Police Body Armor Standards and Testing,

Vol. I

August 1992

OTA-ISC-534

NTIS order #PB92-216100
Recommended Citation:

U.S. Congress, Office of Technology Assessment, Police Body Armor Standards and Testing:

Volume I, OTA-ISC-534 (Washington, DC: U.S. Government Printing Office, August 1992).

For sale by [he U.S. Government Printing Office

Superintendent of Documents, Mail Stop: SSOP, Washington, DC 20402-9328

ISBN 0-16 -037987-3
Foreword

For two decades, the number of police officers shot to death each year has been declining

while the number of officers shot has been increasing. The decrease in the lethality of

shootings is partly attributable to the increase in wearing of bullet-resistant body armor,

especially soft, inconspicuous armor designed to be worn full-time.

A prospective purchaser can see how much of the body an armor garment covers but

cannot see whether it will stop a particular kind of bullet at a particular velocity and protect

the wearer from the impact. To provide benchmarks for protection, the National Institute of

Justice issued NIJ Standard 0101.03 in 1987. It specifies standard procedures for testing

samples of armor. If samples of a model pass, the NIJ or the manufacturer may certify that the

model has the type of ballistic resistance for which it was tested.

The standard has been controversial since it was issued. This Report describes the origin

of the standard, the rationale for particular provisions, and the main points of controversy,

which concern acceptable risks, the validity and discrumination of the test, and the

reproducibility of results. OTA finds that resolving these controversies will require specifying

acceptable risks quantitatively, performing additional research to test validity, and implementing a quality-control program.

To date, all armor of NIJ-certified models has performed as rated in service-but so has

uncertified armor, including armor that would fail the test specified by the standard. This has

provoked charges that the NIJ test is too stringent and fails to discriminate some safe armor

from unsafe armor. The validity and discrimination of the test are technical issues that are

susceptible to scientific analysis—if the NIJ specifies maximum acceptable risks quantitatively. The Report describes illustrative specifications of acceptable risks and an experimental

method for deciding whether the current test, or any proposed alternative, limits the risks as

required. It also describes and compares several options for a quality-control program.

This assessment was requested by Senator Joseph R. Biden, Jr. (Chairman), Senator

Strom Thurmond (Ranking Minority Member), Senator Dennis DeConcini, and Senator

Edward M. Kennedy of the Senate Committee on the Judiciary, Congressman John Joseph

Moakley, Chairman of the House Rules Committee, and Congressman Edward F. Feighan of

the House Committee on the Judiciary and of its Subcommittees on Crime and on Economic

and Commercial Law.

u JOHN H. GIBBONS

Director

iii
Police Body Armor Standards and Testing

Advisory Panel

Lester B. Lave, Panel Chair

James H. Higgins Professor of Economics

Graduate School of Industrial Administration

Carnegie-Mellon University

George N. Austin, Jr.

National Officer

Fraternal Order of Police

Lane Bishop

Statistician

Center for Applied Mathematics

Allied-Signal, Inc.

Alfred Blumstein

Dean and J. Erik Jonsson Professor of

Urban Systems and Operations Research

School of Urban and Public Affairs

Carnegie-Mellon University

Michael Bowman

Vice President and General Manager

Fibers Department

E.I. duPont de Nemours & Co., Inc.

Milton Brand

President

The Brand Consulting Group

James T. Curran

Professor and Dean for Special Programs

John Jay College of Criminal Justice

City University of New York

Donald R. Dunn

President

H.P. White Laboratory, Inc.

Martin Fackler

President

International Wound Ballistics Association

Michael A. Goldfarb

General Surgeon

Monmouth Medical Center

David C. Hill

President

Fibers Division

Engineered Materials Sector

Allied-Signal, Inc.

Max Henrion

Member of the Technical Staff

Rockwell International Science Center

Alexander Jason

Ballistics Consultant

ANITE Group

Harlin R. McEwen

Chief

Ithaca Police Department

Isaac Papier

Managing Engineer

Burglary Detection and Signaling Dept.

Underwriters Laboratories, Inc.

Richard Stone

President

Point Blank Body Armor, Inc.

Dieter Wachter

Vice President of High-Performance Fabric

Clark-Schwebel Fiberglass Corp.

Robert Wantz

President

Personal Protective Armor Association

NOTE: OTA appreciates and is grateful for the valuable assistance and thoughtful critiques provided by the advisory panel members.

