Researching Kevlar Bullet Proof VestsBy 1973, researchers at the Army's Edgewood Arsenal responsible for the bullet proof vest design had developed a garment made of seven layers of Kevlar fabric for use in field trials. It was determined that the penetration resistance of Kevlar was degraded when wet. The bullet resistant properties of the fabric also diminished upon exposure to ultraviolet light, including sunlight. Dry-cleaning agents and bleach also had a negative effect on the antiballistic properties of the fabric, as did repeated washing. To protect against these problems, the vest was designed with waterproofing, as well as with fabric coverings to prevent exposure to sunlight and other degrading agents.
Medical Testing of Body ArmorThe third phase of the initiative involved extensive medical testing to determine the performance level of body armor that would be necessary to save police officers' lives. It was clear to researchers that even when a bullet was stopped by the flexible fabric, the impact and resulting trauma from the bullet would leave a severe bruise at a minimum and, at worst, could kill by damaging critical organs. Subsequently, army scientists designed tests to determine the effects of blunt trauma, which is injuries suffered from forces created by the bullet impacting the armor. A byproduct of the research on blunt trauma was the improvement of tests that measure blood gases, which indicate the extent of injuries to the lungs.
The final phase involved monitoring the armor's wearability and effectiveness. An initial test in three cities determined that the vest was wearable, it did not cause undue stress or pressure on the torso, and it did not prevent the normal body movement necessary for police work. In 1975, an extensive field test of the new Kevlar body armor was conducted, with 15 urban police departments cooperating. Each department served a population larger than 250,000, and each had experienced officer assault rates higher than the national average. The tests involved 5,000 garments, including 800 purchased from commercial sources. Among the factors evaluated were comfort when worn for a full working day, its adaptability in extremes of temperature, and its durability through long periods of use.
The demonstration project armor issued by NIJ was designed to ensure a 95 percent probability of survival after being hit with a .38 caliber bullet at a velocity of 800 ft/s. Furthermore, the probability of requiring surgery if hit by a projectile was to be 10 percent or less.
A final report released in 1976 concluded that the new ballistic material was effective in providing a bullet resistant garment that was light and wearable for full-time use. Private industry was quick to recognize the potential market for the new generation of body armor, and body armor became commercially available in quantity even before the NIJ demonstration program.