hands-on components and illustrations. There are numerous plates of electrical failures that we have created in our research. The creation assures the analysis and description is appropriate. A field exercise will be conducted to see actual equipment and failures. There will be problem solving individually and with a team. The book has hundreds of color photographs. However, printing cost of color is expensive. Bring your computer. The entire book, in color, can be downloaded for personal access during discussions. Enjoy and good learning!
HAPTER 1 - F UNDAMENTALS UNDAMENTALS C HAPTER 1.1
I NTRODUCTION NTRODUCTION
Electrical power is the primary form of energy in residences and business. It is commonly used, but its functions are seldom considered. c onsidered. Electrical systems receive very little attention in proportion to their impact; moreover, most operations are critically dependent on electrical energy. Whether for lighting, heating, motors, computers or environmental systems, electricity has become the most used and flexible energy form.
$ universal engineering symbol
The major reasons that study of electrical system is shunned are three fold. The first reason is fear fear of the perceived perceived hazards associated associated with electricity. The second obstacle is a lack of of understanding understanding of the fundamental theory. theory. The third hurdle is the fact that electrical concepts must be explained explained by nebulous nebulous models. Electricity defies the normal normal senses. One cannot see, hear, taste, smell , or touch electricity without significant hazard. A good grasp and working knowledge of the electrical fundamentals can, nevertheless, be obtained without being a graduate electrical engineer. This book is presented in a form designed to assist future quick reference, as well as to provide a background for understanding electrical electrical phenomena.
Hear no evil, See no evil, Speak no evil
Electricity is a convenient form to transfer energy. Seldom is electrical energy generated and used directly. On the contrary, electrical systems convert an available energy source such as gas, coal, hydro, nuclear, wind, or solar to electrical energy. The generated electricity is then conveniently transferred to a load center. The devices at the load center convert the electrical energy back to another useful energy form such as light, heat, or mechanical motion. A generic electrical system covers equipment from a generator or power supply through controls to a motor or load.
GENERATOR
TRANSFORMER
METER
CONTROLLER
MOTOR
Understanding electricity
This book does not specifically address the transmission and distribution of electrically energy. Rather, the concepts covered are applied to the top of the power pole to the the bottom of the basement. basement. Since every electrical power circuit has the same form, the concepts discussed are applicable to any situation where electric electric energy is used. The items of discussion discussion will be basic terminology, terminology, application, and failure considerations. considerations.
$, t, quality engineering trade-offs
In addition to technology, the design and installation of any electrical system must consider three major items - safety, environment, and cost. In the design, manufacture, and installation of any item there are tradeoffs to achieve a particular dollar, time, or quality value. Failures, then, are a result of poor quality, misuse, or abuse of the product. 3-D: a triad example
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I T ALL ABOUT 3’ S ’ S A T’
Electrical systems, as all physical systems, operate based on the Trinity or Triad Principle [1] which states: Any item than than can be uniquely identified can be further further explained by three components.
The necessary terms for an electrical system can be identified using this grouping of three quantities. If a discussion of a system has either more or fewer items, it is either a combination of unique terms, or an inadequately explained or inadequately defined system.
Pressure is like voltage
1.3
EASURE M EASURE
Only three items can be measured in any energy system. All other components are calculated from these. The measured components are pressure (potential), (potential), flow flow (transfer (transfer rate), and time. It follows, then, that only three items can be measured in an electrical energy system. Flow rate is like current
Parameter ter Symbol V I t
Voltage Current Time
Units nits Volts Amps seconds
What potential flow rate duration
3in 3 measures in 1 term
Voltage (V) - measured as Volts - is the potential force or pressure in a circuit. It exists whether anything is connected or not. Voltage is measured across, or as the difference between, two points. points. Voltage is similar to pounds per square inch (psi) on a water line. Current (I) - measured as Amps - is the rate or quantity of flow through a path. Current can be measured only if a load or fault is connected and operating. The measure for current is an Amp, which is a quantity of electrons per second. Current is similar to gallons gallons per minute on a water line. Time event (t) - measured in seconds - is the elapsed time between events. The reciprocal of time is the frequency frequency (f), whici is measured in in oscillations per second.
The three measurements combine in one term to produce energy (W ). ). Energy is the work or activity performed due to force. It is the common measure between electrical, mechanical, and chemical systems.
Power multiply
1.4
C ALCULATE
From these three measured variables, three things can be calculated. All electrical relationships can be derived from the three measured terms voltage current, and time. Since the terms are unlike, you cannot add or subtract. The only thing left to do, then, is to multiply and divide. Power (S) - expressed in Volt-Amps - is the product of voltage and current. Power is energy or work work that occurs over over some period of time. time. The asterisk simply notes a time change on the current. Impedance divide
Impedance (Z) - expressed in Ohms - is the ratio of voltage to current (Volts per Amp). Impedance is the the opposition opposition to current flow. The relationship is called Ohm’s Law.
Chapter 1
Fundamentals
13
Delay (t d d ) - is the difference is the time between voltage and current. It may be expressed in seconds or in angular angular terms. It is the phase phase shift between voltage being at a maximum and current being at a maximum. In power systems it is called power factor. It is the differential that arises in the Calculus.
Parameter ter Symbol Impedance Z Power S Delay td or
Units nits
What Ohms (Ω) ratio VoltAmps product seconds difference
EXAMPLES Ex 1.4-1
Given: 120 Volts and 10 Amps. What is the impedance?
Ex 1.4-2
Given: 120 Volts and 10 Amps. What is the power?
1.5
Wire corresponds to pipe
I MPEDANCE MPEDANCE
The opposition to current flow is called impedance. Impedance is a consequence of how electrical conductors are configured. As would be expected, there are three types of opposition. Resistance (R) is natural opposition of any conductor. Most conductors are wires made of copper or aluminum. Resistance is the friction of a conductor. A resistor converts electrical energy into mechanical energy in the form of heat. Inductance (L) results from a conductor being bent into a coil. A coil converts electrical energy into a magnet. A coil stores magnetic energy . Coils are used to make relays, motors, and transformers.
Resistor
Inductor – coil of wire
Dielectric Between plates
Plates are Al foil
Outer cover is plastic or metal
Alternating plates Alternating plates connect to terminals
Capacitance (C) results from two conductors being close to each other. A capacitor stores electrical energy . A capacitor can be used to smooth out the electrical energy. Capacitors are used in electronic circuits and to reduce the effect of time delay from a coil. In power circuits, capacitors are often used to assist with motor starting.
For each type of impedance, there is corresponding power consumption. These three combine to create the product Volt-Amp. The most familiar of the three is resistance which creates heat and the resulting power is Watts.
1.6
RECAP
Take a minute to review all the electrical terms. Remember they are always in groups of three. There are three things that can be measured – – voltage (pressure), current (flow rate), and time.
Capacitor
I mpedance Z Energy Resistance R mechanical Inductance L magnetic Capacitance C electric
There are three things that can be calculated – the ratio called impedance, the product called power, and the time delay. Finally there are three types of impedance or opposition – resistance makes heat, coils make magnets, and capacitors store and smooth electricity.
That is all there is
14 H 1
N
H 2
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Tha That is all there is. is. There is nothing else in the fundamentals of electricity.
1.7 W IRE IRE PURPOSE Electricity operates in a circuit. The energy starts at a point, travels through wires to a load that does some work, then returns back to the starting point. Wires have one of three purposes in the circuit. 120 V
120 V
240 V
Standard 120 / 240 V single-phase
Hot conductor carries the current to do the work. When looking at a standard receptacle, this is the short prong. It is the black wire and is connected to the brass color terminal. Neutral conductor is the return or common conductor that completes the current path back to the source. This is the wide prong on a 120V receptacle. It is the white wire and is connected to the silver color terminal. It is carrying current, but, under ideal circumstances, the voltage measured to ground is zero. Ground conductor is the safety path. It does not carry current during normal operations, but is a path for when things go wrong. This is the round prong. It is the green or bare wire and is connected to the green color terminal. All metal associated with the electrical system should be bonded to the ground in in a specified manner.
The neutral is connected to the ground system at one point, and one point only. This is typically in the main circuit breaker panel. If there is a panel and a sub-panel, the neutral in the second panel is not connected to ground. Doing so would make an energized path for current through the ground wiring. 120 / 240 V receptacle
The wires are typically grouped together in a cable. Permanently installed cable in a residence is often NM , or non-metallic sheath, cable. In common usage it may be referred to as Romex®, which is one brand. Appliance and extension cords may not have a ground conductor if there is no risk of a user touching metal that can be energized. These appliances are often referred to as “double insulated”.
1.8 S OURCE OURCE OF POWER All common electrical power is carried in conductors or wires. The arrangement of these wires determines the wire function. There are three fundamental power supplies. Direct current is generally associated with batteries. It delivers a steady, constant voltage. The color scheme used is a red wire for positive and a black wire for the negative. negative.
Standard 120, 15A receptacle
DC – mobile battery
Single-phase (1) is an electrical system that uses only two current carrying conductors. The supply is generally derived from a rotating machine that causes a cyclic voltage variation. The color scheme used is black for the hot side and white, or grey, for the neutral or common. The ground wire is identified with green. This is the most common type electrical system in residences and commercial installations. Three-phase (3) is a system that uses three current carrying conductors. The system is actually three single-phase systems connected together. The color scheme uses any color for the current carrying conductors, although black is the most common. The T he ground wire is still identified by green.
Chapter 1
1.9
Fundamentals
15
N OMINAL OMINAL VOLTAGES
There are many different system voltage levels. For failure analysis these can be separated into three categories – non-lethal , standard , and high energy . supplies less than than 50 volts. Electronics, portable, portable, Non-lethal is electrical supplies and mobile items are typically low voltage items. Common voltages are 3, 5, 9, 12, and 24 volts. Electric welders also operate in this voltage range. Although in a non-lethal system, the voltage is low and will not fatally injure someone, clearly the power systems can still have adequate energy to cause a fire, or to cause some injury.
DC – portable battery
Standard power voltages are typically 120 and 240 Volts, single-phase. This is by far the most common system. They predominate in both residences and commercial installations. A 240 Volt source has two hot conductors. A 120 Volt source uses one of the hot connectors and a neutral. A 240 Volt source is actually two 120 Volt sources with the neutral as the common connection. Because 120/240 Volt systems are so prevalent, they are a frequent source of injury and fire. These installations are covered by the National Electrica Electricall Code. Large energy voltages are anything higher than 240V. Large motors and loads operate at 277 Volts to 7,200 Volts, while utility lines operate between 12,470 Volts and 1,000,000 Volts. Obviously, these are potentially very dangerous to both people and property. However, because they are usually used only by authorized and trained individuals, failure is not as common as standard power systems. Inside facilities, these installations are covered by the National Electric Electric Code. Utility type systems are covered by the National Electrical Electrical Safety Code. Code.
Welder – low voltage but high current
1.10 C ONDUCTORS ONDUCTORS Paths for electricity can consist of simple metal, insulated metal, or a group of paths. Conductors are metal material that is used for an electrical path. The most common metal used for conductors in residential and commercial installations is copper. Aluminum is used outside of buildings and for large feeders in buildings. Gold and silver are used in electronics. Wire consists of a conductor covered with insulation. The components can be compared to the water circuit discussed earlier. The size or diameter of the conductor (pipe) determines how much current can safely flow. The thickness and type of insulation is like wall thickness of pipe and determines the voltage (pressure) rating. The length of the wire (pipe) causes a voltage or pressure reduction at the end.
Three-phase large power
Cable is simply more than one wire that is bundled together. It has an outer covering called a jacket.
Three-phase pole top
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Electrical Failure Analysis
1.11 REVIEW Electrical fundamentals always exist in groups of three. Measured values are
Cables – NM 12, NM 14, UF , UF w/ gnd
Ground Al #2 strand Hot Al #2 strand strand Neutral
Neutral
Ground Wire – stranded, solid
voltage current time
Calculated values are
Impedance (ratio) Power (product) Shift (time difference)
Impedance components are
resistance inductance capacitance
Purpose of a wire is
hot neutral ground
Source of power is
direct current single-phase three-phase
Nominal voltage voltage ranges ranges are
non-lethal standard large-energy
Conductors are used as
single conductor wire cable
Durham
NTERLUDE – ANALYSIS T EAM EAM I NTERLUDE After the electrical concepts and before failure analysis, it is worthwhile to consider how we get there. It is a team effort. Fire investigators look to where the fire originates – the area of origin – origin – and what was the source – cause – cause of ignition . Equipment systems that can fail are electrical, mechanical, or chemical. Engineers look at the systems to determine how the failure occurred and why. The next chapter will look at how electrical systems fail. Then we will look at why or the causes of failure. Engineers look at the mechanism of the failure. Subsequent chapters will look at specifics of particular equipment and systems. An alternative terminology provides differentiation in the scale of the investigation. Investigators look at the large scale – macro. Engineers look at the details – micro – micro. INVESTIGATOR cause of fire where - origin ignition source – electrical, mechanical, chemical macro knowledge of fire Codes – NFPA NFPA 921
ENGINEER cause of failure how system failed why system failed micro knowledge of systems Codes – NEC, NEC, NESC, IEEE
A later chapter will discuss the details of the investigation process.
HAPTER 2 - H OW OW IT FAILS – C HAPTER AILURE URE RESULT OF F AIL 2.1
NTRODUCTION I NTRODUCTION
The investigator determines the area of the origin of the fire and what caused the fire. The cause may be electrical, mechanical, or chemical. The engineer determines the cause of the failure of equipment, if there is a defect, and why the equipment failed. Sometimes there is an overlap on determination of what caused the fire. These chapters give insight into why things fail so there can be greater understanding as to what caused the fire. The first part is the way things fail. The next section is why things fail.
Investigators determine cause of fire fire what is source of ignition Engineers determine cause of failure failure how equipment fails why equipment failed
The discussion will not get into identifying specifics, since that is a very detailed process. Similarly, it will not get into the codes, standards, and regulations. Electrical Electrical activity is a common term for investigators to use when referring to failures that are associated with electrical systems. The term is generic and may refer to either a cause or result.
The presence of electrical activity implies that there is need for further investigation to ascertain whether the electrical system was an issue in the event and to ascertain why the activity was precipitated.
2.2
If you cannot fix it with a hammer, you have an electrical problem. -wry philosophy
M ETALS ETALS
Metals are a key item to investigate a fire. They tend to survive in some condition. Furthermore they hold and show the heat patterns. Steel and stainless steel are iron-based (ferrous) materials. Iron is not often used for an electrical conductor, but is used for enclosures. Steel is used in the core of motors and transformers. Ferrous materials are an adequate conductor that may contribute to an electrical related failure. Appliances and some tools have these materials. Structural members also have ferrous materials. Steels melt about 2600°F or higher; they survive most incidents. Mechanical strength, however, may be lost at much lower temperatures, resulting in structural failure.
Meta tall
°F
°C
Steel
2600
1427
Copper
1981
1082
Aluminum 1220
660
Copper is the predominant electrical material. It has a melting temperature of about 1980°F. It survives most fires in some form and is a primary indicator of electrical electrical involvement in the fire. Aluminum is the second most used electrical wire. Aluminum melts about 1220°F. It seldom survives a fire, but that fact can be used in analysis. Aluminum has several installation issues and the connections can cause a fire. Copper should not be connected to aluminum since a poor connection will result r esult and can cause a fire. Special provisions must be made when this type of connection connection is necessary.
The temperature values described are typical. Different alloys will have other properties.
Energized - generative
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E LECTRICAL LECTRICAL METAL CONDITIONS
Metals are clearly associated with fire both as a contributing cause and as an indicator. How the conductor was used at the time of the incident will determine the pattern or indication of failure. The three conditions for electrical fire relation are energized generative , energized result , and deenergized . The illustrative photos are from actual incidents we have investigated.
Energized - result
Energized generative generative includes electrical items that are the reason for the failure or fire. There are indicators that a wire is energized. Similarly there are patterns and results that show a wire or conductor may be the cause of the event. These are complex and must be evaluated in the context of all the other events, patterns, and information associated with the incident. When the components are the cause of the fire, they are often destroyed by the intense energy at the location of the incident. Therefore, there is very little published information and illustrations about the damaged items; however, adjacent parts may survive in some form. Identification comes about by the process of elimination. This is the part of the scientific method of gathering data, developing hypothesis and testing the hypothesis.
Non-energized
The most common indication is a divot in the metal conductor. There may be a corresponding bead where metal was deposited. If components are found that are the cause they will have this form. However, this form may exist and not be the cause. Energized result result includes electrical items that are energized at the time of the fire, but the damage is due to encroaching heat from the incident. There are resulting indicators that illustrate the wire was energized, but did not fail and cause the event. The most common indication is a bead of metal conductor with a clear line of demarcation. Non-energized Non-energized items cannot be an electrical cause of the failure or incident since there is no electrical energy. Nevertheless, the components are metal and will have distinctive patterns and can be used as an indicator for direction of progression and location of other sources. The most common indication is simply melting and flowing of the metal.
Insulation loss mechanical damage
Balls may be similar to beads, but witout the clear demarcation. Balls will tend to have bubbles from popping gas and impurities in the metal. Metal may be lost from pitting, but it will lack a clear divot. Each of the conditions – energized generative, energized result, and nonenergized – has characteristics and patterns to assist with the analysis. A major part of the process is elimination of other potential sources.
2.4
F AILURES
Failures of electrical systems and components are directly related to the three items that can be measured. Each of the three causes a unique type of failure. There are three ways an electrical system fails – insulation loss, connections , and transients .
Connection loose circuit breaker
Insulation loss causes a voltage breakdown failure. The loss of insulation allows current to take a path other than the preferred path down the wire. The resulting current can create heat.
Chapter 2
How It Fails
21
Loss of insulation can result from mechanical damage, inadequate material during manufacture, and electrical stress from over-voltage. Connections that are inadequate cause a current type failure. A poor connection causes a heat build-up which can ignite surrounding materials. Contaminants such as moisture can begin oxidization which increases the resistance of the connection. Oxidation products can make the connection appear to be tight.
Three common situations create inadequate connections. (1) Switch contacts can be misaligned, pitted, or too small. (2) Contaminants such as water, carbon, and debris can create an unintended path that will get hot. Debris may include damaged insulation. (3) Connectors that are loose get very hot.
Transient noise L-N
Warning: We have created fire with a connection that had a resistance as low as only 0.25 Ohms. That is very close to a solid connection. Transients or surges are time-related, very fast “noise” that gets injected onto the power system. Transients overload the system, cause localized heat, and can cause damage to the insulation.
Transients can be caused by switches, lightning, or intermittent connections. These are perhaps the most difficult to recognize since the situation may not exist for a long period of time and likely is not repeatable. Nevertheless, transients are extremely common events that occur every time any electrical item is energized.
Connection heating*
OURCES OF IGNITION 2.5 S OURCES Sources of ignition from electrical systems can be either from contact with energized metal or non-contact due to radiation. Contact ignition has three forms – connections – connections , sparks, and arcs. Connections cause power type heating. This is also called I 2 R heat failure because the power is equal to the square of the current (current x current) times the resistance. It is also called a high impedance failure because the impedance is greater than preferred. preferred.
The heat generated by this type failure increases with time, current, and the resistance. In this arrangement the temperature of the connection simply increases over time. As heat increases, the impedance of the connection can also increase, causing additional heat generation. Temperatures can easily exceed the ignition temperature of most combustibles. This is by far the most common cause of electrical ignition. Although it is not as dramatic as others such as an arc.
Spark particles flying
Sparks are the heated and luminous metal particles that are ejected through an insulating material such as air or wire insulation. Since these are projectiles, they can traverse a varied path. The particle will be well above the melting temperature of the metal. Although possible, sparks are an uncommon cause because of low power density and rapid cooling. Arcs are a short circuit through an insulation material, including air. An arc-flash can create temperature in excess of 35,000°F, a brilliant flash of light. An arc-blast, which is the result of the arc, can also create a pressure wave that can cause materials to fly and a loud noise. Copper expands 67,000 times during a conversion to vapor and shrapnel can travel at 1600 km/hr (700 mph).
Arc flash – 50A, 250V, 14AWG
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An arc at 240 V is equivalent to 2.4 MW or approximately 2.4 sticks of dynamite. Incidentally, this is also the heat released from a polyurethane sofa.
2.6
N ON ON -CONTACT IGNITION
Non-contact ignition requires a separate analysis and has unique properties. Radiation takes many forms but all are electromagnetic in nature. Radiation is derived from radar and microwaves as well as other high frequency radio transmitters. Radiation heats the molecules of matter through a medium such as air, air , without significantly affecting the air. Radiation heating in microwave*
Microwave ovens typically are heating water molecules. However, metal within the field will cause a disturbance and create extreme heat equivalent to a smelter. Note the microwave oven containing brick that is protecting the metal can. Ignition of most materials will occur if not protected from heat. In addition, I 2 R heating can create enough heat energy to ignite materials that are not in direct contact with the conductor. This is a form of convective heating.
LLUSTRATION 2.7 AN I LLUSTRATION Electric welding – arc, spark, heat*
electrode arc weld metal
weld pool base metal
Arc metal transfer divot
An electric arc-welder and mig-welder are excellent examples of an energized conductor and the various ways that a fire may be the cause or the result. The advantages of using a welder over other illustrations are reduced effects of char, the controllable current, and repeatable results. All three contact ignition conditions exist – connection – connection , sparks, and arc. Sparks do occur, and can ignite combustible materials if they are in the vicinity of a hot spark. By definition an arc is occurring, but there is not typically ignitable material in the area. The high current and contact between the electrode and the the metal cause substantial I 2 R heat. All three metal conditions exist – energized – energized cause , energized result , and de-energized . Like all other ignitions sources, the electrical activity is complex and must be evaluated in the context of all the other events, patterns, and information associated with the incident.
Energized cause, result, nonenergized*
Where the energized electrode strikes the grounded metal, the electrode metal is completely obliterated . There is no evidence of an electrode remaining. Therefore, it is not possible to say where the incident started on the electrode. Nevertheless, there are indications of the remaining items that do show involvement. An energized conductor will have a divot or cup at the place where metal was transferred. This is sometimes called a parting arc, which is redundant. By definition, all arcs are the result of parting contact points. Note the illustration for a welding electrode as well as the other photographs of actual incidents. incidents. An energized result will have a rounded bead or ball associated with the cooling. The two conductors may be welded together. There will be a distinct line of demarcation at the bead.
Non-energized result of heating*
Chapter 2
How It Fails
23
The result of a short circuit on stranded wire shows up as beading on individual conductors. This is the result of heating on the individual wires, rather than ambient heating. A non-energized result of heating will have characteristic pock marks, splatter, and the metal will not flow and join into a weld. The metal may also have indications of stretching. Once a conductor is severed, current ceases to flow in the separated component. That conductor is de-energized and no further electrical activity is possible; however, the energized electrode can continue to have further cause or results. Therefore, it is necessary to track the conductor to the fault farthest from the source to find the initial incident. Remember, just because an electrical conductor is energized and faults does not mean it is the cause of the incident.
Floating neutral created heat & corrosion
2.8 DEBUNKING ARC -MAPPING MYTHS
H1
Question: If a fault occurs in the breaker panel, can there be later faulting at a location downstream of the panel?
There is a significant issue to consider when looking at arcing. On a standard 120/240 Volt power supply, there are two sources. Each hot line or leg is separately energized. Therefore, one leg can be de-energized while the other continues to supply power and can be a cause of failure that is farther from the source.
H2
X Main Breaker
Question: Is the most electrical activity in the area of origin?
D
Some investigators less familiar with the underlying electrical principles attempt to look at all the arcing in an area. They assume the area of most arcing is in the area of orign.
X X
Au contraire. contraire. A fault may occur on a single conductor and trip the supply on that line. Other breakers are still energized and may display activity later in the incident. Warning: Arc-mapping only shows information about activity on a single conductor. Arc-mapping can only validly be used to show the farthest point on a particular circuit.
Arc mapping is another of those “ideas” that many in the industry have taken as gospel, based on a fragment of science, that has later been proven to be unscientific. We have seen very very bad decisions about origins, origins, based on mis-application of this concept. Unfortunately, Unfortunately, arson has been advocated when there was a simple electrical explanation. The concept has been so generally accepted, that it will cause tremors among some. Just because someone does it, does not make it right.
AtracingB – whichCfault occurred E F Arc first? Arc tracing – which fault (x) occurred first?
L1
L2
L3
Based strictly on the figures, the only thing known for sure is that “D” did not occur first, since another a nother fault is further down the line.
L5
X
D X
Arc-mapping has been so improperly misapplied and erroneously used to validate an area of orign that a different term should be used to trace the arcing on a circuit. Arc-tracing or some similar term should be used to identify a particular circuit activity.
L4
X X
X
X
A
B
C
E
F
Arc tracing – which fault (x) occurred first?
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F AULT F ORMS ORMS
Electric faults can follow three forms direct, breaking, and high impedance faults. A relatively low impedance, or direct , fault creates arcs across an insulating material (or air). These type faults generate intense localized heat, high temperature ejecta, and loss of material (divots) in conductors. These type faults are those most easily recognized, particularly by those less experienced in electrical failure. Direct fault – arc through char
Faults created by making or breaking an electrical connection, such as switching or pulling apart energized cable. These type faults have a very high frequency component and a resulting sudden increase in voltage. They can damage insulation, particularly in areas where electrical inductance is high, such as at a bend in wire. These are sometime referred to as “parting arcs”, though this is an unnecessarily limiting term. A relatively high impedance connection fault is a very frequent cause of fires. This type fault is common when electrical contacts misalign, or where insulation on cables is partially damaged, but not completely removed. A loose connection is actually a high impedance connection fault. This type fault results in localized heat that can easily exceed ignition temperature of common combustibles.
Bend in conduit creates higher inductance
1. The most dangerous characteristic of the high impedance type faults is that they draw current more consistent with a load than a short. Protection systems, such as fuses and circuit breakers, would not operate to prevent overheating from this type fault. 2. From our research a fault with an impedance as low as ½ Ω can cause temperatures to exceed 700°F. 3. Faults generating heat as low as 11 – 23 watts has been shown to create enough heat to initiate combustion. There are indications that the amount of power required may be even lower. Example: On a twelve volt circuit, such as on a vehicle or wall-wart power supply, a 23 watt fault would draw approximately two (2) amps. This is a much lower current draw than can be detected by simple fusing.
Risks: High impedance connection faults do not create an easily identifiable “arc”, and thus are not easy to identify visually. High resistance connection caused fire
Conduction Convection Radiation
Heat transfer – three vehicles
EAT TRANSFER 2.10 H EAT Once heat is generated, in order to have a fire, the heat must be transferred to other locations. Energy always transfers from a warmer source to a cooler place. There are three vehicles for heat transfer – conduction , convection , and radiation. These obviously are closely related to heat sources. Good electrical conductors tend to be good heat conductors. Conduction is heat transfer from one material to another by direct contact. Convection is heat transfer by fluid currents from one region to another. The fluids can be liquid, which gives better transfer, or gas, which gives less transfer.
Chapter 2
How It Fails
25
Radiation is the heat transferred by solids, liquids, and gases in the form of electromagnetic waves that occur due to elevated temperatures. No contact or circulation is required.
Note the illustration of the three vehicles of heat transfer. Conduction occurs in the handle due to direct contact. Convection occurs in the fluid due to the circulation between the hot and cold regions. Radiation occurs through air largely due to infrared waves. Heat propagates the results of a failure. Heat patterns and metal condition c ondition are used to ascertain the type of heat transfer and the source of the energy.
Heat patterns on stainless microwave
2.11 T EMPERATURE EMPERATURE AND POWER A failure is related to many components and can be expressed in many ways, all of which are related. The relationships will be simply stated without mathematical complications. A later chapter covers the mathematical treatise in detail, for those interested. Elevated temperature is often the first visible manifestation.
Ignition is dependent on the temperature.
Temperature is the environmental energy over the conversion inefficiency called entropy.
Energy over time is the power.
Power density is the concentration of power over an area.
Power is the product of the current squared and resistance.
