Enclosure fires

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3a cv Dp = – density of normal air (kg/m3 ) – specifi c heat capacity at constant volume (J/kgK) (Q/c pT eA e) 2 23 e Q – heat release rate (W) Cp – specifi c heat capacity at constant pressure (J/kgK) 3e – density of outfl owing gas (kg/m3 ) Te – temperature of outfl owing gas (K) – leakage area (m2 ) A e Q fo = 610(h kA TA W √H) 0.5 Qfo – the heat release rate required to trigger a fl ashover (kW) hk – heat transfer coeffi cient (kW/m2K), which specifi es the amount of heat conducted in enclosure structures AT – internal enclosure area in room (m2 ) AW – ventilation opening area (m2 ) H – height of ventilation opening (m) 610 – constant produced via regression m a = 0,5A w√H – mass fl ux of the infl owing air (kg/s) – opening area (m2 ) H – height of opening (m) ma Aw Q = mDH cx Q – heat release rate (W) DH c – heat of combustion (MJ/kg or kJ/g) x – combustion effi ciency (indeterminate) m – mass loss rate (kg/s) q2 f + q2 ext – q2 loss m = A L v q2 loss – heat loss from the fuel surface (kW/m 2 ) q2ext – radiation from surrounding areas (kW/m2 ) q2f – heat transfer from fl ame (kW/m2 ) m – mass loss rate in g/s A – fuel area in m2 Lv – heat of vaporisation (kJ/g) 185
v* = v/(g × h × b) 0.5 , which gives: v – air current speed (m/s) v* – indeterminate Froude coeffi cient h – height of room (m) g – gravity (m/s 2 ) b – difference in density between the media (indeterminate) 186
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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
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Where the differences in temperatur
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Positive pressure Negative pressure
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Dp = 353(1/Ta - 1/Tg)gh Let us take
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Figure 51 (top). The pressure condi
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Vent just during the early stage of
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In Figure 57 calculations have not
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3.4 Summary In many situations the
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oom and in a fairly closed room (on
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Figure 59. The fi re has spread to
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Figure 60. Flashover occurrence ove
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90 precisely the exact moment when
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The amount of energy released when
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Figure 63. Thermal balance on a fue
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Figure 64. Flame spread under the c
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Access to fuel Figure 67. Fire’s
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The signs indicating that a fl asho
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Figure 69. Different signs indicati
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Smoke gas temperature 700 600 500 4
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106 clear that we need to reach the
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This example illustrates how crucia
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110
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112
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Figure 78. Fire pulsating. Figure 7
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Figure 81 (above). The fi re is abo
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Figure 85. The fi re resumes its de
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122 is suffi ciently big. A fi re
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Figure 89. A backdraught entails a
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Figure 90. The picture shows a vent
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128 The current which results in sm
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130 fans should not be used. You sh
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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
Page 171 and 172: Heat of combustion, This measures t
Page 173 and 174: 172 Suggested solutions to test que
Page 175 and 176: 174 13. In a closed room there will
Page 177 and 178: 176 6. By cooling down the smoke ga
Page 179 and 180: Sample calculations Flammability li
Page 181 and 182: You should bear in mind that this c
Page 183 and 184: Backdraught Sample calculation: The
Page 185: E = (T f/T i)( N b/N u) Tf Ti Nb Nu
Page 189 and 190: 188 gram), Institutionen för brand
Page 191 and 192: Index 62 Watts street 148 Adiabatic
Page 193 and 194: 192 List of fi gures Drawn illustra
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Enclosure fires

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