A flame arrester (also spelled arrestor), deflagration arrester, or flame trap is a device that stops fuel combustion by extinguishing the flame. A flame arrester (also called a deflagration arrester) functions by absorbing the heat from a flame front traveling at sub-sonic velocities, thus dropping the burning gas/air mixture below its auto-ignition temperature: consequently, the flame cannot survive. The heat is absorbed through channels (passages) designed into an element. These channels are chosen and measured as the MESG (Maximum Experimental Safe Gap) of the gas for a particular installation. These passages can be regular, like crimped metal ribbon or wire mesh or a sheet metal plate with punched holes, or irregular, such as those in random packing. Principle Flame arresters are passive devices with no moving parts. They prevent the propagation of flame from the exposed side of the unit to the protected side by the use of metal matrix creating a torturous path called a flame cell or element. All detonation flame arresters operate on the same principle: removing heat from the flame as it attempts to travel through narrow passages with walls of metal or other heat-conductive material, but unlike flame arresters, detonation flame arresters must be built to withstand extreme pressures that travel at supersonic velocities, 1,500 psi (10 MPa) at 2500 m/s is not uncommon with a group D Gas.