Research Information Center

iNational Bureau of Standards

Gaithersburg, Maryland 20899

NBSIR 87-3626 NOV 2 1907

An Overview of Smoke Control

John H. Kioto

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

September 1987

Sponsored by:

General Services Administration

Public Buildings Service

Office of Real Property Development

Buildings Technology and Standards Division

NBSIR 87-3626

AN OVERVIEW OF SMOKE CONTROL

TECHNOLOGY

John H. Klote

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Fire Research

Gaithersburg, MD 20899

September 1987

Sponsored by:

General Services Administration

Public Buildings Service

Office of Real Property Development

Buildings Technology and Standards Division

U.S. DEPARTMENT OF COMMERCE, Clarence J. Brown, Acting Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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TABLE OF CONTENTS

Page

LIST OF FIGURES iv

LIST OF TABLES v

Abstract 1

1 . INTRODUCTION 1

2. CONCEPT OF SMOKE CONTROL 3

3. METHOD OF DESIGN ANALYSIS 4

4. PRESSURE DIFFERENCES 6

5. PRESSURIZED STAIRWELLS 8

6. ZONED SMOKE CONTROL 11

7. ELEVATOR SMOKE CONTROL 13

8. SMOKE PURGING CAUTION 14

9. ACTIVATION OF ZONED SMOKE CONTROL SYSTEMS 14

10. RELIABILITY OF POWER 16

11. ACCEPTANCE TESTING 16

12. SUMMARY 19

13. REFERENCES 20

iii
LIST OF FIGURES

Figure 1. Pressure profiles for pressurized stairwells in three

buildings wfth different leakage characteristics 9

Figure 2 . Some arrangements of smoke control zones . 12

iv
LIST OF TABLES

Table 1. Maximum allowable pressure differences across doors

(Inches Water Gage) 6

Table 2. Suggested Minimum Pressure Design Difference Across Smoke

Barriers (Inches Water Gage) , 8

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AN OVERVIEW OF SMOKE CONTROL TECHNOLOGY

John H. Klote

Abstract

Considerable advances in smoke control technology have occurred in the

last few decades. However, smoke control is just beginning to take its proper

place as a fire protection tool. This paper provides an overview of this

technology, including discussions of the fundamental principles, stairwell

pressurization, zoned smoke control, elevator smoke control, system activation

and acceptance testing. In addition the problems of smoke purging are

addressed.

Key words: acceptance testing, air conditioning, computer models,

elevators, smoke control, smoke movement, stairwells.

1 . INTRODUCTION

In building fire situations, smoke flows through numerous leakage paths

to locations remote from the fire, threatening life and damaging property.

These leakage paths can be open doors, gaps around closed doors, stairwells,

elevators shafts and cracks or openings in construction. As a solution to the

smoke problem, the concept of smoke control has developed. Smoke control

makes use of fans to produce pressure differences and air flows that can

control smoke movement.

The idea of pressurizing stairwells to provide a tenable environment

within egress routes during building fires was first advanced in the late

1960's. At about the same time, the concept of the "pressure sandwich"

evolved. This idea consisted of exhausting the fire floor and pressurizing

surrounding floors with the intent of limiting smoke movement to the fire

floor. The pressure sandwich concept has evolved into today's zoned smoke

control systems.

1
Research and development of smoke control technology has been conducted

worldwide, with the majority having been performed in Canada, England, France,

Japan, United States and West Germany. The American Society of Heating,

Refrigerating and Air-Conditioning Engineers (ASHRAE) published a design

manual for smoke control systems (Klote and Fothergill, 1983). This ASHRAE

Smoke Control Manual was the first document on the subject specifically

intended for use by designers. However, the manual has been used extensively

by fire protection professionals and code officials. Recently, the Smoke

Management Systems Committee of the National Fire Protection Association

(NFPA) has developed a smoke control document, NFPA 92A (1987). This document

is in the NFPA review and approval cycle, and acceptance of it will be voted

on by the NFPA membership at their annual meeting in November 1987.

