BS 476-3 1975

British Standard A single copy of this British Standard is licensed to Giorgio Cavalieri on November 16, 2000 This is an uncontrolled copy. Ensure use of the most current version of this standard by searching British Standards Online at bsonline.techindex.co.uk

BRITISH STANDARD

Fire tests on building materials and structures — I S B © . y p o C d e l l o r t n o c n U , 0 0 v o N 6 1 , e n o n , i r e i l a v a C o i g r o i G : y p o C d e s n e c i L

Part 3: External fire exposure roof test

UDC 614.841.322:620.1:699.81:69.024

BS 476-3:1975

BS 476-3:1975

Co-operating organizations The Petroleum Equipment Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives from the following Government department and scientific and industrial organization: British Gas Corporation British Mechanical Engineering Confederation British Rubber Manufacturers’ Association Ltd. British Steel industry* Council of British Manufacturers of Petroleum Equipment* Department of Energy Oil Companies Materials Association* The Industrial organization marked with an asterisk in the above list, together with the following, were directly represented on the Committee entrusted with the preparation of this standard: Association of Hydraulic Equipment Manufacturers British Chemical Engineering Contractors Association British Industrial Measuring and Control Apparatus Manufacturers’ Association British Plastics Federation British Ship Research Association British Valve Manufacturers’ Association Engineering Equipment Users Association Steel Castings Association

This British Standard, having been approved by the Petroleum Equipment Industry Standards Committee, was published under the authority of the Executive Board on 28 November 1975 © BSI 01-1999

Amendments issued since publication

First published, June 1952 First revision, March 1960 Second revision, November 1975

Amd. No.

The following BSI references relate to the work on this standard: Committee reference PEE/1 Draft for comment 74/74150 DC ISBN 0 580 08817 0

Date of issue

Comments

L i c e n s e d C o p y : G i o r g i o C a v a l i e r ,i n o n e , 1 6 -N o v 0 0 , U n c o n t r o l l e d C o p y . © B S I

BS 476-3:1975

Contents

Co-operating organizations General foreword Foreword 1 2 3 4 5 6 7 8

I S B © . y p o C d e l l o r t n o c n U , 0 0 v o N 6 1 , e n o n , i r e i l a v a C o i g r o i G : y p o C d e s n e c i L

Scope References Definitions Test specimen Test equipment Test procedure Expression of results Test report

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Appendix A Copper asbestos disc radiometer

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Figure 1 — Diagram showing radiation intensities at nine positions on plan of specimen for calibration Figure 2 — Typical roof test apparatus Figure 3 — Path of travel of pilot flame

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Publication referred to

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Page Inside front cover ii iii

Inside back cover

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BS 476-3:1975

General foreword BS 476 was published as a single volume in 1932. A later revision expanded the standard into three Parts: — Part 1:1953, Fire tests on building materials and structures; — Part 2:1955, Flammability test for thin flexible materials; — Part 3:1958, External fire exposure roof tests. In the present revision the three sections of — Part 1:1953 have been revised and published as new and separate Parts in the BS 476 series. Thus the three sections of Part 1 are replaced respectively by: — Part 4:1970, Non-combustibility test for materials; — Part 7:1971, Surface spread of flame tests for materials; — Part 8:1972, Test methods and criteria for the fire resistance of elements of building construction. In addition, during the present revision new Parts have been added to the series as follows: — Part 5:1968, Ignitability test for materials; — Part 6:1968, Fire propagation test for materials. Part 2:1955 has been withdrawn and replaced by BS 2782 “Methods of testing plastics”, Part 5 “Miscellaneous methods”. This British Standard replaces — Part 3:1958 which is withdrawn. At present the BS 476 series comprises Parts 3 to 8 inclusive; other tests are, however, under consideration. DD 36 “Fire tests on building materials and structures: measurement of the optical density of smoke produced by small specimens of materials” has been published as a Draft for Development. This test was originally prepared with the intention of issuing it as BS 476-9, but since it was considered that insufficient tests have so far been carried out to establish reproducibility between laboratories, it has been decided that t he method cannot yet be given the full status of a British Standard in the BS 476 series. The need for a glossary covering terms used in BS 476 has been established and this has been published as BS 4422 “Glossary of terms associated with fire”, with the following Parts: — Part 1: The phenomenon of fire; — Part 2: Building materials and structures; — Part 3: Means of escape; — Part 4: Fire protection equipment; — Part 5: Miscellaneous terms (in course of preparation).

