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