The Problem Is Exposure, Toward a Global Ontology for Blast-related Brain Injury

VIGIL AUSTRALIA

The Problem Is Exposure

Toward a Global Ontology for Blast-related Brain Injury

May 2026

Abstract

Blast-related brain injury is a global military, veteran and family health challenge. Across defence and veteran systems worldwide, the language used to describe it is inconsistent: clinical, compensation, military and research communities are often discussing the same problem using different terms, thresholds and assumptions. This paper argues that the central fault line is between event-based frameworks, which classify injury at a point in time, and the operational reality of cumulative Blast OverPressure (BOP) exposure across a career. It sets out working definitions for blast exposure, blast injury, Blast-induced TBI (BiTBI), and the related mental health and pathology terms most commonly conflated with them. It positions BiTBI as a mechanism-based term that covers the full severity spectrum and preserves space for cumulative low-level exposure that does not fit event-based criteria. The paper draws on evidence and policy developments from the United States, Canada, New Zealand, NATO, Israel and Australia to illustrate how the definitional problem manifests across jurisdictions. Its immediate purpose is to define key terms. Its larger purpose is to start a global conversation about whether the field needs an ontology for blast-related brain injury: a structured way to distinguish exposure, mechanism, injury, severity, symptoms, diagnosis, outcome and entitlement.

Introduction: From Babel toward Ontology

This article is a first attempt to bring order to a field where language is moving faster than agreement.

Vigil's work on blast exposure did not begin from nowhere. From around 2014, inside the Australian community, we were tracking the issue from afar, particularly what was emerging in the Naval Special Warfare community and the broader United States special operations ecosystem. Between 2017 and 2020, while still inside the military system, we were also tracking the issue through capability, safety, health and human performance discussions, increasingly linked to Five Eyes Special Forces awareness. The problem was visible, but it sat inside a wider set of Defence priorities.

We did not set out to continue this work after leaving the military. We believed the work already done inside Defence had been acted on. It had not.

By 2024, sustained advocacy by Vigil and others, combined with veteran testimony, researcher input and media engagement, helped force the issue into public view. On 60 Minutes, the issue was presented nationally: Australian troops were developing serious brain injuries from repeated blast exposure in both combat and training; repeated blast waves were linked to brain injury, suicide and family harm; and Defence was challenged on earlier opportunities to act. The segment also recorded that, while still inside the ADF in 2017, we had asked Defence Science and Technology to conduct a longitudinal study of Australian weapons to understand the risk. That request was denied.

The same report put the Chief of the Australian Army on record. He acknowledged that Army had conducted "research and trials and other work" since 2010, but said what had been missing was "the golden thread of logic". When asked why serving and former personnel should trust Army after past failures, he said trust was "easy lost" and took time to rebuild, adding: "judge me on what I do." He also accepted accountability for the health and wellbeing of Army's people (60 Minutes 2024).

We disagree, respectfully, with the idea that the problem was a missing "golden thread of logic". The logic was there: exposure was occurring, data had been collected, further research had been recommended, and longitudinal study was needed. That had been put to senior leadership in 2019. The problem was not the absence of logic. It was the absence of continuity, ownership and action.

Vigil did not want to keep carrying this from the outside. But the issue remained unresolved, and public acknowledgement had still not translated into a coherent national framework.

Since 2023, Vigil has engaged with military brain health researchers, clinicians, veteran organisations, policy actors and allied programs across Australia, the United States, Canada, the United Kingdom and New Zealand. Those engagements made one issue increasingly clear: blast-related brain injury is not suffering from a lack of interest. It is suffering from a lack of shared meaning.

This thinking has not developed in isolation. Much of Vigil's work has been shaped by a global community of learners: researchers, clinicians, veterans, families, military personnel, advocates and people inside allied systems who have shared evidence, challenged assumptions and helped refine the language. Some of the best ideas in this work are not ours alone. They are the product of repeated engagement with people trying to solve the same problem from different positions.

Coming from a military background, the language problem stood out. Doctrine exists so that people operating under pressure use the same words in the same way. In this field, that is not yet happening. Terms such as blast exposure, low-level blast, repetitive blast, cumulative exposure, mTBI, concussion, BiTBI, PTSD, CTE and brain health are often used differently across countries, agencies, disciplines and research groups.

Vigil has contributed to that problem at times. Earlier work used language such as mild TBI or blast-induced mild TBI because it appeared to describe the gap. Over time, through engagement with clinicians, researchers, veterans and allied systems, it became clear that this wording could pull the issue back into the concussion model. That is one reason Vigil now uses Blast-induced TBI, or BiTBI, as a broader mechanism-based term. We also acknowledge the US colleague who helped sharpen that language.

The ontology framing also came from engagement. A conversation in the United Kingdom last year with a friend from the intelligence community helped clarify the issue. In that world, the problem is familiar: different systems can hold useful information but fail to connect it because they do not share the same structure of meaning. In intelligence and data systems, this is sometimes called the Babel problem: the information exists, but shared meaning breaks down because each system uses its own definitions. The opposite is an ontology: a structured framework of meaning that allows people and systems to describe the same problem consistently. That is the Babel problem this article is trying to address.

The immediate purpose of this article is to define the key terms. The larger purpose is to start a global conversation about whether the field needs an ontology for blast-related brain injury: a structured way to distinguish exposure, mechanism, injury, severity, symptoms, diagnosis, outcome and entitlement.

