10/01/2002, HAVE WE LEARNED THE EVACUATION LESSONS? A COMMENTARY, BY JAKE PAULS,
Despite its long history as a fire safety measure in buildings, evacuation did not become a prominent topic of discussion until the September 11, 2001, attacks on the World Trade Center (WTC). Even with the events of September 11, widespread calls for reconsidering evacuation procedures for large high-rise buildings came mainly from advocacy groups such as the Skyscraper Safety Campaign (SSC) (www.skyscrapersafety.org). This particular group of families, who lost loved ones in the WTC attacks, started gaining public prominence in December 2001 with calls for a comprehensive inquiry into all aspects of the incident.
Within several months, SSC representatives used their considerable influence with the Congressional (House of Representatives) Science Committee and other organizations to include evacuation as an important area for inquiry and change. The World Trade Center Evacuation Study Initiative (www.peopleandfire.com/wtcesi/), a less visible coalition, also aided in the efforts to have evacuation issues included in the advocacy agenda. Since October 2001, this group has been advocating for and facilitating the planning of research into evacuation generally—beginning with interviews of people evacuating from the WTC.
Apparently, the low number of occupants in the towers on the morning of September 11 was the biggest factor in limiting the loss of life—if indeed "limiting" is not an obscene characterization of the carnage caused by the terrorist attacks. An hour later, the same attacks would have been even more horrific: Instead of being relatively successful for occupants below the impact areas, the evacuation—which would have involved three times as many occupants—likely would have been less complete, with many more occupants still using the exit stairs when collapse occurred.
Of course, later aircraft impacts would also have trapped or immediately killed many more people. The inability for otherwise capable people to evacuate raises the most troubling questions. The three exit stairs were too close together for there to be meaningful redundancy. Furthermore, whatever construction separation was around the stairs proved pathetically inadequate. We apparently have placed too much reliance on very limited separation—spatially between or among exits and with construction between the exit stairway spaces and the remainder of the building. Reversing the trend of reducing the effective separations will require challenging the faith many fire protection engineers have placed in automatic sprinklers, for example.
Remarkably, almost 10 years after the 1993 bombing and evacuation of the WTC, there are still significantly different estimates of the number of tower occupants who evacuated then. My best estimate of the 1993 situation is 20,000 persons in each of the Twin Towers; 40,000 total for both towers. National Fire Protection Association (NFPA) researchers' estimate, not necessarily of people evacuating, was 40,000 people working in each tower with more visiting the towers in the course of a day; however, the NFPA states that "more than 100,000 people were evacuated from the WTC plaza."2How can we realistically plan evacuation and other emergency procedures for large high-rise buildings when estimates of even the number of building occupants, let alone many other characteristics of these people, are so crudely estimated?
Assuming eight million square feet of total rentable area for the two towers, with about 270 square feet per occupant, an estimate based on some of my work on office building evacuations in Canada 30 years ago, there would be 30,000 occupants, total, in the two towers. Using the common, unrealistically conservative building code occupant load figure of one person per 100 square feet of gross area, there would be an occupant load of 80,000. According to Port Authority staff figures, reported in the special issue of Fire Engineering in December 1993 (page 11), 60,000 people worked in the WTC complex; with the two towers constituting two-thirds of the rentable area. This would suggest 40,000 persons total for the two towers. The Port Authority figures thus support my 40,000-person, total population estimate for both towers and the assumptions behind my total evacuation time estimates.
It is unfortunate that the major bomb incident and total evacuation of the World Trade Center in February 1993 will not add much to our meager collection of information about vertical evacuation. It is possible—given slightly different smoke generation and movement—that the incident could have turned out much worse than it did (in terms of catastrophic life-loss in at least one of the two 110-story towers). On the other hand, perhaps it could have been a less upsetting and injurious event for the tens of thousands of people who, collectively, spent on the order of 100,000 hours searching for information and a way out (partly by traversing some five million person-flights of stairs). We cannot even say the event was an expensive lesson in terms of new insights into evacuation; it was merely expensive.3
Such [an] information-gathering system—combined with a time-logged record of crucial communications by emergency responders and supervisory staff within the building—would be the equivalent of the black boxes and cockpit voice recorders which are commonly used in aircraft and which have been crucial in crash investigations. Given the ever-decreasing cost of the technology, why can such systems not be provided in large buildings, which could be occupied by tens of thousands of people, as opposed to the few hundreds, at most, occupying a large commercial airliner?
It is frustrating, indeed galling, that more than a year after September 11, 2001, such interviews of a significant scientific sample of survivors have not yet begun, and the prospects of funding such interviews and the subsequent detailed analysis are very poor.
We face at least two important strategic decisions, followed by tactical design choices: Should high-rise buildings be designed and managed to facilitate a total evacuation scenario? If so, what criteria should be set for acceptable total evacuation time?
My answer to the first question is "yes." High-rise buildings should be designed and managed to facilitate a total evacuation scenario.
I do not have a ready or simple answer to the second question. It is a question I have repeatedly posed in presentations, papers, and the Society of Fire Protection Engineers Handbook chapter on "Movement of People"—always with the hope that the fire protection engineering profession (which currently effectively dictates what happens with means of egress requirements) would work on the issue.5
Disappointed before, I once again presented the question to fire protection engineers and related professionals, such as architects, at the SFPE/AIA Symposium, "Fire Protection Strategies for 21st Century Building and Fire Codes," in September 2001.6
Another criterion might be related to the relative time it takes to totally evacuate a high-rise building compared with the time a typical individual would take to descend all of its stories by stairs, say at a moderate speed of three to four stories per minute, an efficient speed typically observed in total evacuations. For the 110-story WTC towers, this would entail about 30 minutes of descent time, and I have suggested this 30-minute time as a starting point for consideration of target total evacuation times.
Using this 30-minute criterion—assuming only stairs are available for egress—the WTC towers would have required, at the lower stories, about four times more exit stair width than was available. This is based on my estimates of a total evacuation time of about 100 minutes minimum for the WTC towers, each occupied by 20,000 persons and having two 44-inch, nominal-width stairs and one 56-inch, nominal-width stair, each with relatively inferior step geometry by today's standards (see "Total Evacuation Time Estimates for Office Buildings" below).
For a hypothetical 41-story office building, the first phase—exit stair descent of up to 10 stories—would take about 10 minutes; the second phase—supervised elevator use—would begin at 15 minutes and end at 35 minutes. The 15-minute delay in beginning elevator use for evacuation allows for the arrival of firefighters, checking the usability of the elevator system, and arranging for firefighter-supervised use of certain elevators for express usage from certain floors at which evacuees would collect. If the building were evacuated by exit stairs alone, its total evacuation time would be nearly 40 minutes.
