A method for stopping {HEAD ~ 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 said conduit body for sensing {TAIL ~ the presence} of said head portion of said bullet means when said bullet means has been deployed 
A method for stopping { HEAD ~ 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 said conduit body for sensing { TAIL ~ the presence } of said head portion of said bullet means when said bullet means has been deployed
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