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