Flammable Atmospheres

Another confined space hazard is an atmosphere that is flammable, or capable of causing an explosion. This situation can be caused by flammable or combustible liquids, vapours, gases, or dust.

For an atmosphere to become flammable, there must be fuel, oxygen, and an ignition source present.

The flammable range, or flammable limits, of a combustible gas in a mixture is the measure of the limits between which the mixture can be ignited or can explode.

The lower flammable limit, or lower explosive level (LEL), describes the leanest mixture that will sustain a flame, while the upper flammable limit, or upper explosive level (UEL), describes the richest mixture that will still burn.

Certain dusts can also produce a flammable atmosphere. When the concentration of flammable or combustible dust reaches a critical level, a source of ignition can create an explosion. These dusts can come from sources such as grain, flour, wood, coal, or plastic.

There is also a hazard when the atmosphere in a confined space contains too much oxygen. This can occur when the oxygen level exceeds 23%. While oxygen itself is not flammable, it does increase the flammability of other materials, gases, and vapors. Fires in oxygen-enriched environments burn very fast and hot. Never use pure oxygen to ventilate a confined space, because an oxygen-enriched atmosphere is a fire and explosion hazard.

To learn more about Firefighter Confined Space visit our Firefighter Confined Space Entry & Rescue Online Training web page.