Landmines - A Resource
Background
Definition
History
The evolution of anti-personnel landmines has been towards a minimum quantity of metal to inhibit detection. The larger, buried blast AP landmines are big enough to very seriously injure or kill those whose step on them. Many however are small in explosive content and are designed to just wound the victim. A wounded soldier takes up more resources to evacuate and treat thus contributing to a slowing of the enemy’s advance.
Since WW2 the landmine has been used around the world, sometimes in planned, well marked minefields that help with post conflict clearance, but they have also been used indiscriminately leaving large swathes of country polluted and too dangerous to occupy or farm by the local population. Treaties have been put in place to ban their manufacture and use but not everyone signed up and millions of legacy landmines are still out there.
Estimates of over 100 millions mine emplaced worldwide.
71 countries afflicted with landmines.
2000 victims of landmines every month (one victim every 20 minutes)
Landmine Types
Anti Personnel Landmine Types
Bounding Mines:
These are designed to spring up to a height of about 1 metre and then fire out steel balls radially to hit the limbs and torso of the victim and anyone else within close proximity. Lethality and injury is driven by the fragments more than blast which dissipates quickly in such a free air, unconfined environment.
Stake and Claymore Mines.
These are both ground based fragmentation landmines. The stake mine acts radially whereas the Claymore is designed to be directional and is mostly used to protect occupied positions or specific route denial. The Claymore can be set to be victim operated or by demand by troops in defence.
Buried Blast Mines:
These are the ones that cause the biggest legacy and clearance problem. They are the ones mostly responsible for lower limb injuries and amputations. The charge size spans from the Russian PMN at 240g explosive content which is trying to kill the victim, through to the PMA-2 of with100g down to the M-14 US landmine with 28g which is designed to wound.
Anti Tank / Anti-Vehicle Landmines
Ground Effects
The ground in which a landmine is buried has a huge effect on how much blast energy it delivers to its victim.
The shock wave will propagate through the landmine from the detonation point but it will basically act as an expanding sphere of hot gas, driving a shock wave ahead of it. Dry, loose sand will allow the downward facing portion of this sphere to penetrate and dissipate with some minor reflection back upwards. Hard packed, sun baked earth or saturated clay are very resistant to such downward effects and reflect a lot this energy back upwards amplifying the energy delivered to the victim.
A lot of solid science was done on this subject by the DRDC in Canada with its pendulum arm. Establishing valid, repeatable ground conditions was a key factor in setting test standards for the assessment of protection measures for both anti-personnel and anti-tank landmines.
Anti Personnel Landmine Injuries and Treatment
Injury Patterns
Injury Distribution
Landmines can cause a variety of injuries, so it is important to have an understanding of where the predominant issues lie. The image shows the distribution of injuries observed during a HALO study in Kuito, Angola between January and October 1995. It can be seen that limb injuries are by far the most common form.
Pattern I: Injury Mechanism
Total disruption of foot / ankle complex.
Contamination of soft tissues higher up.
Propulsion of soil and fragments up tissue planes.
Contusion to muscles.
Amputation Level And Ongoing Function
An above knee amputation (left) requires about 100% more energy to walk.
Social Factors and Clinical Choices
An example of the potential long term reconstruction is the ‘Methods of Ilisarov’ which is focused on the long bones. After such effort it is not unheard of that the apparently healthy looking limb is largely insensate through nerve damage, even to the level that the owner is eventually driven to request an amputation.
A quality, modern prosthetic will actually provide more mobility and ongoing quality of life. Soft tissue and especially nerve damage is much harder to treat with current medical technology.
Surgical Treatment of Pattern I Injury
- General resuscitation of the patient with intravenous fluids or blood.
- High dose intravenous Benzyl Penicillin
- Ant-tetanus toxoid
- General Anaesthesia
- General Wash of the legs
- Use of above knee pneumatic tourniquet to minimise blood loss.
- Amputation above the level of devitalised and contaminated muscle.
- Thorough debridement of soft tissue injuries
- Leave the wounds open
- Bulky absorbant dressing
- Oral antibiotics post operatively
- Back to theatre at 5 days post op
- Closure of wounds if clean with no tension
- Skin grafts to large open areas
- Early physio to prevent knee joint contracture
- Further physio to develop upper body strength until prosthetic fitting
- Adequate prosthetic service with replacement follow up.
Anti Personnel Landmine Protection Measures
The Hands, Torso and Face
The majority of equipment designed for protection against buried AP mines is focused on the needs of those involved in their clearance.
