Fire
Terminology in Building Design
 There
is often confusion when it comes to fire terminology in building design.
What is the difference between fire-resistance rating and flame-spread
rating, how does a fire-resistive coating affect the fire performance of a
building material, and when can fire-retardant treated wood be used are all
questions that might need to be answered during the design process.
The following are some key definitions:
Fire-Resistance Rating: The time in hours or minutes that a material or
assembly of materials will withstand the passage of flame and the
transmission of heat when exposed to fire under specified conditions of test
and performance. (It can also be determined by extension or interpretation
of information derived from fire test results, as prescribed in the building
code.)
Fire-Retardant Coating: A fluid applied to a material, such as wood, using a
brush, roller, or sprayer, which reduces the burning characteristics of the
surface.
Fire-Retardant Treated Wood: Wood or a wood product that has had its
surface-burning characteristics, such as flame- spread, rate of fuel
contribution and density of smoke developed, reduced by pressure treating
with fire retardant chemicals.
Flame-Spread Rating: An index or classification indicating the extent of
spread of flame on the surface of a material, or an assembly of materials,
as determined in a standard fire test as prescribed in the building codes.
The important difference between flame-spread rating and fire-resistance
rating is that flame-spread deals with the propagation of flames across the
surface of a material on a wall or ceiling and the latter deals with
transmission or the spread of fire through a wall or a floor. Therefore
fire-retardant coatings and fire-retardant treatments for wood primarily
affect the flame-spread rating and not the fire-resistance rating. In a
floor or wall, each individual component contributes to the overall
fire-resistance rating of the assembly.
And finally, to dispel any myths that might still exist regarding
fire-retardant treated wood, the treatment does not make the wood
noncombustible. This idea stems from certain earlier building codes that
equated a 25 flame-spread rating to noncombustibility.
Resources:
Canadian Wood Council
(flame-spread ratings)
American Wood Council
(flame-spread ratings)
Underwriters' Laboratory
(flame-spread ratings, fire-resistance ratings and fire-retardant coatings)
Underwriters' Laboratory of
Canada (flame-spread ratings, fire-resistance ratings and fire-retardant
coatings)
Local Building codes (fire-resistance ratings and flame-spread ratings)
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