principles of smoke management - printed

8/10/2019 Principles of Smoke Management - Printed

1/383

PRINCIPLESOF SMOKEMANAGEMENT


2/383

This publicationwas made possible by funds from ASHRAE research.

Principles of Smoke Managementby John and James Milke is an exhaustive treatment of man-

agement, including pressurized stairwells, pressurized elevators, zoned smoke control, and smoke manage-

ment in atria and other large spaces. Recent advancements include heat release rate, toxicity ofnatural atrium venting, minimum depth of an atrium smoke layer, smoke stratification,

detection, tenability systems, and computer analysis. The book includes numerous example calculations.

Methods of analysis include equations, network flow models, zone fire models, scale and hazard

analysis. Computational fluid dynamics (CFD) is also addressed. The book includes a CD of computer soft-

ware for of smoke management systems.

This publication was prepared under ASHRAE Research Project

Cognizant TC: TC5.6, Fire and Control.

ABOUT THE AUTHORS

John H. P.E., Fellow ASHRAE, is a consulting engineer specializing in the design and

review of smoke management systems, as well as code consulting and teaching private management

courses. He conducted research for 19 years at the National Institute of Standards and Technology (NIST)

and has published over 80 papers and articles on smoke management and other aspects of fire protection.

Dr. Klote headed the Building Fire Physics Group at NIST, which conducted research in smoke

ment in buildings. The tools used for this research included full-scale fire experiments, scale fire

experiments, network airflow models, zone fire models, and computational fluid dynamics (CFD).

acted as a consultant in the area of smoke movement for the investigations of the MGM Grand fire and the

First Interstate Bank fire. research was the basis of the 1997 revision to the NFPA Life Safety Code

(section allowing elevators to be used as a second means of egress from towers.

In he e arned a Doctor of S cience degree in mechanical from George W ashington Uni-versity. He is a member of the National Fire Protection Association (NFPA). a fellow of SFPE, and a fellow

of ASHRAE. He has extensive participation in ASHRAE and NFPA committees, including being a past

of ASHRAETC Fire and SmokeControl. Dr. is a registered professionalengineer in the

District of Columbia, North Carolina, California, and Delaware.

James A. is an associate professor and chair of the Department of Fire Protec-

tion Engineering at the University of Maryland. Dr. has been a member of thefaculty and staff of the

department since 1977. He received his in aerospace engineering from the University of Maryland,

with an in structures. He received an M.S. degree in mechanicalengineering and a B.S. degreei n

fire protection engineering, both from the University of Maryland. In addition. he has a B.S. degreei n phys-

ics from College.

Dr. has served as a research fire prevention engineer at the Building and Fire Research Labora-

tory, National Institute of Standards and Technology, as the fire protection engineer for County, Vir-

ginia, and consultant to numerous organizations. Dr. Milke is a fellow of theSFPE and is a of the National Fire Protection Association. the International Association of Fire Safety Science. and the Amer-

ican Society of Civil Engineers. He is the chairman of the NFPA Technical Committee on Smoke Manage-

ment and the ASCWSFPE committee on Structural Design for Fire Conditions. He on the

Fire Council of Underwriters Laboratories.


3/383

PRINCIPLES OF

SMOKE

MANAGEMENT

JohnH.Klote

JamesA.Milke

American Society of Heating, Refrigerating

and Air-conditioning Engineers, Inc.

Society of Fire Protection Engineers


4/383

ISBN 13-99-0

American Society of Heating, Refrigerating

and Air-conditioning Engineers, Inc.

1791 Circle, N.E.Atlanta,GA 30329

rights reserved.

Printed in the United States of America

ASHRAE has compiled this publication with care, but has not investigated, and ASHRAE expressly disclaims any duty

to investigate, any product, service, process, procedure, design, or the like that may be described herein. The appearance'of any

technical data or editorial material in .this publication does not endorsement, warranty, or guaranty byASHRAE of any

product, service, process, procedure, design, or the like.ASHRAE not warrant that the information in the publication is free

of errors, and ASHRAE does not necessarily agree with any statement or opinion in this publication. The entire risk of the use ofany information in this publication is assumed by the user.

No part of this book may be reproduced without permission in writing fromASHRAE, except by a reviewerwho may brief

or reproduce illustrations in a with appropriate nor may any part of this book be reproduced, stored in a

retrieval system, or transmitted in any way or by any means--electronic.photocopying. recording, or other-without permission

in writing fromASHRAE.

ASHRAE STAFF

Editor

Howard

Editor

Christina

Editorial Ass

Barry Kurian

Jayne

Assistant

PUBLISHER

Cornstock


5/383

DEDICATION

This book is dedicated to the memory of George Tamura, who conducted pioneering research in smoke control atthe National Research Council of Canada.


6/383


7/383

TABLE OF CONTENTS

Chapter Page

Preface ix

Acknowledgments

Chapter I-Introduction

Chapter 2-Fire and Heat Release

Chapter 3

-

Smoke and Tenability 27

Chapter Analysis 49

Chapter 5-Effective Areas and Smoke Movement 63

Chapter of Smoke Management 87

Chapter 7-Air Moving Equipment and Systems

Chapter 119

Chapter 9-Hazard Analysis 129

Chapter 10

-

Stainvell Pressurization 139

Chapter l-

Elevator Smoke Control 157

Chapter 12-Zoned Control 171

Chapter 13-Fundamental Concepts for Atria 181

Chapter 14-Atrium Systems 199

Chapter 15-Physical 217

Chapter 16-Computational Fluid Dynamics 225

Chapter 17-Commissioning and Routine Testing 235

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Nomenclature 243

References 247

A-Units of and Physical Data 259


8/383

AppendixB-Bibliography 271

Appendix of Elevator Evacuation Time 277

Appendix D-Applicationof CONTAMW 289

Appendix E-ASMET Documentation

.................................Appendix F

-

ASET-C: A Room Fire Program for Personal Computers 329

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Appendix G-Data and Computer Output for Stairwell Example

. . . . . . . . . . . . . . . . . . . . . . . . . . . .Appendix H-Data and Computer Output for Zoned Smoke Control Example 349

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Appendix I-Inspection Procedures for Smoke Control Systems 355

Appendix J-Test Procedures for Stairwell Pressurization Systems 361

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Appendix K-Test Procedures for Zoned Smoke Control Systems 365

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Appendix L-Inspection Procedures for Atria Smoke Exhaust 369

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .Appendix M-

Test Procedures for Atria Smoke Exhaust Systems 371

Index 373


9/383

PREFACE

In 1983, ASHRAE published Design of Smoke Control Systems for Buildings, written by myself and John

This book was the first attempt to consolidate and present practical information about smoke control

design. Judging by the many favorable comments and suggestions about this first book, I feel that it was a success.

The first publication was limited to systems that control smoke by means of the physical mechanisms of pressuriza-

tion and airflow.

In 1992, ASHRAE and SFPE jointly publishedDesign of Smoke Management written by myself and

James Milke. The term smoke management was used in the title of this publication to indicate that the physical mech-

anisms were expanded from pressurization and airflow to include compartmentation, dilution, and buoyancy. Based

on heightened about supplying combustion air to the fire, a caution was added about the use of airflow for

smoke management.This new publication addresses the material of the two earlier books plus people movement in fire, hazard analy-

sis, scale modeling, and computational fluid 'dynamics. In addition, the material about tenability and atrium smoke

management has been extensively revised. As with the other books, this new book is primarily intended for designers,

but it is expected that it will be of interestto other professionals (code researchers, etc.).

This book and its predecessors are different from other design books in a number of respects. This book is writ-

ten in both English units (also called for inch-pound) and units so that it can be used by a wide audience. To the

extent practical, equations are accompanied by derivations and physical descriptions of the mechanisms involved.

The physical descriptions are worked into the text as simple explanations of how particular mechanisms, processes,

or events happen. The goal of the derivations and physical descriptions is to provide information and understanding

so that readers can apply the material of this book in creative and insightful ways.

As with the first two publications, I hope that this book is of value to the engineering community. Further, I

invite readers to mail their suggestions and comments to me at the address below:

JohnH. Klote, P.E.I I I I Street

VA 22 l


10/383

ACKNOWLEDGMENTS

This project would not have been possible without the support of theAmericanSociety of Heating, Refrigerating

and Air -conditioning Engineers (ASHRAE). Acknowledgment is made to the members of the ASHRAE Smoke

Control Monitoring Committee for their generous support and constructive criticism. The members of this subcom-

mittee are:

A. Webb, Chairman (Performance Technology Consulting, Ltd., Lake Bluff,

John A. Minn.)