The panel does not, however, necessarily approve, disapprove, or endorse this report. OTA assumes full responsibility for the

report and the accuracy of its contents.

iv
OTA Project Staff—Police Body Armor Standards and Testing

Lionel S. Johns, Assistant Director, OTA

Energy, Materials, and International Security Division

Alan Shaw, International Security and Commerce Program Manager

Michael B. Callaham, Project Director

Brian McCue, Senior Analyst

Jonathan Tucker, Analyst (through May 1991)

Administrative Staff

Jacqueline Robinson Boykin

Office Administrator

Louise Staley

Administrative Secretary

v
Acknowledgements

OTA gratefully acknowledges the assistance of the following individuals and organizations for their help

in supplying information or in reviewing drafts of portions of this report. The individuals and organizations

listed do not necessarily approve, disapprove, or endorse this report; OTA assumes full responsibility for the

report and the accuracy of its contents.

Allied-Signal, Inc.

Kevin McCarter

Sam White

Steven A. Young

Aspen Systems, Inc.

Marc H. Caplan

Wendy Howe

Candace McIlhenny

Canadian General Standards Board

Marian L. Gaucher

E.I. duPont de Nemours and Company, Inc.

Thomas E. Bachner, Jr.

William Brierly

Louis H. Miner

Helen A. Slavin

Elgin (IL) Police Department

Charles A. Gruber

General Motors Research Laboratories

David C. Viano

Hartford (VT) Police Department

Joseph G. Estey

Home Office Police Scientific Development Branch

Eric Brown

Jaba Associates (Ontario)

Alan Athey

Point Blank Body Armor, Inc.

Gaetan (Tom) J. Dragone

Second Chance Body Armor, Inc.

Clinton Davis

Lisa Hinz

Lester Shubin

U.S. Department of Commerce

National Institute of Standards and Technology

Keith Eberhardt

Lawrence K. Eliason

Daniel E. Frank

John Whidden

Patent and Trademark Office

Deborah L. Kyle

U.S. Department of Defense

Strategic Defense Initiative Organization

Nicholas Montanarelli

Department of the Army

Ballistics Research Laboratory

Russell N. Prather

Chemical Research, Development, and

Engineering Center

Larry Sturdivan

U.S. Department of Justice

Bureau of Alcohol, Tobacco, and Firearms

Daniel Hartnett

Federal Bureau of Investigation

Bunny Morris

David Pisenti

Charles Barry Smith

National Institute of Justice

Paul Cascarano

Charles DeWitt

Paul Estaver

University of Maryland

Girish Grover

Ann Beth Jenkins

Ian Twilley

Frederick Peter Watkins

vi
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Soft Armor and Hard Armor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Summary of NIJ Standard 0101.03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

FINDINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Benefits of Wearing Armor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Factors Influencing Wearing of Armor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Goals obtesting and Certitfication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Test Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Assuring Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

UNRESOLVED ISSUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

OPTIONS FOR THE DEPARTMENT OF JUSTICE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Specify Acceptable Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Revise NIJ Standard 0101.03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Assure Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sponsor Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

OTHER POLICY OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Expand FTC Activities; Involve OSHA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

LEGISLATIVE OPTIONS . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Fund NIJ-Sponsored Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

7

7

7

13

13

14

16

21

27

27

29

30

32

36

38

39

39

40

40

41

Boxes

Box Page

A. How Soft Armor Works . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B. KevlarR and TwaronR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C. SpectraR and Spectra ShieldTM

. . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

D. Trends in Weapons and Ammunition Used in Assaults on Police . . . . . . . . . . . . . . . . . . . . . . . .

E. Types of Guns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

F. ABCs of Ammunition, Bullets, and Cartridges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

G. Stringency, Validity, and Reproducibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

H. Statistical Confidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

2

3

4

8

9

10

17

18

Figures

Figure Page

l. Certification That a Model of Armor Complies With the NIJ Standard is Based on

Inspection and Testing of Samples Submitted by the Manufacturer . . . . . . . . . . . . . . . . . . . . . 13

2. Instrumented Ballistic Test Range for Testing Armor as Specified in

NIJ Standard 0101.03 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3. Sequence of Aim Points on Each Panel, as Specified in NIJ Standard 0101.03 . . . . . . . . . . 14

