BRE 368

H

_{P Morgan}

B

K

Ghosh

G Garrad

R

Pamlitschka

J-C

De Smedt

L

R Schoonbaert

Design

meth

smoke and

h

ventilation

ST.

J8

OF

Photo

acknowledgomsnts Wont

coe

—

conq

it

Brussels International Airport

Company (MAC)

Rae

_con.'

at

Colt Plates 1,

35

and 6 Cooper Qoip: Plate 4

BRE

Garston. Watford WD2 7JR

Design

methodologies

for

smoke

and

heat

exhaust ventilation

H

P

_Morgan

BSc, PhD, C Phys, M Inst P,

F

I Fire E

B K

Ghosh

MSc, BA, C Phys, M Inst P, Dip Math

G

Garrad

BSc, MSc

Dipi Ing

R

Pamlitschka

(Colonel)

J-CDeSmedt

AlFireE

Prices for all available BRE publications can

be obtained from: CRC Ltd 151 Rosebery Avenue London EC1R 4GB Tel 01715056622 Fax 01715056606 E-mail [email protected] BR 368 ISBN 1 86081 2899

©

Copyright BRE 1999 First published 1999 Published by Construction Research Communications Ltd by permission of Building Research Establishment Ltd Applications to copy any part of this publication

should be made to:

CRC Ltd

P0 Box202

Wattord

WD2 7QG

Front cover photo:

Hot-smoke test at Brussels Airport, Belgium

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produced by BRE

incorporating some material developed under

a contract placed by the Department of the

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______________

Foreword

Use

_by

_{fire engineers ofsmoke}

and heat

_{exhaust ventilation systems (SHEVS}

_{as they have}

become known)

has

grown

in recent

years.

It

is

therefore welcome

that

this

guide has

been

produced

which

_provides

the

_{fire engineer}

with

_{assessment design methodologies for}

the use of

these

systems. SHEVS require

the

most careful design prior

to

introduction.

It

is

important however

to

ensure,

as with

all _{fire-engineering designs,}

that

_{due regard}

is

taken

over

issues

such as

_{escape time}

and

fire growth since

these

_{features provide}

the

base

_upon

which

the

_{design parameters}

can be

made.

It

_{is also important}

that due

_regard

be

_{ultimately made regarding}

the

maintenance

of

any

systems installed

and

current guidance, primarily within

the

British Standards Institution's DI)240 Fire _{safety engineering}

zi

_buildings. DD240

has

introduced

the

overall design process

which

the

fire

engineer should consider. DD240 also makes

it

clear

that

caution

is

necessary

and

that

all options

have to

be

considered before entering

into

a

particular design process. SHEVS

is one

of

those

options

and this book

therefore provides comprehensive identification

of

the

issues

which

need consideration.

It

is

_{particularly important}

to

pay attention,

as

the

document outlines,

to

the

restrictions

of

computer software modelling programs, as

it

is

also for

the

fire _engineer

to

recognize

there are

limitations

as

to

what

any systems (and

that

includes SHEYS)

can

achieve.

With these

_thoughts

in

mind,

this book

provides

a

most useful

and

comprehensive review

of

current thinking regarding SHEVS design methodologies

for

utilization

_{by the}

fire _engineer.

D T

Davis OBE QFSM CEug FiFireE CIMgt

HM Chief

_Inspector

of

Fire Services for Scotland

iv

Preface

This guide summarizes

the

advice available from

the Fire

Research Station,

to

designers

of

Smoke

and Heat

_{Exhaust Ventilation Systems (SHEVS) for atria}

and

other

_buildings.

It

_{builds upon}

currently available published advice (especially BRE Report Design

app

roachesforsm oke control in

atrium _buildings [13]

_,

but

_{also BRE Report Desinprinciblesforsmoke ventilation}

th

enclosedshopping

cenfres24l),

by

including

more

guidance

on

the

use

of

the

methods given, and

by

including

the

results

of

research carried

out

since

the

_publication

of

ref. [13]

in

1994.

In

_particular,

the

use

of

a design fire

size is

considered

in

more

detail, including:

•

a

discussion

of

growing fires,

•

formulae and calculation methods

to

determine

the

deflection ofsmoke curtains

in

fire situations

so

that the

specification

of

smoke curtains

can

become

part

of

the

SHEVS design,

•

the

effects due

to

airflow

on the

_efficiency

of

natural smoke exhaust ventilators

and on the

stability

of

smoke layers.

This guide does

not

consider

the

scenario

where

a

fire

in

a

room connecting

to

an atrium

causes

a

flame plume

to

rise

into

the

atrium.

In this

context,

any

large space adjoining

the fire room may

be considered

to

be an

atrium,

eg

malls

in

shopping complexes.

A

discussion is included

ofthe

factors

which need

to be

considered

when

_specifying

the

hardware (ventilators, smoke curtains,

etc.)

required

to

implement

the

design

in

a

building. Some advice

is

also included on:

•

factors

to

be

considered

in

installing

the

system

in

buildings,

•

how

to

test the

_finctioning

of

the

_{equipment separately}

and

as

a

_{complete system}

once

it

has

been

installed, and

•

'good

practice' measures involving

the

management

and

maintenance

of

the

system

when

the

building is

in

everyday use.

The

_purpose

ofthis book

therefore

is

to

provide practical guidance

on the

design ofsmoke-control systems.

It

reflects

current

knowledge

and is based

on

the

results

of

research where

available,

including

as yet

unpublished results ofexperiments. In addition,

it

draws

on

the

authors' cumulative experience

of

design features required

for

regulatory purposes

in

many

individual

smoke-control applications.

