Combustibility

Combustibility is a measure of how easily a substance will set on fire, through fire or combustion. This is an important property to consider when a substance is used for construction or is being stored. It is also important in processes that produce combustible substances as a by-product. Special precautions are usually required for substances that are easily combustible. These measures may include installation of fire sprinklers or storage remote from possible sources of ignition.

Substances with low combustibility may be selected for construction where the fire risk needs to be reduced, such as apartment buildings, houses, or offices. If combustible resources are used there is greater chance of fire accidents and deaths. Fire resistant substances are preferred for building materials and furnishings.

For an Authority Having Jurisdiction, combustibility is defined by the local code. In the National Building Code of Canada, it is defined as follows:

BS 476-4:1970 defines a test for combusibility in which 3 specimens of a material are heated in a furnace. Non-combustibile materials are defined as those for which none of the 3 specimens either:

Otherwise, the material shall be deemed combustible.

Various countries have tests for determining noncombustibility of materials. Most involve the heating of a specified quantity of the test specimen for a set duration. Usually, the material cannot support combustion and must not undergo a certain loss of mass. As a rule of thumb, concrete, steel, ceramics, in other words inorganic substances pass these tests, which permits them to be mentioned in building codes as being suitable and sometimes even mandated for use in certain applications. In Canada, for instance, firewalls must be made of concrete.

In building construction, buildings are typically divided into combustible and noncombustible ones. The code provisions and safety measures that must be taken into account in the design and construction of a building depend to a significant extent upon whether the structure is made from noncombustible elements, such as concrete, brick and structural steel, or a combustible element such as wood. Combustible structures have more stringent limits on maximum building height and area.

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