Analytical modelling of hydrocarbon pool fires: Conservative evaluation of flame temperature and thermal power

Description

As well known, risk is a combination of probability and consequences of an accident. 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. Since the primary effects of pool fires are connected to thermal radiation and issues of interplant/tank spacing employees' safety zones, firewall specifications are to be addressed on the basis of a proper consequence analysis. By means of real scale experimental tests, it was verified that both the thermal power and the flame temperature 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 temperature. 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 temperature is mainly determined by the increasing difficulty of oxygen diffusion within the internal bulk of gaseous hydrocarbons. In this article, we propose a novel pool fire modelling approach based on the simplified physical phenomena occurring in a circular turbulent diffusion fire and suitable to provide a theoretical insight into the above-mentioned experimental trends and to obtain the maximum values of the flame temperature and of the thermal power. It must be remarked that the developed model, matching fairly well experimental data for different hydrocarbons, can be applied in modelling similar scenarios characterized by different geometric or environmental conditions (e.g. road and rail tunnel fires).

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