CH₄; carbureted hydrogen or marsh gas or combustible gases; formed by the decomposition of organic matter. The most common gas found in coal mines. It is a tasteless, colorless, nonpoisonous, and odorless gas; in mines the presence of impurities may give it a peculiar smell. It weighs less than air and may therefore form layers along the roof and occupy roof cavities. Methane will not support life or combustion; with air, however, it forms an explosive mixture, CH₄+2O₂-->CO₂.2H₂O. The gases resulting from a methane explosion are irrespirable. Methane is often referred to as combustible gases because it is the principal gas composing a mixture that, when combined with proper proportions of air, will explode when ignited. Breathing methane causes ill effects only where the air is so heavily laden with it that oxygen is supplanted.