SL-08-015 -- Smoke Control and Occupant Evacuation at the World Trade Center ✓ Most Recent

This paper examines smoke control and occupant evacuation in WTC 1 and WTC 2 on September 11, 2001, focusing on the impact region and above for each tower. Approximately 2,000 individuals were at or above the area of impact in WTC 1 and WTC 2 who did not successfully evacuate. NIST found that the smoke management (smoke purge) systems in WTC 1 and WTC 2 were not initiated on September 11, 2001. Had the smoke purge sequence (required by the BCNYC for post-fire smoke venting) been initiated in WTC 1 or WTC 2, it is unlikely the system would have been capable of operation, due to damage caused by aircraft impacts. Even if fully operational, none of the hypothetical potential smoke management approaches evaluated would have prevented smoke spread given the damage caused by aircraft impact. During the events occurring on September 11, 2001, stair pressurization would have been ineffective in improving conditions for occupants trying to exit the building due to the extensive damage to the stair shafts. Installation of combination fire/smoke dampers in HVAC ductwork, which was not required in WTC 1 or WTC 2 at the time the WTC was constructed, may have acted to slow the development of hazardous conditions on the uppermost floors of the building, but would likely not have had a significant effect on the ability of occupants to egress the building due to the impassibility of the exit stairways.

Units: I-P