Defining the essential anatomical coverage provided by military body armour against high energy projectiles

Can thoraco-abdominal organ boundaries be accurately determined from X-ray and anthropometric surface scans? Implications for body armour system coverage and design

To optimise soldier protection within body armour systems, knowledge of the boundaries of essential thoraco-abdominal organs is necessary to inform coverage requirements. However, existing methods of organ boundary identification are costly and time consuming, limiting widespread adoption for use on soldier populations. The aim of this study was to evaluate a novel method of using 3D organ models to identify essential organ boundaries from low dose planar X-rays and 3D external surface scans of the human torso. The results revealed that, while possible to reconstruct 3D organs using template 3D organ models placed over X-ray images, the boundary data (relating to the size and position of each organ) obtained from the reconstructed organs differed significantly from MRI organ data. The magnitude of difference varied between organs. The most accurate anatomical boundaries were the left, right, and inferior boundaries of the heart, and lateral boundaries for the liver and spleen. Visual inspection of the data demonstrated that 11 of 18 organ models were successfully integrated within the 3D space of the participant's surface scan. These results suggest that, if this method is further refined and evaluated, it has potential to be used as a tool for estimating body armour coverage requirements.

Ergonomic impact of prehospital clinicians using body armour: A qualitative study

Armed crime constitutes a significant number of offences in England. The associated healthcare burden forms 32% of the workload of London HEMS, requiring these clinicians to use body armour. Much research has explored the ergonomic impact of body armour in police and military populations however the impact on prehospital clinicians is not known. The aim of this study is to explore the perceptions of prehospital clinicians of wearing body armour.Focus groups were conducted until theoretical saturation was reached, utilising hermeneutic phenomenology.Problems with the comfort, safety, time, hygiene, coverage, and female fit of armour were identified. Clinicians feel hot in summer, time to respond to scenes is increased and the fit for females is poor.Consideration should be given to sourcing specific female-fit armour and to the interoperability with the rest of the protective clothing. A redesign of uniform could provide greater flexibility to mitigate some of the issues.

Using CT scans to determine the optimal sizes of hard armour plates to protect the torso for UK female Armed Forces personnel

INTRODUCTION

Hard armour plates provide coverage to essential anatomical structures in the torso that, if injured, would likely be responsible for death before damage control surgery can be undertaken. Existing front and rear OSPREY plates in conjunction with Mark 2 plates used at the sides in current UK Armed Forces personal armour systems are provided in a single size, used by both female and male users.

METHODS

CT scans of 45 female UK military personnel were analysed. Distances between anatomical structures representing threshold (absolute minimum) and objective (the maximum level of coverage beyond which there is limited further benefit) coverage of the torso were determined and compared with OSPREY and Mark 2 plate dimensions. Sample characteristics were compared with the 2006/2007 UK Armed Forces Anthropometric Survey.

RESULTS

No statistical difference was found between sample means for stature (p=0.131) and mass (p=0.853) from those of the anthropometric survey in this sample. The height of both the front OSPREY plates exceeded the threshold coverage (suprasternal notch to lower border of the 10th rib) for all women studied. The height of the Mark 2 plate exceeds the objective coverage from the side for all women studied.

CONCLUSIONS

Based on a plate height providing threshold coverage of all women up to the 50th percentile, the height of the front and rear OSPREY plates could be reduced by 36mm and 31mm respectively. Based on a presumption that a side plate should cover up to the 95th percentile, the Mark 2 plate achieves the objective height and width for the female population studied. Strong evidence was found to support the UK Ministry of Defence requirement for procurement of new front and rear plates of multiple heights for both female and male users.

Cognitive performance of military men and women during prolonged load carriage

BACKGROUND

This study evaluated cognitive workload in soldiers undertaking a long duration march wearing different loads.

METHODS

Military participants (n=12 men and n=10 women) performed four 3-hour loaded marches (12.25 km at 4.9 km/hour) wearing either 21 kg, 26 kg, 33 kg or 43 kg. During the march, accuracy and response time were measured using the verbal working memory n-back test (0, 1, 2 and 3) and two bespoke Go/No Go tests (visual/auditory) to assess inhibition of a pre-potent response.