Many

of

these

design features have evolved over several years by consensus

between

_{regulatory authorities, developers}

and

fire scientists,

rather than

_by

_specific

research.

The

_{methodology underpinning}

the book is

_{explicitly empirical}

_{in approach and can}

_{easily be}

extended

to

most buildings.

Where

guidance

is

necessary

to

address practical design issues but

there are

_gaps

in

the

_{established knowledge-base,}

the

authors

have

exercised

their

professional

judgement

in

offering conservative, pragmatic advice.

When

guidance

is

offered

in

these

circumstances

_any

_{potential weaknesses}

are made

explicit. Related

to

this

is

the

continuance

of

the

philosophy

used in the

book's predecessor BRE Reports'3'241

that even where

a

document is

difficult

to

obtain,

or

_{even verbal private communication}

is the

source

of

advice,

it

is listed

as

a reference.

HPM, BKG, GG,

RP,J-C De

S, LRS

About

the

authors

Howard P _Morgan

Principal Consultant, Fire Protection Systems Centre, Fire Research Station (FRS), BRE

Head, FRS(Asia) Centre

Technical Director, FRSAFSET (Asia) Ltd, Hong Kong Fire Research Station, BRE, Bucknalls Lane, Garston, Watford, WD2 7JR, UK

Email: [email protected]

Gordon Garrad

Fire Scientist, Fire Research Station (FRS), BRE

Fire Research Station, BRE, Bucknalls Lane, Garston, Watford, WD2 7JR, UK

Email: [email protected]

Bijoy Ghosh

Senior Fire Consultant, Fire Research Station (FRS), BRE

V

Fire Research Station, BRE, Bucknalls Lane, Garston, Watford, WD2 7JR, UK

vi

About the

authors

Colonel R Pamlitschka

Head of Fire Prevention Department, Professional Fire Service, Vienna, Austria

Head of _{Smoke-Control Department, Prüfstelle} für

Brandschutztechnik des Osterreichischen Bundesfeuerwehrverbandes, Austria CO Ma. 68, Hauptfeuerwache Mariahilf, Gumpendorfer Gurtel 2, A-1060 _{Wien, Austria}

Jean-Claude De Smedt

Managing Director/Principal Consultant, International Fire Safety Engineering Technology (IFSET), Belgium Managing Director, FRS/IFSET (Asia) Ltd, Hong Kong

NV IFSET SA, Stationsstraat _{35, B-i 730 ASSE,}

Belgium

Email: jcds@ifsetcom

Lieven R Schoonbaert

Senior Consultant, International Fire Safety Engineering Technology OFSET), Belgium

Director, FRSAFSET (Asia) Ltd, Hong Kong NV IFSET SA, Stationsstraat 35, B-1730 ASSE,

Belgium

Contents

Chapter 5

Smoke control on

the

storey

of fire

origin

5.1 Within

the fire room

5.1.1

Plumes above large

fires

5.1.2

Plume above

small fires

VII

Foreword

iii

Preface

iv

Aboutthe

authors

v

Contents

vii

Abbreviations

xii

Nomenclature

Xiii

Chapter

1

Introduction

1.1

Thehazardsofsmoke

1.2 The regulatory

background

1.3 The

role

of

smoke

and heat

exhaust

ventilation

1.4

Smoke and heat

exhaust

ventilation as a

_{part of}

_{fire safety}

_engineering

1.5

A

_{brief history}

of

smoke

ventilation

1.6 The atrium: description

and behaviour

in fire

1.7 Active control

of

the

fire

1.8

_{Implementation}

of a

smoke

and

_{heat exhaust system in}

a

building 1 .9 The

_purpose

of

this book

and

its

relationship

to

earlier

guidance

1 1 1 2 2

4

5 6 7

8

Chapter 2

General

principles

of

smoke production,

movement and control

2.1

Fire

_growth

and

smoke

production

2.2

_{Pressurization and depressurization}

2.3

Throughtiow ventilation

(or smoke exhaust

ventilation)

2.4 Smoke

and

heat exhaust

_{design philosophies}

10

10

12

12

13

Chapter 3

Design-fire

size

3.1

General

3.2 Growingdesignfires

3.3

Steady-state

design fires

3.4 Acceptable failure

rates

14

14

15 16

19

Chapter 4

Escape

times

20

22

22

22

24

viii

Contents

5.1.3 Effects

of

_{adjacent walls}

on

entrainment

into the

_plume

25

5.1.4

Effects

of

sprinkler

25

5.2

The

flow

of

_{hot gases out}

of

the room

of

_{origin into}

25

a

taller

adjacent

space (eg an atrium

or

mall)

5.3

Ventilation

of

_{single-storey}

smoke

reservoirs

27

(including

the balcony space where smoke

is

contained

and exhausted

from

beneath

a

_balcony)

5.4 Smoke layer temperature

28

5.5 Effects

of

sprinkler systems

in

smoke

reservoirs

30

5.6

_Flowing

_layer

depth

30

5.7 Localdeepening

31

5.8 Automatic smoke curtains

31

5.9 Inlet air

32

5.10

Minimum

number

of

exhaust

_points

34

5.11 Throughflowventilation:

area

of

natural

ventilation required

35

5.12 Natural ventilators

and

wind effects

35

5.13

Required

ventilation rate

(powered exhaust)

37

5.14

Slit extract

37

5.15

False ceilings

37

5.16

The use

of

a

_plenum

chamber

above

a

false

_ceiling

38

5.17

Maximum

dimensions

for

smoke

reservoirs

38

Chapter 6

Smoke ventilation within multistorey spaces (eg

the

atrium)