Other scenarios were also modeled—e.g., with elevator use starting five minutes into the evacuation, resulting in a 25-minute evacuation time. Conceivably, even better total evacuation times could be achieved if some occupants, beyond those in the lowest 10 stories, used stairs for all of their evacuation.
Thus, an important strategic decision to be made is the extent to which elevators would be used for egress and under what conditions such use would occur. Notably, several years have passed since 1995, when the second national symposium on the use of elevators during fires was held. At the first such symposium in 1991, some colleagues and I prepared a paper dealing explicitly with human factors, problems, and prospects involved with the use of elevators for egress.8
In 1992, NIST researchers predicted the following times required for stair and elevator use for egress in several government building.9
•For a 13-story building with four 56-inch, nominal-width stairs and five 16-passenger elevators potentially usable for egress, the minimum egress time for 2,980 occupants was predicted to be 15 minutes for evacuation by stairs alone, 24 minutes for evacuation by elevators alone, and 11 minutes for combined usage (including elevators evacuating the upper four floors).
•For an 18-story building with two 44-inch, nominal-width stairs and four 16-passenger elevators potentially usable for egress, the minimum egress time for 1,425 occupants was predicted to be 14 minutes by stairs alone, 29 minutes by elevators alone, and 12 minutes for combined usage (including elevators evacuating the upper four floors).
•For a 36-story building with two 44-inch, nominal-width stairs and three rises of four 16-passenger elevators potentially usable for egress, the minimum egress time for 3,020 occupants was predicted to be 26 minutes by stairs alone, 17 minutes by elevators alone, and 13 minutes for combined usage (including up to 65 percent usage of mid-rise and high-rise elevators by evacuees).
The researchers concluded that elevator evacuation of buildings is feasible, noting that "the potential for reduced evacuation time is generally greater for tall buildings than for shorter buildings" and that such evacuation "involves significant organizational and engineering challenges."
In effect, in terms of high-rise building egress facilities, we have been designing four-story buildings with two or three limited-width exit stairs and then placing 10-story to 100-story buildings on top of them without any increase in the number or width of exit stairs.
Many occupants of both towers of the World Trade Center, having been involved in the total evacuation of 1993, correctly judged that they should evacuate when the first jet hit the North Tower—despite an announcement in the South Tower to the contrary. An unknown proportion of them used elevators for all or part of their evacuation. An unknown number, estimated to be in the range of 3,000 to 5,000 persons in the North Tower, used stairs and, especially after several minutes into the evacuation, encountered an unknown number of heavily laden firefighters climbing up the stairs to begin fire suppression and rescue.
The 44-inch-wide stairs were traditionally believed to permit two-abreast movement, but my evacuation research some three decades ago, published in the 1980s, clearly showed this traditional assumption to be wrong.10 This led to my recommendation for the 56-inch nominal-width stair—with 48 inches clear between handrails—to be the standard preferred width for exit stairways.11 Fortunately, each tower in the World Trade Center had one such stair, Stair B, near the center of the building core. Perhaps, some day, with research, we will have evidence about its usage in the 9-11 evacuation.
Before this, as a member of the NFPA's Technical Committee on Means of Egress, I proposed the 48-inch minimum clear width between stair handrails for exit stairs serving more than 2,000 persons. This was accepted by committees and by NFPA membership for the new NFPA 5000™, Building Construction and Safety Code™; but, when appealed by the U.S. General Services Administration (GSA), with support from the Building Owners and Managers Association (BOMA), the NFPA Standards Council reversed the acceptance and rejected the change. I then petitioned the NFPA Board of Directors to reinstate the change to the wider exit stairs for the high-population stairs in the new NFPA 5000™, Building Construction and Safety Code™. It is depressing that the benefits of the wider stairs—pointed out in architectural literature dating back to the 16th century and documented by research in the 1970s and 1980s—will not be widely realized in new high-rise construction under national model codes for at least several years.
In the NFPA appeal process, the GSA representative claimed there was insufficient justification for the greater width and for the 2,000-person scoping and that this was a "very substantial technical change." Moreover, the appellant claimed that inferences to such widths facilitating evacuations, such as in the World Trade Center, "are still premature prior to a final report's being issued on the World Trade Center disaster." Finally, the appellant noted that, in the FEMA/ASCE report on the World Trade Center collapse12, the Building Performance Appraisal Team (BPAT) "felt that specific extensive technical, policy, and economic study" was needed "before any specific code change recommendations are developed." Notably, evacuation was beyond the scope of the BPAT effort, and that would not change in any "final report" of the team's study.
Regarding "economic study," if applied to a 20-story building, the proposed 27 percent wider stairs—with 37 percent better flow performance—would impact less than 0.1 percent of building area, as the wider width would only be required for the six lowest floors of the building, where the cumulative population per stair exceeded 2,000 persons. (For details on this and other issues, refer to documents on NFPA 5000, Comment 790 and Appeal 02-80(u) available at the NFPA's Web site, www.nfpa.org.)
Relevant to this article's focus on evacuation was the additional proposed new sentence—to which the NFPA committee reacted even more negatively: "Mitigating measures for catastrophic failure, some significant time after low-probability impacts, include greater capacity and redundancy of exits, taking into account total evacuation scenarios based on consideration of actual incidents of terrorism."
Apparently, the NFPA does not want users of the code and the public to be informed about what it covers and what it does not cover. So much for the public's right to know, as set out in the recently adopted Montreal Declaration on People's Right to Safety, available for downloading at www.trauma2002.com.
Only one example of what I consider an irresponsible reaction is the following statement in a recently produced guide from the Council on Tall Buildings and Urban Habitat (CTBUH, www.ctbuh.org): "In the evidence collected in the aftermath of the September 11, 2001, attacks on the World Trade Center Towers in New York City and the Pentagon outside Washington, D.C., nothing suggests that there are fundamental problems with our building codes or design and construction methods."13Comparable assertions appear in the report of the FEMA/ASCE Building Performance Appraisal Team (BPAT) report and in construction industry publications such as Engineering News Record.
Clearly from what is known so far, there are several "fundamental problems" to be addressed (including, for example, an apparent disconnect between structural design and fire protection design). As I have tried to identify in this article, there are also fundamental and detail issues to be addressed regarding evacuation procedure and exit design. As evidence that this is not an isolated opinion, it should be noted that the Institution of Structural Engineers (ISE), in the U.K., had an international working group examine such issues for its report "Safety in Tall Buildings."14 Among its recommendations: "In addition to phased evacuation for emergencies, plan for timely simultaneous evacuation of a large proportion of floors in major emergencies, including use of lifts as well as staircases." Also, addressing a fundamental issue, the ISE working group recommended that we "treat active fire protection, e.g., sprinklers, as an addition to, and not a substitute for, passive fire protection, and do not consider it for extreme events."
