Explosives Safety - Blast Wave Phenomena

Blast Wave Phenomena

Is an incident involving the violent release of energy created by detonation of an explosive device. The sudden and intense pressure disturbance is termed the “blast wave.” The blast wave is characterized by an almost instantaneous rise from ambient pressure to a peak incident pressure (Pi). This pressure increase or “shock front,” travels radially outward from the detonation point, with a diminishing velocity that is always in excess of the speed of sound in that medium. Gas molecules making up the front move at lower velocities. This velocity, which is called the “particle velocity,” is associated with the “dynamic pressure,” or the pressure formed by the winds produced by the shock front. As the shock front expands into increasingly larger volumes of the medium, the incident pressure decreases and, generally, the duration of the pressure-pulse increase. If the shock wave strikes a rigid surface (e.g., a building) at an angle to the direction of the wave’s propagation, a reflected pressure is instantly developed on the surface and this pressure rises to a value that exceeds the incident pressure. This reflected pressure is a function of the incident wave’s pressure and the angle formed between the rigid surface and the plane of the shock front.