火災閃燃與火場重建之電腦模擬技術研究

Numerical Study of Flashover Phenomena and Fire Reconstruction in the Building Fire

王士承(Shih-Cheng Wang)

指導教授 ： 林誠興

元智大學/工程學院/機械工程學系/博士(2008年)

https://doi.org/10.6838/YZU.2008.00240

摘要

建築物火災實例可提供大火高溫與濃煙實際影響火場內部人員安全之寶貴資訊，如能重現火災實例，提供量化的數據供參考，可大幅提升建築物防火安全設計之實用性。實驗是研究火災最直接有效的方法，而火災模擬軟體對於建築物防火安全評估可提供多元化資訊。由於臺灣許多四層樓舊式建築物內部消防安全規劃並不完善，有火災發生時易造成人員嚴重死傷，因此本文以臺灣「大新機車行」火災實例來探討四層樓舊式建築物發生火災時之危險性，以區域模式CFSAT 6.0.10版與場模式FDS 4.0.7版兩套火災模擬軟體與機車燃燒實驗來重建此火場，首先利用定性、定量的方式對火場做有限的驗証與危害分析，再以上層溫度、氣層高度與CO濃度等量化數據來探討各樓層開口開關、通風效應對人員避難逃生之影響，期望能提供火場數值模擬重建技術與四層樓建築物防火安全之資訊。由於目前火災相關模擬軟體並無法分析火災之閃燃現象，而火災發生閃燃之時間為人員可容許逃生時間之重要指標，因此火災發生閃燃時間的控制與預測對建築防火與人員避難都具有相當重大的意義，因此希望能研發更精確的閃燃時間預測模式。本文以兩層區域模式來預測單房火勢非線性成長之特性，以熱煙層質量、能量之熱平衡方程式來推導閃燃物理模型。由於輻射熱回饋對火勢成長影響重大，為閃燃現象發生之主要因子，因此將以NIST(National Institute of Standards and Technology)火災測試資料庫之全尺寸寢室燃燒實驗值來估算閃燃數值模型之輻射熱回饋係數，並將模式預測之閃燃時間與NIST單房實驗結果做比對，以驗證本文閃燃數值模式之精確度。主要探討單房區間內不同t平方火勢成長、開口大小、牆之熱慣性等參數對閃燃時間之影響，由分析結果可得知開口高度與牆壁材質在低強度火勢下對閃燃發生時間影響較為明顯。

關鍵字

火災 ； 濃煙 ； 數值模擬 ； 閃燃 ； 複燃

並列摘要

Accidental building fires present considerable valuable information on fire phenomena and behavior. However, fire and smoke movement quantitative data cannot be obtained directly from a building fire accident. Therefore, computational methods have been widely used to reestablish the fire scenario and obtain a great deal of information for fire study. This paper utilized two types of fire simulation software, CFAST (ver. 6.0.10) zone model and FDS (ver. 4.0.7) field model, and full-scale fire tests for motorcycles to reconstruct a motorcycle shop fire accident in Taiwan. Computational results reasonably agreed qualitatively with post-accident reports. Simulation analysis for backdraft phenomena demonstrated that window size in the limited-ventilation compartment fire greatly influenced smoke leaking from vents, deflagration induction time and fire intensity from a new opening. The impact of natural/forced ventilation on the fire was also studied. The results showed that the larger forced airflow gets into the building, the longer egress time is needed to evacuate to a safe place from the fire. In addition, flashover phenomena were studied. Flashover is an extremely important phenomenon whereby a compartment fire undergoes a rapid elevation in size and intensity. The mechanism that is near simultaneous ignition of all combustible material in an enclosed area is a nonlinear behavior. Therefore, an improved two-layer zone model was proposed for evaluating the transition from ignition to flashover during a compartment fire. The radiation feedback from hot smoke layer was identified utilizing the National Institute of Standard Technology (NIST) full-scale compartment fire tests. Time to flashover for various t-squared fires, wall materials, and ventilation conditions derived. Computational results demonstrated that height of vents and wall materials singinficatly affected flashover-induced time in low intensity fire development.

並列關鍵字

Fire ； Smoke ； Numerical simulation ； Flashover ； Backdraft

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