1、AN-04-1 1-1 (RP-1203) Tenability and Open Doors in Pressurized Stairwells John H. Klote, D.Sc., P.E. Fellow ASHRAE ABSTRACT During building jres, smoke logging of stairwells can have serious consequences. A project was conducted to study the consequences of one or more improperly propped open stairw
2、ell doors on tenability conditions in the stairwell and at other locations in the building. Thisproject used the network buildingflow model CONTAMin conjunction with thezonejre model CFASTto analyze 80 smoke transport scenarios in high- rise buildings. Tenability calculations were performed by a com
3、puter program that was specifically written for this purpose. This basic approach has been used for a number of other applications, and it is the only practical approach to analyze the smoke transport due to fires in high-rise buildings. However, the method of analysis leaves much to be desired, and
4、 sofiare needs to be developed to more realistically simulate smoke transport fromjres in large high-rise buildings. Param- eters included in the analyses are weather, stair geometry, building leakage, enclosed elevator lobbies, elevator vent, stair pressurization systems, type ofJire, location ofjr
5、e, and arrangement of open stair doors. INTRODUCTION It is well known that smoke logging of stairwells can have serious consequences during building fires. This is so in both low-rise and high-rise buildings, but the focus of this project is high-rise buildings. A few examples of fires in high-rise
6、buildings where smoked-logged stairwells were significant are the MGM Grand fire (Best and Demers 1982), the Empire State Building (Hassett 1990), Seattles University Tower Hotel fire (Fire Journal 1975), World Trade Center explosion and fire (Powers 1975), and the One Meridian Plaza fire (Klem 1991
7、). This paper describes a project to develop a quantitative understanding of the impact of one or more improperly propped open stairwell doors on tenability conditions in the stairwell and at other locations in the building. Eighty scenar- ios were analyzed to study the effects of weather, stair geo
8、m- etry, building leakage, enclosed elevator lobbies, elevator vent, stair pressurization systems, type of fire, location of fire, and arrangement of open stair doors. For a more detailed description of this project, see Klote (2002a, 2002b). A fire scenario can be thought of as the outline of event
9、s and conditions that are critical to determining the outcome of a situation. In addition to the fire location and heat release rate, the fire scenario includes the status of the doors, the smoke management system, weather conditions, and all other condi- tions critical to the analysis of the scenar
10、io. The analytical tools for this project consisted of (1) the network airflow model CONTAM (Walton 1997; Dols et al. 2000), (2) the zone fire model CFAST (Peacock et al. 1993), and (3) a tenability model SMOKE. The SMOKE model was written in FORTRAN for this project and is described later. The meth
11、od of analysis used in this project also is discussed later, and this method has been used for a number of applica- tions. Ferreira (2002) describes use of this method for design applications, and Hadjisophocleous et al. (2002) use this method as part of a study of smoke flow in a stair shaft. Klote
12、 (2002) and aote and Milke (2002) also provide information about use of this method. . CONTAM96 was developed for the DOS operating system, and CONTAMW was developed for Windows. The analytical capa- bilities and calculations of CONTAM96 and CONTAMW are identical. Because of input differences, both
13、models were used for this project, and the term “CONTAM as used in this paper applies to both models. John H. Note is a consulting engineer at Fire and Smoke Consulting, Leesburg, Va. 02004 ASHRAE. 61 3 a. (b) Floors AboveGround Floor Without Vestibules .VES1 VES2, S (e) Floors Above Ground Floor Wi
14、thVcttibules c I I I I I I sw1 AS12 (d) Fbors Above Ground Floor Without Enclosed Elevator Lobbies Symbols Notes: AS npartment Space 1. Drawing notto scale. 2. interior partitions and oiher details of the SW Stairwell COR Corridor apartmenis not shown. 3. SW1 extends to the LEY tobby ELEV Elevator -
15、 SingleDoor 4 The elevatr machinery .1. DoubleDoor room Is located at the roof iavel VES Vestibla roof age, and (3) tight. These values are representative of values that can exist in construction as discussed by Klote and Milke (2002) and NFPA 92A (NFPA 2000a). The project examines the effect of bui
16、lding leakage on smoke migration. The effects of door deflection due to exposure to high temperature gases are not included in the leakage values. Some data on warping of fire doors during furnace tests is provided by VanGeyn (1994). For the scenarios of this project, the gas temperature near closed
17、 doors was considerably below that of the furnace tests, and it was considered that the warping of doors could be neglected. Stair Pressurization Systems There are numerous types of stair pressurization systems that have been used. The model codes (BOCA 1999; ICBO 1997; ICC 2000; SBCCI 1997) and the
