I was assisted in understanding the effects of an explosion by a Blast Wave Panel of Experts, led by Professor Anthony Bull from the Centre for Blast Injury Studies.
When an explosion occurs, it causes a blast wave. A blast wave has two component parts. The first is the shock wave. This is a high‑pressure wave of energy, which transmits through material. Behind the shock wave is the blast wind. This follows the shock wave and carries material with it. The material moved by the blast wind comprises ‘primary fragments’, which come from the device itself, and ‘secondary fragments’, which come from the environment.
Blast injuries fall into five main categories.
Primary blast injuries result from the contact of the shock wave with the body. The shock wave transmits through the structures of the body. Where there are spaces between those structures, it causes a tearing or separation. This is particularly significant where the two structures are of different densities, such as in a lung. The shock wave is capable of causing very serious injury.
Secondary blast injuries are caused by objects moved by the blast wind. When they make contact with the body, they can disrupt the anatomy. Being struck by a fragment from a blast has been likened to being shot with a bullet. However, the fragment typically causes more devastation as the energy around the object does not travel in a straight line, rather it is tumbling. This means a small wound from a secondary blast injury can cause devastating internal injuries.
Tertiary blast injuries are the damage caused when the body is thrown against an object or a large object strikes against the body. This commonly occurs when a person is pushed to the floor or against a wall by the force of the blast wind, causing crush injuries. The energy involved is often far higher than in a road traffic collision. This can result in very severe injury.
Quaternary blast injuries are those not due to primary, secondary or tertiary blast injuries. Any part of the body can be affected. Often they are burn or inhalation injuries.
Quinary blast injuries are caused by contaminants in the explosion, such as biological or radiological contaminants.
The first four types of blast injury were caused to those present in the City Room by SA’s detonation. Figure 41 provides a pictorial representation of the way in which blast injuries occur.Figure 41: Types of blast injury