How Does Air Get Into A Sealed Gas System – Testing vs. Theory, International Symposium on Fire Investigations Science and Technology, National Association of Fire Investigators

There are situations that occur when customers and servicemen have difficulty lighting pilots on appliances after the natural gas or propane system has been shut off or following an out-of-gas call in a propane system. The inability to light the pilot light is believed to be due to air getting into the gas system. In some circumstances customers or servicemen will purge the gas line in order to get the “air” out of the lines. Sometimes this results in flammable gas entering the structure resulting in an explosion, flash fire or fire, which causes property damage, serious injuries, and sometimes death.