The Testing of a New "Mine Protection Boot"
During fall 2003 the Austrian Armed Forces Hospital Vienna (HSP) and the Engineer School’s (PiTS) Mine Information Centre tested a new design concept for blast protection of the lower extremities from landmine blasts.
Landmines have commonly been used in military conflicts since the end of World War II. Their wide distribution in almost all modern theatres of war in all parts of the world stems from the simplicity of production, affordability, and easy way of distribution in the field. More than 100 million landmines are buried in more than 80 countries throughout the world, and two to five million new landmines are planted every year. The humanitarian problems associated with uncleared antipersonnel landmines are well known. The most common and severe injury is caused when a person activates a buried landmine by stepping on its pressure plate. According to the International Committee of the Red Cross classification this is called a Pattern 1 injury. The explosion results in traumatic amputation of at least part of the limb directly caught by the detonation and in fragmentation damage to the contralateral leg, which often also requires amputation of that limb. The extent of the damage is related to the size of the charge in the mine.
Contemporary design-concepts to reduce the severity of the trauma sustained in a Pattern 1 injury are based primarily on two considerations. One design relies on a combination of ballistic composites, for example Kevlar and honeycombed light metals to absorb or deflect the blast, the other is based on an exaggerated standoff simply to distance the foot from the explosive. A number of products are available, but none of these designs have been tested accordingly for clinical effectiveness. We conducted, therefore, a series of tests with one of the latest designs for blast protection - a combination of blast attenuation, deflection and increased standoff. The effectiveness of the protection was tested by placing human legs in the boot and by detonating various charges below the boot.
Other types of protective body armour currently used to protect the lower extremities against blast injury are the so-called "spider" boots and the "Yugoslav" mine protection boot. "Spider" boots are based on the concept of increased standoff and absorption. The design looks like Styrofoam square snowshoes measuring 50 x 70 x 30 cm strapped to the standard combat boot. The boot is used by several armies in explosive ordinance disposal (EOD)/demining teams. The effectiveness of this design has not been described in official publications yet. In addition, the boot drastically reduces the user’s mobility. The "Yugoslav" mine protection boot used by the Serbian Army is based on the concept of blast deflection and is, by design, a standard combat boot with an additional steel plate in the sole of the boot. This plate does not provide extra protection against landmine blasts because the steel is too thin and it is even an extra source of metallic fragments.
Tested Material and Testing Methods
The tested mine protection boot (Figure 1) comprises a Koflach (ATOMIC Austria GmbH, Austria) outer boot incorporating TABRE® (AIGIS Engineering Solutions Ltd., UK), an inner boot, and a fragmentation protection gaiter. TABRE (Technology for Attenuating Blast Related Energy) is a resin-bonded, porous aggregate composite. In this test 20 mm of TABRE® and 10 mm of Dyneema (ballistic composite protecting from fragment penetration) were attached to the sole of the Koflach outer boot. The fragmentation gaiter is made of Kevlar. It covers the whole limb, is fixated by a bootstrap around the heel and tightly fastened with a string below the knee. The gaiter weighs approximately 250 g and is flexible (Figure 2).
