Blast injury

Classification

Blast injuries are divided into four classes: primary, secondary, tertiary, and quaternary.

Primary injuries

Primary injuries are caused by blast overpressure waves, or shock waves. Total body disruption is the most severe and invariably fatal primary injury. Primary injuries are especially likely when a person is close to an exploding munition, such as a land mine. The ears are most often affected by the overpressure, followed by the lungs and the hollow organs of the gastrointestinal tract. Gastrointestinal injuries may present after a delay of hours or even days. Injury from blast overpressure is a pressure and time dependent function. By increasing the pressure or its duration, the severity of injury will also increase.

Extensive damage can also be inflicted upon the auditory system. The tympanic membrane (also known as the eardrum) may be perforated by the intensity of the pressure waves. Furthermore, the hair cells, the sound receptors found within the cochlea, can be permanently damaged and can result in a hearing loss of a mild to profound degree. Additionally, the intensity of the pressure changes from the blast can cause injury to the blood vessels and neural pathways within the auditory system. Therefore, affected individuals can have auditory processing deficits while having normal hearing thresholds. The combination of these effects can lead to hearing loss, tinnitus, headache, vertigo (dizziness), and difficulty processing sound.

In general, primary blast injuries are characterized by the absence of external injuries; thus internal injuries are frequently unrecognized and their severity underestimated. According to the latest experimental results, the extent and types of primary blast-induced injuries depend not only on the peak of the overpressure, but also other parameters such as number of overpressure peaks, time-lag between overpressure peaks, characteristics of the shear fronts between overpressure peaks, frequency resonance, and electromagnetic pulse, among others. There is general agreement that spalling, implosion, inertia, and pressure differentials are the main mechanisms involved in the pathogenesis of primary blast injuries. Thus, the majority of prior research focused on the mechanisms of blast injuries within gas-containing organs and organ systems such as the lungs, while primary blast-induced traumatic brain injury has remained underestimated. Blast lung refers to severe pulmonary contusion, bleeding or swelling with damage to alveoli and blood vessels, or a combination of these. It is the most common cause of death among people who initially survive an explosion.

Secondary injuries

Secondary injuries are ballistic trauma caused by impacts of flying shrapnels and other objects propelled by the explosion. These injuries may affect any part of the body and sometimes result in penetrating trauma with visible bleeding. At times the propelled object may become embedded in the body, obstructing the loss of blood to the outside. However, there may be extensive blood loss within the body cavities. Secondary blast wounds may be lethal and therefore many anti-personnel explosive devices are designed to generate fast-flying fragments.

Most casualties are caused by secondary injuries as shrapnels generally affect a larger area than the primary blast area, because debris can easily be propelled for hundreds or even thousands of meters. Some explosives, such as nail bombs, are deliberately designed to increase the likelihood of secondary injuries. In other instances, the target provides the raw material for the fragments thrown into surrounding, e.g., shattered glass from a blasted-out window or the glass facade of a building.

Tertiary injuries

Displacement of air by the explosion creates a blast wind that can throw victims against solid objects. Injuries resulting from this type of traumatic impact are referred to as tertiary blast injuries. Tertiary injuries may present as some combination of blunt and penetrating trauma, including bone fractures and coup contre-coup injuries. Children are at particularly high risk of tertiary injury due to their relatively smaller body weight.

Quaternary injuries

Quaternary injuries, or other miscellaneous named injuries, are all other injuries not included in the first three classes. These include flash burns, crush injuries, and respiratory injuries.

Traumatic amputations quickly result in death, unless there are available skilled medical personnel or others with adequate training nearby who are able to respond quickly, with the ability for rapid ground or air medical evacuation to an appropriate facility in time, and with tourniquets (for compression of bleeding sites) and other needed equipment (standard, or improvised; sterile, or not) also available, to treat the injuries. Because of this, injuries of this type are generally rare, though not unheard of, in survivors. Whether survivable or not, they are often accompanied by significant other injuries. The rate of eye injury may depend on the type of blast. Psychiatric injury, some of which may be caused by neurological damage incurred during the blast, is the most common quaternary injury, and post-traumatic stress disorder may affect people who are otherwise completely uninjured.