Methane is a colourless, odourless naturally occurring gas that is explosive/flammable at 5 to 15% volume.
Methane is usually associated with landfill sites and coal seams.
After a couple of explosions in the 1980’s (Loscoe and Abbeystead) protection against the ingress of naturally occurring methane ground gas has become part of the design of buildings and houses.
The most common methane protection system consists of ventilation and a proprietary gas membrane.