1. Why Definitions Are Failing

The same confusion keeps appearing across different countries and different settings. Researchers use one set of terms. Clinicians use another. Compensation systems use another again. Veterans and families are often left trying to make sense of all three.

This is not a failure of individual competence. It is a structural problem. The frameworks in use across NATO nations, Commonwealth countries and allied defence systems were not designed together, do not share common terminology, and in many cases were built for purposes that do not align with the operational reality of cumulative blast exposure.

NATO identified the definitional problem early. Its work on military TBI noted inconsistent use of mTBI terminology and the difficulty of separating blast mechanisms from blunt force, acceleration, debris and other effects in operational settings. The United States has moved toward a Warfighter Brain Health model. Canada has recognised repeated concussive and sub-concussive forces in veterans' entitlement guidance. New Zealand has adopted a broader brain health hazard frame. Israel's registry work highlights blast-related long-term outcomes that cannot be reduced to PTSD alone. Ukraine is demonstrating the scale and urgency of repeated blast exposure in modern conflict at a level that will demand a coherent international response.

No nation has yet resolved this fully. Each is working within its own classification systems, legal frameworks and evidence standards. The result is that warfighters in high-exposure roles across multiple countries are being assessed against frameworks that were not designed for their exposure profile.

Vigil's experience in Australia reflects the same problem in a specific national context. When Vigil looked for a clear, usable Australian framework, there was not one. There were recognised categories for concussion, moderate to severe TBI, explosive blast injury, PTSD and dementia pugilistica. Each has a role. None provides a complete framework for blast exposure across training and combat, across severity, and across time.

That led to work with specialists and public-facing organisations, including the Connectivity fact sheet and the Dementia Australia page on Blast-induced traumatic brain injury. These were practical attempts to make the problem visible to veterans, families and clinicians in plain language. They were not final doctrine.

The Repatriation Medical Authority (RMA) process in Australia then exposed the deeper issue. The problem was not only evidence. It was classification. The available categories were built around recognised injuries and diseases. Cumulative exposure did not fit neatly. Once the language of blast-induced mild TBI was used, the issue was pulled toward the concussion model, which depends on a defined event. When cumulative exposure did not fit that model, it risked being redirected toward other categories, including dementia pugilistica. This is one national illustration of a classification failure that is visible across multiple jurisdictions.

This is why language matters. The wrong term can force the issue into the wrong framework, in any country, under any compensation or clinical system.

Definitions are failing because they were built for different purposes. Clinical systems classify diagnosis. Compensation systems classify entitlement. Military systems manage exposure and readiness. Research systems test mechanisms. Those purposes overlap, but they are not the same.

The result is predictable: blast exposure, blast injury, concussion, BiTBI, PTSD, moral injury and CTE are often discussed as if they are interchangeable. They are not.

The next section sets out the central fault line: exposure over time versus injury at a point in time.

2. The Central Problem: Exposure Versus Event

The central problem is the gap between how systems classify injury and how blast exposure occurs in military life.

Clinical and compensation systems are largely built around an identifiable event. A person sustains an injury, the injury is assessed, severity is classified, and the diagnosis is linked back to a cause. That model works reasonably well for many conditions. It is suited to a clear concussion, a penetrating traumatic brain injury, a documented explosive blast injury, or a moderate to severe TBI with observable neurological impairment.

Blast exposure does not always behave that way.

For many warfighters, exposure is not one event. It is repeated weapons firing, breaching, mortars, artillery, shoulder-fired weapons, heavy weapons, training serials, enclosed or reflective environments, and years in high-risk roles. No single exposure may produce a recognised injury. Over time, the cumulative load may still become relevant to brain health, performance and symptom burden.

That is where the language begins to fail.

A concussion model asks whether there was loss of consciousness, altered consciousness, amnesia, or a Glasgow Coma Scale finding consistent with mild TBI. Those are appropriate clinical markers for an acute event. They are less useful when the question is cumulative occupational exposure. The DVA-commissioned rapid review on repetitive low-level blast states the issue plainly: repetitive low-level blast is best understood as a cumulative occupational exposure rather than a discrete injury event (Heslop, Fortington & Gardner 2026).

That distinction changes the policy question. The question is no longer only: "Did this person sustain a diagnosable injury on this date?" It also becomes: "What exposure has this person accumulated across a role, a training cycle, a deployment, or a career?"

Those are different questions. They require different data.

Event-based systems need incident reports, clinical signs and diagnostic thresholds. Exposure-based systems need dose, frequency, weapon system, distance, firing position, environment, recovery interval, role history and longitudinal follow-up.

This is where tools such as the Blast Exposure Threshold Survey (BETS) and Generalised Blast Exposure Value (GBEV) become relevant. BETS provides a structured way to record lifetime blast exposure, while GBEV converts that history into a weighted cumulative exposure score. They do not diagnose injury. Their value is that they help move blast exposure from anecdote to record. If refined and validated across populations, tools such as BETS and GBEV may also support more consistent global comparison of cumulative blast exposure. Their use does not answer whether a person has BiTBI. It helps answer whether their blast exposure history is significant enough to warrant attention.

Without that exposure record, the system is left trying to infer cumulative risk from symptoms that are often non-specific.

That creates an obvious attribution problem. Headache, irritability, poor sleep, slowed thinking, balance problems, visual disturbance, tinnitus, mood change and concentration difficulty can sit across multiple domains: TBI, PTSD, depression, anxiety, chronic pain, vestibular injury, hearing injury, sleep disorder, moral injury, medication effects and substance use. The TBICoE review on TBI and PTSD describes the diagnostic difficulty caused by overlapping symptoms and reliance on self-report, particularly in service members and veterans with comorbid mild TBI and PTSD (TBICoE 2025).

