Fire ventilation

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We want to know how large the pressure difference is over the respective openings, ΔP u andΔP n. We simplify the problem by only studying the points 1, 2 and 3 in the upper part of the building. The hydrostatic pressure difference between point 1 and point 2 is: v 1 = v 2 = 0 P 1–P 2 = ρ 2gh 2–ρ 1gh 1 1 ρ g , Tg 3 ΔP u = h ug (ρ a–ρ g) Equation 1 vg a a T ρ, u h ρ g , Tg va hn g v ΔPn a a T ρ, 2 ΔPu Pressure in building Neutral level Atmospheric pressure 31
The hydrodynamic pressure difference between point 1 and point 3 is: v 1 = 0 ρ 1 = ρ 3 = ρ g h 1 = h 3 = h u ρ 3v 2 3 P 1– P 3 = −−−−− 2 ρgv g 2 ΔP u = −−−−− Equation 2 2 We can obtain the speed through the upper opening by using the equations 1 and 2: ρ gv 2 g −−−−− = h u g (ρ a− ρ g) 2 32 √ 2h ug(ρ a–ρ g) vg = −−−−−−−−−−− Equation 3 ρg The relationship between temperature and density is given by the gas law, and we can use this to determine the relationship between the density and temperature. At normal atmospheric pressure we obtain the relationship: ρPM = RT gas law P = 101.3 kPa normal atmospheric pressure M = 0.0289 kg/mol molar density for air R = 8.314 J/Kmol gas constant 353 ρ = −−−−− relationship between density and T temperature The mass fl ow in the opening is given by m˙ = CdAvρ By doing the same thing for the fl ow into the lower opening and equalising the obtained expression with equation 3, an expression is obtained for the position of the neutral plane in relation to the size of the openings: hn Au 2 ρg −−− = −−− × −−−− Equation 4 hu An ρa
Page 1 and 2: T o carry out fire and rescue opera
Page 3 and 4: The content of this book may not be
Page 5 and 6: Inlets 51 Horizontal fi re ventilat
Page 7 and 8: 6 Foreword In this book fi re venti
Page 10 and 11: chapter 1 Fire ventilation The fund
Page 12 and 13: Openings to gain access to a fi re
Page 14 and 15: would be the case, for example, in
Page 16: esults in quicker and more simple e
Page 19 and 20: Pyrolysis Irreversible chemical dec
Page 21 and 22: Flashover results in a fully develo
Page 24 and 25: chapter 3 Fire gases Fire gases is
Page 26: gases is produced that contains inc
Page 29 and 30: 28 The dynamic pressure differences
Page 31: Pressure differences produced by di
Page 35 and 36: 34 The distribution of pressure rou
Page 37 and 38: There can be very complex wind cond
Page 39 and 40: In buildings erected during the 196
Page 41 and 42: Calculation of thermal expansion St
Page 43 and 44: Calculation of thermal buoyancy for
Page 45: 44 The different pressure differenc
Page 49 and 50: Watt Rate of heat release is measur
Page 51 and 52: Calculation of the size of outlets
Page 53 and 54: 52 almost always preferable to stri
Page 55 and 56: The mass fl ow through the inlet ca
Page 57 and 58: Openings and ventilation can be imp
Page 59 and 60: When a room or a fi re cell is cons
Page 61 and 62: 60 sure ventilation can also be app
Page 63 and 64: 62 Negative pressure ventilation is
Page 65 and 66: 64 The pressurising of adjacent roo
Page 67 and 68: Fans can during positive pressure v
Page 69 and 70: 68 A large outlet produces a larger
Page 71 and 72: The volume fl ow in the outlet is g
Page 73 and 74: 72 a hall and no other internal con
Page 76 and 77: chapter 6 Creating openings Opening
Page 78 and 79: Electric motor powered tools The el
Page 80 and 81: The circular saw is used to saw woo
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plastic explosive is placed in the
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84 Example of securing during work
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chapter 8 Openings in different roo
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its way through on its own, without
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drop down on personnel standing on
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It is a good idea if the outer open
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A completely manual shutter, often
Page 98:
In buildings that have systems for
Page 101 and 102:
The measures that are initiated, co
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102 It is only through control that
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104
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A small fi re in a large room cause
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Flashover has still not taken place
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Flashover has taken place and the f
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112 Piercing nozzle (fog nail). Alt
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114 To take into consideration at s
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116 Further reading Bengtsson, L. (
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118 Särdqvist, S. (1994). Övertry
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Fire ventilation

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