NIST Technical Note 1624

Stairwell Evacuation from 

Buildings: What We Know We 

Don’t Know

Richard D. Peacock

Jason D. Averill

Erica D. Kuligowski
NIST Technical Note 1624 

Stairwell Evacuation from 

Buildings: What We Know We 

Don’t Know

Richard D. Peacock

Jason D. Averill

Erica D. Kuligowski

Fire Research Division

Building and Fire Research Laboratory

January 2009

U.S. Department of Commerce 

Carlos M. Gutierrez, Secretary 

National Institute of Standards and Technology 

Patrick D. Gallagher, Deputy Director 
Certain commercial entities, equipment, or materials may be identified in this

 document in order to describe an experimental procedure or concept adequately. Such

identification is not intended to imply recommendation or endorsement by the

National Institute of Standards and Technology, nor is it intended to imply that the

entities, materials, or equipment are necessarily the best available for the purpose. 

National Institute of Standards and Technology Technical Note 1624 

Natl. Inst. Stand. Technol. Tech. Note 1624, 16 pages (January 2009) 

CODEN: NSPUE2
Stairwell Evacuation from Buildings: What We

Know We Don’t Know

R. D. Peacock, J. D. Averill, and E. D. Kuligowski

National Institute of Standards and Technology

Gaithersburg, MD USA

Contact e-mails: richard.peacock@nist.gov, jason.averill@nist.gov, and

erica.kuligowski@nist.gov

Summary. Occupant descent down stairwells during building evacuations is typically described by measureable engineering variables such as stairwell geometry,

speed, density, and pre-evacuation delay. In turn, predictive models of building

evacuation use these variables to predict the performance of egress systems for

building design, emergency planning, or event reconstruction. This paper provides

a summary of literature values for movement speeds and compares these to several new fire drill evacuations. Movement speeds in the current study are observed

to be quite similar to the range of literature values. Perhaps most importantly

though, the typical engineering parameters are seen to explain only a small fraction of the observed variance in occupant movement speeds. This suggests that

traditional measures form an incomplete theory of people movement in stairs. Additional research to better understand the physiological and behavioural aspects of

the evacuation process and the difference between fire drill evacuations and real fire

emergencies are needed.

1 Introduction

Both before and since the World Trade Center tower collapses, there have

been numerous events where there was extensive life loss because there was

insufficient time for safe evacuation from a threatened building. While much

attention has been focused upon the more readily quantifiable input parameters to fire models such as material flammability properties, little effort has

focused on the need for a more fundamental understanding of occupant egress.

High-profile scenarios such as the World Trade Center collapse routinely lead

to public expressions requiring changes to the status quo regarding public

safety. While there are dozens of models to simulate the evacuation of occupants from a given building geometry [1], there is limited contemporary data

to support the model inputs or assumptions and even less information available to validate the models for actual emergencies. Collection and analysis of

basic evacuation data would provide a basis for building code requirements,

the practice of egress system design, and ensure robustness for analysis of

emerging issues. While some models have had extensive validation efforts by

the developers [2, 3] and others have included uncertainty in the analysis for
2 R. D. Peacock, J. D. Averill, and E. D. Kuligowski

a few limited data sets [4], there is still a significant need for independent

data on evacuation behaviour both for further development of the models as

well as independent validation efforts.

As a start to provide such data, this paper provides a review of published

data for movement speeds on egress stairwells, and an analysis of three recent

data sets involving full-building evacuation.

2 Occupant Movement in Building Evacuation

There are many factors and influences that play a role in the evacuation of

building occupants. Gwynne discusses these in his article entitled “A Review

of the Methodologies Used in the Computer Simulation of Evacuation from

the Built Environment” [5] and organizes the factors that influence evacuation

into the following categories:

– configuration of the building/enclosure

– procedures within the enclosure

– environmental factors inside the structure

– behavior of the occupants.

