Gas cloud explosions and resulting blast effects

Abstract

The design of nuclear power plant structures to resist blast effects due to chemical explosions requires the determination of load-time functions of possible blast waves. Whether an explosion of a hydrocarbon gas in the atmosphere will occur in the form of a deflagration or a detonation is largely dependent on the type of flame acceleration process which is closely related to the rate of energy release. Flame propagations at normal flame velocities in a free explosible gas cloud will certainly not lead to detonation. However, with sufficiently large clouds — particularly under adverse boundary conditions — the flame acceleration could become so high that an initial deflagration changes into a detonative process. Results of recent investigations, which will be discussed in detail, show that in a free cloud with deflagrative ignition (flame, heated wire, sparks) the occurrence of a gas detonation can practically be excluded. Apparently, free gas clouds can only be induced to detonate by a sufficiently strong detonative initiation. Independently of the initiating event in the practice of damage analysis, it has become customary to describe the consequences of an explosion by means of the so-called TNT equivalent. Therefore, it is attempted to specify this equivalent for hydrocarbons by means of energetic considerations including the propagation functions for the case of spherically symmetric detonations. Analogous to the safety distances required in the handling and storage of high explosives, a mass-distance relation of the form R = k(L) 1 3 could be considered where L is the mass of spontaneously released hydrocarbon and k varies only with the structural shape of the blast loaded buildings. With the inclusion of an empirical relation which relates the quasi-static design pressure for a building with the normally reflected blast pressure of a blast wave, it is further attempted to establish a relation between the structural capacity of a building — i.e. the pressure resistance of a building structure for detonative dynamic loading and for quasi-static loading — and the unit-mass distance R L 1 3 .