39

6.1 Smokemovementintheatrium

39

6.2

Channelling screens

40

6.3

Entrainment

_{into 'spill plumes' rising through the atrium}

42

6.3.1

The

effective

height

of

rise

from

the

spill edge

42

to

the smoke layer

base

6.3.2

Entrainment

calculation methods

44

6.3.3

Recommendations

for

_selecting

a

spill

plume formula

49

6.4

_High

_temperature

_plume

49

6.5 Firesontheatriumfloor

50

6.6 Throughflow

ventilation: remaining design procedures

50

6.7 Limitations

to

the

use

of

_throughflow

ventilation

50

Chapter 7

Alternative

forms of

smoke control

for

atria

53

(including multistorey malls

but

excluding throughflow ventilation)

7.1

Voidfihling

53

7.2 Compartment

separation

53

7.3

Depressurization ventilation

53

7.3.1

_Principles

53

7.3.2 Natural

depressurization

54

7.3.3 Natural depressurization

and

wind effects

57

7.3.4 Powered

_{depressurization}

58

Chapter 8

Depressurization/smoke ventilation hybrid designs

59

Chapter 9

Atrium

smoke layer temperature

61

Chapter 10

Additional design factors

64

10.1 Atrium

roof-mounted

_{sprinkler systems}

64

________ Contents

ix

10.3

Air-conditioned atria

64

10.4

Channelling

screens

and hybrid

systems

65

10.5

Wind-sensing devices

65

10.6 Crossdraught

within

the

atrium

65

10.7 Crossflowwithin the gas

layer

65

10.8

Wind effects on horizontal ventilators

66

Chapter

11

Interactions with

other

systems

in the

building

67

11.1 Sprinklers

67

11.1.1 Automaticsprinklers

67

11.1.2

Automatic smoke exhaust

ventilation

67

11.1.3

_{Sprinklers combined with smoke}

ventilation

67

11.2

Fire-detection systems

69

11.3

Heating, Ventilation and

Air

Conditioning (HVAC)/

69

Air

Conditioning and Mechanical Ventilation (ACMV)

11 .4

Pressurization

of

stairwells

and lobbies

70

11.5 Lighting

and signage

70

11.6

Public

address

and

voice alarm systems

70

11.7

Security

70

11.8 Computerized

building

control

systems 71

Chapter 12

SHEVS

and

the fire

services

72

12.1

General

72

12.2

Design

objectives

for

SHEVS and implications

for

the

design-fire

72

as

a

basis

for

design

12.2.1

Fundamental fire-fighting objectives

72

12.2.2

Design

objectives

for

SHEVS in connection

73

with

fire-fighting

objectives

12.3

Circumstances which

reduce

or

impede

the ability

of

a SHEVS

76

to

assist

fire-fighting operations

12.3.1

Factors

_{adversely affecting successful}

intervention

77

by the fire services

12.3.2

Additional provisions

for

optimizing the effective

use

77

of a

smoke-free layer

created by

a

SHEVS

for

fire-fighting operations

12.4 Circumstances

where a SHEVS

is of

minor

benefit

77

for

_{fire-fighting}

operations

12.5 Circumstances

where SHEVS

are not

applicable

78

12.5.1

Premises with

risk

of

fast-growing

fires

78

12.5.2

Premises

which

must not

be

entered in case

of

fire

78

because

of

other

prevailing hazards

13 Selection

of

_equipment

79

13.1

General

79

13.2

Natural

smoke

and

heat exhaust ventilators

80

13.2.1

Time

taken

to

come into

full

_operation

80

13.2.2 Coefficient

of

performance

80

13.2.3 Resistanceto

heat

81

13.2.4

Opening under

load:

snow

81

x__________ Contents _________________________ ______________________________

13.2.6 Lowambienttemperature

82

13.2.7

Reliability

82

13.2.8 Ability

to

resist wind

suction

82

13.2.9 Ability

to

resist

rain penetration

82

13.3

Powered

smoke

and

heat exhaust ventilators

82

13.3.1 Time

to

come into full

_operation

82

13.3.2 Resistanceto

heat

83

13.3.3

_{Opening under}

load:

snow

83

13.3.4

Opening under

load:

wind

83

13.3.5 Lowambienttemperature

83

13.3.6

Reliability

83

13.4

Automatic smoke

curtains

83

13.4.1 Time

to

_deploy

to

the

fire-operational position

83

13.4.2 Speedoffallofbottombar

83

13.4.3

Resistance

to

_{high temperature}

83

13.4.4

_Reliability

84

13.4.5

Fail-safe

84

13.5 Air inlets

and

doors

84

13.6

Smoke dampers

84

13.7

Smoke ducts

84

Chapter 14

Installation

—

86

Chapter 15

Acceptance testing (commissioning)

89

15.1

General

89

15.2

_{Testing and commissioning}

₈₉

15.3 Hot-smoketests

91

Chapter 16

Maintenance, management and re-testing

92

Chapter

17

Some common mistakes

in the

_design

of

smoke ventilation systems

94

17.1

Mis-location

of

the point source

of a

_{'point-source'}

smoke

_plume

94

17.2

_Inadequate

_{specification}

of

smoke curtains

94

17.3

Installation

does not follow

_design

94

17.4

Mis-use

of

_computer

models

94

1

7.5

Mistaken

perceptions

of

conflict

between 95

active

_{and passive}

_{fire precautions}

Chapter

18

_{Smoke ventilation design and enforcement}

of

_regulations

96

Chapter

19

_{Acknowledgements}

97

Chapter

20

References

98

Annex

A:

