7-88 Flammable Liquid Storage Tanks

FM Global Property Loss Prevention Data Sheets

7-88 September 2010 Page 1 of 44

FLAMMABLE FLAMMABLE LIQUID STORAGE TANKS

Table of Contents Page 1.0 SCOPE .............. ............... ............... ............... ............... ............... ............... ............... ............... .............. 3 1.1 Changes Changes ................... ............................. .................... .................... .................... .................... .................... .................... .................... .................... .................... .................... .................... .......... 3 2.0 LOSS PREVENTION RECOMMENDATIONS ........................................................................................ 3 2.1 Construction Construction and Location Location ................... ............................. .................... .................... .................... .................... .................... .................... .................... .................... ............ .. 3 2.1.1 General .................................................................................................................................... 3 2.1.2. Aboveground Aboveground tanks ................... ............................. .................... .................... .................... .................... .................... .................... .................... .................... ............ .. 6 2.1.3 Buried Tanks .............. ............... ................ ............... ............... ............... ............... ............... ... 9 2.1.4 Indoor Tanks .............. ................ ............... ............... ............... ............... ............... ............... . 10 2.1.5 Intermediat Intermediate e Bulk Containers Containers (IBC) ................... ............................. .................... .................... .................... .................... .................... ................ ...... 11 2.1.6 Protection Protection against against Flooding Flooding .................... .............................. .................... .................... .................... .................... .................... .................... ................. ....... 12 2.1.7 Earthquake Earthquake .................... .............................. .................... .................... .................... .................... .................... .................... .................... .................... ................... ............. .... 13 2.2 Occupancy .................... ............... ............... ............... ............... ............... ............... ............... ......... 13 2.2.1 General General ................... ............................. .................... .................... .................... .................... .................... .................... .................... .................... .................... .................... .......... 13 2.2.2 Normal Normal and Emergency Emergency Venting Venting .................... ............................. ................... .................... .................... .................... .................... .................... ............ 14 2.2.3 Asphalt Tanks ............... ............... ............... ............... ............... ................ ............... ............. 23 2.3 Protection Protection ................... ............................. .................... .................... .................... .................... .................... .................... .................... ................... ................... .................... ................. ....... 24 2.3.1 Indoor Tanks .............. ................ ............... ............... ............... ............... ............... ............... . 24 2.3.2 Outdoor Outdoor Tanks .................... .............................. .................... .................... .................... .................... .................... ................... ................... .................... ................... ......... 24 2.3.3 Water Water Supply Supply .................... .............................. .................... .................... .................... .................... .................... .................... .................... .................... .................... .......... 25 2.4 Operation Operation and Maintenanc Maintenance e .................... .............................. .................... .................... .................... .................... .................... .................... .................... ................. ....... 26 2.4.1 Repair, Repair, Recondit Reconditionin ioning, g, and Abando Abandonmen nmentt ................... ............................. .................... .................... .................... .................... ............ 27 2.5 Ignition Source Control .................................................................................................................... 27 3.0 SUPPORT FOR RECOMMENDATIONS .............................................................................................. 28 3.1 Background Background information information .................... .............................. .................... .................... .................... .................... ................... ................... .................... .................... .............. .... 28 3.1.1 Hazards Hazards .................... .............................. .................... .................... .................... .................... .................... .................... .................... .................... .................... .................. ........ 28 3.1.2 Types Types of Tanks ................... ............................. .................... .................... .................... .................... .................... .................... .................... .................... ................. ....... 29 3.1.3 Indoor Tanks .............. ................ ............... ............... ............... ............... ............... ............... . 31 3.1.4 Tank Spacing and Containment ............................................................................................ 32 3.1.5 Manifolded Manifolded Vents Vents .................... .............................. .................... .................... .................... ................... ................... .................... .................... .................... .............. .... 32 3.1.6 Asphalt Tanks ............... ............... ............... ............... ............... ................ ............... ............. 34 3.1.7 Fire Protection Protection ................... ............................. .................... .................... .................... .................... .................... .................... ................... ................... ................... ......... 35 3.2 Loss History History ................... ............................. .................... .................... .................... .................... .................... .................... .................... .................... .................... .................... ............. ... 35 3.2.1 Storage Storage Tanks .................... .............................. .................... .................... .................... .................... .................... ................... ................... .................... ................... ......... 35 3.2.2 Manifolded Manifolded Vents Vents ................... ............................. .................... .................... .................... .................... .................... .................... .................... .................... ............... ..... 36 4.0 REFERENCES ............... ............... ............... ............... ............... ............... ............... ............... .............. 36 4.1 FM Global ........................................................................................................................................ 36 4.2 NFPA ................................................................................................................................................ 37 4.3 Others Others .................... .............................. .................... .................... .................... .................... .................... .................... .................... .................... .................... .................... .................... ............ 37 APPENDIX A GLOSSARY OF TERMS ....................................................................................................... 38 APPENDIX B DOCUMENT REVISION HISTORY ....................................................................................... 40 APPENDIX C HYDROCARBON FIRE DURATION .................................................................................... 41 APPENDIX D HAZARDS ............... ............... ............... ............... ............... ............... ................ ............... ... 43

List of Figures Fig. 1. Horizontal aboveground tank .............................................................................................................. 5 Fig. 2. Buried tank with flame arrester ............... ............... ............... ............... ................ ............... ............. 10

©2009 F actory Mutual Insurance Company. Company. All rights reserved. No part of this document may be reproduced, stored in a retrieval system, or transmitted, in whole or in part, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without written permission of Factory Mutual Insurance Company.

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Flammable Liquid Storage Tanks FM Global Property Loss Prevention Data Sheets

Fig. 3. Enclosed indoor tank ........................................................................................................................ 12 Fig. 4. Cone roof vertical tank ............... ............... ................ ............... ............... ............... ............... ........... 13 Fig. 5. Safe gauging methods ............... ............... ................ ............... ............... ............... ............... ........... 15 Fig. 6. Manif Manifolded olded tanks .............. ............... ............... ............... ............... ................ ............... ............... ...... 22 Fig. 7. Required pipe sizing if detonation arrester is smaller than nearby piping .............. ............... ......... 22 Fig. 8. Improper piping around detonation arrester ..................................................................................... 22 Fig. 9. Open top double deck ...................................................................................................................... 30 Fig. 10. Open top pontoon ............... ............... ............... ............... ................ ............... ............... ............... . 30 Fig. 11. Pan-type covered tanks .................................................................................................................. 31 Fig. 12. Detonation arrester ......................................................................................................................... 32 Fig. 13. Storage tank with flame arrester .................................................................................................... 33 Fig. 14. End-of-line flame arrester ............................................................................................................... 33 Fig. 15. End-of-line flame arrester with pipe-away flange ........................................................................... 34 Fig. 16. Backflash interrupter ....................................................................................................................... 34 Fig. 17. Typical conservation vent vent ................................................................................................................ 38

List of Tables Table 1. Support (Saddle) Width for Horizontal Steel Flammable Liquid Tanks ............................................ 4 Table 2. Spacing for Flammable Liquid Storage Tanks and Loading/Unloading Stations ................... ............................ ......... 6 Table 3. Spacing for Flammable Liquid Tank Containment Dikes ......................... ............... ............... ......... 7 Table 4. Indoor Tank Quantity Limits ........................................................................................................... 10 Table 5. Size of Opening for Normal Venting ............................................................................................... 16 Table 6. Required Thermal (Normal) Venting Capacity 1 ............................................................................. 17 Table 7. Typical Vent Line Size for Buried Tanks Tanks ......................................................................................... 18 Table 8. Capacities for Emergency Relief of Excessive Internal Pressure for Aboveground Tanks Operating at 1 psig (7 kPa) or less1 ............................................................................ 19 Table 9. Values for L (M)1/2 ........................................................................................................................... 20 Table 10. Environmental Factors for Emergency Venting Capacity (use only one factor) factor) .......................... 21 2 Table 11. Sprinkler Density for Storage Tank Rooms, gpm/ft (mm/min) (mm/min) ...................................................... 24 Table 12. Hose Stream Demand for TANKS Storing Flammable Liquids 1 ................................................. 26 Table 13. Estimated Water Demand for Fixed Foam Protection for a full Surface Fire. Fire. ............................. 26 Table 14. Safety Distances for Hot Work, Open Flames, Maintenance, Repair or Modification ................. ................. 28 Table 15. Losses over US$100,000 by Occupancy Class Class ........................................................................... 35 Table 16. Losses over US$100,000 by Engineering Peril Peril ............................................................................ 36 Table 17a. Relationship Between Fuel Volume, Pool Size, and Fire Duration (English) (English) ............................. 41 Table 17b. Relationship Between Fuel Volume, Pool Size, and Fire Duration (metric) (metric) ............................... 42 Table 18a. Flow Rate, Pool Diameter, Heat Release Rate, and Flame Height for a Flowing Kerosene Fire (English) (English) ................................................................................................. 42 Table 18b. Flow Rate, Pool Diameter, Heat Release Rate, and Flame Height for a Flowing Kerosene Fire (Metric) (Metric) ................................................................................................... 42

©2009 Factory Mutual Insurance Company. All rights reserved.


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1.0 SCOPE

In this data sheet, the term ‘‘flammable liquid’’ liquid’’ is used synonymously for all three classes of liquids. Where recommendations vary because of flash point, that is indicated. The recommendations in this data sheet apply to chemically stable or unstable flammable liquids when stored in atmospheric pressure (operating at less than 1 psig [0.07 barg]) or low pressure (operating over 1 psig [0.07 barg] and less than 15 psig [1 barg]) tanks. This data sheet applies to storage in horizontal and vertical tanks usually constructed of metal and located abovegroun aboveground, d, underground underground,, or inside inside buildings. buildings. Storage in floating floating roof tanks is not addressed. For guidance on floating roof tanks, refer to NFPA 30, Flammable Liquid Storage in Portable Containers , or equivalent national or international standard. This data sheet provides requirements requirements for intermediat intermediate e bulk containers containers (IBCs), (IBCs), when used to supply liquids liquids to a process. Storage of IBC is covered by DS 7-29, Flammable Liquid Storage in Portable Containers . This data sheet does not cover all aspects of pumping operations as represented by load and unload racks, pump pads at tank farms, or fuel pumping and transfer systems in buildings. Spacing criteria for some of these peripheral operations are provided in Table 2. For other aspects, refer to DS 7-32, Flammable Liquid Operations . The recommendations for drainage, fire protection, separation, or diking do not apply to day tanks or other process tanks. Locate and protect those tanks in accordance accordance with the appropriate appropriate FM Global Global data sheet, such as Data Sheet 7-14, Fire and Explosion Protection Protection for Flammable Liquid , Flammable Gas, and Liquefied Flammable Gas Processing Equipment and Supporting Structures ; Data Sheet 7-30, Solvent Extraction Plants ; Data Sheet 7-32, Flammable Liquid Operations , or Data Sheet 7-43/17-2, Loss Prevention in Chemi- cal Plants . This data sheet does not apply to flammable liquids or gases stored in pressure vessels above 15 psig (103 kPa). See Data Sheet 7-55, Liquefied Petroleum Gases , for such storages. This data sheet addresses methods to prevent flame propagation throughout low-pressure flammable liquid storage tanks that are manifolded together to reduce atmospheric emissions where the presence of an ignitable vapor-air mixture in normal operation is likely. This data sheet does not address preventing flame propagation in fuel gas piping systems (see Data Sheet 6-10, Process Furnaces ) in systems handling acetylene (see Data Sheet 7-51, Acetylene ) or in fume collection systems for process equipment (see Data Sheet 7-78, Industrial Exhaust Systems ). ). 1.1 Changes

September 2010. Changes were made in Table 3, Spacing for Flammable Liquid Tank Containment Dikes . 2.0 LOSS PREVENTION RECOMMENDATIONS 2.1 Construction and Location 2.1.1 General

1. Construct atmospheric tanks (operating at less than 1 psig [0.07 barg]) in accordance with the following recognized engineering standards or suitable national or international equivalents: a) API (American (American Petroleum Institute) Standard 650, Welded Steel Tanks for Oil Storage b) UL (Underwriters Laboratories) 142, Standard for Steel Aboveground Aboveground Tanks Tanks for Flammable Flammable and Com- bustible Liquids c) UL 2080, Fire Resistant Tanks for Flammable and Combustible Liquids d) UL 2085, Protected Aboveground Tanks for Flammable and Combustible Liquids e) UL 2244, Standard for Aboveground Flammable Liquid Tank Systems f) UL 58, Standard for Steel Underground Tanks for Flammable and Combustible Liquids


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Flammable Liquid Storage Tanks

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2. Construct low-pressure tanks (operating at more than 1 psig [0.07 barg] but less than 15 psig [1 barg]) in accordance with the following recognized engineering standards or suitable national or international equivalents: a) API Standard Standard 620, 620, Design and Construction of Large, Welded, Low-Pressure Storage Tanks b) Code for Unfired Pressure Vessels, Section VIII, Division 1 of the ASME Boiler and Pressure Vessel Code c) EN BS 14015, Specification for Design and Manufacture of Site Built, Vertical, Cylindrical, Flat- Bottomed, Aboveground, Welded, Steel Tanks for the Storage OF Liquids at Ambient Temperatures and Above d) EN BS 12285, Part 1, 1, Workshop Fabricated Steel Tanks — Horizontal Cylindrical Single and Double Skin Tanks for Underground for Underground Storage of Flammable and Non-Flammable Water Polluting Liquids e) EN BS 12285, Part 2, 2, Workshop Fabricated Steel Tanks — Horizontal Cylindrical Single and Double Skin Tanks for Aboveground for Aboveground Storage of Flammable and Non-Flammable Water Polluting Liquids 3. Design supports for horizontal cylindrical tanks to minimize settlement or lateral movement that could result in overstress or rupture of the tank or associated pipe and fittings. a) Provide supports of fire-resistive construction (e.g., saddles of reinforced concrete as shown in Fig. 1), with at least one-third of the circumference of the tank bearing on the supports. Protect reinforcing steel in concrete saddles with at least 2 in. (50 mm) of concrete. b) Design Design saddles saddles in accordance with the following following table. Table 1. Support (Saddle) Width for Horizontal Steel Flammable Liquid Tanks