Dave Elovitz (Energy Economics, Inc., Natick, Mass.)

Gary Lougheed (National Research Council Canada, Ottawa, Ontario)

The support and advice of the staff of the Building and Fire Research Laboratory (BFRL) at the National Insti-tute of Standards and Technology (NIST) in Gaithersburg, Md., was invaluable. Particular appreciation is expressed

to Richard Bukowski, Glen and Richard Peacock. Special thanks are due to Daniel Madrzykowski for his

advice regarding oxygen consumption calorimetry and heat release rate. The authors are indebted to Kevin

tan of BFRL for his valuable advice and constructive criticism regarding computational fluid dynamics.

Richard Gann and Barbara Levin of and Braun of Hughes Associates, Baltimore, Md., provided valu-

able information and insight concerning the evaluation of the effects of toxic exposures. Creg Beyler of Hughes

Associates provided constructive criticism in a number of areas. Special thanks are due to Gary Lougheed for his con-

criticism and for bodyof relevant research conducted by him and associates at the National Research

Council of Canada.

Students of fire engineering at the University of Maryland have provided insightful comments on

drafts of several chapters of this book In particular, the students and Naviaser developed the

information about CONTAMW that is included as Appendix D.

content of book is heavily dependent upon work of researchers, design engineers, and other

professionals around the world. So many of these people provided experimental research results, system con-cepts, and analytical methods that it is impossible to thank them all individually. Appreciation is expressed to all

those have to advancement of smoke technology directly or indirectly by their con-

tributions to fire science and fire protection engineering.


11/383

CHAPTER1

Introduction

Smoke is recognized as the major killer in fire situa-

tions. Smoke often migrates to building locationsremote from the fire space, threatening life and

damaging property. Stairwells and elevator shafts

quently become smoke-logged, thereby

and inhibiting rescue and fire fighting. The MGM

Grand Hotel fire (Best and Demers 1982) is an

of the smoke problem. The fire was limited to the first

floor, but smoke spread throughout the building. Some

occupants on upper floors were exposed to smoke for

hours before rescue. The death toll was 85, and the

of the deaths were on floors far above the fire.

23

22

2

20

17

MGM Grand HotelFireLas Vegas, NVNov 21,1980

Note: Renumberedfor

The MGM Grand is not unique in this respect, a s is

illustrated by the fires at the Roosevelt Hotel1964) and Johnson City Retirement (Steckler et

al. 1990). All of these fires were located on the first

floor, but the majority of deaths were on upper floors

(Figure l).'

During the intensive activity of fire fighting andrescue, the locations of some of the bodies are notrecorded. Thus Figure 1. 1 is limited to the deaths forwhich the locations were known.

Retirement8 Fire

L7 Johnson City. TNDec 24,1989

2

I

0 1 2 3

Deaths

2

I

0 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8

Deaths 0 1 2 3 4 5 6 7 8

Deaths

Figure I.I Deaths for fires was


12/383

Chapterl-Introduction

Figure Floor plan of Health Care Test the Annex.

The general public is unaware of how fast a fire can

grow and of how much smoke can be produced by a fire.

This unawareness extends to many designers and other

related professionals. Because such an awareness i s nec-

essary to the evaluation of design parameters for smokemanagement systems, the following example is pro-

vided.

This example is fire test N-54, performed at the

Health Care Test Facility at the National Institute of

Standards and Technology Annex in Gaithersburg, Md.

For technical details of this unsprinklered fi re test, the

reader is referred to a report by et al. 980). T he

floor plan of the test facility is shown in Figure 1.2.

In this test, various fabrics representing common

clothing materials were hung on wire coat hangers and

arranged loosely in a wooden wardrobe. A cardboard

box containing crumpled newspaper was placed on the

floor of the wardrobe. The test started when the crum-pled newspaper was ignited by a match. Following igni-

tion, the left-hand door of the wardrobe was closed

tightly while the right-hand door was partially open

resulting in a 3 in. (76 mm) opening along the vertical

edge of thedoor.

At one second after ignition, no flame or smoke

was visible. At 80 seconds, flames were visible flowing

from the top of the wardrobe, a layer of smoke was cov-

ering the ceiling of the burn room, and smoke had

flowed into the corridor forming a one-foot-thick layer

just below the corridor ceiling. At seconds, flames

were flowing from the top two-thirds of the wardrobe

opening, and the smoke flowing out of the burn roomdoorway had increased significantly. At seconds

after ignition, flames were flowing from the entire open-

ing of the wardrobe door, and the layer of smoke in the

corridor and lobby had descended to approximately 4 ft

(1.2 m) below the ceiling.

Such very rapid fire growth and accompanying

smoke production represent a real possibility in

wardrobe fires and perhaps even closet fires. Many

other fire scenarios are possible. For example, a latex or

a polyurethane filled mattress ignited by an adjacentwastebasket fire would reach about the same stage of

development in six minutes that wardrobe test N-54

reached in two minutes.

Full-scale fire tests by et al. (1997) and

Lougheed et al. (2000, 2001) have shown that success-

fully sprinklered fires can continue to bum and produce

enormous amounts of dense buoyant smoke after sprin-

kler activation. While it appears this smoke production

is greatest for fires that are shielded from sprinkler

spray, some unshielded fires still produced considerable

amounts of buoyant smoke.

The concept of smoke management has developed

as a solution to the smoke migration Smoke

movementcan be managed by use of one or more of the

following mechanisms: compartmentation, dilution, air-

flow, pressurization, or buoyancy. These

are discussed in detail in Chapter 4. The use of pressur-

ization produced by mechanical fans is referred to as

controlby NFPA 92A (NFPA 2000). By this def-

inition, stairwell pressurization (Chapter 7), elevator

pressurization (Chapter and zoned smoke control

(Chapter 9) are all types of smoke control systems.

The primary emphasis of this book is on

that cse pressurization produced by mechanical fans.

The use of pressurization to control the flow of undes-

ired airborne matter has been practiced for at least 50

years. For example, it has been used in buildings, suchas experimental laboratories, where there is dangerof

2. As discussed later in Design Con-siderations,"smoke management is only one of manytechniques available to protection engineers.


13/383

Principlesof

poison gas, flammable gas, or bacteriological material

migrating one area to another; it has been used to

control the entrance of contaminants where a dust-free

environment is necessary; it has been used

tion migration and contamination could occur; and it has

been used hospitals to prevent the migration of bacte-

ria to sterile areas. However, the use of airflow and pres-surization to control smoke flow from a building fire is a

fairly recent adaptation.

INTENT

The primary intent of this book is to provide practi-

cal state-of-the-art to engineers who have

been charged with design of smoke management sys-

tems. The book is also intended to provide information

for the review of designs and development of codes and

standards,. This chapter contains general background

Chapter2 deals with fire development and

the heat :release rate of fires. Chapter 3 discusses the

nature including toxicity, heat exposure, andvisibility through smoke. Chapter 4 people

movement during fire evacuation.

methods are employed to minimize the possibility

doors being proppedopen.

While advances in tenability analysis have

engineering analysis smoke feasible, these sys-

tems are not included in this book. The idea of smoke

shafts is that smoke flows up the shaft due to

where the smoke flows away from the building, but the

authors have concerns about the fundamental effective-

ness of smoke shafts. Further, there seems to be little

interest in smoke

The stair systems known as towers

are misnomers, in that there is nothing about them that

ensures no smoke migration into stairs. Originally, these

towers were separate from the building and were con-

nected to it only by walkways open to the outside. Some

versions of these towers used relatively small openings

in exterior vestibule walls in place of the separate walk-

ways. In the absence of an engineering analysis of these

systems, it can only be stated that the benefits of these

systems are questionable. For these reasons, separatedstair towers are not included in this book, and it is rec-

ommended that the term towers not be

Chapter 5 is devoted to smoke movement in build-

and the individual driving forces of smoke move-

ment are discussed in detail. Chapter 6 contains a EQUATIONS AN D UNITS

discussion of topics that are essential forOF MEASUREMENT

the design of systems to manage smoke movement. It

discusses the mechanisms of compartmentation, dilu-

tion, airflow, pressurization, and buoyancy, which are

used by themselves or in combination to manage

conditions in fire situations.

