地震對火焰結構及火焰行為影響之研究

The effects of earthquakes on fire structure and fire behavior

黃柏誠(Bo-Cheng Huang) ； 吳佳隆(Jia Long Wu) ； 蔡匡忠(Kuang-Chung Tsai)

《燃燒季刊》 109期 (2020/05) Pp. 5-24

https://doi.org/10.30041/CQ.202005_(109).0001

摘要

震後火災（post-earthquake fire）是地震災害的衍生重要問題，以1999年9月21日集集大地震為例，震度6級以上餘震共7起，震後火災共161起。然現今研究大多探討「地震後」造成建築物結構體及消防設備系統損壞之火災，對於地震所產生之振動對於火焰燃燒如火焰高度、脈動頻率、進氣量及燃燒速率是否有直接相關之影響，此類「地震對火災之影響」研究並未於過去侷限或開放空間火焰燃燒現象及延燒的文獻中發現，本研究以震動儀模擬地震所產生之水平震動，木框架作為火源，探討水平地震對火焰結構及火焰行為之影響，本研究發現，在火焰燃燒各階段中發生震動，其熱釋放率會迅速提升，並隨震度增加而增加，這是因為水平震動會造成周圍進氣量增加，震度越大所增加之進氣量越大，另隨著搖晃使火焰範圍增加，加熱之可燃物範圍也隨之增加，進而產生更多的可燃性蒸氣，與所增加之進氣結合，使熱釋放率會隨著震度增加而增加。在不同孔隙率試驗中發現，當燃燒狀態受通風限制越嚴重時，震動對熱釋放率之加乘作用越大。震動會使火焰高度降低、直徑變大。因此原本使用之計算火焰高度經驗式在加入地震後無法估算其熱釋放率與火焰高度之關係，本研究提出震動狀態下之熱釋放率及火焰高度關係式。

關鍵字

地震火災 ； 火焰結構 ； 火焰行為

並列摘要

Earthquake may cause fire. Most of the time, the post-earthquake fire is a serious problem because it results in secondary hazards. Additionally, continuous aftershocks may happen after a devastating earthquake and may lead to fires. For instance, the aftershock of Chi-Chi earthquake in 1999 Taiwan lasted for more than one minutes after the seismic event, and the aftershock was the main reason for building collapses compared with the main 7.3 scale earthquake. Most previous studies focused on the effects of post-earthquake fires on the damage of building structure or firefighting system, etc. However, no investigation has been conducted to discover the effect of earthquake on fire behavior. Therefore, the study used a horizontal vibration apparatus to simulate the situation generated by an horizontal earthquake, and used wood cribs as fuel, to explore the effects of earthquakes on fire structure and fire behavior. Results show that the heat release rate increased with the increased seismic intensity when an earthquake occurred. The HRR increase was a result of the enhancement of the surrounding air entrainment due to earthquake. In addition, the vibration made the flame volume increase, increasing the heating zone and flammable vapors. Combined with the increased air entrainment, the induced vibration changed the structure of the fire, reduced the flame height and increased the fire-base diameter. Therefore, the classic empirical formula for calculating the flame height is unable to estimate the flame height with an earthquake. The study proposes several modified correlations on the heat release rate and the flame height under vibration.

並列關鍵字

seismic fire ； flame structure ； fire behavior