I have noted impediments both in my codes and standards work (especially with the NFPA) and in my observations of the building industry and the relatively weak research organizations such as NIST. Such organizations need to better serve the building industry and, more importantly, public safety.
NIST's building and fire safety resources, for example, do not even include one staff member qualified in human factors (ergonomics) to the extent of holding membership in the Human Factors and Ergonomics Society (HFES) or being certified in ergonomics (as I am with the CPE). By contrast, the U.S. National Transportation Safety Board has at least 10 such staff members, and it can be argued that this is reflected in that Board's relatively thorough examinations of all factors in aircraft crashes. If only the NTSB model were applied to post-incident studies in buildings!
Hopefully, when the National Construction Safety Team Act is implemented at NIST, there will be significant improvements in its capability to study human factors in the evacuation of large buildings. Until then, the United States must continue to rely on evacuation research from other countries, including Canada, where both the past evacuation researcher (myself) and the current one (Guylène Proulx) hold memberships in HFES and are prominent in the field of building evacuation. NIST lacks such in-house expertise and, apparently, even with the infusion of new federal government money, will not be able to afford to hire such qualified staff.
Yet another set of organizational or institutional impediments to improved understanding of evacuation of large buildings is found in academic organizations. Any research conducted with federal funds or to be published in peer-reviewed, scientific literature needs to be approved by Institutional Review Boards (IRBs). The typical, and otherwise justified, cautions about researchers' interacting with human subjects apparently are retarding the kind of extensive interviewing that should be done with WTC survivors' evacuations. It is ironic that, despite official IRB-related concerns about the interview process upsetting people, journalists and others are finding that survivors are mostly anxious to share their experiences in the WTC towers and this sharing of experience is generally therapeutic in reducing the mental health problems encountered by many after September 11.
University-created difficulties in the United States have greatly complicated, for example, having a three-university consortium from Britain (with relatively good funding from British sources) conduct interviews with WTC evacuation survivors. Institutional policies, unfortunately, are impeding instead of facilitating much-needed research into the internationally important issue of evacuation.
As I concluded in my testimony at the NIST hearing in June 2002, interviewing survivors must be a top priority, as the recollections will be lost or tainted over time. Work by journalists—such as those with The New York Times, USA Today, and PBS NOVA—underline the rich accounts survivors can provide. Our scientific understanding must go even further. It would be ironic if, years after the World Trade Center disaster, we have mainly journalistic accounts—and not proper research studies—of survivor behavior to guide our deliberations on improvements to codes and standards requirements for means of egress as well as management and operating procedures for building occupants and emergency responders.
With regard to evacuation, the tragedy of 9-11 is not only that so many people died but also that we did not learn what there was to be learned. Worse still, we appear not to be learning why or how to learn what should be learned.
Generally, we need to reconsider what kinds of flows are important in building safety. The flow of water has dominated much fire protection engineering and firefighting practice. Now, we need to focus much more attention on flows of information (as well as flows of people, the focus of much of this article).
Aside from the huge failures in information flow among emergency responders, there were the desperate attempts by those trapped above the impact areas to get information out (about their location and condition) and to get information in (about what they should do). Testimony in various public hearings, such as that held by the National Institute of Standards and Technology (NIST) on June 24, 2002, is compelling, as can be seen from the following testimony before NIST by Beverly Eckert about her telephone discussion with her trapped husband, Sean, until the moment of building collapse. Sean worked on the 98th floor of the South Tower.
Lack of communication of this policy [about blocked roof access] prevented people from making the right choice in an emergency. My husband and others were completely and tragically unaware that their only rescue option was down, so they expended critical time going up; and, in the meantime, another window of opportunity slammed shut.
I was on the phone with Sean for the last half hour of his life, beginning at 9:30 a.m. He described the situation and what escape routes he had tried, and asked me for information based on what I was seeing on TV. He was calmly and rationally trying to assess his options. I reached 911 on another phone, but a full half hour after the planes had struck they had no information to pass along.
Communication systems among the rescue teams were archaic and inadequate. Failures of communication equipment were rampant. During the hours before the towers collapsed, no constructive information was disseminated to where it could benefit anyone.
So despite advanced technology and a multitude of potential ways to transmit information to those whose lives depended on it, there was no useful information being relayed, even though many of us were in contact with those who were trapped. The technology was there, but the foresight was not.
Imagine the number of lives that would have been saved had those few who had found an escape route from the upper floors of Tower Two been able to communicate to authorities which stairwell was open. It could have been passed along to those in the tower who were in contact with the world outside. Think of it: High-tech wireless communication devices located on every emergency stairwell and fire drills that trained every occupant when and how to use them. I hope that someday this will be a reality.
Sean died because of failures in communication —Beverly Eckert, NIST testimony, June 2002
JAKE PAULS has 35 years of experience in research, codes/standards development, public health advocacy, and consulting, including 20 years at the National Research Council of Canada. He currently serves on several U.S. national committees involved with standards and model codes for building design. He represents the American Public Health Association on seven committees. Educated in architecture and certified in ergonomics, he is well known for bridging among ergonomics, public health, and the development of codes and standards for building use and safety. Much of his work is focused on stairway safety and usability, including stairway use in major evacuations such as that of the World Trade Center. He is co-director of the World Trade Center Evacuation Study Initiative and serves on the Professional Advisory Panel for the Skyscraper Safety Campaign.
EVACUATION OF PEOPLE WITH DISABILITIES
Persons with disabilities, who also experienced the emergency evacuation of the WTC in 1993, told the stories of their escape from the WTC towers September 11. An intriguing theme is that the lessons learned in 1993 facilitated their escape September 11, 2001.
One such story is from John Abruzo. When the first plane hit the tower that day, John, like others, rushed to the stairwell. However, evacuation for John would prove to be much more difficult than for the others, since he is a C5-6 quadriplegic who relies on an electric wheelchair for mobility. With the use of an emergency evacuation chair, John was able to make an escape to safety. "It took us an hour and a half to get down 69 floors."
In the first attack on the WTC in February 1993, John's evacuation took more than six hours, during which time he was carried in his electric chair (he and the chair weighed 350 pounds) from the 69th floor to the 44th floor, where he was then transferred to a stretcher and finally exited the building. John and his group exited the tower and were out of harm's way just 10 minutes before its collapse. Several other people with disabilities were also successfully evacuated with evacuation chairs.
Shortly after the 1993 bombing, a number of products and systems were purchased to aid in the evacuation and life safety of the World Trade Center occupants. The implementation of these products proved successful on 9-11; lights stayed on while John and his friends evacuated, ventilation systems in the stairwells minimized smoke infiltration, and the evacuation chairs purchased by the Port Authority became a real life-saver.
September 11 was a wake-up call for many, no less for people with disabilities. The myriad organizations advocating and representing disability groups expanded their focus on accessibility, per se, to accessibility to emergency egress, and planning.
Below are a few of the Web sites that will lead you to information on egress planning for individuals with disabilities. At the FEMA Web site (www.fema.gov), a search of U.S. Fire Administration publications will lead to a very useful, downloadable report, "Emergency Procedures for Employees with Disabilities in Office Occupancies," Pub. No. FA154. A complementary report for first responders will soon be available from FEMA.
Additional Web sites include the following: ABLEDATA: www.abledata.com; The U.S. Access Board: www.access-board.gov; Eastern Paralyzed Veterans Association (EPVA): www.epva.org; Job Accommodation Network (JAN): www.jan.org; National Organization on Disability (NOD): www.nod.org; Office of Disability Employment Policy (ODEP): www.dol.gov/odep; and Telecommunications for the Deaf, Inc. (TDI): www.tdi-online.org/.—Edwina Juillet, expert on people with disabilities, edwina@shentel.net
TOTAL EVACUATION TIME ESTIMATES FOR OFFICE BUILDINGS
The "Movement of People" chapter in the Society of Fire Protection Engineers Handbook of Fire Protection Engineering includes equations and graphs for predicting total evacuation time as a function of exit stair width and actual population. These equations and graphs are somewhat complex, as the width used in the calculations is the effective width, which is 12 inches less than the nominal stair width or about four inches less than the clear width, handrail to handrail.
The table below simplifies the time prediction process for selected actual evacuation populations per exit stair and three stair widths. For most-efficient evacuations, and for other functional reasons, stairs with nominal widths between 56 and 68 inches are recommended. The traditional 44-inch nominal width does not work very well and, contrary to traditional belief, does not readily permit two-abreast movement.
Note these are minimum times assuming that, at time zero, everyone in the building begins to evacuate simultaneously. In actual evacuations, there are delays that must be taken into account as people gather information on what is happening and what they should do about it, a topic addressed in Professor John Bryan's chapter on human behavior and, to a lesser extent, in the "Movement of People" chapter of the SFPE Handbook.
Also, in actual evacuations, exit stairs are rarely used in proportion to their evacuation capacity. Therefore, great caution must be exercised in applying this table to actual high-rise office buildings; furthermore, the table should not be used for buildings serving other than office occupancies.
Finally, moderate-quality, "7-11" step geometry is assumed for these predictions; a 71/2-inch rise and 10-inch tread depth geometry would be less efficient. (The World Trade Center stair step geometry apparently was approximately 71/2-inch rise with 91/2-inch tread depth, which would have complied with the City of New York Building Code, 1968.)
Within several months, SSC representatives used their considerable influence with the Congressional (House of Representatives) Science Committee and other organizations to include evacuation as an important area for inquiry and change. The World Trade Center Evacuation Study Initiative (www.peopleandfire.com/wtcesi/), a less visible coalition, also aided in the efforts to have evacuation issues included in the advocacy agenda. Since October 2001, this group has been advocating for and facilitating the planning of research into evacuation generally—beginning with interviews of people evacuating from the WTC.
WHAT PROGRESS HAVE WE MADE?
How effective have been these calls for much-needed research into evacuation of large high-rise buildings? To what extent have public perceptions of safety in high-rise buildings affected a few decades of engineering and regulatory reliance on limited evacuation, defend-in-place procedures for such buildings? Most generally, to what extent have we learned the evacuation lessons of the WTC? 1NUMBER OF PERSONS EVACUATED
Perhaps these questions are too complex, or maybe we will need to wait longer for the bureaucratic and other organizational systems to work. Let's make the questions even simpler. How many people evacuated from the WTC towers on September 11? Of these people, how many used exit stairs exclusively for their descent to the ground? How many used elevators exclusively (for example, in the South Tower, after the North Tower was hit but before the South Tower was hit)? How many people used a combination of stairs and elevators? We do not have well-documented answers for even these relatively simple questions; although, thanks to skilled journalists from USA Today and The New York Times, respectively, we have reasonable estimates—10,000 to 14,000 total occupants in the two towers at the time of initial impact plus the likely locations and numbers of those who died—and some insights into the activities of some who died and some who survived.Apparently, the low number of occupants in the towers on the morning of September 11 was the biggest factor in limiting the loss of life—if indeed "limiting" is not an obscene characterization of the carnage caused by the terrorist attacks. An hour later, the same attacks would have been even more horrific: Instead of being relatively successful for occupants below the impact areas, the evacuation—which would have involved three times as many occupants—likely would have been less complete, with many more occupants still using the exit stairs when collapse occurred.
Of course, later aircraft impacts would also have trapped or immediately killed many more people. The inability for otherwise capable people to evacuate raises the most troubling questions. The three exit stairs were too close together for there to be meaningful redundancy. Furthermore, whatever construction separation was around the stairs proved pathetically inadequate. We apparently have placed too much reliance on very limited separation—spatially between or among exits and with construction between the exit stairway spaces and the remainder of the building. Reversing the trend of reducing the effective separations will require challenging the faith many fire protection engineers have placed in automatic sprinklers, for example.
VARYING POPULATIONS AND ESTIMATES OF POPULATIONS
Even the relatively simple questions—about building population on September 11—will require more than one year to answer. How many years?Remarkably, almost 10 years after the 1993 bombing and evacuation of the WTC, there are still significantly different estimates of the number of tower occupants who evacuated then. My best estimate of the 1993 situation is 20,000 persons in each of the Twin Towers; 40,000 total for both towers. National Fire Protection Association (NFPA) researchers' estimate, not necessarily of people evacuating, was 40,000 people working in each tower with more visiting the towers in the course of a day; however, the NFPA states that "more than 100,000 people were evacuated from the WTC plaza."2How can we realistically plan evacuation and other emergency procedures for large high-rise buildings when estimates of even the number of building occupants, let alone many other characteristics of these people, are so crudely estimated?
Assuming eight million square feet of total rentable area for the two towers, with about 270 square feet per occupant, an estimate based on some of my work on office building evacuations in Canada 30 years ago, there would be 30,000 occupants, total, in the two towers. Using the common, unrealistically conservative building code occupant load figure of one person per 100 square feet of gross area, there would be an occupant load of 80,000. According to Port Authority staff figures, reported in the special issue of Fire Engineering in December 1993 (page 11), 60,000 people worked in the WTC complex; with the two towers constituting two-thirds of the rentable area. This would suggest 40,000 persons total for the two towers. The Port Authority figures thus support my 40,000-person, total population estimate for both towers and the assumptions behind my total evacuation time estimates.
EXPENSIVE LESSONS?