18、 Life Safety Code (NFPA 2000b) have a major impact on the types of stair pres- surization systems used in the United States. These codes do not require compensating pressurization systems,2 so all of the systems of this study are noncompensating. Table 2 lists four systems that are in common use, an
19、d these systems are referred to in this paper by the abbreviated names in this table. FIRE Figure I Floor plans of buildings to be analyzed. WEATHER Based on examination of weather data for the largest metropolitan areas in the U.S. and Canada (ASHRAE 2001), the weather data parameters listed in Tab
20、le 3 were selected. BUILDING A seven-story building and a twenty-one-story building were selected for this project with floor plans as illustrated in Figure 1. These are apartment buildings, but the basic concept has been used for many applications including office build- ings, hotels, student housi
21、ng, and homes for the elderly. The floor to ceiling height is 8 fi. These plans include buildings with and without stairwell vestibules. Buildings with the same floor plans were chosen so that comparison of conditions between the two buildings would be meaningful. The stairwells in the building of F
22、igure 1 are conventional ones consisting of a straight shaft stairwell with a landing between floors. It was also desired to study the effect of scissor stairs. These buildings do not lend themselves to scissor stairs, but scissor stairs can be incorporated in the analysis by use of friction losses
23、appropriate to scissor stairs. The building temperature is considered the same as that of the shafts, and this building temperature is arbitrarily selected as 73F (23C). Building Leakage Construction leakage varies over a wide range, and Table 1 lists three levels of leakage for buildings: (I) loose
24、, (2) aver- Fire Type For this project, sprinklered fires, shielded fires, and unsprinklered fires were used, and heat release rates (HRR) of these fires are shown in Figure 2. The sprinklered fire grows as a fast t-squared fire up to 600 Btu/s (633 kW). Afterward it decays due to sprinkler action.
25、Based on the fire growth rates of NFPA 92B (NFPA 2000c), the fast t- squared fire has an HRR of Q = a8 where Q is the HRR in Btus (kW), t is time from ignition in seconds, and a is 0.04444 Btu/s3 (0.04689 kW/s2). The HRR decay after sprinkler actuation is expressed as Q = Quct e. The mass optical de
26、nsity depends on the material burned and combustion conditions (flaming or pyrolysis). Mulhol- land (2002) provides optical densities of a number of materi- als, and these values range from 590 ft2/lb (O. 12 m2/g) to 6800 ft2/lb (1.4 m2/g). It is well known that flaming combustion of polyurethane pr
27、oduces a dense black smoke. This smoke has amass optical density of 1600 ft2/lb (0.33 m2/g), and this value of mass optical density was used for the analyses of this project. For this project, the following visibility limits were considered: (1) 25 fi (7.62 m) and (2) 100 ft (30.5 m). A visi- bility
28、 of 1 O0 ft (30.5 m) is not expected to interfere with people movement in the building of this project, but people would probably be aware that there is some smoke. However, it is expected that a visibility of 25 ft (7.62 m) or less would hinder evacuation. For this paper, smoke with a visibility of
29、 25 ft (7.62 m) or less is referred to as obscuring smoke, and this smoke obscures vision. Exposure to Toxic Gases. The mass concentration of material burned, Ci, was obtained from CONTAM. The FED can be used f? obtain an approximation of the effects of expo- sure to toxic gases. n CiAt where FED Ci
30、 = fractional effective dose at the end of interval i (dimensionless); = concentration of material burned at interval i, ib/Et3 (g/m3; 622 ASHRAE Transactions: Symposia 500m 250 O o 10 20 30 40 50 60 Exposure Time (minutes) Figure 8 Thermal tolerance for humans at rest, naked with low air movement (
31、adapted from Blocklq 1973). At = time interval, min (min); LCt, = lethal exposure dose from test data, lb fc3 min (g m-3 min). This equation is written here for uniform time intervals as were produced by CONTAM, and it evaluates the FED for the exposure time at the end of interval i (exposure time i
32、s nAt). An FED greater than or equal to one indicates fatality. The concentration is in mass of the material burned per unit volume. An FED of 0.5 can be considered a rough indication of incapacitation. For this project, terms to describe toxic exposure are used as follows: (1) Tenable: FED 0.5, (2)
33、 Inca- pacitating: 0.5 I FED 1, and (3) Untenable: FED 2 1. The LC50 is the concentration of airborne combustion products that is lethal to 50% of the subjects exposed for a specified time. The lethal exposure dose, LCt, is the product of the LC50 and the exposure time. Purser (2002) provides values