4. How Fatal Bullet Wounds in the Torso Would Decrease if the Wear Rate Increased . . . . . 14
Contents—Continued

Page

5. Wear Rate Versus Temperature-Humidity Index (THI) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

6. Wear Rate Versus Month . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 15

7. Wear Rate Versus Areal Density of Armor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

8. “Reenactment” of a Ballistic Test That Armor Shot in an Assault Could Have

Been Subjected To . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

9. Discrimination of the NIJ Test for Protection From the Impact of Stopped Bullets . . . . . . . 23

10. Shots Per Panel in Actual Assaults . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

11. Effect of Wetness on Ballistic Resistance of KevlarR Armor . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

12. Estimates of V50 and V10 Obtained by Logistic Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

13. Notional Control Chart for Sequential Lot-Acceptance Testing . . . . . . . . . . . . . . . . . . . . . . . . . 37

Tables

Table Page

1. Types of Ballistic Resistance Defined by NIJ Standard 0101.03 in Terms of

Bullets and Velocities Specified for Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2. Tyes of Ballistic Resistance Defined by NIJ Standard 0101.03 in Terms of

Guns and Ammunition Against Which Protection is Expected . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3. Choices for Safety Goals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

viii
Police Body Armor Standards and Testing

Examples of Soft Armored Undergarments

Silken body armor of the type Austrian Archduke Francis Ferdinand was reported to have worn on the day he was assassinated

by a shot in the neck in 1914.

SOURCE: Bashford Dean, 1920. [53]

INTRODUCTION

Every year, about 60 sworn police officers are

shot to death in the line of duty.l 2 At the same time,

about 20 are saved by wearing armor. Had all the

officers shot in recent years been wearing armor

when shot, another 15 per year would likely have

been saved from fatal gunshot wounds, roughly

doubling the present number saved, and more than

15 others would likely have been saved from death

by other causes.3

Modern soft body armor containing layers of material made from

synthetic fiber. This armor uses woven fabric; other soft armor

uses sheets of nonwoven material made by bonding synthetic

fibers with adhesive.

SOURCE: Second Chance Body Armor, Inc., 1991.

Most police officers serving large jurisdictions

report they have armor and wear it at all times when

on duty and clearly identifiable as police officers

[102]. The kind of armor usually worn is soft armor,

which is designed to be concealable-most styles

are undergarments-and comfortable enough to be

worn routinely. Such armor is designed for protection from handgun bullets but not from rifle bullets

or edged or pointed weapons such as knives or

icepicks. The distinctive, nonconcealable ‘tactical’

 Most lethal shootings are felonious; a few are accidental.

 such as private 
2 • Police Body Armor Standards and Testing: Volume 1

Box A—How Soft Armor Works

Soft body armor works by catching the bulletin a net-like web of very strong fibers. The bullet stretches not

only the few fibers it hits, but also others in contact with them, and many more that those pull. As in any net, the

key to success is that many fibers, even those not actually touching the bullet, elongate in response to the collision

and so absorb the energy of the bullet. Even so, materials available today do not permit the construction of a vest

from a single ply of fabric-a number of layers, often about one or two dozen, are needed to stop a bullet.

Soft armor has been made from a variety of natural and, more recently, synthetic fibers. For example, silk,

which had been used for armor in medieval Japan, was used in American ballistic (bullet-resistant) armor late in

the nineteenth century. It attracted Congressional attention after President William McKinley was assassinated in

1901, and was said to have been worn by Archduke Francis Ferdinand of Austria when he was killed by a shot in

the head, which precipitated World War I. Although it provided some protection against handgun bullets at low

velocity (e.g., .40-caliber lead or .45-caliber jacketed at 400 feet per second), it could not stop higher velocity

handgun bullets (e.g., .45-caliber jacketed at 600 feet per second), much less rifle bullets. This shortcoming, together

with the expense of silk (then about $80 per garment), made silk armor unattractive to the U.S. Ordnance Department

in World War I. [53]

The tensile-strength-to-weight ratio (“tenacity”) of silk-no more than about 5 grams per denier [89]—was

surpassed by synthetic fibers such as nylon (8 g/d) and, later, KevlarR (26 g/d) and SpectraTM (35 g/d). Some spider

silk has even greater tenacity, [162] but it cannot be cultivated and collected economically as silkworm silk can.

Genetic engineers are striving to develop a way to copy it.

During the Second World War and the conflict in Korea, the United States Army developed soft armor made

of nylon. These vests provided considerable protection, but were very bulky.

Concealable soft body armor as we know it today was made possible in the mid-1960s, when a solvent for

polyaramid plastic was discovered; this permitted the production (“spinning”) of polyaramid fiber (see box B).