The Australian rapid review reaches a similar conclusion from the blast exposure side. Current tools cannot reliably isolate repetitive low-level blast effects from PTSD, depression, sleep disturbance, chronic pain, prior impact TBI and other co-existing factors. The review supports biological plausibility and association, but not causality or threshold-based policy decisions (Heslop, Fortington & Gardner 2026).

That is not a reason to ignore exposure. It is a reason to record it properly.

This is also why blast exposure should not be treated only as a medical problem after symptoms appear. It is an occupational health problem before symptoms appear. If a weapon system, training environment or role creates repeated exposure to blast overpressure, then that exposure should be documented, mitigated and monitored in the same way other occupational hazards are managed. The absence of a validated injury threshold does not remove the obligation to reduce unnecessary exposure.

Allied systems are already moving in this direction. The United States Warfighter Brain Health model shifts the frame from isolated injury toward brain health across a career. TBICoE guidance recognises low-level blast exposure and directs clinicians to document exposure history. New Zealand has adopted a broader brain health hazard frame. Canada has recognised repeated concussive and sub-concussive forces in entitlement guidance. These are not identical frameworks, but they point in the same direction: exposure history is becoming part of the brain health record.

The operational implications are wider than diagnosis. The brain is the human weapon system. Blast exposure can affect the functions that military capability depends on: judgement, reaction time, emotional regulation, memory, sleep, decision-making, balance, vision, hearing and tolerance of stress. Even when causation is not settled, the risk belongs in the readiness conversation, not only the compensation conversation.

This is where current definitions are weakest. They are better at recognising what happened after a defined injury than they are at tracking what accumulated before it.

That is the fault line running through this paper: clinical systems classify events; operational reality accumulates exposure.

3. Working Definitions

These definitions are working terms, not doctrine. They are offered to create a common language across research, policy, clinical practice, compensation systems and lived experience. The aim is not to reduce every case to a label. The aim is to stop different mechanisms, exposures and outcomes being treated as if they are the same thing.

A summary table is provided at the end of this section for quick reference; the discussion below explains each term in turn.

Exposure terms

Blast exposure refers to being exposed to the effects of an explosion or weapons-generated pressure wave. It is not the same as injury. A person can be exposed without having a diagnosable injury, just as a person can be exposed to noise without immediately having measurable hearing loss. The distinction between exposure and injury is essential because prevention depends on recording the hazard before harm is confirmed.

Blast OverPressure (BOP) exposure refers more specifically to the rapid increase in atmospheric pressure caused by an explosion or weapon system. It may occur during combat, but much of the current concern relates to training: breaching, artillery, mortars, shoulder-fired weapons, heavy weapons and repeated firing in enclosed or reflective environments. The term is useful because it describes the physical input that can be measured, recorded and mitigated.

Low-level blast (LLB) refers to lower-intensity blast pressure waves, usually below thresholds associated with acute blast injury or clinically diagnosed TBI. TBICoE guidance states that low-level blast does not typically result in mild TBI, but symptoms can still be reported, particularly after multiple exposures (TBICoE 2025). The Australian rapid review describes LLB as exposure below thresholds usually associated with acute blast injury or clinically diagnosed TBI, often in the approximate range of 1-6 psi, while noting that definitions and thresholds vary across the literature (Heslop, Fortington & Gardner 2026).

Repetitive low-level blast (rLLB) refers to repeated exposure to low-level blast pressure waves over time. This is the term most closely aligned to the exposure problem discussed in this paper. The DVA-commissioned rapid review found no universally accepted definition of rLLB. Studies often use proxies such as occupational role, years in a high-risk role, self-reported blast counts or inferred cumulative exposure during training cycles or careers (Heslop, Fortington & Gardner 2026).

Repeated Blast Exposure (RBE) is a broader operational term for repeated exposure to blast. It is useful because it keeps the focus on repetition and exposure history, but it is not a diagnosis. Cumulative blast dose is the emerging concept that attempts to describe total exposure across time, including frequency, pressure intensity, impulse, duration, proximity, environment and recovery interval. This is where the field needs to move, but current measurement remains inconsistent.

Blast Exposure Threshold Survey (BETS) is a structured survey tool used to estimate a person's lifetime blast exposure. It records exposure history across weapon systems, roles and events. BETS is not a diagnostic tool. It is an exposure-history tool.

Generalised Blast Exposure Value (GBEV) is a weighted score derived from BETS. It is designed to provide a scalable estimate of cumulative blast burden. GBEV does not prove injury or causation. It gives researchers, clinicians and military systems a starting point for stratifying exposure risk.

The strength of BETS and GBEV is scalability. Their limitation is that survey-based tools depend on retrospective recall and weighting assumptions. The strongest approach is likely to combine structured surveys, objective blast gauge data, occupational records and longitudinal health outcomes. This is the direction required for future dose-response work.

Brain exposure or brain health hazard is broader again. It includes blast, impact, recoil, whole-body vibration, noise, muzzle gas and other occupational factors that may affect brain health. This aligns with the direction taken by Warfighter Brain Health models and the New Zealand brain health hazard framing. It also reinforces a prevention lens: the brain should be protected as a military capability, not merely assessed after injury.

