BS 476 Part 6 Building Material Fire Propagation Index Test Apparatus

This Part of BS 476 specifies a method of test, the result being expressed as a fire propagation index, that provides a comparative measure of the contribution to the growth of fire made by an essentially flat material, composite or assembly. It is primarily intended for the assessment of the performance of internal wall and ceiling linings.

The test apparatus (see Figure 1 to Figure 3) shall consist of a combustion chamber with a specimen holder fixed to one face. The combustion chamber shall contain a horizontal gas burner tube and two electrical heating elements and shall be surmounted by a removable steel chimney and cowl.

Combustion chamber

The walls of the chamber shall be made from 12.5 mm thick asbestos cement board2) having a dry density within the range 1 300 kg/m3 to 1 450 kg/m3. The internal dimensions of the chamber shall be 190 mm × 190 mm × 90 mm.

An air inlet slot measuring 96 mm × 25 mm and a mica observation window measuring 50 mm × 50 mm shall be provided together with a hole for the discharge of combustion gases and a suitable fixing for the chimney and cowl.

A steel baffle plate 200 mm × 40 mm shall be fixed horizontally to the top of the combustion chamber above the window. Four steel rods shall be fitted to the combustion chamber to enable the specimen holder to be located and fixed firmly in position during each test.

After allowing any residual gas within the combustion chamber to disperse, simultaneously turn on the gas supply and ignite the jets using the gas igniter; time the test from the time of ignition. After 2 min 45 s, turn on the electrical supply to give an indicated input of 1 800 W; at 5 min after the time of ignition, reduce this indicated input to 1 500 W.