ty of construction sites when this interaction is a 'traffic accident' and the results are desperately ugly, only the fires on Floors 7 to 9 and 11 to 13 grew and lasted until the time of building collapse, performance-based assessment of the effects of fire on WTC 7, potential for injuries to people leaving the building, Progressive Collapse of WTC 7 - 2008 NIST Recommendations - Part 1 of 2, Pro