Development of combustion efficiency model in natural ventilation tunnel fires

Research Project

Project/Area Number	17K01292
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Multi-year Fund
Section	一般
Research Field	Social systems engineering/Safety system
Research Institution	University of Fukui
Principal Investigator	Tanaka Futoshi 福井大学, 学術研究院工学系部門, 教授 (60401791)
Project Period (FY)	2017-04-01 – 2022-03-31
Project Status	Completed (Fiscal Year 2021)
Budget Amount *help	¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000) Fiscal Year 2021: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000) Fiscal Year 2020: ¥780,000 (Direct Cost: ¥600,000、Indirect Cost: ¥180,000) Fiscal Year 2019: ¥650,000 (Direct Cost: ¥500,000、Indirect Cost: ¥150,000) Fiscal Year 2018: ¥910,000 (Direct Cost: ¥700,000、Indirect Cost: ¥210,000) Fiscal Year 2017: ¥1,300,000 (Direct Cost: ¥1,000,000、Indirect Cost: ¥300,000)
Keywords	トンネル火災 / 火災
Outline of Final Research Achievements	Combustion efficiency in tunnel fires was measured using a 1:20 scale model tunnel. The results showed that combustion efficiency was little affected by tunnel length, and average values were 89% for propane fires and 80% for heptane fires, respectively. In the case of a long tunnel, descending smoke and backflow of air vitiated by mixing fresh air with descended smoke occurred, and the fire was completely surrounded by vitiated air. In this vitiated fire condition, a ghosting flame was observed close to the fire, and ultimately the fire self-extinguished due to lack of oxygen. In the vitiated fire, the chemical HRR of the fire decreased to half or less that in the normal fire, but combustion efficiency was 94% for heptane fires. Furthermore, numerical simulation was conducted by using the Fire Dynamics Simulator. The FDS reproduced the suffocation extinguishing of the fire caused by the backflow of smoke.
Academic Significance and Societal Importance of the Research Achievements	本研究では、トンネル延長や煙流動形態によって、トンネル火災における燃焼効率が受ける影響について明らかとした。特にトンネル延長が長くて煙の逆流が発生しているときの燃焼効率を推定できたことには価値がある。この煙流動と関係づけられた燃焼効率こそが、実際にトンネル火災が発生し、避難が行われている最中における燃焼効率に相当する。本研究は、これまで無視されてきた煙流動と燃焼効率の関係にも着目し、今までトンネル防災の枠組みの中で表面化してこなかった新たな問題を明らかにした。