Polyaramid fibers have higher tenacity than nylon does, and less elongation before breaking than silk or nylon. The

first soft body armor for police use, however, was of nylon. Richard C. Davis holds several patents relating to police

body armor, [47, 48,49, 50] including one [47] for a small, light nylon vest designed to protect the wearer’s vital

organs from the short-barreled, medium-caliber handguns known as “Saturday night specials. ” The application for

this patent was filed on May 8, 1972.

Today, several types of polyaramid fiber are marketed under the names KevlarR (by the duPont de Nemours

Co., Inc.) and TwaronR (by Akzo, Inc.). The fiber is woven into fabric by weavers (two or three produce most of

the U.S. ballistic fabric), and the fabric is used in the construction of vests by several U.S. and foreign manufacturers,

The first “save” credited to KevlarR armor occurred in 1973.

More recently, soft armor has been made from fibers of extended-chain polyethylene (ECPE). Produced by

Allied-Signal, Inc., the fiber, marketed as SpectraTM, has greater tenacity and slightly less elongation than KevlarTM.

Although some SpectraTM fiber is woven into SpectraTM fabric for armor, SpectraTM is also used by Allied-Signal

in the manufacture of Spectra ShieldR

, a nonwoven composite material used in soft as well as rigid armor (see box

C). A single thin, flexible sheet of Spectra ShieldR is made by (1) bonding a single layer of closely spaced parallel

fibers together with KratonTM resin (produced by Shell Chemical) to form a single ply, (2) bonding two such plies

together, one rotated 90 degrees from the other, and (3) coating each surface of the two-ply sheet with a film to

reduce friction and abrasion. Several such sheets are required to provide protection from handgun bullets: Spectra

Shield R was first sold to body armor manufacturers in 1988.

Some manufacturers make “hybrid” armor by sandwiching sheets of Spectra ShieldR between layers of

Spectra TM or KevlarR fabric.

Untreated fabric woven from either polyaramid or ECPE fiber loses some ballistic performance when it is wet.

Possibly the water lubricates the intersections of the weave, so that stretching fibers slip on their neighbors rather

than pulling them into sharing the work of stopping the bullet. There are three options for preventing or reducing

this effect:

● The fiber or fabric may be treated by any of several processes to promote water-repellency.

. Armor panels of untreated fabric may be encased in waterproof covers.

● Armor panels may use enough untreated fabric to provide the ballistic resistance desired even when wet.

Upon drying, untreated fabric of either type regains its original ballistic performance. The ballistic resistance of

panels of Spectra ShieldR non-woven composite material is unaffected by wetness.

SOURCE: (Office of Technology Assessment, 1992.
Police Body Armor Standards and Testing: Volume I ● 3

Box B--KevlarR and TwaronR

KevlarR is strong fiber made from polymeric

aromatic amide (polyaramid) plastic by dissolving

it in a special solvent and spraying the solution

through a small nozzle called a spinnerette. The

solvent evaporates, leaving the plastic fiber, which

has a strength-to-weight ratio about five times that

of steel. The possibility of making polyaramid

plastic was hypothesized in 1939. It was synthesized and identified at DuPont in 1960, but polyaramid fiber could not be produced until 1965, when

Stephanie Kwolek, a chemist at DuPont, discovered

a practical solvent.

At about the same time, a team at Akzo, Inc., a

multinational firm headquartered in Holland, independently discovered a practical solvent and applied for a patent for the manufacture of polyaramid

fiber, which DuPont named KevlarR and Akzo later

(1984) named TwaronR. DuPont contested the

patent. A consent decree of the International Trade

Commission settled the dispute; terms of the

settlement included cross-licensing but barred Akzo

from marketing TwaronR in the United States until

late 1990.

Before KevlarR was used for body armor, it was

used as a substitute for steel in the manufacture of

radial tires, including those designed for police cars.

It does not melt but does pyrolyze (decompose) at

very high temperature. It loses some strength as its

temperature is increased but remains strong enough

to be used for applications requiring high strengthto-weight ratio at high temperature--e.g., in the

telescoping nozzles of solid-fuel rocket motors of

the Peacekeeper (formerly MX) missile.

“Kevlar” is a registered trademark of DuPont de

Nemours and Co., Inc. “Twaron” is a registered

trademark of Akzo, Inc.