Background information is provided about ducts,

fans, fire dampers, smoke dampers, and fan-powered

ventilation systems in Chapter 7. Chapter8 is a descrip-tion of the computer programs that are used for the anal-

ysis of smoke management systems.

Chapters 9 through 14 address hazard analysis,

stairwell pressurization, elevator smoke control, zoned

smoke and atrium smoke management. For

applications for which these conventional methods are

inappropriate, the methods of scale and

putational'fluid dynamics (CFD) can be used (Chapters

and 16). Chapter 17 addresses the important topic of

commissioning and routine testing.

It may be noted that pressurized corridors have

been omitted. The presented in this book can

Considering that this book is primarily intended for

design, it seems most appropriate that units should be

specified for every equation. However, the topic of

smoke management is relatively new, and there is no

test to refer to for the derivation of many of the equa-

tions used. Further, it was desired that the text be in both

Inch-Pound (IP) units and the International System

units. It would be unacceptably to present

derivations using both commonly used English units

and units. The equations used for derivations are

homogeneous, and they can be used with

the system, the slug pound system, and the pound

mass poundal system (Appendix A). These dimension-ally homogeneous equations are easily identified

because no units are specified for them in the text.

all of the equations the reader is to use

for design analysis are given in both English and

units. These equations are easily identified because the

appropriate units for the equation are specifically indi-

catedi n the text.

applied to pressurized corridors in a manner similarto their application to other pressurization systems. The

HISTORY OF SMOKE VENTING.

concern with pressurized corridors is that if a fire room Smoke venting has been used extensively todoor is blocked open, the corridor pressurization system age smoke flow during fires. The acceptance of

can force smoke into other rooms off the corridor. For such venting resulted from several major fires,

this reason, pressurized corridors are not generally rec- including those at the Brooklyn which killed

except for applications where practical 283 in 1877; Vienna Ring which killed 449


14/383

Chapter l

AreAreas2 and4on 10 Tower

I I

........................3 on................ Floor....................................

Figure1.3 Typical floor plan of the office at

30Church Street.

in 1881; the Royal, which killed 186 in 1887;

and the Iroquois which killed 571 in All

of these fires started on the stage and resulted inmajor loss of life in the audience. The Palace fire

in Edinburgh in 1911 was an exception. In this fire,

smoke venting through the stage roof was credited for

helping to prevent any loss of life. The buoyancy of the

hot smoke forced the smoke flow through the vent open-

ings, and this venting is called natural venting or gravity

venting.

Over the past few decades, fan-powered smoke

exhaust has become the standard for almost all atria in

North America. In other areas, such as Europe, Austra-

lia, and New Zealand, both natural venting systems and

fan-powered exhaust systems have become for

atria. Modem atria smoke management designs are

based on engineering analysis developed over the last

few decades. These analytical methods are primarily

based on research in smoke plumes fire model-

ing. Information about these analytical methods is pro-

vided in Chapters and 14.

HISTORY OF PRESSURIZATIONSMOKE CONTROL

The idea of smoke protection by pressurization sys-

tems is restrict the movement of smoke a build-

ing fire. To study the effectiveness of pressurization

smoke control, the Brooklyn Polytechnic Institute con-ducted a series of fire experiments at a 22-story office

building at 30 Church street in New YorkCityThis building was scheduled for demolition.

Materials representative of fuels that would be in an

were burned on floors 7 and 10, as shown in Fig-

ure 1.3. This project demonstrated that pressurization

could provide "smoke free" exits during large unsprin-

Experimental Tower

34 LobbySupply

Figure 1.4Typicalfloor plan of NRCCexper-hen-

klered fires. The term"smoke free" is used to mean

essentially free of smoke, with the possibility of such

insignificant amounts ofcombustion products that tena-bility is maintained.

Other full-scale fire tests also demonstrated thatpressurization could provide "smoke free" exits during

large unsprinklered fires (Koplon

Butcher et al. 1976). Cresci (1973) describes visualiza-

tion experiments using a model of the stair shaft at the

Church Street building, where stationary vortices

observed at open doonvays. These vortices are the rea-

son that the flow coefficient through an open

door is about half of i t be otherwise. This

significant effect on airflow is discussed in Chapter

The Research Tower near Ottawa (Figure 1.4) was

used for a joint National Instituteof Standards and Tech-

nology (NIST) and National Research Council Canada(NRCC) study of elevator smoke control. Again, i t was

demonstrated that pressurization could control smoke

from large unsprinklered fires (Tamura and Klote

1988; Klote and Tamura 1987).

In the spring of 1989, NIST conducted a series ofexperiments of zoned smoke control at the Plaza Hotel

in Washington as shown in Figure 1.5 (Klote

1990). A zoned smoke control is a system that

uses pressurization to restrict migration to the

zone of fire origin. Once again, it was demonstrated that

pressurization could control smoke from unsprin-

klered fires.

An analysis based on first principles of engineering

was made of the pressure differences produced thesmoke during the fires at the Plaza Hotel.As is done with zone fire modeling, the pressures

rooms were considered hydrostatic. The general trendsof calculated values were i n agreement with thesurements (Figure and this indicates a of


15/383

Principles of Smoke Management

applicability o f z one fire for analysis o f pres-surization smoke control systems.

OBJECTIVES O FSMOKE MANAGEMENT

Some objectives of a smoke management system

are to reduce deaths and injuries from smoke, reduce

property loss from smoke damage, and to aid firefight-ers. Many designers feel that life safety is the primary

objective of smoke management; however, systemshave been built with the primary objective of protecting

property--especially high-value equipment. Regardlessof the objective, the methods of design analysis pre-sented in book are applicable.

Theoretically, a smoke management system can be

designed to provide a safe escape route, a safe

area,or both. However, a pressurization control)

system can meet its objectives even if a small amount ofsmoke infiltrates protected areas. For this book, pressur-ization systems are designed on the basis that no smoke

infiltration will occur. Hazard analysis (Chapter 9) can

be used for the design of systems that maintain tenabil-ity even when people come into contact with some

smoke.

PERFORMANCE-BASEDDESIGN

recent years, performance-based codes havebecome a topic of considerable attention. Traditional

codes prescribe requirements, while performance-basedcodes require a level of performance. A

based design is developed to meet the level of perfor-mance stipulated in the code.

This book uses a performance-based approach,where the kind of performance is based on the type of

system. Pressurization smoke control systems aredesigned to maintain specific levels of pressurization at

barriers, such as partitions and closed doors. Atrium

smoke exhausts often are designed to keep smoke

descending below a specific level. Further, various

of smoke management systems can be designed to

maintain tenable conditions within specific spaces.

PRELIMINARY DESIGNCONSIDERATIONS

Smoke management should be viewed as only one

part of the overall building fire protection systems. Two

basic approaches to fire protection are to prevent fire

ignition and to manage fire impact. Figure 1.7 shows a

simplified decision tree for fire protection. The building

occupants and managers have the role in pre-venting fire ignition. The building design team may

incorporate features into the building to assist the occu-pants and managers in this effort. Because it is impossi-ble to prevent fire ignition completely, managing fire

impact has assumed a significant role in fire protection

design. Compartmentation, suppression, control of con-struction materials, exit systems, and smoke manage-ment are examples. The NFPA Fire Protection

Handbook(NFPA SFPEHandbook of Fire Pro-

tection Engineering (SFPE and NFPA 550(NFPA 1995) contain detailed about fire

safety.

S 20 25(minutes)

(a)Pressure Difference Near Ceiling

00 5 15 20 25 30

lime (minutes)

(b) Near Floor

Figure 1.5 Figure 1.6 and

Plaza Hotel

tests.


16/383

Chapter1

Objectives

Ignition Impact

Heat-Energy Source-FuelThreat' Exposure'

Sources Interactions

'Note: Smoke managementis one of many fireprotectiontools that can beusedto help manage the threat of fire and manage the exposure of fire.

1.7 decisiontree.

Many factors will affect the design of a man-

agement system. Before the actual mechanical design of

the system can proceed, the potential constraints on the

system should be determined and the design criteria

established. This section introduces some considerations

peculiar to smoke management system design, some of

which are merely listed below, since detailed discussion

is beyond the scope of this book. However. published

works on some of these subjects are cited in the bibliog-

raphy in AppendixB.