_{Design procedure with}

a

_{growing design}

fire

101

Annex

B:

_{Design procedure with}

a

_{steady-state design}

fire

103

Annex

C:

Deflection

of

smoke curtains

106

Annex

D:

A

_comparison

of different

_{spill-plume calculation methods}

109

Annex

E:

User's

_guide

to

BRE

_{spill-plume calculations}

112

Annex

F:

1977 fire at

IMF

_{building, Washington}

DC

_{(based on reference [18])}

117

________________ Contents ______________________________ ________

xi

Annex

H:

Effect

of

_{a buoyant layer on}

the

minimum

_pressure

120

recommended

for

a pressure

differential

_system

Annex

I:

_Aspects

of

hot-smoke tests

to confirm the

_performance

of

SHEVS

121

Annex

J:

_{Case history}

—

smoke-control design

in

'D3

_{Espace Leopold}

123

XII

Abbreviations

ACMV Air conditioning and mechanical ventilation

BRE _{Building Research Establishment Limited} BS British Standard

BSI British Standards Institution

CEA _{Comité Européen des Assurances} CEN Comité Européen de Normalisation

CFD Computational fluid dynamics

Eqn Equation

FRG _{Fire-resisting glazing} FRS Fire Research Station

HST Hot-smoke test

HVAC Heating, ventilation and air conditioning

IFSET _{International Fire Safety Engineering Technology} NIST National Institute for Standards and Technology (USA) NPP Neutral pressure plane

RTI Response time index

Nomenclature

Note: An additional Nomenclature list can be found in Annex E

A Function defined by Eqn (7.3)

Af Area of the fire (m2)

Ag Area of the gaps between smoke curtains, or between curtain and structure (m2)

A Area of inlet (measured) (m2)

Ares Plan area of smoke reservoir (m2)

A5 Area of exhaust ventilator (measured) (m2)

A

Area of opening (window), eg between a side-room and an atrium (m2)

c Specific heat of air (kJkg1K1)

C A constant (kgms1kW')

Cd Coefficient of discharge for a vertical opening

CdO Cd for flows out of an opening where a balcony or canopy projects beyond the opening

CdS Cd for flows ata spill edge.

Ce Entrainment coefficient in Large-fire plume model'

C Coefficient of discharge lie the performance coefficient) for an inlet

C

Dimensionless entrainment coefficient, found experimentally to be 0.44 for a free plume, and 021 for an adhered plume

C5 A constant in Zukoski's small-fire plume modef43 C5 Wind pressure coefficient

Wind pressure coefficient acting on an inlet

CPL Wind pressure coefficient acting on the leeward side of building

Wind pressure coefficient acting on an exhaust ventilator

C5 Coefficient of discharge (ie the performance coefficient) for an exhaust ventilator

d

Horizontal deflection of a smoke curtain, measured at its bottom bar (m)

d1 Visible depth of smoke layer in the smoke reservoir (m)

d0 Depth of an opening between an atrium and a side-room,

measured from top to bottom of that _opening (m)

d2 Effective depth of smoke layer — only used as part of spill plume entrainment calculation (m)

D Depth of smoke beneath an exhaust point (m)

DB Depth of a smoke layer under a balcony (m) Dd Depth of a downstand fascia (m)

Df Diameter of fire (m)

D1 Design depth of a smoke layer in a reservoir (m)

D

Depth of a flowing smoke layer in a vertical opening (m)

Dmax Maximum depth of smoke in an atrium (m)

(Note: This can either be to the floor, or the maximum allowable in a

hybrid SHEVS/depressurization design)

Dmn Minimum allowable smoke layer depth in a hybrid SHEVS/depressurization design (m)

g Acceleration due to gravity (ms2)

h _Height of the top of a vertical opening/window above the base of the fire inside the room (m) hb Height of rise of a thermal line plume from an opening or balcony edge to the smoke layer (m) h5 Height of rise of leakage gases from the base of the hot gas layer in the smoke reservoir to the ceiling

in the _{adjacent protected area} (m) H _Height of a vertical opening (m)

H5 Height of the atrium (m)

H Height to the ceiling (m)

L _{Channelling screen separation; also length} of a spill edge (m)

(Note: L = W for a spill plume rising directly above an opening)

Nomenclature

L _Length of the smoke curtain _{from top} to bottom bar, measured along the fabric (ml

M Mass flow rate _(kgs')

M1) Mass per metre length of the curtain's bottom bar (kgm1)

Mr Mass per m2 of the curtain fabric (kgm2)

M0RIL Critical exhaust rate at an exhaust point prior to the onset of plugholing )kgs

M Mass flow rate of smoky gases exhausted from the smoke reservoir (kg 1)

(Note: Usually Me = M)

Mass flow rate ri the _{plume above} the fire (kgs 1

Mass of gas flowing through the gap between smoke curtains, or between curtain and structure Ikgs)

Mass flow rate under a _{balcony (kgs I)}

Mass flow rate entering a smoke layer in a _{reservoir (kgs1)}

Mass of gas flowing into gas layer in _{protected area, having leaked through gaps in smoke curtains (kgs} 1)

Mass flow rate flowing through a vertical _{opening (kgs1)}

An integer used to identify one stage in an iterative process Number of exhaust points

Perimeter of fire (m) M1 M1, MB M1 M

M

n N P

q Heat release rate 1kW)

q Heat release rate per unit fire area (kWm 2) Q Heat flux 1kW)

Q, Convective heat flux in the gases after the initial flame plume )kW)

Q

Convective heat flux passing through a _{vertical opening (or under} a balcony) (kW)

