Fire around storage tanks for petroleum products can have disastrous consequences for the environment and the population. These fires, due to accident or arson, are very well managed by security divisions but, nevertheless, involve the release of an amount of vapour from the petroleum present in the storage device. The exposure of a non-refrigerated aboveground liquid petroleum or petroleum product storage tank to fire can also lead to internal overpressure. PV-valves ensure that the normal and emergency venting requirements are satisfied, and determination of such requirements is key for the safety of petroleum tanks and should not be underestimated. This paper presents and discusses some methods that can be used to evaluate the vapour flow. In the aim of finding an exact answer rapidly, a thermal analytical approach is first investigated, which reveals the complexity of the solution. Thus, a numerical approach, based on finite-volume description, is used to set the first steps of the flow assessment. Based on a thermodynamic hypothesis, a simplified method is finally put forward for the evaluation of the amount of vapour released. The algorithm used to determine how temperature, pressure and flow evolve over time, which is very useful information for the safety of these devices, is then detailed and the results discussed.< Leer menos