Explosives and explosions


In all explosions there is a rapid conversion of the explosive material into a large volume of hot, high pressure gas, the sudden release of which results in a s0-called blast wave which radiates from the source in all directions.

The physics of blast waves is non-linear and complex.

High order explosives - including nitroglycerine, plastic explosives and other military munitions - undergo detonation which is accompanied by a blast wave that is also a 'shock wave' travelling at supersonic speed. The explosive strength is determined by the amplitude of the over-pressurisation formed by the explosion.

Low-order explosives - typically used as propellants (or fuels), and which combust through a process known as deflagration - the blast wave is subsonic. Energy is released relatively slowly when compared with high-order explosives, and the resulting explosion lacks the type of over-pressurisation blast wave associated with detonation of high-order explosives. Containing/ confining a propellant modifies its explosive behaviour.

Whilst damage caused by blast waves decreases exponentially with distance from the source of the explosion, they are reflected by solid surfaces, and can be amplified within closed spaces; it is difficult to predict precisely the effects of an explosion in such a setting.

The initial blast wave, and superheating of the air surrounding the centre of the explosion, is followed by a short-lived 'blast wind', the speed of which can be sufficient to propel people and objects away from the explosion.

Follow this link to see an animated reconstruction of a bomb blast in an enclosed space.

Blast-related injuries


Blast events are complex, and casualties can be affected by many forms of injury; blast-related injuries can be categorised as follows.

Primary blast injury

Injury due to the interaction between blast-waves and air-tissue interfaces. Air-containing tissues/ organs (and those with air-fluid interfaces) are vulnerable to injury from stress and shear waves, including:

Secondary blast injury

Injury caused by projectiles formed from the explosive device, or from the local environment (leading to blunt and penetrating injuries). Read more about occular injuries here and here.

Tertiary blast injury

Blunt impact injury sustained when a person is displaced (propelled) by the blast wave/ wind into an object or a hard surface (or when an object is propelled into a person).

Quaternary blast injury

Injuries caused by other explosive effects, including burns and inhalation injury.

Quinary blast injury

The clinical consequences of 'post detonation environmental contaminants', including bacterial contaminants and tissue reactions to explosive components.

Complications of blast injuries


In addition to the adverse effects of injuries to individual organs, or organ systems, exposure to an explosion can lead to whole-body physiological disturbances including a 'shock-like' state.

For overviews of blast-related injuries and their clinical management, read here and here.

In severely injured people - including those who sustain severe burns - the complex and incompletely understood 'host response' includes the activation of multiple defence mechanisms (acute inflammation and coagulation cascades, for example). An overwhelming host response to trauma can lead to widespread organ dysfunction/ failure and death.

For more detail on the pathophysiology of polytrauma read here, here, and here and for the pathophysiology of burns, read here.

Public safety


Recent explosion-related mass casualty incidents in the UK (July 7th 2005 - London, and May 22nd 2017 - Manchester)

Emergency medical response

Public safety guidance - via citizenAID

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