Surgery of violence. IV. Blast injuries of the ear.

The shock front of a blast wave is irregular and can be deflected by obstacles in its pathway, depending on their size and position. Consequently, the injurious effects of blast tend to be capricious, and one person may be unharmed while those around him are killed or severely injured. In most explosions solid material is changed suddenly into a gas with an enormous increase in volume and thus of pressure. The blast wave spreads outwards from the site of the explosion, initially faster than the speed of sound. The wave consists of a short positive phase followed by a much longer, but less distinct, negative phase. The positive phase may reach very high pressures, and its duration is usually a few milliseconds. The magnitude of the negative phase cannot be greater than atmospheric pressure, but the duration is much longer than that of the positive phase and is usually tens of milliseconds.