Enclosure fires

More documents

Recommendations

Info

3. This is usually split into normal pressure differences and pressure differences caused by the fi re. Normal pressure differences are caused by the wind, air conditioning and temperature differences between outside and inside air. Pressure differences created by the fi re are inhibited thermal expansion and thermal buoyancy. 4. Premixed fl ames occur when fuel and air are premixed before ignition occurs, whereas diffusion fl ames occur when fuel and air are not premixed when ignition occurs. 5. A premixed fl ame front can travel at around 3–5 m/s. 6. A defl agration is when fl ames spread in a premixed gaseous mass. 7. A detonation is when fl ames spread in a premixed gaseous mass where a shock wave is associated with the fl ame front, which can produce very high pressure and speeds. 8. When the fi re is fuel controlled the heat release rate is controlled by the fuel. In ventilation-controlled fi res the heat release rate is controlled by the size of the openings. It is very important to know whether the fi re is fuel or ventilation controlled, for instance, when you are using a fan. It is then possible to predict the consequences resulting from supplying air. 9. A number of products are formed during a fi re, including carbon dioxide and water, which are the most common. When the combustion effi ciency drops unburnt gases such as carbon monoxide and unburnt hydrocarbons are produced. 10. You can obviously fi nd the products specifi ed in the answer to question 9, as well as a quantity of air, associated with the plume. 11. The rate is controlled by the speed at which the molecules diffuse into each other. This rate increases with temperature, for instance. 12. In an open room there will be positive pressure at the top of the room, which results in smoke gases leaking out. In the bottom part of the room there is negative pressure, which causes air to get sucked in. 173
174 13. In a closed room there will be positive pressure in the entire room because of thermal expansion. But as soon as there is less leakage the increase in pressure due to thermal expansion will fall and the pressure conditions will appear the same as for an open room. 14. During a normal compartment fi re diffusion fl ames dominate. 15. In the order of 2000–7000 Pascal. 16. About 15–20 Pascal. It depends on how hot the smoke gases are. 17. The material releases a certain amount of heat energy during combustion and in some cases, it can drip and spread the fi re. The fl ame spread occurs at different rates, depending on the specifi c material. 18. In many cases, the window panes are still intact by the time the fi re service arrives at the scene. This means that the fi re may have entered a ventilation-controlled process. 19. The additional oxygen can be included on both sides using the symbol X. The additional fuel can be included on both sides in the same way. The equation is balanced with 5 oxygen molecules. The products will be 3 carbon dioxide and 4 water molecules. Propane contains 3 carbon and 8 hydrogen atoms. 20. The fl ame will not be able to exist outside the fl ammability range, as the thermal ballast is too great. This means that the energy released is not suffi cient to heat all the products, allowing combustion to continue. Chapter 4 1. A fl ashover is controlled by diffusion fl ames. 2. About 500–1000 °C. 3. The period varies depending on a number of conditions, including the room’s geometry. Sometimes this period can take just a few seconds. 4. Mainly reradiation from the smoke gas layer and fl ame spread on different surfaces.
Page 1 and 2:
Lars-Göran Bengtsson Enclosure fi
Page 3 and 4:
The content of this book may not be
Page 5 and 6:
4.4 Risk assessment 99 Smoke gases
Page 8 and 9:
Foreword The aim of this book is to
Page 10:
Overview This book assumes that its
Page 13 and 14:
Figure 1. Fire growth curve featuri
Page 15 and 16:
Fire extinguished/burnt out Just sm
Page 18 and 19:
chapter 2 How a fi re starts People
Page 20 and 21:
smoke gases in the compartment, but
Page 22 and 23:
Pyrolysis gases material is subject
Page 24 and 25:
Ignition time Ignition time can als
Page 26 and 27:
Smouldering fi res can therefore re
Page 28 and 29:
2.4.1 Thermal inertia kρc The fl a
Page 30 and 31:
grow to 50 cm, then a 1 m high fl a
Page 32 and 33:
Flammability in solid materials is
Page 34:
6. The fl ame spread rate varies wi
Page 37 and 38:
Figure 22. Smoke gases start to acc
Page 39 and 40:
Figure 25. The different sections i
Page 41:
The production of unburnt gases is
Page 44 and 45:
Heat release rate from a fuel surfa
Page 46 and 47:
Carbon monoxide (CO) is the next mo
Page 48 and 49:
ment to accelerate, but this is obv
Page 50 and 51:
is far too high for a premixed fl a
Page 52 and 53:
is fi lled with fuel molecules, con
Page 54 and 55:
Figure 33. Flames on the under side
Page 56 and 57:
Flammability limits Vent For a prem
Page 58 and 59:
CH4 + 2 + 2 + + 2O2 = CO2 + 2H2O +
Page 60 and 61:
Temperature impact on fl ammability
Page 62 and 63:
energy is required, which can be ex
Page 64 and 65:
ustion takes place in under-ventila
Page 66 and 67:
If turbulence affects the system th
Page 68 and 69:
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 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 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: 172 Suggested solutions to test que
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
show all

Enclosure fires

Create successful ePaper yourself

Delete template?

Save as template?