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  • Enclosure fi res

    Swedish R

    escue Services Agency

    651 80 Karlstad, SwedenTel: +46 (0)54 13 50 00Fax: +46 (0)54 13 56 00www.raddningsverket.se

    Ordernumber U30-647/05 ISBN 91-7253-263-7

    To order from the Swedish Rescue Services Agency:publikationsservice@srv.seFax: +46 (0)54 13 56 05

    Knowledge about fi re development, the spread of smoke gases, pressure conditions and risk assess-ment may be crucial to the outcome of a fi refi ghting operation. Basic knowledge about the factors which control the fi res development is a must for fi re service staff. It is also important to be familiar with and on the lookout for the warning signs which can be observed during an operation. Enclosure fi res brings together the experience acquired by the district fi re service and the research in the form of experi-ments and theoretical studies on the subject. With this book the Swedish Rescue Services Agency wants to contribute to a deeper understanding about fi re development in the case of enclosure fi res. Firefi ghting measures, such as applying an extinguishing agent, fi re ventilation, etc. are discussed in detail in several sections, but the book focuses very much on acquiring an understanding of the processes which control enclosure fi res. This book is primarily intended to be used by the Swedish Rescue Services Agency in its training activities, but is also suitable for active fi refi ghters and anyone else who may be interested.

    Lars-Gran Bengtsson graduated from the Fire Protection Engineering programme at the Department of Fire Safety Engineering at Lund University in 1995. The programme lasted two and a half years, with 1 years further study at the Swedish Rescue Services College in Revinge. Between 1996 and 1998 he was also employed as a postgraduate student at the department, where he wrote his thesis and carried out research into such areas as fi re development, fi re ventilation and fi re extinguishing. In doing so, he fulfi lled the requirements for a Licentiate degree in Fire Safety Engineering. Since 1999 he has worked as a Fire Safety Engineer at the Helsingborg fi re department, where he is head of education and training, as well as being responsible for the development of methods and tactics for fi refi ghting opera-tions. Lasse also works on a variety of projects for the Swedish Rescue Services Agency.

    Lars-Gran Bengtsson

    Enclosure fi res

    Approximate conversion values for rough calculation:

    1 MPa = 10 bar1 kPa = 100 mm water column 1Pa = 0,1 mm water column1 bar = 0,1 MPa = 100 kPa 1 mm water column = 10 Pa

  • Lars-Gran Bengtsson

    Enclosure fi res

    Swedish Rescue Services Agency

  • The content of this book may not be duplicated, wholly or in part, without the consent of the Swedish Rescue Services Agency, in accordance with the Swedish Act on Copyright in Literary and Artistic Works (1960:729). This applies to any duplication by means of printing, copying, recording, etc.

    Enclosure fi resAuthor: Lars-Gran BengtssonFactual check: Bjrn KarlssonEditors: Anna-Lena Gransson, Bo SvenssonTranslation: Tekniktext ABIllustrations: Per Hardestam and others, see separate list on page 192.Designer: Karin RehmanPrinted by: NRS Tryckeri, Huskvarna, SwedenFirst published in 2001Order number: U30-647/05ISBN 91-7253-263-7 Lars-Gran Bengtsson and the Swedish Rescue Services Agency

  • ContentsForeword 7Overview 9

    1. Introduction 11

    2. How a fi re starts 17

    2.1 Initial fi re 172.2 Ignition of solid material 202.3 Flaming combustion and smouldering 242.4 Surface fl ame spread 25

    Thermal inertia, k_c 27

    Surface direction 27

    Surface geometry 29

    Surrounding environment 29

    2.5 Summary 30Test your knowledge! 32

    3. Early stage of fi re development 35

    3.1 Smoke gases and heat release rate 36Fire plume 37

    Content of unburnt smoke gases 44

    3.2 Flames 46Diffusion fl ames 49

    Premixed fl ames 54

    Extinguishing fl ames 63

    3.3 Pressure conditions in open and closed rooms 65Inhibited thermal expansion 68

    Thermal buoyancy 71

    Pressure in a closed or almost completely closed room 74

    Pressure in an open room 75

    Pressure build-up in a room when smoke gases ignite 76

    3.4 Summary 81Test your knowledge! 82

    4. Flashover 85

    4.1. Defi nition of fl ashover 864.2 Conditions resulting in fl ashover 88

    Heat release rate 90

    Increasing the mass loss rate 93

    4.3 Processes taking place in the smoke gas layer 97

  • 4.4 Risk assessment 99Smoke gases colour 99

    Signs indicating an imminent fl ashover 102

    Course of action 105

    4.5 Summary 105Test your knowledge! 106

    Fire in the Stardust Club in Dublin 108

    5. Fully developed compartment fi re and decay period 111

    6. Fire development in a room with limited ventilation 115

    6.1 Pulsations 1156.2 Fire has spontaneously gone out 1176.3 Fire resumes its development 1196.4 Smoke gases auto-ignite 1216.5 Backdraught 122

