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