Definition
Class 0 is defined in ApprovedDocument B,Appendix A13;
this provides two routes to enable a material to be described as
Class 0. The definition is as follows:
The highest product performance classification for lining materials is Class 0. This is achieved if a material or the surface of a compositeproduct is either:-
a) composed throughout of materials of limited combustibility,or
b) a Class 1material which has a fire propagation index, (I) of not morethan 12, and (i1) of not more than 6.
Note: Class 0 isnot a classification identifiedin any British
Standard.
Caution: If youchoose to go down route a), limited combustibilitymust be proven in accordancewith specified test standards.
HowAre BS 476 Part 6AndBS 476 Part 7CombinedTo
Provide***ass 0?
The definition provided in Approved Document B, Appendix
A13; allowsthecombinationof the BS 476 Part 6 and BS 476
Part 7 test results in order to classifya liningproduct as Class
0 (route b).
Initially, the BS476: Part 7 surface spread offlame test is conducted andthe material must obtaina Class 1 (i.e. must not spread flame to a distance of greater than 165mm,with the exception of one specimenwhich can spread flame to a distance of 190mm).
Once this is achieved, the BS 476: Part 6 firepropagation test is conducted. The index ofperformance, I,mustbe≤12 (relating to theoverall testperformance) andthe subindexof performance, (i1),mustbe ≤6 (relating to theperformance during the first three minutes of the test).
Itis important that the productmust be tested in exactly the same manner for both of the above tests(e.g.materials for both tests should be bonded using the same adhesiveand substrate, if anair gap is usedin practice an air gap shouldbe
used in both tests,etc.).