Capacity, gal (m3) Tank diameter, in (mm) Saddle width, in (mm)

(2.1) 48 (1220)

> 550 ≤ 1100 (2.1 – 4.2) 64 (1625)

> 1100 ≤ 9,000 (4.2 – 34) 76 (1930)

> 1100 ≤ 35,000 (4.2 – 133) 144 (3660)

> 35,000 ≤ 50,000 (133 – 189) 144 (3660)

4.5 (115)

6 (150)

6 (150)

9 (230)

10 (255)

≤ 550

c) Provide fireproofing of tank supports that are structural steel with a material having a fire resistance of 2 hrs (concrete in accordance with DS 1-21 or an FM Approved coating rated for process structure or tank protection) protection) or protected protected with automatic automatic water spray nozzles nozzles in accordance with DS 4-1N. d) Provide Provide bracing bracing to prevent movement in locations locations subject to earthquakes earthquakes.. e) In an area subject to flooding, anchor tanks to prevent either full or empty tanks from floating during a rise in water level up to the maximum flood stage. Details are given in Section 2.2.6, Protection against Flooding. 4. Pressure vessels and low-pressure tanks may be used as atmospheric storage tanks. Where unstable liquids are stored, stored, see 2.2. 2.2.2.2 2.2 – 7. 5. Fixed tanks of combustible construction (usually glass fiber-reinforced plastic) may be used: a) for underground installation. b) where required by the properties of the liquid stored. c) for liquids with flash point greater than 200 °F (93°C) stored outdoors where not exposed to the leakage of liquids with lower flash point. d) for liquids with flash point greater than 200 °F (93°C) (or any flash point if required as in b) stored indoors with suitable automatic sprinkler protection and containment and installed in accordance with 2.1.4, below. 6. When glass fiber-reinfo fiber-reinforced rced plastic (FRP) tanks are used: a) Construct the tank in accordance with the following recognized engineering standards or suitable national or international equivalents:



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Fig. 1. Horizontal aboveground tank

1. UL 1316, Standard for Glass Fiber Reinforced Plastic Underground Storage Tanks for Petroleum Products, Alcohols, and Alcohol-Gasoline Mixtures 2. API Specification 12P, Fiberglass Reinforced Plastic Tanks 3. ASTM D3299-Standard Specification for Filament Wound Glass Fiber Reinforced Thermoset Resin Chemical Resistant Tanks. 4. ASTM D4097-Standard Specification for Contact Molded Glass Fiber Reinforced Thermoset Resin Chemical Resistant Tanks. 5. EN BS 13121 GRP Tanks and Vessels for Use Aboveground. Part 1: Raw materials – specification and acceptance conditions Part 2: Composite materials – chemical resistance Part 3: Design and Workmanship Part 4: Delivery, installation and maintenance b) Install aboveground tanks on a concrete pad in the vertical position only. c) Store only chemically stable liquids, compatible with the reinforced plastic. d) Provide separate dikes for all reinforced plastic tanks over 2,500 gal (9.5 m 3). e) Provide spacing for all reinforced plastic tanks in accordance with Table 2. f) On tanks containing liquids with flash point less than 100 °F (38°C), install conductive metal fill and discharge lines, supported internally and extending to within 3 in. (76 mm) of the tank bottom, and provide a static ground to dissipate charges that can accumulate during filling operations. g) Where tanks are located indoors, provide automatic sprinkler protection designed in accordance with section 2.3.1, below. Automatic sprinkler protection may be omitted in low-value buildings that have adequate space separation from important buildings and structures. h) Install buried tanks in strict conformance to the manufacturer ’s recommendations. 7. Construct tanks that have special features, such as corrosion resistance, with strength equivalent to that of steel tanks.


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8. Concrete tanks without liners may be used for the storage of liquids with flash points higher than 100 °F (38°C) and specific gravities greater than 0.8. 9. Concrete tanks with combustible or noncombustible liners may be used for the storage of liquids with flash points lower than 100 °F (38°C) when designed in accordance with recognized engineering standards. Choose the type and thickness of the liner depending on the properties of the liquid to be stored. 10. Provide rectangular steel tanks with internal braces to withstand hydrostatic loads in accordance with recognized engineering standards. 11. Where combustible plastic insulation is used on storage tanks, install a proper fire protective coating over the insulation or install FM Approved Class 1 insulation. See Data Sheet 1-57, Plastic in Construction , for additional guidance. 12. Prior to being placed in service, test all tanks in accordance with the standard under which they were constructed; generally, by filling the tanks with water and observing them for leakage. (PRIOR 2.1.1.5)

2.1.2. Aboveground tanks 1. Locate aboveground tanks on ground sloping away from main facility buildings and plant utility installations. On hilly terrain, provide drainage or dikes to bypass buildings or installations at lower levels. 2. Locate tanks with respect to buildings and other tanks in accordance with Table 2. Table 2. Spacing for Flammable Liquid Storage Tanks and Loading/Unloading Stations

Stable liquids, tank to bldgs of non combustible or better construction (See Appendix A) or open process structures (3) Stable liquids, tank to buildings of combustible construction (See Appendix A) Stable liquids in listed UL 2080, 2085 and 2244 containers Unstable liquids, tank to bldgs of any construction Stable liquids, tank to tank Unstable liquids, tank to tank Tank truck and railcar loading/unloading to tank, (4) Tanks (single or multiple) to LPG storage

Liquid Flash Point (1)(2) > 140°F (60°C) ≤ 140 °F (60°C) 1 D (min 75 ft, 23 m) 0.5 D (min 50 ft, 15 m) 2 D (min 125 ft, 38 m)

1 D (min 75 ft, 23 m)

See 2.1.2 – 6 2 D (min 125 ft, 38 m) 1 D (min 75 ft, 23 m) 0.5 D (min 3 ft, 0.9 m) 0.5 D (min 3 ft, 0.9 m) 1 D (min 5 ft, 1.5 m) 1 D (min 5 ft, 1.5 m) 75 ft (23 m) 50 (15 m) minimum 100 ft (30 m) or 1 D

Notes 1 Where tanks are equipped with internal heating systems and store liquids subject to boil over, froth over, or slop over, evaluate as if containing liquids with flash points = 140 °F (60°C), regardless of their flashpoint. 2 D refers to the diameter of the largest flammable liquid tank. 3 Open process structure refers to areas of one or multiple levels used to manufacture chemicals. Intermediate tanks considered part of the process are excluded from this spacing requirement. 4 For separation between loading/unloading facilities and buildings, see DS 7-32.

3. Provide containment for tanks containing flammable liquids with flash points below 200 °F (93°C) by remote impounding, dikes around the tanks, or secondary containment. (Environmental or other government regulations may require containment for smaller tanks.) 4. Construct dikes used to provide containment around the tanks according to the following criteria: a) Size dikes to hold 100% of the contents of the largest tank within the diked area. The volume occupied by this tank below the top of the dike may be considered part of the dike capacity unless the liquid stored is subject to boil over. The volumes of all other tanks below the top of the dike must be deducted when calculating dike capacity. b) Construct dike walls of earth, steel, concrete, or solid masonry, designed to be liquid-tight and to withstand a full hydrostatic head by release of tank contents. c) Provide earthen walls 3 ft (1 m) or more in height with a flat section at the top not less than 2 ft (0.6 m) wide with the wall slope consistent with the angle of repose of the material of which the wall is constructed.



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d) Control vegetation, desirable protection against erosion, so as not to impede fire fighters or add to the fire hazard. e) Limit the height of dikes, regardless of construction, to 6 ft (2 m) to minimize the chances of pocketing flammable vapors and to facilitate fire fighting. f) Provide drainage to remove water from within diked areas at a minimum uniform slope of 1% away from tanks toward a sump, a drain box, or other means of disposal located at a safe distance from the tank. g) Design drains to prevent liquids from entering natural water courses, public sewers, or drains. Trap drain lines and provide valves on the lines, outside the dike, so they are accessible under fire conditions. Protect the traps from freezing. h) Limit dikes to contain an aggregate capacity of 5,000,000 gal (18,900 m 3), except were individual tank capacity exceeds 5,000,000 gal (18,900 m 3) in which case, ensure the dike contains only one tank. i) Subdivide any dike containing two or more tanks by intermediate dikes or channels as follows: 1. Stable liquids in weak seam roof tanks a. Subdivision for each tank over 420,000 gal (1,590 m 3) b. Subdivision for each group of tanks with total capacity up to 630,000 gal (2,390 m 3), none individually > 420,000 gal (1,590 m 3) 2. Stable liquids in horizontal tanks or vertical cone roof tanks a. Subdivision for each tank over 100,000 gal (380 m 3) b. Subdivision for each group of tanks with total capacity up to 150,000 gal (570 m 3), none individually >100,000 gal (380 m 3) 3. Unstable liquids in any type of tank need individual subdivision. 4. Unstable liquids in any type of tank protected by water spray in accordance with Data Sheet 4-1N can follow the subdivision requirements in “ 2” above. j) Build intermediate dikes at least 18 in high. k) Provide separation between a tank and the dike wall of at least one-half the tank diameter. l) Provide separation between buildings and dike wall in accordance with Table 3. m) Where tanks are arranged in more than two adjacent rows or in an irregular pattern, provide greater spacing between tanks, additional dikes, or roadways so all tanks are accessible for firefighting. Table 3. Spacing for Flammable Liquid Tank Containment Dikes

Stable liquids, dike wall to buildings of noncombustible or better construction (See Appendix A) or open process structures (3)

Liquid Flash Point (1)(2) ≤ 140 °F (60°C) > 140°F (60°C) 1 D (min 75 ft; 23 m; 0.5 D (min 50 ft; 15 m; max. 200 ft, 61 m) max. 200 ft, 61 m)

Stable liquids, dike wall to buildings of combustible construction (See Appendix A)

2 D (min 125 ft, 38 m; 300 ft, 91 m)

1 D (min 75 ft, 23 m; 300 ft, 91 m)

Unstable liquids, dike wall to buildings any construction

2 D (min 125 ft, 38 m; 300 ft, 91 m)

1 D (min 75 ft, 23 m; 300 ft, 91 m)

Notes 1 Where dikes contain tanks equipped with internal heating systems and store liquids subject to boil over, froth over, or slop over, protect as liquids with flash points = 140 °F (60°C) regardless of their flashpoint. 2 D usually refers to the longest dike dimension, length, width, or diameter (if circular).However, where a non-circular dike is present, base the spacing to the exposure on the exposing dimension, i.e., the side that most directly faces the exposed structure, vessel or other dike, not necessarily the longest dimension. 3 Open process structure refers to areas of one or multiple levels used to manufacture chemicals. Intermediate tanks considered part of the process are excluded from this spacing requirement.

5. Design remote impounding used for containment in accordance with the following criteria:


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a) Provide drainage within diked areas at a minimum uniform slope of 1% away from tanks toward the impounding basin. b) Route drainage between the tanks and the impounding basin so that if the liquid in the system is ignited, it will not seriously expose tanks or important buildings (DS 7-83 can provide valuable guidance on the design of the drainage system). c) Provide the impounding basin with a minimum capacity equal to twice the largest tank that could drain to it. d) Equip the impounding basin with means to drain off accumulations of water from precipitation. e) Separate the impounding basin from important buildings and facilities according to the size of the basin and the exposure potential to the building, as follows: 1. From buildings of ordinary or combustible construction (or from buildings containing hazardous materials) having extensive window areas or associated combustible yard storage, spacing distance = 1.8 × basin diameter or diagonal. 2. From buildings of fire resistive or noncombustible construction not having extensive window areas, hazardous materials, or associated combustible yard storage, spacing distance = 0.6 × basin diameter or diagonal. 3. From flammable liquid storage tanks, spacing distance = 0.3

× basin

diameter or diagonal.

f) Provide each diked and/or subdivided area with drainage systems leading to the impounding basin. Hydraulically design the drainage system from each diked or subdivided area as follows: 1. Provide drainage capacity from each subdivision in a dike capable of carrying off liquid at a rate not less than that which could be released assuming a break in a bottom connection from the largest full tank within the subdivision, or the maximum tank fill rate, whichever is greater. 2. Use drainage system piping that is a minimum of 24 in. (60 cm) diameter. 3. Route piping under subdivisions and dikes to culverts or open channels leading to the impounding basin. 4. Design culverts or open channels with the capacity to carry off liquid from all the drainage connections within the diked area having the largest single tank, with the connections flowing at their maximum capacity. 5. Design the culverts or channels with additional capacity to carry off the maximum expected discharge of water from fire fighting operations. 6. Locate open channels a minimum of 50 ft (15 m) from important buildings and facilities. 7. Provide roads with culverts over the channels at intervals to permit access to the tanks for maintenance or emergencies. 8. Pave channels with asphalt or concrete, or line them with smooth stone, metal, or compacted clay to prevent growth of vegetation that could restrict liquid flow. 9. Provide a minimum of 1% slope for channels and culverts. Steeper slopes are advisable to reduce culvert or channel size. 6. Secondary containment tanks (double skinned) listed as meeting the requirements of UL 2080, 2085, 2244, and EN BS 12285, Part 2: a) are limited to a capacity of 12,000 gal (45 m 3) (Locate tanks exceeding 12,000 gal (45 m 3) in accordance with Table 2 and meet all of the remaining criteria in b through i). b) are limited to the storage of stable flammable liquids. c) are spaced a minimum of 5 ft (1.5 m) from building walls or openings. d) are spaced a minimum of 3 ft (1 m) from adjacent tanks of the same type. e) are protected against vehicle impact by suitable barriers except where the tank is specifically listed and marked as having passed vehicle impact testing.



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f) are provided with a means to prevent siphon flow from the tank. g) are provided with a means, accessible to the delivery operator, for determining the level of liquid in the tank. h) are provided with a means to prevent overfilling by sounding an alarm when the liquid level in the tank reaches 90 percent of capacity and by automatically stopping delivery of liquid to the tank when the liquid level in the tank reaches 95 percent of capacity, without restricting or interfering with the proper functioning of the normal vent or the emergency vent. i) do not need additional spill containment by way of impounding basins or drainage.