Thermocouple temperature
From these relationships, there is clearly an interaction of electrical energy to temperature and a resulting potential for failure.
2.12 F IRE IRE For a fire to occur, there have traditionally been three requirements - fuel , ignition source, and oxidizer . Some sources modify the definition to involve a sustainable chemical reaction. Fuel is a combustible material that that provides energy. It will burn or rapidly oxidize. The result is a reduction to its base chemicals. Ignition is the process of initiating combustion or catching fire. It results in elevated temperature of the combustible material.
An oxidizer is a substance that allows combustion to take place. The most common oxidizer in standard combustion is oxygen. Oxygen is an element that combines with most elements, is essential for plant and animal respiration, and is required for nearly all combustion. It comprises about 21% of the air. Chlorine and other halogens are also rapid oxidizers.
2.13 REVIEW A failure can result in catastrophe, such as fire. There are numerous components to the cause of a failure. First is how items fail. Conditions are the following:
Seldom do systems have problems when only one component is improper. Failures and catastrophes are the result of multiple conditions.
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energized cause energized result de-energized
Failures are are the following:
insulation loss connections transients
Sources of ignition are are the following:
connections sparks arcs
Non-contact Non-contact ignition is radiation. Heat transfer transfer is by are the following:
conduction convection radiation
f ollowing: Fire requires the following:
combustible material ignition source oxygen
IBLIOGRAPHY – I LLUSTRATIONS LLUSTRATIONS 2.14 B IBLIOGRAPHY Select photos courtesy of following. following. Permission Per mission requested, pending response. Connections, http://www.flirthermography.com/imag http://www.flirthermography.com/images/gallery/SPLi_irA0716_0 es/gallery/SPLi_irA0716_005.jpg 05.jpg Microwave metal, Photo courtesy Rory Earnshaw, http://www.popsci.com/diy/articl http://www.popsci.com/diy/article/2003-09/smeltinge/2003-09/smelting-microwave microwave Welder, http://www.millerwelds.com/images/home-products-bg2.jpg Weld splatter, http://www.mig-welding.co.uk/gasless http://www.mig-welding.co.uk/gasless/gasless-weld.jpg /gasless-weld.jpg Weld through, http://www.mig-welding.co.uk/thin/dropple.jpg
HAPTER 3 – W HY HY IT F AILS C HAPTER AUSE USE OF F AILURE AILU RE C A 3.1
NTRODUCTION I NTRODUCTION
The previous chapter looked at how equipment fails and the contribution of this failure to a fire. This chapter will discuss why equipment fails. The how is more associated with the equipment while why is more related to the process of design, manufacture or use of the equipment.
Failure Analysis determine cause of failure failure how equipment fails why equipment failed
Seldom do systems have problems when only one component is improper. Failures and catastrophes catastrophes are the result of multiple conditions. conditions. But for one of the problems, there would not be a failure. As an example, a hair dryer may have a fault. There is no consequence until power is applied. It was not the electric power that caused the failure, but this was a necessary ingredient. Failure analysis must look at all the contributing factors to determine which is the crux of the problem.
Failures & catastrophes are the result of multiple conditions.
Often there are multiple contributions to the failure. The interaction of these different factors must be identified in order to determine the consequences of each.
3.2
W HY ? C AUSE OF FAILURE HY ? C FAILURE
There are three parties that may contribute to a failure – supply supply, product , and user . Each has a unique role and experience level. Therefore, the responsibility for segments will be different. Supply is used to describe the electrical system up to the point that the user has some action such as turning on a switch or plugging in an appliance. Supply has three levels – utility, – utility, building, and appliance. The supply then includes the utility as well as the electrical installer.
The utility operates under the National Electrical Electrical Safety Code (NESC) and is usually regulated by the state. The installer operates under the National Electrical Electrical Code (NEC) and is licensed by the state or local jurisdiction. If the utility, or utility contractor, performs work on the building, such as relocating a supply point, the utility is also the installer and must follow the NEC .
NESC – utility standard
Both industry standards have a similar charge for safety. NESC Article NESC Article 010 Purpose states “ The purpose of these rules is the practical safeguarding of persons during the installation, installation, operation, or maintenance of electric supply and communication lines and associated equipment. ” NEC Article 90.1 (A) Practical Safeguarding states “The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. ”
The Why of a supply failure is a result of problems with the installation, operation, or maintenance . Product is used to describe equipment and items whether on the supply side or the user side.
NEC – electrical standard
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The Why of a product failure is a result of defects in design, manufacturing , or distribution . User describes the person that employs the product and the supply. The user is not assumed to be knowledgeable in the supply or product design or manufacture. Why the user can cause a failure is through misuse, abuse, or neglect . Why – Cause of Failure !
Supply : installation, operation, maintenance Product: design, manufacture, distribution misuse, abuse, neglect User:
Switch contacts misaligned
3.3
P ROCESS ROCESS
Product defects are the result of design , manufacture, and distribution. Design is an inherent problem with the product, but it may be manifest only under certain circumstances. Manufacture is an occassional problem because of manufacturing tolerances. Distribution is the process of getting the product from the manufacture to the installer / user and involves storage and handling damage. Supply fails because of problems with the installation , operation , and maintenance .
Installation can be associated with the product, supply, or user. It will separated from those since a different party often makes installation of an appliance. Installation is often directed by industry standards to assure compliance with safe practices at the time.
Typical supply manual
Operation includes how the device is used. This would include things such as input power quality, ambient environmental conditions, and loads placed on the device. Maintenace is how the device is taken care of. This would include lubrication, cleaning, and repair. The user can cause a failure through misuse, abuse, or neglect . Misuse is improper application of the device. In essence misuse is applying the device in a way it was not intended. Abuse is damaging the device. Neglect is ignoring the device and allowing it to deteriorate.
There is clearly an interaction between the processes and their failure consequences. For example, neglect will impact maintenance, which may show a design or manufacturing defect. Hairdryer inlet blocked
3.4
HYSICS P HYSICS
Physics identifies the source of the scientific system that contributes to a failure. Physics are electrical , mechanical , and chemical systems. Each produces a thermal response because of the energy conversion from one form to another. The physics describes both a system and a type of failure. For example, an electrical system can fail because of mechanical and chemical effects.
Electrical, mechanical, chemical
Electrical Electrical systems involve the flow of electrons, magnetic effects, and optical sensing. Electrical is associated with wires, electro-magnetic radiation, and light. Electrical failure is because of loss of insulation (voltage effect) and poor connection (current effect) with time, or from transients.
Chapter 3
Why It Fails
29
Mechanical Mechanical systems involve fluid flow and physical items that can be touched. Mechanical systems include HVAC, plumbing, and machinery. Electrical systems can fail because of mechanical conditions. Chemical systems involve processes and material reactions. Chemical systems include hydrocarbons and plants. Electrical systems can fail because of chemical reactions. Thermal energy is a consequence of each of these physics processes and can be the result of any or all. Thermal energy is measured by temperature change.
Mechanical damage to cord
To make the analysis more interesting, mechanical, and chemical systems generally have electrical energy. Therefore, the separation between systems is very intertwined, and the interactions are subject to interpretation.
3.5
C OMPONENTS OMPONENTS OF SYSTEM
An electrical system consists of three networks - source, path, and feedback . Each of the networks has three elements. The source includes supply, return, and protection. The path includes conductors, switch, and connections . The feedback includes sensor, controls, controls, and load . Chemicals
SYSTEM supply Source return / stray protection conductors Path switch connection sensor Feedback controls load
The resulting system has nine components. Each component of the system is subject to electrical, mechanical, and or chemical effects. Furthermore, each can be be attributed to the product, supply, and/or user parties. Protection Switch Connect Supply Return
Thermal - something got hot
Sensor Controls
Load
Conductor
The source is the energy input. Supply problems include power quality such as voltage variation as well as transients. Return problems are alternate or stray paths including grounds. Protection is fuses, breakers, and surge systems. Protection problems include improper size and connection. Cable, phone, electric source
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The path is the route of the energy. It involves the conductors or wires. The switch is the device to break and control the path. The connections are the joints between different conductors. The problems with the path are predominantly associated with heating from poor connections and high resistance. The feedback is the control of the load. The sensor detects the condition to control, such as temperature, speed, or light. The controls are the circuits including electronics and relays that modulate the load. The load is the energy conversion output to the user. Load can be mechanical motion, heat, or light. Ground resistance > 25 Ω
3.6
M ISSTEPS ISSTEPS
In addition to the equipment and the physics, failure of an electrical system may be a consequence of missteps, misques, misques, and mistakes. mistakes. The three missteps are mis-size , mis-construction, and mis-material . Mis-size of conductors and protection can result in excessive current and resulting heat. Mis-construction Mis-construction will provide inappropriate paths for current and create voltage stress. Mis-material Mis-material is improper material for the application. For example, a low temperature insulation may melt when exposed to heat. 60A wire feeds two 60A breakers
3.7 DETERIORATION MIS-STEPS Mis-size Mis-construction Mis-material DETERIORATION Mechanical User Age Damage Use Wear Environment Application
Equipment and materials deteriorate with age, environment , and use. In addition, users can hasten deterioration by damage, wear , and application. Deterioration can eventually lead to failure and associated catatrophicconsequences. catatrophicconsequences. Deterioration and wear are normal result of age and use. Nevertheless, deterioration from old age should not result in ignition.
3.8 P ROBABILITY ROBABILITY FACTORS The probability of failure and resulting resulting fire depends depends on three three factors proximity to combustibles, cooling loss, and exposure time . This is a variation of the three requirements of a fire - fuel , ignition, and oxygen . Proximity to combustibles involves material properties, distance, and the area of exposure. Cooling loss implies barriers to conduction (heat sink), convection (circulation), and radiation (air flow). The barriers can be from blocked air paths or failure of fans. Lint build-up can block air flow and can be combustible. Exposure time indicates heat exposure that allows temperature to elevate to igntion.
As proximity decreases, cooling loss increases, and exposure time increases, the probability of failure increases. Actual TCO temp: 285F, wire rating: 221F
Chapter 3
3.9
Why It Fails
31
OUTSIDE INFLUENCE
Transients are one of the electrical areas that could precipitate failures. Transients that cause failure are frequently from an outside influence. The influence can be utility , weather , or through the earth. Each has a separate chapter devoted to the issue. Only an introduction is noted at this point. These outside influences are frequently ignored by some investigators as outside the realm. A quip heard is “You cannot subrogate against God or the utility which acts like god.” In essence, the comment implies no one is responsible. That simply reflects an incomplete understanding.
Microwave heat-sink and fan
If a new roof leaks, it is because of weather in the form of rain, which is an act of God. While God is responsible for the rain, the installer or manufacturer is responsible for the damage. Lightning is no different. One of our paper s was titled “Lightning Damage: Act of God or Act of Negligence?” Negligence?” The key key w ord is damage. As the paper illustrates, lightning and weather is an act of God, but the damage is an act of negligence. In virtually every instance of outside influence, the damage caused is because something was done improperly. In most cases it is noncompliance with an existing standard, code, or law. So, you can determine the cause and assign responsibility for damage. A few examples illustrate the issues. 1. Lightning in the area results in failure of flexible gas line. There are usually installation and manufacturing problems.
Generator refueled when hot
2. Power outage results in appliance failure and fire. There are usually code problems by the utility or installer. There may also be manufacturing deficiencies. 3. Someone is shocked and later there may be a fire. There is a code discrepancy by the installer, utility, or manufacturer. 4. Lightning storm results in appliance failure and perhaps fire. There is probable code incompliance by utility and installer. As an example, the Empire State building in New York City has been struck by lightning multiple times each year, yet it is undamaged by the intense energy, because the installation is proper. Note there are usually multiple streamers from the single stroke of lightning. The result is several individual strikes associated with a stroke. If there is a fire associated with conductors in earth, weather, and electricity, there is a probable non-compliance with codes and hence a responsibility for the damage.
LECTRICAL MEASURE 3.10 E LECTRICAL Numerous impact and effects of failure have been discussed. Regardless of the system, mechanism, or problem, electrical failures are the result of one of two electrical issues (voltage and current) and associated time. The issues are dependent on the only items that can be measured.
Loss of insulation is voltage related.
Poor connection is current related.
Controlled lightning*
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Transients and heat are time related. r elated.
That is all there is. There is nothing else to describe electrical failures. Failure should not cause fire!
3.11 REVIEW A failure can result in catastrophe, such as fire. There are numerous components to the cause of a failure. Why it fails is often associated with a personal action. Parties to failures are supply, product, and user. PARTIES Supply Product User Installation Design Misuse Operation Manufacturing Abuse Maintenance Distribution Neglect
Physics describes both a
system and a type of failure .
That’s all there is
electrical mechanical chemical
Thermal is a consequence of energy conversion of physics processes A system is comprised of three networks - source, path, and feedback. SYSTEM supply Source return / stray protection conductors Path switch connection sensor Feedback controls load
Missteps are
mis-size mis-construction mis-material
Deterioration Deterioration of mechanical occurs with DETERIORATION Mechanical User Age Damage Environment Wear Use Application
Lightning control
Probability of failure and resulting fire depends on three factors
combustibles proximity to combustibles cooling loss exposure time Electrical failure is related to the measures.
Loss of insulation is voltage related. Poor connection is current related.
Chapter 3
Why It Fails
33
Transients and heat are time related.
IBLIOGRAPHY - I LLUSTRATIONS LLUSTRATIONS 3.12 B IBLIOGRAPHY Select photos courtesy of following. Permission requested. 1. Lightning, http://turkish.wunderground.com/data http://turkish.wunderground.com/data/wximagenew/g/G /wximagenew/g/GrahamF/ rahamF/ 4.jpg
HAPTER 4 – H EATING EATING DEVICES C HAPTER 4.1
I NTRODUCTION NTRODUCTION
All electrical systems generate heat. Heating devices are electrical appliances and apparatus that use heat as a primary component of their function. Heating devices include space heaters, heating ventilation furnace, clothes dryers, hair dryers, hair irons, clothes irons, electric cook-tops, electric ovens, light fixtures, microwave ovens, and similar equipment. Clearly this is a common use of electrical energy. Heating devices can be broken into three categories based on how they are mounted or operated – fixed fixed , portable, and handy (hand operated). The heating units described above are noted by two major features: First they are electric powered and second they have an electric driven heat source. In many cases, there is a high temperature surface of a resistive heating element that can be involved. Risks: In addition to problems that happen with any electrical device, there are some that are particularly associated with heating devices. Any component of a system can fail. Every type of failure can occur.
Candle warmer
Where particular risks are noted, they are common conditions. Most if not all of the issues, we have personally observed.
4.2
HERMAL CUT -OFFS T HERMAL
The operating temperature of a device is generally controlled by a thermostat. In order to maintain a target temperature, the device increases or decreases power available to the heater element. The temperature limit for heating devices is generally controlled by a thermal cut-off (TCO) device, which is a combination temperature sensor and switch or fuse. There are different designs, shapes, and power ratings for the diverse types of heating apparatus and appliances. A clothes dryer TCO would not be appropriate for a hair dryer.
Typical warning
Thermal cut-off
The TCO will have a temperature limit that causes the circuit to open. The fuse type will blow and remain open. Resettable types will allow power to flow again, once the temperature has decreased. As the temperature lowers, there is a dead-band before the TCO will reset. Risks: There are three common problems that occur with TCO's - failure, range, and location .
The TCO may fail to operate allowing the heat to rise excessively. An improper temperature range may cause the TCO to not control properly. The TCO may be in the wrong location and not sense the correct temperature. Dryer TCO
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4.3
Durham
F IXED IXED
Fixed heating devices are used in one place. They are permanently connected to the structure electrical system. As a result, there is commonality in the power supply, if not in the material that is heated.
4.3.1 S OURCE OURCE The source is typically 120 - 240 Volts. A four wire system has two hot wires for the 240 volts, a neutral to provide the 120 volt return and a separate ground for the safety current. The 120 volts has a single hot wire, a neutral, and a ground. Some older 240-Volt systems used a three wire system that had a common conductor for the neutral and ground. Breaker panel aluminum wires top right
Dedicated circuit breakers are installed. The breakers should be sized at 1.25 times the rated load. Where dual breakers are used, the two trip bars must be tied together by an approved device. Large loads may require multiple breakers to supply the heat. These must be correlated to adequate wire size. Risks:
Energized ground
Mis-size: A circuit breaker that is too large will not trip and provide protection for the wiring. wiring. Mis-construction: Mis-construction: Wiring systems that combine the ground and neutral have current flowing in the ground wire making it an energized conductor without insulation. This has personal safety issues as well as the potential for stray currents.
Wiring systems without a ground will have stray paths when a fault occurs. Any conductive material, including nails, may be energized.
4.3.2 P ATH Connectors – 75C
The conductors should be sized at 1.25 times the rated load. The insulation of the wire has a temperature rating suitable for the environment. Newer wire and non-metallic sheathed (NM) cable have a THHN type insulation suitable for 90°C. However, older wire may only be 60°C and not suitable suitable for high temperature environments. environments. Connectors must be rated for the environment. Twist-lock type wire connectors are rated for 75°C and are not suitable for hotter environments. Relays and starters are frequently used to energize the load. A relay is a magnetic coil operated by a lower voltage. When the coil is energized, the contacts switch and provide higher energy power to the load.
NM cable under board on metal - bad
Risks: Mis-size: Wire that is too small for high current will overheat. Mis-material: Mis-material: Aluminum wires connected to copper will burn. Low temperature wire and connectors may fail and provide fuel. Mis-construction: Mis-construction: Poor connections with high current will result in very high heat.
Result of NM crimped by board
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Heating Devices
37
4.3.3 HVAC HEATERS Construction: Heating, ventilation, and air conditioning (HVAC) systems are permanently affixed to the structure. The electrical system gas only, heat pump, and strip for the heater can be one of three types – gas heat .
Gas heat has low voltage electrical controls. These are typically a thermostat control system operating at 24 volts or less. Although the energy is low, the system is still subject to electrical failures. Next, heat pumps are simply a variation in how the air conditioning compressor is operated. Heat pumps essentially run the A/C cycle in reverse. The final source for HVAC heaters is electric strip heaters. Strip heaters may be used alone for heating in a furnace unit, may be used as supplemental to a heat pump, or may be used in baseboard heaters.
Heater above wood chase
The heat strip is simply a high resistance wire, or conductive bar, that gets hot as current flows through the wire. The wire is suspended on insulators to keep the surrounding structure from getting too hot. Heat strips are usually rated about 5 kW per strip. Multiple units may be used for more heat. Fuses and current limiters are frequently located near the heat strip to protect the circuit c ircuit from overloads. A fan may blow air across the heat strips to transfer the heat to the room. Thermal control: A temperature cut-off (TCO) sensors keeps the heat in the duct from getting too hot. A thermostat in the room keeps the ambient temperature in a desired range.
2-60A breakers on one 6 AWG (65A) wire
Risks: Mis-construction: Mis-construction: A significant problem occurs when the heating system is too close to combustible wood and building material. In time the material can create ignition. International Mechanical Code and other industry standards specify proximity of combustible materials to heat strips. Mis-size: An improper TCO or fuse will not adequately protect the system.
Cooling loss can result from a fan f an quitting or blockage of air. The element may fail and short to the enclosure.
4.3.4 C OOKTOP OOKTOP & OVENS Construction: Food preparation equipment may use conduction, convection, or radiation to transfer transfer heat. A characteristic of cooking heat is localized heating on a pan or container. The units often have exposed elements. The units are rated from 4 kW to 12 kW, with 6 kW being a typical size of one unit.
Oven damage from burned food
Because the elements are specific purpose, resistance of the burners makes them heat limited. Thermal control: A thermostat control switch supplies power to the element to maintain desired temperature.
Cooktop burner left on
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Risks: Neglect: Unattended food is a common problem. Since food is carbon based, it will combust if left in contact with excessive heat for too long. Other combustibles left on burners also contribute to fires. Range elements should also be checked for corrosion and grime.
Aluminum containers and grease are two items frequently associated with fires. Mis-construction: Mis-construction: Poor connection on switches creates a hot spot.
Clothes dryer from plastic fan
Switches have multiple contacts. The indicator may be off while the power switch is still on. This may result in inadvertent overheating if items are left on a burner.
4.3.5 C LOTHES LOTHES DRYERS Construction: Clothes dryers can be moved slightly, but are permanently affixed by the exhaust duct. The power supply is 240 Volts operating with 24 Amps on a 30 Amp breaker. Clothes dryers consist of a rotating drum driven by a 120 volt electric motor. The heating element is typically about 5 kW and consists of a wire element placed on stand-offs. Thermal control: The high-limit thermostat operates at about 250°F. A heating element thermal cut-off (thermal fuse) blows at 360°F. Risks: Neglect: Cooling loss can result from blockage of air due to lint build-up. Lint will collect in the dryer cavity where it cannot be seen or cleaned without disassembly of the dryer. Lint from certain items is ignitable. In addition, placement of combustible materials in the dryer drum can provide a source for ignition. ignition. Clothes dryer internal with lint
Mis-construction: Mis-construction: Cooling loss from fan failure occurs in some models. The fan material in many models is combustible and provides the fuel for a fire.
Users install the cord on the dryer to be compatible with the receptacle. Improper installation and protection of the cord creates a hot spot. Mis-size: An improper TCO or fuse will not adequately protect the system.
The heating element may fail and short to the enclosure. Design: Because of the movement of fabrics, large static potential can build-up. Discharge of the the static can damage electronic controls. controls.
4.3.6 RECESSED LIGHTS Recessed light from arcing to pipe
Construction: Recessed lights are can fixtures that are mounted above the ceiling with the light projecting into the area. The heat from these fixtures is concentrated within the can.
The original model can fixtures had a single metal wall. Any combustibles that contact the wall could ignite. Surprisingly, these units are still available. Newer models have two walls. The outer wall keeps combustibles clear of the hot inner wall. All light fixtures have a maximum watt rating for the bulbs. Larger bulbs create excessive heat. Too large bulb – 125 W in 75 W fixture
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Heating Devices
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Thermal control: Old fixtures have no thermal control. New models have a thermostat that will switch off if the temperature rises too high. If lights go on and off, it is generally a sign of too large bulb.
The thermostat location is designed for a particular orientation of the fixture. If the unit is mounted at an angle, the thermostat may not work properly. Risks:
Recessed fixture TCO
Too large bulbs create excessive heat. Combustible material too close to the metal will ignite. Improper mounting prevents adequate cooling and heat transfer.
4.3.7 F LUORESCENT LUORESCENT LIGHTS Construction: Fluorescent lights are fixtures with high voltage energization that excites metal gas in the lamp. For the same amount of light, the wattage of the bulbs is much less than conventional lamps; therefore, the heat from the lamp is less. The high voltage necessary for excitation of the gas is achieved by a ballast. A ballast is primarily a transformer that steps the normal voltage to a very high value.
Fluorescent fixture has ballast
Newer fixtures have electronic ballasts. This improves the power capacity, but creates substantial electrical noise that may disturb radios. Compact fluorescent less heat but Hg The voltage supplied to the fixture is typically 120 Volt, three wire circuit in residences and small commercial installations. Large commercial and industrial fixtures typically operate at 277 Volts, three wrie. Thermal control: Newer fixtures have a thermal cut-off within the fixture or the ballast. Risks: Ballast failure is noted by bulging or potting material that melts and runs from the fixture.
If the air is prevented from circulating around the fixture, the fixture will become hot. Enclosed fixture use 60 W lamp max
4.3.8 E NCLOSED NCLOSED LIGHTS Construction: Enclosed fixtures are frequently used in residential lighting. The most common is an inexpensive pan light. The lamps are standard, medium based, incadescent bulbs.
Since the fixtures are closed, heat buildup is a problem. The units have a stamped rating for the maximum number of watts for the bulbs. We have found fixtures with too large lamps where the NM cable insulation becomes brittle, then cracks, and finally results in a fault. Other fixtures have gotten so hot that the sheetrock cracks and turns to powder. Thermal control: There is typically no thermal control. Risks: The major risk is over-lamping, which is placing in the fixture more wattageor heat than the fixture f ixture can handle.
Other risks include loose connections caused by trying to fit the conductors into a very small space above the fixture.
GFCI plug
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4.4
Durham
P ORTABLE ORTABLE
Portable heating devices can be moved. The machine is placed in a location, and then placed in use. The devices are connected to the power system by a dedicated purpose cord. As a result, there is commonality in the power connection, but not the material of the cord, and not in the material that is heated.
4.4.1 S OURCE OURCE & P ATH Most, but not all, portable devices are rated at 120 Volts with a current rating less than 16 Amps and a wattage rating less than 1920 Watts. Larger devices are rated at 240 Volts, use a larger size wire, and are connected with a special plug. Heater misplaced TCO
Risks: Mis-use: Physical damage to the cord is not uncommon. Mis-material: Mis-material: Improper material for the cord, connectors, and enclosure will allow the insulation to overheat and burn. Mis-size: Wire that is too small for high current will overheat. Mis-construction: Mis-construction: Poor connections with high current will result in very high heat. Improperly located TCO’s and TCO out of range can cause a fire.
4.4.2 C ERAMIC ERAMIC AND OTHER HEATERS
Lamp, switch at joint
Construction: Portable heaters are devices that are used to provide environmental heat to a small occupied area. Frequently fans are added to disperse the heat. The heating element may be ceramic, quartz, infrared, or heat strip. Some heaters use oil-filled radiators to distribute the heat. All devices have an elevated temperature surface. Thermal control: A thermostat is used to set the level of the heat. A thermal cut-off may be used to prevent overheating. Risks: Proximity to combustible materials will ignite the material. Warnings typically say do not place closer than three feet to combustibles. Unfortunately, Unfortunately, that location will prevent the devices use in many rooms. Therefore, this spacing instruction often goes unheeded.
Standard cord material, with temperature rating of 105°C ( 221°F) is used with heaters with discharge temperatures around 300°F. Toaster
Heater warning-keep at least 3 feet away
4.4.3 L AMPS a nd portable trouble Construction: Table lamps, desk lamps, floor lamps, and lights are noted by the relatively small cord that supplies the appliance. AWG 18 wire has a current rating of 10 Amps. If the wire faults, it can burn in two and not trip trip a standard 20 Amp circuit-breaker. circuit-breaker. Thermal control: There is typically no thermal control. Microwave connector failure
occur if the support post post is rotated. Damage and Risks: Damage can occur breaking of internal connections connections causes faulting and fires.
Chapter 4
Heating Devices
41
Overheating of combustibles and damage to cords occur from misuse and lack of adequate protection for the heated bulb.
4.4.4 K ITCHEN ITCHEN APPLIAN APPLIANCES CES Construction: Kitchen appliances are small items used in food preparation. These include coffee pot, toaster, crock-pot, steamer, and small ovens. Thermal control: Thermostats, often adjustable, control the temperature of the process. Risks: Metal utensils and food can come in contact with exposed elements. Excess food can be left in the devices from repeated use. The food can combust.
Microwave cooling fins & fan
4.4.5 M ICROWAVE ICROWAVE Construction: Microwaves are heating devices that use electromagnetic radiation rather than thermal heat to provide heating energy. The energy is derived from a magnetron tube that operates in the neighborhood of 4000 volts and a radio frequency of 2450 MHz. A large power supply is required. Thermal control: A fan blows across the heat sink.
Printers
Risks: The power supply capacitor is vulnerable to transients and heat.
The connectors at the door switch are susceptible to failure. Power connections on the printed circuit board are prone to improper connection and can overheat.
4.4.6 OFFICE APPLIANCES Construction: Office appliances are used in information processing. These include printers, copiers, and computers, which apply heat in the process. Thermal control: The devices have thermostats to cycle off and fans for cooling. Risks: Fan failure, paper jams, and stalling of the drive can create excessive heat.
Computer printer failure
Improper design of computer power supplies can cause overheating. Computers are susceptible to transient damage.
4.5
H ANDY
Hand operated heating devices are heated while the user is operating the devices. They are cord connected with a flexible cord that may appear to be general purpose. The devices use a standard receptacle for power. As a result, there is commonality in the power connection, but not the material of the cord, and not in the material that is heated.
