Section 11: FIRE RESISTANCE
General. Fire hazards to roof systems are broadly
classified as follows:
External, above-deck fire exposure from flying
brands or burning debris blown over from neighboring buildings on
Internal, below-deck fire exposure from interior
inventory or equipment fires;
Time-temperature or fire resistance
External Fire Resistance
Membranes. Roofing membranes are tested and rated for
their resistance to external fire. They should not spread flame
rapidly, produce flying brands endangering adjacent buildings, or
permit ignition of supporting roof decks.
Tests and Ratings. According to the industry standard
for rating roof coverings, ASTM E 108, Fire Tests of Roof
Coverings, classified roof coverings "are not readily flammable,
do not slip from position, and possess no flying brand hazard."
Their performance is rated as Class A, B, or C, depending on
their resistance to external fires of varying intensity. Class A
coverings provide the greatest resistance, Class C the least.
Internal Fire Hazards
Background Research. Research on acceptable fire
spread from internal (i.e., below-deck) fires has focused chiefly
on steel-deck roof assemblies. Because of its extremely high
thermal conductivity, steel deck immediately transmits the heat
energy of an interior fire to the above-deck roof components.
Safeguard. The chief safeguard required against
internal fire is limitation of flame spread along the underside
of the roof assembly.
Steel Deck. A steel deck roof assembly with 1-inch
(25-millimeter), mechanically anchored, plain vegetable
fiberboard insulation and a four-ply, aggregate-surfaced built-up
membrane has become the standard roof construction for both UL
and FM; the criteria for evaluating other roof-deck assemblies.