Enclosure fires

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List of quantities (T sa – T i) 2 t a = k3c × p 4(q2) 2 T s – T i = 2q2 t 0.5 p 0.5 (k3c) 0.5 Tsa – surface temperature at the moment of ignition (°C) ta – time to ignition (s) q2 – heat supplied W/m2 – Radiation energy (In this case, from the fi re) Ts – temperature on surface (°C) of fuel Ti – initial temperature (°C) on fuel surface (original temperature) k – heat conductivity W/m °C – A high value means that the material easily conducts heat 3 – density in kg/m3 c – specifi c heat capacity in J/kg °C – Means ability of material to store heat t – time in seconds (s) Q = m2A fDH cx Q – heat release rate in W m2 – mass loss rate in kg/m2s or g/m2s Af – size of fuel surface in m2 DHc – heat of combustion in the event of complete combustion in J/kg x – combustion effi ciency controlling how effectively the fuel is consumed (indeterminate) DH c = S (C p × DT) DT – temperature difference (°C) Cp – gases’ heat capacity (J/mol × K) DHc – heat of combustion in the event of complete combustion (MJ/kg or kJ/g) S f = S u × E (m/s) E – expansion factor (indeterminate) Su – rate of laminar burning velocity (m/s) – fl ame speed (m/s) S f 183
E = (T f/T i)( N b/N u) Tf Ti Nb Nu 184 – temperature of products (K) – original temperature (K) – sum of the products available after the reaction – sum of the reactants available before the reaction S f = S u × (T f/T i) S f = S u × b × (T f/T i) b – turbulence factor (indeterminate value) Dp = (3 a – 3 g) gh Dp – pressure difference in Pa g – gravitational constant (m/s2 ) h – height (m) 3a – density of the surrounding gas (kg/m3 ) – density of gases (kg/m3 ) 3 g 3 = pM RT M – molecular weight (kg/kmol or g/mol) R – 8.31 (J/molK) T – temperature (K) NB: do not use C° in the equation. p – pressure (Pa) Dp = 353(1/T a – 1/T g) gh 353 – constant Ta – ambient temperature (K) – temperature of gases (K) T g (p – p a) Qt = p a V3 ac vT a Q – heat release rate (W) V – room volume (m3 ) Pa – normal pressure (Pa) P – pressure created (Pa) t – time (s) Ta – temperature (K)
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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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114
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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
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
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: Backdraught Sample calculation: The
Page 187 and 188: v* = v/(g × h × b) 0.5 , which gi
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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