By John H. Klote, Ph.D., P.E., FSFPE, Michael J. Ferreira, P.E., James A. Milke, Ph.D., P.E., FSFPE | Fire Protection Engineering
The elevator pressurization systems discussed in this article are
intended to prevent smoke from flowing through an elevator shaft and
threatening life on floors remote from a fire. Elevator pressurization
is an alternative to enclosed elevator lobbies. The material in this
article is based on the treatment of pressurized elevators in SFPE’s
smoke control seminars1, 2 and a new smoke control handbook.3 This article does not address smoke control for elevator evacuation, which is discussed in the new handbook.
pressurized elevators are in buildings that have pressurized
stairwells, and the focus of this article is on both of these
pressurization systems operating together. In the rare situation where
pressurized elevators are the only pressurization smoke control system
in a building, the information in this article should be useful.
pressures produced by elevator car motion has the potential to
adversely impact the performance of a pressurized elevator system, and
this elevator piston effect should be taken into account in the design
of a pressurized elevator system. For more information about elevator
piston effect, see the smoke control handbook.3
Network analysis models are often used for design analysis of pressurization smoke control systems, and CONTAM4
is so extensively used for such analysis that it has become the de
facto standard. CONTAM was used for the simulations discussed in this
article. Generally a CONTAM analysis is needed to determine if
pressurized elevators and pressurized stairwells of a particular
building are capable of being balanced to perform as intended.
of pressurized elevators is much more complicated than design of
pressurized stairwells, but there are a number of systems that can deal
with this complexity. The reasons for this complexity are: (1) often the
building envelope is not capable of effectively handling the large
airflow resulting from both elevator and stairwell pressurization, (2)
open elevator doors on the ground floor tend to increase the flow from
the elevator shaft at the ground floor, and (3) open exterior doors on
the ground floor can cause excessive pressure differences across the
elevator shaft at the ground floor.
In most large cities, the fire service props open exterior doors when they get to a fire to speed up mobilization, and the International Building Code5
considers that elevator pressurization functions with open exterior
doors. Occupants also open some exterior doors during evacuation. In
this article, it is considered that elevator pressurization needs to
operate with a number of exterior doors open. If the system cannot also
operate as intended with all exterior doors closed, some of these doors
may need to open automatically before the elevators are pressurized. At
locations where the fire service does not prop open exterior doors, a
different approach to open exterior doors may be appropriate.
elevator pressurization systems discussed here are: (1) the basic
system, (2) the exterior vent (EV) system, (3) the floor exhaust (FE)
system, and (4) the ground floor lobby (GFL) system. The following
discussion of these systems is for buildings that also have pressurized
Thirty-six CONTAM simulations were used to study the performance of the systems in the example building of Figure 1.1
The example building was chosen to illustrate the elevator
pressurization systems mentioned above, and it was based on an actual
building to assure that it had appropriate elevator capacity. For this
reason, the example could be thought of as an update to an existing
building rather than a building designed to a specific code.
Figure 1. Floor plans of the example building for the CONTAM simulations.
the simulations, the pressure difference criteria listed in Table 1
were used, and these criteria are consistent with pressure differences
requirements in the International Building Code.5
The minimum pressure difference criteria are intended to prevent smoke
flow into the elevator shafts and stairwells. The maximum pressure
difference criteria for stairwells are intended to prevent excessive
door opening forces. The maximum pressure difference criterion for
elevators is intended to prevent the elevator doors from jamming.
the CONTAM simulations of the example building, supply air was injected
at the top of the elevator shafts, but about half the supply air was
injected at the top of the stairs and the rest at the second floor.
leakage has an impact on the performance of pressurized stairwell
systems, and various leakage values were used in the CONTAM simulations.
The leakage of exterior walls has a major impact on system performance,
and the leakage classifications of exterior walls were tight, average,
loose, and very loose.
