My dad told me years ago they used to use a hose from a trucks tailpipe to purge natural gas fumes from a cracked gas main,so it could be welded with an arc welder...the theory was the exhaust was inert gas (CO) that couldn't support combustion,and it usually worked fine...till one night when they used a old truck that needed a tune up badly,one cylinder was skipping,and it actually made the resulting explosion all the more spectacular when the main blew apart thanks to the unburnt gasoline in the exhaust and some oxogen to boot...the welder lived,but was burned badly and was deaf for weeks after the incident..he was lucky the blast tossed him away from the shrapnel of the gas pipe that blew apart..
