Q: What is meant by the "explosive limits" for methane?

A: Explosive Range and Flammability - A gas that will burn is said to be "flammable." Any flammable gas can explode under certain conditions. In order for a flammable gas to explode, there must be enough of the gas in the air, enough oxygen, and a source of ignition.

The range of concentrations within which a gas will explode are known as its "explosive range." Figures representing the higher and lower limits of the explosive range are expressed in percentages are are referred to as the LEL, and UEL respectively.

The amount of oxygen that must be present for an explosion to occur is also expressed as a percentage. When the necessary oxygen concentration approaches that found in normal air, the level is expressed simply as "normal air."

The explosive range of methane, for example, is 5 to 15 percent (by volume) in the presence of at least 12.1 percent oxygen.

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