SOURCE: Office of Technology Assessment, 1992.

armor worn by police SWAT (Special Weapons and

Tactics) teams for protection from rifle bullets as

well as pistol bullets is more familiar to many

laymen.

Garments of both types are sometimes called

“bulletproof vests,’ but no garment will certainly

stop any bullet. Indeed, there is no guarantee that a

bullet of a type a garment is designed to stop will not

kill a wearer. Much of the body is not covered by the

protective panels of a particular armor: an astute

purchaser may choose a model from the many on the

market, fully aware of that coverage limitation.

However, the ability of armor to stop bullets--its

“ballistic resistance ’’-cannot be discerned by

inspection; it must be inferred from the results of

tests in which sample armor is shot. Because such

testing is destructive, vests slated for marketing are

not tested. Moreover, the conditions under which an

officer is shot are unlikely to be identical to test

conditions.

In 1972, in an effort to provide police departments

guidance in such testing, the National Institute of

Law Enforcement and Criminal Justice (NILECJ), a

part of the Department of Justice, issued a standard

for ballistic resistance of police body armor,

NILECJ Standard 0101.00. It specified general

procedures and specific types of bullets and velocities to be used in tests to determine whether samples

Example of Tactical Armor Designed for

Protection from Rifle Fire

SOURCE: Point Blank Body Armor, Inc., 1991.
4 ● Police Body Armor Standard and Testing: Volume I

Box C—SpectraR and Spectra ShieldTM

SpectraR is a registered trademark of Allied-Signal, Woven Fabric

inc., for the high-strength synthetic fibers the company

produces from extended-chain polyethylene (ECPE). Key

properties of these fibers (marketed under the brand name

Spectra 1000) include low weight and high strength, as

well as resistance to impact, moisture, abrasion, chemicals, and puncture.

The first successful commercial application for

Spectra fibers, introduced in 1985, was as a substitute for

steel in ropes and cordage. Other applications that

followed include puncture- and cut-resistant safety

gloves.

For soft body armor applications, Spectra fibers are

woven into bullet-resistant fabrics or, more commonly,

used as a reinforcing fiber in a flexible, nonwoven

composite material called Spectra ShieldTM, introduced in 1988. Thicker, rigid Spectra ShieldTM is also made for

use as hard armor in helmets, radomes (protective coverings for radar antennas), sonar, and other applications.

Spectra fibers are made by a process called gel-spinning. Extended-chain polyethylene molecules containing

70,000 to 350,000 carbon atoms are dissolved in a solvent which is heated and forced through tiny nozzles called

spinnerets. The resulting jets of solution cool and harden into plastic fibers, which are drawn, dried, and wound onto

spools for further steps in manufacturing. This fiber-producing process aligns the extended-chain polyethylene

molecules so that the hydrogen atoms of each molecule bond with those of its neighbors. This gives SpectraR 

a

tensile strength greater than aramid fibers. SpectraR is also less dense than other fibers; its specific gravity is only

0.97, so it floats. Pound for pound, it is 10 times as strong as steel.

Spectra ShieldTM is made by aligning SpectraR fibers side by side and bonding them with a flexible Kraton

resin (produced by Shell Chemical) to make a single-ply sheet. Two plies of such sheets are crossed, so that the fibers

in one are perpendicular to the fibers in the other, and bonded together. The resulting 2-ply, cross-plied sheet is

coated on each side with an abrasion-resistant film to make one thin, flexible sheet of two-ply Spectra ShieldTM

composite material for use in body armor (see figure). [4]1 Thicker, multi-ply panels for use as structural armor are

made by cross-plying additional layers before coating.

A ballistic panel for an armor garment could be made by cutting multiple layers of two-ply Spectra ShieldTM

into the desired shape, stacking them up like pancakes without stitching them together, and enclosing them in a cloth

cover. The cover need not be waterproof, because Spectra ShieldTM is highly water-resistant. Exposure to water has

no effect on its ballistic resistance. Spectra ShieldTM is also highly resistant to degradation by chemicals such as

household bleach.

