Whether through an accident or intentional act, explosions are an occurrence that can cause serious injury and death. Explosions have the ability to inflict injuries on many people at the same time resulting in high levels of mortality and morbidity. The type and severity of the impact depends on many factors including, when and where the event took place, the number of people in the area, material in the area of the explosion, and the type of explosion (nuclear, mechanical, or chemical), how far the victim is from the explosion, what protection they had available to them. The principle mechanism driving the extent of the injuries is the amount of kinetic energy released over a short time by the explosion.[1][2][3][4]

Explosives are categorized as high order explosives or low order explosives. High order explosives have a strong supersonic pressure wave, known as the blast wave or shock wave. Low order explosions have a subsonic explosion and lack the high order explosive blast wave. Examples of low order explosives include – pipe bombs, gun powder, petroleum-based bombs. In addition to the blast wave, an explosion can cause blast wind. Blast wind is the flow of superheated air that can interact with people and objects and cause injury or damage.

Chemical explosions cause injuries in four categories (primary, secondary, tertiary, and quaternary). The four categories are based on the impact on the human body due to the blast wave, blast wind, environmental/material factors present in the area of the blast.

Immediate death can occur from an explosion as a result of extensive pulmonary injury with pulmonary hemorrhage causing suffocation. Immediate death can also be caused by a pulmonary air embolism, severe head injury, significant internal injury, amputation, or impalement on an object.[5][6][7]

Blast injuries occur on various scales. In 2014 it was estimated that there were over 10,000 blast injuries related to fireworks in the United States. The Federal Bureau of Investigation reported that from 1987 to 1997, over 4,000 injuries and 448 deaths occurred in the United States due to illegal explosions of bombs or incendiary devices. In 2013, a notable explosion occurred at a fertilizer plant in Texas resulting in 15 deaths and many injuries. On a global scale, explosive devices are used as a means of terrorism. Blast injuries caused the vast majority of injuries to military personnel in recent wars and conflicts.

Primary Blast Injury

Primary blast injury is caused by the blast wave moving through the body. Since only high order explosives create a blast wave, primary blast injuries are unique to high order explosions. The blast wave causes damage to more extensively to air-filled organs. The resulting barotrauma can affect the lungs, auditory organs, the eye, brain, and gastrointestinal tract.

• Blast ear – tympanic membrane rupture and middle ear damage
• Blast lung – injury to the lung parenchyma, can have delayed symptom presentation
• Blast brain – injury to brain parenchyma, even without direct injury to the head
• Blast eye – rupture of the globe of the eye
• Blast belly – injury causing abdominal hemorrhage and perforation (immediate and delayed). It can also cause injury to solid organs and testicular rupture.

Primary blast injuries can be subtle and have a delayed presentation. Blast lung should be considered in any victim that has dyspnea, cough, hemoptysis, and/or chest pain. The respiratory system can sustain significant injury, as a result of the blast wave. If the pressure exceeds 40 psi, the victim could sustain a pulmonary contusion, pneumothorax, air embolism, interstitial parenchyma damage, and/or subcutaneous emphysema. Pulmonary contusion is the most common respiratory system injury and it can be delayed in presentation up to 48 hours. Blast ear should be considered in any victim that has decreased hearing or hearing loss, tinnitus, vertigo and/or bleeding from the ear. If there is bleeding from the ear, consider that the blast was intense enough to cause injury to the lungs and hollow organs. In instances when the ear is over pressurized (greater than 5 psi), the bony ossicles of the ear can be dislocated, fractured and /or permanently destroyed.[8]  Blast belly should be considered in any victim presenting with abdominal pain, nausea, vomiting, vomiting blood, rectal pain, testicular pain, unexplained hypovolemia, abdominal distention, and/or rigidity. The colon is the most common area of hemorrhage and perforation. As with blast lung, intestinal perforation can occur acutely or may have a delayed presentation of up to 48 hours. Solid internal abdominal organs can also be contused or lacerated; however, solid organ damage occurs much less than does hollow organ damage. Blast brain should be considered in any victim presenting with headache, fatigue, confusion, poor concentration, amnesia, decreased level of consciousness, depression, anxiety, and/or insomnia. Blast eye should be considered in victims with eye pain, swelling, contusion or ecchymosis around the orbit, bleeding from the eye, decreased vision, and/or blindness. [9]The heart can also be damaged by the blast wave. Victims can have chest pain, tachycardia, decreased pulse pressure, cardiac dysrhythmias and/or hypotension as a result of heart involvement. In victims with multiple presenting injuries or in incidents with multiple causalities, the injuries could be easy to miss. Victims of primary blast injuries may not initially show any obvious signs of injury.

