Mining Coal is a dangerous occupation. Methane is ever present in coal mines and methane is very flammable, and was often ignited by the candles that miners used for illumination. A British scientist, Sir Humphrey Davy, saved many lives with the invention of the safety lamp, illustrated below.
The lamp consists of a simple oil burner completely surrounded by a cylinder of wire gauze.
Should the atmosphere surrounding the lamp contain methane, it's presence will be indicated by the flame being surrounded by a bluish haze, caused by the methane burning when it comes into contact with the flame. The flame cannot penetrate the gauze and cause an explosion, as the gauze rapidly conducts heat away. The temperature of the flame never rises to the point at which it can cause an explosion.
The Davy Lamp has long since been replaced by electric lamps.