Blast Injury

6th August 2020

Explosions can produce unique patterns of injury with the potential to inflict multi-system life-threatening injuries on multiple casualties, simultaneously.

The extent and severity of blast injuries are determined by a variety of factors including, but not limited to:

  • composition and amount of explosive involved

  • the surrounding environment

  • the distance between the victim and the blast

  • any intervening protective barriers or environmental hazards.

Because explosions are relatively infrequent, blast-related injuries can present unique triage, diagnostic, and management challenges to responders.


Classification of Explosives

Explosives are categorized as high-order explosives (HE) or low-order explosives (LE) with HE producing a supersonic over-pressure blast wave. Examples of HE include TNT, C-4, Semtex, nitroglycerin, dynamite, and ammonium nitrate fuel oil (ANFO).

LE blasts create a subsonic explosion without an over-pressure blast wave. Examples of LE include pipe bombs, gunpowder, and most pure petroleum-based bombs such as Molotov cocktails or aircraft improvised as guided missiles.

Explosive and incendiary (fire) bombs are further characterized based on their source. “Manufactured” implies standard military-issued, mass produced, and quality-tested weapons. “Improvised” describes weapons produced in small quantities, or use of a device outside its intended purpose, such as converting a commercial aircraft into a guided missile.

Manufactured explosive weapons are exclusively HE-based. Terrorists will use whatever is available – illegally obtained manufactured weapons or improvised explosive devices (IEDs) may be composed of HE, LE, or both. Manufactured and improvised bombs cause markedly different injuries.


Types of Blast Injuries

The four traditional mechanisms of blast injury are termed primary, secondary, tertiary, and quaternary:

Primary injuries
Primary injuries refer to the intense high pressure impulse created by a detonated HE. Blast injuries are characterized by anatomical and physiological changes from the direct or reflective over-pressurization force impacting the body’s surface, typically in the form of complete disintegration of the body or traumatic amputations. Immediate deaths in close proximity of a HE blast will be little more than pink mist.

More than 90% of blast injury deaths occur in the first 10 minutes following the blast (1). Early deaths typically occur from an explosion as a result of extensive pulmonary injury, severe head injury, significant internal injury, amputation, or impalement on an object (2-4). . Because of the high mortality rate of primary injuries, survivors with primary injuries account for only 3-5% of casualties (5).


Secondary injuries
Secondary blast injuries are caused by debris that is displaced by the blast wind of the explosion. 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.

Given the high likelihood of immediate death as a result of primary injuries, secondary blast injuries account for the majority of injuries from an explosion event (5). The blast wave can carry debris a considerable distance causing injuries to anyone in its path with initial velocities of up to 6000m/s (6-12). Intentional explosive devices are often constructed with the intent to injure as many people as possible, utilising nails, metal ball bearings, screws, or other objects as ballistic projectiles. (13)

At close range, potentially survivable fragmentation injuries are unlikely and in an open space environment, the maximum effective range for secondary blast injury exceeds primary blast injury by a factor of 100 (14-17).

Illustration of ‘‘Friedlander curve,’’ with maximum effective radius for primary and secondary blast injuries of an open-field 155-mm mortar shell explosion with 200 lbs (100 kg) of trinitrotoluene equivalent; potential injury from fragmentation can exceed 1,800 ft (14-17). Adapted from Champion et al. (14)


Tertiary injuries
Tertiary blast injuries are caused when the person is 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. (18)

Quaternary injuries
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. Wounds can be extremely contaminated with a wide variety of sources. (19)

  • 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 – a 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

  • 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. (20, 21)

Quintenary injuries

Quinternary blast injury is a relatively new concept that includes delayed and wider issues of primary healthcare such as chronic pain, malnutrition and infection; the prognosis of these casualties is vastly dependent on the availability of healthcare, quality of sanitation and endemic diseases at the location of the blast (1).




Selected Blast Injuries

Lung Injury
“Blast lung” is a direct consequence of the HE blast wave. It is the most common fatal primary blast injury among initial survivors. Signs of blast lung are usually present at the time of initial evaluation, but they have been reported as late as 48 hours after the explosion. Blast lung is characterized by the clinical triad of difficulty breathing, slow pulse, and low blood pressure.

Pulmonary injuries vary from scattered petechiae ( a pinprick like rash) to significant bruising. Blast lung should be suspected for anyone with difficulty breathing, persistent cough, coughing up blood (haemoptyisis), or chest pain following blast exposure (18).

Ear Injury
Primary blast injuries of the auditory system cause significant morbidity but are easily overlooked. Injury is dependent on the orientation of the ear to the blast. Tympanic membrane (TM) perforation is the most common injury to the middle ear. Signs of ear injury are usually present at the time of initial evaluation and should be suspected for anyone presenting with hearing loss, tinnitus, earache, vertigo, bleeding from the external canal. (21)

Abdominal Injury
Gas-containing sections of the gastrointestinal (GI) tract are most vulnerable to the primary blast effect. This can cause immediate bowel perforation, haemorrhage (ranging from small petechiae to large bruising), solid organ lacerations, and testicular rupture. Blast abdominal injury should be suspected in anyone exposed to an explosion with abdominal pain, nausea, vomiting, vomiting blood (haematemesis), rectal pain, testicular pain, unexplained hypovolaemia, or any findings suggestive of an acute abdominal injury. These findings may be absent until the onset of complications.