4.5.1 S OURCE OURCE & P ATH The device is 120 Volts and a power rating less than 1920 watts. The cord is exposed to substantial mechanical, heat, water, and chemical damage and contact with combustible surfaces.
Hair dryer heating internal
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Risks: Mis-use: Physical damage to the cord is not uncommon. Mis-material: Mis-material: Improper material for the cord, connectors, and enclosure will allow the material to overheat and burn. Mis-construction: Mis-construction: Poor connections, particularly with switches, will result in very high heat. Poor construction can allow combustible items such as the plastic case to contact heating elements.
4.5.2 H AIR DRYERS Hair dryer elements & TCO
Construction: The heating elements are coils of high resistance wire that are wrapped around a form near the outlet of the device. An element is required for each temperature setting. Thermal control: Multiple heating elements are switched on or off to control the heat output. A thermal cut-off is installed inside the heating element as a back-up. A cooling fan blows across the element. Risks: Blocking the air inlet is a disaster. Hair, lint, and hair products block air flow and are ignitable. ignitable.
Laying the hot element on combustibles is hazardous. Damage to the cord can happen internally or externally. Damage at internal stress relief is particularly common. Hair iron
4.5.3 H AIR IRONS Construction: The heating element is a flat or cylindrical metal surface that is intended to contact the hair. Thermal control: A thermal cut-off is a back-up. Risks: Switch failure is not uncommon.
Leaving the device on and adjacent to combustibles is hazardous.
4.5.4 C LOTHES LOTHES IRONS $13 Clothes iron without TCO
Construction: The iron has a large flat surface for contact with fabric. The heating elements are protected and embedded in the flat surface. Thermal control: A thermostat controls the fabric temperature. A thermal cut-off is a backup temperature control. Some devices have a tilt switch or some have a sensor that detects the unit has not been used for several seconds. Risks: Leaving the device in contact with fabric is an obvious problem.
Leaving the device on and permitting it to get knocked over is a similar problem.
4.5.5 T OOLS OOLS Construction: Tools include devices like soldering irons, wood burning irons, hot glue guns, and other tools with a hot surface. These are similar to the hair irons. Hot surfaces are intended to contact and heat a metal, wood, or other material Thermal control: Thermostats are used to set the temperature of some devices. Battery charger shorted
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43
Risks: Residual heat on both the device and the surface is a concern.
4.5.6 B ATTERY CHARGERS Construction: Battery chargers are used to convert 120 Volt alternatingcurrent to direct-current. There are numerous configuration c onfigurations. s. Thermal control: Charge control is intended to manage temperature. Risks: Covering the charger vents or battery can cause heat build-up.
Placing batteries in backward can lead to explosion. Lithium polymer batteries will fail spectacularly if overcharged. Battery chargers used on batteries of different design can cause overcharging.
4.6
REVIEW
All electric systems generate heat. Heating devices generate heat as their primary function. Heating devices have three categories fixed, portable Welder generator charger and handy. Thermal cut-offs (TCO) are used to prevent overheating of devices. Appropriate size and position of TCOs is crucial. Fixed heating devices are set in a single location, and permanently connected to the building power system. Primary protection for fixed devices is provided by the building breakers. Breakers are sized at 1.25 times rated load. Conductors to the device are also sized at 1.25 times rated load.
HVAC Heaters Heaters Gas, heat pump, strip heat Low voltage controls o TCOs prevent heat from escaping chamber o Improper clearance from building materials o Cooktop & Ovens Conduction, convection or radiation o Resistance of burners limits heat o Thermostats control temperature o Unattended food primary risk o Poor connections – hot spot o o Indicator light may mis-indicate Clothes Dryers o 240VAC / 30 Amp Thermostat ~ 250°F; TCO ~360°F o Lint buildup blocks air flow o Improper or inoperable TCO or fuse o Heating element short to enclosure o Static buildup o Recessed Lights Lights o Primary failure - overlamping Limited airflow o Single wall with combustibles too close o Older fixtures have no TCO o Orientation of fixture o Flourescent Lights Primary failure -ballast overheating o o
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Supply 120VAC / 277VAC Ballast raises voltage to high voltage o Newer fixtures have TCO o Enclosed Lights Lights No TCO o Overlamping causes excessive heat o o Small space holds heat Loose connections o o
Portable heating devices can be moved. Most are 120VAC / <16 Amps / <1920 Watts. Physical damage to cord, improper cord material, poor connections, and too small wire are common failures.
Ceramic / Other Heaters Primary failure - proximity to combustible c ombustible materials o Elements - ceramic, quartz, infrared, heat strip o All hot o o Common problem - 105°C cord but surface near 150°C Lamps Small Wire – AWG 18 can fail and not trip breaker o No other protection o Kitchen Appliances Appliances Thermostatically controlled o Food and utensils in contact with exposed elements o o Excess food debris can combust Microwave Microwave o Use radiation instead of thermal heat Magnetron operates at 4000volts, 2450MHz o Fan cooled o Power supply capacitor subject to transients o Door switch connectors o PCB connections o Office Appliances o Thermostats and cooling fans Fan failure, paper jams, drive stall create excess heat o Cord failure o
Handy devices are handheld while in operation. Operate at 120VAC, <16A, <1920 Watts. Physical damage to cord is common. Poor connections allow overheating. Poor construction allows heat to impact combustible cases.
Hair Dryers Multiple heat coils are switch controlled o TCO to prevent overheating o Blocking inlet air causes overheating o Damage to cord o Proximity to combustibles o Hair Irons Multiple heating elements are switch controlled o TCO backup o o Switch failure Proximity to combustibles o Clothes Irons
Chapter 4
Heating Devices o o o
45
Thermostatically controlled Hot surface in contact with fabric Knocked over
Tools
Thermostatically controlled Switch failure o o Proximity to combustibles Battery Chargers o Covered vents causes overheating Overcharging batteries, especially Lithium Polymer, can o cause rupture o
HAPTER 5 – C OOLING OOLING & OTHER C HAPTER DEVICES 5.1
NTRODUCTION I NTRODUCTION
The previous chapter looked at heating appliances. The additional heat source present in these devices is an obvious potential for ignition. This chapter will take a look at the broad variety of non-heating appliances; included are cooling equipment, fans, refrigerators, electronics, and water appliances. These cooling devices create heat which can cause failure or ignition.
5.2
C OMMON OMMON RISKS
The common components of most appliances are motors, switches, relays, and connections. Because of the common components, there are common risk factors.
Compressor relay connector
Relay: A relay is a coil of wire like a motor or transformer. When the coil is energized, a plunger causes contacts to close or open (make or break). Risks: Contacts may pit and wear with use or the contacts may be misaligned. Either of these situations causes a poor connection, with increased impedance. Problems with contacts that result in a poor connection increase heat. Motor: The stator (frame) of a motor has a steel core with wire wrapped around it to make a magnet. Copper has been the traditional winding material. Aluminum is used for some devices because it is cheaper.
The rotor of the motor is another steel frame with a coil of wire that rotates when power is supplied to the stator winding.
Connection blade to receptacle overheat
Risks: The coil may become misaligned. Aluminum motors have increased heat due to increased resistance of the wire. Motors require cooling to prevent overheating. Too much lubrication may block cooling and too little lubrication may increase friction and wear. Connections: Connections are joints made for wires. Blade and sleeve connections allow a metal sleeve to slide over a blade. The sleeve is held in place by friction. These are good connections for easy installation and removal, if properly installed and undisturbed.
Aluminum can have problems with connections, especially connections to copper. Aluminum/copper connections have increased risk of corrosion, and resulting increased resistance. Aluminum expands and contracts significantly with temperature, allowing connections to become loose. Aluminum, when exposed to air, will form an oxide which is a ceramic. This increases the resistance of the connection. Risks: The connections may become loose from mechanical disturbance, foreign matter, metal expansion, or corrosion which results in a hot spot. Oxide that is formed on the connection will frequently survive a fire. Copper oxides are noted by a brilliant green color while aluminum oxide is a dull white gray.
Refrigerator compressor lower back relay
$, t, quality engineering trade-offs
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Economics trade-off: The classic engineering trade-off is between cost, time, and quality. Economics plays an important component in any appliance. The less expensive appliances by definition are constructed more cheaply. There is a trade-off with safety. Although safe for general use, less expensive devices have a greater propensity for failure than a more expensively constructed device. Risks: Appliances that operate on 120 Volt power and cost less than $100 appear to have greater risk of fire. Plastics burn to propagate fire
Most often it is safer to throw away a device than to repair.
5.3
C OOLING OOLING
Cooling appliances includes refrigerators, freezers, and air conditioners. Cooling involves a compressor to make the refrigerant into a liquid. Heat is generated at this point. In another chamber, the liquid expands into a gas and creates cold. The refrigerant is then passed through coils, where air is blown past and cooled. The compressor is simply a pump combined with an electric motor. In a heat pump, the cooling cycle is in the outside unit, and hot refrigerant is pumped through the coils. When air passes across the hot coils, it is warmed. Ruptured coolant line on air conditioner
The refrigerant is contained in a closed system of piping. Refrigerant mist is very flammable if it escapes from the system. The significant electrical components are the power cord, switches, relays, and motors. Generally two motors are involved. One operates the compressor, the other drives a fan that blows air across the coil to transfer the heat. Controls: Temperature is controlled by a thermostat. The thermostat operates at a low voltage and controls a relay coil which switches higher energy to the compressor. Risks: The risks are primarily those common to motors, switches and relays. In addition, there is a risk of leaking refrigerant. A fine mist of refrigerant is extremely flammable.
Fan blades and shroud
5.4
F AN
A fan is simply a set of blades that is moved by an electric motor. The purpose is to move move air either for heating or cooling. cooling. Controls: In most instances the control is an on/off switch. In addition, a speed control can be included. Risks: Because the fan is moving, there may be mechanical flexing and rubbing of wires. There is also mechanical stress on switches and connections.
If airflow is restricted, the motor can overheat.
Solenoid valve
Chapter 5
5.5
Cool & Other Devices
49
W ATER
Water and electricity do not mix. Leaks damage property and can cause electrical component failure. Water interfaces with electricity in three ways.
Water can be heated by an element.
Water can be switched by a solenoid.
Water can be pumped.
Class 2 transformer
Element: A heating element is a specially designed conductor that is inserted in liquid. It is similar to a stove element. The devices are used in water heaters. Risks: The element must be under water for cooling. Otherwise it can overheat and fail. Solenoid: A solenoid is a valve with a plunger that is moved by an electromagnetic. It has the same basic mechanism as a relay. A solenoid switches water or fluid, a relay switches electricity. The motion of the plunger is in a line. The devices are used in washers and irrigation systems.
Class 2 transformer internal
Risks: Leaks are the biggest failure mechanism. Pump: A mechanical pump is turned by an electric motor. The motion of the pump is typically rotational. The machines are used in water wells, washers, and transfer pumps. Risks: Leaks are the biggest failure mechanism.
5.6
C LASS LASS 2 POWER SUPPLIES
Power limited transformers are commonly used for small power consumer devices. These are euphemistically referred to as “wall warts”. These are small units that plug directly into a 120 VAC receptacle. The output is less than 30 V. Some units have a rectifier inside the case that provides a DC output. These These units charg electronic devices. devices.
High resistance connection caused fire
Class 2 uses a special design with an important characteristic. The device is impedance limited. The windings are very fine wire, even with the secondary shorted, the high impedance of the winding limits the current so that a shock will not occur, and fire hazards are limited. Article 725 of the NEC addresses power-limited circuits. Class 1 is conventional controls. Class 2 is the most power limited. Class 3 is less restrictive power limited. Power limited circuits are differentiated from conventional electric light and power systems, therefore, alternative requirements are applied. Extensive details about the power limiting specification are in Chapter 9 of the NEC.
Class 2 circuit board fire in progress
Risks: One caution should be noted. The heat generated during a short circuit is about the same as a 60 W lamp, so surface temperature can ignited some items that touch the case.
Units for a dry environment are not sealed. Moisture from a hot, damp area can migrate into the unit unit and create a fault. A short of an AC device device will generally not cause the transformer to fail. A short in a DC device can cause the rectifier circuit to overheat, fail and potentially ignite.
Electronics smoke damage
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Electrical Failure Analysis
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Warning: We have been able to generate a fire when the transformer wires are connected through a high resistance connection. High resistnce simply means greater resistance than a solid connection. The resistance may be as lower than 1 Ohm. The temperature increased enough to ignite paper within 1 minute. Other cellulose materials may be expected to ignite with greater time.
Circuit board layers fire start at bottom
Class 2 power supplies that have a DC output contain a circuit board that can catch fire with a high impedance connection. Typically the board begins burning near the rectifiers.This rectifiers.This occurs even if a thermal protection protection is installed. The transformer does not overheat becaute the faulting is not in the transformer.
LECTRONICS 5.7 E LECTRONICS Electronics typically operate at a relatively lower voltage, less than 120 Volts. In addition the current typically is low, so the power is reduced and the resulting fire hazard is reduced. Nevertheless, adequate energy still exists to create ignition. Some of the electronic devices plug directly into the power line. Others have a class 2 transformer which reduces voltage prior to entering the unit. Electronics have passive energy devices. Coils convert electrical to magnetic energy. Capacitors store electric energy. Resistors convert electrical to heat. In addition, there are active devices. These include diodes, transistors, and other solid-state chips. The active devices modify the signal but operate at low energy. Finally electronics may have protective devices such as thermistors, sensors, and fuses. Electronics overheat in cabinet w/o cooling
Controls: Typically the power controls are simple on / off. Other devices may be used to control the functions such as volume. Risks: Electronics are susceptible to transients. These can damage capacitors and permit excessive energy to cause overheating.
Inadequate cooling can allow excessive heat build-up. Solid-state devices can fail resulting in excessive heat.
5.8 REVIEW Non-heating appliances can have risk of failure. Common components have certain risks.
Relays o o
Piting and wear of contacts Increased impedance causes increased heat
Motor Misaligned rotor Lubrication issues o Aluminum windings increase heat o Connections Aluminum expands/contracts – loosens connections o AL/CU connections risk corrosion o o Mechanical (sleeve) connections loosen if moved o
Computer tower
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Cool & Other Devices
51
Oxides increase resistance – increase heat Economics Less expensive appliances often less expensively o manufactured 120VAC appliances < $100 have greatest risk o o
Cooling appliances include refrigerators, freezers and air conditioners. Cooling devices using compression / expansion of refrigerant in order to transfer heat. Heat pumps are simply air conditioners with the components reversed. Refrigerant mist from a leak, is highly flammable.
Fans o o o o
On/off switch, multispeed motor Oscillating components cause wear on wires Reduced airflow causes overheating of motor Mechanical stresses on switches and connections
Water o
Heating
o
Switch
o
Heating elements inserted into water to heat Elements must be under water else overheat Solenoid valve used to turn on/off water flow Leaks biggest risk
Pump
Mechanical pump turned by electric motor Leaks biggest risk Class 2 power supplies Input 120VAC – Output 30 Volts or less o Impedance of winding limits current o Short circuit of output creates heat generated similar to o 60W bulb o High impedance connection (~1Ω) on output generates enough heat for combustion of cellulose High impedance connection of DC device can cause o internal rectifier to fail / ignite Electronics Passive and active electrical devices o Susceptible to transients o Inadequate cooling allows excessive heat especially in o cabinets and enclosed areas
HAPTER 6 – P ROTECTION ROTECTION C HAPTER 6.1
I NTRODUCTION NTRODUCTION
Protective devices includes items that support and guard electrical systems. From the very first chapter, we found there are three electrical measures – voltage, current, and time. There are three corresponding protections mechanisms. There are myriad implementations of the techniques.
6.2
C URRENT URRENT
Over current is the most common protection mode. Current creates heat. Heat is proportional to the square of the current (current multiplied by 2 current) and the resistance or opposition to current. This is called I R heat.
Fuses are the simplest overcurrent devices. A fuse is simply a piece of wire that melts when heat increases. Expending the wire is referred to as “ blowing” the fuse. A fuse is not resettable or reusable. Placing a larger fuse than the rating of the protected device may result in overheating of the other components in the circuit. Circuit breakers, such as those used in residential and most commercial installations, have an element that creates heat from the current flowing to the load. Once the heat builds up, the mechanical lever will trip. A circuit breaker can be reset after the condition is cleared and the device has cooled.
Breaker damage from lightning
Fuse screw-in normal & oversized
Note both fuses and circuit breakers are heat sensitive. They can be tripped from incident fire as well as from current. The determination of whether the trip is a cause or result of fire depends on analysis of the condition of other components in the circuit. In addition, a circuit breaker will trip from a sharp mechanical impact. Therefore, the other circumstances around the scene must be analyzed to determine whether the breaker tripped on overload, incident heat, or impact. Overload / underload protection is used for motors. Overload / underload control is a sensor that trips when current is out of range. The device may be magnetic or electronic controlled. controlled.
6.3
Motor overload protection
OLTAGE V OLTAGE
Over voltage protection is primarily provided by a surge arrestor, which is commonly referred to as a lightning arrestor. These devices may have a space or spark gap, The most common form of these protectors is an electronic device called a metal oxide varistor (MOV). Since an MOV is an electronic device, it will deteriorate to some degree each time it dissipates an overvoltage condition. Arrestor
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During normal conditions, voltage protective devices are passive and do nothing. When voltage spikes, the devices provide a lower impedance path to ground for the excess voltage. Once excessive voltage is removed, the device clears.
6.4 GFCI receptacle with test & reset
GFCI
A ground fault circuit interrupter (GFCI) compares the current on the hot wire with the neutral. If the currents are not equal, then there is leakage current. Leakage current is caused by a failure between the current carrying conductors and ground, such as in submersion of an electric device. When the current difference exceeds 5 milliamps (5/1000 amps), the circuit is opened. The device has a trip and reset button. The trip button should be tested monthly. Because the devices are in wet locations, the electrical sensing system may deteriorate. When was the last time you tested all your GFCI’s? GFCI are required by the NEC to be located in kitchens, bathrooms, garages, and outside. Basically the requirement is any location that is reachable from ground level or from a water pipe.
AFCI & GFCI breakers
GFCI may be incorporated in a receptacle or a circuit breaker. A GFCI is for personnel protection from shock hazards. It does nothing to protect equipment.
6.5 AFCI An arc fault circuit interrupter (AFCI) is a very small, special purpose computer that looks at the shape of the power wave. A normal alternating circuit (AC) is a smooth, continuous signal that cycles 60 times each second (60 Hz sine wave). An arc has sharp spikes when it starts and stops. Arcs occur anytime a switch is closed and opened, from power system operations, and from lightning. Arcs also occur when a connection is intermittent or erratic, or when the insulation on a wire is inadvertantly breached. Transient noise L-N
AFCI are required by the NEC to be located for all electrical circuits in family rooms, dining room, living rooms, parlors, libraries, dens, bedrooms, sunrooms, recreation rooms, closts, hallways, or similar rooms. In essence, arc fault protection is required any place a GFCI is not used. An AFCI is used to prevent arcing fires from intermittent connections. The interrupter is not heat related. AFCI are available in circuit breakers. Some manufacturers combine an AFCI and GFCI into the same device.
URGE P ROTECTION ROTECTION S YSTEMS 6.6 S URGE S YSTEMS True to form, there are three levels of surge protection – true UPS, battery back-up UPS, MOV systems. systems.
True uninterruptible power supply
True uninterruptible power supplies (UPS) isolate the load completely from the power system. Battery back-up UPS have a battery charger floating on the power system so the battery can provide current during a
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Protection
55
power outage. Power strips have metal oxide varistors (MOV) that shunt excess energy to ground.
6.7
T RUE RUE UPS
A true uninterruptible power supply (UPS) is referred to as a true on-line double conversion UPS. The unit is a sophisticated power source that operates from alternating current (AC) line power, switches the power to direct current (DC) for charging a battery, then converts the DC back to AC for supplying the load. They are used as large computer and expensive electronics protection. By converting between AC to DC to AC, the expensive electronic loads are actually isolated from normal power line surges.
True UPS – 1 kVA
These are very sophisticated devices that are generally used in industrial applications and computer server farms. The cost is in excess of $600 for a 1,000 VA unit. The devices are not available in big-box stores. Nevertheless, these are the ONLY device device that provides a reasonable level of protection. They are well worth the investment for valuable data. These are the units we use for our computers and networks.
6.8 B ATTERY B ACK -UP UPS The battery back-up UPS is simply a surge protection power strip with a battery charger. The battery provides power on an outage. These systems do not protect on low-voltage and high energy transients.
Battery back-up UPS
With low-voltage transients we have observed failures on three different UPS units. The failures permitted blowing of capacitors on computer mother boards, failure on video cards, and monitor failures. In addition, one of the back-up UPS had an internal failure. There are multiple receptacles on the devices. Some receptacles only have surge protection. Others have surge and battery backup. Risks: These are expensive surge strips whose incremental value may be in keeping power on for a few minutes to allow controlled shut-down.
URGE SUPPRESSORS 6.9 S URGE Multi-tap surge suppressors are offered by many vendors and distributors. These are a group of receptacles that are intended to protect items plugged into the receptacles. The devices contain one to three MOV’s to shunt overvoltage away from the circuit.
MOVs, circuit breaker, lighted switch
Anything less than three MOV’s provides inadequate protection. Most devices use a very low energy MOV that provides little protection.
We have tested numerous of the competitive devices in our lightning laboratory and have found none that provide significant protection. Several of the devices ruptured explosively. The warranties have so many caveats that they are worth little more than the box they are printed on. Risks: The failure issues are either it does nothing to protect the electronics or it ruptures and creates a fire. The MOVs themselves themselves can provide an ignition source if they fail catastrophically. catastrophically.
Bad news - 1419 V on 120 V circuit
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6.10 P OWER OWER STRIPS Power strips are similar to the surge suppressors but do not have the MOV surge protection. Both devices may have a circuit breaker for overcurrent protection. Some devices have an on/off switch and an indicator light. Risks: Power strips are subject to overload, if there is no circuit breaker. They are also subject to mechanical abuse because of where they are used. Identification of the manufacturer is frequently a problem.
ROTECTED POWER STRIPS 6.11 P ROTECTED
Power strip
A protected power strip has a GFCI built in the plug and provides a shielded cord with metal oxide varistors at the receptacles. This combination protects from common failures. The shield provides mechanical protection of the cord and a path for detection of faults. The GFCI shuts off power with problems in the cord or power strip. The MOVs protect for transients on the power line. This is a very different scheme to protect power strips which commonly have problems.
6.12 C AVEATS - U/L Note carefully the manufacturer and the ratings of the protection devices. Underwriter Laboratories (U/L) provides standards for testing the units. Other nationally recognized testing laboratories (NRTLs) provide similar testing and listing of electrical systems. Often the only component that is listed or approved is the power cord. If the only U/L or other NRTL tag is on the cord, leave the device alone. It is unsafe.
Protected power strip
Even brands that are sold in big box stores and have traditional names are often questionable quality.
6.13 E XTENSION CORDS Extension and other power cords are perhaps one of the most common electrical components that contribute to fires.
U/L listing
There are numerous issues that create problems. 1)
Length of cord causes voltage drop which results in heat.
2)
Size of wire that is too small for the current results in heat.
AWG 25 ft 50 ft 100 ft
3)
The insulation on most cords will burn.
18
7
5
2
4)
The insulation is subject to mechanical damage that causes failure.
16
12
7
3.4
14
16
12
5
5)
A jacket around the insulation provides added material and improved protection.
12
20
16
7
6)
The temperature rating of the insulation must exceed the temperature to which it is exposed during use.
Amp capacity of cords
6.14 REVIEW Protective devices guard electrical systems from failures resulting from the three measured components:
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Protection
57
Voltage Current Time
Overcurrent protection is most common. Three types of overcurrent protection are used. Fuses and thermal-magnetic breakers can trip due to incident heat.
Fuses - non resettable Thermal-magnetic circuit breakers - resettable Electronic-magetic circuit breakers - resettable
Overvoltage protection is provided primarily by surge arrestors. These devices provide a path to ground when voltage exceeds a set value. GFCI protects against leakage current to ground. They are primarily for personnel protection. GFCI protection protection is required in any any wet area. AFCI protects against arcing faults. The are primarily for protection of faults on feeders. The devices are now required in all areas inside a residence not protected by GFCI. True UPS devices completely isolate the load from the power system. Consequently, they provide the best protection scheme. Battery back-up UPS devices provide short duration battery backup to electronics during a power outage. They can have some protection from surges. Surge Suppressors are simply power strips with 1 to 3 MOVs which provide overvoltage protection. Low energy MOVs in these device provide little protection, protection, and can be a source of ignition ignition if they fail. Power Strips are inexpensively made and are subject to mechanical damage. Often there is no protection for cord or internal damage. Extension Cords Cords are a common failure item. They have several issues.
Length increases voltage drop which results in heat Undersized conductors result in heat Insulation is combustible in presence of heat source. Easily damaged insulation results in electrical failure and fire. Low temeperature rating of insulation in presence of high temperature source results in failure.
HAPTER 7 – G ROUNDING ROUNDING C HAPTER 7.1
I NTRODUCTION NTRODUCTION
An electrical ground is a connection to earth. Ground in electrical parlance is the common basis or reference for all electrical measurements, circuits, and safety. There are three functions of grounding systems based on the electrical measurements of voltage, current, and time. Equi-potential (V) keeps the voltage the same between two points. Fault current current (I) has a path back to the source.
i nertia of the earth. Transients (t) are snubbed by the massive inertia Grounding is a very complex topic that is critical to electrical safety. The National Electrical Electrical Code (NEC) has over 28 pages devoted to the requirements plus numerous other Articles that reference the topic. The National Electrical Electrical Safety Code (NESC) has specific requirements for grounding. The Institute of Electrical and Electronics Engineers (IEEE) has multiple standards that are specific to grounding installations. The authors have published over 25 technical papers and have received numerous awards and recognition for their research on grounding and lightning.
7.2
I NVESTIGATOR NVESTIGATOR PERSPECTIVE
The significance of grounding is not readily understood by most engineers and investigators, but it is a major element of every electrical system. It is well recognized that the “hot” wire in an electrical system is dangerous and can cause shock or a fire. Those incidents can only happen if there is a neutral or ground return path for the current from the “hot” wire. As we found in Chapter 1, an electrical system involves a cuit from the source through the wires to the load complete “circle” or cir cuit and then returning back to the source.
A ground, including neutral, path is the return half of every conventional electrical circuit. Any electrical activity on a neutral or ground conductor is a clear indication of faulting involving the ground system. Improper grounding is a common problem. Electrical ignition that is undetermined is likely related to a grounding issue. Grounding issues are a Code, and therefore, a legal violation. In our combined experience of over 65 years in failure analysis investigation and in looking at thousands of incidents, we have found that the ground system is seldom properly investigated.
A complete and thorough examination of an incident has not been conducted until the grounding system is eliminated or the ground measur asurem ements have have been made. One of many grounding articles by authors
60 The proper interconnection of ground system elements, including the grounding electrode, is critical to manage voltage and current in the prevention and mitigation of fires.
Set in stone
Electrical Failure Analysis
7.3
Durham
3-IN -1 -1
The three elements that are critical to electrical safety including fire mitigation are insulation , connections , and ground system system.
The pro The rop per int interc rco onnectio ion n of of gro grou und system elements, inc inclu lud din ing g the grounding electrode, is critical to manage voltage and current in the prevention and mitigation of fires. Notwithstanding Notwithstanding the immense literature on the topic, the fundamentals of grounding are relatively straightforward and naturally consist of three components.
7.4
ROUNDING SYSTEM G ROUNDING
The three components of a grounding system are grounding electrode, grounding electrode electrode conductor , and bonding . Grounding electrode is the contact point with earth. The electrode may be existing metal in contact with earth, metal in concrete, or made electrodes. The grounding electrode may consist of a grid, loop, or rings.
According to NEC requirements, if a made electrode has a contact resistance to earth of greater than 25 Ohms, an additional made electrode must be installed. The NESC is more specific. The ground must be less than 25 Ohms.
