Influence of Doorway Opening Conditions on Vestibule Pressurization Smoke Control in Office Buildings

Influence of Doorway Opening Conditions on Vestibule Pressurization Smoke Control in Office Buildings Mamiko KUJIME Nikken Sekkei Ltd 4-6-2 Koraibashi, Chuo-ku, Osaka 541-8528, Japan Takayuki MATSUSHITA Kobe University, Associate Professor 1 Rokkodai-cho, Nada-ku, Kobe, Hyogo 657-8501, Japan Takeyoshi TANAKA DRS, DPRI, Kyoto University, Professor Gokasho, Uji, Kyoto 611-0011, Japan ABSTRACT A practical calculation method for the vestibule pressurization smoke control systems was provided in previous papers[1][2]. This method covers fire scenarios corresponding to every stage of building evacuation in fire, namely, fire room evacuation, fire floor evacuation and whole building evacuation, and consists of a series of equations which can be successively calculated by a hand calculator to obtain required air supply rates to vestibules and elevator shafts. The required air supply rates may be calculated under the condition that all the doors are open in order to cope with the worst scenario. However, such an opening condition of the doors may not be the worst for the required air supply rates, since the pressures of the corridors and the elevator shafts are affected by the opening conditions in a complex manner. In this study, the effects of opening conditions of fire room doors on the corridor pressure and the required air supply rates at the stage of whole building evacuation are examined. In addition, the influence of closure of staircase doors on the required air supply rates is investigated. Keywords: smoke control, vestibule pressurization, pressure difference, smoke stop, pressure relief, opening condition INTRODUCTION A vestibule pressurization smoke control, which directly pressurizes vestibules of staircases, is an effective method to prevent smoke infiltration into the staircases thereby assuring smoke free means of escape for building occupants and means of access for fire brigade, particularly in high-rise office buildings. Since, this smoke control system produces a corridor pressure rise, it is often accompanied by pressurization of the elevator shafts to prevent smoke spread from the corridor. A simple hand calculation method was proposed in previous papers for determining required air supply rates to vestibules and elevator shafts in this smoke control system [1][2]. This calculation method covers fire scenarios corresponding to three stages of evacuation, i.e: fire room evacuation, fire floor evacuation and whole building evacuation. In addition, it is worth mentioning that this method consists of a series of simple formulas, which can be followed by use of a hand calculator, so that the verification of safety requirements can be carried out by not only a limited number of fire experts but also for a large number of ordinary engineers. FIRE SAFETY SCIENCE--PROCEEDINGS OF THE SEVENTH INTERNATIONAL SYMPOSIUM, pp. 741-752 741 Copyright © International Association for Fire Safety Science However, as easily presumed, the required air supply rates in the smoke control method heavily depend on conditions of openings around the corridor and vestibule. In general, one may assume that the condition that all the doors are fully open is the worst scenario for the air supply rates, because the required flow rates for smoke stop and the rates of air leakage from pressurized zones to the other spaces usually increase with the opening area. Nevertheless, the required air supply rates are not always the largest when the opening areas are the largest, because different opening conditions of doors induce a different pressure field among the spaces involved. The opening conditions of doors on the required air supply rates should be considered carefully. Also, the effect of the opening condition of the doorway of a vestibule into a staircase on the corridor pressure has to be examined. When the door happens to be closed the air which is expected to leak into the staircase in the design will be diverted into the corridor to raise its pressure and may break the smoke seal of the elevator shaft therein. 