04/12/2015
FIRE RESISTANCE
Gypsum board is an excellent fire-resistive building material. In North America, it is the most commonly used interior finish where fire resistance classifications are required. Its noncombustible core contains nearly 21% chemically combined water, as described earlier, which, under high heat, is slowly released as steam. Because steam will not exceed 212 degrees F under normal atmospheric pressure, it very effectively retards the transfer of heat and the spread of fire. Even after complete calcination, when all the water has been released from its core, gypsum board continues to serve as a heat-insulating barrier. Moreover, tests conducted in accordance with ASTM E 84 show that gypsum board has a low flame-spread index and a low smoke-density index. When installed in combination with other materials in laboratory-tested wall and ceiling assemblies, gypsum board serves to effectively protect building elements from fire for prescribed time periods.