Made electrode
The IEEE Green Book on grounding is more specific. “This should not be interpreted to mean that 25 ohm is a satisfactory resistance value for a grounding system.” The Standard gives a specific recommendation. “Resistances in the 1 ohm to 5 ohm ran ge are generally found suitable for industrial plant substation and buildings and lare commercial installations.” Although the Green Book is not specific to residential installations, there is no difference in the earth needs, so its recommendations are still appropriate. Unfortunately, very few installers, inspectors, or investigators measure ground contact resistance, due to lack of equipment, lack of knowledge, or both. As a result, inadequate grounding is a common problem.
Electrode in concrete
Transformer
Entrance
Load
Power H
Power H
Neutral
Neutral
Power H
Ground
Ground
Utility Ground
Service Ground
Water & Other Metal
Grounding electrode, bonding, neutral
Grounding electrode conductor is the wire that connects the grounding electrode to the rest of the system. The wire must be large enough to handle available fault current. The NEC specifies the size of the conductor. Bonding connects metal surfaces that may become energized to the grounding system. Bonding is required between all grounding electrodes.
The NEC fine print note (FPN) advises to bond all metal even that not specifically noted in other sections. FPN: Bonding all piping and metal air ducts within the premises will provide additional safety. An energized ground has current from another circuit. The cause is poor connections and poor ground. The “tell” is melted insulation on the ground wire, or on the jacket of multiconductor cable, even though the energized conductor may not be melted. Melted insulation on a normally unenergized conductor is an interesting “tell” that the ground system has been energized.
Energized ground
Chapter 7
7.5
Grounding
61
N EUTRAL EUTRAL
Neutral is a current carrying conductor. It is identified by white insulation or markings. It is connected to the ground at one point and one point only. If connected at multiple points, the ground would carry part of the neutral current and the ground would be energized.
A neutral can be operated in three ways, two of which create problems. Proper neutral is grounded at one point only, has good low-impedance connections, and carries only the current of the associated circuit.
Energized ground from lightning
Floating neutral has a poor connection to the source that results in heat and current taking an alternate path. Shock and fire can result. Energized neutral has current from another circuit. The cause is poor connections and poor ground. The “tell” is melted insulation on the neutral or ground wire but the normally energized conductor may not be melted. This is particularly observed on devices and fixtures connected to another ground path, such such as a water line. Shock and fire will result.
Neutral is white, common wire
An energized neutral may create saddle burns on top of wooden structural members such as joists and plates.
7.6 S TRAY TRAY Stray currents are the result of improper grounding and bonding. Stray currents result from uncontrolled flow of electrical energy. The current takes an alternate path through the earth. The current can reenter a metal path at some point on its journey back to the source. source. Research has been conducted to evaluate the amount of current that flows in the earth for a power system that has multiple ground points on the neutral. This is typical of most overhead power lines. The research found that 60% of the neutral return current actually travelled thorugh the earth as stray current.
Energized neutral on top of joists
In effect any system that has a neutral with two or more ground points will have the current flow partially through the wires and partially through the earth. Control: Stray current is caused by a neutral that is grounded at multiple points. Stray current can result from a fault of a hot wire to ground. Commonly, stray current is caused by a difference in potential of ground connections. Risks: Stray current will energize unintended metal and will cause a potential difference between the soil and metal. The result is shock to living creatures and risk of fire.
Stray current from overhead power line
Transformer
7.7 S TRAY TRAY 120/240V Interestingly, every 120/240 Volt single-phase system is also constructed as a two-point ground on the neutral. Therefore, it is reasonably expected that up to half of the neutral current will flow in the earth or ground path on its sojourn back to the transformer source. If the impedances are not very low or the grounds are not bonded, stray current will flow through the earth and any other conductive material. The stray current can create a shock or fire hazard.
Entrance
Load
Power H
Power H
Neutral
Neutral
Power H
Ground
Ground
Utility Ground
Service Ground
Water & Other Metal
Stray current from multi-point neutral
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Electrical Failure Analysis
METAL ENCLOSURE ELECTRICAL SHORT
LIVE CONDUCTOR
A WIRE RESIST ANCE
WIRE RESIST ANCE
CONTACT RESISTANCE C
B EARTH
BURIED PIPE
GROUND ROD
PIPE CONTACT RESISTANCE
ROD CONTACT RESISTANCE
SOIL RESISTANCE
SOIL RESISTANCE TRUE GROUND
Ground differences
There is current flowing in the earth. If the ground electrode resistance at the service entrance is not low, as required by the Code, then the ground current has a greater tendency to stray and take alternate paths.
7.8
BODY RESISTANCE
Durham
ROUND DIFFERENCES G ROUND
Contrary to common opinion, the earth is not a monolithic ground. Three things impact the impedance of a ground connection – electrolyte, moisture, and metal. As a matter of interest these are the same three items that cause corrosion. Different soil, moisture, and metal create a different impedance or opposition to current. Different impedances result in a difference of voltage and a current path. Current takes the path of least impedance.
Look at the illustration. Notice the individual can be shocked or a fire can result near the location of his pointing. The ground at “B” and the ground at “C” are not equal, even though they are both in the soil.There is different wire resistance, contact resistance, and soil resistance. Therefore, current can and will flow in the ground wire and the earth.
7.9
G ROUNDING ROUNDING ELECTRODE
An electrical grounding system should use a single point as a reference for all measurements. This is called the grounding electrode. In an attempt to create minimum potential difference in the ground system, a grounding electrode system is mandated by NEC 250.50. “All grounding electrodes as described in 250.52(A)(1) through (A)(6) that are present at each building or structure served shall be bonded together to form the grounding electrode system.” NEC Article 250.52 lists seven alternatives for the grounding electrode.
1) 2) 3) 4) 5) 6) 7)
Metal underground water pipe Metal frame of the building or structure Concrete encased electrode, including rebar Ground ring Rod and pipe electrodes Plate electrodes Other metal underground systems or structures.
ROUND VALUES 7.10 G ROUND Grounding considerations are comprehensively addressed in the NEC and NESC . An understanding of these issues assists in determining responsibility for incidents. Both the NEC and the NESC reference that resistance greater than 25 Ohms is not acceptable for a made electrode. Additional grounding must be performed in order to reduce the value. value. IEEE 142, Grounding of Industrial and Commercial Power Systems, is much clearer in describing the resistance must be lower. The following quote is from paragraph 4.1.3 Recommended Rec ommended Acceptable values. Ground resistance varies
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Grounding
63
The 25 ohm value noted in the NEC applies to the maximum resistance for a single electrode consisting consisting of a rod, pip, or plate . If a higher resistance is obtained for a single electrode, a second electrode of any of the types specified in the NEC is required. This should not be interpreted interpreted to mean that 25 ohm is a satisfactory satisfactory resistance value for a grounding system. NEC has additional requirements of lower resistance for classified areas. The result of this discussion is the Codes allow some flexibility for different conditions. However, in no circumstance is a ground greater than 25 Ohms acceptable.
Electrolyte, moisture & metal
A good ground resistance reference for electronic circuits can be obtained from the standards for intrinsically safe shunt diode barriers. In these systems, ground resistance from the furthest barrier cannot exceed 1 Ohm. This requirement is incorporated into the NEC by reference to ANSI RP 12.06.01. For safety, consider Ohm’s law that we looked at in the first chapter. Impedance is the ratio of voltage to current. For a normal 120 V circuit with a 20 A breaker, a total circuit resistance of less than 6 Ohms is required to trip. In other words, if the hot wire were to touch the earth, the total path resistance would have to be less than 6 Ohms.
The low ground resistance allows objectionable energy, including harmonics, to be dissipated safely into the earth.
All ground must be bonded
Z
V I
120V 20 A
6
LLUSTRATION – CIRCULATING CURRENT 7.11 I LLUSTRATION Ground by definition is connection to earth. Bonding is connection between two metals that may be electrically energized.
Consider two ground rods driven in the earth. There will be a potential difference (VD) between them, because of the difference in ground resistance. Differences are caused by the electrolyte, moisture, and metals. When there is a voltage difference, current (I) will flow.
I
A bond is necessary between the two grounds and all other metal surfaces. The purpose of bonding ground systems together is three-fold. 1. To assure that all the systems are operating at the same reference (V). This is crucial to control voltages seen in the structure.
Vd Grounds unbonded – circulating current
2. To prevent circulating currents (I) from developing in the ground systems. Circulating currents cause overheating of ground and neutral conductors. 3. To allow building and service protection (t) systems to operate effectively and as designed. The fact that the ground system is not bonded together properly creates three problems associated with the voltage, current, and protection time. 1. It allows voltages (V) in the structure to “float” and exceed equipment ratings. 2. It allows circulating currents (I) to overheat the existing ground conductor.
Grounds bonded – no current
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3. It prevents the structure and utility protection systems (t) from operating.
7.12 H OW ? OW MUCH IS TOO MUCH ?
From research on low energy systems, we have been able to ignite cellulose with a “high -resistance” connection that generated power from as low as 11 to 20 Watts. On a 120 V system, 12 Watts is created with a current of only 1/10 Amp. A poor connection, damage to insulation, or stray current can easily generate that level of current. A very small quantity of current flow in an improper path can create fire or personal injury.
EASUREMENT 7.13 M EASUREMENT Since ground values are so important, there must be a method to measure the resistance. Standard voltmeters, current meters, and ohmmeters will not work for this task. Few engineers, electrical contractors, or utilities have made the substantial investment in equipment, technology, and time to make the measurements. Years ago the only technique was the voltage drop (fall of potential) method. This instrument can be used to determine the resistivity of the soil. It can also be used to detemine the resistance of a ground rod.
Voltage fall method – gnd resistance*
The voltage drop off requires additional ground rods be driven in the earth. The spacing between the measurement stakes and the length of the stakes are critical to prevent interference. Soil resistance measurements are often corrupted by existing ground currents and harmonics. Furthermore, measurement results are often distorted and corrupted by underground metal, water, and other conducting paths. Therefore, multiple measurements are required. A second set of driven stakes should always be turned at 90 degrees from the original measurement for a comparison. By changing the depth and distance several times, a contour or profile can be developed that can determine a suitable ground resistance system. Because of the difficulty and the inconsistancy of the voltage drop results, alternative methods are preferred. Over twenty years ago, the clamp-on ground resistance instrument was developed. Now there are multiple manufacturers of these instruments including such well known quality instruments as AEMC, Amprobe, and Fluke. The price ranges around $1200 to $2000.
Gnd resistance - AEMC
The clamp-on ground-resistance instrument greatly simplifies the process of measuring ground resistance, non-intrusive leakage current, and continuity, without breaking the circuit. In addition adding other components such as stakes and rods is eliminated. Furthermore, the hazard of disconnecting parallel ground rods is eliminated. Measurements can be conducted where other methods are not possible, such as inside a building. The technique allows measurement of individual connections.
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The clamp is placed around the ground rod. The instrument induces a known voltage by one-half of the clamp. This signal will be reflected by the boundary between the ground system and the surrounding earth. The other half of the meter measures the size of the reflected signal. By comparing the reflected signal to the original signal, a calculation of ground contact impedance can be made. Then the instrument displays the impedance. The clamp-on resistance metere is is well-tested, accepted, and very mature technology. Not having the capability to determine the ground circuit contact resistance is no longer a professional pr ofessional option.
7.14 G ROUNDING ROUNDING & LIGHTNING Lightning is the discharge of electro-magnetic energy between a cloud and earth. Ben Franklin demonstrated lightning can be controlled in 1760. Three items are necessary for lightning management - air terminal, conductor, and grounding system.
Gnd resistance – Fluke*
The grounding system for lightning is separate from the grounding system from electrical power. Nevertheless, the lightning ground must be bonded to all other grounds. grounds. Grounding is included in the Codes for protection of persons and property. One of the things that grounding provides is a path for transients and lightning. Lightning like wind and rain is an act of God. Protection can be provided if the system is properly installed. If there is damage due to lightning, there is most likely a problem with the installation. A further discussion of lightning and its effects is contained in Chapter 10.
7.15 S UM UM IT UP Improper grounding is a frequent problem. Electrical ignition that is undetermined is likely a grounding issue. Grounding issues are a code, and therefore legal, violation.
7.16 REVIEW Ground is the common reference for all electrical systems. A proper ground has three functions.
Maintain equal voltage between points in the system. Provide path for fault current. Transients are snubbed by ear.th inertia
The pro The rop per int interc rco onnectio ion n of of gro grou und system ele lem ments, inc inclu lud din ing g the grounding electrode, is critical to manage voltage and current in the prevention and mitigation of fires. A grounding system has three components
Grounding electrode Grounding electrode conductor Bonding
Terminal, conductor, ground
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Neutral is the common name for the white or grounded conductor. It must be connected to the ground system at one point and one point only. The neutral carries the unbalanced load current. A neutral can be operated in three ways
Proper neutral neutral Floating neutral neutral Energized neutral Stray Currents are inadvertant current flows through the earth. They are caused by multi-point grounded neutral wires. Stray current can energize metallic surfaces creating shock risk and risk of fire.
IBLIOGRAPHY - I LLUSTRATIONS LLUSTRATIONS 7.17 B IBLIOGRAPHY Select photos courtesy of Fluke. 1. http://support.fluke.com/findsales/Download/Asset/2633834_611 sales/Download/Asset/2633834_6115_ENG_A_W.PDF 5_ENG_A_W.PDF 2. http://us.fluke.com/fluke/usen/Earth-Ground/Fluke1630.htm?PID=56021
C HAPTER HAPTER 8 – C ODES ODES & L A AW W 8.1
NTRODUCTION I NTRODUCTION
Industry standards are consensus practices for conduct within a particular field, such as residential electric, utilities, or HVAC. The standards are developed by interested professionals through organizations involved in an activity. Many standards are subsequently adopted by the American National Standards Institute (ANSI) for more general application. The ANSI standards are coordinated with the International Electrotechnical Commission (IEC) as international standards.
There are three levels of standards. The difference is in the language and requirements for implementation. Standards must be followed. Recommended Recommended Practices Practices should be followed. Guides may be followed. Codes are industry standards that have been adopted by various government jurisdictions. jurisdictions. Law consists of regulations, administrative code, and legislation that carry the power of the political jurisdiction charged with enforcing the activity.
Within the fire investigation field, the National Fire Protection Association (NFPA) is one of the leading organizations which develop standards. Others include, but are not limited to Institute of Electrical and Electronics Engineers (IEEE), American Society of Mechanical Engineers (ASME), American Petroleum Institute (API), Underwriters Laboratories, and International Code Council. The engineering authors are voting members of the NFPA electrical section and are members of the IEEE standards association. The engineering authors have chaired numerous standards within IEEE and API.
8.2
LECTRICAL C ODE ODE N ATIONAL E LECTRICAL
Industry Standard Recommended Practice Guide Code Law
The National Electrical Electrical Code is the most well-known, used, and referenced electrical standard. It is a consensus document developed by the NFPA electrical section as NFPA 70. The NEC is the accepted minimum standard for electrical installations in structures. Article 90.1(A) gives the purpose. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. Article 90.1(B) gives the adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use. Article 90.2(A) gives the areas covered as most any type wiring.
NEC – electrical standard
68
NEC
Mandatory application & Use by insurance inspectors
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This Code covers the installation of electrical conductors, equipment, and raceways; signaling and communications conductors, equipment, and raceways; and optical fiber cables and raceways for the following: (1) Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings... Article 90.4 gives enforcement to government and standards for insurance inspectors. This Code is intended to be suitable for mandatory application by governmental bodies that exercise legal jurisdiction over electrical for use by insurance inspectors.
8.3 J URISDICTION URISDICTION The state of Oklahoma and most other states have adopted the NEC as the standard for electrical installation. The Oklahoma Electrical Licensing Act gives the authority to the Construction Industry Board, which is under the Department of Health. "Electrical construction work" means installation, fabrication or assembly of equipment or systems included in "premises wiring" as defined in the 2008 edition of the National Electrical Code, which is hereby adopted and incorporated by reference. In addition, the state Fire Marshal’s office has adopted this code along with others. The State Fire Marshal agency is charged with the responsibility of enforcing the codes and standards relative to fire safety adopted by the State Fire Marshal Commission under the "Fire Marshal Act”.
Code enforcement
The following national codes and standards are incorporated by reference: (12) NFPA #70 The National Electric Code and its annex's, 2008 Edition. The matter of jurisdiction and inspection is a question for any installation. The NEC is the minimum standard for electrical installations. The State can inspect an installation under the Department of Health Construction Industries or under the authority of the Fire Marshal. For public facilities, the jurisdiction is clear. For private residences there is some challenge because of the castle doctrine. Finally, an insurance company can demand compliance as a condition of the contract.
8.4
LECTRICAL S AFETY C ODE ODE N ATIONAL E LECTRICAL
The National Electrical Electrical Safety Code (NESC) is the recognized authority for electrical utility installations, whether by a utility or individual. The NESC is the minimum standard for safe installation, operation, and maintenance of utility systems. It was developed by the IEEE as IEEE / ANSI C2. Article 010 gives the purpose.
NESC – utility type standard
The purpose of these rules is the practical safeguarding of persons during the installation, operation, or maintenance of electric supply and communication lines and associated equipment. These rules
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contain the basic provisions that are considered necessary for the safety of employees and the public under the specified conditions. Article 011 gives the areas covered.
Codes are not just suggestions, It’s the law.
These rules cover supply and communication lines, equipment, and associate work practices employed by a public or private electric supply, communications, railway, or similar utility in the exercise of its function as a utility. They cover similar systems under the control for qualified persons, such as those associated with an industrial complex or utility interactive system.
8.5 S TATE TATE L AW The state of Oklahoma and most other states have adopted the NESC as the standard for electrical utility installations. The Oklahoma Corporation Commission is responsible for enforcement of those utilities under their jurisdiction. The Commission hereby adopts the minimum requirements of the 2002 Edition of the National Electrical Safety Code (NESC) adopted by the ANSI (ANSI-C2) as its rules and regulations governing safety of the installation and maintenance of electric utility systems. Even for groups not under OCC rate rules, the law establishes that the minimum standard for safe utility construction, operation, and maintenance is the NESC .
8.6
I MPORTANCE MPORTANCE
MINIMUM STANDARD Practical safeguarding of persons & property
Codes are defined for the practical safeguarding. Any installation that does not meet the Code is not safe. Personal or property damage is the result.
An installation that does not meet Code requirements has three basis of fault. One is the violation of accepted industry standard, two is violation of insurance processes, and three is violation of state law. It is incumbent that the investigator knows and understands the Codes and their interpretation to effectively evaluate an electrical failure. Many non-compliant installations and equipment are overlooked because of lack of familiarity with the industry standards and state law. The reason that the Code is mandatory is actually quite simple. Each item in the Code is there because someone had a problem in that area.
8.7 IEEE IEEE 142 142 The IEEE Green Book is the recognized standard for grounding of electrical installations. It was originally developed for industrial and commercial power systems. The NEC Article 250 on grounding systems is the same for all structures. The electrical relation to earth is the same for all installations. Therefore, the Green Book appropriately applies to all structures and installations including residential systems also.
IEEE 142 Standard
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8.8 NFPA 780 The Standard for Installation of Lightning Protection Systems is the recognized standard for lightning protection. It is published by the National Fire Protection Association as NFPA 780. The Standard is reverenced in the NEC. This is not a new or novel topic, regardless of common understanding. The first NFPA standard on the topic was Specifications for Protection of Buildings Against Lightning published by NFPA in 1904. The fundamental procedures were developed by Dr. Benjamin Franklin in the 1760’s.
NFPA 780 Standard
NFPA 780 is one of the many standards published by NFPA to address various safety issues. Since it is a standard, its practices are not optional. A complete lightning protection system is not required for most installations, but lightning risk assessment must be considered as noted in the introduction.
The lightning risk assessment is provided to assist the building owner, safety professional, or architect/engineer in determining the risk of damage or injury due to lightning…Once lightning…Once the level of risk has been determined, the development of appropriiate lightning protection measures can begin. begin. There are several items that increase the risk of damage. 1. Large structures are higher risk 2. Multistory structures have elevated risk. 3. Isolated structures have increased exposure. 4. Structures on hill tops have higher vulnerability. 5. More flammable construction methods increase probability. 6. High value objects increase the risk potential. There are standard practices outlined in the document that are required to mitigate lightning effects. There are a few key items that must be followed for any installation. 1. There must be an adequate ground system for the strucutre. 2. Each electrical system must be grounded. 3. All electrical systems muct be bonded together. 4. All metal that can become energized must be bonded together. 5. The wire size must be adequate for the current exposure. 6. The wires must be installed with bends having a radius greater than 8”. You will note that these are essentially the same requirements as the other Codes that address grounding.
8.9 NFPA 921 Guide
NFPA 921
Guide for Fire & Explosion Investigations was developed by the NFPA as NFPA 921. It is a guide for investigations. As such it is a suggested practice.
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Article 1.2 gives the purpose. The purpose of this document is to establish guidelines guidelines and recommendations for the safe and systematic investigation or analysis of fire and explosion incidents. Article 1.3.3 gives the limitations. Not every portion of this document may be applicable to every fire or explosion incident. As a guide, its use is not enforceable. Since it is a recognized industry document, deviations could result in questioning about the investigators practice. As a result, deviations from this guide should be well reasoned and supportable.
ROFESSIONAL RESPONSIBILITY 8.10 P ROFESSIONAL
Licensed Professional Engineer
A licensed professional engineer and a licensed electrical contractor , under State law, are obligated to operate under the Code. Although these individuals are not attorneys, it is necessary to know the legal requirements of the professions. An installation that does not comply with defined state law is classified as negligence per se by attorneys. Therefore, an understanding of the Code is necessary when conducting a failure analysis that may have resulted in an incident.
8.11 REVIEW There are three levels of industry standards.
Standards – must be followed Recommended Practices – should be followed Guides – may be followed
institutions Codes are industry standards adopted by government institutions Law consists of regulations, administrative code, and legislation. NEC is the most used electrical standard. The purpose is the practical safeguarding of persons and property. The Code covers electrical installations on the user side of the electric meter. NESC is the code for utility type installations. The purpose is the practical safeguarding of persons and propery. The Code covers electrical installations on the utility side of the meter. IEEE Green Book is the standard for grounding installations.
installations. NFPA 780 is the standard for lightning installations.
Wire Use
Amps AWG
Low-voltage lighting and lamp cords
10
18
Extension cords
13
16
Light fixtures, lamps, lighting 15 runs
14
Receptacles, 110-volt air conditioners, sump pumps, kitchen appliances
20
12
Electric clothes dryers, 220volt window air conditioners, 30 built-in ovens, electric water heaters
10
Cook tops
45
8
Electric furnaces, large electric heaters
60
6
Electric furnaces, large electric water heaters, sub panels
80
4
Service panels, sub panels
100
2
Service entrance
150
1/0
Service entrance
200
2/0
HAPTER 9 – E LECTRIC LECTRIC AND C HAPTER OMMUNICATION U TILITIES TILITIES C OMMUNICATION 9.1
NTRODUCTION I NTRODUCTION
Utilities are defined as any supply and signal that is external to the structure. Electrical related utilities are power, telephone, cable, satellite, television, and radio. There are three common features – they bring an electric signal into the structure, they require a ground connection, and they are covered by standards and codes. An overview of the latter two items was covered in previous chapters. This chapter will look at the specifics.
9.2
E LECTRIC LECTRIC UTILITY
Ground connection utility meter pole
The electric utility provides 120/240 volt, single-phase power to most buildings and structures. The power is typically two hot wires and a common that is grounded. The power is derived from a transformer which converts higher voltage, greater than 4160 Volts, to relatively lower voltage. The transformer is simply two coils of wire with the number of turns equal to the voltage ratio. Multiple customer services may be supplied from a single transformer. Larger loads will have a dedicated transformer. The utility installation, operation, and maintenance is controlled by the National Electrical Electrical Safety Code (NESC). Oklahoma and many other jurisdictions have adopted the NESC as the minimum standard for overhead and buried electric service.
Ground inadequate
Control: The utility has fuses on the high voltage side of the transformer. These are not sized to protect the load but only to protect the line that supplies the transformer. NESC has extensive requirements for grounding for protection. Problems are discussed as risks. Risks: There are substantial problems with ground paths, nuisance currents, and multi-point grounds. The utility connects the common or neutral conductor to earth at numerous locations, sometimes as often as every pole. A multi-point ground allows part of the current to flow through the neutral wire and part of the current to flow through the earth. Studies have shown that as much as 60% of neutral current flows through the earth. That means that at some location, the utility current is flowing through metal paths that were not designed to handle the current. Shock and fire is the consequence.
Utility end pole is problem
Another issue is transients or surges that are on the power system because of inadequate protection and operations practices. In some instances, excessive current is delivered to a facility causing failure of electrical components or appliances. The result is fire.
Telephone entrance no ground
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It should be noted that the utility operates the primary or high voltage side as a multi-point ground. However, the secondary or low-voltage side is specifically identified as a separately derived source at the transformer. Therefore, it is not a multi-point ground. If it is grounded at more than one location, the high voltage ground currents will flow into the low voltage system. The consequence will be structure damage in the form of fire and corrosion and biological impact by stray currents. That is very bad.
9.3 Service entrances
C OMMUNICATIONS OMMUNICATIONS
NEC Article 800 defines communications systems.
Communications circuit include voice, audio, video, data, interactive services, telegraph, outside, outside, etc. from the communications communications utility to the the customer’s communication equipment up to and including terminal equipment such as a telephone, fax machine, or answering machine. These are basically analog systems. The wiring may be telephone wire, Cat 6 cable, or coax. Circuits and equipment must be installed in a neat and workmanlike manner so that the wiring will not be damaged in normal use. Wiring and penetrations are made so that the possible spread of fire or products of combustion will not be substantially increased. Wires must have defined separation from other wires and roofs. Ungrounded coax discharge to electric
Control: A primary protector is required on each circuit that is not grounded or interruped with a block and where potentially exposed to power lines or lightning. lightning. That includes every circuit.
The metallic sheath must be interrupted or grounded where it enters the building. The grounding conductor shall be insulated and listed. The conductor shall not be smaller than 14 AWG. The primary protector grounding conductor shall not exceed 20 feet in length. Where separate electrodes are used, a bonding jumper not smaller than 6 AWG shall be connected between the communications grounding electrode and power grounding electrode. Ungrounded dish with lightning damage
Coax with lightning blowout
On a mobile home, the distance to a grounding electrode is extended to 30 feet. The ground must be bonded to the metal frame with 12 AWG or larger. Risks: Coax is designed to carry electromagnetic signals that are in the same frequency range as lightning. Communications lines are a common entrance for transients, including lightning, if not properly installed and grounded. Transients can damage the equipment connected and cause fire.
Voltage up to 85 Volts can exist when a phone rings. Normally the lines are very low voltage and current.
9.4
ELEVISION R ADIO & T ELEVISION
NEC Article 810 defines radio and television antenna systems.
Antenna coax shield connection to ground
Antenna systems include radio and television receiving as well as amateur radio transmitting and receiving equipment. The system includes satellite dishes and the antenna site of community television systems.
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The structure shall be able to withstand ice and wind loading conditions and be located well away from overhead power conductors. Control: Each conductor of a lead in shall be provided with a listed antenna discharge unit that is not located near combustible material. The mast must be grounded.
The discharge unit shall be grounded. The ground conductor shall be 12 AWG copper or larger. The conductor does not have to be insulated. The bonding jumper to the power grounding electrode system shall be 6 AWG copper or larger. Risks: Aluminum cannot be used for direct contact with earth. Grounding is crucial to carry transients transients away from the wiring to the earth.
9.5
CATV coax grounded
CATV
NEC Article 820 defines community antenna television (CATV) or cable systems.
The article covers coaxial cable distribution or radio frequency signals typically employed in community antenna television (CATV) systems. Power up to 60 volts may be applied on the system, which is adequate for shock and fire. Circuits and equipment must be installed in a neat and workmanlike manner so that the cable will not be damaged in normal use. Wiring and penetrations are made so that the possible spread of fire or products of combustion will not be substantially increased. Wires must have defined separation from other wires and roofs. r oofs.
