Experimental study and thermal hazard analysis of large-scale n-heptane pool fires under sub-atmospheric pressure

Tank farms are commonly used for storing large quantities of liquid fuels. The design, construction, operation, and maintenance of a tank farm must be in accordance with standards/codes applicable to specific countries. Existing codes on the design of storage tank farms are largely based on tests performed at standard atmospheric pressure and associated thermal hazard analysis. Studies based on small-scale experiments, however, have shown that the burning behavior and associated radiation impact of liquid fuels could be substantially affected by the reduced pressure at high altitude. In this study, large-scale n-heptane pool fire experiments with different pool diameters were carried out at sub-atmospheric pressure to firstly investigate their burning characteristics. Subsequently, specific fire scenarios for the cases under both standard and sub-atmospheric conditions were selected for assessing and comparing their thermal hazards. The experimental results showed that the burning rate at sub-atmospheric pressure is reduced, whereas the flame height is increased. Correlations for both the burning rate and flame height including the pressure effect were proposed and validated against the experiment data in this and existing studies obtained at different pressure conditions. The flame radiative fraction was found to decrease exponentially with the pool diameter. The thermal hazard analysis showed that whilst the thermal hazard at sub-atmospheric pressure is lower than that at standard atmospheric pressure, this difference gradually reduces with increasing tank diameter. The present results not only are important in understanding the effects of pressure on the burning characteristics of large-scale pool fires but provide guidance on the applicability and limitations in the use of design codes developed for standard atmospheric pressure for plateau regions.