I had to know how these blast-resistant suits worked in real life — so I called up Pravit Borkar, a ballistics engineer at HighCom Security, a firm that manufactures EOD suits for military applications, and asked him to explain.
How a Bomb Kills You
The “EOD ensemble,” as Borkar calls it, is not simply a body-condom version of a Kevlar vest: “It’s a complex composite product consisting of both rigid and soft armor systems.” These two fundamental layers are designed to defeat the two main threats in an explosion: the overpressure pulse, or shockwave; and the fragmentation, commonly known as shrapnel.
The overpressure wave is actually the more dangerous of the two. A microsecond after a bomb goes off, the explosion compresses the surrounding air and blows it outward in a lightning-fast shockwave that ripples through clothing and literally flattens internal organs. Guy Pearce’s character experiences it firsthand at the end of The Hurt Locker’s tense opening sequence:
“You see that the technician gets knocked down well before the debris hits him,” says Borkar. “But how is he killed? That’s power of the overpressure wave: because he was relatively close to the device when it exploded, the pulse has probably punctured or collapsed his lungs.”
How the Suit Keeps You Alive
The EOD suit’s rigid outer armor layer, the first and most important defense against this threat, is composed mainly of aramids: high-tech synthetic materials that are “strain-rate sensitive.” In other words, “the faster something hits them, the harder they become,” says Borkar. (Kevlar is simply the brand name of an aramid manufactured by DuPont.) The entire front-facing portion of the suit is reinforced from head to toe with hardened composites of two or more aramids, optimized for strength and lightness. This rigid layer can literally reflect or bounce some of the overpressure energy away from the technician, while also repelling flying fragmentation.
But the overpressure wave inevitably passes through the rigid armor layer. It then encounters the “anti-coupling material”: a foamy layer of polyurethane or synthetic rubber that absorbs as much of the pulse as possible, like the crumple zone on a car. “It breaks the blast wave,” says Borkar. “These materials will not allow the pressure to pass through without dramatically attenuating it — ideally down to a level that is actually survivable when it reaches your body.”
Behind the anti-coupling layer, closest to the wearer, lies the soft armor: flexible fabric woven or knit from aramid fibers and other materials, which Borkar refers to as the “catcher’s mitt.” By now the overpressure wave has been reduced as much as it’s ever going to be, so this layer mainly acts like a traditional bulletproof vest — it stops any remaining fragmentation that may have penetrated the rigid outer armor. NASA’s space suits also contain soft aramid layers to resist impacts from flying micrometeoroids — the astronaut version of shrapnel.
This three-layer system is amazingly effective, but no EOD suit is perfect. With every step you take closer to the bomb, the destructive force of its blast increases by an exponent of three. “So the difference between being just a small distance away from the explosive device — even a few feet — versus being right next to it, can save your life,” Borkar says.
So, approaching the bomb in an EOD suit is a method of last resort. But here’s how each part of it is designed to give you a fighting chance.
The Helmet and Collar
The “strike face” of the helmet is where the action happens: it’s transparent so the technician can see what he’s doing, and it also takes the brunt of the explosion should anything go wrong. It’s made of a hardened acrylic on top of a softer polycarbonate “catcher’s mitt” layer facing the wearer. (If the faceplate were simply constructed of rigid acrylic all the way through, an explosion could shatter it into the technician’s face.) The helmet is also equipped with anti-fog coating, a lamp, video camera, and a two-way communication link (wireless or tethered) with the technician’s commander.
The fin-like appendage on the helmet houses a forced ventilation fan, which blows fresh air over the technician’s face to relieve perspiration. But Borkar says that this might be one detail that The Hurt Locker got a bit wrong. “In our helmets we try not to add extraneous devices that will change the its geometrical configuration, because the blast wave will just knock that off,” says Borkar. “I don’t know what manufacturer they got that helmet from, but it was a little surprising to see that extending out and up. Normally it would be placed behind the helmet so it wouldn’t face the brunt of the blast.”
The super-high, aramid-reinforced neck collar that surrounds the helmet is the EOD suit’s version of insurance: all its moving parts are designed to heavily overlap with each other, ensuring 100% coverage no matter what position the technician contorts himself into. If the helmet were fused with the collar, the tech would have to turn his whole body, Darth Vader-style, just to look left or right.
The hard-armor plates that cover the tech’s torso, groin and thighs act as the primary absorbers of fragmentation, but their main function is to deflect the deadly overpressure wave. “The suit in the movie didn’t show it, but in the real world, these plates are shaped like flattened boomerangs to literally reflect the pulse energy out and away from the technician,” says Borkar. Since techs usually squat or sit on their knees while working, this rigid armor is thickest around the groin and inner thighs (to protect the femoral artery).
These plates can also be switched in and out depending on the requirements of the mission at hand and the expected blast force of the bomb. The military keeps copious records on the “survivability” of various organs under different magnitudes of overpressure, so EOD techs in the field can configure their armor to provide the optimal amount of protection to each specific area of the body while reducing the overall weight of the suit. “There’s a strategy to configuring the armor before deploying it,” says Borkar. “It’s highly modular, not ‘one size fits all.'”
Boots and Gloves (or lack thereof)
EOD boots have soles reinforced with soft armor and boomerang-shaped titanium plates to reflect blast pressure away. The suits also come with flame-resistant gloves — but in practice, few technicians wear them, preferring the subtle sensitivity of bare fingers instead. “That’s realistically portrayed in the film,” says Borkar. “The truth is, if you’re close enough to a bomb to be touching it with your hands and it goes off, no gloves are going to help you.”
You can’t see it in the film, but underneath all this gear is the EOD tech’s best friend: a flame-resistant inner layer that circulates ice water all over the body. (Defusing bombs in 120-degree Iraqi heat is stressful enough without adding risk of heatstroke to the mix. This layer is also similar to the water-cooled garments that NASA astronauts have worn inside their space suits since the Apollo missions.) The cooling suit runs off of the same onboard battery that powers the suit’s lamp, fan, and comm link; a pump circulates a liter of ice water (stored in a specially shaped bottle) from head to toe. According to Borkar, techs keep an extra bottle on ice in the field so they can swap in new water when the first bottle gets warm. There’s no built-in refrigeration mechanism, but HighCom is developing a next-generation EOD suit that will integrate the cooling system into the entire ensemble — one less thing to worry about when the clock is ticking.
So What is it Like to Actually Wear This Thing?
Current suits on the market weigh anywhere from 60 to 70 pounds, and all that armor plating makes moving around pretty difficult. If there’s any gripe that Borkar has about in The Hurt Locker’s mostly-accurate portrayal of the EOD suit, it’s this: “The techs just walk far too easily.” That opening scene where Guy Pearce hoofs it away from the exploding bomb? Fat chance: according to Borkar, just walking in these suits feels like carrying an anvil between your legs.
Of course, that doesn’t stop real-world EOD technicians from trying. The current world record for running one mile in a full bomb suit was recently set by Staff Sgt. Jeremy Herbert, the explosive ordnance technician team leader for Marine Wing Support Squadron 271: nine minutes and 58 seconds flat! That cooling layer must have been working overtime.
Courtesy : DVICE