A function defined by Eqn (H. 11

I time after ignition Is)

T Absolute temperature of gases (K)

T3 Massweighted average absolute temperature of gas layer under a _balcony (K)

T

Maximum value of absolute temperature in a layer beneath a ceiling or soffit (K)

T Mass-weighted average absolute temperature of gas layer in a reservoir (K) T0 Absolute ambient temperature (K)

v,

Wind velocity at the same height as the top of the _building (m s1) V Volumetric flow rate of gases (m

s

)

V1 Volumetric flow rate of gases exhausted from a reservoir (m3si)

W Width of vertical _{opening (ml}

W Width of balcony (distance from vertical opening to front edge of balcony) (ml W Characteristic width of the ventilator/exhaust point (m)

X _Height from the base of the smoke layer to the NPP (m)

Effective height of rise of a spill plume (m)

y Height above the top of the fuel to the smoke layer immediately above (ml

Y1 Height of the virtual origin of the plume measured above the top of the burning fuel Im) (Note This usually takes a _negative value)

Ypi Height above the NPP in a _{smoke layer} (m)

Y Height from the base of the fire to the smoke layer immediately above (m)

Y Height above the base of the fire to the virtual origin of the _{smoke plume (ml}

(Note: This usually takes a negative value)

i

Coefficient in critica exhaust rate _{eqn (kgm} 3)

y A _{constant defining} the steepness of a _time-squared fire _{growth curve} (kWs21

fiM Entrainment rate into both free ends of a _{spill plume (kgs')}

Empirical height of virtual source below a _{spill edge} (m( ADB Additional smoke depth due to local deepening (m)

Ap Buoyant pressure rise above ambient at a height YNpP above the NPP lPa)

o _Temperature rise above ambient of smoky gases (°C(

°3 Thmperature rise above ambient of smoky gases under a balcony (DC)

0 Temperature rise above ambient of smoky gases in a reservoir 1°C)

o

Temperature rise above ambient of smoky gases in a _{vertical opening} (°C)

p Density of gases lkgmi)

p0 Density i:f ambient air (kgm1l

1

Introduction

1

1.1 The hazards

of

smoke

Smoke

is

potentially lethal,

It

is

a

well established fact

that in the

UK most deaths from tires

are

due

to

smoke

inhalation

rather than

to

the

_{victim having}

been

burned. However,

the

_majority

ofthese

deaths occur

in

_dwellings.

Deaths from fires in

other

_premises

are

_relatively

infrequent. This implies

that the

Iifesafety measures required

by

legislation

for

most public

and

commercial buildings

have been

effective

on the

whole,

In the

context

of

fire

the term

smoke

is used

to

describe

liquid

and/or

solid particulates produced by combustion offuel materials, suspended

in

a

mixture

of

air and

gaseous products ofcombustion, including steam.

It

is thus convenient

to

use

the

word smoke'

_to

include both

the

_{particulate and}

the

_{gaseous products, including any}

air which

is

entrained

into the

_{fire plume and} into

subsequent smoke flows,

The

_{gaseous combustion Products usually include}

toxic _gases,

the

most common

in

_{building fires being}

carbon monoxide, although hydrogen cyanide and

other

toxic gases might

he present to

some extent; irritants such

as

_{Acrolein; and relatively harmless products such as}

water and carbon dioxide, Smoke _pai-ticles themselves

can.

be

_{irritants, and}

can be

_{particularly dangerous}

to

people Who

are

_subject

to

asthma

or other

_respiratory

problems.

'['he

reduction

in

oxygen

due

to combustion

can

itself be

_dangerous

in

sonic situations, and

can

result

in

the

suffocation

ofvictms

_trapped

in

smoke.

The heat

in

the

_gases

due

to

combustion

is

_{also potentially}

hazardous,

either to

people

who

might

be

immersed in

the hot

_gases

_{or by heat}

radiation from

the hot

_smoky

gases

ifthe

gas temperature

is

high enough.

The

reduction

in

_visibility

in

_{smoke also represents a}

severe hazard,

It

_{hampers evacuation}

and the

_rescuing

of

disabled

or

injured occupants ofbuildings

as

well as affecting fire4Ighting operations which

can

result in _large

fires involving serious

threat to

lives and the environment.

In

_general,

ifthe

_{visibility through}

the

smoke is

sufficient

or the

emergency exits

are

visible

to

the

escapees,

the

toxic products will

not

_{stoj:) those people}

from escaping

to

_{safety. In practice this means}

that either

the

_{smoky gas must}

be

diluted with sufficient clean

air to

achieve

a

_{safe visibility (typically}

of

10 iii which

has

come

into) _{widespread use internationally, although}

it

has

a

_very weak scientific _basis,

and

_{should only}

be

_regarded as

approximate),

or

there

should

he

a

physical separation between

the

_{smoky gases}

and the

_people

at

risk. Note

that the direct

_{products of combustion may}

need

to

be

diluted

_by

more

than one

thousand times

_by

volume

to

achieve a safe _visibility.

1.2

The

_{regulatory background}

Each _country

_{in the}

world has

its

OWfl _approach

to

the

creation

and

_{enforcement of regulations covering}

the

topic

of

safety

in

fire.

Each

has

its

_{own history}

_by

which it

developed

that

approach. In

this

section we focus

on the

UK,

in

view of'its

_early

_{and continuing development}

of

fire regulations.

