September 23, 2002—The September issue of Security Management, the monthly magazine published by the American Society for Industrial Security.
(ASIS), examines some of the design and safety lessons learned from the 9/11 terrorist attacks. Among the findings were the possible effects of fireproofing, stairwell design, and the load-bearing capabilities of the structure on the timing of the collapse. Among the findings:
FIREPROOFING:
Some experts say the fireproofing was too thin, and that analysis of the debris revealed that the planes impact knocked off much of the fireproofing in place, which the experts concluded hastened the structural failure of the towers. Suggestions include the need to make fireproofing more durable and to increase the amount of fireproofing in parts of the structure with a higher fire load.
Recently, the National Fire Protection Agency (NFPA) adopted a change requiring that all buildings taller than 420 feet (roughly 40 stories) increase their fireproofing for structural members.
STAIRWELLS:
The WTCs stairwells were in close proximity to each other and thus a number of potential escape routes were cut off simultaneously. The narrow width of some emergency stairwells contributed to rapid congestion, slowing escape. Suggestions include spreading out the stairwells and make them more impact resistant. (The measure needs more study as it could have negative ramifications for fire safety.)
THE TOWERS PROGRESSIVE COLLAPSE:
Eventually the Trade Towers collapsed because large portions of the building were literally removed by the planes impactsabout one-half of the columns running across the faces of both buildings were obliterated.
Some European codes specify that if a column falls, floors must have enough ties to transfer weight loads to another column, preventing a collapse. Some businesses already are asking for “collapse resistance” above and beyond current code requirements.
The article is also available online.