Another notable characteristic of Spectra ShieldTM is the high velocity-12,300 m/s-at which the stress

imparted by a bullet propagates within the armor outward from the point of impact, which allows the bullet’s energy

to be absorbed by a large area of the armor. In the 1 to 2 milliseconds during which a low-energy bullet is decelerated

by armor and backing material, [100] part of its energy would be distributed over and absorbed by the entire ballistic

panel. SpectraR fabric and Spectra ShieldTM can be ignited but only when their temperature reaches 675 ‘F; they

are less flammable than cotton or polyester fabrics typically used for police uniforms. Flame-retardant tactical armor

has been made by enclosing Spectra ShieldTM in a carrier garment made of flame-retardant fabric. SpectraR melts

at about 150 *C (about 300 ‘F), but SpectraR fabric retains 94 percent of its room-temperature ballistic resistance

at a temperature of 160 *F. Armor so hot would be excruciatingly painful and would bum skin in less than a second,

[128] so ballistic resistance at so high a temperature is almost irrelevant.

Spectra ShieldR stored for 90 days at 160 ‘F and then allowed to cool to room temperature regained its

room-temperature ballistic resistance.2

1 sw dso Gary A. Harpeli et & “Ba.Uistic Resistant Composite Article,” U.S. Patent 4,623,574, Nov. 18, 1986.

2 viz., Vw meas~~ per MIL-STD-662D using a .22-caL, 17-gr tiagment-simulating ProjeCtie.

SOURCE: OffIce of ‘Ik&nology Assessment 1992.
Police Body Armor Standards and Testing: Volume I ● 5

Spectra ShieldTM Manufacturing Process

Flexible resin added

/

Spectra

fiber

n

Fibers aligned

Fibers and

flexible resin

of armor had certain types of ballistic resistance based on a quantitative safety criterion and biomedical

defined in the standard. It was a voluntary performance standard-i. e., armor could be sold without

meeting the standard, but if it were tested and

passed, the manufacturer could certify this on the

label. Armor made from any type of material could,

if thick enough, meet the standard.

The .00 standard specified a reproducible but

arbitrary ballistic test, uncorrelated with physiological protection: There was no attempt to correlate

penetration in the test with risk of penetration in

service, and it did not attempt to gauge protection

from injury by stopped bullets.

NILECJ Standard 0101.00 has been superseded

thrice: by NILECJ Standard 0101.01 in 1978, by NIJ

(National Institute of Justice) Standard 0101.02 in

1985, and by NIJ Standard 0101.03, the current

standard, in 1987. The .01 standard was the first to be

experiment (shootings of animals) intended to demonstrate that samples of armor like those passing the

test would perform as required in service.

The current standard, like its predecessors, is

necessarily the result of an implicit trade-off among

simplicity, economy, realism, reproducibility, risk

to consumer, and risk to producer.4 For example, a

wide variety of bullets impact at unknown velocities

in assaults, but, in the interest of reproducibility, the

test requires particular types of bullets to be fired at

velocities varying by no more than 50 feet per second.

Each revision had its proponents and its critics,

but the latest version evoked unusual controversy

when “NIJ funded the retesting of all models tested

under the .02 program. However, less than half-34

out of 84-of models tested passed under the new

standard.”5 [151] This surprised NIJ as well as those

 for each revision is discussed in detail appendix of 

5 of era definite of vests passed, indeed

of which were tested. The issue is further clouded by the fact that permitted the manufacturers of vests passed under .02 to resubmit them under

different designations, and even to submit totally different vests. The Government felt the change from .02 to .03 obliged them to offer a free test, but

the manufacturers could choose what vest to test.
6 ● Police Body Armor Standards and Testing; Volume I

in industry who had been consulted about the

revision. A DuPont spokesman later claimed, ‘‘Both

sides [NIJ and the Personal Protective Armor

Association (PPAA), an industry group] agreed ’03’

was to be no more stringent than ‘02.’ “ [13] The

PPAA devised its own standard, PPAA Standard

1989-05, which is demonstrably less stringent but

also, the PPAA argues, more realistic and reproducible (i.e., results of similar tests are more likely to be

similar). Many purchasers, prospective purchasers,

and wearers of body armor have been confused by

the controversy, and some manufacturers attribute a

decline in sales to the confusion.

Critics of the NIJ standard, including some

manufacturers of armor material and garments, point

to the large fraction of .02-certified models failing

the .03 test as evidence of excessive stringency of the

.03 test. They point to the mixed results of .03 tests

of samples of the same model (sometimes labeled as

different models) as evidence that the .03 test yields

‘‘inconsistent’ results; some critics have called the

test “a crap shoot. ’ They question the rationale for

crucial aspects of the standard, such as a test

intended to gauge protection against serious or lethal

blunt trauma (bruising or tearing of internal organs)

that could be caused by the impact of a bullet

stopped by the armor. They charge that the conservatism of the standard and the variability of test results

induce manufacturers to make armor that is heavier,

stiffer, less comfortable, and more costly than is

necessary to provide the nominal protection certified. Most importantly, they charge that excessive

cost reduces sales, and excessive discomfort reduces

wearing, of certified armor, with the result that

officers who could have been saved by good

uncertified armor (or armor certified to comply with

a less stringent standard) have been killed not

wearing it: “Police officers are not dying in defective body armor. Police officers are dying because

they are not wearing body armor!!” [15] They also

believe that the standards controversy itself reduces

the sales and wearing of good armor.

