Explosions generate a large amount of kinetic energy that can cause a range of injuries. Exposure to the complex, high-pressure blast waves released in an explosion (either direct or indirect) can result in a range of blast injuries to the body, including the brain. Blast-related traumatic brain injury (TBI) is often associated with military conflicts and training but can also occur in the civilian world, for example industrial and mining accidents.
Blast-related TBI is a traumatic brain injury caused by exposure to blast overpressure. Most blast-related TBI is mild TBI. Other terms for blast-related mild TBI include blast overpressure, military TBI1 or blast-induced neurotrauma (BINT)2.
Blast injuries occur with a sudden and significant increase in atmospheric pressure when an explosion happens. The change in atmospheric pressure creates an overpressure wave (blast wave), which moves outward from the source of the explosion at high speeds. This may cause significant damage to internal organs, including the brain.
Blast waves can cause TBI of all severities (i.e. subconcussive, mild, moderate, or severe), though mild TBI3 (concussion) is the most common.
There are many factors that can affect the severity of a blast injury. These include:
• Blast energy (i.e. the amount and type of explosives used)
• Distance from the blast wave
• Body position
• Use of body armour or helmets (these can amplify the effects of the blast wave)
• Environment (e.g. closed environments are usually worse than open spaces)
• Number of and time between blast exposures3,4
• Individual health and susceptibility (pre-existing conditions and overall health can influence injury severity)
• Blast wave duration and frequency (the length and frequency of the blast wave can affect the extent of the injury)
• Secondary projectiles (debris and shrapnel propelled by the blast can cause additional injuries)
• Protective measures (availability and use of protective measures other than armour, such as barriers or shields, can mitigate injury severity)
As with other types of blast injury, blast-related TBI can be classified into four subtypes1. These categories are based on mechanisms related to the explosion that cause injury. For blast-related TBI, these are:
1. Primary blast injury – TBI that is caused by the blast wave itself. Exposure to blast waves can cause concussion, diffuse axonal injury, and other forms of brain damage due to the rapid acceleration and deceleration of the brain tissue.
2. Secondary blast injury – TBI resulting from shrapnel or other debris hitting the head. Penetrating brain injuries may occur if objects pierce the skull and brain tissue.
3. Tertiary blast injury – TBI resulting from exposure to strong blast winds, which can propel people into objects or objects into people. For example, a TBI may result from blunt force trauma to the head when a person gets thrown into a solid object, such as a wall. Tertiary TBIs are the main type of blast TBI2.
4. Quaternary blast injury – This refers to other explosion-related factors such as burns, inhalation of toxic fire gases, or crush injuries. While these factors alone might not cause TBI, they can add to the physiological stress on the body and make brain injuries worse.
The US Department of Defense also recognises a fifth subtype of blast injury5–7. Called Quinary blast injury, this refers to longer-term effects and illnesses that can arise from exposure to toxic materials and environmental contaminants released by explosions. For example, bacterial agents dispersed by an explosion may lead to infections such as encephalitis (inflammation of the brain) or other secondary complications that can worsen blast-related TBI outcomes.
Blast-related TBI most commonly occurs in military training and conflict zones. However, other ways that a person may sustain a blast-related TBI include3:
• Military and Police operations that involve breaching – a tactical technique used to enter closed or blocked buildings or areas, which involves the use of explosives
• Live firing during training exercises
• Terrorist attacks
• Mining accidents
• Industrial accidents
• Non-bomb blasts (e.g. chemical or fireworks explosions)
Each TBI, no matter what the cause, is unique. As such, any part of the brain can be injured when a person experiences a blast-related TBI, and there are many factors that determine the severity and extent of injury. However, studies that have used advanced neuroimaging techniques to better understand the structural and functional changes that happen in the brain following blast-related TBI have found evidence of:
• Decreased cortical thickness
• Decreased amygdala volume
• Decreased thalamus volume
• Differences in thalamic network architecture
• Irregularities in white matter tracts, including those that are commonly associated with TBI such as the corpus callosum and superior longitudinal fasciculus
• Changes in brain activity, especially in the frontal, parietal, temporal and cingulate regions8,9.
The cerebellum also appears to be particularly vulnerable to damage from blast-related TBI10,11. Although it is not yet clear why this is the case, microlesions in the blood-brain barrier and loss of Purkinje cells (a type of nerve cell found only in the cerebellum) are likely to play a role11.
* For more information on these parts of the brain, see the definitions at the bottom of the page.
Blast injuries to the brain can cause a range of physical, emotional, cognitive and behavioural consequences. Amongst the most studied effects of blast-related TBI are post-traumatic stress disorder (PTSD), headache, depression, anxiety, sleep disorders, attention and cognitive disorders9. Most individuals will experience symptoms of blast-related TBI immediately after the injury has occurred. However, about 10-15% of people will have symptoms that persist over months and years12. In addition, military service members with a history or blast exposure have also been observed to have neuroimmune13 and hormonal14 changes. While mTBI and PTSD can co-occur, having a mild traumatic brain injury does not necessarily mean that a person will have post-traumatic stress disorder. They are distinct conditions, and it is possible to have one without the other.
Low-level blast (LLB) are explosions that involve lower blast pressures. Military personnel may be exposed to LLB from firing heavy weapon systems in combat or training environments, as well as some types of explosives used in combat.
In Australia, Military occupations and weapons systems that can increase risk of exposure to LLB include:
• Royal Australian Navy:
– Clearance Divers
– Naval Divers
• Australian Army Arms Corps (including instructors):
– Infantry
– Armour
– Artillery
– Combat Engineers
• Royal Australian Air Force:
– Combat Controllers
• Special Forces
• Australian Police Tactical Groups
• Any personnel working with breaching charges, grenades, shoulder-mounted recoilless weapons, large calibre weapons, indirect fire weapons (such as mortar weapon systems), artillery
LLB do not usually cause mild traumatic brain injury (concussion) from a single exposure. However, it may cause subconcussion – a type of head injury that does not present with any observable symptoms. Frequent exposure to LLB may result in cumulative effects and worsen outcomes from injury.
LLB exposure may cause the following symptoms:
• Neuropsychiatric Symptoms (e.g. irritability, depression, anxiety)
• Cognitive Impairments (e.g. concentration, memory, slowed thinking and reaction time)
• Decreased hand-eye coordination
• Headaches
• Tinnitus (ringing in the ears)
• Difficulty hearing/hearing loss
• Sleep disturbances15–18
• Brain-inflammation (e.g. may cause brain fog, low mood and above-mentioned symptoms)
To learn more about Traumatic Brain Injury Symptoms click here.
Though there have been numerous reports of CTE being found in military service members19, it is difficult to determine whether there is a relationship between blast-related TBI and CTE. This is partly because many individuals who donate their brains for post-mortem study also have a history of non-blast TBI (e.g. TBI from participating in contact sports or motor vehicle accidents). A recent study in which 225 brains of deceased military personnel were examined for the presence of CTE found evidence of CTE in only 3 out of 45 (6.67%) military members that had a known history of blast exposure20.
To learn more about CTE, click here.
The Defence all-hours Support Line is a confidential telephone and online service for ADF members and their families. Call 1800 628 036
Open Arms provides 24-hour free and confidential counselling and support for current and former SFD members and their families. Call 1800 011 046
Soldier On is a national support services provider for Defence personnel, contemporary veterans, and their families. Contact during offices hours via phone on 1300 620 380
Disclaimer
Connectivity does not offer medical advice for individuals. If you have suffered a traumatic brain injury, please seek medical advice.
Created July 2024