Examples of Fire Safety Engineering calculations. - Cooke On Fire

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Determine the rate at which the compartment will fill with smoke, and find the time forthe smoke to fill down to within 5m and 2m of floor level. Determine if occupants aresafe if they leave the building within 3 minutes of ignitionFigure. Cross section through portal framed buildingData given:average height of enclosure = 12.5m i.e. (12+13)/2length of building = 60mwidth of building = 40mambient air temperature, T0= 15 o Cdensity of air, ρ = 1.2kg/m 3specific heat of air C p = 1.92clear air layer needed = 6mfire growth parameter for fast t 2 fire a = 0.0444 kW/s 2height of virtual source above base of fire, z = 0From the literature (e.g. CIBSE Technical Memorandum TM19: 1995):o2⎪⎧t ⎪⎫Q = 1000⎨⎬( CIBSE Eqn 4.1) (1)⎪⎩ t g ⎪⎭where tg= characteristic growth time. For a fast fire tg= 150 and Equation (1) becomesQ = 0.0444t2M1/ 35/ 3= 0.071Qp( z − zo)(CIBSE Eqn 5.6) (2)Q= T(CIBSE Eqn 5.17) (3)pTm+MCpo2
vMTρ Tm= (CIBSE Eqn 5.19) (4)ooA spreadsheet is prepared which calculates smoke layer temperature and thickness as afunction of time.First we assume the worst condition, that the plume height z remains constant as timeprogresses (in reality the plume height reduces as the thickness of smoke layer increasesand thus the height over which air entrainment takes place reduces with time).Substituting data gives:time for smoke layer to reach down to 5m from floor level = 325sectime for smoke layer to reach down to 2m from floor level = 488secAssume now that the air entrainment reduces as the smoke layer increases in thicknessi.e. z reduces. We now have:time for smoke layer to reach down to 5m from floor level = 534sec time for smoke layerto reach down to 2m from floor level = 700secSo we see the large increase in smoke fill time, i.e. from 488 to 700 seconds for smoke toreach to within 2m of floor level. Thus using constant z is conservative – if occupantscould evacuate within this period they would be safe.We are asked if the occupants are safe to complete their evacuation by 3 minutes fromignition. From the calculation the smoke layer is approximately 2m deep (well abovehead height) and at a temperature of 34 o C for constant z and at 38 o C for reducing z, atthis time. The conditions are clearly tenable.3 Thermal deflections/stresses.3.1 The thermal bowing deflection at mid-height of a steel stud fire wallA firewall comprises a fire protecting layer of plasterboard either side of an assembly ofsteel studs. The vertical studs are of a light steel channel section 200mm deep betweenflanges and the studs are 6m high and simply supported at their ends. In an indicative fireresistance test on a 1m high specimen of the whole construction exposed to the ISO 834fire on one face it was found that the thermocouple temperatures of the ‘hot’ and ‘cold’flanges of the steel channel were 700 and 300 o C respectively. The two conditionsconsidered are shown in the figure below.Assuming a) the plasterboard does not affect the bowing behaviour, and b) the steelproperties are unaffected, what is the mid-height deflection ( ∆mid −height) of the 6m highwall in the horizontal direction assuming the same fire exposure?3
Page 4 and 5: We see that we can assume the ends
Page 6 and 7: ∆mid −heightTherefore:α H=2∆
Page 8 and 9: From Equation (3)P = 14 x 10 -6 x 1
Page 10 and 11: Substituting values gives:0.46⎧20
Page 12 and 13: than 2r and this is indicated by ar
Page 14 and 15: EBCHzRectangularradiatorJFGD90 oxyA
Page 16 and 17: 0.5rectangle0.450.4cylinder0.350.30
Page 18: I am grateful to Professor Tanaka f

Examples of Fire Safety Engineering calculations. - Cooke On Fire

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