2.1.3 Buried Tanks 1. Locate buried tanks at least 5 ft (1.5 m) from building foundations and 2 ft (0.6 m) from other tanks and pipelines. Where a choice of location is offered, choose the one farthest removed from below-grade open areas such as pits and basements under important buildings. 2. Anchor the tanks where groundwater conditions are bad or where flooding is possible (Fig. 2). Details are given in Section 2.1.6, Protection Against Flooding, below. 3. Cover buried tanks with 2 ft (0.6 m) of earth, except under concrete paving at least 4 in. (100 mm) thick, where 1 ft (0.3 m) of earth is sufficient. In either case, provide an additional 1 ft (0.3 m) of cover at tank locations over which heavy vehicles pass. Reinforce paving over the tank and extend at least 1 ft (0.3 m) beyond the tank perimeter in all directions to transmit the superimposed load to foundations beside the tank. 4 The equivalent of a location below ground may be obtained with a substantial portion of a tank above grade. Earth is placed over the tank to form a 1 to 2 ft (0.3 to 0.6 m) cover at the angle of repose of the fill used. A concrete retaining wall or lock-sheet steel piling may be placed around the tank and filled with earth to reduce space requirements. 5. Protect tanks against corrosion as follows: a) Provide at least 6 in. (150 mm) of well compacted clean gravel or sand around the tank. b) Locate the tanks above the groundwater level. c) Provide a protective coating on steel tanks. The base coat, usually applied by the manufacturer, acts as a primer. The outer coating, applied in the field, needs to be compatible with the base coat. d) Patch-paint portions of the protective coating damaged when the tank is installed. e) Cathodic protection is an acceptable alternate to protective coatings. 6. Provide openings for normal venting in accordance with Section 2.2.2.1.2. Venting for fire exposure is unnecessary.


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Fig. 2. Buried tank with flame arrester

2.1.4 Indoor Tanks 1. Limit the quantity of flammable liquids in indoor tanks in accordance with Table 4 below. Table 4. Indoor Tank Quantity Limits Liquid Flash Point ≤ 200 °F (93°C)

>200°F (93°C)3

Location of Tank(s) Upper floor Grade level Basement Upper floor Grade level 2 Basement

Maximum Indoor Storage, One or More Tanks gal m3 2,000 7.5 2,000 7.5 Not permitted Not permitted 5,000 20 1 50,000 190 1 5,000 20

Notes 1 Not over 25,000 gal (95 m 3) in one tank 2 Limit FRP tanks to 5,000 gal (20 m 3) and to liquids with flash points greater than 200 °F (93°C) in accordance with section 2.1.1 – 5. 3 Tanks containing liquids heated to within 25 °F (14°C) of their flash point are evaluated in the ≤ 200 °F (93°C) category.

2. Arrange tanks meeting the quantity limits of Table 4 as follows: a) When located at grade level, provide a cut-off room for the purpose of containing the liquid storage tank(s). Provide concrete or masonry construction with a minimum one-hour fire-rating for the cut-off room, including similarly rated doors for any openings into the main building. Important structural steel needs to be similarly protected for one-hour fire resistance. Design the covering specifically for a hydrocarbon fire exposure. Locate the room along an outside wall with openings accessible to firefighters. b) When located above or below grade level, provide a room separated from other occupancies by a wall of at least 3-hour fire-rated concrete or masonry construction and a 3-hour fire-rated resistive covering on any exposed steel. Design the covering specifically for a hydrocarbon fire exposure. c) Repair spalled areas of fire-resistive coatings on structural framing if the spalled area exceeds more than 4 in2 (25 cm2).



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d) Provide hard-piped fill lines terminating outside the building. e) Provide overflow protection using a high-liquid-level device that automatically shuts down filling operations on detection of a high liquid level in the tank using an automatic safety shut-off valve. Locate the safety shut-off valve as close to the tanker truck connection as possible. f) Arrange the discharge line to exit the top of the tank. For tanks with bottom discharge lines, provide a fusible link-operated safety shut-off valve (SSOV) at the tank outlet. g) Provide fire detection that automatically interrupts fill or discharge operations using automatic safety shut-off valves. Approved water flow alarms, heat, smoke, or flame detection are acceptable means of detecting a fire. h) Provide detection for a liquid spill that automatically interrupts fill or discharge operations using automatic safety shut-off valves where the tank room is in a non-industrial occupancy, e.g., retail, office, education, or residential. i) Provide properly sized normal and emergency relief vents hard-piped to a safe location outside the building. See Section 2.2.2 below. j) Provide drainage designed to dispose of the discharge from all sprinklers in the room, as well as spilled liquids, in accordance with Data Sheet 7-83, Drainage Systems for Flammable Liquids . k) Where drainage to a safe location is impractical, provide containment sufficient to hold the contents of all spilled liquid plus a minimum of a 2 in. (5 cm) freeboard and an FM Approved special protection system. Containment can be provided with curbs, dikes, and existing walls. Ensure floors and walls are liquidtight for the height of the required containment. Spilled liquid can include release from the storage tanks or from an uncontrolled release during filling operations. l) Support tanks either directly on the floor or in accordance with Section 2.1.1 – 3. 3. An alternative arrangement to “2” above is to locate the tank in a liquid tight, concrete or brick-walled enclosure with the space between the tank and the wall filled with sand to a depth of 1 ft (0.3 m) above the tank as in Figure 3. In this case, there are no quantity limitations. a) Provide hard-piped fill lines terminating outside the building. b) Provide overflow protection using a high-liquid-level device that automatically shuts down filling operations on detection of a high liquid level in the tank using an automatic safety shut-off valve. Locate the safety shut-off valve as close to the tanker truck connection as possible. c) Provide properly sized normal and emergency relief vents hard piped to a safe location outside the building. See Section 2.2.2.1.2 below. 4. Arrange pumps located inside buildings as follows: a) Install positive displacement pumps. b) Arrange the pump to take suction from the top of the tank. Elevate the pumps to the same elevation as the top of the tank or provide an anti-siphon device. Locate the anti-siphon device as close to the tank outlet as possible. (Some volatile liquids may require special pumping arrangements.) c) Where a pump takes suction from the bottom of a tank, or when the pump is a centrifugal type, provide a safety shut-off valve at the tank, interlocked to shut down the pump in the event of a leak or fire. d) Provide a pressure-relief valve down stream of any positive displacement pump and pipe it back to the tank. e) Implement all other requirements for flammable and combustible liquid transfer systems as required in DS 7-32 under “ transfer by pumping”.

2.1.5 Intermediate Bulk Containers (IBC) 1. Store metal, composite, or plastic IBCs inside or outside in accordance with the requirements of DS 7-29, Flammable Liquid Storage in Portable Containers. 2. Treat IBCs used to supply flammable liquid to any type of process as indoor tanks and implement the recommendations in Section 2.1.4.


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Fig. 3. Enclosed indoor tank

2.1.6 Protection against Flooding 1. Locate tanks (aboveground or buried) so that at least 30 percent of their allowable storage capacity extends above the 100-year flood level, or secure the tank by one of the following methods: a) Anchor the tank to resist movement. b) Attach the tank to a foundation of steel and/or concrete having sufficient weight to provide adequate load for the tank when submerged by flood water to the 100-year flood level (Fig. 2). If the tank can be water-loaded, the anchoring load can be calculated assuming a full tank; otherwise assume an empty tank. c) Adequately secure the tank from floating by other means. d) Fill the tank (buried), or to at least 70% capacity (above-ground), with water from a dependable supply (if that is not impractical or hazardous due to the contents of the tank). 2. Construct any tank that is assumed to be submerged empty to safely resist external pressures. 3. Extend tank vents or other openings that are not liquid-tight above the 100-year flood level. 4. Provide tight closures at tank openings to prevent displacement of the tank contents by flood waters. 5. Where water filling is required to prevent tank floating, develop an emergency plan that includes a water supply for water loading that is independent of public water or power supplies to allow for filling the tanks to increase their weight. 6. Prior to water loading, close all valves not used in connection with the filling operation. 7. Facility fire protection water may be used for filling if: a) other water supplies are lost. b) normal plant operations are terminated and a fire watch is started. c) the loading operation is done through hoses and is constantly attended. d) no fire pump, divisional, or sprinkler control valves have to be shut



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e) the water supplies are not drawn down to seriously affect the required duration of sprinkler or hose stream discharge. f) the loading operation is immediately shut down in the event of a fire emergency. 8. When filling is complete, close and lock all valves on connecting pipe.

2.1.7 Earthquake 1. In FM Seismic Zones 150 and under, provide restraint and appropriate flexibility in piping connections and associated tanks, pipe headers and piping systems per the requirements in DS 1-11, Fire Following Earth- quakes . 2. Where tanks are located indoors, arrange all liquid transfer operations to be shut down during a seismic event using seismic shutoff valves. 2.2 Occupancy

2.2.1 General 1. Make pipe connections to tanks above the normal liquid level. 2. Extend fill, return, and similar pipes below the lowest level of liquid in the tank or within about 6 in. (150 mm) of the tank bottom,(Fig. 1). 3. Where bottom connections are present: a) provide steel shutoff valves bolted or welded to the first flange connection on the tank. b) keep valves closed except when liquid is being transferred. (Fig. 4). c) for tanks exceeding 10,000 gal (28 m 3), provide valves that are manually controllable from a remote location. d) provide a liquid-tight closure, such as a valve, plug, or blind, or a combination of these, on connections below the liquid level through which liquid does not normally flow.

Fig. 4. Cone roof vertical tank

4. Where pumps are provided, implement the requirements for flammable and combustible liquid transfer systems as required in DS 7-32 under “ transfer by pumping‘‘.


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5. Do not permit piping in dikes to pass through a dike wall to an area containing other tanks which could allow a spill or fire to spread to adjacent tanks. 6. Provide manway openings with a bolted, gasketed cover that is kept closed except when the tank is opened for examination or maintenance (Fig. 4). 7. Provide level-gauging or measuring devices for all tanks. 8. Where manual gauging connections are present: a) Where liquids with flash point below 100 °F (38°C) are present, use a method that will not expose the vapor space to outside atmosphere. b) Avoid gauging equipment that will release large quantities of liquid if the equipment is damaged mechanically or by an exposure fire. c) Where a rod and gauging well is provided, extend a pipe down into the tank below the level of the suction intake (Fig. 5[a]) to provide a liquid seal at the bottom of the well that prevents vapors above the main body of liquid from escaping during gauging. d) Install FM Approved devices for safe gauging (level measurement) of tanks . 9. Provide high-level alarms that sound at an attended location. 10. Arrange heating equipment for tanks as follows: a) Provide heat only in the vicinity of the suction intake for tanks storing liquids with flash point below 200°F (93°C). b) Provide only enough heat to ensure free flow of the liquid. c) Arrange suction pipe or outlet pipe connections to ensure that heating coils will always be submerged. d) For metal tanks, use steam, hot water or FM Approved electric heaters. For reinforced plastic tanks, use only steam or hot water. e) Steam heating coils are commonly used on tanks containing No. 5 and No. 6 fuel oil and similar liquids to reduce their viscosity for pumping. In one acceptable arrangement, a horizontal open-ended shell or box contains the steam coils, and suction is taken from inside the shell. Another arrangement consists of a vertical spiral steam coil located around a top-connected suction pipe; this is acceptable if the fill opening is trapped or the fill pipe is extended below the level of the suction intake (Fig. 1). f) Provide a steam pressure-relief valve close to the tank, set at about 5 psi (35 kPa) over normal working pressure, if steam is supplied through a reducing valve. g) Provide FM Approved low-liquid- level and high-temperature interlocks to shut off the heating system. 11. Closely monitor all fill operations either by operator standing by or remote reading level gauges at an occupied location.

2.2.2 Normal and Emergency Venting 1. Provide normal venting to permit the intake and discharge of air during emptying and filling operations and to permit expansion and contraction of vapor due to temperature changes. 2. Provide emergency venting to prevent the tank becoming overpressurized by fire exposure. 3. Where a mixture of several liquids is stored in the same tank, use the most volatile for the design basis. 4. Normal and emergency venting can be provided by one opening with a minimum capacity equivalent to the emergency vent requirement. 5. Provide normally closed venting devices (conservation vents) on tanks storing liquids with flash points less than 73 °F (23°C) and boiling points less than 100 °F (38°C). 6. Provide normally closed venting devices (conservation vents) or an FM Approved flash arrester on tanks storing liquids with flash points above or equal to 73 °F (23°C) and below 100 °F (38°C), and with boiling points above 100°F (38°C) or liquids that can be heated to their flash points under normal operating conditions.



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Fig. 5. Safe gauging methods

7. Prevent condensation in flame arresters on tanks containing liquids that solidify during cold weather by providing a heating arrangement such as a steam coil at the arrester. 8. Where polymerization of a material may occur at the arrester, provide a dual arrester equipped with a threeway valve so one arrester is always in service. 9. Where vent pipes are necessary to conduct vapors to a safe location, install them as follows: a) Terminate vents close enough above the tank to avoid imposing a dangerous liquid head on the tank if liquid overflows through the vent. b) Extend vent pipe connections from indoor tanks to outside the building. c) Terminate vents at a location free of potential ignition sources and away from openings through which vapors can leak back into the building or locations where combustible construction would be exposed by a fire burning at the end of the vent.