The hands are are closest to the threat and are at risk of ‘de-gloving’ which involves the skin and tissue being stripped away by the blast. This can be mitigated by well fitted gloves using a high strength fibre such as an aramid. It is critical however that such protection must not reduce dexterity and ‘feel’. A lot of manual clearance uses prodding and such prodders can become secondary projectiles. Chris Moon MBE lost his hands when the prodder he was carrying was projected upwards through his hand. The integrated prodder and conical shield shown is a viable approach as it diverts the blast away from the hand and the materials used provide protection from the fragmentation. There will be some rapid loading applied to the hand and lower arm but this manageable and preferable to the alternatives.
The greatest proportion of landmines are in hot countries. To minimise the heat stress to deminers, most protective aprons and ensembles account for this by having an open back. It is assumed that if procedures are being followed, the threat will come from in front of the operator. The protection needs to facilitate ease of transition from walking to kneeling and lying prone. The prone position exposes the top of the shoulders to line of site of the blast which is accounted for by large shoulder pads.
The threat to the head and eyes is a combination of blast and fragmentation. Even small blast mines have a casing and throw out the dirt and stones in which they are buried. Lightweight, heat dissipating helmets provide support to impact resistant visors. These visors need to be highly scratch resistant so that the operator is not tempted to lift them (it does happen). If the visor is in a raised position it no longer stops fragmentation and it will capture blast pressure and rotate the head backwards. How injurious this is depends on the very specific circumstances of the individual event.
Footwear
The challenges associated with the protection of the foot and lower limb from buried blast mines are more complex than for other parts of the body. There is a direct coupling between the foot and charge, creating a load path for a lot of energy applied instantaneously. This energy needs to be managed whilst also preventing heat, gaseous and fragmentation effects. In this instance, the fragments can include the mine casing, the soil used to bury it, the sole of the footwear and bones of the foot itself being projected upwards into the rest of the leg.
Like any protection system, AP landmine protection footwear needs to balance conflicting demands. These are the protection level provided, the resulting mobility of the user and the financial aspect – the NGO demining community and even the military do not have limitless funds and have to provide the best affordable protection to the greatest number of users. There have been a number of attempts to produce effective mineboots and they have addressed the trade off in different ways. The models shown below were the key ones when we were actively involved in this area – some of the brand names have changed but after an initial surge in creativity, the market and its offering has not evolved much since.
MICS – Israel
This works on the basis of prevention being better than cure. The weight of the wearer is spread such that the ground pressure is not enough to trigger the device. It also provides some height stand-off between the device and foot. Later versions include some protective materials.
Spring Steel – Serbia
This was sent by allies in a mine action centre and included in a series of tests with human limbs. The protection was provided by a full sole of thin spring steel. It was the only system tested that made the injury worse than a standard combat boot. The steel sheet effectively collected the available energy and delivered it all into the structure of the foot. Image right is that limb post test.
Wellco Boot & Overboot – USA
An early entrant, this is now in a second generation. A boot and overboot of similar sole construction were available. The sole featured a shallow ‘V’ to deflect blast and that V was filled with crushable honeycomb to absorb some energy through mechanical work. Cadaver tests showed that it provided some protection against the smallest AP mines. The addition of the overboot added protection but reduced user mobility. The later version had broadly similar performance but was a more robust design and a better quality of build.
BFR Boot – Singapore
The BFR boot enjoyed commercial success in the early days of the expanding market. Looking like a normal combat boot with uppers to suit local climates and competitively priced it provides modest protection from smaller AP mines. It features an aramid fragmentation protection layer and mechanically compressible forefoot and heel section. These sections do dissipate some energy through mechanical work. The boot does not feature any shaping of the sole or stand off over and above a normal combat boot, so is reliant on this construction and materials alone. The trade off being towards mobility rather than protection is valid if that it is what the customer requires for their particular needs. For general military in a non- specialist mine clearance or combat engineering roles this is understandable. For dedicated high risk roles, less so.
Anonymate – France
This French entry into the market pushes the sole ‘V’ shaping and increased stand-off as the key to protection. The outlying blocks are for stability in normal use and detach quite easily under blast loading so as not to interfere with venting of the hot gases. Computer modelling of the flow of soil and gases under explosive loading has been extensive in investigating the performance of this design. Protection is reasonable but it is no longer a design suitable for general military use.