The reason for this paper is to provide an overview of smoke control

technology including discussions of the advances that have occurred since the

publication of the ASHRAE Smoke Control Manual. In addition, the problems of

smoke purging are addressed. Because smoke control is still in the early

stages of development, no widely accepted view has emerged as to appropriate

applications of this new fire protection tool. Much is known about the

physical capabilities of smoke control technology, however there are still

widely divergent opinions among the experts concerning many practical points

of applying this technology. These areas of difference of opinion are

identified as such and discussed in this paper. The paper is intended for

members of the building design and construction community including HVAC

designers, fire protection engineers and code officials. Design analysis

methods are discussed in general terms only in this paper, since they are

treated in detail in the ASHRAE Smoke Control Manual. Neither this paper nor

the ASHRAE Smoke Control Manual address the problems of smoke management of

atriums and other large spaces. However, the NFPA Smoke Management Systems

Committee is developing a document to address the design of these systems.

In this paper the term "smoke" is used in accordance with the NFPA 92A

definition which states that smoke consists of the airborne solid and liquid

particulates and gases evolved when a material undergoes pyrolysis or

2
combustion, together with the quantity of air that is entrained or otherwise

mixed into the mass.

2. CONCEPT OF SMOKE CONTROL

Smoke control uses the barriers (walls, floors, doors, etc.) in

conjunction with airflows and pressure differences produced by mechanical

fans. Two basic principles of smoke control can be stated as follows:

• Airflow by itself can control smoke movement if the average

velocity is of sufficient magnitude.

• An air pressure difference across a barrier can act to control

smoke movement.

The use of air pressure differences across barriers to control smoke

movement is frequently referred to as pressurization. Pressurization results

in airflows in the small cracks and gaps in barriers , thereby preventing smoke

back- flow through these openings. Therefore, in a strict physical sense, the

second principle is a special case of the first principle. However,

considering the two principles as separate is advantageous for engineering

applications of smoke control. For a barrier with one or more large openings,

air velocity is the appropriate physical quantity for both design and testing.

When there are only small cracks, as around closed doors, designing to and

testing for air velocities is impractical. In this case, the appropriate

quantity is pressure difference.

The ASHRAE Smoke Control Manual discusses Thomas's methods of estimating

the necessary critical air velocity needed to prevent smoke back- flow through

a corridor, and this method can be used to obtain an rough estimate for an

open doorway or other large opening. This critical velocity depends on the

energy release rate and the width of the opening. A room fully involved in

fire could have an energy release rate on the order of 8x10® Btu/hr (2.4 MW),

and for this fire a critical velocity of about 800 fpm (4 m/s) would be needed

in to prevent smoke back- flow through a 3 ft (0.9 m) wide doorway. A

3
wastebasket fire might be on the order of 0.43x10® Btu/hr (125 kW) . To

protect against smoke back- flow during this smaller fire, a velocity of about

300 fpm (1.5 m/s) is needed for the same door width. Smoke from a sprinklered

fire may be considered to be near ambient temperature due to the cooling

effect of water spray. Thomas's method is not appropriate for the small

temperature differences due to a sprinklered fire. Based on an analysis by

Shaw and Whyte (1974), for a temperature difference of only 3.6 “F (2 ®C)

,

an

average velocity of 50 fpm (0.25 m/s) would be needed to prevent smoke backflow.

There are two problems with controlling smoke from unsprinklered fires

by airflow: first the air flow rates are very great requiring expensive fans,

and second the large flows can result in unacceptably large door opening

forces. (What constitutes acceptable door opening forces is discussed later.)

Therefore, airflow is not normally relied on as the primary means to achieve

smoke control in buildings. Airflow is appropriate for special applications

such as tunnels, but it is not discussed further in this paper.

Pressurization is almost always the means by which smoke control is

achieved in building situations. However, the effect of open doors in these

barriers must be considered. If doors are opened for only for the short time

for a person to escape a smoke contaminated space, the resulting small amount

of smoke infiltrating into the protected area probably will not adversely

affect the performance of the smoke control system. The potential danger of

open doors in smoke barriers needs to be evaluated for each application

keeping in mind the fire evacuation plan and the total fire protection system

of the building.

3. METHOD OF DESIGN ANALYSIS

The methods of design analysis presented in the ASHRAE Smoke Control

Manual include applications appropriate for hand held calculators, and more

complicated applications which for practical purposes require computer

analysis. Chapter 3 of the manual describes the computer program for Analysis

of Smoke Control Systems (ASCOS) . Since publication of the manual, a version

4
of ASCOS has become available for use on the IBM PC and compatible machines

.

A disk of this program plus example data files can be obtained for a modest

price from the Society of Fire Protection Engineers (60 Batterymarch Street,

Boston, MA 02110)

.

