The firestop prevents fire and smoke from moving through {TAIL ~ the inner passageways} of the pipes of {HEAD ~ a drainage system} by blocking the inner passageway of the pipes with a fire resistant plug  
The firestop prevents fire and smoke from moving through { TAIL ~ the inner passageways } of the pipes of { HEAD ~ a drainage system } by blocking the inner passageway of the pipes with a fire resistant plug
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH