SSF

[nearlythere]

In a nutshell what is the difference between BS476 Pt 6 & BS476 Pt7?

[Tom Sutton]

BS476 Pt 6 ? Fire test for fire propagation, This Fire Propagation test measures the amount of heat the surface is giving off during the fire.
BS476 Pt 7 ? Surface spread of Flame. The test measures the distance and time a flame will spread across a surface. Class 1 the highest Class 4 the lowest.

The complication arises when we consider class O, it is not a fire test but in fact a classification from The Building Regulations 1991 Fire Safety, Approved Document B.

In order for a system to achieve a Class 0 rating it must meet the following requirements:
 
   1. Achieve a Class 1 fire rating from BS 476 Pt 7 ? Surface spread of Flame
   2. Achieve an index of I = less than 12 and i1 = less than 6 from BS 476 Pt 6

To Summarise:

Class 1 ? Protects your surface from the spread of flames.
Class 0 ? Protects your surface from the spread of flames AND limits the amount of heat released from the surface during a fire.

I think.

[nearlythere]

Thanks Tom. When we are recommending a clasification of SSF we want a standard to pt 7 presumably? Or is it 6 or both?

[Tom Sutton]

If you are recommending surface spread of flame class 1 to 4 then its pt 7 if it is class O then it is pt 6 & pt 7

[kurnal]

BS 476: Part 6 Method of test for fire propagation for products
This test measures the amount and rate of heat evolved by the product while subjected to standard heating conditions. Test results are given as an Index of Performance (I) which is based on three sub-indices (i1, i2, i3). The higher the value of the Index, (I), the greater the material contribution to fire growth. The higher the value of the sub-index, i1 the greater the ease of ignition and flame spread.

BS 476: Part 7 Method for classification of the surface spread of flame for products
This test classifies materials into Classes 1 to 4 in descending order of performance according to the rate and extent of flame spread over their surface under standard heating conditions. Therefore the highest rating (best) of surface spread of flame, is Class 1.

Class 0 is not referred to in either of the above standards,  it is a concept created and defined in Approved Document B as a material
a) Composed throughout of materials of limited combustibility, or
b) A Class 1 (to BS 476: Part 7: 1987) material which has a fire propagation index (I) of not more than 12, and a sub-index (i1) of not more than 6 (to BS 476: Part 6: 1989).

BS476-4 and BS476-11 define tests for the combustibility of materials which inform (a) above.

[Tom Sutton]

If you are recommending surface spread of flame class 1 to 4 then its pt 7 if it is class O then it is pt 6 & pt 7

On reflection if you are recommending surface spread of flame class 1 to 4 then quote "in accordance with BS 476 part 7" but for class O you should quote "in accordance with Building Regulations B2" because you would know which BS's was used to define it.

[wee brian]

But you should really be using the Euroclasses.

[colin todd]

Only until we come out of the EC Wee B.  I still like the old tests personally.