The methods of analysis in the ASHRAE Smoke Control Manual directly

incorporate the effects of friction losses in shafts , temperature differences

between the inside and outside of the building, and wind forces. The fire

effect of smoke buoyancy is not directly incorporated in the methods of

analysis. This fire effect is incorporated indirectly in the analysis by

selection of the minimum design pressure differences as input parameters for

the analysis. The selection of these pressure differences should be based on

engineering understanding of fire protection and of fire growth and

development. Later in the paper some suggested values of this parameter are

presented. Because buildings have many leakage paths, the fire effect of gas

expansion is not incorporated in the ASHRAE Smoke Control Manual methods of

analysis. For unusually tight spaces, such as bank vaults or military ships,

gas expansion should be considered.

An advantage of the analysis approach in the ASHRAE manual is that it is

simple and direct lending itself to the time and cost constraints of the dayto-day design world. Further, this method lends itself to design of systems

for which acceptance testing criteria is straight forward to establish and

apply. Because fire effects are incorporated by the selection of design

pressure differences, smoke control systems are designed for the same type of

airflow conditions for which they operate during their acceptance tests . Thus

acceptance criteria can consist of meeting specific pressure difference

requirements as described later in this paper. Clearly, this analysis

approach is superior to the rule-of-thumb methods that preceded it.

The results of two separate series of fire tests on pressurized

stairwells (DeCicco 1973, Cresci 1973, Koplon 1973) tend to support the belief

that the analysis approach of the ASHRAE manual is appropriate for design of

building smoke control systems. To evaluate the analysis approach further and

to study the interrelation between building fires and zoned smoke control

5
systems, the Center for Fire Research at the National Bureau of Standards

(NBS) is engaged in a project of full scale fires in a building scheduled for

demolition. This project has been jointly funded by the U.S. Veterans

Administration, ASHRAE, the New Jersey Bell Telephone Company, the Bell

Atlantic Telephone Company, and the U.S. West Telephone Company.

4. PRESSURE DIFFERENCES

It is appropriate to consider both a maximum and a minimum allowable

pressure difference across a barrier of a smoke control system. The values

discussed in this section are based on the recommendations in the NFPA 92A.

The maximiom allowable pressure difference should be a value that does not

result in excessive door opening forces, but, it is difficult to determine

what constitutes excessive door opening forces. The force to open a door is

the sum of the forces to overcome the door closer and to overcome the pressure

difference across the door. Clearly, a person's physical condition is a major

factor in determining a reasonable door opening force for that person.

Section 5 -2. 1.4.

of the Life Safety Code (NFPA 1985) states that the force

required to open any door in a means of egress shall not exceed 30 lb (133N)

For this limitation, maximum allowable pressure differences, calculated by the

methods presented in the ASHRAE Smoke Control Manual, are listed in table 1.

Table 1. Maximum allowable pressure differences

across doors (Inches Water Gage)

Door Closer

Force Door Width (inches)

(lb) 32 36 40 44 46

6 0.45 0.40 0.37 0.34 0.31

8 0.41 0.37 0.34 0.31 0.28

10 0.37 0.34 0.30 0.28 0.26

12 0.34 0.30 0.27 0.25 0.23

14 0.30 0.27 0.24 0.22 0.21

Notes

1. Total door opening force is 30 lb (133 N)

2. Door height is 7 ft (2.13 m)

6
Caution should be exercised in evaluating door closer force, because the

force produced by the closer when the door is closing is often different from

the force required to overcome the closer when opening the door. Many door

closers require less force in the initial portions of the opening cycle than

that required to bring the door to the full open position. The door closer

force in table 1 is the force that the door closer exerts on the door at the

very beginning of the opening cycle

.

The previously described method of design analysis directly incorporates

the effects of wind and stack action, but the fire effect is not directly

included in this design analysis. The fire effect is addressed by selection

of the minimum design pressure difference. The smoke control system should be

designed to maintain this minimum value under likely conditions of stack

effect and wind and when there is no building fire (such as during acceptance

or routine testing) . Some suggested minimum design pressure differences are

listed in table 2. The values for nonsprinklered spaces are those that will

not be overcome by the buoyancy forces of hot gases. These values were

calculated for a gas temperature of 1700 °F, for a height above the neutral

plane of 2/3 of the ceiling height, and with a safety factor of 0.03 inches

water gage. If values are desired for other temperatures or ceiling heights,

the calculation method presented in appendix A of NFPA 92A can be used.