Coax with bead started fire
Control: The metallic sheath shall be grounded where it enters the building.
The grounding conductor shall be insulated and listed. The conductor shall not be smaller than 14 AWG or larger than 6 AWG. The conductor shall not exceed 20 feet in length. Where separate electrodes are used, a bonding jumper not smaller than 6 AWG shall be connected between the communications grounding electrode and power grounding electrode. Mobile home distance to a grounding electrode is extended to 30 feet. The ground must be bonded to the metal frame with 12 AWG or larger. Risks: Cable lines are common entrance for transients, including lightning, if not properly installed and grounded. Transients can damage the equipment connected and cause fire.
9.6
Wireless internet
N ETWORK ETWORK POWERED BROADBAND
NEC Article 830 defines network-powered broadband communications systems.
Broadband communications includes any combination of voice, audio, video, data, and interactive services through a network interface unit (NIU). These are basically high speed digital computer networks. Circuits and equipment must be installed in a neat and workmanlike manner so that the cable will not be damaged in normal use. Wiring and penetrations are made so that the possible spread of fire or products of Mobile home service permits 30’ to ground
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combustion will not be substantially increased. Wires must have defined separation from other wires and roofs. Control: A primary protector is required on each circuit that is not grounded or interrupted interrupted with a block, and where potentially potentially exposed to power lines or lightning. The primary protection can be an integral part of the NIU.
The grounding conductor shall be insulated and listed. The conductor shall not be smaller than 14 AWG or larger than 6 AWG. The conductor shall not exceed 20 feet in length. Where separate electrodes are used, a bonding jumper not smaller than 6 AWG shall be connected between the communications grounding electrode and power grounding electrode. Mobile home distance to a grounding electrode is within 30 feet and in sight of the entrance. The ground must be bonded to the metal frame with 12 AWG or larger.
NTERSYSTEM B ONDING ONDING 9.7 I NTERSYSTEM The drawing illustrates the inconnection of the bonding and grounding for the various electrical systems entering a structure.
11
1
2
All bends should be greater than 8 inch radius to keep inductance down for high frequency transients. The maximum length of a ground conductor should be 20 feet to keep high frequency impedance to acceptable levels.
12
3 4 9
10
8
7 M.O. Durham Theway Corp.
6 5
Intersystem bonding & grounding
# 1 2 3 4 5 6 7 8
Device Feeder with utility ground Meter-connect utility gnd to gnding electrode conductor Service panel - neutral connect to ground Intersystem bonding point for all grounds Grounding electrode conductor >#6 Grounding electrode – bond all Grounding electrode within 20 ft of antenna Telecommunications with discharge Network interface with discharge discharge 9 CATV discharge / block unit 10 Antenna discharge unit 11 Antenna coax 12 Antenna ground
NEC NESC 250 250 - II 250.94 250.66 250 - III 810 800 830 820 810 810 810
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9.8 REVIEW Utilities are any supply and signal that is external to the structure. Electric utility utility provides electric power to the structure.
Utility installation, operation, maintenance is covered by NESC. Utility fuses do not protect the structure or equipment. Multi-point grounds are a major problem and source of stray currents. The structure ground is from a derived source and is not multi point. Transients or surges on power lines transfer to the strucutre. Communication circuits are voice, audio, video, data, etc. These systems are governed by NEC Artcles 800 ff.
These are basically analog systems. A primary protector is required on each circuit. The metallic sheath must be interrupted or grounded at the entrance. The ground connection must be < 20 ft away.
Radio and Television Television antennas are governed by NEC Article 810.
Antennas must be located well away from overhead power conductors. Antennas need a discharge unit. The mast must be grounded.
CATV sytems are governed by NEC Article 820.
The metallic sheath of coax must be grounded at at the entrance. The ground must be within 20 ft (30 ft for mobile homes).
Network Powerd Powerd Broadband Broadband systems are governed by NEC Article 830.
Basically this is digital, high-spead computer networks. A primary protector is required on each circuit. The ground connection must be <20 feet from the entrance.
HAPTER 10 – LIGHTNING C HAPTER 10.1 I NTRODUCTION NTRODUCTION Lightning is at once fascinating, dangerous, and little understood by most. Lightning is considered an act of God by many. Think about other weather conditions such as rain and temperature. These are equally an act of God. However, we have learned to control them with buildings and other structures. Similarly, lightning can be controlled and directed by following industry practices and standards.
Ionosphere
+ + + + + + + ++ +
100 MV
1 µF 140 MWHr (1 Hr)
-
The origin of lightning, like other weather, is an act of God. However, damage due to lightning is an act of negligence or omission in most incidences we - -- -- ++ - - - - -+ have investigated. The authors have conducted + research and written extensively about lightning and Lightning circuit grounding. These papers form the basis and background for the observations observations included.
-- - - -- - - -- -
+
100 MV
+
-- - -
10-30 kV/M
+
+ + ++ +
+ +
++++ + + ++ +
-
~10kA Fair Weather 100 V/M
++ + + + ++
-
- --- -
10.2 DIFFERENTIAL POTENTIAL There is a voltage or potential between a cloud and the earth. The voltage is spread over the distance separating the two. The result is an electric field or voltage gradient. Regardless of the presence of a thunderstorm, there is always a gradient in the air. These are all examples of a vertical electric field. Similarly, as a cloud moves over the surface of the earth, a horizontal potential develops between areas under the cloud charge and those outside the cloud. Furthermore, the earth resistance and the electrical ground are not uniform, which causes a horizontal potential.
Discharge on edge of metal vent
Any potential difference, whether vertical or horizontal, can create a discharge resulting in injury or damage.
10.3 LIGHTNING TRANSIENTS Before addressing the failure analysis, the characteristics of lightning and transients should should be identified. identified. There are three possible possible vehicles vehicles for lightning influence. These are (1) a direct strike , (2)an indirect strike or induced potential, and (3)an earth charge.
Lightning discharge on aluminum vent
For the first mechanism, a direct strike , lightning is simply the discharge of electromagnetic energy developed above the earth. It discharges through a conductive path to earth. The discharge path is often metal. However, trees and posts in earth also make a good path. Concrete is also a possible path because of its low resistivity compared to most soils. The actual discharge is a direct strike. A direct strike carries the full energy and results in the most damage. This is what most people think of when they discuss a lightning strike. Lightning discharge on CSST
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The second mechanism, an indirect strike, will also result from a discharge. A potential is built up between the cloud and earth. Any conductive surface within this field will develop a proportional potential. When the cloud discharges, a charge remains on the metal and must be dissipated. This remaining energy will find all possible paths to earth.
Arcing from indirect strike
The charge typically builds on a metal surface with a large area that rises above the earth. This may be a metal chimney, flue pipe, antenna, transmission line, or similar conductor. The charge travels along the metal to a point of discharge. The energy then can discharge to a surface surface that has a lower impedance path to earth. Since the charge build-up and the resulting potential difference is quite large, it can easily “jump” across normal electrical insulation as well as a substantial air gap. For the third mechanism, earth charge, the earth will be energized by lightning in the area of impact. The T he charge creates a higher potential than both the surrounding earth and conductors in contact with the earth. The energy will dissipate to form a uniform field. The result of this dissipation is current flow from the area of impact. All conductive paths in the area will develop current flow. Adjacent conductors will not develop a large potential difference. Remote conductors, however, can have a substantial difference in potential as a result of this this earth charge.
Arcing of lightning on brass gas fitting
TROKES 10.4 S TROKES A lightning strike is not a single event. The strike begins with a down stroke toward the earth. An upward leader meets the stroke. A return stroke then completes the process. A detailed analysis is discussed in the authors’ technical papers. As air is ionized from the initial strike, the impedance of the air is reduced. This may result in multiple strokes in a very short span of time. These may discharge to the same location or a nearby area. This would be recognized as multiple strokes. strokes.
Discharge to bolts on air conditioner
A single strike will create a dispersed field near the area of discharge. The energy is not discharged at a single point; it will be distributed to numerous spots. If the metal surface that carries the charge to earth is lightweight enough, enough, the dispersed discharge will will look like numerous pits pits on the metal surface. St. Elmo’s fire is visual plasma created by a corona discharge about a grounded object during a thunderstorm. The phenomenon clearly shows the dispersed effect of the electromagnetic field. We have observed arrays which distribute lightning energy c reate an effect of St. Elmo’s.
Ball lightning is another dispersed electromagnetic field that is visible. Ball lightning is generally a spherical shape which develops and often travels along a conductor to a discharge point. It is a long duration phenomenon and may last for for seconds.
10.5 C ONTROL ONTROL Discharge between CSST and cable
Lightning is simply the discharge of an electromagnetic (EM) field. Since lightning is electromagnetic energy, it can be managed as any other circuit.
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Lightning
81
Three measurements completely describe EM energy. Voltage is the potential or pressure. Current is the flow rate. Frequency is the inverse of the time for the signal. By controlling all three measures, lightning can be managed. Voltage is clamped at a threshold level that precludes damage. Current is diverted to earth. Energy of a particular frequency is filtered from the conductor. Energy that is developed in a cloud is attempting to return to earth or ground potential as lightning. Hence, an excellent ground network is the critical element of a lightning management system.
10.6 G ROUND ROUND An electrical grounding system uses a single point as a reference for all measurements. This is called the grounding electrode.
Transient control
In an attempt to create minimum potential difference in the ground system, all grounding electrodes that are present at each building or structure served must be bonded together to form the grounding electrode system.
10.7 B OND OND A bond is a connection between metal surfaces that may be energized.Assuming there is an adequate ground, bonding is crucial. Three factors impact the effectiveness of the grounding and bonding conductor.
First, conductor diameter should be AWG 4 or larger, to minimize resistance.
Potential difference panel to ground
Next, the distance from the bond to the ground should be less than 20 feet, to minimize impedance.
Finally, the route must be as direct as possible with only sweeping bends, to minimize inductance.
Other than the size, these factors correlate to NEC Article 820 requirements for communications circuits.
10.8 E RRORS RRORS & OMISSIONS The following are five preventable incidents that were investigated in a three-month period. This is by no means a complete list of our lightning investigations, but is representative of the types of errors that are related to lightning damage. The lightning event was verified by witnesses or lightning reporting services.
Potential difference ground to AC tubing
10.8.1 C LEAR LEAR AIR AND END POLES Must the lightning occur at the point of discharge? No, the charge can build up in one region and travel along a long a conductive path and discharge in another location. Further, the charge can be distributed over a long area such as a power line. Clear-day lightning may build up along an overhead power line. If there is not an alternate path, the discharge is typically at an end pole on the line.
End pole on power line
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The end pole sees a reflection of the incoming wave. As a result the voltage transient at the end of the line is twice as large as at other points.
10.8.2 P OOR OOR GROUND ELECTRODE What is the effect of a high resistance ground rod? Any fault current will take an alternate path to earth and will damage items in the path. A ground rod at a service meter pole had virtually no contact with earth. The resistance was 800 Ω, which is approaching no connection.
Energized neutral melted insulation
A transient fault occurred and took two identifiable paths. One path was another overhead triplex cable. The uninsulated grounded neutral carried excessive energy. This caused the insulation on the other two phase conductors to melt in the shape of the neutral. The insulation on the opposite side was unaffected.
10.8.3 REBAR What is the effect of not bonding concrete encased metal and rebar to the electrical ground system? The potential difference will damage the concrete and create enough discharge energy to ignite combustibles. The ground on the system met the letter of the Code but was not good. The resistance was 6.5 Ω, but sharp bends increased the inductance.
Unbonded rebar arc through concrete
A lightning strike entered the structure at the peak above the second floor on the northwest side. The first contact with metal was a bundle of 21 non-metallic (NM) cables that were routed to the circuit breaker panel. Rather than take the torturous path of the grounding electrode conductor with sharp bends, an alternate alternate path was identified identified by arcing. The circuit breaker panel cover was removed during construction. The panel arced to a metal grate leaning against the panel. The grate arced to the panel cover setting on a concrete floor. The energy arced through the concrete creating spralling.
10.8.4 G AS PIPE Should gas lines be grounded or bonded? The Code is clear that they as well as other metal piping should be, but some jurisdictions prohibit the connection, since they improperly interpret bonding as grounding. In many installations we have found that the connection simply was not made. Flexible pipe arc to wiring
The electrical ground resistance was excellent with 0.7 Ohms. The flue to an HVAC unit is a large metal surface area that protrudes above a structure. It is a ready entrance for lightning energy, whether direct or indirect. A strike will penetrate the cap with nail size holes. Arcing is noted along the pipe joints. The lightning energizes any metal connected to the unit. This includes gas line, copper air-conditioning lines, and electrical conductors. Seldom does rigid steel gas pipe have a failure. However, flexible metal lines will be penetrated if crossing another metal conductor including insulated electrical wires.
10.8.5 S 10.8.5 S ATELLITE DISH & CABLE Satellite dish ungrounded
Will coax cable carry enough energy to cause a fire? Must satellite dish and coax cable be grounded and bonded? Coaxial cable is designed to carry high frequency electromagnetic energy in the form of television
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signals. Lightning is a high frequency signal with substantially more energy. So, lightning will preferentially travel along a coax. Lightning struck struck the post of an ungrounded dish dish mounted to a roof. A hole was blown in the steel post. The cable splitter was destroyed at the terminations. The cable jacket was split but otherwise appeared intact. The foam filler, shield, and copper c opper had become plasma and vaporized.
ROUNDING & LIGHTNING 10.9 G ROUNDING The origin of lightning, like other weather, is an act of God. However, damage due to lightning is an act of negligence or omission in most incidences we have investigated.
Bolts severed on ungrounded dish
Grounding and lightning control is included in the Codes for protection of persons and property. Protection can be provided if the system is properly installed. If If there is damage due to lightning, lightning, there is most likely a problem with the installation. NFPA 780 Standard states in the introduction:
The lightning risk assessment is provided to assist the building owner, safety professional, or architect/engineer in determining the risk of damage or injury due to lightning…Once lightning…Once the level of risk has been determined, the development of appropriate lightning protection measures can begin. begin. Clearly a lightning risk assessment should be made. Then the decision is what type lightning protection is required. If an assessment is not made and an appropriate system installed, the identified parties are negligent or worse. How many assessments are actually conducted? A common perception is that lightning caused incidents have no recourse. That has been proven as incorrect in numerous incidents. The failure to provide and install a proper system is the basis for most incident recovery. You cannot sue God, but you can show negligence by people for improper and inadequate systems.
10.1 LIGHTNING REPORT Lightning activity is recorded by a number of entities. One of the organizations is Vaisala. These reports can be used to identify the proximity of a strike and other other properties of the event. The probability probability of a strike strike depends on a confidence confidence ellipse that calculated from their detection antennas.
is
The illustration is one page of the report and is shown based on the proximity of a strike. Recall that lightning damage can result from a direct strike, indirect strike, and ground current. Therefore, the strike does not have to be at ground zero for it to affect a structure.
Lightning incidents
Vent entrance for lightning
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HAPTER 11 – ARTIFACT C HAPTER IDENTIFICATION NTRODUCTION 11.1 I NTRODUCTION Identification of the device or appliance that failed is a rather involved process of failure analysis. Failure analysis cannot ca nnot be complete without determining the device and its characteristics. This is true for incendiary or accidental fires. Most devices are distributed under a brand name with a model name. The unique identification is the model number and serial number. The brand name is used for marketing and frequently is not associated with the manufacturer. For example, General Electric appliances are not manufactured by GE, but by myriad other companies. Identification labels are often computer printed and stuck to the appliances. Frequently after a fire all labeling is destroyed. Plastics molded with names and model numbers are destroyed. The remains may only be metal components including the cabinet frame and motor frame with some wire. Identification can be challenging. For incendiary incidents, chemicals are typically involved. The residue may be an odor or contaminated byproducts. Test kits and electronic detectors are frequently available. Otherwise, lab tests are required to validate the material identity.
IRST 11.2 F IRST The first step to identification is asking the owner. Unfortunately, most memories are incomplete. Who remembers the model and the serial number? For recent purchases, big ticket devices, and specialty items, memory may be some better. Records, if they existed are often lost in fires or incidents. If the place of purchase is known and a credit card was used, the store may be able to run a database search to ID the device. Obviously, for incendiary incidents, the owner is likely to be less than forthcoming.
11.3 S LEUTH LEUTH The metal framework is a key to identification of unknown units and items. There are numerous variables to consider. 1. Shape is the beginning. This includes rectangular, triangular, and curves. 2. Dimensions are length, width, and height. Cord length, if all of the cord is available may be beneficial. Cord wire size and number of strands of the cord may provide valuable information. 3. The folds and overlap of metal corners gives clues.
1. 2. 3. 4. 5. 6. 7.
ID Shape Dimensions Folds Attachments Stamped Ventilation Printing
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4. Attached plates and covers provide additional parameters. 5. Metal and plastic surfaces may be stamped for strength. The shape of the stamp is identification. 6. Ventilation holes, number, location, and pattern give unique identifiers. 7. Safety instructions stamped in the metal occur occasionally.
11.4 C ORPORATE ORPORATE MEMORY One of the best identification methods we have found is corporate memory. This works on multiple levels. Each of our engineers has over twenty years experience. They frequently recognize a device from a prior incident. The other engineers are an integral resource who can help ID from their prior exposure. We have a storage archive of exemplars used to ferret out the identification. Our documentation includes photos of thousands of previous cases. There may be a photo of of a related device.
11.5 LEGWORK Photos of the incident device are taken to big box stores and internet sites to find similar recent acquisitions. These tend to be time consuming, but may require the services of the engineer. We have an office researcher with an engineering background that does internet searches.
11.6 E XEMPLAR An exemplar is a similar device that can be used to aid identification. In addition the exemplar can aid in placement of the components to a preincident condition. Finally, exemplars may help identify failure information.
EAM 11.7 T EAM The identification of incident devices is a team effort. The first responder, who may be an adjuster, is crucial to retaining all components as complete as possible. Similarly the Origin & Cause investigator in discussions with the owner may be able to identify the device. The legal assistants are valuable in searching eBay and other sites for exemplars. Finally, the engineer must pull all the information together to develop the correct product identification and analysis. Without the product information, the analysis is stymied.
HAPTER 12 – U SER W ARNINGS C HAPTER 12.1 I NTRODUCTION NTRODUCTION Obviously the user is a potential source of problems. The user contributes to failures by abuse, misuse, or negligence . However, if it can be anticipated that a user will do certain things, them the device should have some level of protection against that circumstance. A common situation is leaving a device on after use. Should that cause a problem? Another is leaving the appliance plugged-in. This should certainly be expected since it is a common practice to plug in electrical apparatus and leave it plugged in between uses. In fact, constant plugging and unplugging can create additional stresses on cords and connections.
12.2 W ARNINGS Because of known risks or potential for injury, manufacturers and those responsible for safety use a system of warnings. Warnings are notices to the user about possible consequences. Warnings often reflect a previous problem. Warnings have three levels as noted by the signal words – caution, warning , and danger . The ANSI Z535.5 definitions will be given. OSHA 1910.145 has the same categories and similar definitions with some difference. OSHA is predominantly concerned with the workplace. The signs have the same coloring, but with a different format.
Danger indicates a hazardous situation which, if not avoided, will result in death or serious injury. The signal word "DANGER" is to be limited to the most extreme situations. DANGER [signs] should not be used for property damage hazards unless personal injury risk appropriate to these levels is also involved.
Warning indicates a hazardous situation which, if not avoided, could result in death or serious injury. WARNING [signs] should not be used for property damage hazards unless personal injury risk appropriate to this level is also involved.
Caution indicates a hazardous situation which, if not avoided, could result in minor or moderate injury. CAUTION [signs] without a safety alert symbol may be used to alert against unsafe practices that can result in property damage only.
ANSI has an additional signal word for items not related to personal injury.
Notice is preferred to address practices not related to personal injury. The safety alert symbol shall not be used with this signal word. As an alternative to “NOTICE” the word “CAUTION” without the safety alert symbol may be used to indicate a message not related to personal injury.
ANSI Z535.5 Signs
OSHA 1910.145 Signs
HAPTER 13 – S AFETY C HAPTER 13.1 I NTRODUCTION NTRODUCTION Safety is important to prevent injury. Safety is crucial around electrical systems to prevent a fatality. Traditionally, investigators have been somewhat cavalier about safety. Hence, the discussion may seem excessive compared to normal practices. These are considerations not requirements. Different sites and different environments will require alternative practices. Three areas will be addressed - personal protective equipment (PPE), lock-out/tagout, and scene evaluations. NFPA 921 recommends two individuals be on site for safety considerations.
ERSONAL P ROTECTION ROTECTION E QUIPMENT QUIPMENT 13.2 P ERSONAL PPE is attire and devices to protect the individual. These tend to be inconvenient in the short term of the job, but provide long term protection. Boots have three functions associated with the debris around a failure scene. Boots have a higher side to protect ankles from twisting and also aid knees on uneven terrain. A hard-toe protects from falling items. A hard shank with a thick sole aids in protection from nails and sharps penetrating the sole.
PPE basics
Safety glasses are eye protection with side shields to preclude debris from entering the eyes. The material mitigates breakage when struck by flying objects. Gloves are hand protection. Flexibility is a necessary requirement. The material depends on the environment and the job. Unknown chemicals and water commonly occur at failure scenes. A nitrile coating provides some protection. Wood and metal splinters can disrupt any job and gloves can preclude that event.
Temperature conditions dictate material and utility. Cold weather obviously impacts flexibility. Furthermore, hot weather creates discomfort which may motivate removal of gloves.
Gloves, partial coated nitrile
A compromise that works reasonably well is an open mesh on the back with nitrile on the hand and fingers. Hand warmers can be inserted to aid in warming. Breathing masks are very important health items. The chemicals and vapors created from burning of materials, particularly plastics, are often toxic. The effects of breathing the toxins are not frequently known for years. Inconvenience and discomfort are common excuses for not using masks. A basic vented mask provides some assistance and has tolerable discomfort. A better choice is a chemical mask ventilator.
Safety Glasses
Pants. For normal scenes, the preferred material is denim or twill 100% cotton. This provides tear and burn protection.
Insect spray
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Shirts. Shirt material should be similar to pants. Long sleeve is preferred. However, in hot environments, short sleeve is acceptable. Hard hats provide head protection from bumping or falling items. Seldom are they required in after af ter incident investigations. investigations.
Hardhat
Insect spray comes in handy on some scenes. Fleas, roaches, maggots, flies, and other such irritations can be dispersed. An odorant such as menthol petroleum jelly can help with some of the smells such as animal wastes and decaying matter.
CENE EVALUATION 13.3 S CENE Scene evaluation is critical to determining safety and personal protection equipment requirements. The materials involved, weather, and debris status will impact safety. Energy sources including electrical, fuel gas, and moving or potentially moving structures are key items to consider. All energy sources should be de-energized.
13.4 LOCKOUT / / TAGOUT Propane tank involved in explosion
Lockout / tagout is an OSHA recognized practice for controlling possible energy sources. In short, assure all energy sources are de-energized, then lock or tag the sources so no one will reenergize the system. Electricity. Electricity. As a minimum, first check that the electricity is off. This can be verified by visually checking that the power line is separated. If that cannot be verified, use a meter or energized circuit tester. Notably if the electrical power meter has been removed, and reinstalled using isolation tabs, the tabs do not work. The system may still be energized.
Use a known working sensor such as a voltmeter to verify the removal of electrical energy. Do not rely on any device that cannot be tested to verify it is working before use. Meter removed, but terminals exposed
Gas. Similarly, verify gas valves are off or the line is capped. After a failure incident, the lines may be crushed. Then with disturbing the scene, the line may begin leaking.
Pressure on a natural gas line is only 4 – 7 inches of water column (2.3 – 4 oz/in2). ounces. So, almost anything can plug the line. New propane tank systems may leach out the mercaptan resulting in a loss of odor. The propane tank may have pressure around 200 PSI. The regulator reduces the line pressure in the structure to 10 - 11 inches of water column (5.8 – 6.4 oz/in2.). Volt Ohm meter
DANGER
DO NOT REMOVE THIS TAG SEQUENCE OF APPLYING ENERGY CONTROLS (BY AUTHORIZED EMPLOYEES ONLY) 1. NOTIFY AFFECTED EMPLOYEES 2. PREPARE FOR SHUTDOWN 3. SHUT DOWN EQUIPMENT 4. ISOLATE EQUIPMENT 5. APPLY LOCKOUT / TAGOUT TAGOUT DEVICES DEVICES 6. CONTROL OF STORED STORED EQUIPMENT 7. VERIFY EQUIPMENT ISOLATION 8. PERFORM WORK 9. REMOVE LOCKOUT / TAGOUT TAGOUT DEVICES DEVICES 10. NOTIFY AFFECTED EMPLOYEES
HAPTER 14 – E THICS THICS C HAPTER 14.1 I NTRODUCTION NTRODUCTION What is ethics? What does it have to do with investigations and failure analysis? How do ethics relate to morality? How is ethics different from character? Are there absolutes? Is ethics cultural?
14.2 M ORALITY ORALITY One of the character traits is morality, which is defined as conforming to right and wrong human conduct. Sir Francis Bacon (1561 – 1626) 1626) was an English philosopher and politician during the time of James I. One of his works The Advancement of Learning addressed the subject of morality. For the end of logic is is to teach a form of argument to secure reason, and not to entrap it; the end of morality is to procure the affections to obey reason, and not to invade it… -Sir Francis Bacon
Bacon contended that the result of morality was to cause the emotions to follow reason. He asserted that it was reasonable and logical to pursue morality. It makes sense to follow a moral course.
Sir Francis Bacon*
The word ethics comes to English by Old French from the Greek. It is defined as the study of the general nature of morals and of the specific moral choices to be made by a person; moral philosophy. philosophy. [American] Ethics is the the philosophical philosophical study of morality. morality. Ethics form form a belief belief system.
The founding fathers unequivocally had a philosophy of ethics. The first President, George Washington wrote about these concepts in his First Inaugural Address. There is no truth more thoroughly established than that there exists in the economy and course of nature an indissoluble union between virtue and happiness. - President George Washington, First Inaugural Address
President Washington continued his advocacy of morality in his farewell address. Of all the dispositions and habits, which lead to political prosperity, religion and morality are indispensable indispensable supports. supports. - President George Washington, Farewell Address
He further wrote about guidance from higher authority as enlightenment.
Col. George Washington, Washington, an engineer*
The Enlightenment movement promoted intellectual reasoning to establish an authoritative system of ethics (religion), aesthetics (art), and knowledge (science).
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It will be worthy of a free, enlightened, enlightened, and at no distant period, a great nation, to give to mankind the magnanimous and too novel example of a people always guided by an exalted justice and benevolence. Who can doubt that, in the course of time and things, the fruits of such a plan would richly repay any temporary advantages which might be lost by a steady adherence to it? Can it be that Providence has not connected the permanent felicity of a nation nation with its virtue? The The experiment, experiment, at at least, is recommended by every sentiment which ennobles human nature. - President George Washington
Not 10 Suggestions No other gods
(government cannot control religion) No graven image (government cannot establish a religion) Not take God’s name in vain (public decency) Keep Sabbath day separate (certain business activity is limited) Honor your father and mother (protect elderly) You shall not murder (protect life) You shall not commit adultery (protect marriage & family) You shall not steal (protect property) You shall not bear false witness (perjury) You shall not covet others property (conspiracy)
Basis of all ethics
Not rulesJust doing what’s right
Dr. Huston Smith is a former professor of religion and psychology at MIT. He is the Thomas J. Watson Professor of Religion and Distinguished Adjunct Professor of Philosophy, Emeritus, Syracuse University. Dr. Smith is the author of Religions of Man , which has sold over two million copies. One of his books is Beyond the Post-Modern Post-Modern Mind . On October 26, 2000, he gave a lecture at Kenan Institute for Ethics, Duke University, entitled "Why Religion Matters, The Future of Faith in an Age of Disbelief." Dr. Smith later wrote a book of that title. The essence of Dr. Smith’s presentation is that values matter, even if some in the culture dismiss them. Ethics are absolute. They do not change with time or society. society.