Blast injury terms

Blast injury is any injury caused by an explosion. It is too broad to describe brain injury on its own. NATO has previously noted that the term creates confusion because it covers a wide spectrum of injury mechanisms and outcomes (NATO RTO 2011).

The usual categories are primary, secondary, tertiary and quaternary blast injury. Primary blast injury is caused by the pressure wave itself. Secondary blast injury is caused by fragments or debris. Tertiary blast injury occurs when the body is displaced or thrown. Quaternary blast injury includes burns, inhalation injury, toxic exposure and other effects. These categories help explain why the phrase "blast injury" can describe very different clinical realities. A person wounded by fragments, a person thrown by a blast, and a person exposed repeatedly to low-level overpressure are not necessarily experiencing the same mechanism.

This is why "blast injury" alone is not precise enough for the brain health problem. It names the broad source, but not the mechanism, severity, exposure pattern or clinical outcome.

TBI and BiTBI terms

Traumatic Brain Injury (TBI) refers to injury to the brain caused by external force. It is commonly classified as mild, moderate or severe, using clinical markers such as loss of consciousness, alteration of consciousness, post-traumatic amnesia, Glasgow Coma Scale and imaging findings. That severity model is useful after a clear event. It is less useful for cumulative occupational exposure where no single incident defines the injury pathway.

Mild TBI (mTBI) or concussion is usually defined by a limited period of loss of consciousness, alteration of consciousness, amnesia or a Glasgow Coma Scale score in the mild range. TBICoE's TBI and PTSD review notes that mild TBI diagnosis requires a clinician's assessment and a precipitating injury involving loss of consciousness, altered consciousness or post-traumatic amnesia (TBICoE 2025). This is why the concussion model can miss repeated exposure that does not produce a clear acute event.

Moderate to severe TBI refers to more clinically obvious brain injury, often involving longer loss of consciousness, longer amnesia, abnormal imaging, structural injury or significant neurological impairment. It is already more clearly recognised within clinical and compensation systems. It should not be diluted by discussion of cumulative exposure, and it should not be treated as outside the BiTBI frame when blast is the mechanism.

Penetrating TBI occurs when an object penetrates the skull and brain. In modern conflict this may be caused by bullets, fragments or blast-driven projectiles. It sits within the severe end of the TBI spectrum and has its own clinical pathway.

Blast-induced traumatic brain injury (BiTBI) is the term Vigil uses to describe brain injury caused by blast exposure. It is mechanism-based rather than severity-based. It can include mild, moderate and severe injury. It can include combat and training. It can include single high-level blast injury and, where evidence supports it, cumulative exposure. BiTBI does not replace existing diagnoses. It keeps the blast mechanism visible.

Blast-induced mild TBI (BI-mTBI) was an earlier and more constrained term. Its weakness is that it anchors the issue to "mild TBI", which pulls the discussion toward concussion criteria. That becomes a problem when the core concern is cumulative exposure rather than a single event. The language evolved toward BiTBI because the issue is blast mechanism across severity, not just mild injury.

Mechanism and pathology terms

Blast-related brain effects are not only about symptoms. The literature discusses possible mechanisms including vascular injury, axonal injury, glial activation, neuroinflammation, blood-brain barrier disruption, altered neuronal excitability and metabolic dysfunction. The Australian rLLB review describes these mechanisms as providing biological plausibility, while also stating that human evidence does not yet establish causality or validated exposure thresholds (Heslop, Fortington & Gardner 2026).

Interface Astroglial Scarring (IAS) refers to astroglial scarring at tissue-density interfaces in the brain, including grey-white matter boundaries and perivascular regions, described in some blast-exposed military brains. It is not CTE. It is not present in every blast-exposed person. It is not a clinical diagnostic test for living veterans. Its relevance is narrower and more specific: it supports the argument that blast may produce injury patterns distinct from repetitive head impact.

Blood-brain barrier disruption refers to changes in the vascular barrier that normally protects the brain. Neuroinflammation refers to inflammatory activity in the brain and central nervous system. Axonal, vascular and glial injury describe different cellular or structural pathways through which blast may affect the brain. These terms should be used carefully. They support biological plausibility and research direction; they should not be presented as proof that every exposed person has a defined brain injury.

Biomarkers and advanced imaging are emerging tools, not settled answers. TBICoE notes that blood-based biomarkers and advanced neuroimaging may eventually assist clinicians, but are not yet widely available for routine clinical use (TBICoE 2025). Research tools may help explain mechanisms, but clinical assessment still needs history, symptoms, function and context.

Mental health and moral injury terms

Post-traumatic stress disorder (PTSD) is a trauma-related mental health condition. It is not a brain injury, but it frequently overlaps with TBI and blast-exposed populations. Symptoms can include intrusive memories, avoidance, negative changes in mood and cognition, hyperarousal, irritability, sleep disturbance and impaired concentration. The overlap with mild TBI is substantial, which complicates diagnosis and treatment (TBICoE 2025).

Complex PTSD (C-PTSD) refers to a trauma condition associated with chronic or prolonged trauma, with additional disturbances in emotional regulation, self-concept and relationships. TBICoE notes that ICD-11 recognises complex PTSD and that it may be relevant to military populations, although further research is needed on diagnosis and treatment within military systems (TBICoE 2025). It belongs in the discussion because many veterans have prolonged exposure histories. It should not be used as a substitute for brain injury assessment.

