A pair of {HEAD ~ parallelly disposed vertical trollies} are attached to the side of the building on opposite sides of a plurality of {TAIL ~ emergency exits} 
A pair of { HEAD ~ parallelly disposed vertical trollies } are attached to the side of the building on opposite sides of a plurality of { TAIL ~ emergency exits }
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL