he ignition of an explosive gas in a tank or pipe will trigger a deflagration (explosion). If a flame front propagates through a pipe its speed will increase proportionally to the length of the pipe. A pipe length of more than 50 times its internal pipe diameter may result in a detonation, i.e. a flame front that progresses at supersonic speed. In this case the protected side needs to be protected by fitting a suitable detonation flame arrester.