Although they may not be uniformly appreciated and applied, ethics still exist. The principles of ethics are summarized in the last eight of the Ten Commandments. What if there are conflicting ethical principles in a situation? Then follow the rule of the greater good, i.e. which action, if all seem equally ethical, should be chosen? The dominant one is that which creates the most good, or the least evil. For example the protection pr otection of life supersedes the principles against theft of property. In the common law, self-defense or the protection of others is always a defense to a charge of assault or wrongful death. Protection of property is not. The practice of ethical behavior is clearly stated in the Golden Rule. [Matthew] Do unto others, others, as you would have have them do unto you. you. - Matthew 7:12
The Roman and Jewish politician, Matthew, recorded this particular model about 40 AD. The Golden Rule is recognized in one form or the other by all the great world religions and cultures. Confucius (Kongfuzi) called it reciprocity. [Confucius] Ethics is what what you do when no one is looking. looking.
No you-gottas
Do to others as you want them to do to you
Ethics are a fundamental tenet in traditional Western religious training. There is a US Office of Government Ethics. Each of the major professional societies has a Code of Ethics. [IEEE] Ethics are about how we behave and relate to others.
14.3 E THICS THICS VS LAW Ethics are not law.
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There may be no corresponding legal requirement to an ethical issue. There may be no law requiring you to report a fellow employee that is stealing or falsifying reports, but would it be ethical to suppress this information? Regardless of the legal requirements, ethical character traits are excellent guidelines in dealing with any situation. A question that is occasionally raised is whether it is possible to teach ethics or morality. The contention is that morality is the product of familial and cultural development and cannot be taught. That thought process really begs the question. What are the family and culture doing to instill this sense of morality other than teaching? The Congress that adopted the First Amendment and passed the Northwest Ordinance, the first law governing the western territories, contended that morality could be taught. One of the purposes of public schools schools was to teach morality. morality. [Northwest] Religion, morality, morality, and and knowledge, knowledge, being necessary to good government government and the the happiness happiness of mankind, mankind, schools schools and the means of education shall forever be encouraged. - U. S. Congress, Northwest Ordinance.
Ethics and morality are philosophy with principles. Each course that is taught with an objective of creating understanding simply Territories of Northwest Ordinance – 1787* goes back to the principles or fundamentals, regardless of the topic. Can mathematics be taught? Obviously. How is it taught? Teaching is by relaying mathematical principles and philosophy. Any topic which can be categorized as philosophy can be taught. Therefore, ethics can be taught in the context of philosophy and religion. There is a rational explanation for morality, as was noted above about Sir Francis Bacon over 400 years ago. [Bacon]
LIENT 14.4 C LIENT Ethics is different from law. Ethics is the responsibility to develop the “right” answer, regardless of the client. Every person has a different background, education, and experience.
How can two different experts looking at the same situation and facts come up with differing opinions and both be ethical? “In almost every case except the very plainest, it would be possible to decide the the issue either way way with reasonable reasonable legal justification.” justification.” -Lord Hugh Macmillan, Scottish jurist
Waismann on logic and language observed “Rules of Law are not linguistic or logical rules, but to a great extent rules for deciding ” That is an accurate understanding for investigations and analysis. Each person comes to an investigation with predilection based on previous experience. The ethical responsibility is to temper that with integrity using the scientific method.
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Just because because someone someone does not know something, does not keep it from being true.
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14.5 P REDILECTION REDILECTION In investigations, arson is frequently assumed. If no other understandable cause is found, an incident is often ruled arson. Just because someone does not know something, does not keep it from being true. There are many things not in a person’s background or that they would be expected to know. So it is no surprise that some things are not understood. Lack of background precludes making a reasoned judgment or undetermined.
I recall a 3:00 PM lunch with an investigator after a scene investigation. He mused “I wonder how many fires I have miscalled and sent people to jail.” He had been sure of the cause, but after a joint evaluation evaluation had found there were serious code violations that actually were the cause. He had no way of knowing since the area was far outside of an investigators purview. Ego is a dangerous commodity that clouds a clear analysis and resulting ethics.
NO, Don’t do it!
Conflicting tendencies
It’s OK
Another investigator was sure that an engineer had not conducted a complete and thorough investigation because he only saw part of the process. He had not seen the engineer do the testing and measurements and take 375 photos. He was not familiar with the fault mechanism that the engineer had observed. Because of the investigator’s understandable lack of detailed technical knowledge, he was sure the engineer could not possibly comprehend the failure that caused a fire. There seem to be two conflicting tendencies among investigators. Leave the cause as undetermined in many cases or an aversion to call undetermined. Both are extreme positions. The client is seeking an answer, but it must be ethically and technically correct.
14.6 S UPPORT UPPORT As engineers, we are often called to rule out the electrical system as a contribution to a fire, when arson is indicated. Not infrequently we find that in reality electrical was a contributing cause and it was not arson. There is a serious ethical responsibility when people’s lives are at stake. Most investigations are about loss and determining the cause. It is someone else’s money so the investigator has the ethical responsibility to be correct. Unfortunately, it sometimes occurs for an investigator to color his opinion to put his client in the best possible light. Protecting the client is appropriate, but not when it is unethical. Most of our clients have clearly affirmed that they do not want a stretch. Just tell them what happened without skewing the results. The clients do not want to expend resources pursuing issues that are marginal. Support system
One attorney was told that there was nothing to pursue on the incident. The response was “Good that is why we hire you.”
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14.7 P UBLIC UBLIC AND PRIVATE The public sector is less driven by monetary recovery but there are two issues that are ethically related. Public sector investigators generally look at a fire cause as incendiary or not. It was a former public sector investigator who mused “I had no idea you spent so much time looking at all the details of the electrical system in a fire .” In some instances a public investigator may be driven to determine a cause tempered with other incidents. A bad actor in one arena such as drugs, does not necessarily make him an arsonist when his house burns.
Two Dilemmas
Typically most public investigators do not have the time or resources that are available to private sector investigators. They do an admirable job, but it is not uncommon for the two segments to reach different conclusions. Clients of private investigators have an underlying reason to expend resources: the prevention of recurrent incidents. To that end, the ethical responsibility of both the private and public sector is to reduce recurrence. It is a money issue to private and people’s lives to the public arena. Overhaul of a scene should assure stopping the current incident and preserving evidence and artifacts artifacts so the private sector can preclude preclude future incidents. Ethics is your duty.
Follow the money
14.8 RULES Ethics is not rules; it is just doing what’s right. Some people are so methodical, they cannot see the details. That is not ethics that is ritual. Some people get bound up in rules and being official. That is not ethics that is legalism. As we have noted, ethics should supersede legalism. Some highly religious, rigid law enforcement, and very high “C” personalities impose more stringent rules. Interestingly, these groups tend to have more problems with ethics. They have conflict balancing the rules for every situation, since they are driven to do right in their perspective. As an example of an ethical dilemma, which of the Ten Commandments is most important? There are three responses.
Integrity is simply doing what you say Dad
Some people are so methodical, they cannot see the details.
Statement: Well, they are all equal. Question: What is the greater good? Exclamation: That is religion and not applicable!
10 Commandments
The most balanced is number 2, which looks for the greatest good. Did you ever wonder why the most rigid individuals flip? At some point they realize their rules are not working. So they give up for a new paradigm. Every individual is challenged at times with ethical conflicts. When the conflict cannot be resolved, stress results and poor decisions are made.
I II III IV V
vI vII vIII Ix x
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14.9 RESOLUTION
Above all, do no harm -excerpt from version of Hippocratic Oath
What is right? Every circumstance has potentially conflicting values. How do you make right choices? Select the one of greatest good or least harm. The Hippocratic Oath that guides physicians is over 2500 years old. It is still an excellent guide for all professions. Above all, do no harm. -excerpt from version of Hippocratic Oath
14.10 AUTHORS The authors have published three books on leadership including ethics and personality and two books on theology. They have published several articles dealing with ethics. Dr. Marcus O. Durham is a former seminary professor in apologetics. apologetics.
14.11 B IBLIOGRAPHY IBLIOGRAPHY – ILLUSTRATIONS Select photos courtesy of following. following. 1. Bacon, http://www.bnl.gov/bera/activities http://www.bnl.gov/bera/activities/globe/bacon_fi /globe/bacon_files/bacon.jpg les/bacon.jpg 2. Washington, http://www.vahistorical.org/exhibi http://www.vahistorical.org/exhibits/exhibits_ ts/exhibits_online.htm online.htm 3. Northwest, http://www.earlyamerica.com/earlyamerica/maps/nor http://www.earlyamerica.com/earlyamerica/maps/northwest/enla thwest/enla rgement.html
HAPTER 15 – P RACTICES RACTICES & C HAPTER ROCEDURES P ROCEDURES NTRODUCTION 15.1 I NTRODUCTION Practices and procedures address how investigations are conducted. Why are investigations and analysis made into failures and fires? Follow the money. In the public sector, the investigative goal is typically to determine whether the incident was accidental or associated with an illegal activity, whether arson, drugs, or other actions. Public sector investigation does not look at all failures and fires, particularly if the incident can be determined to be accidental in nature. Private sector failure investigations typically involve insurance, potential litigation, or attempt to mitigate repeat incidents. These are about recovery of costs associated with the incident. In the civil system, cost recovery is the only option. Numerous parties are involved in the investigation for each side. These include initial identifier of the issue, investigator, engineer, and legal. The role of each is unique, but often overlapping. Since it is typically the most involved, an insurance investigation will be used as a discussion point for all investigations whether public or private and litigation or inhouse. We work for virtually all the major insurance companies and myriad law firms, both for plaintiffs or defendants. Every company for whom we have worked is unique in their practices and procedures. Furthermore, the policies and processes change on a somewhat regular basis. Nevertheless, the fundamentals fundamentals stay the same.
Early investigator
Practices are many Principles are few Practices may change Principles never do.
90% In the hundreds of projects we do each year, we made affirmative identification of failure mode in the vast majority of incidents.
As outsiders, our observance of the best practices will be identified through the following discussion.
CONOMICS 15.2 E CONOMICS As analysts and investigators, we are independent and unbiased in our research; nevertheless, we operate with the legal system that is directed solely by monetary considerations. Before we begin a discussion about any business process, first we must identify the objective. The goal of any business activity is to maximize the owner’s wealth. Otherwise, there is no reason to be in business. Unfortunately, many participants are focused on a short term objective and do not grasp the long term goal. There are three components to the equation for maximizing wealth – expense, revenue or income, and benefit.
Benefit Benefit Revenu Revenuee Expens Expensee How is the best way to maximize the benefit?
Maximum benefit requires both revenue & expense be optimized.
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maximize revenue optimize expense
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Typical attempts are to minimize costs. Taken to extremes, however, that is counter - productive. With the minimum cost, zero expense, there is no revenue. On the other extreme is an attempt to maximize revenue. Maximum revenue will bring increased expense. Obviously expense and revenue are related. To maximize benefit requires that the revenue and the expense be optimized. To increase benefit it is better to have more effective expense than to cut expense.
Scientific Method
Identify the problem ↓
Define the problem ↓
Collect data ↓
Analyze the data data ↓
Develop a hypothesis (inductive) ↓
Test the hypothesis (deductive) ↓
Select final hypothesis
15.3 S CIENTIFIC CIENTIFIC METHOD NFPA 921 Guide for Fire & Explosion Investigations is the industry recognized guide for fire investigations. It outlines the seven steps of the scientific method. 1. Identify the problem. 2. Define the problem. 3. Collect data. 4. Analyze the data. 5. Develop a hypothesis (inductive). 6. Test the hypothesis (deductive). 7. Repeat steps 3 to 6 until select a final hypothesis. Testing of the hypothesis can be either physical or analytical. By definition, the investigation is an iterative process. It involves observing information, then eliminating things that do not fit. Because of the wide diversity of events involved in a failure and fire, several people will be involved in the final analysis of any a ny project. It is critical to document both the information that is identified as well as the information that is eliminated.
Photograph documentation
The focal point of documentation is photographs. It is not unusual to have in excess of two hundred hundred photos in most incidents. incidents. Often, there are many more. These provide the visual cues for the investigator to later illustrate the information to the client or the legal c ommunity. Since every potential participant cannot be at the early inspections, the photos provide a tool to both identify the problem and to refute alternative hypothesis.
15.4 F IRE IRE DEPARTMENTS Fire departments are the first responder to most significant failure incidents. Clearly, there is a wide variety of experience, skill, and ability between various fire departments and individuals individuals within the departments. Departments range from metropolitan paid full-time professionals to rural volunteers. Fire department suppression
The first responsibility of any fire department is to protect life, then control the incident. There will likely be a follow-up investigation. The
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fundamental purpose of the investigation is to preclude future incidents, whether arson or the failure of an appliance. The subsequent follow-up should be a consideration in the procedures used for suppression and overhaul. Throwing everything out of a room creates a challenging situation for the investigator. Investigators may be highly trained by the ATF and other professional organizations. Examiners with smaller departments often are limited in their training options. Frequently, a captain will have the investigative task added to his responsibilities of firefighting. Investigation and firefighting are radically different skill sets; therefore, the extent of the investigation will vary greatly.
Fire department control
There is a tendency among investigators to want to identify a cause. This can lead to opinions that are well outside the experience of the inspector. A stated opinion that oversteps the investigator’s skill and experience can later create problems during a more involved inspection. “Undetermined” is a perfectly valid response and should be used unless the result is unequivocal. Calling a fire “ Undetermined”, generates much more respect than making a call that is later shown to be in error. Not all fires have an investigation from the public sector, but virtually all incidents will have some level of investigation from the insurance company. The insurance investigator typically has more time and resources to conduct an in depth examination; therefore, his determination of cause can be at odds with a first call by the department.
Fire department after the incident
15.5 I NITIAL NITIAL IDENTIFIER The initial identifier of a failure issue is typically the adjuster. Adjusters may be independent or a company employee. Their role is to determine if there is a problem, determine if it is covered, and pay under the policy. The adjuster is charged with both customer satisfaction and minimizing costs. That is a tenuous line. As the initial identifier, the adjuster is the determiner if there are further questions about the failure.
For larger risks a cause & origin investigator would be called. If the risk is small and readily identifiable, then the adjuster may retain the artifacts for off-site analysis, generally by an engineer.
In order to preserve information the initial identifier should preserve the scene as much as possible for further investigations. If the artifacts are to be removed, then the following steps are important.
Insurance investigator: Ms. Zeta-Jones
Thoroughly photograph the room that contains the artifacts. Particularly photograph the artifacts in place from several directions and angles. Recover the artifacts, component parts, and all other items that possibly are involved. Especially keep associated parts, such as cords, switches, and circuit breakers. Package or protect the items so they will not be disturbed during transportation. Large zip-type plastic bags generally work well. Public investigator
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15.6 ORIGIN & CAUSE Examination and analysis of fires and explosions of unknown origin are generally first made by an Origin & Cause (O&C) Investigator. These are technical experts trained in fire investigation methodology using a systematic approach as described by NFPA 921. Professional Associations
Investigators are licensed by the state or other jurisdiction either as private investigators or as engineers. Further qualification and certification is made by professional organizations and certified training. Consultants have a particular skill or knowledge that may be relevant to an incident. In contrast, consultants are generally not licensed, and their opinions are limited. Origin & cause investigators are trained in the art and science of fire patterns, fire dynamics, and fire results. Because of their experience and skills they can identify an area of origin when very little remains exist.
O&C identifies origin in attic
We have frequently worked with investigators when a structure is burned to the ground. It is intriguing to see them identify the origin as in the attic above a certain area. When an analysis of the potential ignition sources in that area is conducted, t he investigator’s call is affirmed by the faulting in a device. After working for many years with numerous investigators, I am firmly convinced if two or three investigators look at the scene together, there is virtually no origin that would be misidentified. Origin & cause are the technical experts on fire patterns and are generalists in fire examination. A skilled investigator understands some aspect of all the fire related events. The legal environment has created a situation that requires specialists to analyze the cause of failure. The O&C is a fire expert. It is unreasonable to expect him to know all the technical aspects that have to do with electrical, mechanical, chemical, and metallurgy.
Potential ignition source
I nvestigators stigators determine cause of fire what is source of ignition
Engineers determine cause of failure why equipment failed
As a result, the professional O&C identifies the area of the fire and the potential ignition sources within the area. He then identifies the specialist, typically an engineer, who can be knowledgeable in the codes, standards, and nuances of the potential ignition system. O&C investigators determine the cause of a fire. This includes the area of origin and the potential ignition sources whether incendiary or equipment such as electrical, mechanical, and chemical. He determines what caused the fire. Engineers determine the cause of the failur e of the equipment that provided the ignition. He determines how and why the failure occurred. In the process he may eliminate the equipment as a potential ignition, then it is back to the O&C investigator to look at alternatives.
NGINEERS 15.7 E NGINEERS Engineers, like attorneys and doctors, must be licensed by the state to use the title. Engineers are analysts. They are the specialists in codes and standards for electrical, mechanical, and petro-chemical systems. In addition, they should have a working knowledge of failure and fire analysis.
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Engineers have three separate and distinct roles in investigations. investigations. A. On-Site Under NFPA 921 Article 14.5, engineers are retained to assist Origin & Cause investigators in specialized fields. As such, engineers perform onsite incident analysis with one of three objectives. 1. Identify cause of failure to the system. 2. Rule out system as cause of fire. 3. Establish a record for liability issues. B. Joint Inspection Inspection After the Origin & Cause investigators have identified an area of origin, engineers representing all potential interested parties perform a joint inspection of the item of origin. This generally involves destructive testing of suspect items. The inspection provides the go: no-go decision of the case.
NFPA 921 Guide
C. Lab Incident artifacts are sent to the lab for analysis of its possible failure and resulting contribution contribution to the incident. The lab environment provides provides a setting and equipment so that a more detailed investigation can be conducted. Microscopes, meters, and other specialized analytical equipment are available that cannot reasonably be used in the field. For incidents where artifacts are gathered by either the adjuster or investigator, a lab inspection is a cost effective practice for low loss incidents.
AMScope stereo digital 360X
The work should be under a licensed professional engineer and a certified fire & explosion investigator.
HE REST OF THE STORY 15.8 T HE In virtually any incident, there are two parties that may have opposing interests. Although investigators and engineers should be independent and unbiased, there are numerous nuances and perspectives to the amount of information that is available. Furthermore, experts have different levels of experience, knowledge, and skill. Therefore, each party by necessity must provide their own experts to get to the facts. Rest assured the opposing party is going to do all they can to protect their position. Cutting out steps of the investigative investigative process is a sure way to reduce any potential benefits of the project.
Hi-voltage lab - 100,000 Volts
HAPTER 16 – W ATER A TER I MPACT MPACT C HAPTER 16.1 I NTRODUCTION NTRODUCTION Water application is a common consequence of fire suppression and control. In other circumstances, flooding, roof leaks, water line leaks, or other events may place water on systems. Therefore, water damage must necessarily be considered in failure analysis. Only water consequences on electrical systems are discussed in this arena. The old saw “electricity and water don’t mix” is exactly right.
16.2 3-IN -1 -1 FAILURE MODES What are the ways that water can cause damage? The failure modes are conducting, corrosion, and deposition.
Water on electrical systems
The things that affect water damage are the same things we found in Chapter 7 that caused corrosion - electrolyte, moisture, and metal. Note one of the ways of damage is the same as the things that affect damage.
16.3 C ONDUCTING ONDUCTING Pure water is not an electrical conductor. However, impurities, including minerals, make water an excellent electrical conductor. As a result, when water comes in contact with a live circuit, current can flow through the water.
Corrosion - metal, electrolyte, moisture
Risk: The result can be electrical shock, tripping of protective devices, or shorting of components resulting in failure and possible fire. These events occur while the electrical area is moist.
ORROSION 16.4 C ORROSION Metals are electrical conductors. Metals oxidize when exposed to moisture. The oxidation appears as rust on iron materials and green on copper materials. Oxidation causes poor connections and may provide an improper conductive path. Risk : Oxidation is a slow process, which may not be apparent for a long period of time.
Oxidation at connections
16.5 DEPOSITION The by-products of moisture can be depositions. Like the corrosion on metals, deposition continues to grow, once it is initiated. Depositions are foreign matter that are placed or grow on an electrical system. They are frequently the result of material from the water that continues to develop over time. There are three types of depositions. One, water spots are the rings of minerals that remain after the water has evaporated. Two, mineral depositions are chemicals that are placed on the electrical components. Deposition at connection
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These often grow as a white deposit and are commonly seen on battery terminals. Three, mold is a living organism that begins growing in the presence of water and absence of light. light. It may be black to greenish. greenish. Risk : Both minerals and mold may be conductive enough to modify the performance of the system.
16.6 M ANIFESTATION Moisture’s effect on electrical systems is a deterioration of conditions that then allows the current to flow in unintended paths. The deterioration is a process. Mold on electrical equipment
First, moisture is present on contact. Consequently, moisture migrates into interstices. Interstices are the open spaces between stranded wires, the openings into electrical components, and the space between contacts. The results long outlive the duration of the moisture. The moisture initiates corrosion. The corrosion process can slow down then progress again. The time line for the effect of moisture depends on the failure mode. Conducting or direct path is instantaneous. It may almost immediately show up as a fault or failure. Corrosion is progressive. Noticeably, rust keeps growing with time.
Corrosion & deposition on contacts
Depositions are progressive. Clearly, mold keeps growing and may be virtually impossible to correct.
16.7 M IGRATION IGRATION Water and moisture migrates into wire strands, contacts, and electronic components. Moisture will travel into every wire with an open end that is exposed to water. Wire for wet applications has the interstices filled to mitigate water migration. Nevertheless, corrosion can still occur and migrate into the system. The rate of migration depends on temperature change, pressure change, and elapsed time. Circuit breaker failure from moisture
All electrical wiring that has ends exposed to water should be replaced. Simply repairing the ends is generally not adequate, since moisture that migrates into the interstices of the conductors will not manifest as corrosion for some time. Water can enter electronic circuits. Because of the low energy involved with most electronics, any change from moisture can cause dramatic and erratic performance. Furthermore, the small spaces and proximity of connections permits the least amount of contaminant create an alternate path and to deteriorate performance. performance. Water and moisture migrates into all open electrical components, including contacts on relays and switches. All electrical devices with parts exposed to water should should be replaced or repaired.
Hi-Z connection and corrosion
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16.8 M ITIGATION ITIGATION Mitigation involves reducing the impact of damage to the electrical components. For moisture sensitive components, no dependable method of mitigation assures stopping the progressive damage to the items. Generally, for common devices, it is more expensive to repair the device than to replace the item. As would be expected, with electrical related items, there are three levels of mitigation. Electronics Electronics and wire with exposed ends – replace the offending items. Electrical Electrical – – repair damaged items and clean the area.
Corrosion on switch connection
Mechanical Mechanical elements – clean the contaminated areas and provide a protective coating. coating.
Failure to adequately repair and replace the electrical components and wiring will result in oxidation, erratic performance, and fire.
16.9 M ACHINATION The impact of moisture on electrical items covers the gamut from simple economic loss to catastrophic fire. There are seven tiers of electrical impact. 1. Hi-impedance connections connections derive from corrosion and foreign material at the connections.
Wire conductor corrosion
performance is deterioration of how the equipment 2. Erratic performance works.
3. Progressive failure is a common consequence for delayed development of moisture problems. 4. Economic impact is the result of equipment not being available to the user and will result from loss of business to commercial entities. 5. Delays in access to the equipment for repairs to components results in additional economic impact. 6. Risk of shock shock is commonly associated with water and electricity. 7. Risk of fire increases with time as high impedance connections develop and other improper paths of electrical are a re created. Fused disconnect corrosion
16.10 REVIEW
Water increases risk of electrical incident
Light fixture fire from roof leak
HAPTER 17 – P ETROCHEMICALS ETROCHEMICALS C HAPTER 17.1 I NTRODUCTION NTRODUCTION Electrical energy is often the ignition source for fires and deflagration. The question then becomes is there adequate fuel to promote the event. Petrochemicals include fuel sources as well as most chemicals. Common fuel sources are methane (natural gas), propane, and gasoline. Common chemicals are materials such as polyurethane, plastics, and paint products. Each of these materials is volatile and flammable. Petrochemicals are hydrocarbon-based materials. Hydrocarbons are organic chemicals that contains both carbon and hydrogen molecules. The majority of hydrocarbons naturally occur in crude oil, which is decomposed organic matter. Many other common materials are derived from this petrochemical foundation. Just as carbohydrates provide energy for the body, hydrocarbons produce energy for fuel. fue l.
Crude oil production
Electricity and hydrocarbons do not mix. To prevent a very exciting interaction requires very controlled operation of both the electrical energy and the hydrocarbon fuel.
17.1 U NITS NITS Units of measurement are necessary to explain the amount of energy activity. The units in science and engineering have changed over time. English units have been traditional; British thermal units (BTU), Fahrenheit, and feet have been the conventional units for energy, temperature, and distance. Calories, centigrade, and feet were an interim system.
Crude oil transport
Now, the preferred units are the international system (SI) which uses Joules, Kelvin or Celsius, and meters. SI units are commonly referred to as metric units. Since there is a conversion factor between systems of units, it is not unusual to see a mix of units from the different systems of measurement.
ROPERTIES 17.2 P ROPERTIES The following list is the properties and characteristics of several petrochemical derivatives. These materials can provide fuel during an incident. The information uses predominantly international system (SI) units. The amount of energy (heat) in a particular mass is not greatly different for any of these hydrocarbon derivative materials. Therefore, just looking at heat effects, it would be difficult to tell the difference between propane and plastics that have burned. Units of measure
108 Measure Energy/vol MJ/l
Polyethylene Polyester
Diesel in plastic
Polystyrene
Durham
Electrical Failure Analysis Methane Propane Gasoline Gasoline Die Di esel
Poly- Poly- Poly- PVC Toluene ethylene styrene ester
9 cmpres 25.3 liq. 34.2 .0378 .094 gas gas
37.3
42.6
43.5
35.6 25.2 42.4
26
Vaporization 238 Liquid to gas
270
Ener. density MJ/kg
53.6
49.6
46.4
46.2
46.3
41.4
Density liq’d .415 g/ml
.505
0.737
0.89
1.2
0.903
Sp Grav
1.55
.95
1.04
0.55
LEL – UEL 5.3 - 15 Vol %
2.1 – 10.4
1.4 – 7.6 0.67.5
1.1-6.1
18
66.2
0.867 1.7
1.5 1.2-7.1
TNT has 4.6 MJ/kg.
ONVERSIONS 17.3 C ONVERSIONS Some conversion factors are necessary to relate the different systems of measurement.
Energy density is expressed as energy per mass and in other expressions as energy per volume. Energy per volume is simply another phrase for pressure. Power is measured in units of Watts (W). Energy or heat is measured in units of Joules (J). One Watt is the amount of power delivered by one Joule in one second. Clearly, the conversion of a power source to energy involves time. In fuel analysis, power is sometimes referred to as the heat release rate. The energy in a fuel is directly related to electrical energy measured in kWh. The energy density of TNT is 4.6 MJ/kg, so the heat release of one pound of TNT is about about 2.1 MJ. Similarly, the heat release rate (power) from a polyurethane chair is 1 MW. That is the equivalent of one pound of TNT discharged in 2 seconds.
SURFACE BURN
VERTICAL BURN
HORIZONTAL BURN
17.4 UL FLAMMABILITY RATING Underwriters Laboratory (UL) has developed a flammability rating for materials that are commonly used in manufacture of products. This is particularly important important to the promotion of burning, burning, should ignition ignition occur. The document, UL 94, identifies the ratings and the amount of burn that may occur.
