Claim: In a coal mine containing highly explosive coal dust or methane, the wire mesh of a Davy lamp must be very tightly spaced; while for flame arresters (a device that stops fuel combustion by extinguishing the flame) used as a safety device, it must be protected from damage due to being dropped or struck by another object.
Evidence: In a coal mine containing highly explosive coal dust or methane, the wire mesh of a Davy lamp must be very tightly spaced. For flame arresters used as a safety device, the mesh must be protected from damage due to being dropped or struck by another object, and the mesh must be capable of rigidly retaining its shape during the propagation of a flame front. A flame arrester (also spelled arrestor), deflagration arrester, or flame trap is a device that stops fuel combustion by extinguishing the flame.