Four human lower extremities were obtained from patients who had donated their bodies to scientific research. The approval of the ethical committee was obtained for the scientific experiment. The explosive trials were conducted under the supervision and command of the Engineer School’s Mine Information Centre. This included instrumentation, explosives handling, monitoring, and filming by the Armed Forces Photo and Video Production Service (HBF). At the test site three of the legs obtained were dressed in standard army battle dress uniform and socks before the mine protection boots and fragmentation protection gaiters were put on. The fourth extremity was donned a standard combat boot and designated as reference leg. The test rig was a specifically constructed steel tripod. The leg was suspended freely in the middle of the so-created pyramid (Figure 2). In addition, a weight of 75 kg was loaded onto the hip in order to simulate a standard male soldier with full combat equipment stepping on a mine. Due to the regulations of the Ottawa Landmine Ban Treaty, of which our country is a signatory, no landmines were available. Therefore, we simulated the effects of a landmine blast by using equivalent charge sizes of trinitrotoluene (TNT). Below the boot 50 g or 100 g of TNT were positioned under the heel. The test site was located on non-agricultural soil at the rim of a forest, ideal infantry terrain for laying antipersonnel landmines. The TNT was remote-controlled detonated by a standard army detonator (Figure 3). The whole firing process was recorded by a digital recording system for later analysis. The first firing was done with 100 g TNT under a TABRE mine protection boot (TABRE boot). In this firing session a second tripod with a suspended TABRE booted leg was positioned behind the first leg with a distance of 20 cm between the two thighs. In this way we tried to simulate the gait of a walking soldier, thereby expecting to obtain data of what happens to the contralateral limb during and after detonation. The third TABRE boot was tested with 50 g TNT and the reference standard combat boot was subjected to a 50 g TNT load. After completion of the test firing, all extremities and blasted-off organic parts were collected, remaining in battle dress uniform. Then they were subjected to a computed tomography (CT) scan. This CT enabled us to investigate the damage done to the skeletal structure of the foot in the boot. With the help of Siemens Medical Division, digitally computed three-dimensional models of the injured legs were created.
Results
All TABRE-protected lower extremities directly subjected to the blast hyperextended at the knee during firing. Fractures of these legs showed a pattern of multiple fractures of the heel, open fractures of the lower third of the shinbone, also called tibia, and fractures of the fibula as well as of the tibial plateau. The important finding was that the leg was not amputated, at least the tendons and muscles remained intact. The unprotected reference leg was totally amputated by the blast at the height of the lower third of the shinbone.
The TABRE boot-protected limbs were observed to overextend, leading to an exarticulation of the knee joint. 0.06 seconds after the firing, the bones in the knee joint were snapped back to its anatomical position. During the whole event the soft tissue cover of the leg as well as the ballistic gaiter and uniform remained macroscopically intact.
The thick multilayered rubber and leather sole of the standard combat boot melted at firing (X) and larger parts of the skeleton and the upper boot, especially the metallic eyelets, became a part of the particle beam pushing straight upwards. At X + 0.02 seconds, the foot including the boot was amputated. A spear-like protruding shinbone was the most distant visible part of the extremity. At X + 0.08 seconds the extremity’s excursion was finished. At X + 0.12 seconds, the remnants of the forefoot, primarily the skin and muscles of the dorsal side of the foot, were observed landing on the ground, exactly 0.04 seconds after the rest of the leg. For macroscopic comparison of the outcome between standard combat boots and TABRE protection see Figures 4 and 5.
After firing, the TABRE protected boots kept their shape, the bodies of the outer boots were not breached, and the inner boots remained intact. The soles were destroyed, the rubber and TABRE layer had melted, and the Dyneema plate remained undamaged and fixed to the outer boot. This finding correlates with the design concept. The porous, resin-bonded aggregate composite TABRE is designed to absorb heat and blast energy. The gaiters were pierced with small metallic and non-metallic particles on the outside, the inner surface, however, was not penetrated.
Conclusion and Outlook
As a conclusion the test suggests that the development of footwear with integrated gaiter to protect against antipersonnel mine (blast mine) is feasible. The latest design shows a clear improvement compared to standard combat boots - the observed fractures, however, still represent severe injuries. From medium mines up to charges with the equivalent of 100 g of TNT, limb salvage may be possible but a prevention of all injuries from landmines cannot be ruled out at the current state of technological and research progress. The long-term clinical effects after primary limb salvage have to be assessed after real battlefield employment of the TABRE boot. The physical integrity of the contralateral limb is given when protected with the TABRE system.
In the near future the Austrian Armed Forces Hospital and the Mine Information Centre want to continue the testing of different blast protection models, and also plan to intensify their cooperation and research in blast protection and prevention as well as the treatment of landmine blast victims.
Authors: 1Lt Klaus Stephan Wolff, MD, Austrian Armed Forces Hospital, and Maj Günter Deutsch, Mine Information Centre.