Moral injury refers to psychological, ethical or spiritual harm arising from actions or events that violate deeply held moral beliefs, including betrayal by trusted authorities. It is distinct from PTSD and TBI, although it can coexist with both. TBICoE identifies morally injurious events as relevant to veterans with TBI, including associations with suicidality, PTSD and depression (TBICoE 2025).

Vigil's working lens is the Trinity: PTSD, moral injury and BiTBI. This does not mean every veteran has all three. It means these three domains can overlap and amplify each other. PTSD describes threat and trauma response. Moral injury describes ethical or institutional rupture. BiTBI describes physical brain effects from blast exposure. Keeping them separate improves assessment. Collapsing them into one label does not.

Repetitive impact, CTE and dementia terms

Repetitive Head Impact (RHI) refers to repeated impacts to the head, most commonly in contact sport, boxing, combat sport and some military settings. RHI is not the same mechanism as blast exposure. Repetition alone does not make them equivalent.

Traumatic Encephalopathy Syndrome (TES) is a clinical research construct used in living people with symptoms and exposure history that may raise concern for underlying CTE pathology. It does not confirm CTE. The DVA rapid review distinguishes TES from CTE neuropathological change, noting that TES is a clinical research construct and does not establish that CTE pathology is present (Heslop, Fortington & Gardner 2026).

Probable CTE is a clinical classification or judgement made during life when a person has substantial exposure history and progressive cognitive, behavioural or mood symptoms consistent with TES. It is not confirmed CTE. It should be used cautiously, especially in veterans whose symptoms may also be explained by PTSD, TBI, BiTBI, chronic pain, sleep disorder, depression, substance use or other neurocognitive conditions.

Chronic Traumatic Encephalopathy (CTE) is a neuropathological diagnosis confirmed after death. It is primarily associated with repetitive head impact. Military brain bank research has identified CTE in some military brains, but the prevalence appears low compared with collision sport cohorts, and it should not be used as a catch-all explanation for veteran symptoms (Perl et al. 2022).

CTE neuropathological change (CTE-NC) refers to the specific post-mortem tau pathology used to confirm CTE. Dementia pugilistica is the older term historically associated with boxing-related neurodegeneration. It is not an appropriate default category for cumulative blast exposure. The key distinction is that CTE, TES, probable CTE and dementia pugilistica sit mainly in the repetitive head impact lane. BiTBI sits in the blast mechanism lane.

Neurocognitive disorder and younger onset dementia describe cognitive decline with multiple possible causes. They should not be assumed to be CTE. In veterans, cognitive decline may reflect multiple interacting factors: brain injury, blast exposure, PTSD, depression, sleep disorder, chronic pain, medication, vascular disease, substance use or neurodegenerative disease.

Expectancy effects and narrative risk

Placebo and nocebo effects refer to changes in symptoms influenced by expectation of benefit or harm. These terms need care. They do not mean symptoms are fabricated. They do not negate real exposure, real injury or real distress. They are relevant because narratives can shape how symptoms are interpreted, feared and reported.

This cuts both ways. Attributing everything to PTSD can shut down investigation of physical brain effects. Attributing everything to CTE can create deterministic fear that is not supported by current evidence. A responsible framework must avoid both errors.

The purpose of these definitions is to preserve precision. Exposure is not injury. Blast is not impact. PTSD is not BiTBI. Moral injury is not PTSD. CTE is not a living clinical diagnosis. BiTBI is not a severity label. These distinctions are the basis for the next section: where the frameworks clash.

Summary table

The table below provides quick reference to the key terms used in this paper, the lane each belongs to, and a one-line definition.

Term Lane One-line definition

Blast exposure Exposure Being exposed to the effects of an explosion or weapons-generated pressure wave. Not the same as injury.

Blast OverPressure Exposure The rapid increase in atmospheric (BOP) pressure caused by an explosion or weapon system; the measurable physical input.

Low-level blast Exposure Lower-intensity blast pressure waves, (LLB) typically below thresholds for acute blast injury or diagnosed TBI.

Repetitive Exposure Repeated exposure to low-level blast low-level blast pressure waves over time; the central (rLLB) concept in this paper.

Repeated Blast Exposure Broader operational term for repeated Exposure (RBE) exposure to blast. Not a diagnosis.

Cumulative blast Exposure Emerging concept describing total dose exposure across time: frequency, intensity, duration, proximity and recovery interval.

BETS Exposure tool Blast Exposure Threshold Survey: structured tool for estimating lifetime blast exposure history.

GBEV Exposure tool Generalised Blast Exposure Value: weighted score derived from BETS to estimate cumulative blast burden.

Brain health hazard Exposure Umbrella frame including blast, (broad) impact, recoil, vibration, noise and muzzle gas as occupational risks to brain health.

Blast injury Injury Any injury caused by an explosion. (general) Too broad to describe brain injury alone; subdivided into primary-quaternary categories.

Primary blast Injury Injury caused by the pressure wave injury itself.

Secondary / Injury Fragments and debris (secondary); tertiary / body displacement (tertiary); burns, quaternary inhalation, toxic exposure (quaternary).

TBI TBI Traumatic brain injury: brain injury caused by external force, classified mild, moderate or severe.

Mild TBI / TBI Defined by limited LOC, altered concussion consciousness, amnesia or GCS in the mild range; event-based criteria.

Moderate to severe TBI More clinically obvious brain injury TBI with longer LOC, abnormal imaging or significant neurological impairment.

Penetrating TBI TBI Object penetrates skull and brain; sits at the severe end of the TBI spectrum.