34、 of LCt, for a number of materials. The lethal exposure doses range from 0.0062 lb/ft3 (1 O0 g/m3) to 0.087 Ib/ft3 (1 390 g/m3) for a fuel controlled fire. For a fully developed fire, the lethal exposure doses range from 0.0034 lb/ft3 (54 g/m3) to 0.047 Ib/ft3 (750 g/m3). For this project, the follo
35、wing lethal exposure doses were used: (1) 0.075 lb/ft3 (1200 g/m3) for a fuel controlled fire and (2) 0.033 lb/ft3 (530 g/m3) for a fully developed fire. These values are applicable to the entire class of C, H, O plastics. Klote and Milke (2002) describe other methods (frac- tional incapacitating do
36、se and the N-gas model) of estimating the toxic effects of exposures to various gases. However, these other methods require calculation of the concentrations of gases (O2, N2, CO2, CO, etc.). Calculation of these concentra- tions requires known generation rate of specific fire gases that can be esti
37、mated for a specific fuel. For a known generation rate of specific fire gases, these other methods are generally considered to result in more accurate predictions than those using the FED. For this project and many other applications, the specific information about the fuel is unknown. The FED metho
38、d is a simpler approach, and it can be considered to provide results that have applicability to a range of fuels. Exposure to Heat. Generally, contact with dry air of temperatures greater than 250F (12 1 OC) can be expected to result in skin bums. Also, contact with dry air at a temperature less tha
39、n approximately 250F (121C) leads to hyperthermia. Figure 8 shows the data of Blockley (1973) for the thermal tolerance of naked humans at rest with low air movement. The thermal tolerance depends on moisture. For humid conditions, it can be seen that for a 15-minute exposure the tolerance is about
40、190F (88“C), and for a 30-minute exposure the toler- ance is about 140F (60C). For the sprinklered fire (Figure 5), only the temperature exposure in the fire room might be a concern. The tempera- tures from the CFAST simulations are average values for the zone, and in some locations higher temperatu
41、res would be expected, and the temperature exposure in the corridor might be a concern. For the shielded fire (Figure 6), the temperatures of the fire room exceed the limits of tolerance and result in fatality. For the unsprinklered fire (Figure 7), the high temper- atures in the fire room and corri
42、dor would result in fatality. DISCUSSION OF RESULTS The results of the tenability analyses of the 80 scenarios are summarized in Tables 5 and 6 (descriptions of the scenar- ios are listed in Table 4). Unless otherwise noted in the follow- ing discussion, the word stairwell is used to mean stairwell
43、2. Unpressurized Stairwells Scenarios 1 to 4 were for unpressurized stairwells during winter, and scenarios 5 to 8 were for unpressurized stairwells during summer. For the winter scenarios, the fire was in apart- ment AS12 on the second floor (Figure I). For the summer fires, the fire was in apartme
44、nt AS 12 on the second floor from the top of the building. The basic patterns observed for unsprinklered fires with the conditions of this project and with stairwell doors propped open are that vision is obscured and conditions are untenable on some floors of the stairwell for both winter and summer
45、 scenarios. For unsprinklered fires on the second floor in winter, vision is obscured and conditions are untenable for most of the floors of the stairwell. For unsprinklered fires on the second from top floor in winter, vision is obscured and conditions are untenable for one or two floors near the t
46、op of the stairwell. Base System Scenarios 9 through 18 are with the base pressurization system for the seven-story building with various fires on the second floor. The basic pattern observed for unsprinklered fires with the base system was the same as for those without pressurization. When only the
47、 stair door is open on the fire floor, the smoke spread in the stairwell is less extensive, but the basic pattern remains unchanged. ASHRAE Transactions: Symposia 623 9 624 FED-1 .O 20 20 20 Vis- i O0 2-7 3 ASH RAE Transactions: Symposia Table 5. (continued) Summary of Tenability Analysis i8 FED- 1
48、.O 2-5 2 2 2 Vis- 1 O0 4 Vis-25 2-7 2-7 2-1 2-7 2-7 ASHRAE Transactions: Symposia 625 Table 5. (continued) Summary of Tenability Analysis 27 FED-1.0 2 2 2 2 Vis- 1 O0 G 19,2 1 Vis-25 2-2 1 2-2 1 20 G-2 1 2-21 G-18,20 FED-0.5 19,20 2 3,5-10 626 ASHRAE Transactions: Symposia Table 5. (continued) Summa
49、ry of Tenability Analysis FED-0.5 3 -6 6 2 34 FED-1 .O 2 2 2 Vis- 1 O0 4 Vis-25 FED-0.5 FED-1 .O 2-7 2-7 2-1 2-7 2,3,5-7 7 7 5,6 2-6 2.5.6 2 35 ASHRAE Transactions: Symposia 627 Vis- 1 O0 20 4-6,11,19,21 Vis-25 2-2 1 2-2 1 2-21 FED-0.5 18 8-10 2-2 1 2,3,7-102-18,20 36 FED- 1 .O 2-17 2 2 Vis- 1 O0 3-5 19-2 1 4,5 4,5 Vis-25 2-2 1 2.6-2 1 2-2 1 2.6-2 1 2.3.6-21 FED-0.5 FED- 1 .O 19-2 1 7-10, 12-21 19,20 2-18 2 2 Table 5. (continued) Summary of Tenability Analysis 46 FED-0.5 FED-1.0 6 6 Vis-100 20,21 13-20 21 628 ASH RAE Transactions: Symposia Table 5. (contin
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