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