Buffer effects of confined space on the boiling explosion under rapid depressurization

Confined spaces (e.g., containers, underground warehouses) are common storage places for storage tanks. The safety of confined spaces subjected to boiling liquid expansion vapour explosions (BLEVEs) is of vital significance but still not fully understood. In this study, a small visualization device was used to research the rapid depressurization in confined space. The effect of confined space on the rapid boiling mechanism and two-phase flow of liquids and vapours was investigated. The buffer of the confined space on the superheated boiling of liquids under different leakage conditions is researched by the pressure characteristic parameters. The results show that the superheated liquid leakage process is divided into three stages, i.e., rapid depressurization, slow depressurization, and pressure balance. In the stage of rapid depressurization, the nucleation and growth processes of bubbles can be mainly divided into static, bubble flow, and bullet flow. The vaporization of the leakage flow in the explosion-vented tank will decrease the depressurization rate to buffer the boiling explosion of the storage tank. Thus, as the release pressure increases, the average rate of pressure change increases in both vessels will accelerate the arrival of buffering in the confined space like the explosion-vented tank. In a small-discharge area ratio regime, the pressure change rate in both vessels increases as the discharge area ratio increases. In a large-discharge area ratio regime, the superheat degree no longer affects the pressure change rate due to the buffer of rapid vaporization and saturation of the explosion-vented tank. Finally, the effect of the confined space has been quantified to clarify why BLEVE does not occur in the confined space. This study deepens the understanding of complex failure and rapid depressurization in confined spaces and provides insights into the fire hazards of BLEVE accidents in confined spaces.