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ASHRAE Stair Pressurized Systems | Duct (Flow) | Ventilation (Architecture)
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National Research I Council Canada 1618
On a fait m e 6tude de synthbse sub les divers types de systi5mes de mise en pression, l'utilisation des escaliers lors de 1'Cvacuation et les exigences des codes. Des essais sans feu et de tenue au feu ont C t C effectu6s dans la tow d'incendie de 18 Ctages du Labomtoire national de'19incendie,au Conseil national de recherches du Canada. On a mesun5 la C u e p a d'escalier ouverbe B divers angles. h s profils dsistzaflce B l'koulement de 19air verticaux des Ccarts de pression de part et d9autredu mur de la cage d'escalier et ceux de la pression de vitesse dans l'ouverture de la p r t e d'escalier ont BtC mesuds dans des conditions d'incendie. La cage d'escalier Btant en pression, les vitesses critiques nkcessaires pour empecher le refoulement de la fumBe dans l'ouverture de la porte d'escalier, h 196tage de l'incendie, ont 6tC d6termin6es et compdes aux valeurs calcul6es pour diverses temp6rature de feu.
THIS PREPRINT IS FOR DISCUSSION PURPOSESONLY, FOR INCLUSION IN ASHRAE TRANSACTIONS 1989, V. 95. Pt.2. Not to be reprinted In wholeor in part without wrltten permission of the American Society of Heating. Refrigerating and Air-Conditioning Engineers. Inc.. 1791 Tullie C~rcle, NE, Atlanta. GA 30329. Oplnlons. findings, conclusions, or recommendations expressed in this pap& are those of the author@) and do not necessarily reflect the views of ASHRAE
Codes The requirements in the building codes for stairshaft pressurization systems include supply air rates, required minimum and allowable maximum pressurization, and minimum air velocity through doors for number and location of open stair doors. In Australian Standard 1668, Part 1 (1979), pressure differences with all doors closed are not to exceed 0.20 in of water (50 Pa) or the force required to open the door at the door knob is not to exceed 25 Ibs (110 N). With three doors open, the airflow velocityfrom the stairshaft is to be not less than 200 fpm (1 mls), averaged over the full area of the door opening. The pressurization system is to be automatically controlled such that when operation of doors or other factors cause significant variations in airflow and pressure differences, the above conditions are to be restored as soon as practicable. In BOCA (1984), for buildings with afire suppression system throughout, the smoke-proof enclosures may be eliminated provided that all interior stairshafts are pressurized to a minimum of 0.15 in of water (37.3 Pa) and a maximum of 0.35 in of water (87 Pa) in the shaft relative to the building with all-stairdoors closed. British Standard Institution BS 5588:Part 4 (1978) recommends a simple lobby to reduce the effect of an open door to the pressurized stairshaft. The required pressurization is 0.20 in of water (50 Pa). The City of New York Local Law No. 84 (1979) requires a supply air rate of at least 24,000 cfm (11.33 m3/s) plus 200 cfm (0.094 m3/s) per floor. The maximum velocity of air suppliedat the openings into the stairs is 3000 fpm (15.2 m/s) at its point of dischargewithin the stairshaft.The maximum permissible pressure difference between the stair and the floor space is 0.40 in of water (100 Pa) with the door open or closed. The minimum permissible pressure difference is 0.10 in of water (25 Pa) when all stair doors are closed or not lessthan 0.05 in of water (0.125 Pa) when any three doors are open. As an alternativeto the maintenance of 0.05 in of water (0.125 Pa), a minimum average velocity of 400 fpm (2 rnls) through the stair door with any three doors open is to be maintained. The maximum velocity permitted through a single open door with all other doors closed is 2000 fpm (10.2 rnls). The door-opening force at the door knob is limitedto 25 Ibs (110 N) using mechanical assistance as required. The Supplement to the National Building Code of Canada (1985), Chapter 3, "Measures for Fire Safety in High Buildings," recommends a supply air rate of 10,000 cfm (4.72 m3/s) plus 200 cfm (0.094 m3/s)for every door opening into the stairshaft. The exit door to outdoors in each stairshaft is to be held open when the supply air fan is initiated. The Standard Building Code (1985) specifies smokeproof enclosures. They may be omitted for buildings with a complete sprinkler system provided that all required stairways are equipped with a dampered relief opening at the top and supplied mechanically with sufficient air to discharge a minimum of 2500 cfm (1.18 m/s)through the relief opening while maintaininga minimum.positive pressure of 0.15 in of water (37.3 Pa) relative to atmospheric pressure with all stair doors closed.
