How Blast-resistant Clothing Works

At this very instant, these three scenarios may be unfolding:

A suspicious package is discovered outside a federal building
An Improvised Explosive Device (IED) is being planted alongside a road in Iraq or Afghanistan
An English farmer is about to accidentally unearth an exploded shell from World War II

When bombs, unexploded ordnance (military equipment that includes artillery, cannons and other equipment) or threatening devices are found, they must be neutralized, disarmed, moved or exploded in a safe and controlled manner.

Robots can sometimes be used for these tasks, but all too often the job calls for the expertise, bravery and rock-steady hands of an explosive ordnance disposal (EOD) technician. The term "EOD" is most often used by the military; civilian and law enforcement agencies refer to these devices as unexploded ordnances, or UXO.

Most people dress for work in some combination of cotton and khaki, but an EOD technician wears anything from ceramic plates to Kevlar, the material used in bulletproof vests. Various manufacturers create many different types and designs of bomb suits and other blast-resistant clothing. However, all of them share common components, such as body armor and helmets.

While your typical bomb suit is too bulky, hot and expensive for even the most over-cautious civilian to wear on a trip to the grocery store, blast-resistant clothing is constantly evolving to fit the needs of the people that wear it. There are three main groups of people whose lives depend on blast-resistant clothing:

Military
Civilian/law enforcement
Humanitarians working in war zones

Soon, this clothing may incorporate anything from nanotubes to special materials that thicken as they're stretched out. But before we get much further into our discussion of what blast-resistant clothing is made of and how it protects, let's take a look at the bombs it protects against.

What happens when bombs explode? How can they injure and hurt us? And how does blast-resistant clothing anticipate and protect against these injuries? Find out in the next section.

How Bomb Blasts Cause Damage

A bomb is basically some type of casing or shell that contains explosive material. The casing can be anything from a steel-walled artillery shell to a glass bottle or a sealed-shut length of lead pipe. It can even be as ordinary as a coffee tin or an automobile. Once the casing is penetrated by the force of the explosion, it will fragment outward, each piece of the shell serving as a deadly projectile. The explosive material inside the shell could be any type of high explosive, be it TNT or Semtex. (You can read more about bombs in How Bombs Work.)

A bomb causes damage in several different ways, depending on the point at which the explosion impacts. These different points include the blast wave, shock waves, fragmentation, heat and the blast wind.

Blast wave: When a bomb explodes, the area around the explosion becomes overpressurized, resulting in highly compressed air particles that travel faster than the speed of sound. This wave will dissipate over time and distance and will exist only for a matter of milliseconds. This initial blast wave inflicts the most damage. When this blast wave reaches a structure or person, two things will initially happen. First, the person will feel the force of the blast, which is the primary and initial impact of the shockwave. This will damage a structure or body on impact.
Shockwaves: After a blast wave strikes a surface or body, high-velocity shockwaves, or stress waves, will continue to pass through -- in the body, they travel through the organs and tissues. Shockwaves carry energy through the medium they pass through; they're supersonic and transport more energy than sound waves. Currently, there are no effective ways to prevent shockwaves from passing through protective clothing, and in some cases protective measures may even amplify the destructive effects [source: Skews].
Fragmentation: When the bomb explodes, the bomb casing, as well as any additional shrapnel (nails, screws or other items included in the bomb), will be violently thrown outward and away from the explosion. When these fragments strike buildings, concrete, masonry, glass and even people, they may fragment even further -- and cause even more damage. This is known as secondary fragmentation.
Fire and heat: The explosion may also create a fireball and high temperatures, which will result in burns on a human body or even cause secondary fires or explosions, depending on whether any other fuel sources or flammable materials are located near the blast.

Blast wind: At the explosion site, a vacuum is created by the rapid outward movement of the blast. This vacuum will almost immediately refill itself with the surrounding atmosphere. This creates a very strong pull on any nearby person or structural surface after the initial push effect of the blast has been delivered. As this void is refilled, it creates a high-intensity wind that causes fragmented objects, glass and debris to be drawn back in toward the source of the explosion.

So what can you wear to protect yourself against a blast? Find out in the next section.

Shellshock

Military neurosurgeons are reporting an increase in brain injuries caused by shockwaves and blast wind. The massive change in pressure can result in lasting neurological damage, but this damage can be difficult to diagnose because victims may appear physically unharmed. A 2005 report from Walter Reed Army Medical Center indicates that two-thirds of all wounded soldiers who are unable to immediately return to active duty suffer from injuries to the brain [source: Glasser].

