Assessing the effects of an open-air gas explosion

The rapid expansion of industrial activity, coupled with growing urbanization around high-risk sites, has prompted everyone involved to think about how to protect themselves against the technological risks involved. Explosions, whatever their origin, are rare phenomena with rapid kinetics, which means that they cannot always be anticipated. Indeed, the consequences can be devastating and unpredictable, as a number of major industrial disasters in the past have shown.

The effects of an explosion are mainly characterized by a high-intensity but short-lived pressure wave that propagates through the environment, sweeping away everything in its path. The wave can have both direct effects on individuals and indirect effects when a structure not initially designed to withstand such phenomena collapses. The consequences can then be disastrous for the occupants of a building, or liable to amplify the initiating phenomenon through a domino effect in the case of industrial equipment containing hazardous products. As part of the development of industrial safety, the need to characterize the effects of explosions, despite their apparent complexity, became apparent very early on.

Most of the methods used to assess the consequences of an explosion have their origins in the military field, and are based on test results. However, these empirical methods quickly reach their limits in the case of gas explosions. They fail to take into account the many factors that influence the violence of an explosion, such as the nature of the gas, turbulence, confinement by walls or obstruction by obstacles. This is why a great deal of research has been carried out over the past two decades to gain a better understanding of the mechanisms involved, and to improve methods for predicting the associated effects. These can then be used to define protective measures through appropriate sizing. In parallel with this research work, the availability of ever more powerful computers has enabled the development of specific modeling tools, in particular fluid mechanics calculations, which can now take into account a large proportion of the physical phenomena involved in a gas explosion.

The characterization of pressure levels experienced by individuals or structures can now be correlated with frequency, thanks to the quantified risk analysis approach. This approach makes it possible to design more optimized structures resistant to rare events, without systematically building blockhouses.