Occupancy type and characteristics

Evacuation plan

Refuge areas

Distribution of occupant density

Human life support requirements

Form of detection and alarm

Fire service response-to-alarm

Fire suppression system characteristics

Type of heating, ventilating, and air-conditioning

(HVAC) system

Energy

Building security provisions

Controls

Status of doors during potential fire condition

Potential threatsInternal compartmentation and charac-

teristics

leakage

Exterior

Wind

FLEXIBILITY AN D RESILIENCY

To help ensure smoke management system perfor-

mance, the approaches of flexibility and resiliency can

be employed. The concept of flexibility consists of

using design features that allow for easy adjustment of a

smoke management system in order to achieve accept-

able performance. A resilient system is one that resists

serious adverse effects due to pressure fluctuations.

During the design of a new building, the leakage

paths throughout the building can only be estimated.

Therefore, the smoke management design calculations

constitute only an approximate representation of the

pressures and airflows that will occur as a result of the

smoke management system in the actual building. The

introduction of flexibility into a smoke management

system allows for variations in leakage from the origi-

nally estimated values. Because it is to measure

leakage paths in existing buildings, the concept of flexi-

bility is also useful for retrofit of smoke management i n

existing buildings. In many systems, flexibility can be

achieved by the use of fans with sheaves3 to allow sev-

eral flow rates, a variable flow fan for the same purpose,

or by dampers that can be manually adjusted to obtain

desired pressure differences.

Pressure fluctuations often occur during a fire when

doors are opened and closed and when windows are

opened, closed, or broken. To resist such fluctuations,

resiliency can, be incorporated in a system by use of

A sheave is with aa By exchanging a sheave for

of rotational of the fan

and its flow changed.


17/383

Principles of Smoke

automatic control to reduce the pressure fluctuations.

For example, in pressurized stairwells, automatic con-

trol can be used in the supply fan bypass system to

reduce the effect of opening and closing stairwell doors.

An alternative keep the exterior stairwell door open

during pressurization. This eliminates what is probably

the major source of fluctuations; that the opening and

closing of the exterior stairwell door. The concepts of

flexibility and resiliency are discussed further where

they apply to specific smoke management applications.

SAFETY FACT R S

Smoke management is still a relatively new field,

and it should come as no surprise that there is no -

sensus concerning safety factors, which are commonly

used in many branches of engineering to provide a level

of assurance of system performance. Further, the topic

of factors has attracted little attention in smoke

control design.

Safety factors for sizing fans of pressurization sys-

tems are very different from those intended to maintaina tenable environment in an atrium or other application

based on a hazard analysis. If a pressurization fan is

undersized, it will not maintain acceptable pressure dif-

ferences. This should be apparent and corrected during

commissioning.

Ideally, an analysis of a system intended to maintain

a tenable environment would be based on detailed and

accurate capabilities of simulating smoke transport,

physiological effects of fire-related exposures, human

response to fire, and evacuation analysis. However, this

technology is not so advanced, and these calculations

are of necessity based on a number of conservative

assumptions with conservativedesign parameters. It can

be argued that such conservative calculations may resultin conservative designs even in the absence of any

safety factors. The specifics of the design and the meth-

of analysis would be expected to have a significant

impact on any approach to safety factors.

of the absence of any accepted approaches

to safety factors, this topic is not included in the meth-

ods of analysis of this book.

FIRE SUPPRESSIONSYSTEMS

Automatic suppression systems are an integral part

of many fire protection designs, and the efficacy of such

systems in controlling building fires is well docu-

mented. However, it is important to recognize that whilethe functions of fire suppression and smoke manage-

ment are both desirable fire safety features, they should

not be readily substituted for each other. One of the best

ways to deal with the smoke problem is to stop smoke

production. To the extent that a suppression system

slows down the burning rate, it reduces the smoke prob-

lem. From fires that are suppressed rather than extin-

guished, smoke is produced. This smoke can move

through the building due to various driving forces dis-

cussed in Chapter5. the other hand, well-designed

smoke management systems can maintain tolerable con-

ditions along critical egress routes but will have littleeffect on the fire.

In addition to the fact that the systems dif -

ferent functions, it is important that the designer con-

sider the interaction between smoke management and

fire suppression. For example, in the case of a

sprinklered building, the pressure difference needed to

control smoke movement is probably less than in an

unsprinklered building, due to the likelihood that the

maximum fire size will be significantly smaller than in

an unsprinklered building.

A pressurization (smoke control) system can

adversely affect performance of a gaseous agent (such

as halon, or suppression system when the sys-tems are located in a common space. In the event that

both systems are activated concurrently, the smoke

exhaust system may exhaust the suppressant gas from

the room, replacing it with outside air. Because gas sup-

pression systems commonly provide a single application

of the agent, the potential arises for renewed growth of

the fire.

A general guideline would be that the gaseous agent

suppression system should take precedence over the

smoke control system. An extremely desirable feature in

such spaces would be the ability to purge the residual

smoke and the suppressant gas after the fire is com-

pletely extinguished and to replace them with fresh air.This ability to replace the atmosphere in these spaces in

the post-fire period is very important from a life-safety

viewpoint, since some gas suppressants are asphyxiants

at normal design concentrations.

ENERGY CONSERVATION

The smoke management system must be designed

to override the local controls in a variable air volume

HVAC system so that the air supply necessary to pres-

surize spaces is supplied. Also, if there is an

energy management system or a 24-hour clock

the designer must ensure that the smoke management

system will take precedence over the local control sys-tem so that the necessary air is supplied or exhausted

according to the design approach. It is a good general

rule that smoke management should take precedence

over energy conservation features in both new designs

and retrofits.


18/383


SYSTEM ACTIVATION

System activationisprobably the major area of dis-agreement in the field of smoke control. Primarily, this

disagreement is about automatic activation versus man-

ual activation. In the early days of smoke control, there

was general agreement that activationof"pressure sand-wich" systems should be automatic upon alarm from

smoke detectors. Automatic activation by smoke detec-tors located in building spaces has the clear advantage

of fast response.

Some building designers and fire service officials

began to realize that smoke detectors could go into

alarm on a floor far away the fire. Thus, automatic

activation by smoke detectors could result in pressuriza-tion 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 feel that smoke control

should only be activated manually by fire fighters after

they are sure of the fire location. However, many

involved professionals are concerned that such manualactivation could be so late in the fire development that

significant hazard to life and damage to property would

result. Such delayed activation can suddenly transport a

body of smoke that is highly charged with unbumed

hydrocarbons, carbon monoxide, and other toxic gases

and depleted of oxygen to remote locations. This can

result in a wave-like movement of toxic gases or flame

to remote areas.

The most recent view on the subject is that zoned

smoke control should be automatically activated by an

from either heat detectors or sprinkler water flow.

This can only be accomplished if the detector or sprin-

kler zones are compatible with the smoke control zones.

Using heat detector or sprinkler flow signals for activa-tion increases the likelihood of proper identification of

the fire zone. For smoldering fires, this approach would

result in a significantly longer response time, and smoke

detectors would probably be better suited for applica-

tions where smoldering fires are of particular

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 oper-

ation of the smoke control system. It is hoped that

advances in smoke detector technology and application

will significantly improve the ability of these detectors

to positively identify the fire zone.

Throughout all of this controversy, there has been

complete agreement that zoned smoke control should

not be activated by from manual stations (pull

boxes). The reason can be illustrated by the scenario ofa

man who, while 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 manual

station. If that alarm activated thesmoke control system,

the wrong zone would be identifiedas the fire zone.

Because of the long response time and the mainte-

nance problem of clogging with airborne particles, it is

generally agreed that smoke detectors located in HVACducts should not be the primary means of smoke control

system activation. A means of activationof higher

ability and quicker response time is needed. However,

an alarm from a duct-located detector can be used in

addition to such a primary means of activation. A signal

only this secondary means might be unusual, but it

should be able to activate the smoke control system.

Most stairwell pressurization systems operate in the

same manner regardless of where the fire is located.

Therefore, it generally is agreed that most stairwell pres-

surization systems can be activated by the alarm of any

fire alarm-initiating device located within the building.A possible exception to this is large buildings with hori-

zontal separations, such that smoke is not expected tohave an impact on some stairwells remote from the fire.

