Safety lamp
A safety lamp is any of several types of lamp that provides illumination in coal mines and is designed to operate in air that may contain coal dust or gases both of which are potentially flammable or explosive. Until the development of effective electric lamps in the early 1900s miners used flame lamps to provide illumination. Open flame lamps could ignite flammable gases which collected in mines, causing explosions and so safety lamps were developed to enclose the flame and prevent it from igniting the surrounding atmosphere. Flame safety lamps have been replaced in mining with sealed explosion-proof electric lights.
Background
Damps or gases
Miners have traditionally referred to the various gases encountered during mining as damps, from the Middle Low German word dampf (meaning "vapour"). Damps are variable mixtures and are historic terms.
Firedamp - Naturally occurring flammable mixtures, principally methane.
Blackdamp or Chokedamp - Nitrogen and carbon dioxide with no oxygen. Formed by complete combustion of firedamp or occurring naturally. Coal in contact with air will oxidize slowly and, if unused workings are not ventilated, pockets of blackdamp may develop. Also referred to as azotic air in some 19th-century papers.