Pressure differences produced by smoke control systems tend to fluctuate

due to the wind, fan pulsations, doors opening, doors closing, and other

factors. Short term deviations from the suggested minimum design pressure

difference may not have a serious effect on the protection provided by a smoke

control system. There is no clear cut value of allowable value of this

deviation. It depends on tightness of doors, tightness of construction,

toxicity of smoke, air flow rates, and on the volumes of spaces. Intermittent

deviations up to 50 % of the suggested minimum design pressure difference are

considered tolerable in most cases.

7
Table 2. Suggested Minimum Pressure

Design Difference Across Smoke Barriers^

(Inches Water Gage)

BLDG CEILING

DESIGN

PRESSURE

Type^2 ) HEIGHT DIFFERENCE

AS ANY .05

NS 9 ft. .10

NS 15 ft. .14

NS 21 ft. .18

NOTE 1: For design purposes, a smoke control system

should maintain these minimum pressure differences

under likely conditions of stack effect or wind.

NOTE 2: AS - Sprinklered, NS - Nonsprinklered.

5. PRESSURIZED STAIRWELLS

Many pressurized stairwells are designed and built with the goal of

providing a tenable environment within the escape route in the event of a building fire. It is obvious that a pressurized stairwell can meet its

objectives, even if a small amount of smoke infiltrates the stairwell. The

three major design concerns with pressurized stairwells are:

• nonuniform pressure differences occur over the stairwell height,

• large pressure fluctuations caused by doors being opened and

closed, and

• the location of supply air inlets and fans.

At first it might appear that the pressure differences from the

stairwell to the building would be essentially the same over the height of the

stairwell. Unfortunately, this is not the case. Figure 1 shows pressure

profiles for stairwells located in buildings with three different leakage

8
Height

Top of Stairwell

Building With

Vertical Leakage

Between Floors

Building With

Leakage Through

an Elevator

Shaft

Building

Without

Vertical

Leakage

Between

Floors

Bottom of Stairwell

Pressure Difference

Figure 1. Pressure profiles for pressurized stairwells in

three buildings with different leakage characteristics

9
characteristics, all with the same stairwell temperatures and building

temperatures. These pressure profiles represent winter conditions, that is,

an outside temperature less that the inside temperature.

For the building without vertical leakage through floors or shafts other

than the stairwell, the pressure profile is a straight line. Of course, this

leakage characteristic is not representative of many buildings. However, this

case is useful because it has been analytically solved and it represents a worst case. The analysis is presented in section 4.3 of the ASHRAE Smoke

Control Manual. It is a worst case in that it's minimum pressure difference

is less than that for other, more realistic, leakage configurations; and it's

maximum pressure difference is greater than that for these other leakage

configurations. Computer analysis can be performed to include the effects of

more complicated building leakage arrangements.

When a door is opened in a pressurized stairwell, the pressure

difference across the remaining closed doors can drop dramatically. The two

classes of design concepts that have been used to deal with this problem are

over-pressure relief and feedback control. These concepts are described in

the ASHRAE Smoke Control Manual, however, there is a difference of opinion as

to the relative merits of each. This is the subject of a research proposal

that the ASHRAE Fire and Smoke Control Committee (ASHRAE TC 5.6) has

developed. It is anticipated that this project will lead to more effective

and less complicated systems. An over-pressure relief system that has gained

attention as being simple and cost effective is the "Canadian System." The

essential features of this system are that air is supplied by one or more fans

at relatively constant flow rates and the ground floor exterior stairwell door

opens automatically upon system activation. This system eliminates the source

of the most severe pressure fluctuations, that is the opening and closing of

the exterior door.

There is concern with locating supply air inlets near the exterior

ground floor doors of the stairwell. If a supply inlet is located near this

door, the potential exists for much of the supply air to flow directly through

10
the exterior doorway when it is opened thus effectively reducing stairwell

pressurization. It is believed that locating inlets only one floor away from

exterior doors eliminates this potential.

With any stairwell pressurization system, there is the potential for

smoke feedback into the pressurized stairwell from smoke entering the

pressurization fan intake. Therefore, the capability of automatic shutdown

should be considered. The supply air intake should be separated from all

building exhausts, outlets from smoke shafts, elevator vents and other

openings through which smoke might flow in a building fire. Because hot smoke

rises, consideration should be given to locating supply air intakes below such

critical outlets. However, outdoor smoke movement that might result in smoke

feedback depends on location of the fire, location of the points of smoke

leakage from the building, wind speed and direction, and the temperature

difference between the smoke and the outside air. At present, too little

information ia available about such outdoor smoke movement to warrant general

recommendations favoring ground level intakes rather that roof- level intakes.