It is recommended that zoned smoke control sys-

tems be equipped with a remote control from

which the smoke control system can be manually over-ridden. This should be easily identifiable and

accessible to the fire department. Such a remote control

allows fire fighters to change the mode of smoke

control system operation in addition to system shut-down. Activation of smoke management systems for

atria and other large spaces is addressed in Chapter

RELIABILITY OF SMOKE MANAGEMENT

The intent of this section is to provide insight intothe need for acceptance testing and routine testing and

the relative importance of system simplicity: The fol-

lowing should not be thought of as an exhaustive treat-ment of smoke management reliability. Due to the

of obtaining data about the reliability of com-ponents of smoke management systems, the simple cal-

culations that follow are only very rough estimates.

However, it is believed that the insight gained justifies

this treatment despite these limitations. Further, the

same reliability concerns that apply to smoke manage-

ment systems apply to all life safety systems, and the

following discussion may be of general interest beycnd

smoke management.

The discussion is limited to series systems, which

are systems that operate only if all the components oper-ate, as is true of many smoke management system

designs. Redundancies (such as backup power) are not

included in this analysis. The reliability, R, a series


19/383

Principles ofSmoke Management'

Table1.1:

EstimatedSystem Reliabilityfor NewSmokeManagement

SystemThat Has Not Been Commissioned

No. of HVAC No. of Other of

System System Fans Components Before Commissioning System (months)

1 0 0.97 162 0 3 0.83 46

3 3 9 0.56 14

4 5 18 0.31 8

5 5 54 0.03 3

1. Systemreliabilities calculated Equation For purposesof these calculations, the of fansof a forced airHVAC system weretaken as 0.99, andother components were taken as 0.94.

2. Mean lives calculatedfrom Equation(1.3). For purposesof thesecalculations. the failure rates of fans of a forcedairHVAC system were takenas

per hour, and other components were taken as per hour.

system is the product of the of

ponents.

Usually, discussions of reliability progress from this point

with the assumption that all components operate initially

and that failures occur with time after system installation.

For this assumption to be appropriate, a program of accep-

tance testing and defect correction is necessary. Such com-

missioning must include an installation check of all

components, tests of system during all modes

of operation, repairof defects, and retestinguntil all defects

are corrected. Current construction practices are such that

system commissioning is not always this exhaustive. For

this reason, attention is first given to reliability of systems

without commissioning followed by a discussion of reli-

ability of systems for which all components operate after

commissioning.

RELIABILITY BEFORECOMMISSIONING

For newly installed components, the reliability can

be thought of as the likelihood that the component will

both be installed properly and be in good working con-

dition when it is delivered to the construction site. There

are an enormous number of errors that can occur during

manufacture, transportation, storage, and installation

that can cause a component to fail to operate.

such as motors wired for the wrong voltage, not

connected to power, dampers failing to close, fans run-

ning backward, holes i n walls, and automatic doors fail-

ing to close have been observed in newly built smoke

management systems. Based on experience

testing of smoke management systems, it is estimated

that the reliability of components i n noncommissioned

systems is0.90 or An consideration

regarding the of a component in a

missioned system is if that component is part of an

HVAC system. In hot or cold weather, building occu-

pants demand that the HVAC system provide comfort

conditions. Thus, for a new building in extreme weather,

it can be considered that the reliability of the HVAC sys-tem fan will approach unity. Based on field observa-

tions, it is believed that other components will have a

lower reliability. The following reliabilities were chosen

for example calculations for new systems that have not

been commissioned:

Fans of a forced air HVACsystem 0.99

Other components 0.94

These values were arbitrarily selected, but the rela-

tive values between them are based on the discussion

above. Table I . lists calculated reliabilities of such sys-

tems made up of many components. It can be observed

from this table that the more components a system has,the less likely the system is to operate before it has been

commissioned. The most reliable new system would be

one that only uses the HVAC system fans. A large com-

plicated system consisting of many components (Table

1.1, system 5) has very little chance of operating before

commissioning. The trend of lower reliability for com-

plicated systems agrees with observations of the author

during field tests of systems of various

degrees of complexity. Probably the most important

point to be made from this discussion is the need for

commissioning of new systems.

MEAN LIFE OF COMMISSIONED SYSTEMS

For this discussion, all system components are con-

sidered to operate-at the end of the commissioning pro-

cess. A commonly used relation for the reliability of

components is the distribution,

= .


20/383


I I " ICircuit Breakers

IMechanical

Large

IEq

Figure 1.8 Typical ranges rates Lees[ I

where is the failure rate of the component. The mean

life, L, of a system is

Some typical ranges of failure rates of some

ponents and systems are shown in Figure It can be

seen that failure rates vary over large ranges and that

failure rates vary considerably with equipment type. It

seems that the failure rate of HVAC system fans would

be lower than those of other components. If these fans

fail, building desiring heating o r cooling tend

to put pressure on maintenance personnel to get fans

repaired quickly. Smoke management systems are only

needed for a short time over the life of a building. Thus,

when an HVAC system fan is called for smoke

management duty, it seems that it will be more likely to

operate than other components. To account for this, the

effective failure rate of HVAC system fans can be

thought of as being much smaller than other compo-

nents. The following failure rates were arbitrarily

selected for example calculations, but their relative val-

ues are based on the above discussion:

Fans of a forced air I-[VAC system per hr

Other components per hr

Table 1. 1 shows mean lives of systems composed of

various numbers of components. It can be observed that

systems composed of a fewcomponents have long

lives, while those made up of very components

have short lives. This tends to support the view that sim-

ple systems are more reliable, and this view is supported

by in the field. However, it should be cau-tioned that systems should not be overly simple; that is,

they should have the features needed to achieve desired

performance at likely conditions during a fire. Further,

the above simple analysis did not include the beneficial

effects of redundancies. However, it is safe to conclude

that unnecessary system complexities should be

avoided. The mean lives listed in Table also indicate

that routine testing and repair of smoke management

is needed so that the systems will probably be

in good working order when they are needed. A similar

statement can be made concerning all life safety sys-

tems.


21/383

CHAPTER2

Fire and Heat Release

Probably the most important aspect of a building quences of a fireafter ignition but not with the causes of

fire is the heat release rate (HRR). The tempera- Ignition.

ture and amount of gases produced by a fire are Growth: After ignition, fire growth is determinedthe burning, with influence from

models use the HRR as input. When characterized by an

of air for the fire. Figure 2.2 shows an officefire starting in a corner of an upholstered chair andabout the size of a fire or how big a fire is, they almost

always are referring to the HRR. Other indicators of fire

size are the fire area and fire perimeter, but neither of

these is commonly used to depict how big a fire is in the

predictive models that have gained a high level of

acceptance in recent years. For these reasons, the term

size is used in this book to HRR.

The intent of this chapter is to provide basic

i about fire size and development that should be

helpful concerning evaluation and ofI design fires. A design fire is the challenge that a smoke

management system is designed to withstand. Because

the presence of sprinklers often plays a role in the

mination of a design fire, sprinklers are also included.

The design fire can be a steady fire or an unsteady one.

While the steady fire is not physically realistic, it can

result in very conservative designs and it can simplify

design analysis.

STAGES OF FIRE DEVELOPMENT

Fires in rooms or other compartments are oftendescribed in terms of the stages of fire development,

shown in Figure 2.1. These stages are useful in discuss-

ing fires, but many fires do not go through all of thesestages due to lack of fuel or the action of a suppression

system.

Ignition: Ignition is the period during which thefire begins. management deals with the

growing until it spreads to other objects. As the firegrows, the temperature in the room rises. A fire with

sufficient combustion air is called a fuel fire,and such a fire is also referred to as burning a ir .

Flashover: In engineering, most processes of inter-est consist of gradual changes, but flashover is an excep-tion. is a sudden change from an apparentsteady fire confined to a relatively small space to a fire

that involves a much larger space, such as the entireroom.For the office fire of Figure (c), materials

throughout the room are subject to thermal radiation

from the Flames and the smoke layer under the ceiling.When this radiation is sufficiently high, some of thesematerials ignite. This is followed by other materials

I I I

I Post FlashoverI II I

I II I

Dewy

Time

Figure


22/383

Chapter2-Fire and Heat Release

(a)Fire restricted to inside corner of chair and resulting in smoke layer under ceiling


23/383


Table 2.1:ApproximateValues of CO

Yield for Room

CO

Flamingfires in"free air" 0.04

Fully involved fire (in a roomwithout 0.2materialson ceiling or upper portionof walls)***

These estimates are based onand (2002).

is in CO produced per of fuel burned (org ofCO

produced pergof fuel burned).Fully involvedfires in rooms withcellulosic materials (wood,paper, cardboard, etc.)on ceilingor upper of wallsareexpected to have COyieldsseveraltimes higher

igniting, and then the entire room is involved in fire.Once a fire gets to the stage depicted in Figure 2.2 (c), itonly takes a few seconds for a room to flashover.