Defenders of the NIJ standard, also including

some manufacturers of armor material and garments,

believe that the standard’s testing requirements and

procedures are warranted by the ballistic threats

facing police officers and rebut arguments for

changing it. They claim the PPAA standard is not

stringent enough. They ascribe variation in test

results to variation in vest construction. Gross

variation in the construction of supposedly identical

vests—such as differing numbers of fabric layers—

can be seen in the archives of NIJ’s Technology

Assessment Program Information Center (TAPIC).

A legislative remedy to the controversy has been

attempted twice: Two identical bills introduced in

the 10lst Congress, H.R.4830 and S.2639, would, if

enacted, have made it a criminal offense to manufacture, distribute, or sell armor not complying with NIJ

Standard 0101.03 or any superseding standard

issued by NIJ. H.R. 322, a bill introduced in the

current (102d) Congress, contains the same language.

This report of OTA’S assessment of police body

armor standards and testing was requested by

Senator Joseph R. Biden, Jr. (Chairman), Senator

Strom Thurmond (Ranking Minority Member), Senator Dennis DeConcini, and Senator Edward M.

Kennedy of the Senate Committee on the Judiciary,

Congressman John Joseph Moakley, Chairman of

the House Rules Committee, and Congressman

Edward F. Feighan of the House Committee on the

Judiciary and of its Subcommittees on Crime and on

Economic and Commercial Law.

The purpose of the study was to clarify the issue

of whether NIJ Standard 0101.03 should be revised,

and if so, what actions Congress might take.

Congress would like to know whether the standard

is informative and fair to purchasers and wearers of

armor, as well as to manufacturers of armor and its

component materials. Purchasers and wearers need

to know how confident they can be that certified

armor will protect them or to what degree uncertified

armor will be less protective. Manufacturers are

justified in demanding that the standard not discriminate unfairly against their products. Principal points

of uncertainty are: how confident wearers can be that

samples of a model, other samples of which have

passed the test, will protect them in the line of duty

(and under what circumstances); how confident

manufacturers can be that testing more samples of

the same model would yield similar results; how

confident prospective purchasers can be that they

won’t be defrauded; and whether performance characteristics of dubious value are being tested.

Specific points of contention include the following:

. Whether armor must be tested wet (as well as

dry), as the standard specifies.
Police Body Armor Standards and Testing: Volume I ● 7

●

●

●

●

Whether armor may be patted down between

test shots (which the standard prohibits) to

reduce the ply separation (’‘bunching’ caused

by previous shots.

The incidence and statistical significance of

apparently random variations in outcomes of

similar tests, and, if significant, their causes.

Whether armor should be failed (as the standard

requires) if a nonpenetrating test shot makes a

crater deeper than 44 mm (1.73 in) in the

material on which the armor is mounted; this is

assumed to indicate inadequate protection from

the impact of a stopped bullet.

The protection afforded by the current standard

against false or deceptive advertising or labeling (e.g., of armor as complying with the NIJ

standard, when in fact it has not been tested for

compliance).

In addition, the study was to investigate ancillary

issues, such as the shape of the test fixture to which

the armor is attached for ballistic-resistance testing

and the choice of the backing material (inside the test

fixture) against which the armor is placed to be shot.

BACKGROUND

Soft Armor and Hard Armor

Two types of armor are worn by police: soft armor

and hard armor. Soft armor, designed to stop

handgun bullets, is worn routinely by many officers.

It is often worn in a sleeveless undergarment called

a “vest” (see photo) but is sometimes incorporated

into the lining of a jacket or other outer garment. It

is designed to be inconspicuous, although a person

intent on detecting it might discern it under light

clothing at close range in daylight.