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BS 476-3:1975

Foreword A fire may create a hazard to neighbouring property. The extent of the hazard depends on the distance separating a building from t he fire, the size and severity of the fire and the amount of the heat received on a building. The chief danger arises from radiated heat combined with the burning embers (flying brands) thrown off from the fire. The tests described in this Part of BS 476 are designed to give information on the ability of a roof covering and its supporting deck or supp orts to act as a protective barrier against a fire in a nearby building and on the extent of any surface ignition. Provision is also made for the testing of rooflights, domelights and similar components. Whilst the test has been designed to give information on the performance of a roof to external fire exposure in a building situation, the results obtained do not necessarily show how the roof will behave in any particular fire and therefore should not be considered as an overall indication of the potential fire hazard. No information is obtained from the test on the performance of the roof when subjected to conditions of an internal fire.


When subjected to the performance test the specimen is exposed to radiant heat which can be regarded as, for example, the intensity incident on a roof 7.5 m above ground level from a fire 13.5 m away in a building with a facade of 15 m × 15 m and 50 % window openings. A gas flame is employed in the test to represent flying brands falling on the roof. In this revision of the standard the following modifications have been made. a) The separate spread of flame test has been dropped and in its place a measurement of the extent of surface ignition is mad e at the same time as the penetration test using the same level of radiation intensity. This change also avoids confusion with the surface spread of flame test now covered in Part 7 which relates to the characteristics of wall and ceiling linings under internal fire conditions. b) The requirements for suction under the roof specimen for the purposes of simulating the effects of a wind on the upper surface of a roof has been omitted. The requirement was found to interfere with observation of the underside of the specimen due to the presence of smoke within the enclosed specimen holder. c) To extend the field of application of the test, provision has been made for increasing its duration if required. d) The penetration of fire and surface ignition measurements being combined in one test reduce the number of specimens to be test ed. The specimen size has been increased to 1.5 m × 1.2 m to provide a sufficient area for measurement of surface ignition and at the same time permit a more representative construction to be tested. e) The previous method required the test flame to be applied only once during the early part of the exposure. This was considered to be unrealistic and in the revised method the test flame is applied at intervals during the test. f) The performance of the specimen was previously expressed in terms of definite designations. These designations are replaced by the actual performance data. The above mentioned designations were used for the purposes of building control by grouping certain performance classifications in relation to type of buildings and distance from the boundary.

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BS 476-3:1975

The following table shows examples of the relationship between existing groupings and the new method of expressing a similar performance for penetration. Part 3:1958 AA, AB, AC BA, BB, BC AD, BD, CA CB, CC, CD Unclassifiable

Part 3:1975 P60a P30   

P15 P5

a

P60 means that the specimen passed the preliminary test (see 6.2) and that fire penetration (see 6.3) did not occur in less than 1 h.

Extent of surface ignition characteristics are not included in the new designations given in the above table. In some situations it may be necessary additionally to control these characteristics for which the test report provides full details. NOTE The category designations used in the previous edition of this standard were two letters. The first letter referred to penetration times of the specimen, where penetration had occurred in A for not less than 1 h, B for not less than 30 min, C for less than 30 min and D during the preliminary flame test. The second letter referred to spread of flame of the specimen which occurred, A none, B for not more than 21 in (533.4 mm), C for more than 21 in (533.4 mm) and D which continued to burn for 5 min after withdrawal of the test flame or spread more than 15 in (381 mm) across the region of burning in the preliminary test. Suffix X to category designations denoted dripping from the underside of the specimen tested, and this is now included as a part of the test report.

g) A simulated gutter is positioned at the front end of the specimen to collect any molten materials which may flow from the surface of the specimen during a test. h) An additional section gives the minimum information that should be included in a test report. Attention is drawn to the Health and Safety at Work etc. Act 1974, and the need to ensure that the methods of test specified in this standard are carried out under suitable environmental conditions to provide adequate protection to personnel against the risk of fire, inhalation of smoke and/or toxic products of combustion. BSI has established OC/10, Co-ordinating committee on fire tests, and as a result of the work of this committee it may be necessary to amend this standard at a future date. This standard is expressed in metric terms. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations.

Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 6, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. iv

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BS 476-3:1975

1 Scope

4 Test specimen

This Part of this British Standard specifies tests which are designed to measure:

4.1 Construction of specimens. The test specimen shall be representative of the roof construction including at least one example of each joint, if any used, in each of the materials employed in the construction. Any joints in the roof construction shall be so arranged to occur in the central part of the specimen. The specimen edges shall be sealed with strips of a non-combustible material such as 12 mm thick asbestos board, the tops of the strips being flush with t he upper surface of the specimen.

a) the ability of a representat ive section of a roof, rooflight, domelight and similar components to resist penetration by fire when the external surface is exposed to heat radiation and flame; I S B © . y p o C d e l l o r t n o c n U , 0 0 v o N 6 1 , e n o n , i r e i l a v a C o i g r o i G : y p o C d e s n e c i L

b) the extent of surface ignition of the upper surface with and without supporting radiation.

2 References The title of the British Standard referred to in this standard is given on the inside back cover.

3 Definitions For the purposes of this British Standard the following definitions and those given in BS 4422 apply. 3.1 specimen of roof construction all constituents comprising the roof covering (including any associated membrane or insulating materials fixed above the supporting members) together with the roof slab or decking in contact therewith and the supports thereto but excluding any ceiling or soffit beneath such decking or supporting members NOTE Where the roof covering is intended to be used in conjunction with a stressed skin deck construction the decking shall be a representative section comprising the top skin together with any joist or similar supports.

3.2 penetration time the time at which glowing or flaming appears on t he underside surface of the specimen or the time at which the formation of holes or fissures or collapse of specimen occurs, whichever is the earliest. For this purpose a hole or fissure includes any aperture through which the test flame can be observed from the underside when it is applied to the upp er surface 3.3 extent of surface ignition the maximum distance of lateral flame spread on the upper surface

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NOTE If information is required on the behaviour of the specimen with eaves or verges, these may be included in the construction.

4.2 Size of specimens. The overall size of the specimen, excluding the sealing strips, shall be not less than 1.5 m × 1.2 m (see Figure 1). If the specimen is a rooflight or similar component which is only available in a size other than specified, the next smaller component shall be tested and properly fitted in accordance with 4.1 into the centre of a panel 1.5 m × 1.2 m of an appropriate non-combustible roof construction. 4.3 Number of specimens. Four specimens shall be provided. 4.4 Conditioning of the specimens. The specimens shall be conditioned to equilibrium in an atmosphere at a temperature of 10 °C to 21 °C and 55 % to 65 % relative humidity. They shall be tested as soon as possible after leaving the conditioned atmosphere; the interval between removal from this atmosphere and testing shall not exceed 4 h.

5 Test equipment 5.1 Test environment. The test equipment shall be located in a draught-free atmosphere. In order to maintain the calibration of the equipment during the course of a test it is recommended that the volume of the test enclosure be not less than 1 300 m3 and the floor to ceiling height be not less than 5 m. 5.2 Heating panel. The heating panel shall consist of four 300 ± 5 mm2 radiant heaters mounted on a steel flamework so that their centres occur at the corners of a square having 480 mm sides. The heating panel assembly shall be capable of movement between a position 10° to 45° to the horizontal.

