Smoke

Smoke is a mixture of very small airborne particles (aerosol) that are solid or liquid, produced by gases released during burning. It is most commonly associated with incomplete combustion, which occurs when oxygen is insufficient for all fuel to convert to carbon dioxide and water. Smoke therefore contains carbon particles, soot, and various incompletely burnt chemical compounds.

The color and odor of smoke depend on the type of fuel and combustion temperature. Wood and coal fires produce light or dark heavy smoke; oil fuels produce dark smoke with much soot; clean-burning gas produces little smoke. Smoke rises because it is warmer than the surrounding air and is therefore less dense.

How smoke forms

When fuel heats, gases are released (pyrolysis) before it ignites. If those gases do not receive enough oxygen to burn completely, some of them condense into tiny particles of carbon and tar. These particles suspended in air become what is visible as smoke. The smoke also contains gases that are invisible, such as carbon monoxide, aldehydes, and aromatic compounds.

Health effects

Breathing smoke can affect the respiratory system and lungs. Extremely small particles (known as PM2.5) can reach the lower parts of the lungs. Carbon monoxide attaches to hemoglobin in the blood and blocks oxygen uptake, and is one of the major causes of injury from household fires. People exposed to heavy indoor fuel smoke face constant exposure.

Uses and signs

Smoke is widely used intentionally: for preserving and flavoring meat and fish (smoking), for tobacco use, and as historical long-distance signaling signs. Smoke also serves as a visible sign by which fire is recognized; smoke detectors work by detecting smoke particles in the air.