A method for stopping the propagation of ignited flammable gas in a conduit according to claim 11 further comprising the step of mounting a sensor means outside the inlet end of {TAIL ~ said conduit body} for sensing the presence of said head portion of {HEAD ~ said bullet means} when said bullet means has been deployed 
A method for stopping the propagation of ignited flammable gas in a conduit according to claim 11 further comprising the step of mounting a sensor means outside the inlet end of { TAIL ~ said conduit body } for sensing the presence of said head portion of { HEAD ~ said bullet means } when said bullet means has been deployed
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