Minimum in. H2O (pa)
Maximum in. H2O (pa)
The above criteria are for the
elevator simulations discussed in this article, and some projects may
have different criteria depending on code requirements and requirements
of specific applications.
Table 1. Pressure Differences Criteria for Elevator Pressurization Simulations5
1999, Persily studied building leakage, and found that many buildings
were relatively leaky in spite of the energy conservation concerns of
the time.6 The leakages of toilet exhausts and the HVAC
system were not explicitly included in CONTAM simulations discussed
here, but it was recognized that they are part of the leakage of the
For all the
systems, the amount of pressurization air needed depends on the leakage
of the elevator shaft walls and the elevator doors. For the simulations,
the leakage of interior walls was loose, and that of elevator doors was
about average. Relatively large floor-to-floor leakage (paths in floor
slabs and gaps between the floor slab and curtain wall) tends to even
out extremes of pressure differences across stairwells and elevator
shafts, and the simulations showed that this leakage was important for
the GFL system.
the basic system, each stairwell and elevator shaft has one or more
dedicated fans that supply pressurization air. As mentioned above, the
building envelope is not capable of effectively handling the large
airflow from both the elevators and stairwells, and this is why the
basic system does not result in successful pressurization for most
buildings. By successful pressurization it is meant that the pressure
differences across the elevator shaft (or stairwell) are within the
design minimum and maximum values of Table 1.
the basic system in the example building with average and leaky
exterior walls, it can be seen from Figure 2 that the pressure
differences across the elevator shaft at the ground floor greatly exceed
the maximum criterion. However it also can be seen that with very leaky
exteriors walls, the basic system is successfully pressurized. The air
needed for successful pressurization is 27,700 cfm (13 m3/s) for each elevator shaft and 6,560 cfm (3.1 m3/s) for each stairwell.
is expected that for relatively leaky buildings, there may be enough
wall leakage to accommodate the large amount of pressurization air
needed for elevators, and successful pressurization may be possible with
the basic system. For a specific building, analysis with CONTAM can
evaluate if the basic system is feasible. If not, the systems discussed
below should be considered.
Figure 2. Elevator pressure differences for basic system in the example building.
EXTERIOR VENT (EV) SYSTEM
idea of this system is to increase the leakage of the building such
that successful pressurization can be achieved. Because the example
building is an open plan office building, this can be done by the use of
vents in the exterior walls. For the example building (Figure 3a), the
CONTAM simulations showed that the vents can be sized to meet the design
criteria. In the example building, the EV system needed the same amount
of pressurization air as was needed with the basic system.
a building that is not open plan, the flow resistance of corridor walls
and other walls can have a negative impact on system performance. This
negative impact can be overcome by the use of ducts as shown in Figure
3b. The ducts are a path for airflow from the elevator to the outdoors
thus eliminating the impact of the corridor walls and other walls.
Figure 3. Typical floor plans of buildings with the exterior vent (EV) system.
vents should be located in a manner to minimize adverse wind effects,
and the supply intakes need to be located away from the vents to
minimize the potential for smoke feedback into the supply air. These
vents may need fire dampers depending on code requirements. The ducted
EV system can be used for other occupancies, such as hotels and
condominiums. Duct penetrations of a fire-rated wall may have fire
resistance requirements depending on code requirements.
open, exterior doors, it is not necessary to have exterior vents on the
ground floor. Because the EV system may not be able to achieve
acceptable pressurization with some or all the exterior doors closed, it
may be necessary to have some of the exterior doors open automatically
upon system activation. The number of exterior doors that need to be
opened automatically can be evaluated by the CONTAM analysis.
