Technical Specifications, BS 476

BS 476 Fire Tests on Building Materials and Structures

The UK has for many years relied on BS 476 to determine the performance of building materials, products and assemblies. It is very frequently referred to and continues to have significance in demonstrating fire performance and compliance with building regulations. In the coming years this standard is likely to be gradually replaced with the new BS EN 1364 standard, and in particular BS 476 fire resistance standard replaced with BS EN 1364-1.

The Relevant Sections of BS 476 are:

Fire Tests on Building Materials and Structures

-3: 2004
Classification and method of test for external fire exposure to roofs

-4: 1970
Non-combustibility test for materials

-6: 1989/2009
Method of test for fire propagation for products

-7: 1997
Method of test to determine the classification of the surface spread of flame of products

-11: 1982
Method for assessing the heat emission from building materials

-20: 1987
Method for determination of the fire resistance of elements of construction (general principles)

-22: 1987
Methods for determination of the fire resistance of non-load bearing elements of construction

-3: 2004Classification and method of test for external fire exposure to roofs

-4: 1970
Non-combustibility test for materials

-6: 1989/2009
Method of test for fire propagation for products

-7: 1997
Method of test for fire propagation for productsMethod of test to determine the classification of the surface spread of flame of products

-11: 1982
Method for assessing the heat emission from building materials

-20: 1987Method for determination of the fire resistance of elements of construction (general principles)

-22: 1987Methods for determination of the fire resistance of non-load bearing elements of construction

BS 476

Built-up systems using non-combustible mineral glass fibre type insulation typically perform very well for Integrity and can offer excellent Insulation resistance also. CA Building Products wall cladding systems can generally offer 240 minutes Integrity (E) resistance and a minimum of 15 minutes Insulation (I) resistance, although enhanced options are also available.

Most important is to ensure that any boundary fire wall construction is built in accordance with the tested assembly, using the same components as those tested, or an assessment sought if any products are substituted. For this reason CA Twin-Therm^®, River-Therm^®, Prime^® Rainscreen and SolarWall^® systems are supplied as a complete system ensuring compliance with tested performance.

BS476-3

Classification of External Roofs has Two Indices:

Fire Penetration (First Letter)
‍
A.
Those specimens that have not been penetrated within one hour.
B.
Those specimens that are penetrated in not less than 30 minutes.
C.
Those specimens that are penetrated in less than 30 minutes.
D.
Those specimens that are penetrated in the preliminary flame test.

Spread of Flame (Second Letter)

A.
Those specimens on which there is no spread of flame.

B.Those specimens on which there is not more than 533 mm spread of flame.

C.Those specimens on which there is more than 533 mm spread of flame.

D.Those specimens that continue to burn for five minutes after the withdrawal of the test flame or spread more than 381mm across the region of burning in the preliminary test.

Therefore the best performing products to this standard would be designated AA.

BS476-4

Non-Combustibility test determines whether a product will contribute the the fire load

BS 476-6

Fire propagation of products and determines a fire propagation index, I.

Products that meet the lowest fire propagation index to BS476-6 and also achieve Class 1 surface spread of flame can be considered as being a “Class O Surface”. Please note that there is no Class 0 Surface Spread of Flame under Building Regulations for England, the best classification under BS476-7 is Class 1 although this is regularly confused with the definition of Class O Surface.

BS 476-7

BS 476-7 is the spread of flame standard, with 4 classifications, Class 1 - 4.

Products that meet the lowest fire propagation index to BS476-6 and also achieve Class 1 surface spread of flame can be considered as being a “Class O Surface”. Please note that there is no Class 0 Surface Spread of Flame, the best classification under BS476-7 is Class 1 although this is regularly confused with the definition of Class O Surface.

BS 476-11

BS 476-11 is a heat emission test similar to a combustibility test and is used to determine how a material might contribute to a fire.

BS476-22

BS476-22 is the necessary standard when determining the fire resistance of an assembly, and involves a test on the complete assembly of products. Where alternative products might be substituted from those used in the physical test it may be necessary to obtain an assessment on the assembly that it intended to be used on a particular project, this assessment from an accredited fire research or testing facility. Such assessments cannot be used for ‘Relevant Buildings’ i.e. buildings with a storey with dwelling or residence above 18m.

BS476-22 considers three Resistance ratings, REI:

R Structural Resistance or resistance to collapse. Cladding are non-load bearing therefore will have no R resistance. This is provided by the structural frame
E Integrity, the ability to contain a fire or flames, resist cracks or gaps opening up and prevent the spread of flame to the other side of the construction for the resistance period
I Insulation, the restriction on heat or temperature rise on the far side of the construction

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