Bulletproof Kevlar has strength in numbers

Some of the secrets behind the material that saved a Baltimore officer's life last week.

For The Record

July 30, 2000|By Jonathan Pitts | Jonathan Pitts,Sun Staff

When Detective David F. Azur of the Baltimore Police tried to make a car-theft arrest last Monday, he encountered every officer's worst nightmare: an armed suspect who shot him at point-blank range.

Azur, though, was wearing Kevlar body armor under his shirt and sustained mere bruises to the chest. He became one of roughly 1,500 U.S. police officers whose lives have been saved by body armor since the International Association of Chiefs of Police began keeping track in 1987.

Most police body armor is made of Kevlar, a high-strength industrial fiber discovered by a chemist at the DuPont Co. in 1964. A chemical compound known as a polymer, Kevlar is closely related to materials used to manufacture Frisbees, toilet seats and two-liter soda bottles. It first became available for commercial use in 1975.

Some other facts and figures about Kevlar:

* DuPont chemist Stephanie Kwolek -- one of only 12 female researchers at the company in 1964 -- discovered the compound by accident. Anticipating a possible gasoline shortage, she and co-workers were seeking a lighter-weight material to reinforce car and truck tires.

* A polymer is a chain made of many similar molecular groups called monomers. Those monomers are bonded together much in the way boxcars are in a train. Each Kevlar monomer contains 14 carbon atoms, 2 nitrogen atoms, 2 oxygen atoms and 10 hydrogen atoms.

* The polymer chains in Kevlar are arrayed in parallel fashion, much like uncooked spaghetti strands in a box. This orderly, untangled arrangement of molecules, called a crystalline structure, accounts for much of Kevlar's strength and rigidity. It is, in fact, one of the strongest materials in the world. Its tensile strength measures at 525,000 pounds per square inch, as compared with 36,000 psi for steel. Specialty tools must be made to cut Kevlar.

* DuPont manufactures Kevlar in 62-inch-wide bolts that cost $29 per yard.

* Some body armor is made of Spectra, an alternative synthetic fiber manufactured by Honeywell Inc. It is lighter and more expensive than Kevlar.

* Objects made of polymers (not necessarily Kevlar) include Frisbees, trash bags, rubber bands, Scotch tape, hearing aids, toothbrushes and disposable razors.

* Kevlar is also used in trampolines, fiber-optic cables, radial tires, boat hulls, tennis rackets, high-pressure hoses, airplane parts, firefighters' protective gear, repair putties, fishing line, windsurfing sails and parachutes, among many other products. It also serves as a replacement for asbestos in brake linings and gaskets and as a reinforcing agent in concrete.

* Kevlar is extremely fire- and heat-resistant. Its melting point is 1,200 degrees Fahrenheit.

* The average Kevlar vest contains 21 layers of the material in both the front and the back. Stacked together, those 42 layers are less than a quarter-inch thick.

* The National Institute of Justice lists four stages of toughness in body-armor vests: threat-level I is the lightest, threat-level IV the most heavy-duty. The stronger a vest is, the more it costs. A threat-level II vest, the typical grade in police body armor, repels high- velocity 9mm bullets or .357 magnum bullets and costs $330.

* A typical threat-level II Kevlar vest weighs between 4 and 6 pounds, depending on the size of the officer. Kevlar vests can irritate the skin of some wearers and can be very hot. Houston manufacturer 21st Century Hard Armor and other manufacturers are experimenting with various "cool-pack" designs, some of which hold ice or cooling gels, to decrease the heat.

* In most jurisdictions, a manufacturer or distributor can legally sell body armor to any customer. 21st Century sells mostly to law-enforcement agencies, private security agencies and police suppliers. "We try never to sell to civilians," says Robert King, company vice president. As the year 2000 approached, 21st Century Hard Armor received dozens of orders from unaffiliated civilians across the country. In each case, company officials notified local law-enforcement agencies of the transactions.

* Locally, both Maryland Police Supply in Baltimore County and the Cop Shop in Baltimore sell only to authorized law-enforcement officials.

* The Bulletproof Vests Partnership, a federal agency, provides funding for police body armor. In municipalities of fewer than 250,000, the partnership will cover as much as 50 percent of the cost of such armor.

Sources: DuPont Co.; Lawrence Berkeley National Laboratories; U.S. Department of Justice Response Center; Massachusetts Institute of Technology; Smithsonian Institution; Baltimore Police.

Baltimore Sun Articles
|
|
|
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.