RESULTS

The physical demands of the march increased with load and march duration but remained at moderate intensity. N-back test accuracy ranged from 74% to 98% in men and 62% to 98% in women. Reduced accuracy was observed as load and time increased. Accuracy during the visual Go/No Go test also reduced with load, accuracy ranged from 69% to 89% in men and 65% to 90% in women. No differences due to load or time were observed during completion of the auditory Go/No Go task; accuracy ranged from 93% to 97% in men and 77% to 95% in women. A number of participants were unable to complete the march due to discomfort. Reports of discomfort were more frequent in women, which may have contributed to the greater reductions in accuracy observed.

CONCLUSION

These data provide further evidence that cognitive performance of military personnel can be affected during long duration loaded marching. Women reported discomfort from equipment more frequently than men, which may make them more susceptible to declines in cognitive performance. These findings highlight important considerations for equipment procurement.

Do thoracoabdominal organ boundaries differ between males and females? Implications for body armour coverage and design

To optimise fit and protection of body armour systems, knowledge of the location of thoracoabdominal organ boundaries is required. The aims of this study were (i) determine the effect of sex on essential and desirable thoracoabdominal organ boundaries, and (ii) compare essential thoracoabdominal organ boundaries with small and large hard ballistic plate sizes from the National Institute of Justice (NIJ) and determine if coverage requirements differ between sexes. 33 males and 33 females underwent supine magnetic resonance imaging of their thoracoabdominal organs. Male participants on average displayed more laterally and inferiorly positioned essential and desirable organ boundaries than females. Based on NIJ plate sizes, insufficient coverage of essential organs was identified for male and female participants. A greater range of body armour sizes and designs that better cater to the diverse anatomy of soldier populations is warranted, but must be considered in the context of ergonomic and performance implications.

Danish military fatalities in international operations 2002-2018

INTRODUCTION

This study describes deaths among Danish soldiers in international operations 2002-2018. Having been part of UN and later NATO forces in ex-Yugoslavia, in 2002 the first Danish contingent took part in the International Security Assistance Force mission in Afghanistan as well as Iraq. The changing role of the Danish military in international operations meant casualties, in numbers that had not yet been experienced, and necessitated a review of our procedures for handling fatalities in the military.

METHODS

The study is a retrospective review of autopsy reports, Military Police reports and medical reports, and the purpose is to examine all Danish fatalities in international operations in 2002-2018 to identify potential areas of improving treatment and protection and to review the contribution of the autopsies. The mechanism of injury, the fatal injuries and causes of death and the time of death within the chain of evacuation were identified. Casualties dying at any time from site of injury until definitive care were included.

RESULTS

A total of 53 soldiers died from injuries during international operations in the years 2002-2018. The majority of these (43) died from combat injuries and 10 from accidents. Four of the victims with combat injuries were not autopsied. The majority (36) of the combat deaths were caused by blast/explosions (improvised explosive devices, rocket propelled grenades, fragments), while 7 were caused by bullets. 39 combat victims died instantly on the site or at the arrival to the field hospital, 4 were treated in field hospital and 2 of these were transported back to Denmark.

CONCLUSIONS

Most combat fatalities result from fragmentation and blast injury. Forensic autopsies provide valuable information regarding injuries, weaponry, the efficiency of protective equipment and the quality of medical intervention in military fatalities and are recommended in all military fatalities in order to prevent avoidable casualties in the future.

Penetration of Energised Metal Fragments to Porcine Thoracic Tissues

Energised fragments from explosive devices have been the most common mechanism of injury to both military personnel and civilians in recent conflicts and terrorist attacks. Fragments that penetrate into the thoracic cavity are strongly associated with death due to the inherent vulnerability of the underlying structures. The aim of this study was to investigate the impact of fragment-simulating projectiles (FSPs) to tissues of the thorax in order to identify the thresholds of impact velocity for perforation through these tissues and the resultant residual velocity of the FSPs. A gas-gun system was used to launch 0.78-g cylindrical and 1.13-g spherical FSPs at intact porcine thoracic tissues from different impact locations. The sternum and rib bones were the most resistant to perforation, followed by the scapula and intercostal muscle. For both FSPs, residual velocity following perforation was linearly proportional to impact velocity. These findings can be used in the development of numerical tools for predicting the medical outcome of explosive events, which in turn can inform the design of public infrastructure, of personal protection, and of medical emergency response.

Better be prepared: the spectrum of neuropsychiatric impairment among Libyan war victims transferred to Germany for trauma rehabilitation

Background

The current Libyan civil war has originated many casualties, imposing medical challenges. War injuries are complex, requiring specialized knowledge and interdisciplinary assessment for adequate patient and intercultural management.