In a very large room, such as an open floor

plan, only a portion of the room may flashover. The

smoke layer temperature at which flashover occurs is

generally in the range of 930F to 1300F (500C to700C). The criteria for flashover is sometimes taken to

be a smoke layer temperature of (600C) or a

radiant heat flux of 1.8 (20 at the floor

of the fire (Peacock et al. 1999).

Fully Developed Fire: This stage of fire develop-

ment has the highest temperatures. For small and

medium rooms, the HRR of a fully developed fire

depends on the amount of air that reaches the fire. Such

a fully developed fire is ventilation

In a ventilation controlled fire, more volatile gases

are produced by the burning materials than can be

bumed in the room with the oxygen available, and the

fire can be characterized by flames consisting of burn-ing volatile gases extending from open doonvays of the

fire room. For very rooms, as in an open office

floor plan, the fire may not ever become ventilation con-

trolled. Fully developed fires are characterized by

cient combustion and high production of CO (Table

2.1).

Decay: As the fuel is consumed, the HRR of the

fire and the temperature of the room drop. The fire may

change from ventilation controlled to fuel controlled.

Strictly speaking, the term post-flashover

includes both fully developed and decay stages, but the

is often used to mean a fully developed fire.

MEASUREMENTOFHEAT RELEASE RATEIn the early days of fire research, of

the HRR during a fire was very crude. Typically, materi-

als were burned on a load cell (scale), and the HRR was

estimated from the mass loss and the heat of combustion

of the material. If the load cell became too hot, mass

MeasureTemperature,Flow Rate, GasConcentrations.

Figure2.3 Open air calorimeter:

measurements would be meaningless. Various schemes .

to keep the load cell from heating up were devised, but

they all interfered to some extent with the measure-

ments. The situation was even worse when pieces of

burning material would fall from the load cell.To further exacerbate the difficulties with such

HRR determinations, many items burned are composites

of several different materials, each with its own heat of

combustion. For example, a desk might be made of

wood, fiberboard, sheet plastic and molded plastic

doors, and drawer fronts. Not only do these materials

have different heats of combustion, but they burn at dif-

ferent times during the course of a fire. For these rea-

sons, an HRR estimated from measured mass losses is

often unreliable.

Oxygen Consumption

In the fire research laboratories around theworld worked to develop a method of calorimetry that

was not subject to the problems of the old method dis-

cussed above. The new method is based on the osygen

used upin the fire and is called

(and sometimes depletion

While oxygen consumption calorimeters often have

load cells, the measurements from these cells are for

information and not for calculation of the HRR.

The key to this technology is that the heat released

per unit oxygen consumed is almost a constant for most

materials. Huggctt (1980) found that this heat release

constant is 5,630 Btu per Ib of oxygen

MJ per kg of oxygen consumed). For most materials

involved in building fires, this constant has an uncer-tainty of about 6%.

Figure 2.3 shows a calorimeter where furniture is

burned under a hood connected to an exhaust, such that

all the is drawn into the exhaust. From measure-

ments of the mass flow of exhaust and the content of


24/383

2- and Heat Release

MeasureTemperature. Flow Rate,and GasConcentrations.

SmokePlume

Front View

Figure2.4 Room calorimeter:

the exhaust, the time rate of consumption can be cal-

culated. From this, the HRRcan be calculated. Because

some of the is not completely consumed, gas mea-

surements also include CO and Parker (1982) pre-

sents equations for calculation of the for various

applications.

consumption calorimeters are calibrated by

burning a gaseous fuel (methane, propane, etc.) at a

measured flow rate. The uncertainty of the calorimeter

depends on the uncertainties of (1) the operation of the

calorimeter, (2) the calorimeter calibration process, and

(3) the heat release constant. Calorimeter operation is

not always as intended. Some of the smoke may not be

captured by the hood, or burning materials may fall off

the fire and away from the calorimeter. With such unin-

tended operation, uncertainties in excess of 20% could

result. For a well-calibrated calorimeter operated as

intended, the uncertainty of measured HRR may be in

the neighborhood of 10%. For more information about

the uncertainty of consumption calorimeters, see

et al. (2000).

Open air calorimeters (Figure 2.3) are sometimes

called furniture calorimeters because theyare often used

for furniture. However, they can be used for any fuel

package provided that all of the smoke from the fire

is collected, and (2) the heat released does not damage

the calorimeter including the pollution control equip-

ment. Typically, these calorimeters are located indoors

to protect the fire from the wind. The hoods are usually

to 20 (3 to G m) square, but the size is only con-

strained by the practicalities of construction.Other types of consumption calorimeters are the

room calorimeter and the cone calorimeter. The room

calorimeter (Figure 2.4) is used when the effects of the

walls and ceiling on the HRR are to be

Section View

Time

Figure2.5 Three kiosk

of materials (data

[I

cant. The cone calorimeter is a"bench scale" laboratoryinstrument developed at NIST (Babrauskas 1990).

HRROF SOME OBJECTS

When duplicate objects are burned, there are devia-

tions in HRR as illustrated with the three kiosk fires of

Figure 2.5. These kiosks are for selling T shirts. The

deviations of HRR are due to a number of factors,

including (I ) minor variationsi n arrangement of the T-

shirts, (2) variations in composition of T-shirts, (3) vari-

ations in the dimensions of the kiosk, (4) variations in

materials of the kiosk, and (5) variations in the air cur-

rents near the kiosk. However, the shapes and peak

HRRs of kiosk curves are similar.

Figures 2.6 to 2.19 show HRRs of other objects. The

peak HRR of Scotch pine Christmas trees burned byStroupet al. (1999) were in the range of' to 5000

(1900 to 5300 kW), as shown in Ahonen et


25/383


26/383


looc

0360

l ime

Figure2.11 Upholstered chair with

padding and weighing 25 (11.5 kg)

(datafroni et

00 300 600 900 1200 1500 1800

lime

Figure2.1 2 foam

and 62 (28.3

et al. 9841).

Figure 2.13Sofa padding

et al.

Figure2.14 Metal wardrobe cotton

(data al.

Time(S)

Figure Wardrobe of 0.5in. (12.7

et al.

8000

Unfinished

Fire Retardant 6000. Paint:

4000 2Coats 4000

KI

2000

., .

Figure2.16 of in.(3.2

cotton

et al.


27/383

Principlesof Smoke Managemerit

20 W

15001500.

m,I

500 I

500

01200 1800 2400

lime Time(min)

Figure2.17Two-divider workstation with Figure2.19Automobiles(data from Joyeux

tional desk and credenza (data from

Madrzykowski and Vettori

lime

Figure2.18Three-divider with an open

top and shelf (data from

tion from other spaces. The workstation(Figure 2.17) has a peak HRR of 1700 (1800 kW)at The three-divider workstation (Figure 2.18) has

a peak HRR of 6400 (6800 kW) at 550 A

reason for the higher HRR of the three-sided

tion is probably the increased radiation feedback from

the additional divider and the shelves. For further infor-mation about the HRRs of workstations, readers arereferred to Madrzykowski

Figure shows HRR data of automobiles mea-sured by Joyeux 997). Joyeux showed that cars made

in the had a higher HRR than those made earlier,and this may be due to increased use of polymers and

other materials.-Because of these higher

HRRs, a car fire in a parking garage can ignite an adja-cent car.

Cribs and piles of wood pallets are used in research

and testing when reproducible solid fuel fires are needed(Figures 2.20 and 2.21). Cribs are geometrically

arranged piles of sticks. The crib shown in Figure 2.20

Figure2.20Crib of geometrically arranged

was used for tests of the smoke management system atthe Plaza Hotel (Klote 1990). This crib was made of

wood sticks, in. (38 mm) by 1.5 in. (38 mm) by 2 ft(0.61 long, and it had a peak HRR of aboet 1400

(l kW) when burned in free air. The stack of

nine wood pallets shown in Figure has a peak HRR

of about 3,500 (3,700 kW) when burned in free

air. Gross ( 1 Block( 197 and Walton (1988)burned cribs of various sizes and stick

Babrauskas (2002) provides heat release data of cribsand pallets.