Some designers provide both ground level and roof- level intakes so that if

smoke is detected in one intake that fan can be shut down without loss of

stairwell pressurization.

6. ZONED SMOKE CONTROL

A Building can be divided into a number of smoke zones , each separated

from the others by partitions and floors. A smoke control zone can consist of

one floor, more than one floor, or a floor can consist of more that one smoke

zone. Some arrangements of smoke control zones are illustrated in figure 2.

In the event of a fire, pressure differences and airflows produced by

mechanical fans can be used to limit smoke spread to the zone in which the

fire initiated (the smoke zone) . The concentration of smoke in this zone may

render it untenable. Accordingly, in zoned smoke control systems, building

occupants should evacuate the zone in which the fire occurs as soon as possible after fire detection.

11
+

+

+ Smoke +

-

' Zone * - + +

+

±

(a) (b)

+

+

+

+ +

+ +

+ +

-

1 Smoke -

-

1 Zone 1 -

- - + +

+ +

+ +

+

+

+

(c) (d)

+ + +

+ + +

+ + } - + + +

+ + +

+ + +

Smoke

Zone

Note: In the Above Figures the Smoke Zone Is Indicated by a Minus Sign and

Pressurized Spaces Are Indicated by a Plus Sign. Each Floor Can Be a

Smoke Control Zone as in (a) and (b) or a Smoke Zone Can Consist of More

Than One Floor as in (c) and (d). All of the Non-Smoke Zones in a Building

May Be Pressurized as in (a) and (c) or Only Non-Smoke Zones Adjacent to

the Smoke Zone May Be Pressurized as in (b) and (d). A Smoke Zone Can

Also Be Limited to a Part of a Floor as in (e).

Figure 2 . Some arrangements of smoke control zones

12
7. ELEVATOR SMOKE CONTROL

A joint project to study elevator smoke control is being conducted by

NBS and the National Research Council of Canada (NRCC) . The intent of the

project is to extend smoke control technology to elevators in an effort to

help solve the fire evacuation problem of people who can not use stairs

because of physical disabilities. Smoke protection is one of the many

obstacles to the use of elevators for fire evacuation that are discussed by

Klote (1984), and all of the obstacles other than smoke protection can be

addressed by means of existing technology.

Elevator smoke control includes pressurization of the elevator shaft and

lobbies. The lobbies must be protected from smoke for the time that people

are waiting for elevators. Generally, pressurization of the elevator

machinery room is not a concern, because it can be indirectly pressurized by

air flowing from the elevator shaft through the large holes for elevator

cables that connect the shaft to the machinery room.

The major design concern with elevator smoke control is the pressure

fluctuations that result due to opening and closing of elevator doors and

other building doors. A feedback control system was studied by computer

modelling, and this study indicated that this system is capable of dealing

with the pressure fluctuations problem (Klote and Tamura 1986). Also, this

study indicated that elevator smoke control could be achieved by pressurizing

the lobbies directly, pressurizing the shaft directly, or pressurizing both

directly. These feedback controlled pressurization systems do not include air

flow through vents from the elevator shaft to the outside. This can be

achieved by elimination of these vents or by closing a damper in the vent

during smoke control operations . Full scale fire experiments conducted at the

10 story fire research tower near Ottawa (Tamura and Klote 1987) verified the

computer study and also showed that a pressure relief system was capable of

dealing with the pressure fluctuation problem. This pressure relief system

includes an elevator shaft vent to the outside.

13
Another concern is the transient pressures produced when an elevator car

moves in its shaft. Some design engineers believed that this "piston effect"

might overcome an elevator smoke control system. Analytical and experimental

studies of piston effect have been conducted (Klote and Tamura 1987) , and a simple relationship has been developed which is appropriate for design of

systems that are not adversely effected by piston effect.

Before elevator smoke control can become a reality, the information

developed about elevator smoke control by the NBS/NRCC joint project needs to

be put in a form readily usable by design engineers.