Configuration of the building/enclosure involves what is traditionally covered by the codes and standards, such as building layouts, number of exits,

exit widths, travel distances, etc. Gwynne proposes that occupants can commit behavioral violations to this factor in a number of ways, for instance exit

misuse, because they may be unfamiliar with the building and be without

staff guidance to aid in the evacuation. Another main issue that is frequently

studied with building configuration is the way people move throughout the

different components of the building, including both horizontal and vertical

movement. Fruin [6], Nelson and Mowrer [7], Pauls [8], and Proulx [9] have

studied this topic to understand movement through building components

such as corridors, doorways, and stairways.

Proulx [9] and others have studied the delay from initial notification of a

fire event to the beginning of evacuation, often termed pre-evacuation time,

but more accurately described as evacuation initiation delay. In three office

buildings, Proulx [9] found an average delay of 50 s. Brennan reported delays

averaging 150 s in a severe fire in a high rise office building [10]. Lord, et.

al. [4] reviews a number of sources on evacuation initiation delay. Values

reported for office occupancies average 165 s ± 71 s (uncertainty is expressed

as standard deviation).

Stairway geometry, another configuration aspect of the building, also affects movement of the occupants. Overall stairwell effectiveness in building

evacuation is impacted by a number of factors including the number and location of stairs in the buildings, the stair geometry, the number of occupants

per floor, the number of occupants descending from above a given location,
Stairwell Evacuation from Buildings 3

and any obstacles the occupants may encounter during descent (such as fire

responder counterflow). Occupant speed is affected by the number of steps,

the angle of the stairway, depth of the tread, height of the riser, and the

presence and location of handrails [5]. Proulx [9] found stairway movement

involves a complex set of behaviours, such as resting, investigation, and communication. Movement on stairways is also affected by the amount of personal

space needed per occupant, whether or not a person is carrying something

(such as a child or personal items), and the mobility of the person travelling

either up or down a flight of stairs. People sometimes become obstacles in

the evacuation process, due to exhaustion or injury.

Literature values are available for movement down stairwells. Proulx [9]

and Lord [4] reviewed data on occupant speed, flow, and density. The range

of values for occupant speed is shown in Table 1, below. For occupants with

mobility impairments, the literature ranges from 0.16 m/s to 0.76 m/s; for

occupants with no impairments, 0.49 m/s to 1.3 m/s (not including Fruins

crush load value).

3 Current Study

As part of a program to better understand occupant behaviour during building emergencies, the Building and Fire Research Laboratory at the National

Institute of Standards and Technology (NIST) has been collecting stairwell

movement data during fire drill evacuations of office buildings. These data

collections are intended to provide a better understanding of this principal

building egress feature and develop a technical foundation for future codes

and standards requirements.

While real emergency data is most desirable and might provide the most

realistic predictor of behaviour, it is not as readily available as fire drill data.

For practical purposes, fire drill data is often used to study emergency behaviour. A key assumption, consistent with most of the data presented in

section 2 of this paper, is that fire drill data can be used to approximate

the response of individuals in an actual emergency [9]. 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, as is the case in

this study, it is conceivable that a significant portion of the population has

not been exposed to enough fire cues to be certain if it is an emergency.

Information from real emergencies can inform fire drill data collections and

provide a check of the validity of fire drill data.

NIST has collected fire drill evacuation data in six high-rise buildings. The

data collection has utilized video technology in the stairwells in order to measure individual descent speeds, crowd density, stair entry time (evacuation
4 R. D. Peacock, J. D. Averill, and E. D. Kuligowski

Table 1. Occupant Movement Speeds in Stairwells

Year Movement Notes Source

Speeds

(m/s)

0.52 ± 0.24a 18 - 29 year old Variousb, from Lord et. al. [4]

0.52 ± 0.23 30 - 50 year old Variousb, from Lord et. al. [4]

0.49 ± 0.18 > 50 year old Variousb, from Lord et. al. [4]

0.16 - 0.76 Disabled occupant Variousb, from Lord et. al. [4]

1969 0.58 ± 0.15 Predtechenskii and Milinskiic [11]

1972 0.762 Maximum Fruin [6] from Pauls [8]

1972 0.6096 Moderate Fruin [6] from Pauls [8]

1972 0.4826 Optimum Fruin [6] from Pauls [8]

1972 0.2032 Crush Fruin [6] from Pauls [8]