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d) Arrange horizontal runs of pipe to drain back to the tank. e) Arrange the outlet and drains of vents on tanks operating at pressures in excess of 2.5 psig (17 kPa) so they do not direct vapor discharge back onto the tank. f) Terminate open vents either with a weather protective hood or a U-bend to keep out rain and provide coarse screens to prevent foreign matter from obstructing the pipe. g) Do not permit manifolding of tank vents for vapor recovery or air pollution control except in accordance with Manifolded Vents in Section 2.2.2.3. 2.2.2.1 Normal venting 2.2.2.1.1 Aboveground Tanks 1. For tanks with less than 50,000 gal (189 m 3) capacity, the vent opening to meet normal venting requirements can be in accordance with Table 5 but at least as large as the largest of the fill or withdrawal connection. Table 5. Size of Opening for Normal Venting Tank Capacity, gals (m 3 ) Less than 2,500 (9.5) 2,500 – 3,000 (9.5 – 11) 3,001 – 10,000 (11 – 38) 10,001 – 20,000 (38 – 76) 20,001 – 35,000 (76 – 132) 35,001 – 50, 000 (132 – 189)

Minimum diameter, nominal pipe size, in. (mm) 1 ¼ (30) 1 1 ⁄ 2 (40) 2 (50) 2 1 ⁄ 2 (65) 3 (75) 4 (100)

2. For tanks with a capacity exceeding 50,000 gal (189 m 3) provide venting as follows: a) Provide inbreathing (vacuum) capacity of 1 ft 3 /hr free air for each 7.5 gal/hr of the maximum emptying rate (1 m 3 /hr inbreathing capacity for each 1 m 3 /hr emptying rate) plus the thermal venting capacity given in Table 6. b) For tanks storing liquid with a flash point ≤ 100°F (38°C), provide outbreathing (pressure) capacity of 1 ft3 /hr free air for each 3.5 gal/hr of the maximum tank filling rate (1 m 3 /hr free air for each 0.47 m 3 /hr of the maximum tank filling rate) plus the thermal venting capacity given in Table 6. c) For tanks storing liquids with a flash point >100°F (38°C), provide outbreathing (pressure) capacity of 1 ft3 /hr free air for each 7.0 gal/hr of the maximum tank filling rate (1 m 3 /hr free air for each 0.94 m 3 /hr of the maximum tank filling rate) plus the thermal venting capacity given in Table 6.



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Table 6. Required Thermal (Normal) Venting Capacity 1

gal

Tank Capacity 42-gal barrels

m3

42,000 84,000 126,000 168,000 210,000 420,000 630,000 840,000 1,050,000 1,260,000 1,470,000 1,680,000 1,890,000 2,100,000 2,520,000 2,940,000 3,360,000 3,780,000 4,200,000 5,049,000 5,880,000 6,720,000 7,560,000

1,000 2,000 3,000 4,000 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 50,000 60,000 70,000 80,000 90,000 100,000 120,000 140,000 160,000 180,000

160 320 480 640 800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 9,600 11,200 12,800 14,400 16,000 19,200 22,400 25,600 28,800

Vacuum All Stocks ft3 /hr m3 /hr 1,000 28 2,000 57 3,000 85 4,000 113 5,000 142 10,000 280 15,000 420 20,000 570 24,000 680 28,000 790 31,000 880 34,000 960 37,000 1,050 40,000 1,130 44,000 1,250 48,000 1,360 52,000 1,470 56,000 1,590 60,000 1,700 68,000 1,930 75,000 2,120 82,000 2,320 90,000 2,550

Pressure Liquid Flash Point ≤ 100 °F (38°C) >100°F (38°C) ft3 /hr m3 /hr ft3 /hr m3 /hr 1,000 28 600 17 2,000 57 1,200 34 3,000 85 1,800 51 4,000 113 2,400 68 5,000 142 3,000 85 10,000 280 6,000 170 15,000 420 9,000 255 20,000 570 12,000 340 24,000 680 15,000 420 28,000 790 17,000 480 31,000 880 19,000 540 34,000 960 21,000 590 37,000 1,050 23,000 650 40,000 1,130 24,000 680 44,000 1,250 27,000 760 48,000 1,360 29,000 820 52,000 1,470 31,000 880 56,000 1,590 34,000 960 60,000 1,700 36,000 1,020 68,000 1,930 41,000 1,160 75,000 2,120 45,000 1,270 82,000 2,320 50,000 1,420 90,000 2,550 54,000 1,530

1.

Based on API Standard 2000, Venting Atmospheric and Low Pressure Storage Tanks , 5th Edition, 1998. (These requirements are also in NFPA 30)

2.2.2.1.2 Buried Tanks 1. Provide vent pipes sized in accordance with Table 7 for the maximum flow in or out of the tank, but not less than 1.25 in. (30 mm) nominal inside diameter to prevent blowback of vapor or liquid at the fill opening while the tank is being filled. 2. Extend vents a minimum of 12 ft (3.7 m) aboveground level for liquids with flash points below or equal to 100°F (38°C), and a minimum of 6 ft (1.8 m) aboveground level for liquids with flash points above 100°F (38°C). 3. Arrange vent pipes without traps or pockets so liquid condensate can drain back to the tank. 4. Arrange vent pipes to discharge upward or horizontally away from adjacent walls. 5. Locate vent outlets so vapors will not be trapped by eaves or other obstructions and at least 5 ft (1.5 m) from building openings and 15 ft (4.5 m) from powered air-intake devices.


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Table 7. Typical Vent Line Size for Buried Tanks gpm 100 200 300 400 500 600 700 800 900 1000

Maximum In/Out Flow m3 /hr 50 ft 20 45 70 90 115 135 160 180 205 225

1-1 ⁄ 4 in 1-1 ⁄ 4 in 1-1 ⁄ 4 in 1-1 ⁄ 4 in 1-1 ⁄ 2 in 1-1 ⁄ 2 in 2 in 2 in 2 in 2 in

15 m 30 30 30 30 40 40 50 50 50 50

mm mm mm mm mm mm mm mm mm mm

100 ft 1-1 ⁄ 4 in 1-1 ⁄ 4 in 1-1 ⁄ 4 in 1-1 ⁄ 2 in 1-1 ⁄ 2 in 2 in 2 in 2 in 2 in 2 in

Vent Pipe Length 30 m 200 ft 30 30 30 40 40 50 50 50 50 50

mm mm mm mm mm mm mm mm mm mm

1-1 ⁄ 4 in 1-1 ⁄ 4 in 1-1 ⁄ 2 in 2 in 2 in 2 in 2 in 3 in 3 in 3 in

60 m 30 mm 30 mm 40 mm 50 mm 50 mm 50 mm 50 mm 75 mm 75 mm 75 mm

2.2.2.2 Emergency Venting 1. Provide aboveground storage tanks containing stable liquids with emergency relief venting in the form of construction or a device to relieve excessive internal pressure that develops from fire exposure. a) Relieving construction can be in the form of a floating roof or weak seam roof. b) A relieving device can be in the form of a floating manhole arranged for relieving, an open pipe, or a pressure relief valve suitable for the service. (UL 142, July 2002, section 8.10 – 12, provides design criteria for floating manways.) c) Emergency relief venting can be provided by the same device used for normal venting, provided it has adequate capacity and pressure rating. d) Stamp each commercial venting device, regardless of type, with its start-to-open pressure, the pressure at which it reaches its full-open position, and the flow capacity of the device at that pressure. Express all flow capacities in either cubic feet per hour of air at 60°F and 14.7 psia or cubic meters per hour of air at 15°C and 100 kPa absolute. e) Emergency venting is not required for FRP tanks as the tank will fail at around 200°F (93°C) f) Emergency venting is not required for tanks over 12,000 gal (45 m3) capacity containing liquids with flash points above 200°F (93°C) that are not exposed to spills from liquids with flash point less than or equal to 200°F (93°C ). Note: Normal in-and out-breathing is still required. 2. Where stable liquids are stored in tanks operating at 1 psig (7 kPa) or less, provide relief capacity/size of the relieving device or construction in accordance with Table 8 below. (Note: Tanks with weak seam roof construction have adequate emergency venting but would need normal venting for in-breathing and outbreathing)



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Table 8. Capacities for Emergency Relief of Excessive Internal Pressure for Aboveground Tanks Operating at 1 psig (7 kPa) or less 1 Wetted area of tank 2 ft2 m2 20 30 40 50 60 70 80 90 100 120 140 160 180 200 250 300 350 400 500 600 700 800 900 1,000 1,200 1,400 1,600 1,800 2,000 2,400 2,800 and over5

1.9 2.8 3.7 4.6 5.6 6.5 7.4 8.4 9.3 11.2 13.0 14.9 16.7 18.6 23.2 27.9 32.5 37.2 46.4 55.7 65.0 74.3 83.6 92.9 112 130 149 167 186 223 260 and over5

Vent Capacity 3 ft3 free air per m3 free air per 3 hour (ft /hr) hour (m3 /hr) 21,100 597 31,600 894 42,100 1,191 52,700 1,491 63,200 1,789 73,700 2,086 84,200 2,383 94,800 2,683 105,000 2,970 126,000 3,570 147,000 4,160 168,000 4,750 190,000 5,380 211,000 5,970 239,000 6,760 265,000 7,500 288,000 8,150 312,000 8,830 354,000 10,020 392,000 11,090 428,000 12,110 462,000 13,070 493,000 13,950 524,000 14,830 557,000 15,760 587,000 16,610 614,000 17,380 639,000 18,080 662,000 18,730 704,000 19,920 742,000 21,000

Minimum opening, NPS 4 in mm 2 2 3 3 3 4 4 4 4 5 5 5 5 6 6 6 8 8 8 8 8 8 8 10 10 10 10 10 10 10 10

50 50 75 75 75 100 100 100 100 125 125 125 125 150 150 150 200 200 200 200 200 200 200 250 250 250 250 250 250 250 250

1.

This table is based on hexane. For other materials, Table 9 can be used for vent capacity adjustments. The wetted area of the tank is defined as 55% of the total exposed area of a sphere or spheroid, 75% of the total exposed area of a horizontal tank, and the first 30 ft (10 m) above grade of the exposed shell area of a vertical tank. Include the bottom surface area of vertical tanks mounted on supports, above grade. 3. Based on atmospheric pressure of 14.7 psia and 60 °F (100 kPa abs. and 15 °C) 4. Based on open vent pipes of the noted diameter not more than 12 in. (0.3 m) long with a tank venting pressure of not more than 2.5 psig (17 kPa). 5 For tanks operating at pressures less than 1 psig (7 kPa) and having wetted areas exceeding 2800 ft 2 (260 m2), complete fire involvement is unlikely and overheating will probably cause loss of metal strength in the vapor space before the development of a maximum vaporevolution rate. For such tanks, the maximum listed relief capacity is adequate. For tanks operating at more than 1 psig (7 kPa) and having wetted areas exceeding 2800 ft 2 (260 m2), the venting requirements are provided in Section 2.2.2.2 — 3. 2.

3. For tanks operating at pressures greater than 1 psig (7 kPa) and having exposed wetted areas greater than 2800 ft2 (260 m2), calculate the emergency venting capacity by one of the following formulae: V = 1107 A0.82 (English) V = 220 A0.82 (metric) Where V = hexane vent requirement, ft3 /hr or m3 /hr (at standard conditions) A = exposed wetted surface, ft2 or m2


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4. Where the stored liquid is other than hexane, adjust the emergency venting capacity as follows: V’ = V 1337 / L (M)1/2 V’ = V 3110 / L (M)1/2 Where: V = hexane vent requirement from Table 8, ft 3 /hr or m3 /hr V’ = stored liquid vent requirement, ft3 /hr or m3 /hr L = latent heat of vaporization of stored liquid, Btu/lb or kJ/kg M = molecular weight of stored liquid, no units Table 9 lists L (M)1/2 for a number of common liquids. Data on other liquids can be found in most handbooks. Note: the vent capacity determined from Table 8 is conservative compared to the other liquids listed in Table 9; that is, if the capacity of the existing vents is adequate for hexane, it will be adequate for most other liquids. Table 9. Values for L (M) 1/2 L (M)1/2

Chemical English

(1)

Metric

English

Acetic Acid Acetic Anhydride Acetone Acetonitrile

1350 1792 1708 2000

3140 4168 3973 4652

n-Amyl alcohol iso-Amyl alcohol Aniline Benzene n-Butyl acetate n-Butyl alcohol iso-Butyl alcohol Carbon disulfide

2025 1990 1795 1493 1432 2185 2135 1310

4710 4629 4012 3473 3331 5082 4966 3047

Chlorobenzene Cyclohexane Cyclohexanol Cyclohexanone o-Dichlorobenzene cisDichloroethylene Diethylamine Dimethyl acetamide Dimethyl amine

1422 1414 1953 1625 1455 1350

3308 3289 4543 3780 3384 3140

Ethyl acetate Ethyl alcohol Ethyl chloride Ethylene dichloride Ethyl ether Furan Furfural Gasoline n-Heptane n-Hexane Methyl alcohol Methyl ethyl ketone n-Octane n-Pentane n-Propyl acetate n-Propyl alcohol iso-Propyl alcohol Tetrahydrofuran

1403 1997

3263 4645

Toluene o-Xylene

1676

3898

(1)

L (M)1/2

Chemical (1)

(1)

Metric (1)

1477 2500 1340 1363

3436 5815 3117 3170

1310 1362 1962 1370 – 1470 1383 1337 2680 1623

3047 3168 4564 3187 – 3419 3217 3110 6234 3775

1412 1300 1468 2295 2225 1428

3284 3024 3415 5338 5175 3322

1500 1538

3489 3577

L (heat of vaporization) in Btu/lb or kJ/kg

5. The venting capacity as determined by 2, 3 and 4 above, can be reduced for the effect of drainage, sprinklers, insulation and low heat of combustion liquids (alcohols) using the Environmental Factors presented in Table 10. 6. The total emergency venting capacity can be provided with specific construction or devices alone or in combination with the opening(s) provided for normal venting.



