Definitions for "Methane gas"
Is formed during the decomposition of organic matter in the absence of oxygen. In the case of coal this decomposition took place when the coal was being formed.
Explosive (when highly concentrated) gas that is formed when organic materials decompose in anaerobic conditions which exist in landfills. Landfill operators must have a method of venting methane gas before it becomes volatile.
Methane is a common, naturally occurring and human-produced gas that can have serious climate change impacts when it is not captured. When captured, it can be used as a fuel. Methane produced by decomposition in landfills and through other human activities can be burned to produce energy for turbines and even fuel cells.