A blast injury is a complex form of physical trauma resulting from exposure to an explosion. The sudden release of energy creates a hazardous environment that can injure a person through multiple distinct mechanisms. Medical professionals categorize these specific forms of trauma based on the physical force that causes the damage. This classification system separates blast injuries into four distinct types, describing how the explosive energy interacts with the human body. Understanding these distinctions is important for emergency response personnel and treatment planning.
Primary Blast Injuries Caused by the Pressure Wave
The primary blast injury is unique to high-order explosives, resulting solely from the supersonic over-pressurization wave, often called the shock wave, impacting the body. This wave travels through tissues, causing damage where tissues of different densities meet, a process known as barotrauma. Gas-containing organs are particularly vulnerable to this mechanism because the rapid pressure changes cause a destructive effect at the air-tissue interface.
The most common fatal primary blast injury is “blast lung,” which involves pulmonary contusion and hemorrhage deep within the lung tissue. If the pressure exceeds approximately 40 psi, the victim can sustain alveolar damage, leading to pulmonary edema, air embolism, and respiratory distress, which may be delayed up to 48 hours. The auditory system is also highly susceptible; tympanic membrane rupture is a frequent sign of significant blast exposure, as the eardrum is the most sensitive organ to the pressure wave.
The gastrointestinal tract can also suffer damage, resulting in hemorrhage and perforation. This “blast belly” injury may present with abdominal pain or bleeding that is not immediately apparent, making delayed presentation a serious concern. While the eye is relatively protected by the bony orbit, a powerful shock wave can cause globe rupture. The blast wave can even cause traumatic brain injury without any direct impact to the head, potentially by transmitting pressure through the skull.
Secondary Blast Injuries Caused by Fragments
Secondary blast injuries are the result of material propelled by the explosion. The blast wind accelerates objects—ranging from the explosive device’s casing to environmental debris like glass, metal, and stones—turning them into high-velocity projectiles. These projectiles cause penetrating or blunt trauma upon striking the body.
The severity of the resulting wound depends on the mass, velocity, and shape of the fragments. Terrorist devices are often intentionally packed with materials like nails and ball bearings to maximize the number of secondary injuries. Wounds from fragmentation can range from minor lacerations to severe penetrating injuries that cause damage similar to a ballistic wound.
These fragments may strike any part of the body, causing fractures, traumatic amputations, and extensive soft tissue damage. Even a small entry wound can conceal a devastating internal injury, as the speed of the projectile can propel it deep into the body, damaging major blood vessels or internal organs. The exposed areas of the body, such as the head, neck, and extremities, are at the highest risk for fragment penetration.
Tertiary Blast Injuries Caused by Body Displacement
Tertiary blast injuries occur when the powerful blast wind physically accelerates the victim, causing the entire body to be thrown against a solid surface, such as a wall or the ground. This mechanism results in blunt force trauma. The acceleration and subsequent sudden deceleration upon impact are the primary forces causing damage.
Common injuries in this category include bone fractures, joint dislocations, and traumatic amputations, especially if the body part strikes an object at a high velocity. Traumatic brain injury (TBI) is a major concern, resulting from the head impacting a hard surface, leading to closed or open brain injuries. Additionally, victims thrown into or trapped under collapsing structures may sustain significant crush injuries and compartment syndrome.
The size of the victim plays a role, as individuals with a smaller body mass, such as children, are at a higher risk of being displaced by the blast wind. The pattern of injury is determined by the object the victim strikes, meaning the trauma can be highly varied, including internal organ damage from blunt impact to the torso.
Quaternary Blast Injuries Caused by Environmental Factors
Quaternary blast injuries include all other injuries resulting from the explosion event that are not classified as primary, secondary, or tertiary. These injuries stem from the environmental aftermath created by the detonation, including exposure to heat, light, and toxic substances. This category encompasses a wide range of trauma.
Thermal injuries, such as flash burns and flame burns, are a common result of the intense heat generated by the explosion. Victims may also suffer from respiratory problems due to the inhalation of smoke, dust, and toxic gases released by the explosive materials or surrounding burning structures. This toxic inhalation can lead to asphyxia or long-term pulmonary damage.
Quaternary injuries include the exacerbation of pre-existing medical conditions, such as a heart attack or asthma attack, triggered by the stress of the event. Crush injuries resulting from structural collapse or prolonged entrapment, which are not related to the body being initially thrown, also fall under this classification.