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Table 10. Environmental Factors for Emergency Venting Capacity (use only one factor) Environmental Factor (F) 1 Drainage 1 Water spray or sprinklers 2 & drainage Water spray or sprinklers only Insulated 3 Water spray & insulated None of the above

Basic 4 0.5 0.3 0.3 0.3 0.15 1.0

For low heat of combustion liquids 4, 0.25 0.15 0.15 0.15 0.15 0.5

5

1

Adequate drainage to remote impoundment in accordance with 2.2.2 – 5 above FM Approved water-spray installations in accordance with DS 4-1N or automatic sprinklers in accordance with Section 2.4.1 below. 3 FM Approved coating rated for process structure or tank protection 4 Use either basic credit or low heat of combustion credit, not both 5 Capacity reduction permitted for liquids whose heat of combustion and rate of burning are equal to or less than those of ethyl alcohol (ethanol) 2

7. Where unstable liquids are stored, provide tank-venting capacity that accounts for the effects of heat or gas produced by polymerization, decomposition, or self reactivity and the possibility of a two-phase relief. Follow the design guidance for reactive systems in DS 7-49, Emergency Venting of Vessels. 2.2.2.3 Manifolded Vents 1. Do not manifold vent collection systems of tanks containing incompatible materials. 2. Do not manifold vent pipes from tanks containing liquids with flash points below or equal to 100 °F (38°C) with tanks containing liquids with flash points above 100°F (38°C). 3. Protect low-pressure storage tanks interconnected with fume recovery or collection systems against explosion propagation if they normally contain ignitable mixtures AND ignition sources could be (spontaneous heating) or are normally present (continuous flames as in flares, fume incinerators, etc.) by one of the following methods: a) Oxidant concentration reduction (e.g., inerting or purging). This method is limited to operations without open manway activities, such as sampling, liquid or solids addition, etc. (NOTE: Do not use inerting in tanks with monomers containing inhibitors that require oxygen to maintain activity. Examples: hydroquinone and methyl ether of hydroquinone.) See Data Sheet 7-59, Inerting and Purging of Tanks, Pro- cess Vessels, and Equipment. b) Combustible concentration reduction (e.g., ventilation). See Data Sheet 7-78, Industrial Exhaust Sys- tems . c) Explosion isolation (detonation arresters). 4. Where an explosion isolation system is needed, provide Approved detonation arresters as follows (Fig. 6): a) At each tank, in the piping connecting it to the vapor recovery system. b) At the end of the manifold immediately upstream of the feed nozzle for any vapor processing equipment; for example, incinerators and scrubbers. Note: Detonation arresters may not be appropriate in systems where powders are handled or added on a regular basis. The arrester could become plugged and fail to handle normal in-and-out breathing.

5. Provide detonation arresters with temperature sensors on each side, and as close as possible to the face of the arresting element. Arrange the sensor to automatically close valves or initiate other actions that will eliminate the possibility of a stabilized flame burning on the arrester element. Do not locate the sensor in a thermowell that will delay its response. If the sensor is to be a metal-sheathed thermocouple, it must be of small diameter, e.g., 1 ⁄ 4 in. (6 mm), and must be inserted bare through a suitable packing gland. 6. Within 120 pipe diameters of the detonation arrester, install piping of equal or smaller diameter than the detonation arrester. (Fig.s 7 and 8 are showing pipe sizing around dda to meet this criteria)


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Fig. 6. Manifolded tanks

Fig. 7. Required pipe sizing if detonation arrester is smaller than nearby piping

Fig. 8. Improper piping around detonation arrester

7. Where conditions of operation will significantly exceed approximately atmospheric pressure and temperature, specifically test detonation arresters under the actual operating conditions. Detonation arresters are capable of successfully stopping detonation fronts only in systems initially at approximately atmospheric pressure and temperature. 8. Install detonation arresters where easily accessible for maintenance and inspection. 9. Install vapor-collection system piping in accordance with ASME B31.3, Chemical Plant and Petroleum Refinery Piping , or international equivalent, designed for a maximum allowable working pressure of 150 psig (10 barg). 10. Provide the flow capacity in common portions of manifolded vapor collection piping for the maximum flow of all vents connected to that portion of the system.



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11. Consider insulation and/or heat tracing of the system and arrester in cold climates where freezing or condensation of the vapor is possible. The heat tracing must be kept below the accepted operating range of the arrester. 2.2.2.4 Indoor Tanks 1. Provide continuous low-level mechanical ventilation as specified in DS 7-32, Section 2.1.3.1, Ventilation. 2. Provide inert gas blanketing where tanks store liquid with a flash point less than 100°F (38°C). 2.2.3 Asphalt Tanks Asphalt storage tanks have been a frequent source of fire or explosion events. In addition to the other criteria applying to outdoor tanks, the following represent good operating practice. 1. Ensure tank roofs are watertight. 2. Inspect tanks vents and the underside of the roof for accumulation of condensed material on a regular basis and keep records of the inspection results. 3. Use tanks with weak seam roof (pressure relieving) construction per API 650 or similar. 4. Provide tanks with only one breather vent to minimize introduction of air into the vapor space. 5. Keep roof gauging and manway hatches closed to prevent unintended entry of air into the vapor space. 6. Use gauging hatches rather than manways when checking liquid level to minimize air entry into the tank vapor space. 7. Do not use pressure-vacuum (conservation) vents as condensed materials could prevent operation of the vent. a) Where inerting of the vapor space is used, conservation vents will be needed. b) Inject the inert gas below the vents to keep them free of accumulations. c) Inspect the vents on a regular basis and keep records of the inspection results 8. Maintain tank liquid levels above any internal heating coils that could cause localized overheating, cracking of the liquids generating light ends and creating condensed deposits on the roof. Provide a reliable method to monitor tank liquid level. 9. Route supply piping for heating systems below the lowest liquid surface level or insulate the pipe with a nonpermeable material. 10. Monitor the tank temperature with sensors located where it will be representative of bulk liquid temperature. Keep sensors away from tank walls, near submerged heating coils, or and below normal operating levels. 11. Maintain tank temperatures at safe levels with the following considerations: a) Keep temperatures at least 25°F below the flash point (out of the flammable range). b) Keep temperatures out of the range of 212°F – 265°F (100°C- 130°C) to avoid water condensation. c) Temperatures above 350°F (177°C) encourage asphalt condensation on the roof surface. Deposit can oxidize, generate heat and possibly autoignite above 375°F (190°C). d) Provide inert gas blanketing (oxygen concentration of 3% to 5%) for tanks operating at 350°F to 450°F (177°C-232°C) to prevent oxidation of deposits. e) Don’t store materials at temperatures above 450°F (232°C) which can promote cracking and production of light hydrocarbons and increase the likelihood of operation in the flammable range. 12. Don’t allow entry of piping or any fixtures to or through the tank roof which would hinder deployment of the weak seam roof in an explosion. 13. Inspect internal tank heating coils for cracks, corrosion, and other damage whenever the tank is out of service and keep records of the inspection results.


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14. Take precautions to safely oxidize pyrophoric deposits before taking the tank out of service (see API RP 2016 for details). 15. Follow a written procedure for returning long-idled tanks to service that addresses at least the following: a) Water accumulations that could boil on heating. b) Residual product that may heat irregularly with localized overheating until the entire contents have reached a uniform temperature. c) Lighter products that might have been previously in the tank and addition of hot material that could rapidly vaporize material and exceed vent capacity or cause the vapor space to enter the flammable range. 16. Develop an emergency response plan to address fire, explosion, and unexpected liquid release that identifies the hazards, site layout, protection equipment, shutoff valves, etc., as well as specific response to each type of event. Ensure outside responders are familiar with the response plan. 2.3 Protection

2.3.1 Indoor Tanks 1. Provide automatic sprinkler protection in the tank room/vault designed as specified in Table 11 over the entire tank room/vault area. 2. Provide sprinklers below tanks that are elevated and have greater than 3 ft (1 m) diameter or a plan area of 10 ft2 (0.9 m2), or encase all tank supports in 3-hour fire-rated concrete. 3. Where pumps are present, extend a sprinkler down to within 2 ft of the pumps. 4. Provide an allowance of at least 500 gpm (1900 L/min) for hose stream use. Table 11. Sprinkler Density for Storage Tank Rooms, gpm/ft 2 (mm/min) Ceiling height Flash point ≤ 200 °F (93 °C) No drainage, no foam With drainage, no foam Foam with or without drainage Flash point > 200 °F (93 °C) No drainage, no foam With drainage, no foam Foam with or without drainage

≤

15 ft (4.5 m)

> 15 ft (4.5 m) up to 30 ft (10 m)

Not permitted 0.3 (12) As required by foam Approval*

Not permitted 0.3 (12) As required by foam Approval*

0.3 (12) 0.2 (8) As required by foam Approval*

0.4 (18) 0.2 (8) As required by foam Approval*

*See Approval Guide listing for ″ foam water sprinklers ″ .

2.3.2 Outdoor Tanks The basic protection for tank farms is hose streams along with adequate spacing and containment as specified in Section 2.1.2. This will generally limit fire involvement to all tanks within a common dike or three large tanks that are individually diked. For large tanks or tanks farms, manual fixed foam protection may be appropriate (automatic foam is rarely justified). Automatic water-spray protection is of value mainly for exposure protection of buildings where tanks are located too close. An alternative protection method is fire-rated construction for the building. 1. Provide hydrants within 200 ft (60 m) of tanks so they can be reached by hose streams or monitor nozzles from outside the dike. 2. Locate hydrants so every tank can be reached by hose or monitor streams from at least two directions. 3. Provide each hydrant with a minimum of two outlets controlled by individual valves.



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4. Provide FM Approved combination straight stream/water spray nozzles for each hose. A straight stream discharge can cool exposed tanks or facilities, while a high-velocity spray discharge can control or extinguish fires in liquids with flash points above 200°F (93°C). 5. Provide foam monitor nozzles or foam hose streams for exterior protection and spills in the dikes where there are tanks that contain stable liquids with flash points below or equal to 200 °F (93°C) or unstable liquids of any flash point. 6. Provide fixed foam outlets and supply piping to a remote point outside the dike installed in accordance with DS 4-7N on vertical cone-roof tanks storing stable or unstable liquids with flash points below or equal to 200°F (93°C) when one or more of the following conditions exist: a) The tank capacity exceeds 50,000 gal (190 m3) or there are multiple tanks in the same dike whose aggregate capacity exceeds this value. b) The tanks present a serious exposure to important buildings, process equipment, or utilities due to inadequate spacing. c) The tank-to-tank spacing and containment is deficient compared to the requirements of this standard. d) The tank contents are of considerable value or are essential for continued operations and are not readily replaceable. The contents can be readily salvageable after foam contamination. e) Other unfavorable situations that cannot be corrected. 7. Where spacing between tanks and nearby buildings is inadequate (not in accordance with Section 2.1.2) provide one of the following: a) Provide building construction in accordance with DS 1-20 using guidelines for yard storage and consider the tanks as high-hazard occupancy. b) Provide deluge water spray (installed in accordance with DS 4-1N) on the exposed wall at a rate of 0.3 gpm/ft2 (12 mm/min) of exposed wall using the criteria in DS 1-20 to determine the extent of the exposed wall. Include water supply duration for 2 hours and at least 500 gpm (1,900 L/min) for hose streams. 8. Where spacing between adjacent tanks is inadequate (not in accordance with Section 2.2.2), provide deluge water spray (installed in accordance with DS 4-1N) on all exposed tanks at a rate of 0.3 gpm/ft2 (12 mm/min) of tank surface. Include water supply duration for 2 hours and at least 500 gpm (1,900 L/min) for hose streams. 9. Where spacing to rail or truck load/unload stations is inadequate (i.e., not in accordance with Section 2.2.2) provide deluge water spray (installed in accordance with DS 4-1N) for the load/unload station (vehicle and pumps) at a rate of 0.3 gpm/ft2 (12 mm/min) of tank surface. Include water supply duration for 2 hours and at least 500 gpm (1,900 L/min) for hose streams. 2.3.3 Water Supply 1. Calculate the water demand as the sum of the following: a) The hose stream demand for tanks storing all classes of liquids as determined from Table 12 and supplied at a minimum pressure of 50 psi (345 kPa). b) Water required for fixed foam equipment, when provided, supplied at minimum Approved pressure. For purposes of estimation, see Table 13. c) Provide water supply duration for a minimum of 4 hr for liquids with a flash points below 140 °F (60°C) and 2 hour for liquids with a flash points above or equal to 140 °F (60°C).


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Table 12. Hose Stream Demand for TANKS Storing Flammable Liquids 1 Flash point of liquid < 140°F (60°C) ≥ 140 °F (60°C) 1 2

Largest Tank Involved in Fire gpm L/min

Largest Exposed Tank gpm L/min

2

10002 750

2

5002 250

3,800 2,800

1,900 950

Required flows may be reduced by half for horizontal tanks. Add 250 gpm (950 L/min) for each 100 ft (30 m) increase in tank diameter above 100 ft (30 m). Table 13. Estimated Water Demand for Fixed Foam Protection for a full Surface Fire. Tank Diameter ft 50 100 150 200 250 300

Water Demand m 15 30 45 60 75 90

gpm 200 800 2,000 3,200 5,000 7,100

L/min 750 3,000 7,500 12,100 19,000 27,000

2.4 Operation and Maintenance

1. Implement a formal mechanical integrity program, as described in DS 7-43, Loss Prevention in Chemi- cal Plants, for all flammable-liquid storage tanks. 2. Conduct monthly visual inspections of aboveground and indoor tanks for the following (where applicable): a) Leaks, corrosion, settlement b) Condition of attached piping, piping supports, gauging, level control systems, alarms, emergency and breather vents, instrumentation, grounding, ladders, accessways c) General housekeeping, water accumulation, and vegetation in dikes d) The physical condition of berms/dikes/containment e) Clear and operable drainage systems along with accessibility of any applicable valves f) Operation of inerting systems 3. Conduct annual recorded inspections of tank vents, vent pipes, screens, and flame arresters and keep them free from obstructions (e.g., stones, dirt, insect nests, polymerized material, etc.) that could prevent proper operation and possibly overpressurization of the tank. 4. Conduct recorded inspections of detonation arresters in manifolded piping systems for damage and accumulations of debris caused by polymerization, condensation, corrosion, etc., which could impair operability. Replace damaged units (or repair if the damage does not affect their functionality) and remove accumulations. a) Conduct inspections at least quarterly during the first year and as experience dictates thereafter, but at least annually (where practical). b) Conduct inspections at least quarterly where powders are added to the system. (Arresters in this service are particularly susceptible to accumulations and may be inappropriate for use.) 5. Conduct annual recorded inspections of the performance of cathodic protection (CP) systems by qualified persons for the attainment of satisfactory CP criteria, proper functioning of equipment and that the level of CP applied is properly controlling corrosion. Criteria for determining the effectiveness of CP include NACE RP0169, 0285 and API 651.



