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