Consulting-Specifying Engineer - January 2008 - (Page 32) Rethinking high-rise egress, top to bottom In the wake of Sept. 11, designers devise more efficient ways to get building occupants out—and first responders in. BY SCOTT SIDDENS, Senior Editor G ood egress design was fairly simple when high-rises first became popular: Provide enough stairways and doors for people to get out, and designers were set. Not true anymore—Sept. 11 changed all that. Now engineers must think about reinforced stairways, evacuation by elevator, and mass notification systems. Engineers can’t talk about fire and life safety in high-rises these days without first addressing the issues of Sept. 11 and the subsequent report from Gaithersburg, Md.based National Institute of Standards and Technology (NIST), which analyzes disasters and provides guidelines for the future. NIST’s final report, released in April 2005, on the World Trade Center (WTC) disaster, “Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Report of the National Construction Safety Team on the Collapses of the World Trade Center Tower,” presented a list of 30 broad recommendations. Many of these recommendations involve structural issues, given the nature of the how the WTC towers collapsed, but some are germane to egress, evacuation, and mass notification: • Improve active fire protection systems to provide performance, reliability, and redundancy. Designers need to develop advanced fire alarms and communications systems that provide continuous, reliable, and accurate information on life safety conditions. • Improve the evacuation process to facilitate safe and rapid egress; methods for ensuring clear and timely emergency communications to occupants; and better occupant preparedness for evacuation during emergencies. Two recommendations in particular have to do with egress: designing tall buildings to accommodate a total building evacuation of occupants if necessary, and maximizing the remoteness of egress components such as stairways and elevators without unduly increasing travel distances. In the original WTC towers, stairways were in close proximity, with the result that all egress stairways were destroyed by a single plane impact at each tower. Tallest buildings now safer Just as you cannot avoid a discussion of the NIST report, engineers also must look at the systems that are going into the new structures on the WTC site. Because of the unprecedented expense and amount of life safety design at the new site, no other structures can compare, and the site may 32 Consulting-Specifying Engineer • JANUARY 2008
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