By: Erica Kuligowske, Fire Protection Engineer
Enginering Laboratory
National Institute of Standards and Technology
Imagine that a serious fire develops in a high-rise building, initiating a full building evacuation. With ample time before the situation becomes dangerous, all occupants immediately take note of the information provided by the fire alarm, completely comprehend the situation, and move calmly and efficiently in single file lines to their nearest exit, familiar to them from recent and regular fire drills. Since all occupants in the building are physically-fit and fully capable of efficient stair usage, they evacuate safely and quickly via the stairs, leaving them open for use by incoming firefighters.
The idealized scenario above, enshrined in building codes and emergency plans across the country, is also the mental model used by designers and building owners for full-building evacuation. Unfortunately, the reality can be quite different. Practical experience and decades of research have illustrated that evacuations are not as efficient as they are assumed to be. For example, significant lengths of time can pass while occupants discuss the seriousness of the situation before deciding that evacuation is necessary. Additionally, assuming even distributions of occupants among all available stairs and providing enough stair capacity for the largest occupant load floor (independent of the number of floors serviced by the stairs), may not provide adequate capacity if and when a full building evacuation becomes necessary.
The evacuation of One World Trade Center in 2001 provides a useful example that is far from the idealized scenario described above [Averill et al. 2005]. The plane’s impact at 8:46 am destroyed the public address system, eliminating the ability of building officials to communicate with occupants – occupants were left to make evacuation or shelter decisions amongst themselves. Some evacuated their floors immediately while others delayed evacuation for over 15 minutes. Since elevators were unavailable to occupants and firefighters, occupants were forced to traverse the stairs from floors as high as the 90th. Therefore, occupants were still descending the stairs at the same time as first responders were ascending. Also complicating stair travel were peers assisting disabled or injured individuals (sometimes even carrying people to safety) and occupants who needed to stop and rest on or just outside of the stairs during evacuation. Despite the scale of the disaster on September 11th, the problems encountered during the evacuation are far from unique.
The Engineering Laboratory (EL) at the National Institute of Standards and Technology (NIST) is conducting ongoing research to enable advances in fire fighter safety, fire ground operations, and effectiveness of the fire service to enhance fire fighting operations and equipment, fire suppression, fire investigations, and disaster response. The focus of any fire fighting operation is fire suppression and search and rescue of occupants unable to evacuate. However, interaction with and management of evacuating occupants can take significant resources as well. Improved understanding of human behavior during fire emergencies can help improve occupant response and evacuation efficiency, allowing firefighters to do their jobs as quickly, safely and efficiently as possible. The study of people during evacuations can shed light on meaningful improvements to building codes and evacuation procedures by answering the following questions: How wide should the stairs be for very tall buildings where firefighters may encounter evacuees? Should stair numbers or widths vary by building height, occupant loads, or occupant types? Who should evacuate and who should stay in place? Can we improve evacuation efficiency and emergency response by hardening elevators for occupant and firefighter use during high-rise fires? Are there other practical approaches to address the hazards? This type of research can reduce the barriers to egress for all occupants (including disabled or mobility-challenged) and improve access for firefighters performing both rescue and suppression operations.
NIST has been collecting information on how people evacuate buildings during fire drills of office and residential buildings. These data collections are specifically designed to provide a better understanding of occupant performance on stairwells to support optimal building codes and standards requirements and to build a solid technical foundation for evacuation design, planning, and modeling. As of Spring 2011, NIST has collected video data from 12 buildings in the U.S. ranging from six to 62 stories in height; ten are office buildings and two are assisted living facilities where stair descent devices were used for evacuation. In all of these buildings, occupant movement in two to four different stairwells was documented.
Prior to the start of the evacuation drill, video cameras were strategically placed at various locations inside the stairs in order to provide information on how people moved through the stairs. The video cameras were positioned out of the way of building occupants and firefighters to record an overhead view of occupant movement in the exit stair during the evacuation. Examples of the information collected from full-building evacuations include movement speeds of people down stairs, number and distribution of people within the stairs, travel distance within the stairs, time before entering in the stairwells, and door size. NIST researchers are also interested in how occupants stagger themselves over the stair geometry, body sway, body size, and the influence of firefighter counterflow on the movement speeds of both firefighters ascending the stairs and occupants descending the stairs.
In a few participating buildings, NIST also distributed a survey to building occupants to better understand their behavior before the alarm sounded, while they were on their floor, and during their stair or elevator evacuation – mainly the information not typically observable in the stairway videos. The survey is also used to obtain information on occupant characteristics (such as gender, age, abilities, and management or fire safety role in the building), previous fire safety education and training, previous experience in fire evacuations, and awareness of the event in order to relate these factors to the decisions made and the actions performed by occupants during the building evacuation.
While there is no substitute for the value of data obtained during a real building fire crisis, the rarity of capturing that type of data necessitates that fire drill data be used as a proxy for emergency behavior [Peacock, Hoskins, and Kuligowski 2010]. A key assumption is that fire drill data can be used to approximate the response of individuals in an actual emergency [Proulx 2002]. This is, of course, dependent on whether the population is directly exposed to smoke and/or fire cues; meaning that fire drill data may best approximate the reaction and conditions experienced of those who are not close enough to the hazard to identify it as an emergency. In many high-rise evacuations, it is conceivable that a significant portion of the population would not have been exposed to significant fire cues to be able to determine the nature of the emergency, if in fact the event is a real fire emergency. Information from real emergencies can inform fire drill data collection and provide a check of the validity of fire drill data. For that reason, evacuation surveys can be tailored to evacuees of an actual fire emergency or other type of disaster to obtain information on how people responded in a real event.
NIST is providing information on its egress project via the following website: http://www.nist.gov/el/fire_research/ egress.cfm. The website contains more information than just the evacuation data collection, including a description of the ways in which information on evacuation behavior was collected, NIST publications on human behavior in fires, infrastructure of building egress, the use of elevators during fire emergencies, analysis of information on evacuation movement and behavior during fire drills, and a review of current computer models used to calculate evacuation times from buildings. Also available on this website is access to the raw, numerical data captured from video observations of five of the twelve building evacuations. Numerical information on evacuation timing throughout the building is currently provided in spreadsheet form and can be downloaded by interested individuals by filling out a brief registration form.
Finally, in addition to the evacuation website, NIST summarizes recent research related to fire service safety and effectiveness through http://www.fire.gov. Ensuring that the latest research findings used to improve fire service practices will help to ensure that the U.S. fire service can continue to deliver the high level of services our communities have come to expect.
References:
Averill, Jason D., Dennis S. Mileti, Richard D. Peacock, Erica D. Kuligowski, Norman Groner, Guylene Proulx, Paul A. Reneke and Harold E. Nelson. 2005. Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Occupant behavior, egress, and emergency communications. Report NCSTAR 1-7. Gaithersburg, MD: National Institute of Standards and Technology. (Also available at http://wtc.nist.gov/NISTNCSTAR1-7.pdf).
G. Proulx. Movement of People: The Evacuation Timing, chapter 3-13, pages 3-341 – 3-366. In The SFPE Handbook of Fire Protection Engineering. Society of Fire Protection Engineers, Bethesda, MD, third edition, 2002.
Richard D. Peacock, Hoskins, Bryan L., and Kuligowski, Erica D. 2010. Overall and Local Movement Speeds During Fire Drill Evacuations in Buildings up to 31 Stories. NIST Technical Note 1675. Gaithersburg, MD: National Institute of Standards and Technology.
