Continuous boilover behaviors of large-scale kerosene pool fires under sub-atmospheric pressure

Abstract

Accidental fire is a major safety concern in chemical parks, highlighted by the several major fire accidents involving storage tanks in recent years. Boilover is considered as one of the most destructive tank fire scenarios, which occurs when a liquid fuel burning on a water layer, leading to the explosive evaporation of water and consequently a sudden increase of the heat release rate (HRR) and associated flame height due to the splashing of burning fuel. Previous studies on boilover with large-scale pool fires were mostly conducted under normal atmospheric pressure. However, chemical parks are often located in plateau regions, where the effects of reduced pressure on boilover behaviors were rarely examined. Moreover, following the initial boilover, continuous boilover could occur, and its understanding is particularly important in the thermal hazard and risk analysis and firefighting of tank fires. In this study, thin-layer boilover experiments were conducted under sub-atmospheric pressure using aviation kerosene (RP-3) with various initial fuel thicknesses and pool diameters. The burning process, boilover intensity, temperature in the fuel and water layers and associated thermal hazard were analyzed. Experimental results showed that continuous boilover occurred in all test conditions, characterized by a high intensity initial boilover followed by a series of subsequent ones with gradually reduced intensity. The mass burning rate and flame height varied significantly during boilover. It was found that the boilover intensity increases with the initial fuel thickness but decreases with the pool diameter and approaches a nearly constant value when the pan diameter is sufficiently large. The temperature at the fuel/water interface was found to increase from 93 ℃ to around 108 ℃ during boilover, both of which are lower than those observed under normal atmospheric pressure due to reduced water boiling point. The thermal hazard calculated for the initial boilover is highest as expected, and that of subsequent boilovers gradually decreases but could still be higher than that at the steady burning stage. The findings in this work will contribute to risk assessment of continuous boilover in fire accidents.