flow coefficient, dimensionless area of opening, ft2(m2) gravitational conversion factor, 32.174 Ib,/lb, ft/s2(9.806 m/s2) = density of fluid, Ib,/ft3 (kg/m3) P p, - p2 = pressure difference across the stair door opening, Ib,/ft2 (Pa) K is a constant made up of a contraction coefficient, a friction loss coefficient, and an approach factor. The tests to determine the flow coefficients were conducted on the fifth floor of the experimentalfire tower. They involved measuring the pressuredrop across the stair door with a diaphragm-type magnetic reluctance pressure transducer and the flow rates at the airflow measuring station, and calculating the flow coefficient,K , using Equation 1. For all calculations, A was taken as 21 f f (1.95 m2). For the first series of tests, without people, the supply air was injectedat the bottom of the stairshaft and allowed to flow up to the stair door opening on the fifth floor. The supply air rates were adjusted to give a pressure difference of 0.10, 0.15, or 0.20 in of water (25, 37.5, or 50 Pa) across the stair door opening for door angles of 90, 70, 60, 23O, and 5O. This series of tests was repeated with supply air injected inside the stairshaft on floors l , 3 , 5, 7, and 10. The second series of tests was conducted with people in the doorway, with the door open at the 60 angle to approximate the position used when a door is opened to enter astairshaft.The supply air was injected at the bottom of the stairwell. The test subjects were as follows: Person Physical Characteristics 6 ft 1 in (1.84 m), 160 Ib (72.6 kg) A 5 ft 9 in (1.75 m), 170 Ib (77.2 kg) B 5 ft 7 in (1.70 m), 150 lb (68.1 kg) C 5 ft 0 in (1.52 m), person C crouched D A number of 1 ft (0.305 m) diameter cardboard cylinders of heights corresponding to the test subjects were used as well for the tests. Tests were conducted with each person standing at the door opening or with two people placed 1 f i (0.305 m) on either side of the door opening. These tests were repeated with the cardboard cylinders.
Q = K A [ 2 g g ( ~1~ 2 ) r
Critical Velocity The tests to determine the critical velocity to prevent smoke bacMlow at the stair door opening were conducted on the second floor with the gas burners, Static pressure taps to measure the pressure differences across h e wall of the stairshaft on the corridor side were installedat ,3 ft, (0,396 m, 2.183 m, and 3,048 m) above floor ft, and level,Thermocoup~es to measuretemperatures inside and outside the stairshaft were installed at these levels. Bi-directional gas velocity probes (McCaffrey and Heskestad1976) were installed along with thermocouples in front of and at the vertical centerline of the stair door opening at 1.33 ft, 2.66 ft, 4.00 ft, 5.33 ft, and 6.66 ft (0.405 m, 0.811 m, 1.220 m, 1.625 m, and 2.032 m) above floor level (Figure 3). Measurements were made under the following test conditions on the second (fire) floor with the supply air ductlstairshaft system sealed as before. 1. With the stair door closed and without stairshaft pressurization,tests were conducted at fire temperatures
Door angle-60 Supply air to stairshaft-bottom injection Test stair door on fifth floor of experimental fire tower
21 P O I N TT R A V E R S E A 15 P O I N TT R A V E R S E 9P O I N TT R A V E R S E
Note: A Male, 6ft 1 in (1.84 rn), 160 Ib (72.6 kg) B Male. 5 R 9 in (1.75 rn), 170 1 b (77.2 kg) C Male. 5 R 7 in 1 70 m , 150 lb (68.1 kg) D Male, 5 ft 0 in [1:52 rn], person C crouched A' Cardboard cylinder, 6 ft 0 in (1.83 rn), 1 R (0.305 m) diarn. B' Cardboard cylinder, 5 ft 9 in (1.75 rn), 1 R (0.305 rn) diarn. D' Cardboard cylinder, 5 ft 0 In (1.52 rn), 1 ft (0.305 rn) diarn.