Does not ignite With hotter flame 5VA 5VB
Self extinguishing V0 Best V1 Good V2 Drips
Slow burn rate Takes more than 3 min to burn 4 inches
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UL 94 Flammability Flammability ratings
Rating 5VA Surface Burn
5VB Surface Burn
V-0 Vertical Burn
Properties Burning stops within 60 seconds after five applications of five seconds each of a flame (larger than that used in Vertical Burn testing) to a test bar. Test specimens MAY NOT have a burnthrough (no hole). This is the highest (most flame retardant) UL94 rating. Burning stops within 60 seconds after five applications of five seconds each of a flame (larger than that used in Vertical Burn testing) to a test bar. Test specimens MAY HAVE a burn-through (a hole). Burning stops within 10 seconds after two applications of ten seconds each of a flame to a test bar. NO flaming drips are allowed.
V-1 Vertical Burn
Burning stops within 60 seconds after two applications of ten seconds each of a flame to a test bar. NO flaming drips are allowed. V-2 Vertical Burn Burning stops within 60 seconds after two applications of ten seconds each of a flame to a test bar. Flaming drips ARE allowed. H-B Horizontal Burn Slow horizontal burning on a 3mm thick specimen with a burning rate is less than 3"/min or stops burning before the 5" mark. H-B rated materials are considered "self-extinguishing". This is the lowest (least flame retardant) UL94 rating.
Smurf tube very flammable
LECTRICAL FAULT AND FLAMMABILITY 17.5 E LECTRICAL Often, someone claims a material will not burn unless a heat source is continuously applied. Notice that any material may burn for up to 10 seconds. If there is another source of heat before the flame is extinguished, then the material will continue to burn. Consider an electrical fault. The electrical energy can ignite a material and provide heat until the circuit protection operates. For circuit breakers and fuses, this can take many seconds to minutes. By the time the electrical protection clears, the flame may spread to other materials with different flammability properties.
Horizontal burn on PVC wire
Consider the electrical sources of ignition. There are arcs, high impedance (hot) connections, and radiation. By far, the most common source of ignition is high impedance connections that generally will not show pitting or other indications of faults. The hot connections will continue for long periods of time and can propagate ignition in almost any material.
17.6 H EAT EAT RELEASE RATE The heat release rate available from fuel indicates the power contribution to the event. The power available from propane is illustrated. Although the calculation is for propane, the process is similar for natural gas and vapors from paint products. Conventional units are used, since that is still the most common outside of engineering analysis.
Connection blade to receptacle overheat
1. Consider two (2) gallons of liquid propane released from a tank. 2. There is 0.1337 cu ft / gal of liquid propane. 3. Liquid propane expands 270 times to yield propane vapor. 4. This calculates to approximately 36.6 cu ft of propane vapor per gallon of liquid. 5. Based on the amount of liquid propane, the quantity of propane gas is about 73 cu ft. Propane bottle burned in fire
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6. For a neutral propane flame, the oxygen required is five times the propane quantity. With air containing about 20% oxygen, the ratio of air to propane necessary for a neutral flame is 25:1. 7. Consider a structure with an enclosed area of approximately 200 sq ft. Based on a standard eight (8) foot walls, the volume of the structure is 1600 cu ft. 8. Propane is heavier than air and will have a tendency to settle. However some will be dispersed, and there will be a range from a more dense mixture of propane at the floor to less dense at the ceiling. Propane tank
9. Assuming a uniform distribution, the average mixture in the structure would be 73 ft 3 (propane gas) / 1600 ft 3 (air) = 0.045 or 4.5 % propane. 10. The lower flammability limit of propane is 2.15%. The upper limit is 9.6%. 11. In reality, propane will be much more concentrated near the floor. If it were assume the propane gas had a uniform concentration in the lower two (2) feet, then the mixture would be 18% propane.
Deflagration from improper propane
12. Based on the above calculations, and the fact that distribution of propane will be non-uniform, there are many areas of the structure that fall well into the flammability range of propane. 13. Any spark or heat source would cause ignition and deflagration of the propane / air mixture. During deflagration, the distribution of propane in the structure would significantly change, bringing additional areas of the structure into the flammability range. The structure is a bomb waiting for f or ignition.
ODES 17.7 C ODES Propane and natural gas installations are covered by Codes and regulations. Some of the significant references are noted. Codes are consensus documents developed by individuals within the industry. As such, they are a practical safeguard for installations. This includes safety and property damage. NFPA 58
J.P. Getty first oil & gas lease in Oklahoma
The Liquefied Petroleum Gas Code, NFPA 58, is the recognized authority for liquid petroleum gas installations. NFPA 58 is the minimum standard for installations. installations. 1.
Article 1.1. Scope. This Code applies to the storage, handling, transportation, and use of LP gas.
2.
The Code provides definitions for where the Code is applicable.
3.
The Code provides requirement for training of propane handlers to be at least every three years.
4.
Pressure regulators should be installed on the vessels.
5.
Chapter 6 addresses the installation of LP gas systems.
6.
A container with a 250-gallon capacity must be at least 10 feet from important buildings.
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7.
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Article 7.2.2.2 states that when noncompliance of the installation is found, the owner must be notified.
The last note is significant since it places a responsibility based on observation. That is different from most other codes.
17.8 N ATIONAL F UEL UEL G AS C ODE ODE The National Fuel Gas Code , NFPA 54, is the recognized authority for gas and piping systems. 1.
Article 1.1.1.1 This Code is a safety code that shall apply to the installation of fuel gas piping systems, appliance, equipment, and related accessories….
2.
Article 8.1.1.1 Prior to acceptance and initial operation, all piping installations shall be inspected and pressure tested to determine that the materials, design, fabrication, and installation practices comply with the requirements of the code.
3.
Article 8.1.5.1 The piping system shall withstand the test pressure specified without showing any a ny evidence of leakage or other defects…
Natural gas sales meter
17.9 REGULATIONS Several government agencies regulate liquid petroleum (LP) gas. An example of one state establishes appropriate practices. These may vary in other jurisdictions, but they are an overview of requirements. r equirements. 1.
Liquefied petroleum gas is regulated by the "Oil & Gas Act, Oklahoma Statute, OS 52". 52". The liquefied petroleum gas industry operates under "Liquefied Petroleum Gas Rules, Oklahoma Administrative Code, OAC Title 420 and 422". 422" .
2.
Oklahoma Administrative Code, OAC 420:10-1-5. Permits:
NFPA 54
(a) Permits required. No person, pers on, firm, fir m, corporation, cor poration, association or other entity shall engage in the manufacturing, assembling, fabrication, installing or selling of any system, container, container, or apparatus apparatus to be used in this State in or for the transportation, storing, dispensing, or utilization of LPG, nor shall any transporter, distributor, or retailer of LPG store, dispense and/or transport over the highways of this State any LPG for use in this State in any system, container, apparatus or appliance without having first obtained a permit to do so as provided provided in this this section. section.
3.
Oklahoma Administrative Code, OAC 420:10-115. Standards for Installations of Gas Appliances, Gas Piping and Testing. (a) The standards for installation of gas appliances, gas piping and testing, thereof adopted by the National Fire Protection Association and published in its Handbook No. 54, have been adopted by the Legislature Legislature in 52 O.S.
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112
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1991, Section 420.3 (e) and shall be the accepted standards for the State of Oklahoma. (b) Pressure tests and/or leak tests that are required by NFPA 54, 58, 1192, and this chapter, shall be documented on an approved Form 4 or other Board approved form. The form shall be completed with one (1) copy in file at the office or branch office serving the account, one (1) copy filed with the LP Gas Administration within fifteen (15) working days after tests are performed, and one copy to the owner, renter or responsible person.
NFPA 1192
(c) Form 4's and other approved forms must be completed in their entirety, legible and with all required signatures. When Form 4's are completed completed by a Class IV or IV-D permit holder employed by of a Class I or Class X manager, then the Class I or Class X manager must co-sign the Form 4. If Form 4's are not completed properly they will not be accepted as a testing record. Form 4's or other Board approved forms shall be utilized to document pressure tests or leak tests as follows: (1) Prior to injecting gas in a system for the first time (new customer), or if a period of 24 months has passed since gas was injected into a system previously serviced. serviced.
Propane fire from lightning to tree
The reference establishes NFPA 54, 58, and 1192 as state law. Form 4 identifies the tests that must be completed by the filler of the propane.
17.10 ANALYSIS An analysis of one installation in comparison to the Codes and State Law revealed several critical discrepancies.
Old propane tank with wrong fittings
Detonation from improper propane
1.
NFPA 54 Section 8 requires pressure tests and leak tests to be performed on gas systems. systems.
2.
The tank was installed and filled by the propane supplier prior to the piping being being connected to the house. house.
3.
By being filled prior to connection to the house, it is not possible that leak tests and pressure tests could be performed, as required by NFPA.
4.
Documentation of a regulator is not possible since no regulator existed, based on observation of the equipment. Without a regulator, maximum tank pressure is exposed to the connections and ultimately to the house.
5.
A walk through visual check was not possible, since the piping system was was not installed.
6.
The tank was not filled according to industry standards and state law.
7.
A
very
dramatic
explosion
resulted.
HAPTER 18 – E NERGY NERGY A C HAPTER ANALYSIS IRE M OVEMENT OVEMENT AND E NERGY NERGY F IRE RANSPORT T RANSPORT NTRODUCTION 18.1 I NTRODUCTION For years many analysts have treated the study of fire and its results as an art learned from years of experience. It is something you see and have a feel for. Fire study has often been taught as recognizing particular patterns without the the underlying science and mathematics. mathematics. Fire and its effects are subject to the rules of science. The interpretation of these effect is then a science. Since it is a science, it can be studied and calculated. Clearly fire involves heat. Heat movement is one of the oldest engineering disciplines called thermodynamics. Thermo is from the Greek meaning heat or energy; dynamics is from the Greek meaning powerful and is used in the the sense of motion. The study of thermodynamics is really that simple. It is the study of energy motion. Unfortunately, thermodynamics is often taught as a convoluted process, not unlike electrical engineering. Like most engineering, when broken down to its fundamentals, energy motion and resulting fire study is quite straightforward.
Early investigator
+ Thermo + dynamics
Engineering and scientific tasks fit into three categories. Design is developing a procedure to build a system. Analysis is looking at how a system operates. Application Application is using the system. In fire systems, the firefighter is involved in application of techniques to control the fire. Origin & cause investigators are involved in application of techniques to determine where and why a fire occurred. Engineers are involved in the analysis of the system to determine what operation failed or did not work as designed. This chapter is oriented to analysis and the science behind energy. There are numerous terms and concepts in this chapter that may at first appear complex. Some take the form of mathematics. The concepts are illustrated with mathematics no more complex than division and multiplication. The most difficult part is realizing that numerous different words are used to define the same idea.
Application
Scientific tasks Analysis
Design
18.2 E NERGY NERGY Energy is the common measure between mechanical, electrical, and chemical systems. Energy is the work or activity performed due to force.
Energy can be analyzed three ways. First, energy can be exerted at a point for solids. The process is called mechanics . Second, energy can be exerted on a fluid using volume. The process is called fluid flow . Third, energy can be distributed over an area in a gas. The process is called energy transport . Energy transport is the process related to temperature and as a result it is used for fire analysis.
ENERGY TRANSPORT
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A brief discussion of fluid flow will provide the foundation for energy. That will be followed by a more detailed discussion of energy transport and temperature for fire analysis.
Flame fluid flow
The technology for each system of analysis developed independently over time using different processes. Therefore, there is not a uniformity of terms. Unfortunately, the same concept has numerous different terms. Even more confusing is the different symbols. There are a limited number of letters to use for symbols, so the same letter is often used to represent two very different ideas. Moreover, units of measurement are constrained to use similar letter representation.
18.3 U NITS NITS Units of measurement are necessary to explain the amount of energy activity. The units in science and engineering have changed over time. English units have been traditional: British thermal units (BTU), Fahrenheit, and feet have been the conventional units for energy, temperature, and distance. Calories, centigrade, and feet were an interim system. Now, the preferred units are the international system (SI) which uses Joules, Kelvin or Celsius, and meters. Since there is a conversion factor between systems of units, it is not unusual to see a mix of units from the different systems of measurement. Units of measure
It is important to remember that energy crosses all systems, whether electrical, mechanical, or chemical. Therefore, the relationships may be redefined in different energy analysis.
T’ 18.4 I T ALL ABOUT 3’ S ’ S A The trinity or triad principle holds for energy like a ll the sciences.
3-D: a triad example
Any item than than can be uniquely identified can be further further explained by three components. The necessary terms for an energy or fire system can be identified using this grouping of three quantities. If a discussion of a system has either more or fewer items, it is often a combination of terms, or an inadequately explained or defined system.
18.5 DISTANCE SIDEBAR b
d
s
In any three-dimensional energy system of measurement there are three distances. These are depth or lever arm, motion direction, and volumetric . Although these are spherical in nature, local analysis typically looks at the 3-D perpendicular projections. Each dimension has a positive and negative or forward and backward direction from the origin reference. Depth (b) is the rotational tendency. Depth in the direction of the force creates energy. Depth is the penetration into a material.
Energy cone distances
Motion (d) is the distance in the direction of movement. It begins at the apex and bisects the heat cone. Volumetric or shearing (s) is the space distance across the cone of motion.
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The three measurements combine in one term to produce volume. For curved, spherical, and solid structures, these are vectors including cross and dot products, which give three dimensional values.
18.6 E NERGY NERGY - M EASURE EASURE Only three items can be measured in any energy system. These three are the only items required to describe the system parameters. All other components are calculated. The measured components are a potential (pressure), transfer (flow) rate, and time.
Parame arameter Units nits 3 Pressure joules/m 3 Flow m /sec seconds Time
What potential transfer rate duration
3in
Pressure (P) is the potential for activity. Pressure is the term for force exerted over an area. Pressure or potential exists whether there is movement or not.
3 measures in 1 term
Flow rate (Q) is the volume of fluid moved over a time duration. Flow rate gives the quantity of material moved. There is direction associated with movement. Flow or transfer rate can be measured only if there is movement.
Power multiply
Time event (t) - measured in seconds - is the difference in time between events. The reciprocal of time is the frequency (f).
The three measurements combine in one term to produce energy (W ). ).
18.7 E NERGY NERGY - C ALCULATE All energy relationships can be derived from the three fundamental measured terms - pressure and flow rate with time. Since you cannot add or subtract unlike terms, the only thing left to do with two items is to multiply and divide.
Impedance divide
Power (S) is the product of the pressure and the flow rate. Power is the energy over time. Power exists only if there is work and movement.
Impedance (Z) is the opposition to movement. Impedance is the pressure divided by flow rate. It is simply a ratio.
Parame arameter Symbol Units nits Watt Power S
What product ratio Impedance Z Delay td or seconds difference
Time Delay (t d d ) - is the difference is the time between pressure and flow rate. It may be expressed expressed in seconds or in angular terms. terms. It is the phase phase shift between pressure being at a maximum and flow being at a maximum. It is the differential that arises in the Calculus.
18.8 E NERGY NERGY - REVIEW The three measures of fluid energy are pressure , flow rate, and time. The three combine to provide energy.
Stopwatch = time delay
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Energy (W) (W) is the work or heat involved in activity. Power (S) Power (S) is energy that occurs over some period of time. Power is also noted as the heat release rate (HRR). Impedance is the opposition to energy movement. That is all there is
18.9 T RANSPORT RANSPORT - M EASURE EASURE
Parame arameter Units nits What joules/m potential m/sec transfer rate seconds duration
Pressure Velocity Time
Heat is simply a specific type of energy that may be associated with conversion between systems or transport from one location to another. Energy transport is the study of the transfer or transport of energy across an area perpendicular to the movement. Fire analysis is simply the study of heat transport.
Only three items can be measured in any energy system. All other components are calculated. The measured components are potential or pressure, transport or or flow rate, rate, and time. It follows, then, that only three items can be measured in a heat transport system.
Energy density Is Pressure
Pressure (P) is the term for force exerted over an area. Pressure is the potential for activity. Pressure is the energy density, which is the energy stored over a volume of space. Since heat and fire is three-dimensional, the distance of movement is included with the surface area to give threedimensional volume. Pressure or potential exists whether there is movement or not.
Velocity (v) is the distance moved in a direction over a time duration. Velocity gives the extent of movement. There is direction associated with movement. If there is direction there must be a starting point. The apex of the flow is the starting point or origin. Velocity or transfer rate can be measured only if there is movement. Time event (t) - measured in seconds - is the difference in time between events. The reciprocal of time is the frequency (f).
The three measurements combine in one term to produce surface energy (W/A). Surface energy balance
Surface energy also correlates to surface tension. Surface tension results in curvature of the area. Surface tension is the force parallel to the surface and perpendicular to the direction of movement.
18.10 Intensity is Density by velocity
RANSPORT - C ALCULATE T RANSPORT
All energy transport relationships can be derived from the three fundamental measured terms – pressure – pressure, velocity , and time. Since the terms are unlike, you cannot add or subtract. The only thing left to do, then, is to multiply and divide.
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Intensity is the product of the pressure and the velocity of movement. Intensity is an expression of the power (S) spread over a perpendicular surface area (A). Intensity is the energy density multiplied by velocity and is called the Poynting vector of electromagnetic waves. Intensity exists only if there is movement.
Power multiply
Fluid impedance (z) is the opposition to movement. Impedance is the pressure divided by velocity. Fluid impedance is also called acoustic impedance, air flow resistance, drag coefficient and coupled mechanical losses. It is simply a ratio.
Impedance divide
Delay (t d d ) - is the difference is the time between pressure and transport rate. It may may be expressed in seconds. It is the phase shift between between pressure being at a maximum and velocity being at a maximum. maximum.
18.11 T RANSPORT RANSPORT - I MPEDANCE MPEDANCE The opposition to flow is called impedance. Impedance is a property of materials and how they are structured. As would be expected, there are three types of opposition.
Parameter ter Symbol Units nits Nt/m-s Intensity S/A Nt-s/m Impedance z Delay td or seconds
Resistance (R) is natural opposition of any movement. Resistance is the friction of motion. Resistance converts moving energy into mechanical energy in the form of heat. Resistance is the reciprocal of conductance. Inductance (L) results from inertia or tendency for continued movement. Inductance provides a path to redirect energy or to change its direction. Inductance depends on mass and any bends or obstructions in the path.
Heat inductance on metal
Capacitance (C) is the tendency to store energy.
The inductance and capacitance are complimentary components that can result in oscillatory or wavelike movement. Steel has very high impedance. It opposes burning. Steel allows very little impingement depth. However, it does have some inductance to cause heat to continue movement along the steel.
Heat capacitance
Cellulose has very low impedance. It will burn readily. However, it does have some capacitance to hold heat. In general heat insulators have capacitance and metals have inductance. For each type of impedance, there is a corresponding power. These three combine to create the product. The most familiar of the three is resistance which creates heat and the resulting power is Watts.
I mpedance Z Energy Resistance R mechanical Inductance L inertia Capacitance C storage
RANSPORT - REVIEW 18.12 T RANSPORT All fire and thermal effects reflect transport of heat energy. The three measures of energy transport are pressure , velocity , and time. The three combine to provide surface energy. Energy density density is the energy (W) distributed over a space volume (V). That is all there is
What product ratio difference
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1 2 3 4 5
Relationship
6
7
8
9
10
11 12 13 14
Impedance is the opposition to energy heat transport. Heat is the movement of thermal energy from a substance at a higher temperature to another substance at a lower temperature.
18.1 T EMPERATURE EMPERATURE Thermal energy is heat that is absorbed. Higher temperature corresponds to higher heat. Temperature is a direct indication of intensity. The heat is proportional to the surface area exposed. Intensity is the product of temperature change and transport factors. Heat is transported in three modes – convection , conduction , and radiation. Each mode has a different factor of transfer. The transport factor depends on the material property and the shape of the medium that is absorbing the heat. Convection is the transfer of heat by movement or circulation in fluids. Convection represents a phase change from solid to fluid. Hotter fluids rise while cooler fluids descend. The temperature change change is the surface temperature minus the bulk temperature at a distance “far” from the surface. The factor (k V) must be derived or found experimentally for every system analyzed.
Conduction is the transfer of heat along a material by direct contact. Conduction depends on the mass of the material. Interestingly good electrical conductors tend to be good heat conductors. The temperature change is measured from one end of the material along a distance or length (d) to the other end. The factor (k C) is the coefficient of conductivity.
Generic terms frequently used
# 1 2 3
Relationship
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Intensity is the product of pressure and velocity. Intensity is the product of density and velocity. Intensity is the power (S) dissipated over an area (A).
For Engineers Inquiry
#
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Radiation is the transfer of heat by waves. The transfer may be through a vacuum. No mass is involved. The temperature difference is between the surface temperature and absolute zero. The heat is impinged on the perpendicular surface area. The factor (h B) is the Boltzmann’s constant and the frequency is for a particular wave.
For a spectrum of radiation, the form becomes the Stefan-Boltzmann Law. Emissivity (ε) is a fraction of how well energy is radiated and sigma (σ) is the Stefan -Boltzmann constant. Since the emissivity is dependent on the material and structure, the radiation must be derived or found experimentally for every system analyzed.
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Although heat transport is well defined, the determination of the coefficients is less definitive. Therefore models are subject to considerable experimental bias.
18.2 I GNITION GNITION TEMPERATURES Ignition of material depends on the heat intensity, which in turn depends on temperature, material property, and time. The ignition intensity may be from auto-ignition, from pilotage, or it may be from long duration exposure . Auto-ignition tests are typically conducted in a Stinner tunnel. These tests are conducted in a laboratory environment which is very different from actual conditions.
Corner heat source
Pilotage ignition occurs when a heat source is applied directly to the material. This ignition temperature is lower than the auto-ignition. Long duration exposure to heat can result in a change in the material properties. It has been known for over 100 years that materials can ignite at much lower temperatures than the pilotage value. Underwriters Laboratory (U/L) has long recognized that 70 F over ambient could result in ignition of wood. Cases of steam pipes igniting wood have been observed.
Because of the thermodynamics of the structure and the combination of material properties, stating an actual temperature of ignition may be very difficult.
Plume
LUMES 18.3 P LUMES Plumes are a form of effluent in water or emissions in air. A plume is the heat rising from a fire. A plume predominantly results from convective heating. Some radiation is also involved. If there is material, such as a wall, near the plume then conduction will contribute to the heat transport. A plume spreads as it rises since the heat transport is diluted by additional air. The dilution results in decreasing temperature as the heat moves away from the source. Because of the dilution and spread, the general shape of a plume is a cone. The power supplied, called heat release rate, (HRR), can be determined by the fuel source. This is the input into the fire heat. Ventilation and adjacent materials can deflect the plume.
Plume from house fire
How high will a plume rise? Notice the relationship for convection does not include height, although height is clearly a factor in a plume. The temperature distribution of plumes and the height of the plume from a power source are based on correlations correlations and models. Various models are available from several sources. The analysis of these models are a matter of considerable debate.
18.4 A THING CALLED ENTROPY Usable energy is transported from one location to another. The transport may be through the modes of transfer- convection, conduction, or
Plumes from house burning
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radiation. In addition, energy may be converted to different forms, such as thermal. The energy that is not transported or recovered is irreversibly lost as increasing entropy. Entropy is the transport and conversion inefficiency loss. Since entropy is always increasing in every energy conversion, entropy will be greater than one.
Entropy > 1
Cooler temperature which results from increasing inefficiency or entropy represents a decreasing orderliness to the universe. The loss of energy goes into space and is unrecoverable. In other words, each conversion of heat illustrates the universe has less total available energy. However, there is so much available energy that millennia would be required to even detect decay. Nevertheless, small localized results are observable. For example the deterioration of the human body is one example of localized increased entropy. N
S
18.5 REALMS OF ENERGY Like other real systems, there are only three realms of energy. All matter consists of three regents - mass ( m), charge (q), and magnetism ( p) p). In addition, energy can exist in waves or bundles independent of the regents.
Regents of energy
Thus energy exists in three realms – mass, electro-magnetic, and waves. These may be combined or treated completely independent. The transport of energy is dependent on these three realms. Many sources improperly associate all radiation with electro-magnetics. Radiation is wave related. A wave may be realized as light. It is well established that light is corpuscular (has mass), electro-magnetic, and is composed of waves. The three realms r ealms are independent.
18.6 REVIEW Light: mass, em, wave
Take a minute to review all the energy terms. Remember they are always in groups of three. Energy has three things that can be measured – – pressure, flow, and time. The three measures combine into one term to produce energy . There are three things that can be calculated – – the product is power, ratio called impedance, and the time delay. Fire and thermal effects reflect transfer of heat or energy. Energy transport has three things that can be measured – measured – pressure, velocity, and time. The three measures combine into one term to produce surface energy energy. There are three things that can be calculated – calculated – the product is intensity, ratio called fluid impedance, and the time delay.
That’s all there is
Temperature is a direct indication of intensity. Intensity is the product of temperature change and transport factors for each mode of transfer. The modes of transfer are convection, conduction, and radiation.
Tha That is all th there is. is. There is nothing else in the fundamentals of energy and fire study.
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Everything else is an implementation of these fundamentals. All fire patterns are a re simply a combination of these parameters. The patterns are commonly related as intensity (pressure * velocity) and movement (direction with time).
HAPTER 19– B IOLOGICAL IOLOGICAL E FFECTS FFECTS C HAPTER 19.1 I NTRODUCTION NTRODUCTION We have surveyed hundreds of people about their experience with electrical shock. Surprisingly, over 90% have been shocked. That is a serious statistic. The most dramatic incidents involve electrical injury or worse. Obviously, if they completed the survey, they were not electrocuted. What allows some people to be shocked and not be as negatively impacted? The hazards of electricity are well known. Nevertheless, numerous people are injured each year. The most common incidents involve the ubiquitous 120 Volts. In our investigation of incidents, unfortunately, we see a significant number involving distribution level voltages in the 15,000 Volt range.
Electrocute means to be killed by electric energy.
19.2 ROUTES Electrical systems have been in use for about 130 years. Yet each generation “discovers” something new. From the time a concept is first introduced until it gains some acceptance takes about 20 years. The discovery phase is the state of stray current and electromagnetic field effects. Since our target audience is wider than just engineers, a background of information and clarification of terminology is in order. There are three routes for electrical effects – direct contact , stray current , and electromagnetic fields . The first, direct contact to energized electrical conductors, is the most obvious cause of electrical effects via shock injury. The second, indirect or stray current is a common, but less recognized source of electrical injury. The third, electromagnetic fields , radiates from every live electric circuit.
LECTRICAL / IOLOGICAL RESEARCH 19.3 E LECTRICAL / B B IOLOGICAL Why are we discussing biological effects of electrical shock? Which profession performs profession performs the research about measurement of electrical effects on humans and other biological species? The first reaction would be the medical profession. However, on further analysis, consider some of the electrical measurements that are commonly available. An electrocardiogram (EKG) measures heart signals. An electroencephalogram (EEG) measures brain waves. An electromyogram (EMG) measures muscular activity. Galvanic skin response (GSR) measures the electrical conductivity of the skin. Research and theory into the electrical impact on anatomy has been predominantly done by electrical engineers. It is well known that many of the major strides in medicine have been in technology. These devices are developed by electrical engineers and scientists applying technology to solve problems for just another system, in this case a biological system. Engineers understand the physics and develop experimental models, while medical doctors apply the technology. Engineers operate in the environment where electrical energy occurs, whether direct, stray, or electromagnetic.
3 routes
Scientific foundations
EEG
EKG
GSR
EMG Biological electric signals
124 Complete Survey located in PREFACE
1.
Have you ever been shocked? Yes ___ No___
2.
What voltage? 9V___ 12V___ 24V___ 48V___ 120V__ 200V__ 400V__ Higher V__
3.
Was the voltage ac___ rf___ frequency ___
4.
What was the cause? intentional___ accidental contact___ failure of what component________________________
5.
What was the machine / device / equipment ________________________
6.
What insulation or material was between you and the electrical circuit? none___ material___________________________
7.
Part of anatomy contacting the energized point _____________________________
8.
Part of the anatomy contacting the metal or ground or common ________________
9.
Could you still control your muscle movement? Yes___ No___
dc___
10. How did you “get off” the energized circuit? fall___ someone assisted___ removed self___ brushing contact___ explain other _______________________ 11. Discuss any sensations you recall a.