Brain Injury
Primary blast waves can cause concussions or mild traumatic brain injury (MTBI) without a direct blow to the head. Consider the proximity of the victim to the blast particularly when given complaints of headache, fatigue, poor concentration, lethargy, depression, anxiety, or insomnia.

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Incident Management

  • Make yourself safe. Initial blasts are often followed by secondary blasts, either by design to cause further destruction or as a result of secondary fires which break out following the initial blast.

  • Obtain and record details about the nature of the explosion, potential toxic exposures, environmental hazards, and casualty location.

  • Expect an inverse triage; the least injured will be the first to be discovered. These should be assessed, treated and ‘cleared’ as soon as possible at the scene to avoid front-loading hospitals with ‘walking wounded’. As the management of the scene progresses expect injuries to become worse.

  • More than 90% of fatalities will happen in the first 10 minutes meaning those casualties who have survived have a low likelihood of mortality but significant injuries which will be labour and time-intensive to manage. Expect resources to become stretched, quickly.

  • Double the first hour’s casualties for a rough prediction of the total ‘first wave’ of casualties (22). Things will get worse before they get better.

  • If structural collapse occurs, expect increased severity and delayed arrival of casualties.


References

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  2. Dokoupil M, Marecová K, Uvíra M, Joukal M, Mrázková E, Chmelová J, Handlos P. (2019) “Fatal delayed hemopericardium and hemothorax following blunt chest trauma”. Forensic Sci Med Pathol.  15(2):272-275

  3. Robinson ME, McKee AC, Salat DH, Rasmusson AM, Radigan LJ, Catana C, Milberg WP, McGlinchey RE. (2019) “Positron emission tomography of tau in Iraq and Afghanistan Veterans with blast neurotrauma”.  Neuroimage Clin.  21:101651.

  4. Kauvar DS, Thomas SB, Schechtman DW, Walters TJ. (2018) “Predictors and timing of amputations in military lower extremity trauma with arterial injury”.  J Trauma Acute Care Surg. 87 (1S Suppl 1). S172-S177.

  5. Kang DG, Lehman RA Jr, Carragee EJ. (2012) “Wartime spine injuries: understanding the improvised explosive device and biophysics of blast trauma”.  Spine J. 2012;12(9):849-857.

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  11. Bowyer GW, Cooper GJ, Rice P. (1996) “Small fragment wounds: biophysics and pathophysiology”. J Trauma. 40(3 Suppl): S159–64.

  12. Wightman JM, Gladish SL. (2001) “Explosions and blast injuries”. Ann Emerg Med. 37:664–78.

  13. Shuker ST. Emergency Treatment of Blast, Shell Fragment and Bullet Injuries to the Central Midface Complex. J Maxillofac Oral Surg. 2019 Mar;18(1):124-130.

  14. Champion HR, Holcomb JB, Young LA. (2009) “Injuries from explosions: physics, biophysics, pathology, and required research focus”. J Trauma. 66:1468–77; discussion 1477.

  15. Stuhmiller JH, Phillips YY III, Richmond DR. (1991) “The physics and mechanisms of primary blast injury”. In: Bellamy RF, Zajtchuck R, eds. Textbook of military medicine: conventional warfare: ballistic, blast, and burn injuries. Washington, DC: US Government Printing Office. 241–70

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  17. Stein M, Hirshberg A. (1999) “Medical consequences of terrorism. The conventional weapon threat”. Surg Clin North Am. 79:1537–52.

  18. Jorolemon MR, Lopez RA, Krywko DM. “Blast Injuries”. [Updated 2020 Apr 23]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan. https://www.ncbi.nlm.nih.gov/books/NBK430914/ Accessed 5th August 2020

  19. Singh AK, Ditkofsky NG, York JD, Abujudeh HH, Avery LA, Brunner JF, Sodickson AD, Lev MH. (2016) “Blast Injuries: From Improvised Explosive Device Blasts to the Boston Marathon Bombing”.  Radiographics. 2016 Jan-Feb;36(1):295-307.

  20. Prat NJ, Daban JL, Voiglio EJ, Rongieras F. (2017) “Wound ballistics and blast injuries”.  J Visc Surg.  Dec;154 Suppl 1:S9-S12.

  21. Van Haesendonck G, Van Rompaey V, Gilles A, Topsakal V, Van de Heyning P. (2018) “Otologic Outcomes After Blast Injury: The Brussels Bombing Experience”.  Otol. Neurotol.  Dec. 39(10):1250-1255.

  22. Centre of Disease Control (2006) “Explosions and Blast Injuries: A Primer for Clinicians.”