Methods

This retrospective study analyzed records of 78 Libyan patients admitted from July 2016 to November 2017 to neurological and trauma surgical departments of Krankenhaus Nordwest, Frankfurt, Germany. Issues of system preparation of the hospital, demographics, injury patterns and therapies were analyzed. The chi-squared test was used to analyze differences in injury patterns in explosion and gunshot injuries.

Results

Seventy-seven of seventy-eight patients were male (mean age 30.6 years). The patients received primary and secondary treatment in Tunisia (n = 39), Libya (n = 36) and Turkey (n = 23). Forty-eight patients had gunshot injuries, 37 explosion injuries, 11 both. Preparation for management of injuries included hygienic and isolation protocols, organization of interpreters and intercultural training. Patients presented with a broad variety of neurological, psychiatric and trauma surgical injuries. Fifty-six patients had sensory, 47 motor deficits. Nine reported headache, 5 vertigo, 13 visual impairment, 28 psychiatric symptoms. Eighteen patients had central nervous damage, 50 peripheral nervous damage. Central nervous damage was significantly more common in gunshot than explosion injuries (p = 0.015). Peripheral nervous damage was more common in explosion than gunshot injuries (p < 0.1). Fifty-one patients had polytrauma and 49 suffered from fractures. Therapy included surgical interventions (n = 56) and physiotherapy. Structured rehabilitation programs were often indicated.

Conclusion

Specialized knowledge about war injuries and their management including hospital preparation and planning regarding infrastructure may be required anytime. Injuries include a broad variety of neurological, psychiatric and trauma surgical injuries. Therefore, an interdisciplinary approach is crucial.

Comparing the medical coverage provided by four contemporary military combat helmets against penetrating traumatic brain injury

INTRODUCTION

Modern military combat helmets vary in their shapes and features, but all are designed to protect the head from traumatic brain injury. Recent recommendations for protection against energised projectiles that are characteristic of secondary blast injury is to ensure coverage of both the brain and brainstem.

METHOD

Graphical representations of essential coverage of the head (cerebral hemispheres, cerebellum and brainstem) within an anthropometrically sized model were superimposed over two standard coverage helmets (VIRTUS helmet, Advanced Combat Helmet (ACH)) and two 'high-cut' helmets (a Dismounted Combat Helmet (DCH)) and Combat Vehicle Crewman (CVC) helmet), both of which are designed to be worn with communications devices. Objective shotline coverage from representative directions of projectile travel (-30 to +30 degrees) was determined using the Coverage of Armour Tool (COAT).

RESULTS

VIRTUS and ACH demonstrated similar overall coverage (68.7% and 69.5%, respectively), reflecting their similar shell shapes. ACH has improved coverage from below compared with VIRTUS (23.3% vs 21.7%) due to its decreased standoff from the scalp. The 'high-cut' helmets (DCH and CVC) had reduced overall coverage (57.9% and 52.1%), which was most pronounced from the side.

CONCLUSIONS

Both the VIRTUS and ACH helmets provide excellent overall coverage of the brain and brainstem against ballistic threats. Coverage of both would be improved at the rear by using a nape protector and the front using a visor. This is demonstrated with the analysis of the addition of the nape protector in the VIRTUS system. High-cut helmets provide significantly reduced coverage from the side of the head, as the communication devices they are worn with are not designed to provide protection from ballistic threats. Unless absolutely necessary, it is therefore recommended that high-cut helmets be worn only by those users with defined specific requirements, or where the risk of injury from secondary blast is low.

Impact of military medicine on civilian medical practice in the UK from 2009 to 2020

INTRODUCTION

The positive impact of advances in military medicine and the influence these have had on civilian medical practice have been well documented throughout history: this review will be looking specifically between 2009 and 2020.

AIMS

Review of innovations that have been implemented or have influenced civilian practice within the areas of trauma, disease outbreak management and civilian systems between 2009 and 2020. This review will also aim to explore the impact that working with or within the military can have on individuals within civilian healthcare systems and the future challenges we face to maintain skills.

RESULTS

Using a narrative approach to this review, we found that there have been numerous changes to trauma management within the UK, based on military practice and research during conflict, which have improved survival outcomes. In addition, the use of niche military skills as part of a coordinated response, during both internal and international disease outbreaks, are thought to have supported civilian systems enabling an efficient and prolonged response. Furthermore, adaptation of military concepts and their application to the NHS through consultant-led prehospital teams, centralisation of specialties in the form of major trauma centres and the introduction of guidelines to manage 'major incidents and mass casualty events' in 2018 have improved patient outcomes.