1988 0.33 ± 0.16 Locomotion disability Boyce, et. al. [12]

1988 0.7 ± 0.26 Boyce, et. al. [12]

1995 1.1 Relatively fit Proulx [13]

1995 0.5 Proulx [13]

2001 0.2 9/11 WTC towers Averill et. al. [14]

2004 0.76 - 1.3 Varied walking angle Fujiyama [15] adapted by Hostikkad

[16]

2007 0.57 ± 0.23 Photoluminescent stairwell

markings

Proulx [17]

2007 0.64 Hostikka [16]

a - uncertainties are expressed as 1σ.

b - includes data from Fruin [6], Predtechenskii and Milinskii [11], Boyce [12], Proulx

[13], Proulx, et. al. [18], Fahy and Proulx [19] and Webber [20].

c - includes movement speeds for densities the authors define as typical for stairwell

evacuation.

d - data converted from horizontal speed to speed along incline with given stair

geometry.

delay), and stair entry floor (distance evacuated). The primary video analysis

identified the following for each occupant to facilitate these measurements:

– time each person exited the stairwell (or entered the stairwell in the case

of firefighters ascending the stairwell),

– times that each person passed each camera in the stairwell,

– density or crowdedness of that stair as indicated by the number of other

persons nearby each person as they passed by each camera in the stairwell,

and

– floor of entry for each person.

This paper focuses on the first three of these evacuations. The three buildings included in this paper ranged from six to 18 stories in height and were
Stairwell Evacuation from Buildings 5

typical office occupancies. Typically 100 to 300 people used a stairway for

evacuation. The stairs in these three buildings varied in width from 0.91 m

to 2.24 m wide. A brief description of the three buildings is shown in Table 2.

Table 2. Buildings Included in Current Study

Building 1 Building 2 Building 3

Occupancy Office Office / Office

Educational

Floors 6 11 18

Stair Widtha (m) 1.44 / 1.54b 1.22 / 1.22 0.91 / 0.91

Stair Riser (mm) 302 186 191

Stair Tread (mm) 283 238 254

Exit Width (m) 1.83 / 1.73 2.01 / 2.39 0.91 / 0.91

Evacuees 127 / 150 119 / 15 286 / 197

Evacuation Time (s) 411 442 1031

a - Full stair width including handrails.

b - Stairwell A widened to 1.68 m at the third floor. Stairwell B widened to 2.24 m

at the third floor.

Six-story Building - The large office building had with seven wings

adjoining and parallel to each other. During the drill, evacuation from two

of 14 stairwells was observed. The stairwells (Stairwell A, 1.44 m wide and

Stairwell B, 1.54 m wide) were in separate, neighbouring wings. The wings

observed were mirror images of each other, with the same number of elevators,

stairwells, and exterior exit doors. The stairwells in each wing were accessible

from all rooms and floors and led occupants into a lobby through double

doors. After travelling through the lobby, occupants travelled down a small set

of steps to a vestibule. The vestibule then led to the exterior of the building.

A total of 277 occupants were observed in the quasi-unannounced drill1 (127

in Stairwell A and 150 in Stairwell B). In Stairwell B, two groups of three

firefighters each travelled up the stairwell at 40 s and 80 s after activation of

the building fire alarm to study the impact of firefighter counterflow on the

descending occupants. Total evacuation time for this fire drill was 411 s.

Eleven-story Building - The building was an office occupancy for an educational institution housing faculty offices and research laboratories. Typical

of many office buildings, there were two stairwells, both 1.22 m wide, located

at opposite corners and accessible from all floors of the building. Both stairwells widened at the lower floors. One of the stairwells was directly adjacent

to the building elevators. The stairwells opened directly to the exterior of the

1 Occupants were told that a fire drill would take place in the near future, but

were not told when the evacuation would take place. Normal alarm procedures

were followed for the drill without further notification of the nature of the event.
6 R. D. Peacock, J. D. Averill, and E. D. Kuligowski

building. 134 occupants took part in the quasi-unannounced drill, with more

than 89 % using the stairwell adjacent to the elevators. Total evacuation time

was 442 s.