FLOOR EXHAUST (FE) SYSTEM
FE system deals with the building envelope issue by reducing the amount
of supply air used. In the FE system, a relatively small amount of air
is supplied to the elevator shafts and the stairwells, and the fire
floor is exhausted such that acceptable pressurization is maintained on
the fire floor where it is needed. It is common to also exhaust one or
two floors above and below the fire floor. Because the FE system only
maintains pressurization at some floors, it must be approved by the AHJ.
the example building, the FE system is shown in Figure 4a. The
simulations of this building showed that each elevator shaft needed
15,100 cfm (7.1 m3/s), and each stairwell needed 3,800 cfm (1.8 m3/s). The floor exhaust ranged from 4,800 (2.3 m3/s) to 5,400 cfm (2.5 m3/s),
depending on the particular floor being exhausted. For a building with
many interior partitions, the exhaust can be from the corridor that the
elevators and stairwells open onto as shown in Figure 4b.
with the EV system, some of the exterior doors on the ground floor may
need to open automatically upon activation of the FE system, and the
number of such doors can be evaluated by the CONTAM analysis.
Figure 4. Typical floor plans of buildings with the floor exhaust (FE) system.
GROUND FLOOR LOBBY (GFL) SYSTEM
system has an enclosed elevator lobby on the ground floor, but the
other floors do not have any enclosed elevator lobbies. This system is
the complete opposite of the normal practice of having enclosed elevator
lobbies on all floors except the ground floor, but it has the potential
for successful elevator pressurization.
can be seen from Figure 2, elevator pressurization systems have a
tendency to produce very high pressure differences across the elevator
doors at the ground floor, and an enclosed elevator lobby can reduce
this pressure difference. The GFL system often has a vent between the
enclosed lobby and the building with the intent of preventing excessive
pressure differences across the doors between the enclosed lobby and the
The criteria of Table 1
apply to the GFL system with some modifications. There is no established
criterion for the maximum pressure difference across the lobby doors,
but the pressure should not be so high as to prevent the doors from
remaining closed. This value depends on the specific doors and hardware.
For the CONTAM simulations, a maximum pressure difference for the lobby
doors was chosen as 0.35 in H2O (87 Pa), but this value
might be different for some applications. Because of the enclosed ground
floor lobby, the minimum pressure difference criterion does not apply
to the elevator doors on the ground floor.
5 shows the ground floor of the example building with the GFL system.
The pressure difference across the lobby door and the elevator door
depends on the area of the vent, and this vent needs to be adjustable to
allow for balancing during commissioning. CONTAM simulations of the GFL
system in the example building showed that the criteria can be met with
loose exterior walls, but not with tighter walls. The air supplied to
the shafts was nearly the same as that needed for the basic system and
the EV system. For the example building, the floor-to-floor leakage can
have a significant impact on the performance of a GFL system. This
leakage consists of the leakage of the floor and that of the curtain
Figure 5. Ground floor of the example building with the ground floor lobby (GFL) system.
H. Klote, Ph.D., P.E., FSFPE, is with John H. Klote, Inc., Michael J.
Ferreira, P.E., is with Hughes Associates, Inc., James A. Milke, Ph.D.,
P.E., FSFPE, is with the University of Maryland.
Klote, J.H., and Ferreira, M.J. Seminar: Smoke Control Session I— Fundamentals and Pressurization Systems, Society of Fire Protection Engineers, Bethesda, MD, 2011.
Klote, J.H. and Turnbull P.G. Seminar: Smoke Control Session I—Fundamentals and Pressurization Systems, Society of Fire Protection Engineers, October 27, Bethesda, MD, 2010.
Klote, J. H., Milke, J. A., Turnbull, P. G., Kashef, A., Ferreira, M. J. Handbook of Smoke Control Engineering, ASHRAE, Atlanta, GA, 2012. 4 Walton, G. N., Dols, W. S. CONTAM 2.
User Guide and Program Documentation,
NISTIR 7251, National Institute of Standards and Technology,
Gaithersburg, MD, 2010.
ICC, International Building Code, International Code Council, Country Club Hills, IL, 2012.
Persily, A. K. Myths about Building Envelopes, ASHRAE Journal, Vol. 41, No. 3. 1999.