使用簡易二層法模擬小空間煙層下降之研究

Abstract

本研究之主要目的為發展一套適用小居室之簡易二層法，並運用該軟體分析火場情境。由於天花板低、堆積可燃物發熱量大，採用「建築物防火避難安全性能驗證技術手冊」進行居室避難安全性能驗證時，有其困難性，故擬針對小居室採用簡易二層驗證技術，確認避難是否安全。本程式發展之目的在適用範圍內能準確預估火場情境，且其結果與火災模擬軟體FDS、「建築物防火避難安全性能驗證技術手冊」及實驗相互比較驗證本程式之可靠度。 本研究以撰寫程式之方式考量於居室內發生火災之情境，並推導相關公式以符合火災情境。透過輸入居室相關條件及火源大小，即可進行小居室火場避難安全逃生分析，並藉由無排煙與自然排煙情境與相關實驗驗證。結果顯示，在煙層溫度的考量上考慮輻射的結果比不考慮的結果更趨近實驗煙層溫度，故熱輻射的考量相當重要。 案例討論的對象共有兩項，分別為：(1)無排煙情境下相同居室體積但不同面積、樓高比(2)自然排煙情境下相同排煙口面積但不同面寬、高比。由案例一無排煙情境得知，在居室體積相同的情境下，樓高越高煙層下降的速度越快，原因在於樓高越高，煙生成率越高。最後，由案例二自然排煙情境得知，在排煙口面積同的情境下，開口遮蔽率及開口下緣對排煙效果的好壞有絕對的影響。 本研究經由與實驗比較，整理出各參數對簡易二層法模擬之影響：(1)熱輻射對煙層溫度的影響相當重要；(2)室內外的壓力差是自然排煙的主要驅動力；(3)開口遮蔽率及開口下緣皆會影響自然排煙效果。

The main purpose of this study is to develop the two-layer zone model suit for small space and use it to analyze the fire place. Because of the low floor and the huge heat release of accumulative combustible, there is some difficult when using「The Building of Fire Safety and Evacuation Verification technical manuals」to verify the safety of evacuation in small space. So we adopt the two-layer zone model to verify whether the evacuation is safe or not. The main purpose of develop this program is to predict the fire place in proper conditions and compare the results with FDS、「The Building of Fire Safety and Evacuation Verification technical manuals」and some experiments, to verify the reliability of the program. In this research, we’ll take the condition of fire place into consideration by means of programming, and develop relevant formulae so as to coordinate the condition of fire place. By inputting some conditions relevant to small space and heat release, the analysis of fire place will be launched immediately. By verifying the program results with some related experiments, the results show when we take the heat radiation into account the result can get closer to the experimental temperature distribution in natural condition. The heat radiation is a really important factor. There are two cases studies: (a) The some space volume but in different ratio of floor area and floor height in no vent flow condition(2) The some vent area but in different ratio of breadth and height in natural flow condition. By the case study one, the higher the room floor height ,the faster the smoke descending rate is in the same room volume situations, because of the higher room floor height, the smoke generation rate is higher. Finally, the case of two shows that the opening rate and the lower edge of the opening have a great influence on smoke exhaust Finally, by comparing to some experiments, here are some conclusions about the effect of parameters in two-layer zone simulation. (1)Heat radiation have a great influence on smoke layer temperature; (2)The pressure difference between indoor and outdoor space is the main driving force of natural flow (3) The performance of natural flow are affected by the occupancy of the vent and the lower edge of vent.