CONCLUSION

From 2009 to 2020, lessons learnt from the British and other nations' militaries have been integrated into UK practice and have likely contributed to improved outcomes in the management of major incidents both nationally and internationally.

Torso body armour coverage defined according to feasibility of haemorrhage control within the prehospital environment: a new paradigm for combat trauma protection

Developments in military personal armour have aimed to achieve a balance between anatomical coverage, protection and mobility. When death is likely to occur within 60 min of injury to anatomical structures without damage control surgery, then these anatomical structures are defined as 'essential'. However, the medical terminology used to describe coverage is challenging to convey in a Systems Requirements Document (SRD) for acquisition of new armour and to ultimately translate to the correct sizing and fitting of personal armour. Many of those with Ministry of Defence responsible for the procurement of personal armour and thereby using SRDs will likely have limited medical knowledge; therefore, the potentially complex medical terminology used to describe the anatomical boundaries must be translated into easily recognisable and measurable external landmarks. We now propose a complementary classification for ballistic protection coverage, termed threshold and objective, based on the feasibility of haemorrhage control within the prehospital environment.

Extending existing recommended military casualty evacuation timelines will likely increase morbidity and mortality: a UK consensus statement

INTRODUCTION

Future conflicts may have limited use of aviation-based prehospital emergency care for evacuation. This will increase the likelihood of extended evacuation timelines and an extended hold at a forward hospital care facility following the completion of damage control surgery or acute medical interventions.

METHODS

A three-round Delphi Study was undertaken using a panel comprising 44 experts from the UK armed forces including clinicians, logisticians, medical planners and commanders. The panel was asked to consider the effect of an extended hold at Deployed Hospital Care (Forward) from the current 2-hour timeline to +4, +8, +12 and +24 hours on a broad range of clinical and logistical issues. Where 75% of respondents had the same opinion, consensus was accepted. Areas where consensus could not be achieved were used to identify future research priorities.

RESULTS

Consensus was reached that increasing timelines would increase the personnel, logistics and equipment support required to provide clinical care. There is a tipping point with a prolonged hold over 8 hours, after which the greatest number of clinical concerns emerge. Additional specialties of surgeons other than general and orthopaedic surgeons will likely be required with holds over 24 hours, and robust telemedicine would not negate this requirement.

CONCLUSIONS

Retaining acute medical emergencies at 4 hours, and head injuries was considered a particular risk. This could potentially be mitigated by an increased forward capacity of some elements of medical care and availability of a CT scanner and intracranial pressure monitoring at over 12 hours. Any efforts to mitigate the effects of prolonged timelines will come at the expense of an increased logistical burden and a reduction in mobility. Ultimately the true effect of prolonged timelines can only be answered by close audit and analysis of clinical outcomes during future operations with an extended hold.

Gelatine Backing Affects the Performance of Single-Layer Ballistic-Resistant Materials Against Blast Fragments

Penetrating trauma by energized fragments is the most common injury from explosive devices, the main threat in the contemporary battlefield. Such devices produce projectiles dependent upon their design, including preformed fragments, casings, glass, or stones; these are subsequently energized to high velocities and cause serious injuries to the body. Current body armor focuses on the essential coverage, which is mainly the thoracic and abdominal area, and can be heavy and cumbersome. In addition, there may be coverage gaps that can benefit from the additional protection provided by one or more layers of lightweight ballistic fabrics. This study assessed the performance of single layers of commercially available ballistic protective fabrics such as Kevlar^®, Twaron^®, and Dyneema^®, in both woven and knitted configurations. Experiments were carried out using a custom-built gas-gun system, with a 0.78-g cylindrical steel fragment simulating projectile (FSP) as the impactor, and ballistic gelatine as the backing material. FSP velocity at 50% risk of material perforation, gelatine penetration, and high-risk wounding to soft tissue, as well as the depth of penetration (DoP) against impact velocity and the normalized energy absorption were used as metrics to rank the performance of the materials tested. Additional tests were performed to investigate the effect of not including a soft-tissue simulant backing material on the performance of the fabrics. The results show that a thin layer of ballistic material may offer meaningful protection against the penetration of this FSP. Additionally, it is essential to ensure a biofidelic boundary condition as the protective efficacy of fabrics was markedly altered by a gelatine backing.

