Apparatus and method for stopping the propagation of {HEAD ~ ignited flammable gas} in {TAIL ~ a conduit} 
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Apparatus and method for stopping the propagation of { HEAD ~ ignited flammable gas } in { TAIL ~ a conduit }
OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL