Applications of Elevators for Occupant Egress in Fires

Issue 38: Applications of Elevators for Occupant Egress in Fires

By Richard W. Bukowski, P.E., FSFPE

For more than two decades, the elevator industry said that elevators may not be safe to use for occupant egress during a fire. The Safety Code for Elevators and Escalators (ASME A17.1)1 and the building codes have required signs in every elevator lobby to advise occupants to use the stairs and not elevators in case of fire. Their main concern was that elevators may entrap occupants where they might be exposed to smoke before the fire department can effect a rescue.

Following the World Trade Center attacks of September 11, 2001, it became clear that evacuation of a very tall building can take too long (evacuation of the WTC towers with the design occupant load was estimated to require 4 hours).2 Such evacuations also involve significant issues, including fatigue, people with pre-existing disabilities or injuries received in the initiating event, and unfamiliarity with the egress stair system.

Since 2004, the National Institute of Standards and Technology (NIST), American Society of Mechanical Engineers (ASME), the elevator industry, and other interested parties have been developing requirements and procedures for occupant self-evacuation elevators that will be safe to use in fires. The obvious benefits of using elevators for egress include timely evacuation of very tall buildings, the provision of an effective evacuation means for people with disabilities, and the ability to provide for egress from assembly spaces high in buildings without the need for increased stair capacity. These benefits are offset by the cost in reduced rentable space of a building. However, egress elevators have been installed in numerous tall buildings throughout the world prior to the development of requirements and procedures.

During the development process, numerous technical papers were presented at international conferences by participants discussing approaches that were under discussion and were likely to be incorporated into the final regulations.3,4,5,6 These papers became the basis for many of the arrangements that were incorporated into buildings as performance based design elements. Some existing buildings even incorporated elevator evacuation protocols that were shown to reduce total evacuation times. The result is many systems in use that do not incorporate all of the features deemed necessary and which are one-of-a-kind arrangements that may lead to confusion as the standardized systems are put in place.

Stratosphere Tower7 (Las Vegas, NV)

Figure 1. Plan of the lower two floors of the pod showing the elevators and single egress stair within the shaft.

One of the many unique buildings gracing the Las Vegas skyline is Stratosphere Tower, which is essentially an 11 story building (called the pod) atop a slim base that is nearly 800 feet (240 m) tall. The pod includes an observation deck, amusement rides, and a restaurant; and it is accessed by four, double deck elevators that run between ground level and the bottom two floors of the pod. These floors are designated as areas of refuge (sized to accommodate the entire occupant load in a noncombustible, sprinklered and pressurized space) and contain additional elevators and escalators that provide access to the other floors.

The base contains no occupied spaces, only the four elevator hoistways and a single stairway (the base is so slim that a second stairway would not be "remote"). From the outset, it was clear that the elevators would need to be the secondary means of egress, if not the primary. The project fire protection consultant began working with the Las Vegas Fire Department to develop a performance-based design that could be approved.

Because the elevators have only two stops (bottom and top) and there is no fire exposure to the hoistway through the entire base, many of the traditional concerns were not present. The double deck elevators were to be under the control of trained operators at all times, so no automatic protocol was needed. Two, separate machine rooms and a fire-rated, dedicated shaft for emergency power provided needed redundancy. One double-deck elevator would be used for fire department access, leaving three for evacuation.

In consultation with the fire department, it was decided that the performance criterion would be to evacuate the entire occupant load in one hour by using the elevator. If one elevator was out of service for maintenance or repair, the permitted occupant load (of 2600) would be reduced by one third to maintain the one hour target. Entering and exiting occupants are counted as they pass through turnstiles to control the occupant load. The design was approved and the building is nearing its 15th anniversary.


Petronas Towers (Kuala Lumpur, Malaysia)

Figure 2. Petronas Towers are connected by a skybridge at mid-height.

The Petronas Towers took the title as tallest building(s) in the world in 1998. One tower is the corporate headquarters building for Petronas Oil (the national oil company of Malaysia) and the other is leased space. The two towers are connected at the 41st and 42nd floors by a 58 m (190 ft) long skybridge. Built in accordance with a combination of US and British codes, both towers have a reinforced concrete core and contain firefighting shafts (with elevators) in accordance with BS 5588 part 5.8

When first occupied, the emergency plan was based on the assumption that the separation of the towers meant that no single event would impact both. Thus, to reduce evacuation time, the plan was for occupants of the affected tower below the skybridge to use the stairs to the level of exit discharge, and occupants at or above the skybridge to use the stairs to the skybridge, cross to the other tower, and use the elevators to grade.

Shortly after the September 11, 2001 attacks in New York, there was a bomb call to Petronas Towers that did not specify in which tower the bomb was supposed to have been placed. The authorities decided to evacuate both towers simultaneously, resulting in chaos. The bottom half of both towers evacuated without problem, but the occupants above the skybridge in Tower 1 tried to cross to Tower 2 as the occupants above the skybridge in Tower 2 tried to cross to Tower 1. The skybridge jammed and it took several hours to untangle the mess.9

In the aftermath, knowledge of the work getting underway in the US caused the authorities to consider elevator evacuation. The new plan was for the lower floors to evacuate by stair as before, but at or above the skybridge occupants were to use the elevators in their tower to grade. A drill to test the new plan resulted in total evacuation of both towers simultaneously in just 20 minutes.

Taipei 101 (Taipei, Taiwan)

Taipei 101 took the tallest building designation from Petronas Towers in 2004. Originally planned for traditional stair evacuation, a drill conducted as the building neared completion resulted in an evacuation time of about 2 hours. Aware of the activities underway in the US, the Taipei Fire Department wondered if they could do better using the elevators. They ran another drill incorporating the elevators and observed an evacuation time of 57 minutes. This became the plan used when the building opened.10

With both Petronas Towers and Taipei 101, the inclusion of evacuation by elevator was made after construction so only limited modifications could be made to enhance reliability; both buildings were constructed with concrete cores and were fully sprinklered, so expansion of emergency power to all egress elevators was considered sufficient.

One World Trade Center (New York, US)

Figure 3. One group of service cars provide fire access and egress in 1 WTC.

Designed by Skidmore, Owings and Merrill (SOM), the new One World Trade Center is currently under construction on the former WTC site. The building incorporates many design features in response to the NIST recommendations from the WTC investigation, including some elevators for occupant evacuation in fires, and a fire fighting shaft with elevator.

In the building, one group of (five) service cars is configured for use in fires; one for fire service access and four for occupant evacuation. As service cars, they are of larger capacity and stop at every floor, but the number is only a fraction of the total, so most occupants are expected to use the stairs. Until the building evacuation plans are available, it is not clear who will have access to these elevators (the disabled?) and how this will be controlled (fire wardens?). The emergency generator supplying this group is located at the top of the building so that the feeders do not need to be protected for the entire height of the building.11

Applications in Asia

The building codes in China and several other Asian countries require the provision of refuge floors every 15 or 20 floors in high rise buildings. These floors (which usually share mechanical floors) provide a space to rest, transfer between stairways, or to await assistance during an evacuation. As egress elevators have been added to the system, they frequently utilize shuttle cars (high speed and capacity cars that travel only between the refuge floor and a skylobby) to move people quickly to a safe place from which they can use stairs or another elevator to reach the level of exit discharge. The impact on reducing total egress time with and without these elevators has been estimated for several buildings to be on the order of 25% (2 hrs 15 min for stairs only versus 1 hr 45 min for stairs and elevators from the refuge floors). A limitation for people with disabilities is that they still need to use the stairs to reach a refuge floor from which they can access the elevator.

In very tall buildings, zoned elevators are generally more efficient in daily use; moving more people with less wait time and fewer elevators. Also, current elevators are limited to a maximum lift height of about 500 m (1640 ft) due primarily to the weight of the steel cables. The development of new cable materials (polyimide ropes or PU coated steel belts) should result in more height capability. Also, most very tall buildings are mixed use, separated vertically. It is common to provide separate elevator banks and lobbies for the different uses, so some elevators travel through another use zone between grade and the destination floors. This is often a section of blind shaft (no openings) which is less exposed when passing a fire floor due to the rated shaft wall, but presents issues of access for extraction of entrapped passengers should an elevator stop in the blind shaft section.

