Ceiling thermal impingement spread characteristics induced by wall-attached fires under various sub-atmospheric pressures

Ceiling thermal impingement fire spread induced by indoor uncontrollable energy combustion occurred frequently and caused many casualties and property damage. The sub-atmospheric pressure environment has a great impact on uncontrollable energy combustion characteristics of hazardous combustible gaseous fuel fire. China west high-altitude cities develop rapidly due to the economic development, and fire accidents frequently occur. This paper focused on experimentally studying the ceiling fire impingement hazard characteristics induced by wall-attached fires under sub-atmospheric pressures, the various sub-atmospheric pressures (from 55 kPa to 100 kPa), energy heat release rates (from 0.25 kW to 2.5 kW), and source-ceiling heights (0.475 m, 0.38 m, 0.285 m, 0.19 m and 0.095 m) were selected as an variable. The ceiling flame extension lengths of facing and lateral directions were measured and analyzed. Result showed that, the dimensionless ceiling flame extension area is higher in sub-atmospheric pressures. There are many differences between them due to the lower buoyancy in various sub-atmospheric pressures. By accounting for the air entrainment change characterization, it is found that the air entrainment of wall-attached propane jet fire is weaker in sub-atmospheric pressures. The influence of pressure on the flame expansion area is related to the 4/5 power of the ratio of the entrainment coefficient ((alpha/alpha(100))(4/5)). And a new model was finally obtained to correlate ceiling flame extension area induced by wall-attached fires with various sub-atmospheric pressures. This work provides can help understand ceiling impingement flow and hazard characteristics under various sub-atmospheric pressures. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study shows that the dimensionless ceiling flame extension area is higher under sub-atmospheric pressures. Due to lower buoyancy in different sub-atmospheric pressures, there are significant differences between them. By considering the change characterization of air entrainment, it was found that in sub-atmospheric pressures, the air entrainment of wall-attached propane jet fire is weaker. The pressure's influence on flame expansion area is related to the 4/5 power of the ratio of the entrainment coefficient.