Taste _________________________
b.
Smell_________________________
c.
Hearing_______________________
d.
Sight__________________________
e.
Touch / feeling __________________
f.
Mental / thoughts ________________
12. Describe any known permanent injuries as result _____________________________
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19.4 S OME OME P LAYERS LAYERS Dr. William B. Kouwenhoven was an electrical engineering Professor at Johns Hopkins University. He did the principal experimentation on electric shock and effects of electricity on the heart which lead to closed chest defibrillators. After his retirement, he was a lecturer in the School of Medicine. Professor Charles F. Dalziel was an electrical engineering Professor at the University of California. He did the principal experimentation on human and animal response to electrical current. He wrote the book and his research established the standard for electrical safety. He was the inventor of the Ground Fault Circuit Interrupter (GFCI) now required in all wet environments. Prof. Dalziel was a member of the same Industry Applications Society of IEEE as the authors. He received the second highest award – IAS Outstanding Achievement Award. His and our awards are on the same page of the IAS website. Dr. Marcus O. Durham is a practicing engineer and was an electrical engineering Professor at Oklahoma State University and University of Tulsa. He had the personal experience of the effects of electrical shock on the human body on several instances. He had the unfortunate experience of being severely shocked on a 480 / 832Y Volt control panel. He had the fortunate experience of surviving and being able to develop a broad knowledge of the effect of shock and electro-magnetic fields on the human condition. The description of electrical shock effects on the body given later is based partially on personal experience. Dr. Durham has conducted research and has taught courses in the area and has developed some of the cutting-edge models to explain the effects of electromagnetic energy on biological organisms. The research received a prize paper award from the Industry Applications Society of the Institute of Electrical and Electronics Engineers. He was honored with the Richard Harold Kaufmann medal, the highest award by the Industry Applications Society of the IEEE. The citation reads “for development of theory and practice in the application of power systems in hostile environm ents.” He has been accepted in court as an authority on electrical effects.
FFECT OF S HOCK 19.5 E FFECT S HOCK From experience, research, and papers we have published, the following scenario reflects the effects of shock on a human. The effects are increasingly intense as the severity and time of the shock increase.
13. Describe any additional details of your experience with electrical shock? _________________________________
14. Approximate age at time of incident _______
A shock victim is consciously aware that he is being shocked and is in intense pain.
In addition, he is very aware there was nothing he can do to control his muscles and get off the electrical circuit.
He can taste metal like copper in his mouth.
His muscles are contracting then expanding 60 cycles per second.
His muscles are aching.
15. Profession / major ___________________ City ______________________ State____
16. Optional: name__ _________________ _________________ __________ email ___ Return to: Dr. Marcus O. Durham, PhD, PE THEWAY Corp. PO Box 33124 Tulsa, OK 74153
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Electrical contact causes the muscles to contract, which can result in slipping and turning.
His nervous sensations are stimulated.
Current Range & Effect On A 150 Pound Man Current Physiological Feeling or 60 Hz Phenomenon Lethal Incidence < 1 ma none Imperceptible
Extended exposure causes burning and cooking of the flesh.
1 ma
If he is not removed from the circuit, this continues until his demise.
19.6 I T ’ S T HREES T’ HREES The three electrical measures are voltage (V), current (I), and time (t). These multiply to produce energy. ener gy. The voltage is the potential or forcing function of electricity. As such, it is outside the body. The critical factor is current. Current is the quantity of electricity that flows through an organism. Clearly, the duration of exposure enters in the effect of electricity on a biological system. Professor Dalziel amazingly was able to measure and determine the biological effects of current on animals then humans. The results are shown in the adjacent table. The amount of current is measured in milliamps, which is 1/1000 Amp. This is an extremely small current compared to a 20 Amp breaker on common circuits. Impedance is the opposition to flow of electricity. It is simply the ratio or dividing voltage by current.
Galvanic skin response is a measure of impedance and is a component of “lie detectors.” Impedance depends on age, sex, health, cleanliness, attitude, and numerous other biological conditions. Each person is different, has different impedance, and has a different sensitivity to electrical current.
perception threshold
1 - 3 ma
Mild sensation
3 - 10 ma 10 ma
Painful sensation paralysis threshold of arms
Cannot release handgrip. May progress to higher current 30 ma respiratory Stoppage of paralysis breathing. Frequently fatal 75 ma fibrillation Heart action not threshold, 0.5% coordinated. Probably fatal 250 ma fibrillation threshold, 99.5% > 5 second exposure 4A heart paralysis Heart stops for threshold duration. no fibrillation May restart on interruption Usually not fatal from heart dysfunction >5A tissue burning Not fatal unless vital organs burned
If the current that causes injury is fixed, but individual impedance changes, then the outside voltage necessary to induce an incident will change. In general, no known significant injury has occurred at potentials less than 50 volts. Consequently, OSHA has codified that number as the threshold for safe work practices in OSHA 1910-269.
19.7 W HAT ? HAT ’ ’ S THE DIFFERENCE ? The effects and extent of injury varies greatly between individuals. What is the difference? The difference is the three conditions. First is the model of the human body, second is the location of contact for the energized conductor and the return conductor - commonly earth, and third is the time of exposure. The generally assumed electrical characteristic of an adult male human body are noted. Values of internal body resistance are generally 500 Ohms for each limb and 100 Ohms for the torso. The torso has multiple parallel paths and substantial substantial moisture resulting resulting in less impedance. impedance. The external body resistance varies from 15,000 to 40,000 Ohms. The skin provides the major resistance. If the skin breaks down, the resistance
500
100
500
500
500
Biological electric model
500
100
500
Biological electric circuit
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LIVE CONDUCTOR
A WIRE RESIST ANCE
WIRE RESIST ANCE
BODY RESISTANCE
CONTACT RESISTANCE C
B EARTH
BURIED PIPE
GROUND ROD
PIPE CONTACT RESISTANCE
ROD CONTACT RESISTANCE
SOIL RESISTANCE
SOIL RESISTANCE TRUE GROUND
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lowers to the internal value. This is detrimental, since more fatal current flows. The second consideration is the current path and the sensitivity of the organs in the path. The brain and the heart both operate with small electrical signals as noted above. A shock has a much stronger energy level that overrides the other body signals. The heart, brain, and muscles begin reacting 60 times a second rather than the normal rate. For example, a typical heart rate is about 70 pulses per minute. When controlled by electrical shock, the heart is attempting to operate at 60 times faster or 4200 beats. A path between two points on the same limb will cause localized damage, but likely no damage to other body parts that are not in the circuit. circuit. The third consideration is time. A short duration exposure may leave no visible scars or indicators of electrical energy. An extended exposure may leave substantial evidence of burning tissue.
As noted by the current range chart, damage may be internal only. For example, nerve or muscle damage may not be visible. Therefore, claims of injury can be subjective. Like all other areas of failure analysis, the incident, the individual, and the measured responses must be considered.
ODE B ASIS ? 19.8 C ODE ? Time increases damage
The National Fire Protection Association establishes numerous standards to safeguard persons and property. NFPA 70 National Electrical Electrical Code is the recognized standard for electrical installations. It states in Article 90.1(A) Practical Safeguarding “ The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.” The NEC is recognized and required by Statues in Oklahoma and most other jurisdictions. The Canadian Electrical Code has a similar purpose “In its preparation, consideration has been given to the prevention of fire and shock hazards, as well as proper maintenance and operation.” NFPA publishes 70E, Standard for Electrical Safety in the Workplace . “The purpose of this standard is to provide a practical safe working area for employees relative to the hazards arising from the use of electricity.” The Institute of Electrical and Electronics Engineers (IEEE) publishes IEEE C2, National Electrical Electrical Safety Code Code.. “The purpose of these rul es is the practical safeguarding of persons during the installation, operation, or maintenance of electric supply and communication lines and associated equipment.” This is the standard for utilities and similar industrial installation.
Electrical Safety
The National Fire Protection Association also provides NFPA 921, Fire and Explosion Investigations. Since this document also covers electrical systems, the scientific method in the guide can be used for all investigations, including shock incident. According to NFPA 921, interviews are an appropriate input to developing opinions.
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It is well recognized that standards exist for safety in dealing with electrical systems. Nevertheless injuries still occur. Why? It falls to the electrical investigator to determine what caused the event.
19.9 S TRAY TRAY C URRENT URRENT
I
After the above discussion on direct contact, the second route of exposure is stray current. Stray current is sometimes incorrectly called stray voltage. Stray current is a result of failure in the electrical return path. The most common cause is a neutral that is grounded at multiple points resulting in multiple paths through the earth. Published research Vd indicates as much as 60% of neutral current travels through the earth.[3] Grounds – stray current The current flowing in the earth is a source of stray current. A second cause of stray current is improper grounding. If ground resistance is not adequately low, the ground current will attempt an alternate path. A third cause of stray current is inadequate bonding. If the potential between two electrical systems is not equalized by proper bonding, then current will take alternate paths resulting in stray current. Because we are a society that does not experiment on humans, we must rely on other research for electrical stray current impact. The most notable impact of stray current has been in the dairy industry where the effect in cattle has been observed. The effect on the animals are avoidance, listless, low milk production, and limited reproduction.
19.10
EM radiation – close to head for long time
E LECTROMAGNETIC LECTROMAGNETIC E NERGY NERGY
The third route of exposure is electromagnetic energy. Electromagnetic (EM) energy radiates from every live electrical circuit. It is well-known that EM energy in the form of X-rays and microwaves has a deleterious effect of biological systems. The radiation effect of normal electrical power operating at 50-60 Hz is less recognized. The first correlations were noted in 1979. The limitations on human research has continued to provide data primarily in correlations. Interestingly, the predominant information has come from Russia, Sweden, and other European countries. The author developed a comprehensive model of biological effects that illustrate the sensitivity to particular frequencies and to both electric (voltage) and magnetic (current) fields. In general the following guidelines should be observed, based on information at this time.
EM radiation – transformer, line, cellphone
1. Keep any magnetic devices (electrical coils) at least 3 feet from the head, particularly when sleeping. 2. Stay at least 50 feet from any distribution power transformer. 3. Stay at least 300 feet from any high-voltage transmission lines. Quite frankly much of the lack of action in this country has been the concern about cost of modifications. Corrections to preclude these EM impacts would require the redesign and relocation of virtually every power system and much of the house wiring in existence. That would be prohibitively expensive. A reasonable alternative is to relocate the biggest offenders and to change change standards for future construction. construction.
EM radiation – transmission line
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Unfortunately, the solution is not simply burying the lines. That will compensate for the electrical field, but the apparently bigger offender, the magnetic field is not attenuated by earth. The health effects that have been associated with EM fields has predominantly been leukemia, leukemia, brain tumors, and cancers.
19.11
S UMMARY J UST ’ S J UMMARY - I T T’ UST P HYSICS HYSICS
Interestingly, every route and phenomenon that causes biological effects can also cause physical effects on inanimate objects in the form of fire. Health effects consequence
Direct contact and electromagnetic radiation are used to intentionally create heat in the forms of heating elements and microwaves respectively. All three routes – direct, stray, and electromagnetic – can inadvertently cause fires resulting in damage or destruction of property. What is the differences in electrical effects on biological and physical systems? The difference is the type system. The T he physics are the same.
19.12
IBLIOGRAPHY - I LLUSTRATIONS LLUSTRATIONS B IBLIOGRAPHY
1. Dalziel, C.F., and Lee, W.R., “Reevaluation of Lethal Electric Currents”, IEEE Currents”, IEEE Transactions Transactions on Industry Industry and General General , Vol. IGA-4, IGA4, pp. 467-476, Sept/Oct. 1968; 1968; Applications Applications discussion pp. 676-677, Nov/Dec, 1968. 2. Durham, Marcus O. "A " A Universal Systems Model Incorporating Electrical, Magnetic, and Biological Relationships," IEEE Transactions on Industry Applications , Vol. 29, No. 2, March/April 1993, pp 436-446. 3. Zipse, Donald W., Death by Grounding, Proceedings Proceedings of IEEE / PCIC Technical Technical Conference Conference, Sept. 22, 2008, IAS/PCIC 08-03.
HAPTER 20 – P ROJECTS ROJECTS C HAPTER 20.1 I NTRODUCTION NTRODUCTION To aid in the understanding of the electrical concepts and systems, several straightforward projects are suggested. These should only be done by professionals with proper equipment and understanding of the safety issues. Do not attempt this at home.
1. 120 Volt receptacle and breaker 2. 240 Volt receptacle and 2-pole breaker 3. GFCI receptacle 4. AFCI receptacle 5. Burn lines 6. Compare solid and stranded effects
Early investigator
HAPTER 21– P LATES LATES – ELECTRICAL FAILURE PHOTOS C HAPTER 21.1 I NTRODUCTION NTRODUCTION The following plates are photographs of actual failures and events. It is clear that electrical energy can create dramatic temperature, resulting faults, and ignition of normal materials. These incidents can cause severe burns, shock and fatality. fatality. This research was done by professionals with proper equipment. Do not attempt this at home.
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Plate 1 - Class 2 Power Supply High Impedance Connection
Plate 2 - Class 2 Power Supply High Impedance Connection
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Plates – Electrical Failure Photos
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Plate 3 - 20 Amp Arc-Fault Breaker – Line
Plate 4 - 20 Amp Arc-Fault Breaker – Neutral
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Plate 5 - 20A Touching – Line (Top View)
Plate 6 - 20A Touching - Line (Side View)
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Plate 7 - 20A Touching - Neutral (Top View)
Plate 8 - 50A Line-Gnd Fault
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Plate 9 - 50A 240V Touching – Line 1 Fault
Plate 10 - 50A 240V Touching - Line 1 Fault
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Plate 11 - 50A 240V Touching - Line 2 Fault
Plate 12 - 50A 240V Touching - Line 2 Fault
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Plate 13 - AL Alloying 14AWG
Plate 14 - Alloying vs. Fault
Chapter 21
Plates – Electrical Failure Photos
139
Plate 15 - Melted 16AWG Stranded
Plate 16 - Melted 14AWG NM
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Plate 17 - Melted 14AWG NM
Plate 18 - Melted 14AWG NM
Chapter 21
Plates – Electrical Failure Photos
141
Plate 19 - Arc Through Char 16AWG Stranded 120VAC
Plate 20 - Arc Through Char 14AWG Solid 120VAC
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Plate 21 - Misdriven Nail (Conductors) 120VAC 14AWG
Plate 22 - Misdriven Nail (Nail) 120VAC 14AWG
Chapter 21
Plates – Electrical Failure Photos
143
Plate 23 - Mechanical Damage Energized Zip Cord (16AWG)
Plate 24 - Foreign Metal between Conductors 120VAC
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Plate 25 - Arc Flash 50A 240VAC
AUTHORS DR . M ARCUS O. DURHAM , PE, CFEI, CVFI Marcus O. Durham, PhD, PE , is a Principal Engineer of THEWAY Corp, Tulsa, OK who provides design and failure analysis of facilities and electrical installations. Professional recognition includes the following.
Life Fellow, Institute of Electrical & Electronics Engineers Life Fellow, American College of Forensic Examiners Life Senior Member, Society of Petroleum Engineers Diplomate, Am Board of Forensic Engineering &Tech Licensed Professional Engineer - multiple states Licensed Electrical Contractor Licensed Commercial Radiotelephone & Amateur Extra Certified Fire & Explosion Investigator, NAFI Certified Vehicle Fire Investigator, NAFI Certified in Homeland Security, ABCHS Registered Investigator, ABRI Member, Int’l Assoc of Arson Investigators-OK & Nat’l Member, IEEE Standards Association Voting Member-Electrical, Nat’l Fire Protection Assoc Professor Emeritus, U of Tulsa He has been awarded the IEEE Richard Harold Kaufmann Medal “for development of theory and practice in the application of power systems in hostile environments.” He was recognized with six IEEE Awards for his Standards development work. He has been awarded numerous times for the over 135 technical papers he has co-authored. He has published seven books and five eBooks used in university level classes. He is acclaimed in Who’s Who of American Teachers, National Registry of Who's Who, Who’s Who of the Petroleum and Chemic al Industry of the IEEE, Who’s Who in Executives and Professionals, and Who’s Who Registry of Business Leaders. Honorary recognition includes Phi Kappa Phi, Tau Beta Pi, and Eta Kappa Nu. Dr. Durham received the B.S. in electrical engineering from Louisiana Tech University, M.E. in engineering systems from The University of Tulsa, and Ph.D. in electrical engineering from Oklahoma State University.
DR . ROBERT A. A. DURHAM , PE, CFEI, CVFI Robert A Durham, PhD, PE is a Principal Engineer of THEWAY Corp, Tulsa, OK, an engineering, management and operations group that conducts training, develops computer systems, and provides design and failure analysis of facilities and electrical installations. He is also Principal Engineer of D2 Tech Solutions, an engineering and technology related firm concentrating on Mechanical and Electrical systems and conversions. Professional recognition includes the following.
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Sr. Member, Institute of Electrical & Electronics Engineers Licensed Professional Engineer - multiple states Licensed Electrical Contractor Certified Forensic Consulatant, Am College of Forensic Examiners Certified Fire & Explosion Investigator, NAFI Certified Vehicle Fire Investigator, NAFI Member, Int’l Assoc of Arson Investigators -OK Member, IEEE Standards Association Chairman, Elec Submersible Cable Standards Working Group Chairman, Production Subcommittee, IEEE/IAS/PCIC Voting Member-Electrical , Nat’l Fire Protection Assoc CESE Professional Engineering Instructor, U of Tulsa He is a nationally recognized author; having received several awards for the over 46 papers and articles he has co-authored. He has published three books and five eBooks used in university level classes. Dr. Durham’s extensive client list includes the development of a broad spectrum of forensic, electrical and facilities projects for many companies. He specializes in power systems, utility competition, controls, and technology integration. His technical emphasis has been on all aspects of the power industry from electric generating stations, to EHV transmission systems, to large-scale distribution systems and power applications for industrial locations to audit of market participation in competitive utility markets.
Dr. Durham received a B.S. in electrical engineering from the University of Tulsa, and M.E. in Technology Management from the University of Tulsa. Dr. Durham earned a PhD in Engineering Management from Kennedy Western University.
ROSEMARY DURHAM , CFEI, CVFI Rosemary Durham is the Chief Administrative Officer and PastPresident of Theway Corp. in Tulsa, OK. Professional recognition includes the following.
Certified Fire & Explosion Investigator, NAFI Certified Vehicle Fire Investigator, NAFI Licensed FCC Amateur Radio Tech Member, Int’l Assoc of Arson Investigators -OK She has co-authored two technical papers. She has co-authored three books on leadership, two books on theology, and two eBooks for university level classes. She is acclaimed in the National Registry of Who’s Who. Who. She is a photographer, who has analyzed the photography record for over 1000 fires and failures. She has been active in traveling to over 15 countries on business and development. She has extensive training from The Crowning Touch Institute. Her credentials are Certified Advanced Color Analyst: Introduction, Intermediate, and Advanced Color analysis and Image analysis. Rosemary received the AB from Ayers Business College. She has additional studies at Imperial Valley College, Tulsa Community College,
Authors
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Oral Roberts University, Southwest Biblical Seminary and Trinity Southwest University.
J ASON A. A. C OFFIN , CFEI, CVFI OFFIN Jason Coffin is a Technical Consultant for Theway Corp. in Tulsa, OK. His specialty is information systems and failures. He is a Construction Manager who develops upscale properties. He is also a natural resources developer and operator who owns interest in numerous properties. Professional recognition includes the following.
Certified Fire & Explosion Investigator, NAFI Certified Vehicle Fire Investigator, NAFI Certified Lead Renovator, EPA Member, Int’l Assoc of Arson Investigators-OK & AR He has actively worked hundreds of fires and failures. Mr. Coffin received the BS in Information Systems from Rogers State University in Claremore and the MS in Information Systems from The University of Tulsa, Oklahoma.
UPPLEMENTAL S UPPLEMENTAL 22.1 E LECTRICAL LECTRICAL F AILURE QUESTIONS – INITIAL 1.
Electrical voltage best relates or compares to which of the following? (a) pressure or potential (b) flow rate, liters/min (c) energy in propane
2.
Electrical current best relates or compares to which of the following? (a) pressure or potential (b) flow rate, liters/min (c) energy in propane
3.
Impedance (opposition to current flow) can be defined as voltage and current: (a) division (ratio) (b) multiplication (product) (c) sum
4.
Power (energy per time) can be defined as voltage and current: (a) division (ratio) (b) multiplication (product)
(c) sum
5.
A spark can best be described by: (a) ejected material (b) short circuit thru insulation (c) (c ) less than 1-Ohm impedance
6.
An arc can best be described by: (a) ejected material (b) short circuit thru insulation (c) (c ) less than 1-Ohm impedance
7.
A high resistance connection can best be described by: (a) ejected material (b) short circuit thru insulation (c) (c ) less than 1-Ohm impedance
8.
How many ways may electrical energy create a fire directly? (a) 1 (b) 3
(c) over 7
9.
A normal 120 Volt circuit applies power on the hot and returns power on the: (a) other hot (b) ground (c) neutral
10.
The color of the wires on a normal 120 Volt circuit are: (a) black, red, white (b) black, white, green
(c) black, red, green
11.
Evidence of an electrically caused fire on a copper wire may be indicated by a: (a) bead (b) divot (c) ball
T F
12.
In many electrical fires, the intense heat generated destroys evidence of the cause.
T F
13.
A shiny, white metal pitting on copper wire is an indication of alloying.
T F
14.
A small plug-in power supply or wall-wart (Class 2) used to charge a phone can cause a fire.
T F
15.
Stray current can cause a fire if there are two ground connections or a poor ground.
T F
16.
NFPA 70 ( NEC NEC ) must be followed as the minimum standard for electrical installations.
T F
17.
NFPA 921 must be followed as the minimum standard for fire investigations.
__________ DATE
________________________ ________________________ NAME
___________ ID #
___________________ ___________________ INSTRUCTOR
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22.2 E LECTRICAL LECTRICAL F AILURE QUESTIONS – FOLLOW -UP 1.
Electrical voltage best relates or compares to which of the following? (a) pressure or potential (b) flow rate, liters/min (c) energy in propane
2.
Electrical current best relates or compares to which of the following? (a) Pressure or potential (b) flow rate, liters/min (c) energy in propane
3.
Impedance (opposition to current flow) can be defined as voltage and current: (a) division (ratio) (b) multiplication multiplication (product) (c) sum
4.
Power (energy per time) can be defined as voltage and current: (a) division (ratio) (b) multiplication multiplication (product)
(c) sum
5.
A spark can best be described by: (a) ejected material (b) short circuit thru insulation (c) ( c) less than 1-Ohm impedance
6.
An arc can best be described by: (a) ejected material (b) short circuit thru insulation (c) ( c) less than 1-Ohm impedance
7.
A high resistance connection can best be described by: (a) ejected material (b) short circuit thru insulation (c) ( c) less than 1-Ohm impedance
8.
How many ways may electrical energy create a fire directly? (a) 1 (b) 3
(c) over 7
9.
A normal 120 Volt circuit applies power on the hot and returns power on the: (a) other hot (b) ground (c) neutral
10.
The color of the wires on a normal 120 Volt circuit are: (a) black, red, white (b) black, white, green
(c) black, red, green
11.
Evidence of an electrically caused fire on a copper wire may be indicated by a: (a) bead (b) divot (c) ball
T F
12.
In many electrical fires, the intense heat generated destroys evidence of the cause.
T F
13.
A shiny, white metal pitting on copper wire is an indication of alloying.
T F
14.
A small plug-in power supply (Class 2) used to charge a phone can cause a fire.
T F
15.
Stray current can cause a fire if there are two ground connections or a poor ground.
T F
16.
f ollowed as the minimum standard for electrical installations. NFPA 70 ( NEC NEC ) must be followed
T F
17.
NFPA 921 must be followed as the minimum standard for fire investigations.
__________ DATE
________________________ ________________________ NAME
___________ ID #
___________________ ___________________ INSTRUCTOR
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22.3 E LECTRICAL S URVEY LECTRICAL S HOCK HOCK S URVEY Please complete an additional survey, if you have been shocked more than one time.
1. Have you ever been shocked?
Yes ___
No___
2. What voltage?
9V___ 12V___ 24V___48V___120V__ 200V__400V__Higher V__
3. Was the voltage
ac___ dc___ rf___
frequency ___
4. What was the cause? intentional___ accidental contact___ failure of what c omponent____________ omponent____________ 5. What was the machine / device / equipment _________________________ ______________________________________ ___________________ ______ 6. What insulation or material was between you and the electrical circuit? none___ material_________ 7. Part of anatomy contacting the energized point___________________________ point______________________________________ _______________ ____ 8. Part of the anatomy contacting the metal or ground or common ______________________________ ______________________________ 9. Could you still control your muscle movement?
Yes___ No___
10. How did you “get off” the energized circuit?
fall___ someone assisted___ removed self_____
brushing contact___ contact___ explain other ________________ _______________________________ __________________________ ____________________ _________ 11. Discuss any sensations you recall a.
Taste __________________________ _______________________________________ ____________________________ ___________________________ ________________ ____
b. Smell_________________________ Smell______________________________________ _________________________ _______________________ __________________ _______ c.
Hearing________________________ Hearing_____________________________________ ____________________________ _____________________________ ________________ __
d. Sight________________________ Sight_____________________________________ _________________________ ________________________ ______________________ __________ e.
Touch / feeling ____________________________ ________________________________________ ________________________ ______________________ __________
f.
Mental / thoughts_________________ thoughts______________________________ ____________________________ __________________________ ________________ _____ ____________________________ __________________________________________ _________________________ ________________________ ______________________ _________
12. Describe any known permanent injuries as result _________________________________ __________________________________________ _________ 13. Describe any additional details of your experience with electrical shock? ______________________ ________________________ ______________________________________ ___________________________ __________________________ ________________________ _________________ ______ ________________________ ______________________________________ ___________________________ __________________________ ________________________ _________________ ______ 14. Approximate age at time of incident _______ 15. Profession / major ____________________________ ____________________________ City _________________________ _________________________ State____ 16. Optional: name_______________________ name_______________________ email email _____________ Return to: Dr. Marcus O. Durham, PhD, PE THEWAY Corp PO Box 33124
[email protected] www.ThewayCorp.com
Tulsa, OK 74153
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22.4 E VALUATION VALUATION F ORM ORM - ELECTRICAL FAILURE ANALYSIS It has been a pleasure to have you you participate in this program. To assist in conducting future Continuing Continuing Education programs, we would would like you to evaluate the contents of this short course. Please take a minute to complete this evaluation form. Name
Title
Organization
FAX
E-mail
What is your overall evaluation of this program? (
) Excellent
(
) Good
( ) Satisfactory
(
) Unsatisfactory
What did you most like about the program? What areas were best covered? What areas would you like to discuss more or in more detail? 1. _________________________________ 2. 3. For people in your position, what information could be reduced? _______________________________ _
What were your expectations for the class at the beginning? _____________________ ______________
Did the class meet your expectations? _____________________________________________________ For our use in possible promotional materials for future programs, we would like to have your comments on this short course:
What is your job description? ( )Adjuster ( )SIU ( )Subro ( )O&C ( )Attorney ( )Staff ( )Engineer ( )Other___________ Are you licensed? ( )PI ( )Attorney ( )Engineer ( )Electrician ( )Public ( )Other ____________ Are you certified? ( )CFI ( )CFEI ( )CVFI ( )Insurance ( )Others ________________________ ___________________ _____ To which professional association(s) do you belong? ___________________________________________
How did you first hear of this short course? ( )brochure ( )received at association meeting ( )mail
( )email ( )word of mouth
( )other - please explain ___________________________________ _______________________________________________________________ ____________________________ Who in your company should be contacted about future programs (Please give name, title, and contact info)
NOTE: PLEASE COMPLETE AND RETURN TO THE PROGRAM COORDINATOR OR INSTRUCTOR. THANK YOU!
FINIS
