New thoughts on using elevators in skyscraper evacuations
The long-held belief that elevators in skyscrapers should not be used in evacuations during emergencies, particularly fires, is getting another look amid new research into how the World Trade Center towers collapsed on Sept. 11.
"Yes, the country is exploring the idea of using elevators in evacuations," said Dennis S. Mileti, a professor emeritus at the University of Colorado and a member of a special National Institute of Standards and Technology panel that studied the evacuation of the trade center.
Smoky conditions, power failure, malfunctioning heat sensitive door buttons and electric eyes were all things safety experts feared could make elevators death traps.
"Don't use elevators in fires is one of the most successful public education [safety] campaigns in history," added Jason D. Averill, an expert on fire safety for NIST, who agreed that elevators are getting a second look.
But in the wake of catastrophic loss of life on 9/11 and a growing trend toward taller buildings around the world, the role of elevators in mass evacuations, especially in fires, is getting serious consideration.
Just how serious is shown by recent actions by two major national organizations involved in building safety. Both the National Fire Protection Association, which provides model fire codes, and the American Society of Mechanical Engineers, which develops engineering standards, have prepared or are proposing standards for the use of elevators in high-rise evacuations.
Hundreds of fire and engineering experts are expected to attend an ASME conference in December focusing on using elevators in fires and other emergencies.
While officials at the Port Authority were guarded in remarks about the role of elevators in emergencies, a spokesman strongly suggested they are being considered in the overall evacuation plans for the new One World Trade Center tower at Ground Zero. "I would say we are giving consideration to every aspect of the building that would include life safety consideration," said Stephen Sigmund, a spokesman for the authority, when asked if the agency is considering elevators in evacuation procedures.
Sept. 11 disaster studied
The push toward elevators comes after years of analysis of the Twin Towers showed how inadequate stairs were, said Edwin Galea, a professor at the University of Greenwich in England.
All three tightly bunched and poorly protected emergency stairways in Tower One were cut at the point of impact by American Airlines Flight 11 from the 93rd to 99th floors. A computer simulation by Galea's staff showed that had just one staircase survived, everyone trapped above the impact could have escaped.
Although elevators in both towers were disabled in the attack, a NIST study of the South Tower found that in the 16 minutes before that structure was hit by United Airlines Flight 175, an estimated 3,000 people safely evacuated using the elevators.
"The [World Trade Center] incident was a wake-up call on the difficulty of undertaking full building evacuations for high-rise and super-high-rise buildings," said Galea.
As a result of its four-year study of the trade center collapse, NIST has made a number of recommendations to ensure buildings can be evacuated in emergencies such as earthquakes, tornadoes, fires or terrorist attacks. Among them are calls to strengthen elevator shafts and stairways, including making sure stairwells aren't clustered. NIST also recommended that consideration be given to "protected/hardened elevators."
Since then, independent engineering and building code groups have formed task forces to come up with model building codes, which local jurisdictions can voluntarily adopt for new construction. NFPA's life safety code published in 2009 says elevators should be in "noncombustible hoistways" with fire resistant shafts separated from the building, and have power supplies that won't cut out when sprinklers are used.
Elevator industry officials back the emerging standards.
"My organization feels that our products can easily be used safely to get people out of buildings, but are ancillary to all required exits," said Brian Black, a safety consultant for the National Elevator Industry Inc., a trade group.
But permitting elevator evacuations is not the same thing as requiring them, noted professor Norman Groner of John Jay College, who also worked on the NIST study.
Codes set by cities, states
Because there is no federal building code, it is up to states and cities to come up with their own requirements. New York City requires all new high-rise construction to include impact-resistant fire stairs and spacing stairwells placed away from each other. The emergency stair requirements were among a number of major building code changes signed into law by Mayor Michael Bloomberg in 2004, said Assistant Commissioner James Colgate of the city Department of Buildings.
The city building code now also requires hardened elevator shafts and vestibules where people can wait during evacuations.
Today, while the Port Authority is not covered by the city building code, the new One World Trade Center tower is being constructed with the city's tougher construction requirements in mind, including those for emergency stairs, said Sigmund, the PA spokesman.
"We conform to the building code and try to exceed it and are doing so in this building," said Sigmund.
Sigmund said the elevator shafts will be within a steel core, which itself is to be shielded by a 3-foot-thick concrete core. He said stairways will also be separated by the required distance, which under the city code would amount to one-third of the diagonal of a building footprint.
But while it may be relatively easy to deal with the various electrical and mechanical issues to make elevators safer for evacuations as model codes recommend, Galea said the real test is to have people want to use them for mass evacuations. FDNY Chief Richard Tobin said the department still instructs people not to take elevators in fires unless emergency workers determine otherwise.
Eventually, as experts come to understand the human and technical aspects of emergencies, the best approach might be a blending of evacuation methods, said Galea, who said technology has to first evolve so that the elevators are considered safe.
"I feel that by exploring these issues we will better understand how elevators and stairs can be jointly used for the efficient evacuation of high rise buildings," he said.
What delayed people from leaving the Twin Towers:
Gathering personal items: 40 percent
Seeking out friend/co-worker: 33 percent
Searching for others: 26 percent
Phone calls: 18 percent
Shutting down computer: 8 percent
Waiting for direction: 7 percent
Gathering safety equipment: 5 percent
Changed shoes: 3 percent
Seeking permission to leave: 1 percent
*1,444 responses from occupants of World Trade Center towers who evacuated on Sept. 11.
SOURCE: DR. ROBYN GERSHON, MAILMAN SCHOOL OF PUBLIC HEALTH OF COLUMBIA UNIVERSITY.