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

Combustible gas indicators are calibrated to read 100% of the Lower Explosive Limit (L.E.L.) when the gas concentration reaches the lower threshold of the explosive range. For methane, the 5% concentration represents the L.E.L.; therefore, reaching this concentration triggers a 100% L.E.L. reading on the instrument.