Blast-resistant Suits

A blast-resistant suit provides the most comprehensive protection against a blast. When a bomb strikes a blast-resistant suit, the force is diminished by the suit's tightly woven fibers. These fibers spread the blast's force throughout the suit. Ballistic plates help deflect force and repel the shrapnel and secondary fragmentation. The heat and flames produced by a bomb will be neutralized by the flame-resistant quality of the suit. You can read How Body Armor Works and How Liquid Body Armor Works for further explanation.

Let's look at the materials and components that do the diffusing.

Bomb suits are made of Kevlar or some other aramid-based product. Aramid (the generic name for Kevlar) consists of synthetic fibers woven from polymers -- large molecules made from strands of smaller molecules called monomers. Aramid's outstanding strength-to-weight ratio makes it an ideal fabric for bulletproof and blast-resistant clothing.

Additional foam or other padding may be incorporated throughout the bomb suit. This offers protection to the wearer not only from flying debris, but also from the force of impact that occurs when the wearer of the suit is thrown to the ground.

The garment has internal pockets consisting of webbing and Velcro inside which ballistic plates can be inserted. These plates are made of steel, aramid or coated ceramic. They're designed to protect the wearer from fragmentation.

Bomb suits also include these protective features:

A blast-resistant helmet may be constructed with an aramid core, some type of molded protective outer layer and a suspension harness for comfort. Helmets have a clear, anti-ballistic visor, and some have built-in headphones and a microphone, as well as the ability to transmit signals. These specialized helmets may have an internally powered ventilation system that cools the wearer and de-mists the visor. There may also be brackets where the technician can mount a hands-free video camera or light.
A high collar protects the neck and extends up to the helmet.
Overshoes are typically sewn onto the bomb suit and fit over the technician's footwear.
Generally arranged to protect the throat, chest and groin areas, blast plates can also be placed inside internal pockets on the front of the arms, legs and ribcage.
Blast-resistant clothing typically includes quick-release straps to free an injured technician from the material for easier transport or medical aid.
Since the heat inside a bomb-resistant suit can become unbearable, some incorporate internal cooling mechanisms. These devices circulate water collected from a melting ice pack throughout a network of tubes that are sewn into the suit or into a vest worn beneath the suit.

Although great advancements are being made in blast-resistant clothing, there are limits to the level of protection such materials can afford an individual. If a bomb is big enough, and you are close enough to it, there may be nothing that can prevent the damage the bomb blast and resulting fragmentation and shockwaves will do to you. No materials or structures are ever entirely bombproof.

For some professions, it's not practical to wear a full blast-resistant suit every day on the job, but it's still necessary to have protection against bombs and IEDs. How do these professionals protect themselves? We'll learn about some other blast-resistant options on the next page.

Other Blast-resistant Options

Not everyone who encounters a bomb will be fully garbed in a blast-resistant suit. An exposed turret-gunner in an armored vehicle that's passing a roadside bomb is at as great a risk as an EOD technician tasked with approaching and disarming a similar device. Both must wear blast-resistant clothing -- but different kinds to fit their needs. Law enforcement officers and FBI officials will also need to protect themselves on the job. No matter what type of bomb they may encounter -- pipe bomb, letter bomb, truck bomb or unknown explosive device -- local law enforcement agencies and the FBI must risk their lives to disable the weapon.

Humanitarian relief workers also need protection when demining a landmined nation or delivering supplies to the people who live there. Two protective accessories they use include anti-mine boots and demining aprons.

Anti-mine boots are used by those who demine minefields or who must work near or pass through heavily mined areas. These boots have soles that are several inches thicker than those of regular boots. Tabre is another material that's sometimes used in soles. Tabre is constructed from tiny, resin-coated grains of stone and is designed to diffuse the force of the blast. When the shock wave strikes the network of tiny stones, its energy is forced through the maze they form, which releases and decreases energy [source: BBC]. Boots may also incorporate materials like steel plates as well as Kevlar to protect the foot against penetration from shrapnel or debris.