Defining the medical coverage of ballistic protection to the pelvis and thigh

INTRODUCTION

Pelvis, lower limb and associated genital injury caused by explosive devices was responsible for mortality and considerable long-term morbidity for the UK Armed Forces during combat operations in Afghanistan, resulting in the issue of a pelvic protection system in 2010. The aim of this current research was to determine the medical coverage of the pelvis and thigh and to define the vertical dimensions of ballistic protective material for future pelvic protection (PP).

METHOD

CT scans from 120 male UK Armed Forces personnel were analysed to identify the anthropometric landmarks and vertical boundaries of coverage for the pelvis and thigh. Pelvic height was the vertical distance between the upper border of the iliac crest in the midaxillary plane to the most inferior point of the ischial tuberosity of the pelvis. Upper thigh height was proposed as a 100 mm fixed distance below the ischial tuberosities, enabling a tourniquet to be reproducibly applied. These distances were compared with the ballistic component of the five sizes of tier 1 PP using a paired t-test.

RESULTS

The vertical components of coverage measured using CT scans were all significantly less (p<0.01) compared with all five sizes of tier 1 PP; for example, the ballistic component of the smallest size of tier 1 PP measured 410 mm, which was larger than the 99th percentile male, which measured 346 mm on CT scans.

CONCLUSIONS

While all sizes of tier 1 PP provide coverage to the pelvis and upper thigh structures, there is an opportunity to optimise future PP. For example, comparing the large size of tier 1 PP to the 50th percentile male demonstrated an opportunity to reduce the ballistic protective component by 31%. Reducing the quantity of material used will improve heat dissipation and user comfort and reduce material mass and acquisition costs.

Determining the optimum anatomical coverage of side plates for the VIRTUS body armour and load carriage system

INTRODUCTION

Side plates are worn by UK Armed Forces as part of the VIRTUS body armour and load carriage systems to protect the thorax and abdomen from high-velocity threats. The VIRTUS project has provided the impetus to objectively demonstrate the anatomical coverage provided by side plates.

METHOD

CT scans of 120 male UK Armed Forces personnel were analysed to ascertain the vertical distance between the anterior axillary fold and iliac crest, and horizontal distance between anterior and posterior borders of the liver, delineating the boundaries of essential medical coverage from the side aspects. The percentage of shot-lines intersected by the existing Enhanced Combat Body Armour (ECBA) plates as well as an optimised plate based on the maximum potential dimensions of essential coverage was determined in the Coverage of Armour Tool.

RESULTS

ECBA plates were 101 mm shorter and 4 mm narrower than a plate with dimensions providing essential medical coverage for the 50th percentile subject (157×315 mm). Coverage increased by 35% when using two ECBA plates as side coverage in addition to using the front and rear OSPREY plates in the VIRTUS vest. Two side plates with dimensions providing essential medical coverage for the 50th percentile increased anatomical coverage by a further 16%.

CONCLUSIONS

This analysis has provided strong evidence that ECBA plates are already optimised for side protection, despite not being originally designed for this purpose. They are correctly positioned within the VIRTUS soft body armour vest and the width of the ECBA plate is only 3% less than what would be optimum size for the 50th percentile. Although the height of the plate could be increased to further enhance the anatomical coverage, it is unlikely that this would be acceptable in terms of the human factors, equipment integration or additional mass.

Minimum depths to essential structures in a UK military population using computed tomography: application to stab-resistant body armour

INTRODUCTION

Edged weapons are a known domestic threat to the police forces of the UK. This threat is mitigated by wearing stab-resistant body armour that is either worn overtly or covertly depending on role. Although the UK military have traditionally focused their body armour design upon ballistic and fragmentation threats, future roles may require protection against an edged weapon threat. Since 2017, UK police body armour requirements for anatomical coverage for both edged weapon and ballistic threats are now based upon the requirements of UK military. This revised coverage may need additional research to determine minimum distances to essential structures.

METHOD

Three entry locations and penetration vectors were chosen using the limited available information in the literature, in combination with a specialist in edged weapons defence. One hundred twenty CT trauma scans of male military service personnel were subsequently analysed to ascertain minimum distances from skin surface to the first structure encountered that is included in essential coverage (heart, aorta, vena cava, liver and spleen) at 3 specific entry points.

RESULTS

Individuals ranged between 18 and 46 years, with a mean body mass index of 24.8. The absolute minimum depth from skin surface to a structure within the auspice of essential coverage was 17 mm to the liver in entry point 3 and 19 mm to the heart in entry point 2.