Fire _saiCty

in

_{buildings must,}

in

the

_{UK, conform}

_to

the

relevant regulations (eg guidance for England

and

Wales

is given

in

_{Approved 1)ocument B1l).}

The

_principal

objective

ofthese

regulations is

to

safeguard life l:y:

•

reducing

the

potential for fire initiation,

•

controlling fire propagation

and

spread,

•

the

_provision

of

_{adequate means}

of

_escape :ibr

the

building's occupants.

Means

of

escape

in

case offire was first introduced

to

the

Building Regulations for England

and

Wales

in

1973. Prior

to

_{that date the powers}

of

control

in

_England and Wales

over means

of

_escape

had been

contained

in

other legislation •2•-4•,

Historically,

the

prevention of fire _{growth within (or}

between) buildings

has been

achieved by

the

containment

of

the

fire

and its

_products,

_by

means

of

coinpartmentation

and/or

separation.

The

design

of

structural compartmentation

and

_{separation has been}

largely empirical and

the

concepts gradually refined and enhanced

in

such

a

_{way that the}

_{Building Regulations} now cC)ver _primarily

_{lifesafety and the}

_protectio

i

of

means of escape.

It is

necessary

to

consider four major aspects ofbuildings '— purpose, size, separation and resistance

to

fire

to

_{promote safe design.}

Smoke and

beat

exhaust ventilation

does

not

appear directly

in the

UK's regulations, except

in

some Local

2

Design methodologies

for

SHEVS

Acts.

It

has formed

_part

of the

recognized package

of

measures

needed

to

merit

a

Relaxation from

the

_Building

Regulations

for

shopping malls since

1972;

and

at

the

time

of

writing has become

an

indirect requirement

of

Approved Document

which

requires

that new

malls

in

_England

and

_{Wales comply with British Standard}

BS 5588:

Part

io61

which

in

turn

_requires

that

malls should have smoke ventilation as

an

essential

_part

of

their

safety provisions.

It

is

expected

that

a

similar

link

will

be

established

between

future editions

of

Approved Document B

and

British Standard BS 5588:

Part

7

for

atria7.

Several

other

countries

have

_{legislation concerning}

the

protection

of

property in

case

of

fire — especially

that

property

neighbouring

an

object

on

fire — and

the

protection

of

the

environment

(eg

air pollution

and/or

contamination

of

water and

_soil)

which

will

be

endangered

if

a

fire

is

likely

to

reach an

unmanageably large size.

1.3

The role

of

smoke and heat exhaust

ventilation

This

book

focuses

on the

use

ofsmoke and heat

exhaust ventilation,

rather than other

forms

of

smoke control

such as

smoke control

_using

_pressure differentials

(although

it

does also discuss

the need

to

allow for

the

interactions

between such

_systems

when

_designing).

As

mentioned

in

section 1.1,

the

combustion products

from building

content

fires

_may

_require

a

_very

_large dilution

to

achieve

a

safe _visibility.

With

_{typically smoky}

fuels

_{such as many}

_polymers

this

dilution

can reach

one thousand

times the

initial volume

of

combustion _gases. This

is

difficult

to

achieve

for

the

size

of

fire

we

_typically

have

to

consider

in

_{designing fire safety measures,}

and

is rarely

a

feasible option —

but

it

may

be

possible

where the

design

fire is

small,

and the

building volume is large.

Physical separation

of

smoke

and

people is

conventionally achieved using walls

and

doors,

and

is specified

in the

regulations

of

most

countries, differing

only

in

details.

This

approach cannot,

by

definition,

be

used where the

_people

_(or

_property,

or

_{escape routes)}

being protected from smoke

are in the

same undivided space as

the

fire;

and in

_many

modern

buildings, large undivided spaces

are used to

_improve

the

_{appearance and}

environmental ventilation.

It

is

this scenario

where

smoke

and heat

exhaust ventilation

is

of

value.

The

principles

are very

simple.

Hot, buoyant

gases from

a

fire rise

to

form

a

_{stable layer}

in

a

reservoir

below the

_ceiling

such that

a

cooler

clear

_layer

of

sufficient

_height

_may

be

present

for

_long

_enough

to

achieve safe evacuation

of

occupants. Often

it

is

necessary

to

vent the

smoke from

the

reservoir

_using

a

natural

or

mechanical exhaust. In

this book such

a

Smoke

and Heat

Exhaust Ventilation

System will

be

referred

to

using the

acronym SHEVS.

It

is

rare

to

find circumstances

where

a

SHEVS is

required

within

a

small room.

It

is

usually sufficient in

such circumstances

to

ensure

_safety

_by

a

combination

of

fire-resisting compartmentation, sufficiently

short

travel

distances for escape,

and

_{measures for detecting}

the

fire

in an

_{early stage}

_{and alerting the}

_occupants

of

the

building.

It

should

be

noted, however, that

compartmentation

may

not be

sufficient

_{by itself}

to

assist

fire fighting. Facilities

to

remove smoke

_{and heat may}

be

of

benefit

for fire

_{fighting operations,}

and in

some cases a reduction

of

compartmentation may

be

inevitable as a result

of

_{fire fighting practice (eg smoke}

_{may spread}

out

of

a

small

room into

a

number

of

other

_{rooms through}

door

_openings

_{held open by}

_{fire hoses).}

The

assessment

of

suitable facilities

to

remove smoke

and heat

from such small rooms

and their

_{neighbouring spaces during and}

after extinguishing procedures will

be

a

_case-by-case

decision

in

accordance

with the

_experience

and

_training

of

fire fighters,

and not as

a

result

of

calculation. These precautions

for

removing smoke

and

heat

are

not

within

the

_scope

of

this

book.

