This figure should probably be even higher since it is difficult to be certain whether death has resulted from burns or toxic combustion products when victims are severely burned. Smoke and toxic gases and vapours usually occur together at fires and it is difficult to distinguish clearly which product of combustion is responsible for the harmful effects. Before discussing them, smoke, gas and vapour should be defined as these terms are used in the present Digest. Smoke is particulate matter consisting of very fine solid particles and condensed vapour. It constitutes most of the visible part of the products of combustion observed at a fire.
Gas is a product of combustion that remains a gas even when cooled to normal building temperatures.
Vapour is a product of combustion that is gas when produced but reverts to solid or liquid at normal temperatures. Vapours will gradually condense on cool surfaces as they migrate from the fire. Smoke will often impede the escape of occupants from a burning building and result in prolonged exposure to the harmful effects of toxic products. Toxic gases and vapours can cause death if they are present in sufficient quantities and for a sufficient time. Certain ones can also trap occupants by acting as irritants.