Guidance for estimating the blast load from vapour cloud explosions in traffic environments using the multi-energy method

The accidental release of a flammable gas on a road can result in a vapour cloud explosion (VCE). Such VCEs generate a blast wave that propagates away from the explosion, potentially damaging nearby structures. The TNO Multi-Energy Method is commonly used for a simplified estimate of the blast load resulting from a VCE. The method characterises the severity and duration of the blast wave using a case-specific strength class and combustion energy (which the method relates to the gas volume of the equivalent blast source). However, no specific guidelines for estimating the strength class in urban roads or related settings (such as carparks) are currently available in the literature. This makes implementing the method in such scenarios challenging and imprecise. The authors’ work used computational fluid dynamics (CFD) to evaluate multiple gas explosion scenarios and proposed recommendations for determining the strength class and gas volume at the blast source. These scenarios comprised a group of vehicles engulfed by a stoichiometric propane-air cloud. It was concluded that the strength class could be reasonably estimated based on the number of vehicles in the transverse direction. Furthermore, the guidance for estimating the gas volume at the equivalent blast source was based on the critical gas volume, after which no further enhancement of overpressure was obtained. The recommendations were implemented in several scenarios and compared with corresponding CFD analyses. The results showed very good agreement for predicting impulse. Predicting overpressure was affected by the inherent asymmetry of the scenarios, although it was possible to achieve acceptable and conservative results.