A

SHE

VS

is

_{more likely}

to

be

_advantageous

in

a

larger room,

such

as

an

exhibition hall, shopping mall,

or

a

factory,

where there is no

internal compartmentation and

where

the

travel distances

are

_appreciable.

A

SHEVS

is no

different

in

_principle

whether

_designed

for

a

_large

_{single-storey space}

which

_{is essentially}

a

_large

box

_{(eg many}

factories,

or

_{exhibition halls),}

or

for a

complicated (but undivided) space containing many storeys

of

balconies

or

mezzanine levels with potential fire locations

in

rooms

to

the

side

of

but

open

to

the

main space.

As can be

seen below,

the

former

can

be

regarded. as

a

_{special case}

of

the

latter.

1.4

Smoke and heat exhaust ventilation

as

a part

of

fire

_{safety engineering}

Every

fire is

a

chemical

and

physical process producing energy (mainly heat)

and

smoky gases

as

well as

other

less hazardous products. Therefore, every fire prevention concept must have

the

same

main

objectives:

•

to

avoid ignition

and thus the

outbreak

of

a

fire

at

all,

•

to

_protect

_{human beings, goods,}

the

_building

and

the

environment from

the

hazardous effects

of

the

products

of

the

fire

(eg heat and

smoke)

as long as

they

are

still

_being

_produced

_{by the}

fire,

•

to

hamper and

finally stop

the

production

of

heat

and

smoke (ie

to

extinguish

the

fire).

Any

fire prevention

concept

therefore should

be

a

composite ofwell-selected measures

being in tune

with

each

_other,

and

which

_hamper

or

_{stop the}

_{production of}

heat and

smoke,

and/or

which protect the

objects whicl

are

intended

to

be

protected

(people, property, etc.) by separating

them

from smoke

and heat. Where this

last

cannot

be

_fully uchieved,

the

purpose must

be to

diminish

the

effects

on

the

_{protected people}

and/or

_objects.

These

_{relationships}

are

illustrated

in

Figure 1.

The

thick

arrows represent those influences

which

diminish

the

_production

of

smoke

and heat;

or

which reduce

then

effects;

or

which keep the

hazardous products

of

combustion away from

the

endangered people

or

objects

1 Introduction

INFLUENCES

SMOE

ha

.raslr ('OrOSOfl Reduction of effect of smoke and heat by removing them

ORGANISA1IONAL RRE

PRECAUTIONS SMOKE AND HEAT EXHAUST

noperatiorts

VENTILATK)N SYSTEM

andto eaceaflon tetervening plans, (SHEYS)

pnwisfon ofeidingulsh1ngaents _________________________

Figure 1 The role of SHEVS in Fire Safety Engineering

INFLUENCES

3

between the

different activities

which

_{produce those}

influences.

Figure 1 demonstrates

that

any

SHEVS exists within a much

more

_{comprehensive}

fire

_{prevention concept.}

Structural _(passive)

_fire

_{precautions separate}

what

is protected

(eg

people, goods) from

the

products

of

combustion (eg smoke

and

_heat)

_by

structural means, In most cases this means

that

the

relevant structure will be fire resisting. This form

of

protection implies

that

everything inside

a

fire compartment

may

be

lost

if

no further active measures

to

extinguish

the

fire

take

place or cannot

be

performed;

these

active measures

can

include

an

_{attack by}

the fire

services. _People

have

to

be able to

leave

the

_{compartment which}

is

on

fire

and reach either

a structurally protected safe place,

or

the

exterior

of

the

building,

in

a

sufficiently

short

time

if

they are

to

be

safe.

A

SHEVS

can

remove

the

_{hazardous products}

of

combustion, smoke

and

heat, from

the

_{compartment and}

can

_separate

the

_objects

and/or

_people

to be

protected from smoke and

heat

_{already inside}

the

_{compartment, at}

least until the

fire

has

reached

a

_{certain size (design} -fire

size) wherever

the

SHEVS has

been

designed

to

create a smoke-free layer

beneath

a

_{buoyant smoky layer.}

Because

of

this smoke-free layer,firefightthg operations

can

be

performed

more

easily

by the

fire services, which

will control and stop production

of

smoke

and heat

more quickly

and

lessen

their

effect

on

any people

and

goods

remaining

in

the

building.

It

follows from this,

that there

is

a

close correlation

between

the

effect

of

a

SHEVS and

possible fire-fighting measures, including

the

effect

of

the

latter on the

_{likely design-fire size (see} Note 1,

next

page),

which in turn

influences

the

_design

of

a

SHEVS.

Technicalfire precautions mainly affect

the

reduction

of

the

time

between

_ignition

and the

_{fire being attacked}

STRUCTURAL (PASSIVE) FIRE PRECAUTIONS

Fft

resistant stmcturea for

compartments. means of escape,

access rotitas, cc bustbiIity of structure

Limitation of fuel, preventing the spread

of products of combustion

TECHNICAL FIRE PRECAUTIONS tire deteciton systems,

extinguishing and fire suppression systems,

fix installed fire _{fighting equipment} I risers, C/, LU

C)

z

LU

D

-J

7

PRODUCTS OF COMBUSTION HEAT fru

spa

ther

l

res

t

struGturc

Reduction of fire duration

4

Design methodologies

for

SHE VS successfully, thus preventing further growth.

•

Automatic fire suppression

or

_{extinguishing systems,}

eg

sprinklers, attack

the

fire directly.

•

Automatic fire

detection

_{systems (especially} smoke

detection systems)

shorten the

time

until

successful

fire fighting operations

can

be

performed. This is especially

true where the

fire services

are

called automatically

on the

operation

of the

detection system.