    Defi nition of backdraught 124

    A typical backdraught scenario 126

    Gravity current 128

    Ignition of premixed area 130

    Conditions resulting in a backdraught 135

    6.6 Risk assessment 137Warning signs 137

    Course of action 139

    6.7 Summary 144Test your knowledge! 146

    Fire at 62 Watts Street 148

    7. Smoke gas explosion 151

    7.1 Defi nition of smoke gas explosion 1527.2 Conditions required for smoke gas explosion 152

    Factors affecting the power of a smoke gas explosion 153

    7.3 Risk assessment 155Signs indicating an imminent smoke gas explosion 155

    Course of action 155

    7.4 Summary 157Test your knowledge! 158

    Explosion at the Grand Hotel in Helsingborg 160

  • 8. Grey areas between the various phenomena 163

    8.1 Differentiating between fl ashover and backdraught 1638.2 Differentiating between smoke gases auto-igniting in the

    opening and a backdraught 1648.3 Differentiating between smoke gases auto-igniting and a fi re

    resuming its development 1648.4 Differentiating between a backdraught and a smoke gas

    explosion 1648.5 Differentiating between a fl ashover and a smoke gas

    explosion 1658.6 Summary 165

    Sauna fi re in Kiruna 166

    Glossary 168Suggested solutions to test questions 172

    Chapter 2 172

    Chapter 3 172

    Chapter 4 174

    Chapter 6 175

    Chapter 7 177

    Sample calculations 178Flammability limits 178

    Flashover 181

    Backdraught 182

    List of quantities 183References 187Index 190List of fi gures 192

  • 7

    ForewordThe aim of this book is to provide a deeper understanding of

    how fi re behaves during enclosure fi res. This book has been

    written primarily with fi refi ghters in mind.

    Every year around a hundred people die throughout Swe-

    den as a result of fi re, with most dying in house fi res. Fire also

    causes extensive damage to property, with the insurance sec-

    tor putting an estimated fi gure of 3.4 billion Swedish kronor

    (approx. 260 million) on the value of the property destroyed

    every year. This is why it is important to prevent fi re. If consid-

    erable resources are channelled into fi re prevention this can

    reduce both the number of deaths and the cost. When a fi re

    breaks out it is vital that it can be tackled at an early stage, tak-

    ing the appropriate action.

    The aim of this book is to help provide a deeper under-

    standing of how fi re behaves during enclosure fi res. It focuses

    on understanding the processes involved in an enclosure fi re.

    The main purpose, however, is not to look at how to actually

    fi ght this type of fi re, by using smoke venting or applying a

    particular extinguishing medium, for instance, even though

    appropriate actions like these will be discussed in some sec-

    tions. When discussing fi refi ghting measures, reference will be

    made instead to relevant manuals dealing with smoke venting

    and extinguishing media.

    Nor does this book claim to provide an exhaustive insight

    into this area. For instance, a fi res behaviour in industrial

    premises is different, compared to in house fi res. This book

    mainly describes fi res in smaller areas such as fl ats or houses.

    Firefi ghters need to have basic knowledge about the factors

    controlling the behaviour of these types of fi re. In this situa-

    tion, as with other operations, there is a great deal of pressure

    in terms of taking the right course of action. It is also obvi-

    ously very important to be familiar with and look out for the

    warning signs which can be picked up during an operation.

    During the last 10 years great strides have been made in the

    research into these areas. This has led to a change in the ap-

    proach to compartment fi res in certain respects. Some of this

    research provides the basis for this book, along with the prac-

    tical experience of the local fi re service.

  • 8

    The book is intended to provide the basic material for

    teaching about fi re development in Swedens Rescue Services

    Agency colleges. This is the group which the book is mainly

    targeted at. It may also be of interest, however, to people in

    other professions who encounter problems relating to enclo-

    sure fi res. I hope that the book will manage to serve this pur-

    pose, both in terms of being used as a teachers guide and as a

    basic handbook helping to increase the knowledge about fi re


    I am sincerely grateful for all the assistance I received at the

    various stages in writing this book. Th