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2.4.1

Repair, Reconditioning, and Abandonment

Prior to working on any tank that has contained flammable liquids, take the following precautions as appropriate: 1. Drain any residual liquids remaining in the tank. 2. Purge flammable-liquid tanks with steam or warm air before repairs are made or before the tanks are reused. Route displaced flammable vapors to a safe location. Avoid excessive pressure or vacuum. (See DS 7-59, Inerting and Purging OF Equipment) 3. Use an FM Approved flammable vapor indicator to determine whether vapors have been eliminated. Make additional tests at frequent intervals. 4. Remove all remaining scale and sludge with nonferrous scrapers. 5. Fill the tank with an inert gas, such as carbon dioxide, or maintain positive continuous air movement through the tank if cutting or welding torches are used on the outside of the tank. 6. Use a hot work permit system to control welding operations on a tank. (see Data Sheet 10-3, Hot Work Man- agement ) 7. Supervise workers and provide sufficient ventilation when welding is being done inside a tank. Station at least one person outside near the manhole to watch the welder and assist in an emergency. 8. Remove, repair, or recondition underground flammable-liquid tanks that are no longer of any use. Prior to removal, inert the tank. If removal of the tank is not possible, it may be left in place after doing the following: a) Remove all of the liquid from the tank. b) Purge the tank of flammable vapors. c) Remove all suction, inlet, gauge, and vent lines. d) Fill the tank with a solid inert material (e.g., sand, diatomaceous earth, perlite, etc.). e) Cap all remaining underground piping. f) Re-bury the tank and fittings. 2.5 Ignition Source Control

1. Install electric lights and other fixed or portable electrical equipment near storage tanks containing liquids with flash points below or equal to 100°F (38°C) or liquids with higher flash points heated to within 25°F (14°C) of their flash point in accordance with the following: a) Provide electrical equipment suitable for Class I, Division 1 or Zone 1 hazardous locations as defined in Article 500 of the National Electrical Code when located within 3 ft (1 m) of vents. b) Provide electrical equipment suitable for Class I, Division 2 or Zone 2 hazardous locations as defined in Article 500 of the National Electrical Code when located between 3 and 5 ft (1 to 1.5 m) of vents. c) Provide electrical equipment suitable for Class I, Division 2 or Zone 2 hazardous locations when located within 10 ft (3 m) of any other tank openings or when located within a diked area. d) Provide electrical equipment suitable for Class I, Division 1 or Zone 1 hazardous locations when tanks are located in a room or vault. e) Refer to Data Sheet 5-1, Electrical Equipment in Hazardous (Classified) Locations, and Data Sheet 5-7, National Electrical Code , for additional information regarding electrical installations. 2. Provide static grounding connections on tanks that are out of contact with the earth if piping is ungrounded or nonconductive. (Ordinarily, special electrical grounding connections will not be needed. Adequate grounding for a tank is provided by its own contact or the contact of its connected piping with the earth.) (See DS 5-8, Static Electricity )


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3. Electrically bond all tank plates, internal structural members, fittings and isolated metal parts or pipe sections on tanks containing liquids with flash point less than or equal to 100 °F (38°C) or liquids with higher flash points heated to within 25°F (14°C) of their flash point to reduce the danger of internal sparks from lightning or charged liquid. (See Data Sheet 5-8, Static Electricity for further information on grounding and bonding.) 4. Prohibit the discharge of liquids with flash points below or equal to 100 °F (38°C) or liquids with higher flash points heated to within 25°F (14°C) of their flash point above the liquid level in the tank (usually called ’’splash filling‘‘) as it creates the possibility of static buildup and spark discharge to grounded components. 5. Prohibit hot work, maintenance, repair, or modification in or near (see Table 14) tanks, pumps, and other handling equipment, tank truck or railcar loading and unloading, or fume-collection systems where flammable vapors could be present until the tank or system is isolated, drained, and purged or blanketed with an inert gas. Use a hot work permit system to control the progress of such work. (See Data Sheet 10-3, Hot Work Management .) 6. Prohibit smoking or open flames in or near (see Table 14) tanks, pumps, and other handling equipment, tank truck or railcar loading and unloading, or fume-collection systems where flammable vapors could be present. Provide designated safe areas for such activity. Table 14. Safety Distances for Hot Work, Open Flames, Maintenance, Repair or Modification Safety distances for hot work, open flames, maintenance, repair or modification*, ft (m) Flash point = 100°F (38°C) or heated to within > 100°F (38°C) 25°F (14°C) of their flash point Tanks outdoors 50 (15) 35 (10) Within dikes or tank rooms Not allowed Truck or railcar loading/unloading 75 (22.5) 35 (10) Pumps or other handling equipment 75 (22.5) 35 (10) * allowed after hot work permit process is completed

3.0 SUPPORT FOR RECOMMENDATIONS 3.1 Background information

Tanks containing gasoline, alcohol, benzene, and other flammable and combustible liquids have been involved in serious fires. The contents of a large tank can cause extensive damage if released during a fire. The design and construction of such tanks needs to ensure a high degree of confinement and reliability. 3.1.1 Hazards Flammable and combustible liquids are classified by various US and international regulatory bodies for the purposes of packaging, transportation, and handling. The various definitions can make the application of storage standards across a broad spectrum difficult. For the most part, this document limits differentiation by using a breakpoint of 140°F (60°C) for spacing criteria and 200°F (93°C) for protection. Crude oil (not addressed in this standard) and other liquids containing components with a wide range of boiling points, and some free water, present the additional hazards of boil-over, slop-over, or froth-over. Boilover is a phenomenon that may occur spontaneously during a fire in an open-top tank of crude oil that has been burning for an extended period of time. In time, a sudden expansion of a steam-oil froth beneath the liquid surface can occur, resulting in a sudden explosion of hot residual oil from the tank. Generally, four conditions have to exist for a boil-over to occur: 1. The tank must contain free water or a water-oil emulsion near the tank bottom. This is a normal condition in crude-oil storage tanks as well as in some tanks storing heavier, residual oils. 2. The tank must be open-top. Experience indicates that fire in an open-top tank will result if an explosion blows the roof off or if the pan or deck in a floating-roof tank sinks. 3. The oil must be capable of forming a heat wave of 300°F (145°C) or more. The heat wave is created when lighter components in the liquid (e.g., pentane, hexane, etc.) distill off and burn at the liquid surface leaving a residue of higher density than the liquid just below it. This residue has a temperature in excess of 300 °F ©2009 Factory Mutual Insurance Company. All rights reserved.


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(145°C) and, if it sinks at a rate substantially faster than the rate of regression of the liquid surface, the heat wave is formed. The heat wave is created by convection (within the stored liquid) not conduction. 4. The oil must contain sufficient heavy ends to produce a persistent froth of oil and steam. The boil-over tendencies of the oil can be evaluated by small-scale tests. While all crude oils are not susceptible to boil over, successive storages may exhibit boil-over potential. Thus, always design, install, and protect tanks storing crude oil recognizing the possibility of boil over. Other liquids can exhibit slop-over or froth-over tendencies. Slop over occurs when a water stream is applied to the surface of a burning viscous oil. The resultant frothing and ejection of liquid is generally much less severe than a boil over because only the surface of the liquid is involved. It could present a hazard to fire fighters. Froth over occurs when a hot viscous liquid, such as asphalt or oil, floats on a water layer in a tank. In time, the water is superheated and erupts, ejecting liquid from the tank. Unlike boil over or slop over, there is no fire. Froth overs have occurred with sufficient violence to blow off tank roofs and spread the tank contents over a large area. 3.1.2 Types of Tanks 3.1.2.1 Atmospheric Tanks Atmospheric tanks are used to store large quantities of liquids at pressures ranging from atmospheric to 1.0 psig (7 kPa). The following are the principal types of atmospheric tanks: Cone roof tanks are the most widely used for flammable liquid storage. They are usually welded and may have either weak roof or weak shell-to-roof seams designed to fail preferentially to the tank shell in the event of a fire or internal explosion. Their major disadvantage is the vapor loss caused by breathing (the normal expansion and contraction of the tank contents with atmospheric changes). The normal operating range of the tank is ± 11 ⁄ 2 in. of water (± 370 Pa). Floating roof tanks are constructed with a roof floating on the liquid surface. The roof may be of doubledeck or pontoon-type construction (Figs. 9 and 10). By eliminating the vapor space, breathing losses become negligible, and the fire and explosion hazard is greatly reduced. The seal provided between the roof edge and the tank wall allows the roof to move freely within the shell. Drainage facilities are provided to prevent the accumulation of water on the roof surface. Covered floating roof tanks are similar in construction to cone roof tanks, except for a metal pan (or, occasionally, a double or pontoon internal roof) that floats on the liquid surface (Fig. 11). Since the floating cover is protected from the weather, no provision for drainage or for rain or snow loading is required. Vents are provided around the periphery of the tank. Lifter or expansion roof tanks resemble cone roof tanks, except the entire roof assembly has limited freedom to move up and down within the shell. A vapor-tight liquid seal, which maintains a slight pressure on the contents of the tank, provides a seal between the roof assembly and the shell. The moving roof minimizes normal breathing losses. An expansion roof tank is occasionally used with a group of fixed roof tanks to take up their composite vapor change. Breather roof tanks are used where the liquid storage is not frequently disturbed. The horizontal flexible diaphragm, or roof, is attached to the top edge of the tank shell and maintains a variable vapor space by moving up and down. The roof, by confining the vapor, exerts a slight pressure upon the liquid, reducing evaporation losses. Vapordome tanks employ a dome containing a plastic diaphragm, which is free to move with the expansion of vapor in the tank. This is an effective method of reducing vapor loss from the top of the tank. Cylindrical tanks are used for small quantities of liquids. Heads may be dished or flat. The long axis may be either horizontal or vertical and the tank buried or aboveground.

3.1.2.2 Low-Pressure Tanks Low-pressure tanks have a maximum working pressure of 15 psi (103 kPa). They are used to store volatile liquids, such as those with flash points below 73°F (23°C) and boiling points below 100°F (38°C) (Class


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Fig. 9. Open top double deck

Fig. 10. Open top pontoon

IA), under their own vapor pressure. Such tanks may be spheres, spheroids, or cylinders. In general, the requirements applicable to atmospheric storage tanks apply to low-pressure storage tanks, with some modifications in construction, venting, and spacing.



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Fig. 11. Pan-type covered tanks

3.1.3 Indoor Tanks Putting large quantities of a flammable liquid inside an important building is not recommended. Tank storage of flammable liquids creates the potential for many fire scenarios, including overflow during filling, overpressurization when exposed to fire, leak in a discharge line, or tank failure (a very low likelihood event, but one that has the potential for significant consequences). The main goals of the recommendations are to isolate the tank from non-flammable liquid occupancies, provide adequate protection for most fire scenarios and to ensure adequate access to the tank room for firefighters. Since all of the fire scenarios in a tank room involve a liquid release, adequate isolation must include provisions for containment and emergency drainage. In cases where tanks are not only inside a building, but are also located either below or above grade, additional safeguards are needed. Access to these tanks for manual firefighting will be very limited. The overall severity of a liquid release and fire involving the tank will be entirely dependent on what was provided for active and passive protection around the tank. In buildings where the potential loss is significant, there is a need to ensure any potential flammable liquid release/fire is contained to the tank room. The only reliable way to accomplish this is through the use of a 3-hour fire rated vault with only limited openings for fresh air. This combination will limit the fire severity and help ensure survival of the room regardless of the size of the liquid release. The design goal for pumping and transfer systems is to ensure the liquid stays in the piping system and can be shut down when necessary (e.g., leak or fire). The best way to accomplish this is to use welded steel piping, positive displacement pumps and safety shut-off valves. There will always be several potential leakage sources in this type of system that can produce a liquid release and fire. The most likely source of leakage is the pump. Pump rooms must be isolated from other occupancies. Since the pumping system creates similar hazards as the storage tank, it may be cost effective to locate the pumps in the tank room/vault. A small fire at the pump can grow because the initial fire will produce additional failures. Sprinklers that are extended from the ceiling to within 2 ft (0.6 m) of the fuel pumps can help to prevent those additional failures. A second potential leakage source is flanged or threaded pipe joints/unions. Welded piping systems require the use of flanged joints to permit equipment maintenance and repair. Leaks at flanged joints can be caused by poor maintenance or fire exposure to a gasket that can melt. Threaded joints are inherently weaker because the pipe wall thickness has been reduced. Locate flanged or threaded joints/unions in rooms that are properly isolated and protected for a flammable liquid fire exposure.


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3.1.4 Tank Spacing and Containment Tank spacing criteria were developed by comparison with existing standards and by analysis of pool fire simulations for all three classes of liquid assuming a 20 mph wind during the event. The final simplified criteria were based primarily on heat flux predictions rather than existing standards. 3.1.5 Manifolded Vents Environmental regulations have increased the use of emission control systems on tanks. The emission control systems can include carbon bed adsorbers, scrubbers, condensers, incinerators, etc. (Fig. 6). In some cases, the system could be handling vapors within the flammable range. An ignition at one point in the system could cause a flame front to propagate throughout with damaging results. The ignition source could be static, lightning, an incinerator flame, etc. Proper design of the system can prevent such a situation. Flame propagation is not possible in the manifold piping and connected vessels if the vapor-air mixture is out of the flammable range. This is most often achieved by an inert gas system to decrease the oxygen to an acceptable level. To accept such a system in lieu of arresters, it must be reliable. The criteria in Data Sheet 7-59, Inerting and Purging of Tanks, Process Vessels, and Equipment , will provide this reliability as long as open manway operations do not occur. The propagation velocity in a piping system containing a flammable mixture depends on the inherent turbulence in the system caused by flow, bends, valves, and fittings as well as the turbulence of the combustion process itself. It has been recognized that a deflagration flame front can transit to detonation velocities with significant increase in the pressures within the piping and the potential for failure of the piping. Transition to detonation in pipe lengths of 50 to100 diameters are typically reported. Flame-arresting devices that successfully stop the deflagration fail to stop the detonation or even a ’’ fast‘‘ deflagration. Detonation arresters (Fig. 12) can stop detonation fronts, and test procedures are available to Approve/list these devices. Detonation arresters are rated for a specific gas or class of gases. Some classifications are based on National Electrical Code groupings (A, B, C, D), while others are based on minimum experimental safe gap (MESG) required to quench a flame.