Eighteen-story Building - The building housed a business occupancy

in three wings adjoining a fourth corridor at one end of the wings. Of the

twelve 0.91 m stairwells available for egress, visual observations were made

in five. Two of these, located in separate wings, were used for this paper.

Several of the stairwells exited to the lobby area on the fifth floor through

single 0.91 m wide doorways; others continued to the ground floor and exited

directly out of the building. The lobby area exited directly to the exterior of

the building. 727 occupants participated in the quasi-unannounced fire drill

(286 in Stairwell 1 and 197 in Stairwell 12). In Stairwell 12, a total of 17

firefighters travelled up the stairwell in two groups following activation of the

building fire alarm. Total evacuation time was 1031 s.

A summary of the pre-evacuation delay times and average stairwell descent speeds is shown in Table 3. Figure 1 shows the range of individual

movement speeds for the three fire drills. For each camera location, the mean

speed is shown for occupants who were first observed evacuating at that camera location (With cameras typically located at every other floor landing, this

means entering either at the floor where the camera is located or at one floor

above the camera location). With the possible exception of the first three

floors of the 6-story building, the data generally fall within experimental

uncertainty of each other for all floors in the three buildings.

Table 3. Occupant Movement Speeds (with Standard Deviation) in Stairwells

Building Pre-evacuation Delay Time (s) Speed (m/s)

6-Story, No FF 144 ± 68 0.83 ± 0.18

6-Story, FF 140 ± 53 0.73 ± 0.26

11-Story 89 ± 54 0.62 ± 0.10

18-story, No FF 220 ± 144 0.40 ± 0.09

18-Story, FF 188 ± 93 0.54 ± 0.18

The distribution of stairwell movement speeds in the three buildings

shown in Figure 2a and the cumulative distribution functions shown in Figure

2b provide additional details of the range of speeds in the evacuations. Overall, 19 % of the occupants move slower than 0.4 m/s (and these are nearly

all in the 18 story building; less than 1 % of the occupants in the 6- and 11-

story buildings moved slower than 0.4 m/s) and 6 % move faster than 1 m/s.

Profiles for stairwells with fire fighter counterflow show a broader variation

in movement speeds than those without in both the 6- and 18- story buildings. In the six story building, occupants moved slower in the stairwell with

firefighters compared to the stairwell without firefighters while they moved
Stairwell Evacuation from Buildings 7

Fig. 1. Occupant movement speeds (with standard deviation) down stairwells in

three fire drill evacuations.

faster in the 18-story building. This is likely due to congestion in the 18-

story building stairwell from the much higher occupant load in the stairwell

without firefighters. Additional data are needed to understand and verify the

observed differences.

Comparing the recent evacuations to historical data (Figure 3) shows

these data are typically within the range of data in the literature and quite

similar to the ”optimum” or moderate movement speed of Fruin [6]. Values

for very dense evacuations (Fruin’s crush load [6], the 9/11 World Trade

Center evacuation [14] are significantly lower than both the current study and

average values from the literature. This may be indicative of the difference

between fire drill evacuations and real emergency situations or due to higher

occupant densities in the slower stairwells. While the current study does

not support recent concerns over slowing evacuation speeds resulting from

increased obesity rates and lower fitness levels, additional study is needed,

particularly to understand the impact of emergency conditions compared to

fire drill evacuations.

To investigate the underlying causes for differences in movement speeds,

a causal model was constructed to explore the components affecting occupant descent speeds in the stairwells. These included the typical engineering

parameters that can be directly measured during the evacuation as follows:
8 R. D. Peacock, J. D. Averill, and E. D. Kuligowski

a - Probability Distribution

b - Cumulative Probability Distribution

Fig. 2. Cumulative distribution function of movement speeds down stairwells in

three fire drill evacuations.
Stairwell Evacuation from Buildings 9

Fig. 3. Comparison of current study stairwell descent speeds with literature values. Where available, data points include standard deviation of average movement

speeds.

1. Delay in evacuation initiation. Delay evacuation may cause occupants to

encounter more or fewer people in the stairwell which may impact their

speed (For evacuation initiation delay, only data from the 6- and 11-story

buildings were available. Data from the 18-story building is forthcoming).

