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Smoke Quantity and Quality

The smoke produced at a fire, will greatly varyfrom fire to fire and from time to timein the same fire.

The plume of hot gases above a fire will have many constituent parts, which will generally fall into three groups:

1). Hot vapours and gases given off by the burning material;

2). Unburned decomposition and condensation of matter;

3). A quantity of air heated by the fire and entrained into the rising plume.

The cloud surrounding most fires is called "smoke". It consists of a well-mixed combination of these three groups and it contains gases, vapours and dispersed solid particles.

The volume of smoke produced, its density and toxicity will all depend on the material which is burning. The combustion of the solid materials in a fire involves the heating of those materials, usually by the adjacent burning material, and hot volatile combustible vapours are given off. They ignite so that above the fire a column of flames and hot smoky gases rises. Density of this column is lower than the cold surrounding air and so the column has a definite upward movement As a result, the surrounding air is entrained into the rising stream and mixes with it.

Part of this air will supply the oxygen needed for the combustion of the gas evolved by the decomposing fuels, and flames will be produced. However, because of the temperature in the plume being not high enough, and the mixing of the oxygen into it being not complete, the combustion of these gases will be incomplete and the dispersed solid particles forming the sooty component of the smoke will be produced.

At the height of the flames, the column of rising hot gases invariably contains much more air than is required for the combustion of the fuel gases. But by this time the excess air has been heated and well mixed with the hot smoky products of com­bustion, and so forms a large inseparable component of the smoke.

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