NOTE: -1000 S T A I RD O O RO P E N I N G 0~3n x7n (0.92 m x 2.13 m)
of 570F (300C) and 1300F (700C) and with the outside wall vents of 10 ft2 (0.929 m2)closed and also with them open to simulate broken windows. The fire temperatures were measured directly above the burners and just below the ceiling and were controlled at the test temperatures by adjusting the propane gas flow rate. The tests were conducted to obtain vertical profiles of pressure differences across the stairshaft wall caused by the fire. 2. With the stair door open at 90' and without stairshaft pressurization,tests were conducted at fire temperatures of 570F (300C) and 1300F (700C) and with the outside wall vents closed and also with them open. They were conducted to obtain the vertical profiles of pressure differences across the stairshaft wall and the velocity pressures at the stair door opening. 3. With the stair door open at 90 and with the stairshaft pressurized with bottom injection, tests were conducted at afire temperature of 570F (300C); the outside wall vents were closed. The supply air rate was adjustedto the point of no gas backflow into the stairshaft and the rate recorded. The test was repeated with the outside wall vents open. 4. With the stair door open at 90 and with the stairshaft pressurized with bottom injection, tests were conducted at afire temperature of 1075OF(600C); the outside wall vents on the second floor were open, as the windows are likely to break at this temperature. The supply air rate to the stairshaft was adjusted to the point of no gas backflow at the stair door opening. 5. Same asTest 3, except that the stair door was in the 60 open position. 6. Same asTest 4, except that the stair door was in the 60 open position.
RESULTS AND DISCUSSIONS Hot Wire Anemometer Traverse The results of the 9-, 15-, and 21-point traverses are shown in Figure4. With the airflow in one directionthrough the door opening, the airflow rates were calculated by multiplyingthe average air velocity by the area of the door opening. These were plotted against the rates measured at the airflow measuring station in the supply air duct. The airflow rates obtained usingthe 9-pointtraverse were about 20% higher, while the airflow rates obtained with the 15and 21-pointtraverses agreed with those measured at the airflow measuring station. Becausethe difference in time taken to conduct a 15-or a 21-point traverse is minimal, the 21-point traverse is recommended for a standard-sized door when testing a stair pressurization system in the field. Flow Resistance of Stair Door Opening For each test condition, the value of the flow coefficient, K, was calculated for pressure differences of 0.05, 0.10, and 0.15 in of water (12.5,25, and 37.5 Pa). The value of K was relatively constant and within 2% of its average value for the range of test pressure differences; hence, only the average values are presented in Table 1. The values of K for various door angles for both bottom air injection and multiple injection (floors 1,3,5,7, and 10) are shown in Figure 5. The angle of 5 O is intended to represent an opening with a 2.5 in (63 mm) diameter fire hose in a doorway, 60 an opening when a person is passing through a doorway, and 90 a fully open door. The curve, fitted to the data, is relatively smooth for multiple injection, with values of 0.06,0.65, and 0.73 for 5O, 60, and 90, respectively. The values obtained with bottom injec-
0 . 0/
tion are above and below this curve; the corresponding values are 0.14, 0.59, and 0.85. The values of K were apparently affected by the method of air injection, which affected the approach and entry conditions of the airflow at the door opening. The values of K with people or body simulators in the door opening (door open at 60) with bottom injection of supply air to the stairshaft are given in Table 1. Without anybody in the doorway, K was 0.59; with one person, K varied from 0.51 to 0.52 for heights varying from 5 ft (1.52 m) to 6 ft, 1 in (1.84 m), i.e., a reduction in K of 12% to 13%. With the body simulators of 1 ft (0.3048 m) diameter, the reduction was 8% to 10%. With a person or body simulator on both sides of the door opening, the reductions in K varied from 16% to 21%. The data obtainedfrom these tests give some indication of the effect of people on K value and can be used in computer modeling for studying the performanceof stair pressurizationsystems. The body simulatorscan be useful for fire tests.
