Effect of ballistic impacts on batteries and the potential for injury.

INTRODUCTION: On military operations, ballistic impact damage is possible to lithium ion (Li-ion) batteries worn on the body by military personnel and the potential for exothermic reactions may result in injury. This paper investigated the effect of impact on batteries that might be worn in front or behind body armour. METHODS: Li-ion batteries were subjected to ballistic impact both without and in combination with body armour using 7.62×39 mm ammunition (mean velocity=769 m/s) at charge levels up to 40%. The effect of penetrating impacts on charged batteries was also investigated using an outdoor range. RESULTS: The backface signature due to ballistic impact was reduced by including a battery pack between fabric body armour and an armour plate, however the batteries were crushed and mechanically disrupted. Ballistic impacts on batteries mounted in front of an armour plate resulted in perforation of the batteries. Increases in temperature, fire and toxic gas emission were noted when batteries were penetrated by an impact. CONCLUSIONS: Batteries provided limited ballistic protection disproving the hypothesis that batteries could replace or enhance existing body armour solutions. Ballistic impact of charged batteries could lead to injury due to heat/flame and toxic discharge. It is recommended that batteries need to be carried in a position from which they can be rapidly removed from contact with the body.

A systematic review of military head injuries.

INTRODUCTION: This commissioned review discusses military head injuries caused by non-ballistic impacts, penetrating fragments and bullets (including parts of bullets) and behind helmet blunt trauma (BHBT). METHOD: A systematic review of the literature was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses method. The openly accessible literature was reviewed to investigate military head injuries and their severity. RESULTS: Fifty-four sources were identified that included pertinent openly accessible information relevant to this topic. Limited injury data exist for non-ballistic head injuries for UK forces, although some international data exist for parachutists. The majority of fatal head injuries are due to projectiles penetrating through the face rather than through the area of the head covered by the helmet. Penetrating head injuries are primarily caused by fragments, but helmets are more commonly perforated by high-energy rifle bullets than by fragments. No reports of a BHBT injury have been located in the literature. CONCLUSIONS: The description of body segment varies among articles and this makes comparisons among datasets difficult. There is a lack of detail regarding the precise position and severity of injuries, and long-term outcome for casualties. It is demonstrated that wearing military helmets reduces fatalities on and off the battlefield. The risk of BHBT injuries is widely referred to, but evidence of their occurrence is not provided by the authors that describe the risk of BHBT occurring. Further research into the causes and severity of head injuries would be useful for designers of military helmets and other associated personal protective equipment, particularly as advances in materials technology means lighter, thinner and more protective helmets are achievable.

Is behind armour blunt trauma a real threat to users of body armour? A systematic review.

INTRODUCTION: Behind armour blunt trauma (BABT) has been defined as a non-penetrating injury caused by the rapid deformation of body armour. There has been an increasing awareness of BABT as an injury mechanism in both the military and civilian worlds; whether BABT results in serious injuries is debatable. METHOD: A systematic review of the openly accessible literature was conducted using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses method to investigate those injuries classified as BABT and their severity. RESULTS: 50 sources were identified that included pertinent information relevant to this systematic review on BABT injuries. Typical injuries reported included skin contusion, laceration and penetration, rib fracture and contusions to lungs, kidneys, spleen and (rarely) the heart. No evidence of fatal injuries due to BABT was identified. CONCLUSIONS: Whether BABT can lead to life-threatening injuries when small-arms ammunition impacts body armour components designed to stop that ammunition is debatable. It should be emphasised that other data may be available in government reports that are not openly available. Further research should be considered that investigates developments in body armour, including initiatives that involve reducing burden, and how they affect BABT.

The effect of fabric and stabbing variables on severance appearance.