8. SMOKE PURGING CAUTION

Dilution of smoke in a zone in which a fire occurs is not a means of

smoke control. This process is sometimes referred to as smoke purging, smoke

removal or smoke exhaust. Many people have unrealistic expectations about

what this approach can accomplish. There is no theoretical or experimental

evidence that using a building's HVAC system for smoke dilution will result in

any significant improvement in tenable conditions within the fire space. It

is well known that HVAC systems promote a considerable degree of air mixing

within the spaces they serve. Because of this and the fact that very large

quantities of smoke can be produced by building fires , it is generally

believed that dilution of smoke by an HVAC system in the zone in which there

is a fire will not result in any practical improvement in the tenable

conditions in that zone.

9. ACTIVATION OF ZONED SMOKE CONTROL SYSTEMS

Probably, system activation is the major area of disagreement in the

field of smoke control. Primarily, this disagreement is about automatic

activation versus manual activation. In the early days of smoke control,

there was general agreement that activation of "pressure sandwich" systems

should be automatic upon alarm from smoke detectors . Automatic activation by

smoke detectors located in building spaces has the clear advantage of fast

response.

14
Some building designers and fire service officials began to realize that

smoke detectors could go into alarm on a floor far away from the fire. Thus

automatic activation by smoke detectors could result in pressurization of the

zone in which the fire occurred. This would result in the opposite of the

desired operation, that is smoke would be forced into other zones. As a result, a vocal minority of officials feel that smoke control should only be

activated manually by fire fighters after they are sure of the fire location.

However, most involved professionals feel that such manual activation would be

so late in the fire development that extensive hazard to life and property

damage due smoke would have occurred.

The most recent view on the subject is that zoned smoke control should

be automatically activated by an alarm from either heat detectors or sprinkler

water flow. Obviously, this approach increases the likelihood of proper

identification of the fire zone. For smoldering fires, this approach would

result in significantly longer response time. However, for flaming fires, it

is believed that the response time with this approach would be short enough so that significant benefit would be realized by the operation of the smoke

control system. It is hoped that advances in smoke detector technology and

application will improve significantly the ability of these detectors to

positively identify the fire zone.

Throughout all this controversy, there was complete agreement that zoned

smoke control should not be activated by alarms from pull boxes . The reason

can be illustrated by the scenario of a man who observing a fire on an upper

floor of a building decides that the first thing he should do is to get out of

the building. On the way down the stairs, he thinks of his responsibility to

the other occupants . He stops on a lower floor long enough to actuate a pull

box. If that alarm activated the smoke control system, the wrong zone would

identified as the fire zone.

Generally, it is agreed that stairwell pressurization systems can be

activated by the alarm of any detector located within the building.

15
10. RELIABILITY OF POWER

Many designers and code officials feel that standby electrical generator

sets should be provided for systems that are intended for the purpose of smoke

control only. Generally, these dedicated systems have lower power

requirements than systems that employ the building's HVAC system fans. Most

pressurized stairwells are dedicated systems, and most zoned smoke control

systems are non-dedicated systems. Some designers and code officials feel

that standby power is not appropriate for non-dedicated systems, because of

the costs associated with a standby generator set to provide all the power

needed to operate all the HVAC fans in a large building. However, some HVAC

systems are so arranged that out of the many HVAC fans only a few are needed

for the smoke control operation. For such systems, standby power would be

less expensive.

The considerations discussed above do not address the role of smoke

control in a building's overall fire protection system. For buildings without

fire suppression systems, smoke control can be a very important feature.

Standby power for smoke control in such a building would be desirable.

Further, the benefits of multiple power feeds should be considered either

alone or in conjunction with standby power. Because smoke control is a new

technology, no consensus has been reached concerning reliability of electric

power; however, it is recommended that each case be evaluated individually

considering the total fire protection system of the building.

11 . ACCEPTANCE TESTING

Regardless of the care, skill and attention to detail with which a smoke

control system is designed, an acceptance test is needed as assurance that the

system, as built, operates as intended. Further, many smoke control systems

will require adjustments of supply air flow rates or pressure relief vent

openings to accommodate the particular leakage characteristics of the

buildings they are part of. These adjustments can be made in conjunction with

16
the acceptance test. All measurements made during acceptance testing should

be recorded and saved for inspection.

NFPA 92A provides a general description of acceptance tests intended to

demonstrate that the final integrated system installation complies with the

specified design and functions properly. If standby power has been provided

for the smoke control system, acceptance tests should be conducted with both

normal power and standby power.

For zoned smoke control systems, one zone should be put into the smoke

control mode, and the pressure differences at the boundaries of that zone

should be measured. After smoke control operation in that zone has been

deactivated, another zone should be tested in the same manner. This should be

repeated until all smoke zones have been tested. Systems with automatic

activation should be activated by putting an appropriate detector into alarm.

