A bulletproof vest – also called body armour (U.S. body armor) – is an article of protective clothing that works as a form of armour to minimize injury from being hit by a fired bullet. They are commonly worn by police forces and the military.

The above name is somewhat of a misnomer since most such protective vests are of little or no protective value against rifles regardless of the type, style, materials or caliber of the rifle ammunition (ammo) or even against handgun caliber ammo fired from a rifle. (The exception is the common .22 LR, which can usually be stopped by these vests even when fired from a rifle.) These vests are generally protective against handgun ammo fired from handguns--again, regardless of type, style, materials or caliber of the handgun ammo.

Some types of vests may be augmented with metal (steel or titanium), ceramic or polyethylene plates that provide extra protection to vital areas. These "trauma plates" have proven effective against all handguns and some rifles, if the bullet actually hits the plate. These types of vests have become standard in military use, as advances in ballistic technology have rendered kevlar-only vests ineffective - The CRISAT NATO standard for vests includes titanium backing. Some vests are also designed to protect against knife attacks as well. This is done by coating the outer surface of the vest with tiny crystals of a sandpaper-like material or hiding a very thin plate of resin hardened glass-fibre sheet between the kevlar layers. This is important for the safety of law enforcement and prison guard personnel.

The most recent U.S. military-issue body armour, the Interceptor Multi-Threat Body Armor System issued in the late 1990's, has small-arms protective inserts made of ceramic which can stop, shatter, and catch 7.62 mm rifle rounds.

A vest does not protect the wearer by deflecting a bullet. Instead, the individual layers of material catch the bullet and spread its momentum over a larger portion of the body, deforming the round and hopefully bringing it to a stop before it can penetrate into the body. While a vest can prevent a bullet from penetrating, the wearer can still be affected by the kinetic energy of the bullet, with results ranging from bruises to serious internal injuries.

History

The oldest bulletproof fabric was made from silk. This was capable of stopping some slow rounds from black powder guns. A more modern "flak jacket" was developed in World War II from nylon fabric but was only capable of stopping flak and shrapnel, not bullets. Modern bulletproof vests made from Kevlar were tested by United States police forces in 1975. Since then several new fibers for bulletproof fabric have been developed besides Kevlar, such as DSM's Dyneema, Akzo's Twaron, Toyobo's Zylon (now controversial, as new studies report it that degrades rapidly, leaving wearers with significantly less protection than expected (http://www.policeone.com/Zylon/)), or Honeywell's GoldFlex. These newer fibres are advertised as being lighter, thinner and more resistant than Kevlar, although much more expensive.

Performance standards

Both the Underwriters Laboratories (UL Standard 752) and the United States National Institute of Justice (NIJ Standard 0101.04 (http://www.nlectc.org/pdffiles/0101.04RevA.pdf)) have specific performance standards for bulletproof vests. The US NIJ rates vests on the following scale against penetration and also blunt trauma protection (deformation) (Table from NIJ Standard 0101.04 (http://www.nlectc.org/pdffiles/0101.04RevA.pdf)):

Bomb disposal officers often wear heavy armor designed to protect against most effects of a moderate sized explosion, such as bombs encountered in terror threats. Full head helmet, covering the face and some degree of protection for limbs is mandatory in addition to very strong armour for the torso. An insert to protect the spine is usually applied to the back, in case an explosion blasts the wearer. Visibility and mobility of the wearer may be severely limited.

In terms of Kevlar, a IIA vest has around sixteen layers and a IIIA vest around thirty layers.

German standards allow for bullet impact depression of 20 millimeters on the mannequin's wax body under the vest, the US standards allow for more than twice that (44 millimeters), which can be potentially lethal.

In addition, there are vests available for police dogs which offer a measure of protection for the animals.

A vest's material must not get wet, because it will lose its protective capability until dry again, or in some cases be permanently degraded (water acts as a lubricant, helping the bullet slip through between the fibres). Most bulletproof vests have panels in sealed enclosures, but waterproofing is usually not perfect.

See also

• PASGT, US Military standard personnel armour
• physics of firearms
• ballistics

External links

• Photo of an injury typical among soldiers wearing Kevlar vests to protect the chest and abdomen:

http://www.nejm.org/_IMAGES/2004/20041209/pe8.gif