During a stabbing, apparel fabrics are usually damaged and may be penetrated. Despite numerous studies considering forces required to penetrate skin and human stabbing performance, none have systematically evaluated which variables affect severance appearance from a textile science perspective using a human stabbing participant assessment. Although the human performance aspects of stabbing attacks have been previously studied, there has been a bias towards male assailants. The effects of fabric elasticity and tension applied have been identified as major factors influencing the severance profile in the fabric resulting from a stab attack. However, previous studies have considered limited fabric types with little emphasis on the physical and mechanical textile properties. The purpose of the current research was to use a human participant study (male n=5; female n=5) to determine the effect of fabric extension (0%, 10%) on the severance profile. Fabric type (single jersey; 100% cotton; 93% cotton/7% elastane), age (not laundered; laundered 60 times) and knife type (carving, bread) were also considered. Severance length was affected by participant sex, fabric type, laundering and knife type. The severances formed in this study were not significantly affected by the amount a fabric was extended when stabbed. Variability was observed in the severance appearance among participants where prior training influenced the angle of impact and knife withdrawal technique.

Gunshot induced indirect femoral fracture: mechanism of injury and fracture morphology.

INTRODUCTION: Indirect ballistic fractures occur when a projectile passes close to, but not contacting, the bone. The mechanism of how these fractures occur is not yet proven, but recently the acoustic shockwave has been excluded as a cause. The objective of this study is to determine whether the expanding temporary cavity, the collapse of this cavity or its oscillation causes these fractures. In addition, we describe the fracture morphology and biomechanical causes of this injury. METHOD: 40 fresh deer femora were strain gauged and embedded in ballistic gelatin before being shot with four different projectiles with varying distances off the bone. Pressure recordings, chronographs and radar allowed assessment of local pressures and energy transfer. High-speed video allowed the temporal relationship between the temporary cavity and fracture formation to be analysed, while sample dissection allowed the fracture morphology to be described. RESULTS: The fractures produced were consistently wedge-shaped and caused by the expansion of the temporary cavity, flexing the bone beyond its yield point, causing tension failure on the cortex opposite the expanding temporary cavity and a compression wedge on the side of the cavity. Local pressure was not predictive of fracture formation but the energy transfer to the gelatin block was predictive. CONCLUSIONS: Indirect fractures are caused by the expansion of the temporary cavity and relate to the proximity of this cavity to the bone. Fractures occur from flexion of the bone and classically display wedge-shaped fracture patterns with the apex of the wedge pointing away from the expanding cavity.

Identifying the source of bullet wipe: a randomised blind trial.

OBJECTIVE: To assess the usefulness of scanning electron microscopy and energy dispersive x-ray spectroscopy in matching bullet wipe to the bullet. HYPOTHESIS: Bullet wipe can be used to match a bullet type to a crime scene.

Face, neck, and eye protection: adapting body armour to counter the changing patterns of injuries on the battlefield.

Recent international papers have suggested an urgent need for new methods of protecting the face, neck, and eyes in battle. We made a systematic analysis to identify all papers that reported the incidence and mortality of combat wounds to the face, eyes, or neck in the 21st century, and any papers that described methods of protecting the face, neck, or eyes. Neck wounds were found in 2-11% of injuries in battle, and associated with high mortality, but no new methods of protecting the neck were identified. Facial wounds were found in 6-30% of injuries in battle, but despite the psychological effects of this type of injury only one paper suggested methods for protection. If soldiers wore existing eye protection they potentially reduced the mean incidence of eye injuries in combat from the 4.5% found in this analysis to 0.5%. Given the need to balance protection with the functional requirements of the individual soldier, a multidisciplinary approach is required. Military surgeons are well placed to work with material scientists and biomechanical engineers to suggest modifications to the design of both personal and vehicle-mounted protection. Further research needs is needed to find out how effective current methods of protecting the neck are, and to develop innovative methods of protecting the vulnerable regions of the neck and face.

The development of a quantitative flexibility test for body armour and comparison with wearer trials.

