May, 2009 - Gas Meter Hazard - Jeweler Torches, PSEG. "The natural gas industry has experienced incidents in prior years where flashback from a jeweler’s torch assembly reached the gas meter, causing an ignition and rapid expansion.
Jeweler torches, normally used to perform simple welding, brazing or soldering, are set up to operate with gas/oxygen mixtures where oxygen pressure is set much higher than natural gas pressure (NG-1/4 psig; O2 -up to 70 psig). Torch flashbacks can occur when the tip of a jeweler’s torch is blocked or when oxygen is turned on prior to turning on the gas supply. As a result, oxygen will flow back through gas piping toward the meter. When the torch is ignited under this condition, a flashback can reach the gas meter and ignite an explosive gas-oxygen mixture.
Current installation guidelines (PSE&G Gray Book) and industry codes require jeweler torches to have a "Check Valve" installed on the gas line to ensure that oxygen used in the welding operation does not reach the gas meter. The absence of a check valve in the gas line may have contributed to past meter explosion incidents.
These installation guidelines apply to any hot work operation where natural gas is combined with oxygen, such as welding torches used by jewelry stores, muffler shops and auto body repair shops."