Fig. 12. Detonation arrester

Detonation arresters are normally bidirectional; that is, they will stop a detonation front approaching from either direction. Since it is not possible to ensure the direction of flame approach, use of unidirectional arresters usually is not appropriate.



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Testing has demonstrated that a detonation arrester is likely to fail if installed in piping whose diameter increases within a distance of 120 pipe diameters from the detonation arrester in either direction.

Fig. 13. Storage tank with flame arrester

Fig. 14. End-of-line flame arrester

This data sheet, NFPA 30, Flammable and Combustible Liquids Code , and other standards specify the requirements for installation of flame arresters on tanks. Although some FM Approved flame arresters are equipped with flanges at both ends for short pipe-aways (Figs. 13 and 15) of the released vapors, they cannot be used in extended piping systems. The testing organization’s listing will detail limits between the open pipe end (to atmosphere) and the arrester. They are based on the test conditions, and additional length could permit a deflagration flame front to increase velocity, even up to a detonation front, and result in failure of the device to stop the flame. Conservation vents are installed on many low pressure tanks to minimize the release of vapors during tank idle times while permitting release of pressure or vacuum created during filling or emptying. This data sheet, NFPA 30, and other codes accept these devices in lieu of flame arresters where vented directly to atmosphere. The pressure setting (typically 3 ⁄ 4 in. water gauge [190 Pa]) and the device design create local velocities in excess of the propagation velocity of ordinary combustion flames, thus preventing flashback into the tank. These velocities and the general construction are insufficient for stopping detonation propagation. These are not acceptable alternatives to detonation arresters in manifolded piping systems . Using rupture disks on elbows, or direction changes in the piping system, to provide explosion venting is not considered effective in halting the progress of a flame front. Venting the piping in this manner will at least


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Fig. 15. End-of-line flame arrester with pipe-away flange

Fig. 16. Backflash interrupter

temporarily relieve the pressure but may not stop the flame front, which could continue on to interconnected vessels. The flame front will continue down the pipe and, if it is not vented at regular intervals (50 to 100 diameters), it could transit to detonation velocity. Other methods of explosion isolation are available. These include fast-acting valves, rapid discharge extinguishing (blocking) systems and flame-front diverters or backflash interrupters (Fig. 16). None of these devices presently are FM Approved and therefore are not discussed in detail. There is limited information available on installation criteria and applicability limits. All are designed to interrupt deflagrations, not detonations. 3.1.6 Asphalt Tanks Loss history shows a disproportionate number of events involving tanks containing asphalt. Factors in these events include: • Tanks

often operate at temperatures near the flash point.

• Material

can condense on tank roof surfaces, overloading the roof.



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•

Condensed material can be pyrophoric, iron sulfides, or carbonaceous.

• Water •

can accumulate on the bottom and froth over on addition of hot materials.

Operating procedures are not always followed.

3.1.7 Fire Protection The severity of flammable liquid tank fires requires that fire protection be provided. Normally, only hydrant protection is required. Fixed or portable foam-making equipment or water spray systems may be required to control fires where the quantities of liquids stored or tank sizes are unusually large. Special precautions are required for the storage of crude oil and other liquids subject to boil over. Storage tank fires involving liquids with flash points of 100°F (38°C) or lower are difficult to control and extinguish and frequently burn for days. Do not consider provision of fixed foam or water spray systems as a substitute for adequate spacing of tanks from important plant facilities. Fixed foam systems have been effective in extinguishing fires in cone roof tanks, but have sometimes failed for the following reasons: a) Fires in tanks storing liquids with flash points of 100 °F (38°C) or lower have originated with an explosion in the vapor space of the tank, damaging one or more foam distribution devices. b) The roof support members have fallen into the liquid, preventing formation of a uniform foam blanket over the liquid surface. Even under these adverse circumstances, fixed foam systems may provide partial control until manual firefighting can be organized. Subsurface application could improve the operating experience of fixed foam extinguishing systems for fires in cone roof tanks. Some standards consider subsurface foam a requirement for successfully extinguishing fires in tanks exceeding 200 ft (60 m) in diameter. Floating roof tanks are less susceptible to serious fire loss than cone roof tanks. Seal fires in floating roof tanks can be readily extinguished with either portable extinguishing equipment or fixed foam extinguishing systems, depending upon the size of the tank. For new installations, do not consider fixed foam systems as equivalent to adequate spacing and diking, selection of proper tank construction, or provision of exposure protection where needed. 3.2 Loss History

3.2.1 Storage Tanks Loss history was developed for storage tanks handling flammable liquids for the period 1984 – 2004. A total of 303 events at FM Global client locations resulted in a gross loss of US$280 million (all figures indexed to 2005 dollars). Of these events, a total of 115 exceeded $100,000 gross loss, accounting for about 70% of the total loss. The losses by industry group are shown in the Table 15. Metal working, plastic, wood and paper and office, retail, and warehouses had the highest number of events. The largest single event in this class was a tank explosion caused by cutting and welding at a paper mill. Table 15. Losses over US$100,000 by Occupancy Class Occupancy None listed Textiles Metal Working Plastic, Wood & Paper Food & Beverage Chemical & Pharmaceutical Power Generation Office, Retail, Warehouses Residential Misc Properties Grand Total

Number 5 2 34 20 5 7 9 22 2 9 115


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Table 16 provides a breakdown of the engineering peril associated with the 115 losses. Of the 115 losses reported over US$100,000 gross, losses caused by leakage and contamination were the most common. There were a total of 57 incidents with a total gross loss of US$31 million. There were a total of 29 fires and explosions with a total gross loss of US$133 million with fires accounting for US$118 million. Of these, improper cutting and welding was often the cause. “Oil” was the most common liquid involved in events, but asphalt was next most common with 12 events and a total gross loss of about US$10 million. Table 16. Losses over US$100,000 by Engineering Peril Engineering Peril Fire Explosion Escaped Liquid Damage Riot & Civil Commotion Collapse Water-Liquid Damage Implosion Mechanical Breakdown Impact Miscellaneous Total

Number 16 13 27 1 2 3 2 1 1 49 115

3.2.2 Manifolded Vents There has been at least one FM Global loss involving manifolded vapor recovery systems on storage tanks. In addition, a recent study in the province of Alberta, Canada, showed flame arrester failure in sour gas flaring operations (related to crude oil production) was responsible for 10 to 20 oil storage tank explosions per year. 4.0 REFERENCES 4.1 FM Global

Data Sheet 1-57, Plastic in Construction Data Sheet 4-7, Low Expansion Foam Systems Data Sheet 5-1, Electrical Equipment in Hazardous (Classified) Locations Data Sheet 5-7, National Electrical Code Data Sheet 5-8, Static Electricity Data Sheet 6-10, Process Furnaces Data Sheet 7-14, Fire & Explosion Protection for Flammable Liquid, Flammable Gas, & Liquefied Flam- mable Gas Processing Equipment & Supporting Structures Data Sheet 7-29, Flammable Liquid Storage in Portable Containers Data Sheet 7-30, Solvent Extraction Plants Data Sheet 7-32, Flammable Liquid Operations Data Sheet 7-43/17-2, Loss Prevention in Chemical Plants Data Sheet 7-51, Acetylene Data Sheet 7-59, Inerting and Purging of Tanks, Process Vessels, and Equipment Data Sheet 7-78, Industrial Exhaust Systems Data Sheet 7-83, Drainage Systems for Flammable Liquids



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Data Sheet 10-3, Hot Work Management 4.2 NFPA

NFPA 11, Standard for Low, Medium and High Expansion Foam (2005) NFPA 30, Flammable and Combustible Liquids Code (2003) In section 4.4.2, reference is made to testing criteria for the integrity of secondary containment tanks. Below is that reference: 4.4.2.3 Underground secondary containment tanks and horizontal aboveground secondary containment tanks shall have the primary (inner) tank tested for tightness either hydrostatically or with air pressure at not less than a gauge pressure of 20 kPa (3 psig) and not more than a gauge pressure of 35 kPa (5 psig). The interstitial space (annulus) of such tanks shall be tested either hydrostatically or with air pressure at a gauge pressure of 20 to 35 kPa (3 to 5 psig), by vacuum at 18 kPa (5.3 in. Hg), or in accordance with the tank ’s listing or manufacturer ’s instructions. The pressure or vacuum shall be held for not less than 1 hour or for the duration specified in the listing procedures for the tank. Care shall be taken to ensure that the interstitial space is not over pressured or subjected to excessive vacuum. 4.4.2.4 Vertical aboveground secondary containment – type tanks shall have their primary (inner) tank tested for tightness either hydrostatically or with air pressure at not less than a gauge pressure of 10 kPa (1.5 psig) and not more than a gauge pressure of 17 kPa (2.5 psig). The interstitial space (annulus) of such tanks shall be tested either hydrostatically or with air pressure at a gauge pressure of 10 to 17 kPa (1.5 to 2.5 psig), by vacuum at 18 kPa (5.3 in. Hg), or in accordance with the tank ’ s listing or manufacturer ’s instructions. The pressure or vacuum shall be held for 1 hour without evidence of leaks. Care shall be taken to ensure that the interstitial space is not over pressured or subjected to excessive vacuum. NFPA 70, National Electric Code 4.3 Others

American Petroleum Institute, API 620, Design and Construction of Large, Welded, Low-Pressure Storage Tanks , Tenth Edition, 2002 (American Petroleum Institute, API 650, Welded Steel Tanks for Oil Storage, Tenth Edition, 1998) American Petroleum Institute, API 2000, Venting Atmospheric and Low Pressure Storage Tanks, Fifth edition, 1998 American Petroleum Institute, ANSI/API 2610, Design, Construction, Operation, Maintenance, and Installa- tion of Terminal and Tank Facilities, Second edition, 2005 American Petroleum Institute, ANSI/API 651, Cathodic Protection of Aboveground Petroleum Storage Tanks , Second edition, 1997 American Petroleum Institute, API Standard 2015, Requirements for Safe Entry and Cleaning Petroleum Stor- age Tanks American Petroleum Institute, API Recommended Practice 2016, Guidelines and Procedures for Entering and Cleaning Petroleum Storage Tanks American Petroleum Institute, API Recommended Practice 2023, Guide for Safe Storage & Handling of Heated Petroleum Derived Asphalt Products & Crude Oil Residua American Society of Mechanical Engineers (ASME), Boiler and Pressure Code, Section VIII, Unfired Pres- sure Vessels, latest edition American Society of Mechanical Engineers (ASME), B31.3, Chemical Plant and Petroleum Refinery Piping, latest edition ASTM International, ASTM D4206, Standard Test Method for Sustained Burning of Liquid Mixtures Using the Small Scale Open-Cup Apparatus , 2001 Code of Federal Regulations, 33 CFR, Part 154, Appendix A, Guidelines for Detonation Flame Arresters Code of Federal Regulations, 49 CFR, Chapter I, Subchapter C, Parts 171 – 180 Department of Transportation, Hazardous Materials Regulations


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International Standards Organization, ISO 2592, Determination of flash and fire points — Cleveland open cup method , 2000 National Association of Corrosion Engineers, NACE RP-0169, Control of External Corrosion on Under- ground or Submerged Metallic Piping Systems National Association of Corrosion Engineers, NACE RP-0285, Corrosion Control of Underground Storage Tanks System by Cathodic Protection APPENDIX A GLOSSARY OF TERMS Conservation vents : These devices have both vacuum and pressure relief capacity. Vents usually open when the positive or negative pressure in the tank reaches 3 ⁄ 4 to 1 in. water column (185 to 250 Pa). They are normally closed and vent pipes equipped with conservation vents do not need flame arresters. The velocity through the openings is normally sufficient to prevent flashback. A typical conservation vent is shown in Figure 17.

Fig. 17. Typical conservation vent

Exposed Wall Categories: Combustible Wall: A wall made of any combustible material, including overhanging wood eaves, any metal faced plastic insulated sandwich panels that are not FM Approved, and any wall with single pane, annealed (not tempered) glass windows. Increase separation by 25% for asphalt-coated metal walls. Noncombustible Wall: Materials include FM Approved Class 1 insulated, steel, or aluminum faced sandwich panels with thermoset plastic insulation; EIFS assemblies having noncombustible insulation and gypsum board sheathing, and aluminum or steel panels that are uninsulated or insulated with noncombustible insulation such as glass fiber, mineral wool, or expanded glass. It also includes cementitious panels or shingles over steel or wood. There can be no overhanging wood eaves. Any windows should be multipane or tempered glass. Fire Rated Wall: The wall should meet the required fire rating per FM Global Loss Prevention Data Sheet 1-21, Fire Resistance of Building Assemblies . Any openings should be protected with a comparably firerated door. Any windows should be fire rated to match the rating of the wall.



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Flammable Liquid: Any liquid rated as NFPA Class I, II or III or DOT/UN Class 3. FM Approved : References to ‘‘ FM Approved’’ in this data sheet mean the product or service has satisfied the criteria for FM Approval. Refer to the Approval Guide , a publication of FM Approvals, for a complete listing of products and services that are FM Approved. Intermediate Bulk Container (IBC): Any container that has a volumetric capacity of not more than 793 gallons (3,000 L) and not less than 119 gallons (450 L) as defined and regulated by the U.S. Department of Transportation in CFR Title 49, Part 178, subpart N, and the United Nations Recommendations on the Transport of Dangerous Goods, chapter 6.5.

