Limiting values of the thermal power and flame temperature from hydrocarbon pool fires

As well known, risk is a combination of probability and consequences of an accident. Different concepts were developed in evaluating accident consequences. First, the worst-case concept, meaning that the most negative consequences imaginable are described. A more applied approach is the reference to the maximum credible accident scenario. In analyzing the consequence of accidental hydrocarbon fires and the potential for domino effects, the evaluation of the flame extent and temperature are of the utmost importance. The primary effects of pool fires are due to thermal radiation and issues of interplant/tank spacing employees' safety zones, fire wall specifications are to be addressed on the basis of a proper consequence analysis. In order to avoid too conservative results, imposing anti-economic geometric constraints, for example in term of spacing, a realistic scenario evaluation is therefore needed. By means of real scale experimental tests it was verified that both the thermal power and the flame temperature T increase as the pool area increases, up to reach maximum values in connection with a "critical pool dimension". Dealing with pool areas higher than the critical one, experimental results, performed by different researchers at different scales, show a decrease of T. An in-depth analysis of the different concurring phenomena connected to a pool fire development allowed identifying the limiting step controlling the flame temperature. In fact, the trend of T is mainly determined by the increasing difficulty of oxygen diffusion within the internal bulk of gaseous hydrocarbons. In this paper, we propose a pool fire model suitable: to provide a theoretical insight into the above-mentioned experimental trends; to obtain the maximum values of the flame temperature and of the thermal power, considering the pool size and the chefnico-physical characteristics of the hydrocarbon.