Fire ventilation

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ΔP uρ, T a ahuv gPressure inbuildingNeutral levelρg, T gh nv aAtmosphericpressureΔP nWe want to know how large the pressure difference is over the respectiveopenings, ΔP u andΔP n .1ρg, T gv3g2ρ, T a aWe simplify the problem by only studying the points 1, 2 and 3 in the upperpart of the building. The hydrostatic pressure difference between point 1 andpoint 2 is:v 1 = v 2 = 0P 1 –P 2 = ρ 2 gh 2 –ρ 1 gh 1ΔP u = h u g (ρ a –ρ g ) Equation 131
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 uρ 3 v 2 3P 1 – P 3 = −−−−−2ρ g v g2ΔP u = −−−−− Equation 22We can obtain the speed through the upper opening by using the equations1 and 2:ρ g v 2 g−−−−− = h u g (ρ a − ρ g )2√2h u g(ρ a –ρ g )v g = −−−−−−−−−−− Equation 3ρ gThe relationship between temperature and density is given by the gas law, andwe can use this to determine the relationship between the density and temperature.At normal atmospheric pressure we obtain the relationship:ρPM = RTP = 101.3 kPaM = 0.0289 kg/molR = 8.314 J/Kmolgas lawnormal atmospheric pressuremolar density for airgas constant353ρ = −−−−−relationship between density andTtemperatureThe mass flow in the opening is given by ṁ = C d AvρBy doing the same thing for the flow into the lower opening and equalisingthe obtained expression with equation 3, an expression is obtained for theposition of the neutral plane in relation to the size of the openings:h n A u 2 ρ g−−− = −−− × −−−− Equation 4h u A n ρ a32
Page 1 and 2: To carry out fire and rescue operat
Page 3 and 4: The content of this book may not be
Page 5 and 6: Inlets 51Horizontal fire ventilatio
Page 7 and 8: ForewordIn this book fire ventilati
Page 10 and 11: chapter 1Fire ventilationThe fundam
Page 12 and 13: Openings to gain access to a fire t
Page 14 and 15: would be the case, for example, in
Page 16: esults in quicker and more simple e
Page 19 and 20: PyrolysisIrreversible chemicaldecom
Page 21 and 22: Flashover results in afully develop
Page 24 and 25: chapter 3Fire gasesFire gases is a
Page 26: Fire gases containsproducts such as
Page 29 and 30: The dynamic pressure differences ca
Page 31: Pressure differencesproducedby diff
Page 35 and 36: Direction of windnegative pressurep
Page 37 and 38: There can be verycomplex windcondit
Page 39 and 40: In buildings erectedduring the 1960
Page 41 and 42: Calculation of thermal expansionSta
Page 43 and 44: Calculation of thermal buoyancy for
Page 45: The different pressure differences
Page 49 and 50: For practical reasons it can someti
Page 51 and 52: Calculation of the size of outletsT
Page 53 and 54: almost always preferable to strive
Page 55 and 56: The mass flow through the inlet can
Page 57 and 58: Openings andventilation can beimple
Page 59 and 60: When a room or a firecell is consid
Page 61 and 62: 60sure ventilation can also be appl
Page 63 and 64: Negative pressure ventilation is no
Page 65 and 66: The pressurising of adjacent rooms
Page 67 and 68: Fans can during positivepressure ve
Page 69 and 70: A large outlet produces a larger vo
Page 71 and 72: The volume flow in the outlet is gi
Page 73 and 74: a hall and no other internal connec
Page 76 and 77: chapter 6Creating openingsOpenings
Page 78 and 79: Electric motor powered toolsThe ele
Page 80 and 81: 12 3The circular saw is used to saw
Page 82:
Water cutting.plastic explosive is
Page 85 and 86:
Lowering deviceFall damperConnectin
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chapter 8Openings in differentroof
Page 90 and 91:
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 areinitiated, coo
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It is only through control that a s
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104
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elatively cold and diluted. Because
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Flashover has still nottaken place
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Flashover has takenplace and the fi
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Piercing nozzle(fog nail).Alternati
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To take into consideration at stair
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Further readingBengtsson, L. (1999)
Page 119 and 120:
Särdqvist, S. (1994). Övertrycksv
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120
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Fire ventilation

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