Enclosure fires

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Smoke gas temperature 450 400 350 300 250 200 150 100 50 0 200 400 600 800 1000 to the room is opened the smoke gases can escape, but the gases are fairly cold and do not ignite, which makes the fi re easy to extinguish. 6.3 Fire resumes its development We now have a situation where the fi re has managed to spread to a number of other objects before the oxygen becomes defi - cient. The heat impact in the fi re room has been considerable. Smoke gases have fi lled up the fi re room, containing a large amount of unburnt gases. This means that the fi re has the opportunity to grow into a fully developed fi re if it is supplied with air again. Now let us assume that the BA fi refi ghters open the door to the house or a window breaks with the heat. As a result of this, the smoke gases will escape out of the top part of the opening, while air will fl ow in through the bottom part of the opening and the neutral plane will rise. The stream of air will stoke up the fl ames in the initial fi re again and the fi re will grow. The fl ames then reach the smoke gas layer and a fl ame front spreads throughout the room. This scenario is a continuation of the fi re’s interrupted development. Its growth is much the same as when a fi re develops and progresses to fl ashover in a room which has already had an opening right from when the fi re started. Figure 85 (on the following page) illustrates this process. Secs Figure 83. Temperature in a closed room. Temp Flashover Point A Point B Fully developed compartment fire Oxygen deficiency Figure 84. The fi re resumes its development resumes and becomes a fully developed fi re. 119 Time
Figure 85. The fi re resumes its development. The door is opened and the smoke gases escape. After a while you can see fl ames up under the ceiling and soon fl ames can be seen throughout the whole room. Figure 86. The smoke gases auto-ignite when they come into contact with air. 120
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Lars-Göran Bengtsson Enclosure fi
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The content of this book may not be
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4.4 Risk assessment 99 Smoke gases
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Foreword The aim of this book is to
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Overview This book assumes that its
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Figure 1. Fire growth curve featuri
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Fire extinguished/burnt out Just sm
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chapter 2 How a fi re starts People
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smoke gases in the compartment, but
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Pyrolysis gases material is subject
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Ignition time Ignition time can als
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Smouldering fi res can therefore re
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2.4.1 Thermal inertia kρc The fl a
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grow to 50 cm, then a 1 m high fl a
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Flammability in solid materials is
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6. The fl ame spread rate varies wi
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Figure 22. Smoke gases start to acc
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Figure 25. The different sections i
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The production of unburnt gases is
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Heat release rate from a fuel surfa
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Carbon monoxide (CO) is the next mo
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ment to accelerate, but this is obv
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is far too high for a premixed fl a
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is fi lled with fuel molecules, con
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Figure 33. Flames on the under side
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Flammability limits Vent For a prem
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CH4 + 2 + 2 + + 2O2 = CO2 + 2H2O +
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Temperature impact on fl ammability
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energy is required, which can be ex
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ustion takes place in under-ventila
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If turbulence affects the system th
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Neutral plane The differences in pr
Page 70 and 71: Where the differences in temperatur
Page 72 and 73: Positive pressure Negative pressure
Page 74 and 75: Dp = 353(1/Ta - 1/Tg)gh Let us take
Page 76 and 77: Figure 51 (top). The pressure condi
Page 78 and 79: Vent just during the early stage of
Page 80 and 81: In Figure 57 calculations have not
Page 82 and 83: 3.4 Summary In many situations the
Page 84: oom and in a fairly closed room (on
Page 87 and 88: Figure 59. The fi re has spread to
Page 89 and 90: Figure 60. Flashover occurrence ove
Page 91 and 92: 90 precisely the exact moment when
Page 93 and 94: The amount of energy released when
Page 95 and 96: Figure 63. Thermal balance on a fue
Page 97 and 98: Figure 64. Flame spread under the c
Page 99 and 100: Access to fuel Figure 67. Fire’s
Page 101 and 102: The signs indicating that a fl asho
Page 103 and 104: Figure 69. Different signs indicati
Page 105 and 106: Smoke gas temperature 700 600 500 4
Page 107 and 108: 106 clear that we need to reach the
Page 109 and 110: This example illustrates how crucia
Page 111 and 112: 110
Page 113 and 114: 112
Page 115 and 116: 114
Page 117 and 118: Figure 78. Fire pulsating. Figure 7
Page 119: Figure 81 (above). The fi re is abo
Page 123 and 124: 122 is suffi ciently big. A fi re
Page 125 and 126: Figure 89. A backdraught entails a
Page 127 and 128: Figure 90. The picture shows a vent
Page 129 and 130: 128 The current which results in sm
Page 131 and 132: 130 fans should not be used. You sh
Page 133 and 134: Figure 97. A larger part is premixe
Page 135 and 136: Figure 101. There are still combust
Page 137 and 138: Figure 103. Sauna. A common scenari
Page 139 and 140: Fires in enclosed spaced with minim
Page 141 and 142: Figure 107. The smoke gases are str
Page 143 and 144: Figure 110. The fi xed lance versio
Page 145 and 146: Four fi re scenarios: 1. The fi re
Page 147 and 148: 146 to occur. If a backdraught occu
Page 149 and 150: 148 Fire at 62 Watts Street The New
Page 152 and 153: chapter 7 Smoke gas explosion Throu
Page 154 and 155: ignition source required to ignite
Page 156 and 157: ity is also affected by turbulence
Page 158 and 159: 7.3.2 Course of action If smoke gas
Page 160 and 161: Test your knowledge! 1. Why do smok
Page 162: Corridor Space in between Sauna app
Page 165 and 166: 164 gases the fl ames would come ou
Page 167 and 168: Figure 119. Plan drawing of the bas
Page 169 and 170: 168 Glossary Adiabatic fl ame If al
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Heat of combustion, This measures t
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172 Suggested solutions to test que
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174 13. In a closed room there will
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176 6. By cooling down the smoke ga
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Sample calculations Flammability li
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You should bear in mind that this c
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Backdraught Sample calculation: The
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E = (T f/T i)( N b/N u) Tf Ti Nb Nu
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v* = v/(g × h × b) 0.5 , which gi
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188 gram), Institutionen för brand
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Index 62 Watts street 148 Adiabatic
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192 List of fi gures Drawn illustra
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Enclosure fires

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