In another of the very few research-focused publications addressing aspects of the evacuation of the World Trade Center in 1993, I wrote (with italic emphasis added here):It is unfortunate that the major bomb incident and total evacuation of the World Trade Center in February 1993 will not add much to our meager collection of information about vertical evacuation. It is possible—given slightly different smoke generation and movement—that the incident could have turned out much worse than it did (in terms of catastrophic life-loss in at least one of the two 110-story towers). On the other hand, perhaps it could have been a less upsetting and injurious event for the tens of thousands of people who, collectively, spent on the order of 100,000 hours searching for information and a way out (partly by traversing some five million person-flights of stairs). We cannot even say the event was an expensive lesson in terms of new insights into evacuation; it was merely expensive.3
LOOK AND LEARN RAPIDLY, IF NOT IN REAL TIME
In the same paper, I first recommended video monitoring of the discharge areas of the exit stairs of high-rise buildings so that, in addition to getting real-time information about egress flows of evacuees and ingress movement by emergency responders, we could—within hours—examine recordings of those videos to determine the actual number of evacuees (plus many other useful quantitative data such as peak and sustained flows as well as qualitative data about the condition of the evacuees). As noted in that paper:Such [an] information-gathering system—combined with a time-logged record of crucial communications by emergency responders and supervisory staff within the building—would be the equivalent of the black boxes and cockpit voice recorders which are commonly used in aircraft and which have been crucial in crash investigations. Given the ever-decreasing cost of the technology, why can such systems not be provided in large buildings, which could be occupied by tens of thousands of people, as opposed to the few hundreds, at most, occupying a large commercial airliner?
LISTENING AND LEARNING
Incidentally, Fire Engineering was the first to cover the very limited evacuation research that was done after the 1993 bombing in the World Trade Center. Edwina Juillet, long-time advocate for life safety for people with disabilities, described initial insights from lengthy interviews with 27 individuals who were assisted in their evacuation.4 To this day, with no funding for further research—including a detailed study of the interview videotapes, which have been kept inaccessible from legitimate researchers—the Fire Engineering article is still the best preliminary account of how this important aspect of evacuation was handled. Judging from the detailed accounts people wanted to, and could, give of their evacuation experience, it is clear that listening carefully to survivors of horrific events like those in 1993 and 2001 can contribute much information needed to plan for future emergencies.It is frustrating, indeed galling, that more than a year after September 11, 2001, such interviews of a significant scientific sample of survivors have not yet begun, and the prospects of funding such interviews and the subsequent detailed analysis are very poor.
TOTAL EVACUATION OF LARGE HIGH-RISE BUILDINGS
One of the many reasons we should be studying the evacuation of the World Trade Center very carefully is that the events of 9-11 underline the need to better understand the problems and prospects of total evacuation of large high-rise buildings.We face at least two important strategic decisions, followed by tactical design choices: Should high-rise buildings be designed and managed to facilitate a total evacuation scenario? If so, what criteria should be set for acceptable total evacuation time?
My answer to the first question is "yes." High-rise buildings should be designed and managed to facilitate a total evacuation scenario.
I do not have a ready or simple answer to the second question. It is a question I have repeatedly posed in presentations, papers, and the Society of Fire Protection Engineers Handbook chapter on "Movement of People"—always with the hope that the fire protection engineering profession (which currently effectively dictates what happens with means of egress requirements) would work on the issue.5
Disappointed before, I once again presented the question to fire protection engineers and related professionals, such as architects, at the SFPE/AIA Symposium, "Fire Protection Strategies for 21st Century Building and Fire Codes," in September 2001.6
TOTAL EVACUATION TIME CRITERIA
Clearly, one extreme criterion for total evacuation time is the expected structural stability of the building when subjected to major, uncontrolled fires.Another criterion might be related to the relative time it takes to totally evacuate a high-rise building compared with the time a typical individual would take to descend all of its stories by stairs, say at a moderate speed of three to four stories per minute, an efficient speed typically observed in total evacuations. For the 110-story WTC towers, this would entail about 30 minutes of descent time, and I have suggested this 30-minute time as a starting point for consideration of target total evacuation times.
Using this 30-minute criterion—assuming only stairs are available for egress—the WTC towers would have required, at the lower stories, about four times more exit stair width than was available. This is based on my estimates of a total evacuation time of about 100 minutes minimum for the WTC towers, each occupied by 20,000 persons and having two 44-inch, nominal-width stairs and one 56-inch, nominal-width stair, each with relatively inferior step geometry by today's standards (see "Total Evacuation Time Estimates for Office Buildings" below).
USING BOTH STAIRS AND ELEVATORS FOR EGRESS
Alternatively, we need to work on strategies that utilize both stairs and elevators in a controlled fashion that makes best use of their capabilities while mitigating their shortcomings. An early analysis of such a strategy was presented in 1977 at the ITT Research Institute "Designing to Survive Severe Hazards" conference."7 It entailed 4,500 occupants' using stairs to descend to certain floors and—after system checking and fire department approval—board elevators, which then descended through blind shafts (express fashion) to the ground.For a hypothetical 41-story office building, the first phase—exit stair descent of up to 10 stories—would take about 10 minutes; the second phase—supervised elevator use—would begin at 15 minutes and end at 35 minutes. The 15-minute delay in beginning elevator use for evacuation allows for the arrival of firefighters, checking the usability of the elevator system, and arranging for firefighter-supervised use of certain elevators for express usage from certain floors at which evacuees would collect. If the building were evacuated by exit stairs alone, its total evacuation time would be nearly 40 minutes.
Other scenarios were also modeled—e.g., with elevator use starting five minutes into the evacuation, resulting in a 25-minute evacuation time. Conceivably, even better total evacuation times could be achieved if some occupants, beyond those in the lowest 10 stories, used stairs for all of their evacuation.
Thus, an important strategic decision to be made is the extent to which elevators would be used for egress and under what conditions such use would occur. Notably, several years have passed since 1995, when the second national symposium on the use of elevators during fires was held. At the first such symposium in 1991, some colleagues and I prepared a paper dealing explicitly with human factors, problems, and prospects involved with the use of elevators for egress.8
In 1992, NIST researchers predicted the following times required for stair and elevator use for egress in several government building.9
•For a 13-story building with four 56-inch, nominal-width stairs and five 16-passenger elevators potentially usable for egress, the minimum egress time for 2,980 occupants was predicted to be 15 minutes for evacuation by stairs alone, 24 minutes for evacuation by elevators alone, and 11 minutes for combined usage (including elevators evacuating the upper four floors).
•For an 18-story building with two 44-inch, nominal-width stairs and four 16-passenger elevators potentially usable for egress, the minimum egress time for 1,425 occupants was predicted to be 14 minutes by stairs alone, 29 minutes by elevators alone, and 12 minutes for combined usage (including elevators evacuating the upper four floors).