Note that where the

automatic smoke

detection

_{system triggers}

the

SHEVS,

the

_{fire-fighting}

approach

and

attack

are supported by the

smoke-free layer

created

by

the

SHEVS

_by

_calling

the

fire services

at

a

very

early

stage

of

fire development. Such detection systems also

alert

_occupants

_of

a

_building

who in turn may

be

able

_(supported

_by

a

smoke-free

layer

due

to

an

effective SHEVS)

to

attack

an

automatically detected, and usually therefore still small,

fire

themselves

with

technical fire precautions

such

as

the

_{portable extinguishers}

or

hosereels

provided

in the

building, even before

the

fire brigade is

on

site.

In this

_{way, SHEVS interact with technical} fire

precautions

and

fire-fighting operations,

which

together

have the

_potential

to

influence

the

_{design-fire size.}

It

has

to

be

admitted, however,

that the

effectiveness

of

first-aid fire fighting

by the

occupants

of

a

building is questionable

in

_{many cases,}

and

should

not be

considered when assessing

the

design fire. _{Nevertheless,}

the

effectiveness

of

a

fire-fighting approach

can

be

improved

if

trained staff familiar

with

_{fire-fighting techniques}

and the

technical fire precautions

are present and are

supported

by

an effective SHEVS.

This leads

to

_{organizationalfire precautions,}

which are

a

part

of

the

Fire Safety Management arrangements for a

building. These include:

•

trained staff to:

— _{start fire fighting}

_(eg

_{'Works Fire Brigades'),}

_and/or

—

manage evacuation,

and/or

— _{assist fire-fighting activities performed by}

_the

_fire

brigade

(eg by

delivering all information needed about usage

and

_population

of

the

_{building, critical}

items inside

the

building, technical building equipment including technical

fire

precautions and

their

intended _function);

•

intervention plans, including

such

_{provisions for}

emergency management as:

— _{fire prevention plans}

of

_the

_{building, or} — _{fixed installed communication devices, or} —

extinguishing agents

in

store

ready

for use

by the

fire

services (especially

if

distinctive agents

are to be

Note:

used for

_{certain fuels present,}

which must

not

be

attacked

_by

_{plain water);}

The concept of the design fire is discussed in more detail rn Chapter 3, For the present purpose, where a SHEVS is designed to assrst operational fire-fighting, the design-fire size is the most pessimistic but still realistic assumption of an area, or more precisely of a volume, involved in the fire and producing a certain amount of heat, when the estinguishing measures the attack on the

fire by the fire services) become successful so thatthe fire does not 5mw any larger.

•

organizational precautions for assisting evacuation

of

the

_building

_{which may}

include:

— _acoustic

guidance systems

or

— _{trained evacuation staff.}

All

these

_{organizational fire precautions will assist fire-}

fighting operations because

they

allow more

of

the

fire

brigade resources

to

concentrate

on

extinguishing operations with fewer

or no

crews having

to

be

employed

in

searching

or

rescuing people.

All

the

_{precautions listed above, technical and}

organizational, enhance

an

early successful attack

on the

fire. Thus,

the

hazard caused by

the

_products

of

combustion (smoke

and heat)

to

people,

the

building and

its

environment

is

diminished.

It

has

to be

born

in

mind, however,

that

the

effectiveness

of

all

the

_{precautions listed above benefit}

considerably from

the

creation

of

a

smoke-free layer produced by

a

well-designed SHEVS.

In other

words, a SHEVS should

he

an

_integral

_{component ofan}

overall fire prevention

concept and

of

the

fire-fighting strategy,

which

_{becomes considerably less effective}

in the

absence

of

a

SHEVS

to

create

a

smoke-free

_layer

at

an

_{early stage}

in the

fire.

1.5

A brief

_history

of

smoke ventilation

Smoke ventilation is

not

new.

Our

distant ancestors knew

that

if

_{they wanted}

to

light

a

fire inside

a

_{hut they}

needed

to

make

a

hole in the

roof, otherwise

the

occupants

of

the

hut

would

be

choked

_by

smoke. Modern smoke

ventilation merely applies

the

_{same principle}

to

large fires

in modern

_buildings.

Smoke ventilation

as

a

_{dedicated fire precaution}

became popular

for

_{industrial buildings following some}

large fires

(eg

General

_{Motors plant}

in

Michigan, USA, in 1953,

see

Plate 1;

theJaguar plant in

Coventry, UK, in

1957, and Vauxhall Motors

at

Luton, UK,

in

1963). Only

the

last

of

these three

_plants

had

automatic ventilators81.

During

the

1960s

the

Fire Research Station (FRS)

in

the

UK developed design algorithms suitable for

circumstances

where

the

fire would

be

directly

below the

thermally buoyant smoke

layer

formed

beneath the

ceiling9'10.

The

technique

was

mostly

used

as

a

way of

reducing

property

damage

by

allowing fire fighting

to

become much more effective.

A

fire

in the

linked Wulfrun

and

_{Mander Shopping}

Centres

in

Wolverhampton,

UK

in

1968 [11], alerted people

to

the

_{tremendous potential}

for the

_spread

of

smoky gases

in

covered malls.

It

was

realized

that

such

a

fire

could cause

a

_{large loss}

of

life

if

it

occurred

when

the

mall

was

_{being used by the}

_public.

Researchers realized

that

the

smoke ventilation approach already developed

for

large spaces could

be

adapted

to

keep smoke entering

a

mall safely above

peoples' heads; thus protecting

the

means

ofescape in

the

mall. Research

_{into the way in}

which smoke moves within malls continued

through the

1970s, leading

to

the development

of

design formulae for calculating the