VENTILATION-CONTROLLED FIRES

As already stated, the HRR of a

trolled fire depends on the amount of air that reaches thefire. Further, the HRR can be expressed as a function of

the openings to the fire room as

where


28/383


Q = heat release rate of fire, kW

A, area of ventilation opening, f? (m2);

H, = height of ventilation opening, (m);

=

Equation (2. l )appiies to rooms of construc-

tion and size with only one rectangular opening. Figure2.22 shows the ofa ventilation-controlled fire as a

function of width of the door or other opening. Equation

(2.1) provides useful estimates for rooms made with

normal construction materials concrete, wood,

etc.), but it is not appropriate for metal rooms, such as

on a ship with steel decks and bulkheads. For large

rooms (over 300 [30 the appropriateness of

Equation (2.1) is questionable. For information about

the effects of construction materials and room sizes, see

Walton and 995).

For a number of rectangular openings with the same

bottom and top elevations, the heights are the same, and

the effective area is the sum of the individual areas.

where

A , effective area of all the ventilationopenings,ft2

area of ventilation opening from = to

(m').

This is illustrated for two openings in Figure 2.23.

Figure2.2 Stacko f

Example 2.1 Ventilation-Controlled Fire

For a roomwith a single doorway opening that is fullyinvolved in how big will the fire be? The doorway open-ing is 3 (0.914m)wideby7 (2.13 high.H,=7 (213 m);A, = =21

thetire is ventilation controlled, Equation (2.1) isapplicable.

Q

SPRINKLERS

Figure illustrates t-squared fire growth with

the three possible responses to sprinkler spray: (a) sprin-

klers overpowered by fire, (b) constant and (c)

reduction ofHRR. Sprinklers can be overpowered by an

extremely fast growing fire due to burning materials that

exceed the sprinkler design. Sprinklers can also be over-

powered when the smoke reaching the sprinklers has

cooled due to plume entrainment, happen with

fires in spaces with ceilings that are relatively high com-

pared to the arrangement of fuel. For this to happen, the

Door

DoorWidth

Figure 2.22 HRR a

medium-sizedroom

Foropenings with the same andbottom elevations.A,

Figure2.23Combining openings

of sizeo f


29/383


Time

(a) SprinklersOverpowered by Fire

I

Conservative Estimate

of Constant HRR

Time

(b) Conservative Estimate of ConstantHRR After Sprinkler Activation

Time

(c) Fire Decay After Sprinkler Activation

Figure2.24 Interaction between and sprinklers.

flame height is typically less than the ceiling height, androom air cools the gases in the

plume. Methods of calculating the plume temperature

are in Chapter 13. If the sprinklers do activate, the spray

could evaporate before the droplets reach the fuel.

DECAY DU ETOSFRINKLERS

A constant HRR after sprinkler actuation is a con-

servative estimate for many applications. Fire

after sprinkler actuation is more realistic. Fire decay can

be expressed as

where

= post sprinkler actuation HRR, kW

= sprinkler actuation, kW

t = time from ignition,

= time of sprinkler actuation,

= time constant fire suppression,

For a number of fuel likely to be found in

offices, and (1992) conducted

sprinklered fire experiments with a spray density of

(0.07 of water. They determined that a

fire decay curve with a time constant of 435 had ahigher HRR than most of the sprinklered fires (Figure

2.25). Evans (1993) used these data and data for wood

crib fires with sprinkler spray densities of

(0.041 and 0.097 (0.066 from

(1976) to develop the following correlation:

where

= spray density,

C, = 6.15

While Equation (2.4) has not been experimentally

verified, it does allow us to adjust the decay for

sprinkler densities other than those of

Sprinkler Response

While the information in this section is primarily

about sprinklers, it also applies to vents actuated by fus-

ible links and fixed temperature detectors.

The responsiveness of sprinklers is tested by the

plunge test, where a sprinkler is into a heated

in which heated air is circulated. The of

the plunge test is mathematically the as that o f a

small piece of hot metal suddenly quenched in a cool

fluid, as described in heat transfer textsand This analysis is based on

the assumptions that (I ) the internal resistance of the

sprinkler is negligible, (2) the sprinkler is instanta-

neously put the oven, (3) the convective heat transfer

is constant, (4) the gas temperature i n


30/383

Chapter 2-Fire and Heat Release

oven is constant, and the only heat transfer is from

the sprinkler to the gas.

The temperature of the sprinkler increases

as shown in Figure The time constant, of

the sprinkler is

where

=

m =

C =

h, =

A =

time constant,

mass of the sprinkler, (kg);

specific heat of the sprinkler, "F "C);

convective heat transfer "F

surface area of the sprinkler, (m2).

. The time constant, is the time at which the tem-

perature of the sprinkler has reached 63% of the way to

thegas temperature. The convective heat transfer

cient varies with velocity, so that the time constant alsovaries with the velocity at which it is measured.

The response time index (RTI) was developed as a

measure of sprinkler responsiveness that is independent

of velocity.

where is the velocity,

In the plunge test, the to actuation and the gas

velocity are measured. Then the time constant can be

calculated from the to actuation, and the RTI is

calculated from Equation The RTI of standsrd

sprinklers varies from about 140 to 280

to 155 and the RTI of quick-response sprin-

klers (QRS) varies from about 50 to 100 (28 .

to 55

The response time index does not account for con-

ductive heat transfer from the sprinkler. To account for

conduction, a virtual RTI can be calculated as

RTI,

where

RTI, = virtual RTI,

= conductivity factor,

. .

'I:is time constant

Time

Figure2.26

Paper Cart Fuel PackageSecretarial Desk Fuel PackageExecutiveDesk Fuel Package

. Office Fuel PackageI Fuel Package

Sofa Fuel. Work Station I Fuel Package-- Work Station Fuel Package

Wood Cribs

0 200 400 600 800

Time, t-

Figure 2.25 to a of

(0.07


31/383

Principlesof SmokeManagement

Actuation

Actuation depends on gas temperature and velocity

near the sprinkler. In a fire, a jet of hot gases flows

ally from where the smoke plume intersects the ceiling.

Computer programs have been developed that use corre-

lations for such a ceiling jetto predict actuation time.

The program DETACT-QS (Evans and Stroup

1986) assumes that the thermal device is located ina rel-

atively large area, that only the ceiling jet heats the

device, and that there is no heating from the accumu-

lated hot gases in the room. The required program inputs

are the height of the ceiling the fuel, the distance

of the thermal device from the axis of the fire, the actua-

tion temperature of the thermal device, the response

time index (RTI) for the device, and the rate of heat

release of the fire. The program outputs are the ceiling

gas and the device temperature, both as a

function of time and the time required for device actua-

tion. DETACT-T2 (Evans et al. 1986) is similar to

DETACT-QS, except it is specifically for t-squaredfires. Several zone fire models (such as FAST,

and JET) are capable of calculating ceiling jet

temperatures and predicting actuation (Chapter 8).

DESIGN FIRES

A design fire curve is the description of the devel-

opment of a design fire that can be used in a fire sce-

nario. The curve is for HRR as a function of time. This

curve can be as simple as a constant, and it can also be a

simple function of The design fire curve can also

be a complicated sequence of lesser for some or

all of the stages of tire development described at the

beginning of this chapter.

A fire scenario includes more than just the design

fire curve. The word means an outline of

events, asi n a play or other theatrical production. A fire

scenario can be thought of as the outline of events and

conditions that are critical to the outcome

of alternative designs. In addition to the HRR and fire

location, a scenario could include the type of materials

burned, airborne toxicants and soot produced, and peo-ple movement during fire.

are not intended to be located in the space are referred to

as

A few examples of transient fuels are Christmas

decorations, paint and solvents in stairwells during

redecorating, unpacked foam cups in cardboard boxes

after delivery, cut up cardboard boxes awaiting removal,

and closely stacked upholstered furniture after delivery.Sometimes, transient fuels remain in place for long peri-ods. Some examples are a number of polyurethane

mattresses delivered to a dormitory and waiting for dis-tribution in the next school year, (2) automobiles on dis-

play in a shopping mall, (3) boats and campers on

display in an arena, and (4) a two-story colonial house

built for display inside a shopping mall.

