Abstract
The calculation and modeling of ignition probability of a flammable gas cloud and of flammable vapors is a fundamental step within a Quantitative Risk Assessment (QRA). The numerical quantification of these probabilities can substantially change the resulting scenarios and events likelihood assessment, and consequently the assessed level of risk. Calculation and modeling of ignition probabilities is frequently approached with very simple models, widely used despite the fact that the same authors often declared their methods as "highly speculative". A critical review on the commonly used data and methodologies reveals that, in most cases, these models are based on small data populations, highly localized, thus giving rise to doubts about their general applicability and validity. Moreover most methods lack capability of predicting differences between immediate and delayed ignition with a reasonable accuracy. On this basis, the focus of the present paper is to develop a more sophisticated framework, still simple and quick to apply, for calculating immediate and delayed ignition probabilities on a sounder manner than currently allowed by the "traditional" methods.
