A roof is required to protect a building against external damage
including the hazards presented by fire in a neighbouring building;
it is not required to confine a fire inside a building and is not
therefore expected to withstand the same fire conditions described in
B.S. 476 as for walls, columns, etc., nevertheless it should resist
the penetration of fire from a neighbouring building and should not
allow flame to spread over its surface. The two tests described here
have been designed to measure these qualities. In the penetrations
test, specimens are exposed to radiation of an intensity approximately
equivalent to that which might be expected on a roof at a point 25 ft.
above ground level from a fire in a building 45 ft. away, and with a
facade of 50 ft. x 50 ft., and 50 percent window openings; and since
a roof may be exposed to wind at the same time as fire, provision is
made to simulate the air movement of a wind at (15 mile/h approx.)
In the spread of flame test the intensity of radiation varies in
different parts of the specimen. Roofs are graded according to the
duration of their resistance to penetration of flame coupled with the
resistance they offer to superficial spread of flame. Some roofing
materials melt when involved in fire, and allow burning drops to fall;
behaviour in this respect to be observed and to be recorded during tests.
