Blast Injuries

Blast Injuries is a topic covered in the 5-Minute Emergency Consult.

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Basics

Description

Tissue damage inflicted when an explosion creates acute pressure differentials:
  • Four categories:
    • Primary: Induced directly by increased pressure of shock wave striking subject
    • Secondary: Airborne debris induced, related to physical acceleration
    • Tertiary: Victim thrown against fixed object, related to physical acceleration
    • Miscellaneous: Exposure to harmful substance (e.g., chemicals, dust, toxin) or burns (direct thermal or blast-related fires)
  • Shock wave creates acceleration of air via classic Newtonian physics (F = ma) such that relatively small forces can create large accelerations of lightweight gases
  • Explosions have four sources of energy:
    • Mechanical: Structural failure of a compressed container releases hydraulic force
    • Electrical: Heat generated from electrical arc creates sudden increase in pressure
    • Nuclear: Fission or fusion generates heat
    • Chemical: Reactants can be diffuse (flammable gas or particulate matter) and mix with air to create energy, or condensed (i.e., liquid or solid) and are generally classified as low order or high order
  • Most common cause of accidental or intentional blast injuries are chemical explosions. Solid/liquid explosive becomes gas when ignited, pressure and temperature of space are increased. Pressure creates shock waves of 6–8 km/s that cause a peak overpressure above the ambient pressure, which is often very brief and intense
  • Peak overpressure of a shock wave in air decreases inversely with the distance from the explosion to the third power such that, e.g., a reaction must create 8× the peak overpressure to cause twice as much damage
  • Shock waves propagate through denser material with higher peak overpressure, shorter duration, and faster velocity
  • Reflections of a shock wave in enclosed spaces cause higher overpressure, longer duration, and more primary blast injuries
  • Shock wave propagation through tissues causes most primary injury at margins of different densities, e.g., lungs, bowel, tympanic membranes. Potential for injury is directly related to duration and height of peak overpressure and pressure-duration graphs exist to predict likelihood of specific clinical outcomes

Epidemiology

  • Secondary, tertiary, and miscellaneous injuries are more common, but primary blast injury is unique to explosions. Terrorist bomb victims most often have superficial secondary blast injuries, the more serious injuries occur within 10–15 m of the explosion source
  • Most common primary blast injury is linear tear in the inferior part of the tympanic membrane. Can occur at pressures of only 2–5 psi. Cochlear damage is also common and leads to tinnitus and sensorineural hearing loss
  • Second most common primary blast injury is to the lungs via diffuse lung contusion and alveolar hemorrhage, which occurs between 15–50 psi of peak overpressure. Systemic air emboli can occur via fissures between alveoli and pulmonary veins; suspect this source when victims have abnormal neurologic exam, sudden death, or cardiac arrest after a blast injury
  • Primary blast injury to bowel requires high peak overpressure and is more common when shock wave propagates through water. Serosal tears, intramural hemorrhage, and perforations can occur
  • TBI can result from increased intravascular pressure, especially with blast waves to thoracic cavity, even in the absence of direct head trauma

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Basics

Description

Tissue damage inflicted when an explosion creates acute pressure differentials:
  • Four categories:
    • Primary: Induced directly by increased pressure of shock wave striking subject
    • Secondary: Airborne debris induced, related to physical acceleration
    • Tertiary: Victim thrown against fixed object, related to physical acceleration
    • Miscellaneous: Exposure to harmful substance (e.g., chemicals, dust, toxin) or burns (direct thermal or blast-related fires)
  • Shock wave creates acceleration of air via classic Newtonian physics (F = ma) such that relatively small forces can create large accelerations of lightweight gases
  • Explosions have four sources of energy:
    • Mechanical: Structural failure of a compressed container releases hydraulic force
    • Electrical: Heat generated from electrical arc creates sudden increase in pressure
    • Nuclear: Fission or fusion generates heat
    • Chemical: Reactants can be diffuse (flammable gas or particulate matter) and mix with air to create energy, or condensed (i.e., liquid or solid) and are generally classified as low order or high order
  • Most common cause of accidental or intentional blast injuries are chemical explosions. Solid/liquid explosive becomes gas when ignited, pressure and temperature of space are increased. Pressure creates shock waves of 6–8 km/s that cause a peak overpressure above the ambient pressure, which is often very brief and intense
  • Peak overpressure of a shock wave in air decreases inversely with the distance from the explosion to the third power such that, e.g., a reaction must create 8× the peak overpressure to cause twice as much damage
  • Shock waves propagate through denser material with higher peak overpressure, shorter duration, and faster velocity
  • Reflections of a shock wave in enclosed spaces cause higher overpressure, longer duration, and more primary blast injuries
  • Shock wave propagation through tissues causes most primary injury at margins of different densities, e.g., lungs, bowel, tympanic membranes. Potential for injury is directly related to duration and height of peak overpressure and pressure-duration graphs exist to predict likelihood of specific clinical outcomes

Epidemiology

  • Secondary, tertiary, and miscellaneous injuries are more common, but primary blast injury is unique to explosions. Terrorist bomb victims most often have superficial secondary blast injuries, the more serious injuries occur within 10–15 m of the explosion source
  • Most common primary blast injury is linear tear in the inferior part of the tympanic membrane. Can occur at pressures of only 2–5 psi. Cochlear damage is also common and leads to tinnitus and sensorineural hearing loss
  • Second most common primary blast injury is to the lungs via diffuse lung contusion and alveolar hemorrhage, which occurs between 15–50 psi of peak overpressure. Systemic air emboli can occur via fissures between alveoli and pulmonary veins; suspect this source when victims have abnormal neurologic exam, sudden death, or cardiac arrest after a blast injury
  • Primary blast injury to bowel requires high peak overpressure and is more common when shock wave propagates through water. Serosal tears, intramural hemorrhage, and perforations can occur
  • TBI can result from increased intravascular pressure, especially with blast waves to thoracic cavity, even in the absence of direct head trauma

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