BiTBI Blast mechanism Blast-induced TBI: mechanism-based term covering mild, moderate and severe blast-related brain injury, combat and training, acute and cumulative.

BI-mTBI (legacy) Blast mechanism Blast-induced mild TBI; earlier term, now superseded because it anchors discussion in the concussion model.

IAS Mechanism / Interface Astroglial Scarring at pathology tissue-density boundaries; observed in some blast-exposed military brains. Not CTE.

BBB disruption / Mechanism / Vascular barrier changes and neuroinflammation pathology inflammatory activity proposed as biological pathways; supports plausibility, not causation.

PTSD Mental health Trauma-related mental health condition. Not a brain injury, but frequently overlapping with TBI and blast exposure.

Complex PTSD Mental health Trauma condition associated with chronic or prolonged trauma; recognised in ICD-11.

Moral injury Mental health Psychological, ethical or spiritual harm from events that violate deeply held moral beliefs. Distinct from PTSD and TBI.

RHI Repetitive Repetitive head impact, primarily impact from contact sport and boxing. Different mechanism from blast.

TES Repetitive Traumatic Encephalopathy Syndrome: impact clinical research construct in living people. Does not confirm CTE.

Probable CTE Repetitive Clinical judgement during life based impact on substantial exposure history and symptoms. Not confirmed CTE.

CTE Repetitive Chronic Traumatic Encephalopathy: impact neuropathological diagnosis confirmed only after death.

CTE-NC Repetitive CTE neuropathological change: the impact specific post-mortem tau pathology used to confirm CTE.

Dementia Repetitive Older term historically associated pugilistica impact with boxing-related neurodegeneration. Not appropriate for cumulative blast exposure.

Placebo / nocebo Narrative Symptom changes influenced by effect expectation of benefit or harm. Do not mean symptoms are fabricated.

4. Where Frameworks Clash

The definitions do not clash because people are careless with language. They clash because different systems are trying to solve different problems. That dynamic is visible across every nation that has engaged with blast-exposed veteran populations.

NATO identified the definitional problem earlier than most. Its work on military TBI noted inconsistent use of mTBI terminology and the difficulty of separating blast mechanisms from blunt force, acceleration, debris and other effects in operational settings. A separate NATO blast injury symposium noted that "blast injury" itself is a broad and confusing term, because it spans the full range of injuries caused by explosions (NATO STO 2015; NATO RTO 2011). Fourteen years later, the terminology problem has not been resolved.

The United States has moved toward a Warfighter Brain Health model that shifts the frame from isolated injury toward brain health across a career. TBICoE guidance recognises low-level blast exposure and directs clinicians to document cumulative exposure history, including blast number, role, weapon systems and years in high-risk environments. That is an important shift: it recognises that absence of a classic concussion event does not make exposure history irrelevant (TBICoE 2025).

Canada has moved further than most Commonwealth nations in entitlement terms. Veterans Affairs Canada recognises repeated concussive and sub-concussive forces, including in breachers and personnel repeatedly firing powerful weapons, within its TBI entitlement guidance. That does not settle the science globally. It shows that a Commonwealth veterans system has accepted repeated exposure as relevant to entitlement and demonstrates a pathway other nations can examine.

New Zealand has taken a broader brain health hazard approach. NZDF material recognises that brain health risks in military activity can arise from blast overpressure and related occupational exposures, not only from direct head impact. This aligns more closely with a prevention and monitoring model than a narrow post-injury diagnostic model.

Israel's registry and research work highlights blast-related long-term psychiatric and neurological outcomes that cannot be reduced to PTSD alone. Ukraine is demonstrating, in real time, what repeated blast exposure at scale looks like and what will be required of veteran health systems in the years ahead.

Australia's experience with the Repatriation Medical Authority (RMA) process illustrates the classification problem in a specific compensation law context. The RMA is designed to assess whether there is sound medical-scientific evidence linking a defined injury, disease or death to service. That structure requires categories, thresholds and causal pathways. It works best where the condition is already recognised and the exposure pathway is well described. It is less suited to an emerging exposure model where the central problem is repeated low-level blast, uncertain thresholds and symptoms that overlap with other conditions.

When the issue was framed as blast-induced mild TBI, the language pulled the discussion toward the concussion model. Concussion and mTBI are still largely event-based. They look for loss or alteration of consciousness, amnesia or related clinical signs. If cumulative blast exposure does not produce a clear event, it is difficult for that model to hold it. The risk is that the issue is pushed toward the nearest available category, including dementia pugilistica or CTE-related constructs, even though those sit mainly in the repetitive head impact lane. This is one national instance of a classification failure that is, in structural terms, not uniquely Australian.

The DVA-commissioned rapid review on repetitive low-level blast takes a more exposure-based view. It describes rLLB as a cumulative occupational exposure, not a discrete injury event. It also states the limits of the evidence: human studies support biological plausibility and association, but not causality, validated exposure thresholds or blast-specific diagnostic markers. The review does not say there is no problem. It says the problem cannot yet be reduced to a simple diagnostic test or threshold-based rule (Heslop, Fortington & Gardner 2026).

SOF Bridges is an unpublished Vigil dataset capturing exposure history and symptoms among Australian special operations veterans and serving members in high-risk roles. In the cohort of 182 respondents, only 8 reported loss of consciousness. That finding does not prove BiTBI or causation. It does show that a framework built around loss of consciousness will miss most people in a highly exposed cohort when the exposure pattern is repetitive rather than acute. The question becomes less about whether a single qualifying event occurred and more about whether exposure history has been adequately captured. This pattern is not unique to Australian special operations personnel; it is a predictable finding in any high-exposure cohort assessed against event-based criteria.