Transient fuels must not be overlooked when select-

ing a design fire. One approach to incorporating tran-

sient fuels in a design fire is to consider the fire

occurring over 100 (9.3 m2) of floor space with a

heat release rate density of 20 Btuls ft2

(225

This amounts to an allowance for transient of 2000

(2100 kW).

Steady Fires

It is the nature of fires to be unsteady, but the steady

fire is a very useful idealization. Steady fires have a con-stant heat release rate. In many applications, use of a

steady design fire can lead to and con-

servative designs.

HRRper Unit Area

Morgan (1979) suggests a typical rate of heat

release per unit floor area for mercantile occupancies of

44 (500 Fang and Breese (1980)determined about the same rate of heat release for resi-dential occupancies. Morgan and Hansell (1987) and

Law (1982) suggest a heat release rate per unit floor

area for office buildings of 20 f? (225

For smoke management applications, a heat release rate

per floor area of 20 Btuls ft2 (225 is suggested

for restricted fuel spaces, and 44 Btuls ft2 (500

is suggested for spaces with furniture, wood, or other

combustible materials. A occurring over 100 (9.3

m2) of floor space would result in 2000 Btuls kW)

for restricted fuel space and 4600 kW (4400 Btuls) fora

space with The heat release densities ofIn many spaces, the fuel loading is severely

Table 2.2 can be useful in determining design fires.restricted with the intent of restricting fire size. Such

spaces are characterized by interior finishes of metal,

brick, stone, or gypsum board and furnished with Unsteady Fires

objects of similar materials plus plants. Even for Fires frequently proceed through an incubation

such a space, there can be an almost period of slow and uneven growth, followed by a period

unlimited number of objects that are in the of established growth as illustrated in Figure 2.27 (a).

space for short periods. Such combustible materials that Figure 2.27 (b) shows that established growth - is often


32/383


33/383

wheretis considered the time from effective ignition. For

I-Punits, the following form of Equation (2.9) is

used:

where

Q = heat release rate of fire,

time after effective ignition,

= growth time,

When = Equation (2.10) gives a value ofQ =

Table 2.3 lists fire growth values from

NFPA 92B (NFPA 2000) and NFPA 72 (NFPA 1999).

The fire growths corresponding tothe NFPA values

are shown on Figure 2.28. Unless otherwise stated in

this book, the terms slow, fast, and fast

fire growth refer to the NFPA 92B values.

Fuel Package Approach

The base fuel package is the maximum probable

size of package that is likely to be involved in fire

for a specific application. A fuel package can be made

up of a number of fuel items (sofa, chair, bed, table, cur-

Time,t

(a) Typical HRR curve

Time,t

(b) Idealized Parabolic curve

2.27 Fire


tains, The key to selecting the items that make

the base package is that the radiant flux bum-

ing one of the items will lead ignition of the other

items in the base package but not to ignition for

items outside the base package.

The point source radiant model (Figure 2.29) con-siders the flame as a small thermal source such that the

intensity of thermal radiation is proportional to the

inverse of the square of distance from the source. Ther-

mal radiation also is calledradiant

The intensity of thermal radiation is

where

intensityof thermal radiation,

= radiant releaseofthe fire, (kW);

R = distance from the of the fire, ft (m).

Table 2.3:

Fire Growth Constants for T-Squared Fires

NFPA 92 8

Slow

Thin Plywood Corrugated Cardboard

Cartons1.5 (4.6m)High -Various: Contents

0 200 400 600 800

Medium

Fast

Fast

TimeFrom

Figure2.28 of

0.002778 0.002931

0.01 0.01 127 300

0.04444 0.04689

0.1778 0.1878 75

400

150

NI A


34/383

Chapter2-Fireand Heat Release

OrientedFire Normal

The point source model is a goodapproximationprovided thatR

Figure2.29Point sourceradiation model.

The point source radiant model is appropriate pro-

vided that the distance from the of the flame is

greater than twice the diameter of the fire (R The

radiant heat release of the fire is

where

Q heat releaserateof the fire, (kW);

= radiativefraction.

Heat transfer a is by conduction, con-vection, and radiation. For most fires, conductive heat

transfer from the is negligible. The radiant frac-

tion can be expressed as

where is the convective fraction.

The radiative fraction depends on the material

burned and the diameter of the fire, and the radiative

fraction varies from about 0.1 to 0.6. Low sooting fuels,such as methanol, have low radiative fractions, and high

sooting materials, such as gasoline and polystyrene,

have high radiative fractions. However, for design appli-

cations, values of 0.3 and = 0.7 are common.

The idea of separation distance is useful evalua-

tion of what items should be in the base fuel package.Using the point source radiant model, the separation dis-

tance is

where

= separation distance from the ofthe fire to

a target, (m);

= intensityof radiation needed for

ignition,

Fuel items less than away from the fire would

be expected to ignite, and fuel items farther than

away would not be expected to ignite. The radiant flux

needed for nonpiloted ignition varies from about 0.9(10 for thin easy-to-ignite materials to

1.8 (20 for thick materials.

For a fire, the heat release rate, that results in

ignition of an object at a distance ofR away is

For radiant heat transfer where R is less than twicethe diameter of the fire, a method other than the point

source model is needed. Several texts have general

information about radiant heat transfer and

1992; lncropera and 1985; Kreith 1965).

For information about radiant heat transfer of fire, read-ers are referred to Quintiere

and and Croce (1995).


35/383


36/383

Chapter2 andHeat Release

Sofa Sofa

Chair2Note:R, m)

Figure2.30 the of

Example

time(a) Draw curveforsofa 1,and ignitionpointof chair

. .

(b) Draw for chair

4000

Time(c) Locate ignition point and draw curve for sofa 2

Time(d) Get base fuel package by adding the 3 othercurves

Figure2.31Graphic of base

package Examnple2.2.


37/383

CHAPTER3

Smoke and Tenability

In this book, the term is used in accordance ard. Frequently, people become disoriented in fire

the definition of NFPA 92A (2000) and NFPA tions because they cannot see through heavy smoke. If92B which states that smoke consists of the they remain in the building too long, they fall victim to

airborne solid and liquid particulates and gases evolved exposure to toxic gases or elevated temperatures. Fur-

when a material undergoes pyrolysis or combustion, ther, in buildings with balconies, smoke obscuration can

together with the quantity of air that is entrained or result in fatal falls.

mixed into the mass. The products of combustion

usually include particulates, unburned fuel, water

carbon dioxide, carbon monoxide, and some other toxic

and corrosive gases. As smoke moves through a build-

ing, air mixes into the smoke mass and the concentration

of combustion products in the smoke decreases. Includ-

ing air that is entrained or othenvise mixed facilitates

discussions about fire smoke management in atriums

and other spaces. Generally. smoke is thought ofas

being visible, but the above definition includes

Smoke management systems can be designed with

the objective of providing a tenable environment in the

means of egress or at other locations during evacuation.

Such a tenability system needs to be designed to meet

tenability criteria. Such criteria need to include expo-

sure to toxic gases, heat, and thermal radiation. Further,

the criteria often include visibility. As discussed at the

end of this chapter, criteria for a tenability design

depend on the specific application.

ble produced by burning of materials that pro-

duce little or no particulate matter, such as hydrogen,

natural gas, and alcohol.

Information about smoke hazards is useful in

effects of small quantities of smoke migrating

into "protected spaces," and it is useful in evaluating the

consequences of smoke migration without smoke pro-

tection. This chapter concentrates on hazards due

to toxicity, temperature, and smoke obscuration. The

hazards of temperature consist ofhear which

can occur when a person comes into bodily contact with

hot gases, and can

occur a person receives thermal radiation from

flames or hot smoke that are some distance away from

the person.

Many different methods of expressing smoke

obscuration are used in fire science and fire protection

engineering, and this section discusses the common

methods. There is a lack of uniformity concerning

smoke obscuration, and some engineering publications

use different terminology or have different mathemati-

cal definitions for the same terms. These differences

could result in significant errors, and readers are

ticned to take care to verify the exact meanings of

obscuration terms used in other publications. The termi-

nology that follows was selected with the intent of beingconsistent with technical publications in this field.

Exposure to toxic gases, heat. and thermal radiation The fraction of light transmitted through the

can be a direct hazard to life, and reduced visibility due length of smoke is called thetransniittance and is writ-

to smoke obscuration can be a significant indirect haz- ten as


38/383


39/383


Table 3.1:Comparison of Differ

principles of smoke management - printed

Documents