CONCLUSIONS

Minimum distances to critical structures were significantly larger than those described in previous studies on civilians. This study will be used to supplement existing evidence to support existing UK police requirements for stab-resistant body armour. Using the weapon entry sites and vectors described in this study, overmatching to a behind armour depth of 17 mm would cover all of this population in this study.

Modelling primary blast lung injury: current capability and future direction

Primary blast lung injury frequently complicates military conflict and terrorist attacks on civilian populations. The fact that it occurs in areas of conflict or unpredictable mass casualty events makes clinical study in human casualties implausible. Research in this field is therefore reliant on the use of some form of biological or non-biological surrogate model. This article briefly reviews the modelling work undertaken in this field until now and describes the rationale behind the generation of an in silico physiological model.

Optimising ballistic facial coverage from military fragmenting munitions: a consensus statement

VIRTUS is the first United Kingdom (UK) military personal armour system to provide components that are capable of protecting the whole face from low velocity ballistic projectiles. Protection is modular, using a helmet worn with ballistic eyewear, a visor, and a mandibular guard. When all four components are worn together the face is completely covered, but the heat, discomfort, and weight may not be optimal in all types of combat. We organized a Delphi consensus group analysis with 29 military consultant surgeons from the UK, United States, Canada, Australia, and New Zealand to identify a potential hierarchy of functional facial units in order of importance that require protection. We identified the causes of those facial injuries that are hardest to reconstruct, and the most effective combinations of facial protection. Protection is required from both penetrating projectiles and burns. There was strong consensus that blunt injury to the facial skeleton was currently not a military priority. Functional units that should be prioritised are eyes and eyelids, followed consecutively by the nose, lips, and ears. Twenty-nine respondents felt that the visor was more important than the mandibular guard if only one piece was to be worn. Essential cover of the brain and eyes is achieved from all directions using a combination of helmet and visor. Nasal cover currently requires the mandibular guard unless the visor can be modified to cover it as well. Any such prototype would need extensive ergonomics and assessment of integration, as any changes would have to be acceptable to the people who wear them in the long term.

Injury representation against ballistic threats using three novel numerical models

Injury modelling of ballistic threats is a valuable tool for informing policy on personal protective equipment and other injury mitigation methods. Currently, the Ministry of Defence (MoD) and Centre for Protection of National Infrastructure (CPNI) are focusing on the development of three interlinking numerical models, each of a different fidelity, to answer specific questions on current threats. High-fidelity models simulate the physical events most realistically, and will be used in the future to test the medical effectiveness of personal armour systems. They are however generally computationally intensive, slow running and much of the experimental data to base their algorithms on do not yet exist. Medium fidelity models, such as the personnel vulnerability simulation (PVS), generally use algorithms based on physical or engineering estimations of interaction. This enables a reasonable representation of reality and greatly speeds up runtime allowing full assessments of the entire body area to be undertaken. Low-fidelity models such as the human injury predictor (HIP) tool generally use simplistic algorithms to make injury predictions. Individual scenarios can be run very quickly and hence enable statistical casualty assessments of large groups, where significant uncertainty concerning the threat and affected population exist. HIP is used to simulate the blast and penetrative fragmentation effects of a terrorist detonation of an improvised explosive device within crowds of people in metropolitan environments. This paper describes the collaboration between MoD and CPNI using an example of all three fidelities of injury model and to highlight future areas of research that are required.

Angled shots onto body armour using 9 mm ammunition: the effect on potential blunt injury

INTRODUCTION

Some military specialists wear body armour that is more similar to police armour and provides protection from ammunition fired from pistols. During ballistic testing, these armours are mounted on a standardised type of modelling clay and the back face signature (BFS; depth of depression) formed as a result of the non-perforating impact event on to the armour is measured. This study investigated the effect of impact angle on the BFS and on the deformation of the bullet.

METHODS

Two commonly worn types of armour (HG1/A+KR1 and HG1+KR1) were considered that provide protection from pistol ammunition and sharp weapons. Armours were tested against two types of pistol ammunition (9 mm full metal jacket and 9 mm hollow point) at eight different impact angles (0°, 15°, 30°, 45°, 60°, 70°, 75° and 80°).

RESULTS

Increased impact angles resulted in smaller BFSs. Impact angle also affected whether bullets were retained in the armour; as the impact angle increased, the probability of a round exiting the side of the armour increased. Bullet deformation was affected by impact angle.

CONCLUSIONS

Understanding the deformation of bullets may assist with recreating a shooting incident and interpreting forensic evidence.