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BS 476-3:1975

Before a test the heating panel shall be controlled t o provide a maximum incident radiation intensity of 14.6 ± 0.5 kW/m2 at the centre of the surface of the specimen measured by a radiometer. The apparatus shall be calibrated to give the distribution of radiation intensity in the p lane of the upper surface of the specimen at nine positions as shown in Figure 1. These intensities shall be measured without a specimen being in place. The monitoring of radiation intensity before a test shall be by means of four radiometers placed symmetrically in front of the radiant heaters at the corners of a square of 610 mm side. A suitable method is to use copper asbestos disc radiometers, as described in appendix A, placed at a distance of 125 mm in front of the radiant heaters. 5.3 Test flame. The test flame shall consist of a luminous coal (simulated town) gas or natural gas flame 200 mm to 250 mm long issuing from a tube when held in a vertical position with an orifice of 9 ± 0.5 mm diameter (see note). The tube shall be provided with a flexible length of pipe so that the test flame can be moved over the surface of the specimen.

NOTE It has been found that this can be achieved when using coal (simulated town) gas (calorific value 4 450 kcal/m3) at a flow rate of approximately 3 730 cm3/min or natural gas (calorific value 10 730 kcal/m 3) at a flow rate of approximately 1 550 cm3/min.

5.4 Specimen holder (see Figure 2). The specimen shall be supported by a metal framework that allows an unobstructed view of the underside of the specimen and does not restrict its thermal movement. The frame shall be provided with means of adjustment for the height of the specimen and its angle of inclination from 1° to 45° t o the horizontal. The specimen on its frame shall be capable of movement from an unexposed position to the test position within 5 s. A metal gutter extending the full width of the specimen shall be fitted to the f ront of the frame, located about 50 mm below the front edge.

Figure 1 — Diagram showing radiation intensities at nine positions on plan of specimen for calibration

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BS 476-3:1975


Figure 2 — Typical roof test apparatus

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BS 476-3:1975

6 Test procedure 6.1 Mounting of specimens. Each specimen shall be mounted with its upper surface at an angle of 45° to the horizontal. If the specimen represents a construction which is intended to be used at a lesser angle, then the appropriate slope shall be used in the test with a minimum slope of 1°. 6.2 Preliminary ignition test. One specimen shall be supported as specified in 5.4 and the test flame, specified in 5.3, shall be applied to its upper surface without incident heat radiation. The orifice through which the flame is issuing shall be held 5 mm to 10 mm from the surface at the centre of the specimen with the tube held at an angle to enable the flame to maintain contact with the upper surface. The flame shall be removed 1 min after application and observations made of any continued flaming on the upper surface and fire penetration to the underside. If penetration occurs the subsequent tests shall not be carried out. 6.3 Fire penetration and surface ignition test 6.3.1 Three specimens shall be tested. The heating panels shall be stabilized to provide the radiation intensity on the upper surface of the specimen as specified in 5.2. This is normally achieved at a distance of 580 ± 5 mm from the plane forming the radiant heaters, the distance being measured at right-angles to the centre of the specimen. 6.3.2 The specimen shall be moved from the unexposed position to the test position within 5 s. The test starts at the moment the specimen is in the test position. The test shall be of at least 60 min duration, unless penetration occurs earlier. The test period may be extended beyond 60 min to a maximum of 90 min.

6.3.3 The test flame shall be applied over the upper surface of the specimen for a period of 1 min, the first application being at 5 min from the st art of the test. Throughout the duration of the test successive applications shall be made at 5, 10, 15, 30, 45 and 75 min from the start of the test unless the test has been terminated at an earlier time. The test flame shall be directed towards the top edge of the specimen (see Figure 1) with the orifice 5 mm to 10 mm from the surface of the specimen and the tube held at an angle to enable the flame to maintain contact. At each application of the test flame it shall traverse the specimen from one side edge to the other at least once, in a d irection parallel to the X–X axis (see Figure 1) and so as to pass over the central area of the specimen. Where rooflights are incorporated the path of the pilot flame should be as shown in Figure 3. The test flame shall be moved slowly over the surface at an average speed of 2 m/min covering joints and other positions which appear susceptible to flaming; it may be held at any point for up to 15 s if ignition of the surface seems imminent. 6.3.4 Immediately following the application of the flame to the surface of the specimen the test flame shall if required be applied to any molten material collecting in the gutter. 6.4 Test observations. The following observations shall be recorded in respect of each specimen. a) The time and occurrence of any flaming on the upper surface and its duration. Where sporadic or intermittent flaming occurs without a measurable progression of the flame front, it shall be recorded under other observation [see clause 8 e)]. b) The time at which glowing or flaming appears on the underside. c) The time of development of holes or fissures, or collapse. d) Visual changes in appearance. e) Any fall of molten materials into the gutter at the front or from the underside of the specimen and any flaming of the molten material. f) Behaviour at eaves when these are incorporated. g) The maximum distance of lateral flame spread on the upper surface which has occurred at any time during the test shall be measured to the nearest 25 mm, as follows: 1) maximum spread in any direction in the preliminary ignition test (see 6.2); 2) maximum spread measured along the X–X axis (see Figure 1) in the fire penetration and surface ignition test (see 6.3).