Demining aprons are also used in humanitarian missions -- often carried out by the United Nations -- that involve clearing of heavily mined areas within war-torn nations. The demining apron provides protection where a person needs it most: in the front, neck, shoulder and groin area. Much like a chef's apron, there is no back to this garment (the wearer doesn't need protection from the rear), which cuts down on its weight and excessive heat it generates.

In the next section, we'll take a look at some of the blast-resistant materials and technologies of tomorrow and beyond.

Other Blast-resistant Developments

Buildings can be reinforced with Paxcon, a polymer that is sprayed on walls to strengthen surfaces against blasts and to hold broken pieces in place if a projectile strikes [source: Sofge].
Blast doors, constructed with two steel plates that sandwich a cavity containing a steel rebar grid that's backfilled with concrete, can be sealed to keep out chemicals -- even liquid napalm.
Blast-resistant glass and blast curtains hold broken shards in place to protect people inside a bombed building as well as people outside the building, who can be struck with debris when the blast wind hits. The curtains are also fire-retardant.
Bomb blankets deflect the force of a blast and prevent fragments of the bomb from striking bystanders.
Bombproof buses are being developed in Israel to limit the carnage caused by suicide bombers who detonate explosives after boarding a bus. Many buses are already armored and feature blast-resistant windows. Special turnstiles, exit-only backdoors and bomb sensors are also being tested.
Bombproof trashcans diffuse the force of the blast, preventing fragmentation from injuring bystanders and directing the blast upward instead of outward.

Blast-resistant Technology of the Future

There are several new and emerging technologies in the explosive ordnance disposal (EOD) field. Let's examine a few of them.

Shaped plates. The United States Army is conducting tests on advanced body armor it hopes to distribute to soldiers by 2012, if not sooner. These vests utilize six ballistic plates as opposed to the current two. Additionally, the plates are specially shaped -- a design that leaves less unprotected space between plates provides more protection to the spine [source: Schogol].
Zetix. Zetix is a material manufactured by the company Auxetics Technologies, Ltd. It actually increases in size as it's stretched out. Picture a length of bungee cord. If you stretch it out, it gets thinner. However, if you wrap a piece of twine around the bungee cord and draw the twine taut, the weave effectively becomes thicker. This is the idea behind auxetics. When these auxetic fiberwraps are bundled together, the bundles also get thicker when stretched out. Such a fabric could be used in blast resistance in many different capacities. If it were used to construct a blast curtain, the helix-shaped structures could be constructed of steel, titanium or carbon fiber. It could potentially allow the force of the blast to pass through the fabric while the fabric itself expands, preventing tears in the blast curtain and to more effectively protect against fragmentation.

Liquid armor. Liquid body armor is not actually liquid -- it consists of Kevlar plates that have been dipped in a sheer thickening liquid. When force is applied to this substance, it hardens and then liquefies again within a few fractions of a second. When Kevlar has been soaked in this substance, it becomes many times more powerful.
Nanotubes. Carbon can be bonded in different ways that create entirely new properties. Nanotubes are seamless, cylindrical tubes of carbon molecules that can be as small as one-billionth of a meter wide -- yet up to 60 times stronger than steel. Cloth woven from nanotubes may provide for incredibly efficient body armor -- more resistant to projectiles than steel, yet light enough to provide protection for the entire body [source: Neff].

For more information on bomb, blast-resistant technology and other related information, visit the links on the next page.

Back to the Beginning

The advancement of bomb disposal techniques has progressed out of necessity at a pace roughly equal to the advancement of the bomb itself.

In World War I, the increased manufacture and use of artillery shells led to many "duds" -- unexploded ordnance (UXO). These duds had to be safely removed from both the battlefield and civilian areas. This, in turn, necessitated the advent of bomb disposal units. In the beginning, the training was mostly done on the job: Disarming the ordnance was a new and extremely dangerous task.

In World War II, the Nazis created new sources of confusion and calamity by designing bombs that behaved like duds, but were, in fact, set on long timers or designed to explode when the shell casing was breached by a UXO member. The bomb disposal teams effectively became the target of the bombs. This led to a lethal match between the bomb-makers and the UXO technicians.

Since then, bomb disposal advancements and methods have been held to the highest levels of secrecy so that bomb designers will find it harder to circumvent the efforts of the UXO teams.

Lots More Information

Sources

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American Forces Press Service. "The Bomb Suit's Always Been a Matter of Trust." 25 May 2001. http://www.defenselink.mil/news/newsarticle.aspx?id=45831
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