With all stairwell doors closed, pressure differences across each

stairwell door should be measured. Then one door should be opened, and

pressure difference measurements made at each closed stairwell door. This

should be repeated until the number of doors opened equals the number of doors

required by the code authority to be opened.

A caution needs to be given concerning the use of smoke bombs . The

major problem with most smoke bomb tests of smoke control systems is that they

are intended to test some improvement of smoke conditions in the zone where

the fire is located. This is based on the mistaken belief that smoke control

is capable of producing a significant improvement in tenable conditions within

the zone where the fire is located. These tests are described here in general

terms so that the reader can recognize this t)rpe of test and understand the

problems with them. The smoke control system is put in operation. In the

zone which is being exhausted, a number of smoke bombs are ignited. The smoke

bombs produce all their smoke in a few minutes, and the zone rapidly fills

with smoke. Because the smoke control system is exhausting air and chemical

smoke from this zone, the concentration of chemical smoke decreases with time.

If at some specific time after ignition, a specific object (such as an exit

17
sign) is visible by a human observer at specific distance (such as 20 ft)

,

the

smoke control system is declared a success.

The problems with this type of smoke bomb test are numerous. The

criterion for successful operation is not objective. Further, the potential

danger of exposing the observer or other people to toxic chemical smoke must

dealt with. The obscuration of smoke from a building fire is much different

from that of chemical smoke. Most flaming fires produce a dense black smoke,

while smoke bombs produce a white smoke. At present, no information is

available relating smoke obscuration of chemical smoke to that of smoke from

building fires. These problems can be overcome by modifications to the test

method. However, this would not yield a test relevant for a smoke control

system. Because a smoke control system is intended to maintain pressure

differences at the boundaries of the smoke zone, the system should be tested

by measuring pressure differences. A very serious problem with this type of

smoke bomb test is that it can give building occupants and fire service

officials a false sense of the security. The test can lead people to wrongly

think that smoke control is capable of achieving a significant improvement in

tenable conditions within the fire space.

Testing the performance of smoke control systems with chemical smoke

from smoke bombs is not realistic for flaming fires in unsprinklered

buildings. Probably the flow of unheated chemical smoke is similar to that of

smoke from a sprinklered fire or a smoldering fire. However, the gases

produced by a large flaming fire in a building are in the range of 1200 to

1800 ®F. For chemical smoke to produce the same buoyant pressure differences

as these gases , the chemical smoke would have to be heated to the same

temperatures. Obviously, this is impractical because of the associated danger

to life and property.

Chemical smoke or a tracer gas (such as sulfur hexaflouride) can be used

to test for smoke feedback into supply air. The general procedure for testing

with chemical smoke is described here. A number of smoke bombs are placed in

a metal container, and all bombs are simultaneously ignited. The container is

located near exhaust inlet in the smoke zone being tested so that all of the

18
chemical smoke produced by the bombs is drawn directly into the exhaust air

stream. If chemical smoke is detected in the supply air, its path should be

determined, the path should be blocked, and then the smoke feedback test

should be conducted again.

Smoke bombs can be useful in locating the leakage paths that sometimes

defeat a smoke control system. For example, if the construction of stairwell

is unusually leaky, pressurization of that stairwell may not be possible with

fans sized for construction of average tightness. Chemical smoke generated

within the stairwell will flow through the leakage paths and indicate their

location so that they can be caulked or sealed.

12. SUMMARY

Smoke control makes use of mechanical fans to produce pressure

differences and air flows that can control smoke movement. The methods of

design analysis presented in the ASHRAE Smoke Control Manual directly

incorporate the effects of friction losses in shafts, temperature differences

between the inside and outside, and wind forces. Further, these methods of

analysis indirectly incorporate fire effects by the selection of design

pressure differences. Pressurized stairwells and zoned smoke control are the

two smoke control systems in common use today, and research is ongoing to

develop smoke control technology for elevator protection. It is generally

believed that dilution of smoke by an HVAC system in the zone in which there

is a fire will not result in any practical improvement in the tenable

conditions in that zone.

