具有外牆覆材之高層建築物火災模擬及其消防對策

Fire Simulation of the High-Rise Building with Exterior Wall Cladding and Its Fire Prevention Countermeasures

在都市人口快速且密集的成長趨勢下，現今住宅亦朝向集合化且高密度化發展，並以住商混合之多元化及設備複雜化之方式呈現。就相對較寒冷或炎熱地區的高樓建築物而言，須採用保暖或隔熱包覆材將外牆覆蓋，以達到節能效果；當這類建築物發生火災而消防車在進行救難時，由於高度的限制及包覆材的阻擋下，難以從大樓外部進行撒水滅火，唯有依靠大樓內部可供自救的消防設備來降低火場溫度、滅火並緩解火場伴隨著高溫的煙霧瀰漫情況。為了進一步了解此種特殊材質之建築火災，本研究利用火災動態模擬器（Fire Dynamics Simulator, FDS）軟體針對此類高樓層複合式建築物進行火災模擬，並以FDS的撒水模組模擬自動感知撒水。文中以英國倫敦格林菲爾大樓為例，探討了高樓層發生火災時的溫度、能見度、氧氣、一氧化碳及煙濃度的分佈趨勢，以及撒水系統對於滅火性能與高溫抑制之效果。由研究結果顯示，當室內沒有任何消防系統時，火焰會由4樓室內延燒至室外形成外部火災，而其火焰與濃煙，會在外牆包覆材之間的空腔中形成煙囪效應，並迅速地向垂直方向延燒，當火焰與濃煙向其他樓層擴散時會形成二次室內火災。而在第二次火災形成前，各個樓層的室內能見度會隨著樓層高度增加而逐漸下降；當外牆包覆材料間的空腔中流體速度達到10－15 m/s時，其煙囪效應會非常明顯。室內撒水頭撒水時可以迅速對火場中的高溫產生有效的抑制，且液滴粒徑越小效果越顯著；外牆的撒水頭撒水時雖然對高溫也有抑制效果，但是室內的火源或高溫未被有效抑制時，室外撒水頭僅能將高溫抑制在該樓層窗戶處；不論是室內或室外的撒水頭均可針對溫度進行抑制，但若燃燒反應未被撲滅，濃煙仍會持續向其他樓層擴散。本研究認為此類建築包覆材料的應用，對於火災發生時依然存在著許多威脅及不確定性，故建議法規應予以嚴格規範並限制其使用。 For high-rise buildings that located in the relatively cold or hot areas, their outer walls must be covered with keep-warm or thermal insulation cladding materials to achieve energy-saving effects. When a fire broke out in such a building and the fire engines were in rescuing, the height restrictions and the barrier of the exterior wall materials make the fire engines difficult to sprinkle water from the outside of the building. One can only rely on the self-rescue fire-fighting equipment inside the building to reduce the temperature of the fire, to extinguish the fire and to alleviate the smoggy condition accompanied by the high temperature. In order to further understand the building fire of such special material, this study employs Fire Dynamic Simulator (FDS) software to simulate fires on such high-rise composite buildings and applies the FDS sprinkler module to simulate the automatic sprinkling action. By using the Grenfell Tower of London, UK as an example, this paper discusses the distribution trends of temperature, visibility and concentrations of oxygen, carbon monoxide, and smoke within the building; the effects of sprinkler system on the fire extinguishing and high temperature suppression are also discussed during the high-rise building fire. According to the study results, fire spreads from the 4th floor rooms to the outside and form the outdoor fires when the indoor fire protection system is absent. The flames and smoke of outdoor fires form a chimney effect in the cavity between the cladding materials of the outer wall, and they will rapidly propagate in the vertical direction. When fires and smoke spread to other floors, a secondary indoor fire is formed. However, before the formation of the second fire, the interior visibility of each floor has gradually decreased as the floor height increases; and the chimney effect becomes very obvious when the air velocity in the cavity between the cladding materials of the outer wall reaches 10-15 m/s. The water sprayed by the indoor sprinkler can quickly inhibit the high temperature of the fire, and the effect becomes more significant when the droplet size is smaller. Although the sprinkler heads of the external wall are effective in suppressing high temperatures when spraying water, these sprinklers can only inhibit high temperature at the outside window of the fire source room if neither the indoor fire nor the high temperature is effectively suppressed. Whether indoor or outdoor sprinklers can only suppress temperature, the smoke can continuously spread to other higher floors should the combustion reaction is not extinguished. This study shows that the application of such building cladding materials still poses many threats and uncertainties in the event of a fire; therefore, it is recommended that regulations should be strictly regulated to limit their use.