Experimental study of the flame behaviors and radiation impact of medium-scale pool fires with different ullage heights

Tank fires represent a prevalent type of industrial hazard. The thermal radiation generated by the primary ignited vessel dictates the effectiveness and safety of emergency rescue interventions. Consequently, this study performed a series of medium-scale gasoline fire trials utilizing various pool diameters ( D = 0.8, 1, and 1.5 m) and ullage heights to evaluate radiation impacts and flame dimensions. The findings reveal a four-stage combustion life cycle: initial development, steady burning, decay, and extinguishment. Specifically, within the steady-state phase, an inverse relationship was observed between the dimensionless ullage height ( h * = h/D ) and both the upper flame length ( L upper ) and radiant heat, while the down-reaching flame length increases. For tank fires with ullage heights, the high-temperature sidewalls alter the radiative flux reaching neighboring targets, which is most pronounced during the decay phase when the fire is largely confined within the tank. Drawing upon these experimental measurements and dimensionless analysis, an empirical equation was established to determine the ratio of L upper to the total flame length. After successfully validating this formulation against current and existing data, this correlation was subsequently incorporated into the standard solid flame model to account for the shielding effect of the heated tank sidewall, enabling prediction of external radiative fluxes with an overall prediction error within 15%. The results are of importance for understanding the flame behaviors and radiation impact of tank fires to improve firefighting and rescue efficiency.