The clash is the point. Each system asks a different question:

A clinician asks: "What diagnosis can I make today?"
A compensation authority asks: "What condition can be connected to service?"
A commander should ask: "What exposure am I imposing on my people?"
A researcher asks: "What mechanism explains this pattern?"
A veteran or family member asks: "Why has something changed, and what can be done?"

Those questions overlap, but they are not the same. Until the frameworks are aligned, blast-exposed personnel will continue to be sorted into imperfect categories. Some will fit recognised moderate to severe injury pathways. Some will be diagnosed with PTSD, chronic pain, sleep disorder or vestibular dysfunction. Some will be told they do not meet concussion criteria. Some will fear CTE. Some will have multiple conditions at once.

That is why definitions are not a side issue. They determine which question gets asked first.

5. Why Vigil Uses BiTBI

Vigil uses Blast-induced traumatic brain injury, or BiTBI, because the existing language does not hold the problem cleanly.

The issue is not whether concussion, moderate to severe TBI, PTSD, moral injury or CTE exist. They do. The issue is that none of those terms, on its own, describes blast-related brain injury across mechanism, severity, setting and time.

The earlier term blast-induced mild TBI had a limitation. Once the phrase "mild TBI" is used, the discussion is pulled toward concussion criteria: loss of consciousness, altered consciousness, amnesia and a defined injury event. That may work for a recognised blast-related concussion. It does not work well for repeated low-level Blast OverPressure exposure where there may be no single qualifying event.

BiTBI is mechanism-based. It starts with the mechanism: blast. It does not start with severity. This allows the term to include severe blast injury, moderate blast-related TBI, mild blast-related TBI and the emerging concern around cumulative exposure where the evidence supports investigation but current categories do not yet provide a clean pathway.

This is a critical point. BiTBI includes severe blast injury. It does not diminish it. A veteran with recognised moderate to severe TBI from an RPG, IED, indirect fire or other blast event is not outside the frame. They sit clearly within it. The unresolved gap is not their legitimacy. The unresolved gap is what happens to personnel with repeated exposure who do not meet event-based concussion criteria but report persistent neurological, cognitive, vestibular, visual, sleep, mood or behavioural changes.

Using BiTBI also avoids pulling blast exposure into the wrong lane. CTE, TES and dementia pugilistica sit mainly in the repetitive head impact field. They are relevant terms and need to be defined, but they should not become the default explanation for blast-exposed veterans. Military neuropathology research shows CTE can occur in military populations, but it does not support treating CTE as the dominant explanation for military neuropsychiatric symptoms (Perl et al. 2022). Blast may produce different mechanisms, including vascular, glial and inflammatory pathways, and in some cases neuropathological findings such as Interface Astroglial Scarring. Those mechanisms should not be collapsed into the sport-concussion narrative.

Nor should blast-related symptoms be absorbed into PTSD by default. PTSD is real and common. Moral injury is real and often under-recognised. Both can coexist with TBI and BiTBI. But neither term explains every cognitive, vestibular, visual, sleep, headache, pain or balance-related complaint after blast exposure. The TBICoE review is clear that PTSD and mild TBI overlap substantially and that distinguishing them can be difficult, especially where assessment relies heavily on self-report (TBICoE 2025).

BiTBI therefore performs a practical role. It keeps the blast mechanism visible while assessment occurs. It does not declare causation in every case. It does not replace diagnosis. It prevents premature misclassification.

It also aligns with the direction of allied work. The DVA-commissioned rapid review frames repetitive low-level blast as cumulative occupational exposure, while acknowledging uncertainty around causation, thresholds and diagnostic markers (Heslop, Fortington & Gardner 2026). The United States Warfighter Brain Health model and TBICoE blast guidance similarly move toward exposure history, brain health monitoring and cumulative risk rather than relying only on acute injury events.

That is the direction Vigil is following. Not because the science is settled, but because the existing categories are not enough.

The purpose of BiTBI is to ask a better question. Not simply: did this person have a recognised concussion? But: what blast exposure occurred, what mechanism may be relevant, what symptoms or impairments are present, what other conditions coexist, and what assessment or care is required?

That is why Vigil uses BiTBI. It includes severe injury. It protects against concussion, PTSD and CTE misclassification. It keeps the discussion anchored to blast.

6. The Trinity and Whole-Person Assessment

At the individual level, the problem is rarely a single clean label.

Many veterans present with overlapping domains: trauma symptoms, ethical or institutional injury, cognitive change, sleep disruption, pain, headaches, vestibular disturbance, visual problems, tinnitus, irritability, fatigue, memory problems and family-reported behavioural change. Some of these may be related to PTSD. Some may relate to moral injury. Some may relate to TBI or BiTBI. Some may come from chronic pain, sleep disorder, medication, substance use, depression, anxiety or other medical conditions.

That is why Vigil uses the Trinity as a practical lens: PTSD, moral injury and BiTBI.

PTSD describes a threat-based trauma response. Moral injury describes ethical, spiritual or institutional rupture. BiTBI describes physical brain effects from blast exposure. These domains can coexist and reinforce each other, but they should not be collapsed into one diagnosis.