1 SIMPLE HAND CALCULATION METHOD In the beginning, the calculation method for the required air supply rate for fully developed fire scenario proposed in the previous paper is summarized as follows: 1.1 Layout of Floor of Office Building A typical layout of floor plan of office buildings, which has two staircases connected by one corridor as shown in Figure 1 is considered in the investigation of this method. Needless to say there is a wide range of possible layouts of floor plans of office buildings, the plan of this type can be often found in real office buildings and is one of the most simple m RO and popular floor plan to consider pressurization smoke control system. Fire room (R) P R m CR ∆ P CR Figure 1 also illustrates a typical flow Corridor (C) pattern at the openings. The spaces on ∆ P LC1 P C ∆ P LC2 m LC1 m m LC2 the floor, i.e, the fire room, corridor, EC Staircase1(S1) ∆ P EC Staircase2(S2) P L1 P L2 vestibule, elevator shaft and staircase, are m LS1 m LF P E m LS2 identified by letters R, C, L, E and S, Vestibule1(L1) Fire elevator Elevator Vestibule2(L2) respectively. The multiple spaces of shaft(F) shaft(E) identical use are distinguished by adding ‚vL1 ‚vE ‚vL2 numerals to the characters. A doorway Air supply Air supply Air supply connecting two spaces is identified by a Figure 1 Assumed plan and flow pair of letters corresponding to the spaces. 1.2 Scenario Corresponding to the Stage of Whole Building Evacuation The scenario adopted for fire at whole building evacuation stage is as follows: 1) The fire is fully developed so the windows in the fire room have been broken. 2) The smoke extraction in the fire room has been shut down due to closure of the fuse damper to avoid fire spread through the duct. 3) Some of the doors between 'the fire room and corridor' are left open so the corridor is contaminated with smoke. 4) After all the occupants from the fire floor have escaped to the staircases, it is sufficient to stop smoke between 'the corridor and vestibule', to support fire brigade operation and occupants evacuation in the staircase. At the same time, it is necessary to prevent smoke to spread from the corridor to the elevator shaft. 742 1.3 Relationships which Hold for the Pressures and the Opening Flow Rate The relationships which hold for the room pressures and the flow rates are as follows: Pressures PPPCR= + ∆ CR (1) PPPLC1 = + ∆ LC1 , PPPLC2 = + ∆ LC 2 (2) PPPEC= + ∆ EC (3) Flow rates Fire room (R): mCR = mRO (4) Corridor (C): mLC1 + mLC 2 + mEC = mCR + mCO + u C (5) Vestibule (L1): WL1 = mLC1 + mLS1 + mLF (6) Vestibule (L2): WL2 = mLC 2 + mLS 2 (7) Elevator shaft (E): WE= m EC + mEO (8) 1.4 Smoke Stop Criteria Once the corridor temperature is given, the average pressure differences and doorway mass flow rates corresponding to smoke stop criteria between 'the vestibules and corridor' ∆PLC and mLC, and 'the elevator shaft and corridor' ∆PEC and mEC are given as follows: 4 2 ∆P =()ρ − ρ g h and m)()(= α A 2 ρ ρ− ρ g h (9) LC 9 L C LC LC 3 LC L L C LC 4 2 ∆P =()ρ − ρ g h and m= ()α A 2 ρ ( ρ− ρ )g h (10) EC 9 E C EC EC 3 EC E E C EC where, ρL and ρE are the initial air density of the vestibule and elevator shaft, and ρC is an air density of the corridor. hLC and hEC are the heights of the openings between 'the vestibule and corridor', and between 'the elevator shaft and corridor', respectively. 1.5 Calculation Procedure for Air Supply Rates Based on the above relationship, the air supply rates required to realize the smoke stop criterion given by Eqns.(9) and (10) can be calculated by the following procedure as follows: [Step 1] Determine temperatures of the fire room ∆TR and corridor ∆TC, which can be obtained using some appropriate means such as the simple formulas proposed by Tanaka et al. [3]. 2/ 3 1/ 3 1/ 6 ∆TKFTR = 3.0 R OR τ a (11) 1/ 3 4/ 9 2/ 9 5/18 ∆TFKFTC = 1.35 OC R OR τ a (12) where Ta is the ambient air temperature. The four parameters in the above formulas, KR, FOR, FOC, and τ, are given by the following Eqns.(13)-(16). ARO h RO K R = (13) ARO h RO + ARC h RC ARO h RO + ARC h RC FOR = (14) ARW ARC h RC + ACO h CO FOC = (15) ACW τ=tdev k ρ c = 0.3 tdev (16) Where, ARO h RO , ACR h CR , ACO h CO are the ventilation factors of the openings between 'the fire room and outdoors', between 'the corridor and fire room' and between 'the corridor and outdoors', respectively. ARW is the total surface area of the fire room, ACW is the total surface area of the corridor, k is heat conductivity, ρ is density and c is specific heat. tdev is safety goal 743 time, such as the evacuation time. [Step 2] Calculate the flow rates and the average pressure differences for smoke stop criteria between 'the vestibule and corridor' mLC and ∆PLC, and 'the elevator shaft and corridor' mEC and ∆PEC by Eqns.(9) and (10). [Step 3] Calculate the corridor pressure PC by 2 ()mLC1 + mLC 2 + mEC − u C PC = 2 (17) 2ρC () αA CO where (αA)CO is the effective opening area calculated by combining the series or parallel openings which connect the corridor to outdoors. [Step 4] Calculate the average pressures of the vestibule PL1 and PL2 using Eqn.(17) to Eqn.(2).

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