In this paper a mechanical flexibility test is developed which can be used to assess multi layer body armour systems. This is compared with a subjective manual test, and then with the results of wearer trials conducted using the recently approved ISO body armour standard ISO 14876-1 (2002). A series of trials was conducted on six different ballistic and/or stab resistant body armour types with a variety of protection levels and constructions. These were tested using the mechanical test system in which the armour was forced through a 200 mm hole by a 100 mm hemispherical plunger. The results of this test were then compared to a second set of trials in which flexibility of the same armour was assessed by manual handling and flexing of the armour. Finally an ergonomic wearer trial was conducted with four armours according to ISO 14876-1 (2002) each armour being assessed by four volunteers and the results compared to flexibility data collected in the first two trials. It was shown that the mechanical flexibility test produced results which were in good agreement with a purely subjective flexibility assessment. These results in turn showed reasonable but not exact correlation with the wearer trials. The ISO wearer trials addressed other factors such as overall comfort and fit of the systems and so the results were not purely a function of flexibility.

Wounding patterns and human performance in knife attacks: optimising the protection provided by knife-resistant body armour.

BACKGROUND: Stab attacks generate high loads, and to defeat them, armour needs to be of a certain thickness and stiffness. Slash attacks produce much lower loads and armour designed to defeat them can be far lighter and more flexible. METHODS AND SUBJECTS: Phase 1: Human performance in slash attacks: 87 randomly selected students at the Royal Military College of Science were asked to make one slash attack with an instrumented blade on a vertically mounted target. No instructions on how to slash the target were given. The direction, contact forces and velocity of each attack were recorded. Phase 2: Clinical experience with edged weapon attacks: The location and severity of all penetrating injuries in patients attending the Glasgow Royal Infirmary between 1993 and 1996 were charted on anatomical figures. RESULTS: Phase 1: Two types of human slash behaviour were evident: a 'chop and drag' blow and a 'sweep motion' type of attack. 'Chop and drag' attacks had higher peak forces and velocities than sweep attacks. Shoulder to waist blows (diagonal) accounted for 82% of attacks, 71% of attackers used a long diagonal slash with an average cut length of 34 cm and 11% used short diagonal attacks with an average cut length of 25 cm. Only 18% of attackers slashed across the body (short horizontal); the average measured cut length of this type was 28 cm. The maximum peak force for the total sample population was 212 N; the maximum velocity was 14.88 m s(-1). The 95 percentile force for the total sample population was 181 N and the velocity was 9.89 m s(-1). Phase 2: 431 of the 500 patients had been wounded with edged weapons. The average number of wounds sustained by victims in knife assaults was 2.4. The distribution of wounds by frequency and severity are presented. CONCLUSIONS: Anti-slash protection is required for the arms, neck, shoulders, and thighs. The clinical experience of knife-attack victims provides information on the relative vulnerabilities of different regions of the body. It is anticipated that designing a tunic-type of Police uniform that is inherently stab and slash resistant will eventually replace the current obvious and often bulky extra protective vest. Attempts at making a combined garment will need to be guided by ergonomic considerations and field testing. A similar anatomical regional risk model might also be appropriate in the design of anti-ballistic armour and combined anti-ballistic and knife-resistant armour.

An assessment of human performance in stabbing.

Stab-resistant body armour is now becoming a standard item of equipment for police officers in the United Kingdom. In the UK these are usually required to have a stab resistance as specified by the Police Scientific Development Branch KR42 standard [G. Parker, PSDB Stab Resistant Body Armour Test Procedure, Police Scientific Development Branch, Publication No 10/93, 1993]. There are several other test standards, all of which specify that body armour must resist penetration by a specific blade type delivered at a specific energy level or range of levels. However, the actual range of energy levels specified varies over almost an order of magnitude and the basis for these levels is not clearly defined. This paper describes tests to determine the energy range and characteristics of stabbing actions that might be directed against stab resistant body armour by an assailant. The energy and velocity that can be achieved in stabbing actions has been determined for a number of sample populations. Volunteers were asked to stab a target using an instrumented knife that measured the axial force and acceleration during the stabbing. The maximum energy obtained in underarm stabbing actions was 64 J whilst overarm stabbing actions could produce 115 J. The loads produced on contact with the target often approached 1000 N.