Combustibility

Combustibility is the property of a material that determines its ability to ignite and sustain combustion. It is a central consideration in fire safety, engineering design, and product labeling. Many building codes distinguish combustible and noncombustible materials. Flammability is related but not identical; flammability typically refers to ease of ignition and burning behavior, especially of liquids, while combustibility is used in some codes to describe broader burning potential.

For liquids, the primary criterion is the flash point—the lowest temperature at which its vapors can ignite in air. Liquids with low flash points are classified as flammable; those with higher flash points are called combustible. For solids, ignition temperature, heat of combustion, and burning rate determine combustibility, and materials may be self-heating or spontaneously combustible under certain conditions.

Measurement and standards: Noncombustibility can be assessed by tests such as ASTM E136, which determines whether a material will ignite under high-oxygen conditions. Flash point testing uses closed cup (ASTM D93) or open cup (ASTM D56) methods. Fire performance of plastics may be rated under UL 94 or related standards. In practice, measurements consider heat release, smoke generation, and flame spread.

Applications and codes: Building codes classify materials as combustible or noncombustible to regulate fire resistance, assembly construction, and occupant safety. Storage and handling of flammable and combustible liquids follow specific limits. Dusts, fibers, and aerosols may present additional classes of combustibility and explosion hazards.

See also: inflammable, autoignition, spontaneous combustion.