Understanding the Potential for Detonations in Large-Scale Vapor Cloud Explosions

Large-scale unconfined vapor cloud explosions can generate significant damage and destruction over extremely wide areas. The most common methods used in industry to assess their consequences are flame acceleration methods, which relate the contribution of explosion energy to regions of congestion and confinement. If a deflagration-to-detonation transition (DDT) occurs, however, it has, in theory, the potential to involve the entire flammable cloud, significantly increasing the consequences of a vapor cloud explosion event.

As recent studies have identified a number of incidents where detonations may have occurred, it is imperative to develop models that can better quantify their effects. In this work, prior studies on detonation propagation limits are reviewed to illustrate the inherently unstable nature of detonation waves, with a focus on the critical cloud dimensions and concentration gradients which can support a propagating detonation wave.

These criteria are then applied to representative flammable cloud concentration distributions. Evaluating these criteria, it is found that a detonation propagating throughout the entire flammable cloud is extremely unlikely. Local detonations, however, may occur and propagate beyond the source of congestion. This work demonstrates how these critical conditions can be used to estimate the portion of the cloud that can support detonation.