挑高中庭之性能式火災煙控設計研究

Abstract

挑高中庭建築具有大空間、跨樓層，具有相當的高度與面積、能容納大量人群的特徵，因此其消防安全需要特殊的防災設計。然而國內目前的消防相關法規，均以規格式法規為主，對於挑高空間建築物無法以傳統法律條文規範其防火安全，需要以性能式設計之方法來確保其防火設施之效能。因此本研究利用性能式設計法（performance-based design method）之驗證程序和步驟，以及數值火災模擬軟體FDS（Fire Dynamics Simulator）以及SIMULEX人員逃生避難軟體分別進行煙控系統設計分析與避難性能評估。主要的內容分為三個案例，案例一與案例三都為挑高中庭建築案例，案例二為戲院案例。案例一與案例三雖然都為挑高中庭之案例，但是案例三有較多的逃生出入口偏向於一方且每層中庭區域的電扶梯呈不規則分佈；而案例一的蓄煙區為玻璃材質會受到夏季高溫影響而導致層化現象的發生。至於案例二，其建築特色為樓地板與天花板皆呈階梯狀，因此不適用於簡易二層法或建築物防火避難安全性能驗證技術手冊的計算方法。在進行此三個案例煙控模擬設計，首先考慮火源大小來搭配煙控策略進行模擬，以FDS計算出距離地板高1.8公尺之火災溫度分佈、CO濃度分佈、能見度分佈、熱輻射分佈，然後驗證在相關設計下是否能符合人員安全逃生之環境要求。接著再利用動態避難模擬Simulex模擬計算人員避難逃生情形和避難所需時間，以評估人員避難安全。之後再詳細探討案例一之層化現象影響程度以及各案例之煙流向和人員避難方向之關係、補氣口風量速度是否符合NFPA 92B與BRE之建議值。經由模擬結果可以得知，所有案例的煙控系統設計均能滿足人員生命安全的標準；也比較出均勻分佈的逃生開口較有助於避難逃生的順暢；並且發現案例一層化現象隨著高度遞減而越不明顯；另外在案例三補氣口的流速大於NFPA 92B所建議流速值(1m/s)，但小於BRE所建議流速值(3m/s)，其原因為該案例開啟的排煙機較多，導致補氣口的速度也會較大。

The atrium building has the characteristics of large space, floor opening connecting two or more stories, high altitude, large area and large volume of occupants that it is almost impossible to comply with the requirements of present Taiwan fire codes, which are prescriptive. In such case, the “performance-based design method” is adopted to carry out the alternative fire safety engineering design, which is allowed by the fire code now. This research analyzes the performance designs of smoke control system and the occupant evacuation, respectively, by utilizing the verification procedures and steps of performance-based design method. The numerical simulation softwares, FDS (Fire Dynamics Simulator) and SIMULEX, are used as the computational tools. The contents of this research consist of three cases, which case 1 and case 3 are the atrium buildings and case 2 is a theater. Although both case 1 and 3 are the atrium buildings, the evacuation exits are partially concentrated to one side and the elevators in the neighborhood of atrium in each floor are irregular distributed in case 3. The ceiling material of atrium in case 1 is made of glass, therefore, the phenomenon of “Smoke Stratification” due to the high atmospheric temperature in summer is needed to consider. Because the floors and ceiling of theater are in shape of stairways, it is inadequate to use the zone models, which are based on BRI-2 or Building Research Institute Handbook of Fire Safety Protection Performance, to calculate the smoke descending rate in such compartment. These are the motivations to carry out this research. At the beginning, FDS is used to calculate the distributions of temperature, concentration of CO, visibility and radiation at height 1.8 m from the floor along the evacuation routes under the given fire source and the corresponding smoke control system to verify whether the performance of calamity system can maintain the attainable conditions of life safety. After that, Simulex is applied to calculate of the conditions of evacuating occupants and the available evacuation time. Finally, the time needed for smoke to descend to 1.8m-height is compared with the evacuation time to ensure the requirement of life safety. In addition, this reseach discusses the influence of smoke stratification in case 1 and the relationship between the smoke and occupant movement directions in all cases, and whether the velocities of make-up air at entrance exceed the suggested values by NFPA 92B and BRE in all cases. From the simulation results, they confirm that the designs of smoke control system in all cases can comply with the safety requirements for occupant evacuation. It is also found that the uniformly distributed evacuation exits are helpful to evacuate occupants smoothly, and smoke stratification is not as obvious as the altitude decreases in case 1. However, in case 3, the velocity of make-up air at entrance is greater than the one suggested by NFPA 92B (1m/s), but smaller than the one suggested by BRE (3m/s). This suggests that extra evacuation exits may need in this case.