Safety lamp is the name of a variety of lamps for safety in coal-mines against coal dust, methane, or firedamp, a highly explosive mixture of natural gas apt to accumulate in them.
The best known safety lamps are the Davy lamp, invented by Sir Humphry Davy and the Geordie lamp, invented by George Stephenson. Both of those were invented in 1815 and have been superseded by the Gray, Muesler, Marsant, and other lamps; most later lamps are constructed on the principle discovered by Davy, that a flame enveloped in wire gauze of a certain fineness does not ignite firedamp.
Prior to the invention of these safety lamps, miners used canaries to alert them to the presence of gas, and barometers to tell them if atmospheric pressure was low (in which case more methane seeped out of the mine into the air). Alternative methods involved igniting the gas deliberately to cause explosions, thus evacuating the mines of the majority of explosive or easily flammable material present.
Nowadays, safety lamps are mainly electric, and traditionally mounted on miners' helmets, sealed to prevent gas penetrating the casing and being ignited by electrical sparks.