 

Middle East Applications

Most tall buildings being designed and built in the Middle East are being equipped with occupant evacuation elevators following similar requirements to those under development in the US. Some designs utilize refuge floors and some do not. In general, not all elevators are arranged for evacuation use, and the design may assume about half the occupants use elevators and half stairs. They typically provide protected lobbies to wait for the elevator with direct access to an exit stair should they decide not to wait. The emergency plans typically follow phased evacuation and they assign (trained) building staff to operate the elevators in an emergency to control the process.

The Burj Khalifa (Dubai UAE), now the tallest building in the world, incorporates some elevators for occupant egress from each of the three use areas (hotel, office, and residential). Comparison of total evacuation time by stairs alone and by stairs (55% of 19,000 occupants) and elevators estimated a 45% reduction in total evacuation time (to 90 min) with the elevators.

References

  1. Safety Code for Elevators and Escalators, ASME A17.1-2007, American Society of Mechniccal Engineers, New York, NY.
  2. Averill, J. et al., Federal Building and Fire Safety Investigation of the World Trade Center Disaster; Occupant Behavior, Egress and Emergency Communications, NIST NCSTAR 1-7, National Institute of Standards and Technology, Gaithersburg, MD, 2005.
  3. Bukowski, R.W., Emergency Egress from Ultra-Tall Buildings, Tall & Green, Typology for a Sustainable Urban Future, CTBUH, Dubai UAE, March 2008.
  4. Bukowski, R.W., Emergency Egress from Buildings, 7th International Conference on Performance-based Codes and Fire Safety Design Methods, Auckland, NZ, SFPE, 2008. and NIST TN1623, Nat Inst Stand Tech, 2009.
  5. Bukowski, R.W., Emergency Egress Strategies for Buildings, Interflam 2007. (Interflam '07). International Interflam Conference, 11th Proceedings. September 3-5, 2007, London, England, 159-168 pp, 2007.
  6. Bukowski, R. W.; Fleming, R. P.; Tubbs, J.; Marrion, C.; Dirksen, J.; Duke, C.; Prince, D.; Richardson, L. F.; Beste, D.; Stanlaske, D., Elevator Controls, NFPA Journal, Vol 100, No 2, 42-57, March/April 2006.
  7. Quiter, J. R. Application of Performance Based Concepts at the Stratosphere Tower, Las Vegas, Nevada. Rolf Jensen and Associates, Inc., Deerfield, IL. Fire Risk and Hazard Assessment Symposium. Research and Practice: Bridging the Gap. Proceedings. National Fire Protection Research Foundation. June 26-28, 1996, San Francisco, CA, 118-126 pp, 1996.
  8. BSI 5588, Part 5, Fire Precautions in the Design, Construction and Use of Buildings. Access and Facilities for Fire-fighting, British Standards Institution, London, 2004.
  9. Arliff, A., Review of Evacuation Procedures for the Petronas Twin Towers, Strategies for Performance in the Aftermath of the World Trade Center. CIB-CTBUH Conference on Tall Buildings. Proceedings. Task Group on Tall Buildings: CIB TG50. CIB Publication No. 290. October 20-23, 2003, Kuala Lumpur, Malaysia, Shafii, F.; Bukowski, R.; Klemencic, R., Editors, 35-42 pp, 2003.
  10. Hsiung, K.H., Wen, W.J., Chien, S.W., and Shih, B.J., A Research of the Elevator Evacuation Performance for Taipei 101 Financial Center, Proc 6th Int Conf on Performance-based Codes and Fire Safety Design Methods, June 14-16, 2006, Tokyo, Japan, SFPE Bethesda, MD 213-225p, 2006.
  11. Galioto, Carl, High Rise Evacuation and Life Safety, Skidmore, Owings and Merrill (NY) presentation to AIA Annual Convention, Dallas, TX, 2005.

Richard Bukowski is with Rolf Jensen and Associates

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