TBICoE's review on TBI and PTSD makes the overlap problem clear. Mild TBI and PTSD share symptoms, rely heavily on self-report, and can be difficult to differentiate in military and veteran populations (TBICoE 2025). The Australian rapid review reaches the same practical conclusion from the blast exposure side: current tools cannot reliably isolate repetitive low-level blast effects from PTSD, depression, sleep disturbance, chronic pain, prior impact TBI and other coexisting conditions (Heslop, Fortington & Gardner 2026).

This does not mean the symptoms are vague or unserious. It means the assessment has to be wider.

The Canadian discussion Vigil reviewed made this point in practical clinical language. The panel described a recurring polytrauma triad involving TBI, mental health conditions and chronic pain. It also highlighted subtle problems that are often missed in standard assessment, especially visual, vestibular and balance-related impairments. One example involved a senior soldier with extensive blast exposure whose cognitive testing and EEG were normal, but whose visual system was severely affected.

That is the type of presentation that can be lost if the assessment starts and ends with PTSD, or with whether the person lost consciousness.

A whole-person assessment should include exposure history, neurological assessment, cognitive function, mental health, moral injury, sleep, pain, medication, substance use, vestibular function, hearing, vision and family observations. It should also distinguish between diagnosis and management. A person may not yet meet criteria for a specific blast-related diagnosis, but still need care for symptoms and monitoring of exposure history.

Families need to be part of this frame. They often identify changes before systems do: sleep, mood, memory, judgement, irritability, withdrawal, risk-taking, loss of confidence, or changes in parenting and relationships. The warfighter is not the only person affected by brain injury, trauma or moral injury. Families carry the consequences of poor definitions, delayed recognition and fragmented care.

There is also a narrative risk. Over-attributing symptoms to CTE can create fear and fatalism not supported by the evidence. Dismissing everything as PTSD can shut down investigation of physical brain effects. Both errors harm decision-making. A better approach is to document exposure, assess the whole person, avoid premature conclusions, and build care around the actual pattern of impairment.

The Trinity is not a doctrine. It is a working lens. It says that for many veterans, the relevant question is not whether the problem is PTSD, moral injury or BiTBI. The better question is how much of each is present, how they interact, and what support is required.

Practical Priorities for a Global Ontology

The following priorities are applicable to any defence or veteran system grappling with cumulative blast exposure. They are not nation-specific, and they are not Vigil's prescription. They are offered as a starting point for a global conversation about what an ontology for blast-related brain injury would need to include and achieve. Vigil draws on Australian evidence and experience as its primary vantage point, but the structural problems described here are visible across allied nations.

Use mechanism-based terminology.

Consider BiTBI as a mechanism-based term for blast-related brain injury across severity, setting and time. It should sit within a broader ontology that preserves recognised clinical pathways for concussion, moderate to severe TBI, explosive blast injury, PTSD, moral injury and neurodegenerative disease. The goal is not to impose a new label but to stop blast mechanism from disappearing into event-based classifications that were not designed to hold it.

Treat blast exposure as an occupational hazard.

Document exposure history through structured tools such as BETS and GBEV, supplemented where possible by blast gauge data and occupational role records. The absence of a validated injury threshold does not remove the obligation to record the hazard. This shift, from post-injury assessment to pre-symptom documentation, is foundational to any exposure-based system.

Review compensation and entitlement frameworks.

Each nation should examine whether its veteran entitlement pathways can accommodate cumulative low-level Blast OverPressure exposure. The Canadian and United States precedents provide reference points. Where classification routes do not yet exist, the evidentiary and policy work required to create them should begin now.

Embed whole-person assessment.

Clinical assessment of blast-exposed veterans should include vestibular, visual, sleep, hearing, pain, cognitive, mental health and moral injury domains, and should incorporate family observations. Systems that assess only for PTSD or only for concussion will miss the range of impairment that cumulative blast exposure can produce.

Invest in longitudinal, dose-response research.

Single-point diagnostic tools are not sufficient. Exposure surveys, blast gauge data, biomarkers and neuroimaging need to be combined across time in cohorts with known occupational histories. The field will not advance without investment in studies designed around exposure from the outset.

Align frameworks across allied nations.

NATO, Five Eyes, Commonwealth and other allied nations should work toward interoperable terminology and shared exposure data standards. Research and clinical guidance produced in the United States, Canada, New Zealand, Israel and Australia is more useful when it can be compared directly. Parallel frameworks that cannot be aligned are a structural barrier to progress.

Conclusion

Blast-related brain injury does not fail to fit current frameworks because the issue is imaginary. It fails because the frameworks were built for different purposes.

Clinical systems classify diagnosis. Compensation systems classify entitlement. Military systems manage risk, readiness and exposure. Research systems test mechanisms. None of those systems is wrong. But when they use different language for overlapping problems, warfighters, veterans and families are left between categories. That is not an Australian problem, a United States problem or a NATO problem. It is a problem shared by every defence and veteran system that deploys people into high-exposure roles without a coherent framework for recording and responding to cumulative blast exposure.

BiTBI is not a final framework. It does not replace concussion, moderate to severe TBI, PTSD, moral injury, CTE or any other recognised condition. It is a mechanism-based term used to keep blast visible across severity, setting and time. It includes severe blast injury. It also creates space for cumulative low-level Blast OverPressure exposure, particularly in training and high-risk roles, where exposure may accumulate without a single qualifying injury event.

The next step is not to force every veteran into a new label. It is to record exposure properly, assess the whole person, reduce unnecessary risk, support families, and stop using definitions that hide the problem they are meant to describe.

BiTBI is not the final answer. It is a correction to the question being asked.

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