Zeeman – Germany
This was a later entry into the market and the design was decided upon after assessing the benefits and perceived shortcomings of existing designs. It goes for a materials rather than shape based solution with a manageable stand off along its length. Although it features a traditional looking boot upper, it is not suitable for infantry type roles. The published testing seen did not use suitably biofidelic limbs or instrumentation but its position in the performance spectrum can be broadly assessed from the mechanical limbs used.
PPE100 – United Kingdom
This design is intended for specialist demining high threat use from the outset. It uses blast mitigation material and a fragmentation protection layer in the sole, both of which also contribute to stand-off. The boot shell, based on a mountaineering boot provides good support to the ankle complex. A removable inner boot provides cushioning and can be replaced to extend the life of the system as a whole. Knee high integrated gaiters provide fragmentation protection to both the impacted limb and to the adjacent limb (Pattern II Injury). Development testing was undertaken with amputated human lower limbs, restricted to move in a single vertical axis. Different instrumentation was employed to investigate correlations between measurements and clinical outcome. Work on this project contributed to improvements in design of biofidelic mechanical surrogates. This work also led to the invitation of Steve Holland and Eddie Chaloner onto the NATO Human Factors in Medicine, Technical Group TG024 to help define better test procedures.
Med-Eng, Spider Boot – Canada
Built around decoupling and stand off the Spider boot is a modern iteration of an ad-hoc design from World War II. There is no direct load path from the landmine to the foot and the ‘leg’ that impacts the mine will be blown away ensuring disconnection. Larger than one might, think the footplate hinges to aid movement but this is definitely a design that emphasises protection over mobility. It is a deliberate positioning in a niche sector of the market place without compromise. In this, it is very effective.
Ranking
Anti Tank Landmine Damage and Injury Mechanisms
There are many ways in which hitting an anti tank/vehicle landmine can result in death and injury and some of the key, predictable ones will be discussed here. Outside of these key issues there is always the unpredictable nature of the road traffic accident you are about to have even if you survive – this can end up in a side impacts, a rollover, fire and has even resulted in death by drowning in irrigation ditches.
The most obvious mechanism is that the blast breaches the floor of the vehicle, directly exposing the occupants to very high blast overpressure, heat and fragmentation. The torn and damaged floor structure can contribute to that fragmentation. Just outside of where the floor is breached it can undergo excessive deformation into the lower limbs and back of the occupants.
The next two mechanisms are in which the floor essentially maintains its integrity but with consequences. A rigid vehicle floor can act like a thick drum skin and undergo high speed vibration which kicks up anything that was sitting on the floor such as poorly stowed equipment. The tools shown in the image with the crash test dummy were left on the floor deliberately to illustrate this point. This has been used to illustrate the importance of discipline in equipment stowage. The rapid, local floor deformation and shock transmission can be enough to cause such tension in the back face of the floor that metal ‘scabs’ to come away and be thrown upwards at high speed.
A vehicle can be designed to resist the blast shock wave that would result in hull breach, and so look as as if it has defeated the landmine. The impulse of the explosive event might still be sufficient to lift and throw the vehicle. This rapid upwards acceleration creates a range of potentially lethal human factors which have become the focus of a lot of vehicle blast mitigation design, both in terms of the overall structure and internal fit out.
Human Factors and Vehicle Impulse
Lower Leg
Thoraco-Lumber Spine
Cervical Spine
There are two very different criteria relating to the neck. The first is axial compression, which is similar to the DRIz at the lower spine in terms of the acceleration/time relationship and the second is forward/rearward turning moment (whiplash).
An interesting issue with this is the helmet. It is obviously required protect the skull from all the rapid movements and potential impacts that can happen during a landmine event. In terms of neck axial loading it does eat up headroom which, depending on the vehicle layout, can increase the chance of hitting the ceiling and adding to the axial load.
The mass of the helmet itself will provide some inertia to the combined mass supported by the neck. This will contribute moderately to the axial load and in a much bigger way to the turning moment at the neck. Tests are conducted with the head in an upright position but should the occupant be leaning forward, this whiplash effect would be much more significant.
Overpressure Effects
For both closed and open topped vehicles, overpressure can be injurious. The mandatory criteria looks beyond the effect on pressure sensitive ears to the more life threatening mechanism of chest wall velocity and the transfer of shock to the lungs and other internal organs.
The short duration of this pressure loading means that air in the lungs cannot vent though the mouth and nose. Because of this, the chest wall moves inwards, the internal pressure increases, the chest and abdomen become stiffened and so provide increased resistance to further inward movement. This complex relationship is calculated by an established chest wall velocity prediction calculation that uses input from an external chest mounted pressure gauge. For simplicity this pressure gauge is set on the outer face of any body armour that the ATD will be wearing.