FIRE TEMPERATURE, "C 400 800
1000 "0
Critical Velocity In this paper the average air velocity at the stair door opening on the fire floor required to prevent smoke from entering the stairshaft is referred to as the critical velocity to prevent smoke backflow. It iscalculated by dividing the airflow rate that is just sufficient to prevent smoke backflow by the area of the stair door opening. Figure 6 shows the pressure difference across the wall of the stairshaft (stairshaft pressure - burn area pressure) without stairshaft pressurization; that is, the pressure difference caused only by the buoyancy force for fire temperatures of 570F (300C) and 1300F (700C). The pressure differences are about the same, whether the stair door is closed or open. The neutral pressurelevel is located 4.80 ft (1.46 m) above floor level. Pressure differences across the walls of the stair and elevator shaft were measured at the 10 ft (3.048 m) level in
a previous study on fire pressures by Tamura and Klote (1988). These previousvalues, along with the pressuredifferences measured in this study, are plotted against fire temperatures in Figure 7. The neutral pressure level of the elevator shaft is located at 5.58 ft (1.7 m) above floor level. The pressure differences were calculated using the following buoyancy equation: P , - Pf = ghp,(T, - T,) I Ti (2) where P , - Pi = pressure difference across the shaft wall = gravitational constant 9 h = distance from the neutral pressure level
(580 "C)
'"a\.
Figure 8 Centerline wlocity pressure profile at open stair door (90)
FIRE TEMPERATURE, "C
shaft outside the fire compartment = fire compartment The calculated values for the stairshaft and elevator shaft, usingtheir respectiveneutral pressurelevels, are also shown in Figure 7. Because of the lower neutral pressure level, the pressure differences across the walls of the stairshaft are higher than those of the elevator shaft. For both shafts the temperatures near the ceiling above the gas burners (Figure 2) were used in the calculations, although spatially the temperatures in the burn area varied greatly. Using this temperature in Equation 1, which assumes a uniform space air temperature, however, gave a good estimate of the pressure differences across the walls of both elevator shaft and stairshaft. Figure 8 shows the centerline velocity pressure profiles at the stair door opening without stairshaft pressurization for fire temperatures of 570F (300C) and 1300F (700C). The velocity pressures referenced to the burn area pressure at 6.66 ft (2.03 m) were -0.014 in of water (-3.5 Pa) for a fire temperature of 570F (300C) and -0.019 in of water (-4.7 Pa) for afire temperature of 1300F (700C). These values compare with pressure differences measured across the stairshaft wall at the 7 ft (2.13 m) level of -0.014 in of water (-3.5 Pa) and -0.021 in of water (-5.2 Pa), respectively (Figure 6). With stairshaft pressurization, the flow rate was increased until no backflow was observed. At a stair door opening of 900, when the velocity pressurewas balanced at the top of the door opening, the direction of flow was from the stairshaft into the burn area for the full height of the stair door (Figure 9) and, hence, smoke backflow was pre= =
A MEASURED VALUES FOR DOOR ANGLE OF 60"
o f 60 and 90
vented. During tests this was verified visually by running a smoke pencil for the full height of the opening. The flow rates required to prevent smoke backflow were 7380 cfm (3.48 m3ls) for afire temperature of 570F (300C) with the exterior wall vents either closed or open and 9200 cfm (4.34 m3/s)for afire temperature of 1076OF (580C) with the exterior wall vents open (the temperature of 1300F (700C) was not reached because of cooling effect of pressurization air in the burn area). The corresponding critical velocities were calculatedto be 350 fpm (1.78 mls) and 438 fpm (2.22 mls), respectively. At a stair door opening of 60, the critical velocities were306fpm (1.55 mls) and 377fpm (1.92 mls) for fire tem-