•For a 36-story building with two 44-inch, nominal-width stairs and three rises of four 16-passenger elevators potentially usable for egress, the minimum egress time for 3,020 occupants was predicted to be 26 minutes by stairs alone, 17 minutes by elevators alone, and 13 minutes for combined usage (including up to 65 percent usage of mid-rise and high-rise elevators by evacuees).
The researchers concluded that elevator evacuation of buildings is feasible, noting that "the potential for reduced evacuation time is generally greater for tall buildings than for shorter buildings" and that such evacuation "involves significant organizational and engineering challenges."
IMPEDIMENTS TO ELEVATOR USE FOR EVACUATION
Based on discussions at the 1991 and 1995 symposia and other input, it appears that a major impediment is the U. S. elevator industry's opposition to using elevators for evacuation during fires. But elevator safety is not only the responsibility of the elevator industry. With design and construction contributions by other professionals, measures should be employed to provide reliable power supplies, design for water, and compartmentalized elevator lobbies so that elevators can operate in an environment protected from fire, heat, and smoke. Impediments to using elevators more extensively for evacuation appear to be more attitudinal than technical.OCCUPANT ATTITUDES ABOUT EVACUATION PROCEDURES
With regard to attitudinal factors, the greatest topic of uncertainty—post 9-11—is the extent to which typical occupants of high-rise office buildings trust the partial-evacuation, defend-in-place assumptions built into the design of typical high-rise buildings.In effect, in terms of high-rise building egress facilities, we have been designing four-story buildings with two or three limited-width exit stairs and then placing 10-story to 100-story buildings on top of them without any increase in the number or width of exit stairs.
Many occupants of both towers of the World Trade Center, having been involved in the total evacuation of 1993, correctly judged that they should evacuate when the first jet hit the North Tower—despite an announcement in the South Tower to the contrary. An unknown proportion of them used elevators for all or part of their evacuation. An unknown number, estimated to be in the range of 3,000 to 5,000 persons in the North Tower, used stairs and, especially after several minutes into the evacuation, encountered an unknown number of heavily laden firefighters climbing up the stairs to begin fire suppression and rescue.
MANY EXIT STAIRS NOT DESIGNED FOR EFFECTIVE EGRESS OR COUNTERFLOW
As is clear in examining the photographs taken by John Labriola in his descent down one of the two narrower (44-inch-wide) stairs in the North Tower (see Fire Engineering, September 2002), the progress of evacuees was impeded by their need to crowd to the right side (outside) of the dog-leg configuration stairs. The left, inner side—with the slightly shorter travel path and better handrails—was, as in the 1993 evacuation, left more or less available for ascending emergency responders and occupants descending with injuries and people helping those with injuries.The 44-inch-wide stairs were traditionally believed to permit two-abreast movement, but my evacuation research some three decades ago, published in the 1980s, clearly showed this traditional assumption to be wrong.10 This led to my recommendation for the 56-inch nominal-width stair—with 48 inches clear between handrails—to be the standard preferred width for exit stairways.11 Fortunately, each tower in the World Trade Center had one such stair, Stair B, near the center of the building core. Perhaps, some day, with research, we will have evidence about its usage in the 9-11 evacuation.
IMPEDIMENTS TO CODE REQUIREMENTS FOR IMPROVED EXIT STAIRS
In recent months, individuals and organizations have been expressing support for greater use of the wider stairs for exit in new construction (for example, in the hearings in New York City relative to NIST's research program and the public forum about recommended changes to the New York City Building Code).Before this, as a member of the NFPA's Technical Committee on Means of Egress, I proposed the 48-inch minimum clear width between stair handrails for exit stairs serving more than 2,000 persons. This was accepted by committees and by NFPA membership for the new NFPA 5000™, Building Construction and Safety Code™; but, when appealed by the U.S. General Services Administration (GSA), with support from the Building Owners and Managers Association (BOMA), the NFPA Standards Council reversed the acceptance and rejected the change. I then petitioned the NFPA Board of Directors to reinstate the change to the wider exit stairs for the high-population stairs in the new NFPA 5000™, Building Construction and Safety Code™. It is depressing that the benefits of the wider stairs—pointed out in architectural literature dating back to the 16th century and documented by research in the 1970s and 1980s—will not be widely realized in new high-rise construction under national model codes for at least several years.
In the NFPA appeal process, the GSA representative claimed there was insufficient justification for the greater width and for the 2,000-person scoping and that this was a "very substantial technical change." Moreover, the appellant claimed that inferences to such widths facilitating evacuations, such as in the World Trade Center, "are still premature prior to a final report's being issued on the World Trade Center disaster." Finally, the appellant noted that, in the FEMA/ASCE report on the World Trade Center collapse12, the Building Performance Appraisal Team (BPAT) "felt that specific extensive technical, policy, and economic study" was needed "before any specific code change recommendations are developed." Notably, evacuation was beyond the scope of the BPAT effort, and that would not change in any "final report" of the team's study.
Regarding "economic study," if applied to a 20-story building, the proposed 27 percent wider stairs—with 37 percent better flow performance—would impact less than 0.1 percent of building area, as the wider width would only be required for the six lowest floors of the building, where the cumulative population per stair exceeded 2,000 persons. (For details on this and other issues, refer to documents on NFPA 5000, Comment 790 and Appeal 02-80(u) available at the NFPA's Web site, www.nfpa.org.)
OTHER REJECTED CHANGES TO HIGH-RISE BUILDINGS CODES
The Means of Egress Technical Committee for the new NFPA 5000 building code rejected a proposal calling for video monitoring systems for discharge areas of larger buildings (as discussed above). I also submitted a comment to clarify explicitly that the new NFPA 5000 code did not address the kinds of collapses that occurred with the WTC towers. The clarification to the code's scope was as follows: "Terrorist actions, having catastrophic consequences by way of local or global collapse, are assumed to have a probability too low to warrant extraordinary strengthening and redundancy in building structures beyond that otherwise required by this code." (The terminology about probability was similar to other scope statements already adopted in the code and dealing with natural hazards and structural design.)Relevant to this article's focus on evacuation was the additional proposed new sentence—to which the NFPA committee reacted even more negatively: "Mitigating measures for catastrophic failure, some significant time after low-probability impacts, include greater capacity and redundancy of exits, taking into account total evacuation scenarios based on consideration of actual incidents of terrorism."
Apparently, the NFPA does not want users of the code and the public to be informed about what it covers and what it does not cover. So much for the public's right to know, as set out in the recently adopted Montreal Declaration on People's Right to Safety, available for downloading at www.trauma2002.com.
