Firedamp's a flammable gas found in coal mines. It's actually the name given to a number of flammable gases, including methane. It's particularly commonly found in areas where the coal's bituminous. Firedamp's explosive at concentrations between 4% and 16%, with most violence at around 10%, and caused much loss of life in coal mines before the invention of the Davy lamp. Even after the safety lamps were brought into common use, firedamp explosions could still occur from sparks produced when coal… (More on Firedamp)