Enclosure fires

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15. When you open the door to an apartment the gases autoignite immediately. Is this usual? Why is this the case? 16. Explain how a ventilation-controlled fi re can result in a fl ashover. 17. What determines the size of a fi re ball when a backdraught occurs? 18. How is it that a fl ame can escape at a rate of 15–20 m/s when a backdraught occurs, while fl ames usually move much more slowly? 19. Can a fi re burning a single object be dangerous from the point of view of a backdraught occurring? 147
148 Fire at 62 Watts Street The New York fi re service received a call on 24 March 1994 to say that smoke was coming out of a chimney on a three-storey house in Manhattan, New York. 42 The building contained four apartments, with one on each fl oor. All the apartments could be accessed from a common stairwell, apart from the apartment at basement level, which had a separate entrance. The building, which dated from the end of the 19th century, but had been recently renovated, was considered to be very exclusive. Figure 112 shows a sketch of the building. When the fi re service arrived at the scene, with three fi re engines and two ladder engines, smoke was coming from the chimney, but there were no other visible signs of any fi re burning. The fi refi ghters were instructed to open the roof hatch at the top of the stairwell and two crews of fi refi ghters with breathing apparatus were instructed to enter the apartments on the ground and fi rst fl oor respectively using the same stairwell. The crew on the ground fl oor opened the apartment door and noticed air being drawn in to the apartment. This was followed by a hot outgoing current of air, which caused a backdraught with fl ames reaching from the door right out into the stairwell. The fl ames then stretched from the ground fl oor even right up through the roof hatch in the stairwell and lasted six and a half minutes. The crew on the ground fl oor managed to duck and get themselves back out through the stairwell. The crew on the fi rst fl oor did not have any escape route and the three fi refi ghters perished in this backdraught. This example illustrates that caution is required, even during operations which, on the surface, seem to be routine and familiar. There may be factors involved which mean that the operation will have devastating consequences if the usual measures are taken in wrong situations. Where did all the fuel come from that was able to sustain the fl ames for so long? A sketch of the ground fl oor is shown in Figure 113. The apartment owner had left home at around 6.30 AM. He had placed a bin liner on the gas hob, which was switched off. But it was probably the cooker’s pilot fl ame which ignited the bin liner. The fi re then spread
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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
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
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Page 113 and 114: 112
Page 115 and 116: 114
Page 117 and 118: Figure 78. Fire pulsating. Figure 7
Page 119 and 120: Figure 81 (above). The fi re is abo
Page 121 and 122: Figure 85. The fi re resumes its de
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: 146 to occur. If a backdraught occu
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 and 186: E = (T f/T i)( N b/N u) Tf Ti Nb Nu
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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