The test for determination of fire rating is carried out, as per the procedure laid down in IS;3809-1979, as follows :
A test specimen representative of the complete element of construction, on which information is required, is prepared in the prescribed size. The materials used, construction and workmanship are required to be representative of those in actual practice. In the case of load bearing elements the test specimen is subjected, before exposure to fire, to a load which induces, in the critical parts of the elements, stresses of the same magnitude as are produced in the full size structure under normal working conditions.
After preparation and conditioning, the test specimen is exposed to the prescribed fire/heating conditions and is observed for signs of failure in any of the three critical parameters as follows:
Load Bearing Capacity :
The stage at which a test specimen can no longer support the test load is taken as the stage of failure. The length of time for which the test specimen has withstood the fire, supporting the test load, is recorded.
The point of failure of an element in terms of insulation is determined on the basis of the rise in temperature on the unexposed face of the specimen. The length of time taken for the temperature on the unexposed face to rise to the prescribed limit is recorded.
The failure of a structure in terms of integrity is caused by the development of cracks, holes or other openings, through which flames or hot gases tend to pass. The length of time for which the test specimen withstands the prescribed heating conditions without showing any sign of integrity failure is recorded.
As stated earlier the fire rating of a structure is eventually determined taking into account its performance in terms of some, or all the three basic parameters; viz. load bearing capacity, insulation and integrity, depending on its critical functions in the building.
It is thus clear that fire rating has more to do with complete structures than with materials alone. In the case of sheet materials used in building interiors for partitions etc. (whether wood based or non-wood based) a desired fire rating for any system has to be achieved by adopting a proper design incorporating comprehensive specifications for materials, construction and workmanship. Thereafter a prototype of that element may be tested for evaluation of fire rating in an institution like CBRI. It makes no sense asking for the fire rating of any single material. It is a whole structure or system that is fire rated.