Secondary Blast Injury

Secondary blast injuries are caused by debris that is displaced by the blast wind of the explosion. The secondary blast injuries are caused by debris that penetrates or interacts with the body surface. The debris can be from pieces of the explosive device itself and its contents, or material located around the initial blast device at the time of the explosion.

Secondary blast injuries account for the majority of injuries from an explosion event. The blast wave can carry debris a considerable distance causing injuries to anyone in its path. In intentional explosive devices, often they are constructed with the intent to injure as many people as possible. The device could be constructed with nails, metal ball bearings, screws, or other objects with the intent that they will be forcefully displaced during the blast to increase injuries to anyone in their path.

Secondary blast injuries are more common than primary blast injuries. Secondary blast injuries are the most common cause of mortality in victims of an explosion. Exposed areas of the victims’ body are at high risk for penetration of debris that is propelled by the explosion. Often areas of highest risk for injury are the head, neck, and extremities. Secondary blast injuries can be obvious or be deceiving. The force of the explosion can propel debris many times faster than a bullet. Thus, a seeming small wound could be hiding a devastating injury underneath. Injuries can include fractures, amputations, lacerations, dislocations, and any type of soft tissue injury.[2]

Tertiary Blast Injury

Tertiary blast injuries are caused when the person in displaced through the air and impacts on another object by the blast wind, or when a structure collapses and causes injury to the person. The resulting injury can be either blunt trauma due to the impact or penetrating injury if the victim is propelled and the striking structure enters the body. Injuries are determined by what the victim strikes. The strength of the explosion determines the severity of the injuries sustained. High explosive blasts can cause skull fractures, fractured bones, head injuries, or any traumatic injury (open or closed injuries, chest, abdominal, pelvic injuries, amputations, spinal injuries, and any others).

Structural collapse and entrapment can cause crush injuries and compartment syndrome. The longer it takes to extricate the victim the higher their mortality.

Quaternary Blast Injury

Quaternary blast injuries are comprised of all injuries that are not included in primary, secondary, or tertiary blast injury categories. Quaternary blast injuries can be caused by exposure to resulting, fire, fumes, radiation, biological agents, smoke, dust, toxins, environmental exposure, and the psychological impact of the event. As a result of all the debris, wounds can be extremely contaminated with a wide variety of sources.[10]

• Fire – burn injuries (flash, partial, full-thickness, airway)
• Fumes/smoke/dust – inhalation injuries and respiratory compromise
• Toxins – toxidromes from chemical exposures
• Environmental – heat/cold, exposure injuries
• Radiation – minor injury to death, depending on the type, amount, and exposure time to the source.
• Biological – variety of illness related to the agent released

A casualty’s underlying medical condition has a major impact on the effects on the impact of the resulting exposure on their mortality and morbidity.

• Lung disease – exacerbation of chronic obstructive pulmonary disease (COPD) or asthma.
• Heart disease – unstable angina, acute myocardial infarction
• High blood pressure – hypertensive emergency or urgency

Psychological disease – exacerbation of anxiety, depression, contribute to post-traumatic stress disorder (PTSD).

In an intentional explosion, other substances can be added to cause more injury, illness, or to induce more fear and panic in the community.[11][8]