以FDS探討正壓通風對於風驅動高樓火災之消防效果

Using FDS to Investigate the Effect of Positive Pressure Ventilation for Fighting Wind-driven High-rise Fires

高層建築火災在受到外界風的影響時，會產生相當危險的火場環境。根據紐約市消防局的統計，在1980～2008年間的14起風驅動高樓火災中，共造成11位平民死亡及5位消防員殉職的不幸後果。採用正壓通風策略（Positive Pressure Ventilation, PPV）能夠有效的降低火場溫度、排除煙霧、提高能見度以提升火場逃生及救難人員的安全；然而其有效性會受到建築物結構佈局、外界風況與PPV風機佈署之影響。因此，本研究透過火災動態模擬器（Fire Dynamics Simulator, FDS）軟體來進行高層建築火災的模擬，並測試正壓通風策略在上述相關參數影響下之效能表現。由研究結果顯示，採用單一風機實施正壓通風時，即可有效的阻擋煙霧進入樓梯間並降低火場溫度，但外界風速達到5 m/s以上時（測試風速0～10 m/s，NIST警告之外界風速為4.5 m/s），將會對火場產生嚴重影響，且會造成單一風機之正壓通風策略失效。為此，本研究透過兩部風機來增強正壓通風之效能；由研究結果發現，當並聯使用風機時，對於降低火場溫度及排除煙霧之效果可顯著提升。最後透過並聯風機與建築物內部之防火鐵捲門搭配使用後，吾人發現可以有效增加火場氣密性，同時引導氣流經由預先規畫之路徑離開建築內部，大幅增加了正壓通風策略在排除火場煙霧、降低溫度及提高能見度之能力；使重要通道之溫度均被控制在接近室溫且能見度均維持在30公尺以上。由此可知，在建築物內部沒有機械通風設施的情況下，透過消防員所實施的正壓通風策略，仍可為火場人員提供更加安全的環境。 Wind can create extremely dangerous environments when it affects high-rise building fires. According to the statistics of the New York Fire Department, 14 wind-driven high-rise building fires between 1980 and 2008 caused unfortunate consequences of 11 civilians' and 5 firefighters' death. Positive pressure ventilation (PPV) can effectively reduce fire temperature, eliminate smoke, improve visibility and increase the safety of fire escapers and rescuers. However, various parameters can influence the efficacy of PPV, such as building structure layouts, wind conditions, and PPV deployment configurations. Therefore, this study employs the Fire Dynamics Simulator (FDS) software to simulate the high-rise building fire and test the performance of PPV strategy under the influence of the aforementioned relevant parameters. The study results show that when using a single fan PPV, it can effectively block the smoke from entering the stairwell and reduce the temperature of the fire. However, when the external wind speed reaches 5 m/s or more (test wind speed ranges from 0 to 10 m/s, the warning wind speed is 4.5 m/s according to the NIST), it will have a serious impact on the fire scene, and will case the PPV strategy failure by using a single PPV. Therefore, this study enhances the PPV efficiency through two fans. The research finds that the parallel fans can significantly improve the effects of lowering the fire temperature and eliminating the smoke. Finally, after using the parallel fans with the fire resistant metal rolling gates inside the building, one can effectively increase the air impermeability of the fire floor, while guiding the airflow to leave the interior of the building through a pre-planned path. In the same time, one can significantly increase the ability of PPV to eliminate smoke, reduce fire temperature and improve visibility; the temperature is controlled to near ambient and the visibility is maintained above 30 meters at the important aisles. Therefore, in the absence of mechanical ventilation inside a building fire, a PPV strategy implemented by the firefighters can ultimately provide a safer environment for the personnels inside the fire.