According to the Defense and Veterans Brain Injury Center (DVBIC), over 50% of injuries sustained in combat are the result of explosive munitions including bombs, grenades, land mines, missiles, and mortar/artillery shells (Coupland & Meddings). The polytrauma conditions sustained by these explosions affect various systems of the body. TBI has been associated with between 59% and 61% of blast-associated injuries seen at Walter Reed Army Medical Center (WRAMC). Since November 4, 2006, blasts have been the most common cause of injury among American soldiers treated at WRAMC (Ippolitito).
How The Explosion Creates a Blast Wave
Blast injuries result from the complex pressure wave generated by an explosion, causing an instantaneous rise in pressure over atmospheric pressure. This is called a blast over-pressurization wave (CDC, Mass Casualties).
Primary blast injury occurs from an interaction of the over-pressurization wave and the body. The resulting injuries affect various organs. Air-filled organs such as the ear, lung, and gastrointestinal tract are especially vulnerable to blast injury. Equally susceptible are organs surrounded by fluid-filled cavities, such as the brain and spinal cord (Elsayed; Mayorga). The over-pressurization wave dissipates quickly, causing the greatest risk of injury to those closest to the explosion.
There are two categories of explosives:
- High-order explosives (HE) such as TNT, C-4 and dynamite produce a definitive supersonic over-pressurization shock wave.
- Low-order explosives (LE) such as pipe bombs, gunpowder and Molotov cocktails create a subsonic explosion and lack HE’s over-pressurization wave.
How The Blast Wave Creates Blast Injuries
There are four basic mechanisms of blast injury, all of which may result in Central Nervous System (CNS) injuries (CDC, Mass Casualties).
- Primary: "Blast wave" refers to the intense over-pressurization impulse created by a detonated HE. Injuries are caused by impact to body surfaces as in tympanic membrane rupture, traumatic brain injury, or blast lung (pulmonary barotrauma).
- Secondary: Brain injuries can occur by impact from blast-energized debris, penetrating the head or eye.
- Tertiary: Injuries resulting from the individual being physically thrown, resulting in fractures or traumatic amputation.
- Quaternary: Injuries such as burns and/or inhalation of gases and vapors, closed and open brain injury, asthma, COPD, angina, hypertension.
Injury patterns following such events depend on (CDC, Mass Casualties):
- the composition and amount of the materials involved
- the surrounding environment and delivery method (if a bomb)
- the distance between the victim and the blast
- any intervening protective barriers or environmental hazards
Enclosed areas, such as the driver’s compartment in a HMMWV (High Mobility Multi-Purpose Wheeled Vehicle), may increase the chance of head injury. Blast waves cannot dissipate as they can in open areas, so the concussive wave may be stronger.
Difficulties experienced as a result of a closed-head blast injury include post concussion complaints such as:
- decreased memory
- decreased attention/concentration
- headaches
- slower thinking
- irritability
- depression
While some of these symptoms are similar to those of PTSD, clinicians are making efforts to differentiate diagnoses. See Quick Facts for a comparison of symptoms. This is a topic that is receiving further attention.
Understanding Explosives and The Injuries They Cause
Understanding the physical properties of an explosive wave helps anticipate what types of injuries will result. Air-filled and fluid-filled organs are particularly susceptible to the high pressure wave created from a blast. Brain, lung and ears are likely to be affected, in addition to wounds from physical impact to all parts of the body.
For more information see "Blast Injuries Include Traumatic Brain Injury."
Sources
CDC Mass Casualties: Explosions and Blast Injuries: A Primer for Clinicians (2006). Accessed online 1/17/10.
Coupland, C. R. M., & Meddings, D. R. (1999). Mortality associated with use of weapons in armed conflicts, wartime atrocities, and civilian mass shootings: literature review. British Medical Journal, 319, 410-412.
Defense and Veterans Brain Injury Center (DVBIC) website. Accessed 1/17/10.
Elsayed, N. M. (1997). Toxicology of blast overpressure. Toxicology, 121, 1-15.
Ippolitio, Charles J. (2007). Battlefield tbi: blast and aftermath. Applied Neurology, Vol. 3, No. 8.
Mayorga, M. A. (1997). The pathology of primary blast overpressure injury. Toxicology, 121, 17-28
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