Military

Body Armor

Body Armor is a bullet resistant metal or other material worn by a person to provide protection from weapons or bodily injury.

Moving at 2600 feet per second-more than twice the speed of sound, a bullet hits its target with as much energy per unit area as a 50-ton truck traveling faster than 200 miles an hour. This is because the bullet's much lower energy is focused into an even smaller area. If the target is a human being, the consequences can be deadly.

Body armor technology has advanced in the past century to protect the head and torso against high-velocity handgun bullets and fragmenting munitions, such as those from artillery shells, mortar shells, mines and grenades. The nylon "flak" vest for ground troops and steel helmet from the 1960s were replaced by Kevlar vests and helmets during the 1980s in a product called Personnel Armor System, Ground Troops (PASGT). At the users' request, performance increased with the PASGT system but weight remained about the same.

During the Vietnam War, 70 percent of casualties with penetrating chest wounds and 33 percent of casualties with penetrating abdominal wounds died. Throughout Operation Iraqi Freedom and Operation Enduring Freedom, as of March 2005 only 5 percent of casualties resulted from torso wounds. Reducing the number of penetrations in this region has a significant effect on reducing the total fatality rates. The large reduction in fatalities from torso injuries can be directly attributed to the improved protection provided by the combination of the improved body armor being worn by Marines on the battlefield today as well as the amazing medical care that is available so close to the combat zones.

Police officers run the risk of being targets at any time. To lower their risk of death, many officers wear protective vests made of very strong, specialty materials such as Kevlar or Spectrashield synthetic fibers, which are stronger than steel. The current generation of "bulletproof" vests, employed both by the law enforcement and military communities, evolved from the development of body armor using Kevlar,TM which was sponsored by NIJ (then the National Institute of Law Enforcement and Criminal Justice of the Law Enforcement Assistance Administration) in the late 1960s and early 1970s.

The current generation of of body armor was developed specifically to protect against injury from assault with handguns. The use of lightweight protective body armor has been widely used by law enforcement personnel for nearly 30 years. During that time the US Department of Justice, Office of Justice Programs, National Institutes of Justice (NIJ), estimated that its use has saved the lives of more than 2,700 officers by 2005.

Another type of body armor is a "bulletproof" vest with titanium or ceramic inserts that offers some rifle and bullet protection. This armor affords rifle fire protection over the entire area that it covers. Work is currently on-going to develop hard-facing surfaces to increase the properties of titanium for use as body armor. Ceramics are rapidly becoming the material of choice for many armor applications including body armor. Sophisticated body armor with ceramic plates provides a margin of safety for our troops in a dangerous environment.

Lightweight Body Armor, a new technology developed for the Department of Defense, can stop 30-caliber armor piercing bullets yet has an aerial density of only 3.5 pounds per square foot. To make the new self-adjusting reinforced helmets and body armor, which can be tailored to fit the mission, researchers used a new boron-carbide ceramic plate that weighs 10 to 30 percent less than conventional armor and delivers equal or greater protection.

In the early days of the war on terrorism, there was a shortage of interceptor armor. The services issue body armor to those most in need of it; however, some servicemembers -- both active and reserve component -- bought their own protection. Some active duty soldiers and reservists spent as much as $650 out of pocket to buy Interceptor Body Armor vests and small arms protective insert plates to replace the Vietnam era flak vests issued when they arrive in Iraq.

Legislation passed by Congress in 2005 authorized the services to reimburse servicemembers for the expenditures. The legislation applies to a specified set of personal protection equipment and can be claimed "by either the member or by another person on behalf of the member for the member's personal use in anticipation of, or during, the member's deployment for operations Noble Eagle, Enduring Freedom or Iraqi Freedom."

In October 2005 David S.C. Chu, the undersecretary of defense for personnel and readiness, approved the directive that allows servicemembers to be reimbursed "for privately purchased protective, safety or health equipment." The order covers the period between Sept. 10, 2001, and Aug. 1, 2004. Pentagon officials said "relatively few" servicemembers are affected by the order.

Reimbursement is limited to the actual purchase price, plus shipping, of the equipment, and servicemembers must have the receipts. Under the legislation, those claiming reimbursement must turn in their privately purchased gear. The services will destroy the equipment, as it may not meet government standards. Under the policy, reimbursement cannot exceed $1,100 for any one piece of equipment.

The services can request to add items to the list. The list includes the complete outer tactical vest or equivalent commercial ballistic vests. The components of the vest -- the groin protector, throat protector, yoke and collar assembly, collar protector, ballistics inserts and small arms protective inserts -- are covered individually. The list also includes the Kevlar helmet, ballistic eye protection and hydration systems.

How Body Armor Works

When an individual is hit by a bullet, the extent of the injury sustained depends on where the bullet strikes the body and the path or trajectory of the bullet into or through the body. Injury to the vital organs is most often fatal. Thus, the armor's primary and most obvious purpose is to prevent a bullet from penetrating the torso.

In the case of hard armor, such as metal, rigid reinforced plastic, or ceramic materials, it is possible to use armor of such a thickness that it does not appreciably deform from the bullet impact. If, however, the armor that covers the torso deforms from the bullet impact, the surface of the armor against the body at the point of impact will be forced against or into the skin.

Unlike a penetrating wound, in which the skin is broken and the bullet tears through the body, the deformation of armor from bullet impact results in blunt trauma. This type of nonpenetrating injury can cause severe contusions (bruises) or internal damage and can even result in death. Standard also evaluates the capabilities of the armor to prevent injury from blunt trauma.

When a handgun bullet strikes body armor, it is caught in a "web" of very strong fibers. These fibers absorb and disperse the impact energy that is transmitted to the vest from the bullet, causing the bullet to deform, or "mushroom." Additional energy is absorbed by each successive layer of material in the vest, until such time as the bullet has been stopped.

Because the fibers work together both in the individual layer and with other layers of material in the vest, a large area of the garment becomes involved in preventing the bullet from penetrating. This also helps in dissipating the forces that can cause nonpenetrating injuries (what is commonly referred to as "blunt trauma") to internal organs. Unfortunately, at this time no material exists that would allow a vest to be constructed from a single ply of material.

The reliability body armor is directly related to their use and maintenance. Ballistic-resistant material, including Zylon®, can degrade due to environmental factors, thus reducing the ballistic resistance safety margin that manufacturers build into their armor designs. Visual inspection of body armor and its ballistic panels does not indicate whether a particular piece of Zylon®-containing body armor has maintained its ballistic performance.

It is likely that the ballistic performance degradation in Zylon®-containing armors is closely related to the chemical changes in poly-p-phenylene benzobisoxazole (PBO), the chemical basis of Zylon® fiber. The breakage of one particular part of the PBO molecule, known as the oxazole ring, correlates with degradation of the mechanical properties of Zylon® fibers. The breakage in the oxazole ring can be monitored using an analysis technique known as Fourier transform infrared (FTIR) spectroscopy. Preliminary investigations into Zylon® degradation mechanisms have suggested that oxazole-ring breakage occurs as a result of exposure to both moisture and light. When there was no potential for external moisture to contact Zylon® yarns, there was no significant change in the tensile strength of these yarns. External moisture may be necessary to facilitate the degradation of Zylon® fibers.

Today's generation of concealable body armor can provide varying levels of protection to defeat most common low- and medium-energy handgun rounds. Body armor designed to defeat rifle fire is of either semirigid or rigid construction, typically incorporating hard materials such as ceramics and metals. Because of its weight and bulkiness, it is impractical for routine use by uniformed patrol officers and is reserved for use in tactical situations, where it is worn externally for short periods of time when confronted with higher level threats.




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