Lower & Upper Explosive Limits for Flammable Gases and Vapors

(LEL/UEL)

Before a fire or explosion can occur, three conditions must be met simultaneously. A fuel (ie. combustible gas) and oxygen (air) must exist in certain proportions, along with an ignition source, such as a spark or flame. The ratio of fuel and oxygen that is required varies with each combustible gas or vapor.

The minimum concentration of a particular combustible gas or vapor necessary to support its combustion in air is defined as Lower Explosive Limit (LEL) for that gas. Below this level, the mixture is too lean to burn. The maximum concentration of a gas or vapor that will burn in air is defined as the Upper Explosive Limit (UEL)

Above this level, the mixture is too rich to burn. The range between the LEL and UEL is known as the flammable range for that gas or vapor.

The values shown in this table are valid only for the conditions under which they were determined (usually room temperature and atmospheric pressure using a 2 inch tube with spark ignition). The flammability range of most materials expands as temperature, pressure and container diameter increase.

Sources: Data extracted from Gas Data Book, 6th edition, copyright 1980 by Matheson Gas Products, and from Bullrtin 627, Flammability Characteristics of Combustible Gases and Vapors, copyright 1965 by U.S. Department of Interior, Bureau of Mines.All Concentrations in percent by volume.