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Like any other chemical process, combustion releases substances. We will see in further detail what these substances are.


Smoke is a colloidal dispersion of solid particles in a gas (most often, the atmosphere). Smoke is one of the products of combustion, especially if this takes place when oxygen is scarce. The particles dispersed in the air are the consequence of an incomplete combustion of fuel When the temperature of the smoke is still higher than 100°C, there are particles of water and other substances, like tar, carbon, or other organic compounds, inside of it. In a later phase, the temperature decreases and the steam splits from other particles, producing white smoke.  The other particles will produce black smoke. Smoke greatly irritates the respiratory tract, and it prevents breathing way before the maximum tolerable temperature for a human body is reached. Smoke can also be useful to quickly recognise the kind of fuel that caused the fire, since every fuel releases different unburned particles in the air, colouring differently the smoke. The following table shows some examples:

Colour of the smoke



Phosphorus, straw


Cellulose nitrate, gunpowder, sulfur, sulfuric acid


Paper, wood, cloth


Cooking oil


Naphtha, diluent


Tar, plastic, petrol, lubricant