Ma, W.Y.L.1967. "The averaging pressuretubesflowmeter for the measurement of the rateof airflow in ventilating ducts and for the balancing of airflow circuits in ventilating systems." Journal of the lnstitute of Heating and Ventilating Engineers, February, pp. 327-348. MacLennan, H.A. 1985. "The problem with estimating the safe time required for egress." ASHRAE Transactions, Vol. 91, Part 28, pp. 1254-1236. McCaffrey, B.J., and Heskestad,G. 1976. "A robust bidirectional low velocity probe for flame and fire application." Combustion and Flame, Vol. 26, pp. 125-127. Melinek, S.J. 1975. "An analysis of evacuation times from buildings." CIS Symposium, Symposium on the Control of Smoke Movement in Building Fires, Vol. 1, Paper 5, Watford, pp. 49-58. National Fire ProtectionAssociation, Fire protectionhandbook, 16th Ed. "Concept of egress design." Section 7lChapter 3, pp. 7-20-7-40. Boston: NFPA. National ResearchCouncil of Canada. 1985.Supplementto the National Building Code of Canada. Chapter 3, Measuresfor fire safety in higk buildings," pp. 87-111. Ottawa: NRCC. Owen, A.G.V. 1967. "Dilution techniques of flow measurement." Journal of the lnstituteof Heatingand Ventilating Engineers, July, pp. 117-120. Pauls. J.L. 1975. "Evacuation and other fire safetv measures in high-risebuildings." ASHRAE Transactions, ~ol:81,Part 1, pp. 528-533. Pauls, J.L. 1977. "Movement of people in building evacuations." Human Response to Tall Buildings, chapter 21, pp. 281-292. Stroudsburg, PA: Community Development Series, Vol. 34.
Pauls, J.L. 1980a. "Building evacuation: research methods and case studies." Fires and Human Behavior, chapter 13, pp. 227-248. New York: John Wiley and Sons Ltd. Pauls, J.L. 1980b. "Building evacuation: research findings and recommendations."Fires and Human Behavioc chapter 14, pp. 251-275. New York: John Wiley and Sons Ltd. Shavit, G. 1983. "Smoke control with feedback." ASHRAE Transactions, Vol. 89, Part IB, pp. 379-384. Shavit, G. 1988. "Information-basedsmoke control systems." ASHRAE Transactions, Vol. 94, Part 1, pp. 1238-1252. Shaw, B.H. 1974. 'Air movement through doorways-the influence of temperature and its control by forced airflow." BuildingServices Engineers, Vol. 42, December, pp. 210-218. Southern Building Code Congress International. 1985. Standard Building Code, Section 506. Birmingham AL. Tamura, G.T. 1974. "Experimental studies on pressurized escape routes." ASHRAE Transactions, Vol. 80, Part 2, pp. 224-237. Tamura, GT. 1980. "The performance of a vestibule pressurization for the protection of escape routes of a 17-story hotel." ASHRAE Transactions, Vol. 86, Part 1, pp. 593-603. Tamura, G I , and Klote J.H. 1988. "Experimental fire tower studies on mechanical pressurization to control smoke movement caused by fire pressures." Presented at the Second International Symposium on Fire Safety Science, June, Tokyo. Thomas, pH. 1970. "Movement of smoke in horizontalcorridors against an airflow." Institutionsof Fire Engineers, Vol. 30, No. 77, pp. 45-53. Thornberry, R.!? 1982. "Designing stair pressurizationsystems." Society of Fire Protection Engineers, Technical Report 82-4.
Ce document est distribud sous forme de M-&part par 1'Institut de recherche en construction. On peut obtenir une liste des publications de I'Institut portant sur les techniques ou les recherches en matibre de bitirnent en ecrivant A la Section des publications, Institut de recherche en construction, Conseil national de recherches du Canada, Ottawa (Ontario), KIA 0R6.
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