The explosive range of methane is 5% to 15% by volume in air. This means a vapor/air mixture of __________.

Correct Answer: Option B — 5 percent methane by volume will give a reading of 100 percent L.E.L. on a combustible gas indicator

The Lower Explosive Limit (L.E.L.) represents the minimum concentration of vapor in air capable of ignition. By definition, 5% methane by volume is the L.E.L., which corresponds to 100% on a calibrated combustible gas indicator. Concentrations below this are too lean, while those above are too rich.