2. Distance travelled during evacuation. Evacuation from higher floors may

lead occupants to encounter more congestion in the stairwells or allow

occupants to tire more than those evacuating from lower floors leading

to lower movement speeds.

3. Presence or absence of firefighters travelling in flow counter to the descending occupants. Firefighters moving up the stairwell may impede

those descending the stairs or may encourage the occupants to move

more quickly.

4. Stairwell width. Wider stairwells may allow occupants to descend side by

side or allow faster evacuees to pass slower ones. Narrow stairs may lead

to congestion.

5. Density of people encountered during the evacuation. The presence additional persons in the stairwells nearby each evacuating occupant that

may impede the evacuation of a given building occupant by limiting the

maximum attainable speed of the occupant (For occupant density, only
10 R. D. Peacock, J. D. Averill, and E. D. Kuligowski

data from the 6- and 11-story buildings were available. Data from the

18-story building is forthcoming).

Using multivariate linear regression, we can relate these factors to movements speed in a simple regression equation

Yˆ = β1X1 + β2X2 + β3X3 + β4X4 + β5X5 + eet , (1)

where the β-coefficients, β1, β2, ... , β5 are coefficients of the regression,

X1, X2, ... , X5 are the vectors of the measured engineering parameters

above, Yˆ is the vector of measured occupant stairwell descent speed, and eet

is an added error term that includes all causes not specifically included in

the model. The magnitude and sign of the β-coefficients show the relative

strength of the relationship between each variable the measured movement

speed. That is, how important is the variation in variable X in predicting the

variation in speed relative to other variables included in the model? For this

simple model, only direct effects of each parameter on movement speed are

considered.

Figure 4 shows the results of the causal analysis. Numbers on the connector arrows in Figure 4 are the β-coefficients of the regression for each

variable. Firefighter counterflow, delay, distance travelled, and stair width

each had statistically significant impact on occupant movement speed during

the evacuation. For example, occupant evacuation speed was inversely related to the distance travelled by the occupant; the higher the starting floor,

the slower the overall movement speed. Distance is seen as twice as important as firefighter counterflow or stair width and three times as important

as pre-evacuation delay in predicting speed. Stairwell density did not vary

sufficiently in the two evacuations included to see a significant impact on

evacuation speed.

However, the most notable result of the regression is that all of these

easily measurable engineering variables together accounted for only 13 % of

the variance in occupant speed. Thus, the vast majority of the variance in

occupant evacuation speed is not explained by these typical engineering parameters used to describe stairwell flow. Physiological and behavioural factors

may be more important in determining occupant speed. While occupant demographics were not available for the current study, NIST [14] has estimated

that 6 % of the occupants who evacuated the World Trade Center towers

on September 11, 2001 reported having a mobility impairment that hindered

their evacuation. Kuligowski and Gwynne [21] discuss the need to account

for human behaviour and note that inaccurate results from simplifications

about behaviour can lead to unsafe building designs and procedures. Clearly

there is a need to better understand all the factors that impact the ability

of building occupants to take appropriate protective action in the event of a

building emergency.
Stairwell Evacuation from Buildings 11

Fig. 4. Model of occupant stairwell descent speed.

4 Conclusions

This paper has summarized the typical engineering variables used to describe

stairwell movement during building evacuations, reviewed literature values for

movement speeds, and presented data from three new fire drill evacuations.

The following conclusions are evident from the study:

– An “engineering approach” is insufficient to understand variance in occupant stairwell descent speeds. Better understanding of behavioural and

physiological factors may improve explained variance across evacuations.

– Firefighter counterflow is a small but significant impact on stairwell movement speeds (in a six story building). The effect in taller buildings is yet

to be studied.

– Understanding the context of observed evacuation drills is critically important. For the observed densities in the current study, stairwell width is

a minor parameter. At higher occupant densities, literature suggest that

stairwell width should be important [7].

– Early evidence does not support the hypothesis that people are moving

more slowly, but additional research is needed to understanding movement

speeds for a range of buildings and environmental conditions.
12 R. D. Peacock, J. D. Averill, and E. D. Kuligowski

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