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 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:
- The ears (e.g. leading to ruptured eardrums - tympanic membranes);
- Air-containing sinuses in the skull (read more about injuries to the facial skeleton here, here and here);
- The lungs (i.e. 'blast lung' (pulmonary barotrauma), which can be associated with haemopneumothorax (an abnormal collection of blood and air in the chest cavities), tension pneumothorax (where an abnormal collection of air in the chest cavity leads to a mechanical interference with the function of the heart), pulmonary contusion (bruising of the lung substance), air embolisation (the abnormal passage of air into the bloodstream, causing a mechanical obstruction to blood flow in small-calibre blood vessels in distant tissues and organs), and subcutaneous emphysema (an abnormal collection of air under the skin)); and The lungs (i.e. 'blast lung' (pulmonary barotrauma), which can be associated with haemopneumothorax (an abnormal collection of blood and air in the chest cavities), tension pneumothorax (where an abnormal collection of air in the chest cavity leads to a mechanical interference with the function of the heart), pulmonary contusion (bruising of the lung substance), air embolisation (the abnormal passage of air into the bloodstream, causing a mechanical obstruction to blood flow in small-calibre blood vessels in distant tissues and organs), and subcutaneous emphysema (an abnormal collection of air under the skin)); and
- The intestines (e.g. leading to bowel perforation).
Secondary blast injury
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.
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.
Blast-related injuries: pathophysiology and mechanisms
- Blast physics and pathophysiology of explosive injuries
- The physical basis of explosion and blast injury processes
- The pathology of primary blast overpressure injury
- Explosions and blast injuries - A primer for clinicians
- Histologic, immunohistochemical and ultrastructural findings in human blast lung injury
- Blast-related fracture patterns: a forensic biomechanical approach
Blast-related injuries and injury patterns
- Blast injuries
- Blast injuries: from IEDs to the Boston Marathon bombing
- Primary blast injury: update on diagnosis and treatment
- Blast injuries (Emergency management)
- Wounding patterns of blast injury
- Bombings: injury patterns and care
- Suicide bombing attacks: can external signs predict internal injuries?
Blast-related traumatic brain injury
Blast-related injuries - radiology