REACTIONARY NATURE OF RESPONSE TO SAFETY CONCERNS
It has been remarkable that so many professionals and organizations have warned of "knee jerk" changes to codes following 9-11. In my professional opinion, it is a more irresponsible "knee jerk" reaction to discourage overdue reconsideration of code requirements, including those for means of egress.Only one example of what I consider an irresponsible reaction is the following statement in a recently produced guide from the Council on Tall Buildings and Urban Habitat (CTBUH, www.ctbuh.org): "In the evidence collected in the aftermath of the September 11, 2001, attacks on the World Trade Center Towers in New York City and the Pentagon outside Washington, D.C., nothing suggests that there are fundamental problems with our building codes or design and construction methods."13Comparable assertions appear in the report of the FEMA/ASCE Building Performance Appraisal Team (BPAT) report and in construction industry publications such as Engineering News Record.
Clearly from what is known so far, there are several "fundamental problems" to be addressed (including, for example, an apparent disconnect between structural design and fire protection design). As I have tried to identify in this article, there are also fundamental and detail issues to be addressed regarding evacuation procedure and exit design. As evidence that this is not an isolated opinion, it should be noted that the Institution of Structural Engineers (ISE), in the U.K., had an international working group examine such issues for its report "Safety in Tall Buildings."14 Among its recommendations: "In addition to phased evacuation for emergencies, plan for timely simultaneous evacuation of a large proportion of floors in major emergencies, including use of lifts as well as staircases." Also, addressing a fundamental issue, the ISE working group recommended that we "treat active fire protection, e.g., sprinklers, as an addition to, and not a substitute for, passive fire protection, and do not consider it for extreme events."
I have noted impediments both in my codes and standards work (especially with the NFPA) and in my observations of the building industry and the relatively weak research organizations such as NIST. Such organizations need to better serve the building industry and, more importantly, public safety.
NIST's building and fire safety resources, for example, do not even include one staff member qualified in human factors (ergonomics) to the extent of holding membership in the Human Factors and Ergonomics Society (HFES) or being certified in ergonomics (as I am with the CPE). By contrast, the U.S. National Transportation Safety Board has at least 10 such staff members, and it can be argued that this is reflected in that Board's relatively thorough examinations of all factors in aircraft crashes. If only the NTSB model were applied to post-incident studies in buildings!
Hopefully, when the National Construction Safety Team Act is implemented at NIST, there will be significant improvements in its capability to study human factors in the evacuation of large buildings. Until then, the United States must continue to rely on evacuation research from other countries, including Canada, where both the past evacuation researcher (myself) and the current one (Guylène Proulx) hold memberships in HFES and are prominent in the field of building evacuation. NIST lacks such in-house expertise and, apparently, even with the infusion of new federal government money, will not be able to afford to hire such qualified staff.
Yet another set of organizational or institutional impediments to improved understanding of evacuation of large buildings is found in academic organizations. Any research conducted with federal funds or to be published in peer-reviewed, scientific literature needs to be approved by Institutional Review Boards (IRBs). The typical, and otherwise justified, cautions about researchers' interacting with human subjects apparently are retarding the kind of extensive interviewing that should be done with WTC survivors' evacuations. It is ironic that, despite official IRB-related concerns about the interview process upsetting people, journalists and others are finding that survivors are mostly anxious to share their experiences in the WTC towers and this sharing of experience is generally therapeutic in reducing the mental health problems encountered by many after September 11.
University-created difficulties in the United States have greatly complicated, for example, having a three-university consortium from Britain (with relatively good funding from British sources) conduct interviews with WTC evacuation survivors. Institutional policies, unfortunately, are impeding instead of facilitating much-needed research into the internationally important issue of evacuation.
As I concluded in my testimony at the NIST hearing in June 2002, interviewing survivors must be a top priority, as the recollections will be lost or tainted over time. Work by journalists—such as those with The New York Times, USA Today, and PBS NOVA—underline the rich accounts survivors can provide. Our scientific understanding must go even further. It would be ironic if, years after the World Trade Center disaster, we have mainly journalistic accounts—and not proper research studies—of survivor behavior to guide our deliberations on improvements to codes and standards requirements for means of egress as well as management and operating procedures for building occupants and emergency responders.
With regard to evacuation, the tragedy of 9-11 is not only that so many people died but also that we did not learn what there was to be learned. Worse still, we appear not to be learning why or how to learn what should be learned.
Endnotes
- Office building evacuation is the focus of this article. For a discussion of evacuation in other types of high-rise buildings, refer to "High Rise Evacuation: A Questionable Concept," Guylène Proulx, Proceedings of 2nd International Symposium on Human Behaviour in Fire, 2001, 221-230.
- Fahy, Rita and Guylène Proulx, "A Study of Human Behavior During the World Trade Center Evacuation," NFPA Journal, March/April, 1995, 59-67.
- Pauls, Jake, "Vertical Evacuation in Large Buildings: Missed Opportunities for Research," Disaster Management, 1994; 6:3, 128-132.
- Juillet, Edwina, "Evacuating People with Disabilities," Fire Engineering, 146:12; 1993, 100-103.
- Pauls, Jake, "Movement of People." In The SFPE Handbook of Fire Protection Engineering, Second Edition. Society of Fire Protection Engineers and National Fire Protection Association, Section 3, Chapter 13, 3-263, 3-285. (In the Third Edition, Guylène Proulx is the author of this chapter.)
- Pauls, Jake, "Evacuation of Large High-Rise Buildings: Reassessing Procedures and Exit Stairway Requirements in Codes and Standards," Proceedings of Fire Protection Strategies for the 21st Century Building and Fire Codes Symposium, Society of Fire Protection Engineers, Bethesda, Md., 2002.
- Pauls, Jake, "Management and Movement of Building Occupants in Emergencies." Proceedings of Second Conference on Designing to Survive Severe Hazards, IIT Research Institute, Chicago, 1977, 103-130.
- Pauls, Jake, Edwina Juillet, and Albert Gatfield, "Elevator Use for Egress: The Human Factors, Problems, and Prospects," Proceedings of Symposium on Elevators and Fire, American Society of Mechanical Engineers, New York, 1991, 63-75.
- Klote, John, Daniel Alvord, Bernard Levin, and Norman Groner, "Feasibility and Design Considerations of Emergency Evacuation by Elevators," National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 4870, 1992.
- Pauls, Jake. "Building Evacuation: Research Findings and Recommendations." In Fires and Human Behavioured. D. Canter. (New York: John Wiley and Sons, 1980), 251-275.
- Pauls, Jake, "The Movement of People in Buildings and Design Solutions for Means of Egress," Fire Technology, 1984, 20:1, 27-47.