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BS 476-3:1975


Figure 3 — Path of travel of pilot flame 6.5 Test results

7 Expression of results

6.5.1 Preliminary ignition test. If the duration of flaming exceeds 5 min after the withdrawal of the test flame or if the maximum distan ce of flaming in any direction exceeds 370 mm, the performance of the specimen shall be expressed by the letter X. If the duration of flaming after the withdrawal of the test flame is less than 5 min or if the maximum distance of flaming does not exceed 370 mm, the performance shall be expressed by the letter P. If penetration of fire occurs in this test the penetration time for the whole sample shall be reported as 1 min.

The results obtained for each roof specimen tested shall be given as follows. a) Inclination of the roof. b) Performance in the preliminary ignition test. c) The penetration time in minutes. d) The extent of surface ignition in millimetres.

8 Test report The test report on the specimens shall include the following information.

6.5.2 Fire penetration and surface ignition test. The penetration time to the nearest minute shall be given for each specimen. If no penetration has occurred, the time shall be taken as the maximum duration of the test.

a) Name of testing laboratory.

The extent of surface ignition shall be given for the three specimens at 60 min or at the time of penetration to the nearest 25 mm.

e) Test results, as specified in clause 7 including any observations under 6.4.

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b) Name of sponsor. c) Date of test. d) Complete description of construction and conditioning of test specimens.

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BS 476-3:1975

Appendix A Copper asbestos disc radiometer The copper asbestos disc radiometer is constructed from a copper disc, 0.376 mm thick and 25.4 mm diameter, to which is soldered chromel and constantan thermocouple wires, 0.719 mm diameter. Discs of asbestos paper, 0.254 mm thick, 32 mm diameter and with a mass per unit area of 175 g/m2, are secured to both sides of the copper disc by sodium silicate adhesive. The sodium silicate adhesive consists of an aqueous syrup of composition between Na2O:3.2SiO2 and Na2O:3.4SiO2, having a relative density between 1.41 and 1.43. The thermocouple wires are soldered to the copper disc at diametrically opposite points near the edge using a high melting point solder (750 °C). After soldering, the disc is thoroughly cleaned on both sides by dipping in a cleaning mixture consisting of concentrated sulphuric acid and chromic acid or sodium dichromate in the ratio 4 to 1 by volume.

After washing and drying the disc, care being taken not to handle the surface of the copper with the fingers, a drop of silicate adhesive is applied to the centre of the disc from a 6 mm diameter rod that has been immersed to a depth of 30 mm in the silicate adhesive. The asbestos disc is then placed on top and worked round with the finger spreading the adhesive over its surface until it becomes tacky. The disc is then centralized and pressed down firmly. This process is repeated for the other side of t he disc, care being taken to ensure that the asbestos paper is pressed down firmly round the thermocouple wires and is well sealed round the edge. The completed copper asbestos disc radiometer should be used with the thermocouples side facing the source of radiation. The output, in millivolts, from the radiometers is obtained from the following relationship: 4.187 E 2 + 79.56E – 100I = 0 where E is the e.m.f. (mV); I

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is the intensity of radiation (kW/m 2).

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BS 476-3:1975

Publication referred to This standard makes reference to the following British Standard: BS 4422, Glossary of terms associated with fire.


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BS 476-3 1975

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