Anti Vehicle / Tank Landmine Protection Measures
Floor Shaping
Blast Mitigation Materials
Blast mitigation used in connection with ballistic materials, offer a weight advantage over steel and have been for retrofit solutions both in the NGO demining support support sector and for deployed military vehicles as part of an enhancement package. To see more on the SJH Projects XPT material and the Mineshield Click Here
Seating
Footpads
Active Systems
Testing and NATO Technical Groups
Historically, the protection of vehicles and personnel against blast has been an active area of research interest amongst the NATO members and other key players such as the Australians. The active member countries sometimes worked on joint programmes and sometimes alone. For each programme the test aims, start conditions, measurement regime and interpretation was determined locally with valid assumptions. The issues arose in trying to directly compare results from one test with another performed elsewhere. It also resulted in tests having to be repeated around NATO to meet each members specific criteria. This was hardly efficient and was inhibiting the build up of useful large data sets.
To address this shortcoming, an Exploratory Team meeting ET007 was held at the Queen Astrid Military Hospital in Brussels in February 2000. This meeting included the research communities for vehicles and for dismounted personnel at risk of stepping on AP mines. The outcome of this meeting was the setting up of Technical Group 024 (TG-024) which would focus on anti-personnel landmines and TG-025 which would focus on underside blast threats to vehicles. Both would have to address similar issues in setting up a suitable test frameworks but did not always draw the same conclusions.
TG-024
Test Limb Surrogates
Mechanical Surrogates
Animal Models
Human Cadaver
Isolated Human Limb
Computer Modelling
Frangible Surrogate Limb
The FSL or ‘Frangible Surrogate Leg’ is designed to mimic the behaviour of a human leg under the rapid loading experienced when you step on an anti-personnel landmine or are in a vehicle hit by an IED.
By having bones that break at the same levels and in the same way as human bones and by taking measurements of the forces experienced, it provides invaluable information to both clinicians and engineers. This data will help in the development of systems to protect the lower limb for both mounted and dismounted personnel in areas in which landmines and buried IEDs may be found.
To see more on the FSL Click Here.
Complex Lower Limb
Test Conditions
TG-024
Testing the underside of military vehicles against buried landmines is a complex and expensive business. Not having to repeat it to meet the individual requirements for each potential customer within NATO is desirable. They key survivability criteria have been discussed above and the 50th percentile Hybrid III ATD is the tool of choice. Properly set up ATDs measure much more than the mandatory criteria and so provide a more complete record of the experience from the occupant perspective.
Options for additional instrumentation around the vehicle are not critical, but are often used to better understand the mechanical behaviour of the vehicle as a structure. Typically such additional measurements can include pressure gauges, strain gauges, accelerometers and displacement gauges. Multiple real time cameras and specialist high speed cameras are very useful for analysis and determining the order of events, desirable and otherwise.
The outcomes from TG-025 formed the basis the NATO document AEP55 Volume 2: “PROCEDURES FOR EVALUATING THE PROTECTION LEVEL OF ARMOURED VEHICLES – VOLUME 2: MINE THREAT”
Test Conditions
Ground Preparation
TG-025 adopted a specfically graded mix of sandy gravel with defined compacted density and moisture limits as standard ‘NATO soil’. The mix is isolated from its surroundings in a robust, lined pit. The pit size is normally 2 x 2 x 1.5m deep but can be altered depending on the likely crater size. Detailed preparation, repeated compaction and inspection means that such pits can take a team a couple of days to complete. It has become practice with some ‘National Authorities’ to have the completed pit fully saturated just before the test to maximise the blast effects.
Charges and Positioning
AEP55 Volume 2 links to Stanag 4569 in setting standardised threat levels. Unlike the TG-024 panel, which selected military PE as it fill, TG-025 chose cast TNT. As the power of most explosives are referred to in terms of their TNT equivalence, this does have an academic simplicity. In practical terms however cast TNT is not simple to obtain, adds significant cost and logistical burden and those that have used it will be aware that shrinkage and micro-cracking can make it unreliable. Most tests are now conducted with military PE using a TNT equivalence for buried charges.
The depth of burial, position and orientation of the detonator and exactly how the charge is buried in relation to the vehicle wheel or track are carefully defined. In every instance, the National Authority of the country concerned is at liberty to deviate from the standardised procedures but usually only does so for specific purposes.
Mine Clearance and Disposal