IBCs can be constructed of metal, plastic or a metal-plastic composite. In the UN and US DOT regulations, metal IBCs are designated 31A, 31B, and 31N (for liquids, and the letter code is for steel, aluminum, and other metals, respectively.), rigid plastic are designated by the codes 31H1, 31H2, and composite are 31HZ1, 31HZ2. Listed : Equipment or materials included in a list published by an organization that maintains periodic inspection of production of listed equipment or materials and whose listing states that either the equipment or material meets appropriate designated standards or has been tested and found suitable for a specified purpose. Stable liquid: Any liquid not defined as unstable. Tank Aboveground tank : A tank that is installed above grade, at grade, or below grade without backfill. Atmospheric tank : A storage tank that has been designed to operate at pressures from atmospheric through a gauge pressure of 1.0 psig (6.9 kPa) measured at the top of the tank.

Double-skinned tank : See Secondary Containment Tank, a term used in European Union (EN) standards. Floating roof tank: An atmospheric tank intended for storage of high vapor pressure liquids such as crude oil and gasoline with vapor pressure exceeding 15 psig (103 kPa or 1 bar gauge) with a roof floating on the liquid surface. (Floating roof tanks are not covered by this standard.) Design according to the criteria in API 650, Appendix C or H, or other recognized equivalent standard. External floating roof: A roof that sits directly on the liquid surface, usually on pontoons with a seal attached to the roof perimeter to cover the annular space between the roof and the shell. Design criteria are in API 650, Appendix C. This type has inherent buoyancy and are difficult, though not impossible, to sink. Internal floating roof: A roof similar to the external floater but with a fixed roof above, intended for weather protection or quality assurance. The internal floater is often a simple pan or plastic membrane floating directly on the liquid surface with little or no inherent buoyancy and is subject to sinking. Design criteria are in API 650, Appendix H. Pontoon type roofs similar or identical to external floaters are possible but not common. Unless the internal floater has the inherent buoyancy of a pontoon type, treat the tank as a cone roof tank. Low-pressure tank: A storage tank designed to withstand an internal pressure of more than 1 psig (6.9 kPa) but not more than 15 psig (103 kPa or 1 bar gauge) measured at the top of the tank. Portable tank: Any closed vessel having a liquid capacity over 60 gal (230 L) and not intended for fixed installation. This includes intermediate bulk containers (IBCs) as defined and regulated by the U.S. Department of Transportation in CFR Title 49, Part 178, subpart N, and the United Nations Recommendations on the Transport of Dangerous Goods, chapter 6.5. Protected aboveground tank: An aboveground storage tank that is listed in accordance with UL 2085, Standard for Protected Aboveground Tanks for Flammable and Combustible Liquids, or an equivalent test procedure that consists of a primary tank provided with protection from physical damage and fire-resistive protection from exposure to a high-intensity liquid pool fire. Secondary containment tank : A tank that has an inner and outer wall with an interstitial space (annulus) between the walls and that has a means for monitoring the interstitial space for a leak. Storage tank : Any vessel having a liquid capacity that exceeds 60 gal (230 L), is intended for fixed installation, and is not used for processing.


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United Nations Recommendations on the Transport of Dangerous Goods : Model Regulations directed at providing safe packaging criteria but only related to the transport of all types of dangerous solids, liquids, and gases. Hazard class 3 addresses flammable liquids. Unstable liquid : A liquid that, in the pure state or as commercially produced or transported, will vigorously polymerize, decompose, undergo condensation reaction, or become self-reactive under conditions of shock, pressure, or temperature. A liquid with an NFPA instability hazard rating of 2 or greater in accordance with NFPA 704, Standard System for the Identification of the Hazards of Materials for Emergency Response . Vent, normal: Pressure relief opening on a tank to permit the intake and discharge of air during emptying and filling operations and to permit expansion and contraction of vapor due to temperature changes. Sometimes called breather vent. Vent, emergency relief : Pressure relief opening on a tank to prevent overpressurizing the tank in the event of fire exposure. Weak seam roof (weak shell-to-roof joint construction): The attachment of the roof to the shell forms a frangible joint that, in the case of excessive internal pressure, will rupture before rupture occurs in the tank shell joints or the shell-to-bottom joint. Design criteria can be found in UL 142 or API 650. APPENDIX B DOCUMENT REVISION HISTORY

September 2010. Changes were made in Table 3, Spacing for Flammable Liquid Tank Containment Dikes . March 2009. Minimum spacing requirements in Table 3, Spacing for Flammable Liquid Tank Containment Dikes, were modified. May 2008. Minor editorial changes were made for this revision. January 2008. Minor editorial changes were made for this revision. May 2007. Corrections were made to Table 2. April 2007. Minor editorial changes were made to January 2007 version. January 2007. The following changes were made: • Removed

the recommendation against bottom connections on FRP tanks to be consistent with referenced standards.

• Extended

the recommendation for containment to all tanks with flash points below 200°F (93°C). Previously, no containment was required for tanks of less than 15,000 gal (57 m3) except to protect buildings.

• Simplified

the spacing and diking recommendations.

• Upgraded

the recommendation for indoor tanks, including automatic fire and leak-detection systems.

• Added

recommendations for secondary containment tanks.

• Eliminated

the exemption to the recommendations for cutoffs for small fuel oil tanks serving heating appli-

ances. •

Added recommendations for IBCs when supplying flammable liquids to a process.

• Added

earthquake recommendations, including seismic shutoffs for indoor tanks.

• Added

section on asphalt storage tanks.

• Added

recommendations for monitoring tanks during fill operations, level-gauging, and high-level alarms to an attended location.

• Moved

information on carbon disulfide to Data Sheet 7-23N, Hazardous Chemical Data.

• Added

section on asphalt storage tanks.

• Added

recommendations for monitoring tanks during fill operations, level-gauging, and high-level alarms to an attended location.



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• Moved

information on carbon disulfide to Data Sheet 7-23N, Hazardous Chemical Data.

September 2000. This revision of the document has been reorganized to provide a consistent format. October 1994. Added information on manifold vents in systems, and detonation arrestors. July 1976. Miscellaneous revisions and updating. May 1971. Miscellaneous revisions and updating. November 1967. Updated and consolidated material from handbook. 1959. original guideline in Factory Mutual handbook of Industrial Loss Prevention. APPENDIX C HYDROCARBON FIRE DURATION

Spills in defined areas (e.g., curbed area in a room, tank contained by dike, etc.): See Table B1 below. 1. Determine if the dike will contain the largest expected spill: Volume = (Depth of Dike) x (Area of Dike) 2. Determine the depth of the spill in the confined area: Depth of Fuel = (Volume of Spill) / (Area of Dike) 3. Determine the liquid fire duration: Fire Duration = (Depth of Spill) x [(7 minutes) / (1 in.)] (English) Or Fire Duration = (Depth of Spill) x [(7 minutes) / (2.5 cm)] (metric) Spills in undefined areas: Assume an average spill depth of 1 ⁄ 16 in. (1.5 mm) for a relatively flat surface and use these equations to calculate the area of the spill. Thermal damage will occur to everything touched by the spill. The duration of this type of liquid spill fire will be limited. See Table 17 below. The spill area can be calculated as follows: Area of Spill = (Volume of Spill) / 1 ⁄ 16 in. (English) Or Area of Spill = (Volume of Spill) / 1.5 mm (metric) Table 17a. Relationship Between Fuel Volume, Pool Size, and Fire Duration (English) Liquid Volume, gal

Spill Area, ft 2 for 1 ⁄ 16 in depth

100 200 300 400 500 600 700 800 900 1000

2600 5100 770 10300 12800 15400 18000 20500 23100 25700

Spill Depth (in.) for Liquid Pools of Defined Area 1000 ft2 2000 ft2 0.2 0.1 0.3 0.2 0.5 0.2 0.6 0.3 0.8 0.4 1.0 0.5 1.1 0.6 1.3 0.6 1.4 0.7 1.6 0.8

Fire Duration (min) For Liquid Pools of Defined Area 1000 ft2 2000 ft2 1.1 0.6 2.3 1.1 3.4 1.7 4.5 2.3 5.6 2.8 6.7 3.4 7.9 3.9 9.0 4.5 10.1 5.0 11.2 5.6


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Table 17b. Relationship Between Fuel Volume, Pool Size, and Fire Duration (metric) Liquid Volume, liters

Spill Area, m 2 for 1.5 mm depth

380 760 1,100 1500 1900 2300 2600 3000 3400 3800

240 480 720 950 1200 1400 1700 1900 2100 2400

Spill Depth (mm) for Liquid Pools of Defined Area 93 m2 190 m2 5 3 8 5 13 5 15 8 20 10 24 13 29 15 33 15 37 18 41 20

Fire Duration (min) For Liquid Pools of Defined Area 93 m2 190 m2 1.1 0.6 2.3 1.1 3.4 1.7 4.5 2.3 5.6 2.8 6.7 3.4 7.9 3.9 9.0 4.5 10.1 5.0 11.2 5.6

Continuous Spills Depending on the spill rate, a flammable liquid may be fully consumed before it reaches the floor or it will create a burning pool on the floor. The pool diameter is controlled by the rate at which the liquid is being consumed in the fire and the rate at which it is being released. The pool diameter will stop growing when these two rates are equal. Table 18 below provides some expected pool sizes, heat release rates, and flame heights for various flow rates of kerosene. Diesel fuel will produce similar results. Since even small spill rates will produce sizable fires, the key issue in deciding if building steel will be damaged is the fire duration. The duration of this type of fire is controlled by the volume of fuel available to be spilled and the rate at which it is spilled. The spill fire duration can be calculated as follows: Fire Duration = (Volume of Fuel) / (Spill Rate) Table 18a. Flow Rate, Pool Diameter, Heat Release Rate, and Flame Height for a Flowing Kerosene Fire (English) Flow Rate (gpm) 1 2 3 4 5 10 15 20 25

Pool Diameter (ft) 3 5 6 7 7 10 13 15 17

Pool Area (ft 2 ) 9 17 26 34 43 86 128 171 214

Heat Release Rate (MW) 2 4 6 8 10 20 30 40 50

Flame Height (ft) 13 16 19 21 23 30 34 38 41

Table 18b. Flow Rate, Pool Diameter, Heat Release Rate, and Flame Height for a Flowing Kerosene Fire (Metric) Flow Rate (l/min) 3.8 7.6 11.4 15.2 19.0 38.0 57.0 76.0 95.0

Pool Diameter (m) 1.0 1.4 1.7 2.0 2.2 3.2 3.9 4.5 5.0

Pool Area (m 2 ) 1 2 2 3 4 8 12 16 20

Heat Release Rate (MW) 2 4 6 8 10 20 30 40 50


Flame Height (m) 3.9 5.0 5.8 6.5 7.0 9.1 10.5 11.7 12.6


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APPENDIX D HAZARDS

The National Fire Protection Association and various US federal and state regulations use the following liquid classifications: 1. Flammable liquids are defined as liquids having closed cup flash points below 100°F (38°C) and vapor pressures not exceeding 40 psia (276 kPa) at 100°F (38°C). Flammable liquids are referred to as Class I liquids, and are subdivided as follows: a) Class IA liquids are those having flash points below 73°F (23°C) and boiling points below 100°F (38°C). b) Class IB liquids are those having flash points below 73°F (23°C) and boiling points at or above 100 °F (38°C). c) Class IC liquids are those having flash points at or above 73°F (23°C) and below 100°F (38°C). 2. Combustible liquids are defined as liquids having closed cup flash points at or above 100°F (38°C). Combustible liquids are referred to as either Class II or Class III liquids and are subdivided as follows: a) Class II liquids are those having flash points at or above 100°F (38°C) and below 140°F (60°C). b) Class IIIA liquids are those having flash points at or above 140°F (60°C) and below 200°F (93°C). c) Class IIIB liquids are those having flash points at or above 200°F (93°C). The U.N. Recommendations on the Transport of Dangerous Goods has only defined flammable liquids (hazard class 3) as follows: Flammable liquids are liquids, or mixtures of liquids, or liquids containing solids in solution or suspension (for example, paints, varnishes, lacquers, etc., but not including substances otherwise classified on account of their dangerous characteristics) which give off a flammable vapor at temperatures of not more than 60.5°C (141°F), closed-cup test, or not more than 65.6°C (150°F), open-cup test, normally referred to as the flash point. This class also includes:

(a) Liquids offered for transport at temperatures at or above their flash point; and (b) Substances that are transported or offered for transport at elevated temperatures in a liquid state and which give off a flammable vapor at a temperature at or below the maximum transport temperature. Liquids meeting the above definition, with a flash point of more than 35°C (95°F) which do not sustain combustion need not be considered as flammable liquids for the purposes of these Regulations. Liquids are considered to be unable to sustain combustion for the purposes of these Regulations (i.e., they do not sustain combustion under defined test conditions) if: (a) They have passed a suitable combustibility test (see SUSTAINED COMBUSTIBILITY TEST prescribed in the UN Manual of Tests and Criteria ); (b) Their fire point according to ISO 2592 — 2000 is greater than 100°C (212°F) or (c) They are water miscible solutions with a water content of more than 90% by mass. The UN system applies to materials in transport. The current U.S. Department of Transportation Code 49CFR 171 defines hazard class 3 slightly more broadly, as follows: (a) Flammable liquid. For the purpose of this subchapter, a flammable liquid (Class 3) means a liquid having a flash point of not more than 60.5 °C (141°F), or any material in a liquid phase with a flash point at or above 37.8°C (100°F) that is intentionally heated and offered for transportation or transported at or above its flash point in a bulk packaging, with the following exceptions : (1) Any liquid meeting one of the definitions specified in § 173.115 Class 2, Divisions 2.1 (flammable gas), 2.2 (non-flammable, nonpoisonous compressed gas —including compressed gas, liquefied gas, pressurized cryogenic gas, compressed gas in solution, asphyxiant gas and oxidizing gas), and 2.3 (gas poisonous by inhalation). (2) Any mixture having one or more components with a flash point of 60.5 °C (141°F) or higher, that make up at least 99 percent of the total volume of the mixture, if the mixture is not offered for transportation or transported at or above its flash point.


7-88 Flammable Liquid Storage Tanks

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