Probably, activation of zoned smoke control systems is the major area of

disagreement in the field of smoke control. The idea of automatic activation

by smoke detectors became unpopular when it was realized that detectors could

go into alarm on a floor far away from the fire. Many feel that zoned smoke

control systems should be activated automatically by water flow from

sprinklers or heat detectors , while a vocal minority feel that activation

should only be manually by the fire service. There is general agreement that

zoned smoke control should not be activated by alarms from pull boxes

.

19
Generally, it is agreed that stairwell pressurization systems can be activated

by the alarm of any detector located within the building.

There is considerable difference of opinion as to the circumstances

under which standby power should be required for smoke control systems. It is

recommended that the requirements for standby power for each case be evaluated

individually considering the total fire protection system of the building.

The acceptance tests evaluating the performance of smoke control systems

should consist of pressure measurement tests. Chemical smoke from smoke bombs

is not recommended for testing the performance of these systems. However,

chemical smoke can be use to test for smoke feedback into supply air and to

locate the leakage paths in construction that sometimes defeat a smoke control

system.

13. REFERENCES

Cresci, R.J. 1973. Smoke and Fire Control in High-Rise Office Buildings - Part II: Analysis of Stair Pressurization Systems, Symposium on Experience and

Applications on Smoke and Fire Control at the ASHRAE Annual Meeting, June

1973, Louisville, KY, Atlanta, GA, pp. 16-23.

DeCicco, P.R. 1973. Smoke and Fire Control in High-Rise Office Buildings - Part I: Full-Scale Tests for Establishing Standards, Symposium on Experience

and Applications on Smoke and Fire Control at the ASHRAE Annual Meeting, June

1973, Louisville, KY, Atlanta, GA, pp. 9-15.

Klote, J.H. 1984. "Smoke Control for Elevators", ASHRAE Journal, Vol. 26, No.

4, pp. 23-33.

Klote, J.H. and Fothergill, J.W. 1983. "Design of Smoke Control Systems for

Buildings", ASHRAE, Atlanta, GA.

Klote, J. H. and Tamura, G. T. 1986. Smoke Control and Fire Evacuation by

Elevators, ASHRAE Transactions, Vol 92, Part la, pp 231-245.

Klote, J. H. and Tamura, G. T. 1987. Experiments of Piston Effect on Elevator

Smoke Control, accepted for publication in ASHRAE Transactions, Vol 93, Part

2a.

Koplon, N.A. 1973. Report of the Henry Grady Fire Tests, City of Atlanta

Building Department, Atlanta, GA.

NFPA 1985. Code for Safety to Life from Fire in Buildings and Structures,

NFPA 101-1985, Quincy, MA, National Fire Protection Assn.

20
NFPA 1987. Recommended Practice for Smoke Control Systems, proposed document

NFPA 92A, Quincy, MA, National Fire Protection Assn.

Shaw, B.H. and Whyte, W. 1974. Air Movement through Doorways -- The Influence

of Temperature and its Control by Forced Air File, Building Services Engineer,

Vol 42.

,

pp. 210-218.

Tamura, G.T. and Klote, J.H. 1987. Experimental Fire Tower Studies on

Elevator Pressurization Systems for Smoke Control, accepted for publication by

ASHRAE Transactions, Vol. 93, Part II.
FORM NBS-1 14A (REV.1 1-84) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSTRrrB 7/3626

2. Performing Organ. Report No. 3. Publication Date

September 1987

4. TITLE AND SUBTITLE

An Overview of Smoke Control Technology

5. AUTHOR(S)

John H. Klote

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

U.S. DEPARTMENT OF COMMERCE

GAITHERSBURG, MD 20899

7. Contract/Grant No.

8 . Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street, City, State, ZIP)

General Services Administration

Public Buildings Service

Office of Real Property Development

Buildings Technology and Standards Division

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

Considerable advances in smoke control technology occurred in the last few

decades. However, smoke control is just beginning to take its proper place as a fire protection tool. This paper provides an overview of this technology,

including discussions of the fundamental principles, stairwell pressurization,

zones smoke control, elevator smoke control, system activation and acceptance

testing. In addition the problems of smoke purging are addressed.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper nomes; and separate key words by semicolons)

acceptance testing; air conditioning; computer models; elevators; smoke

control; smoke movement; stairwells

13. AVAILABILITY

Uni imited

I I For Official Distribution. Do Not Release to NTIS

Order From Superintendent of Documents, U.S. Government Printing Office, Washington, DC

20402.

[Xj Order From National Technical Information Service (NTIS), Springfield, VA 22161

14. NO. OF

PRINTED PAGES

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15. Price

$11.95

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