- "World Trade Center Building Performance Study: Data Collection, Preliminary Observations, and Recommendations," Federal Emergency Management Agency, Washington, DC, and American Society of Civil Engineers, 2002.
- Council on Tall Buildings and Urban Habitat, Building Safety Enhancement Guidebook, 2002, 7.
- "Safety in Tall Buildings," Institution of Structural Engineers, London, July 2002.
Generally, we need to reconsider what kinds of flows are important in building safety. The flow of water has dominated much fire protection engineering and firefighting practice. Now, we need to focus much more attention on flows of information (as well as flows of people, the focus of much of this article).
Aside from the huge failures in information flow among emergency responders, there were the desperate attempts by those trapped above the impact areas to get information out (about their location and condition) and to get information in (about what they should do). Testimony in various public hearings, such as that held by the National Institute of Standards and Technology (NIST) on June 24, 2002, is compelling, as can be seen from the following testimony before NIST by Beverly Eckert about her telephone discussion with her trapped husband, Sean, until the moment of building collapse. Sean worked on the 98th floor of the South Tower.
Lack of communication of this policy [about blocked roof access] prevented people from making the right choice in an emergency. My husband and others were completely and tragically unaware that their only rescue option was down, so they expended critical time going up; and, in the meantime, another window of opportunity slammed shut.
I was on the phone with Sean for the last half hour of his life, beginning at 9:30 a.m. He described the situation and what escape routes he had tried, and asked me for information based on what I was seeing on TV. He was calmly and rationally trying to assess his options. I reached 911 on another phone, but a full half hour after the planes had struck they had no information to pass along.
Communication systems among the rescue teams were archaic and inadequate. Failures of communication equipment were rampant. During the hours before the towers collapsed, no constructive information was disseminated to where it could benefit anyone.
So despite advanced technology and a multitude of potential ways to transmit information to those whose lives depended on it, there was no useful information being relayed, even though many of us were in contact with those who were trapped. The technology was there, but the foresight was not.
Imagine the number of lives that would have been saved had those few who had found an escape route from the upper floors of Tower Two been able to communicate to authorities which stairwell was open. It could have been passed along to those in the tower who were in contact with the world outside. Think of it: High-tech wireless communication devices located on every emergency stairwell and fire drills that trained every occupant when and how to use them. I hope that someday this will be a reality.
Sean died because of failures in communication —Beverly Eckert, NIST testimony, June 2002
JAKE PAULS has 35 years of experience in research, codes/standards development, public health advocacy, and consulting, including 20 years at the National Research Council of Canada. He currently serves on several U.S. national committees involved with standards and model codes for building design. He represents the American Public Health Association on seven committees. Educated in architecture and certified in ergonomics, he is well known for bridging among ergonomics, public health, and the development of codes and standards for building use and safety. Much of his work is focused on stairway safety and usability, including stairway use in major evacuations such as that of the World Trade Center. He is co-director of the World Trade Center Evacuation Study Initiative and serves on the Professional Advisory Panel for the Skyscraper Safety Campaign.
EVACUATION OF PEOPLE WITH DISABILITIES
Persons with disabilities, who also experienced the emergency evacuation of the WTC in 1993, told the stories of their escape from the WTC towers September 11. An intriguing theme is that the lessons learned in 1993 facilitated their escape September 11, 2001.
One such story is from John Abruzo. When the first plane hit the tower that day, John, like others, rushed to the stairwell. However, evacuation for John would prove to be much more difficult than for the others, since he is a C5-6 quadriplegic who relies on an electric wheelchair for mobility. With the use of an emergency evacuation chair, John was able to make an escape to safety. "It took us an hour and a half to get down 69 floors."
In the first attack on the WTC in February 1993, John's evacuation took more than six hours, during which time he was carried in his electric chair (he and the chair weighed 350 pounds) from the 69th floor to the 44th floor, where he was then transferred to a stretcher and finally exited the building. John and his group exited the tower and were out of harm's way just 10 minutes before its collapse. Several other people with disabilities were also successfully evacuated with evacuation chairs.
Shortly after the 1993 bombing, a number of products and systems were purchased to aid in the evacuation and life safety of the World Trade Center occupants. The implementation of these products proved successful on 9-11; lights stayed on while John and his friends evacuated, ventilation systems in the stairwells minimized smoke infiltration, and the evacuation chairs purchased by the Port Authority became a real life-saver.
September 11 was a wake-up call for many, no less for people with disabilities. The myriad organizations advocating and representing disability groups expanded their focus on accessibility, per se, to accessibility to emergency egress, and planning.
Below are a few of the Web sites that will lead you to information on egress planning for individuals with disabilities. At the FEMA Web site (www.fema.gov), a search of U.S. Fire Administration publications will lead to a very useful, downloadable report, "Emergency Procedures for Employees with Disabilities in Office Occupancies," Pub. No. FA154. A complementary report for first responders will soon be available from FEMA.
Additional Web sites include the following: ABLEDATA: www.abledata.com; The U.S. Access Board: www.access-board.gov; Eastern Paralyzed Veterans Association (EPVA): www.epva.org; Job Accommodation Network (JAN): www.jan.org; National Organization on Disability (NOD): www.nod.org; Office of Disability Employment Policy (ODEP): www.dol.gov/odep; and Telecommunications for the Deaf, Inc. (TDI): www.tdi-online.org/.—Edwina Juillet, expert on people with disabilities, edwina@shentel.net
TOTAL EVACUATION TIME ESTIMATES FOR OFFICE BUILDINGS
The "Movement of People" chapter in the Society of Fire Protection Engineers Handbook of Fire Protection Engineering includes equations and graphs for predicting total evacuation time as a function of exit stair width and actual population. These equations and graphs are somewhat complex, as the width used in the calculations is the effective width, which is 12 inches less than the nominal stair width or about four inches less than the clear width, handrail to handrail.
The table below simplifies the time prediction process for selected actual evacuation populations per exit stair and three stair widths. For most-efficient evacuations, and for other functional reasons, stairs with nominal widths between 56 and 68 inches are recommended. The traditional 44-inch nominal width does not work very well and, contrary to traditional belief, does not readily permit two-abreast movement.
Note these are minimum times assuming that, at time zero, everyone in the building begins to evacuate simultaneously. In actual evacuations, there are delays that must be taken into account as people gather information on what is happening and what they should do about it, a topic addressed in Professor John Bryan's chapter on human behavior and, to a lesser extent, in the "Movement of People" chapter of the SFPE Handbook.
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Finally, moderate-quality, "7-11" step geometry is assumed for these predictions; a 71/2-inch rise and 10-inch tread depth geometry would be less efficient. (The World Trade Center stair step geometry apparently was approximately 71/2-inch rise with 91/2-inch tread depth, which would have complied with the City of New York Building Code, 1968.)
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