Hard armor is domed, often over soft armor, by

police on special assignments expecting an unusual

risk of rifle fire or stabbing. It maybe inconspicuous

but is often quite distinctive: television viewers

recognize it as the armor worn by SWAT (Special

Weapons and Tactics) teams (see photo). Police call

it “tactical armor’ and generally find it too hot,

heavy, or conspicuous for routine wear. It may

include panels of sheet steel or titanium, perhaps

coated or tiled with ceramic.

Most bullets that kill police officers are fired by

handguns (see box D). Some soft, concealable body

armor is designed to offer protection against the full

spectrum of handgun bullets. Lighter, less expensive

models offer protection against the most common

handgun bullets.

Many officers are killed by shotguns firing shot or

slugs; soft armor has apparently saved many officers

from such projectiles.

Many officers are killed by rifles. Soft armor has

apparently saved a few officers from carbine fire,6

but hard armor is usually required to meet the NIJ or

PPAA standard for protection from rifle fire.

Summary of NIJ Standard 0101.03

A Performance Standard

The .03 standard is a performance standard, not a

construction standard. It does not specify the area of

coverage, nor does it specify any material to be used

in the armor. This permits and encourages technical

innovation, including the development of materials

and designs providing better ballistic resistance,

greater comfort, or lower cost. However, some

aspects of the standard were introduced specifically

to provide stringent tests of likely weak points of

Kevlar fabric armor, which at the time was almost

the only type of concealable body armor marketed in

the United States.

Certification of Compliance

NIJ Standard 0101.03 provides for the manufacturer to certify, on the label, that armor is of a model

that has a type of ballistic resistance defined by the

standard if samples of the same model have passed

the test specified by the standard for that type of

ballistic resistance, regardless of who conducts it.

Such a test could be conducted by the manufacturer

or by an independent ballistic laboratory under

contract to the manufacturer. A manufacturer could

truthfully certify a model of armor to comply with

NIJ Standard 0101.03 even if it failed the test

repeatedly before finally passing it. Partly because

of this, a manufacturer’s certification, by itself, may

provide little assurance of design quality.

However, manufacturers (or any other interested

party) may submit samples of a model of armor to

NIJ for NJ-supervised testing by an NIJ-approved

6 A ~bin~ is ~ compact fie tit f~e~ ~~dge~ designed for ~es or pistols, B~ause of its short b~el, it does not accekrate fle bullets tO the

velocity they would attain if fired from a longer-bamelled rifle.
8 • Police Body Armor Standards and Testing: Volume I

Box D—Trends in Weapons and Ammunition Used in Assaults on Police

Jurisdictions all across America report an upswing, during the last few years, in the confiscation of guns of

greater firepower, as measured by caliber, muzzle velocity (which increases with barrel length), magazine capacity,

and rate of fire (e.g., fully automatic). These include so-called “assault rifles” and automatic pistols (see box E)

that fire “high-energy” ammunition such as .357 Magnum, .44 Magnum, and 9-mm Parabellum (see box F).

Officers feel they are more threatened by these guns than they were in the past. [102] Some blame the increase on

the affluence of criminals involved in the drug trade; others see it as an unfortunate side effect of the largely

successful campaign to ban the short-barreled, small-caliber handguns known as “Saturday night specials. ”

Mysteriously, this trend toward long guns and high-energy handguns is barely perceptible in the guns actually

used to shoot police officers. It may be that most of the increasingly numerous submachine guns seized were

purchased for show or to shoot other criminals; with few exceptions—about one per year-they are not being used

to attack police-at least, not yet. The few cases of their use against police-generally with no greater effect than

a revolver—are highly publicized, which may inflate the perceived magnitude of the threat they pose.

The trend toward increased use of high-energy handguns in assaults on police, although slight, is real. Part of

the increase is attributable to the issuing of .357 Magnum revolvers or 9-mm automatic pistols rather than .38

Special revolvers by many police departments responding to a perception (or projection) that their officers will face

firearms similar to those they confiscate. However, about a fifth of all officers who are shot are shot with their own

gun or their partner’s, so an upgrade of the officers’ own sidearms increases the threat they face and against which

they are well advised to protect themselves.

SOURCE: Office of Technology Assessment, 1992.

independent laboratory and, if it passes, for certifica- A body armor MODEL is a manufacturer designation of compliance by NIJ. NIJ’s criteria for certifying compliance, which include the standard itself

and a host of other memoranda, prohibit accepting

armor of a model that has previously failed an .03

certification test.7 TAPIC, to which samples must be

submitted for NTJ-authorized testing and (if successful) certification, inspects samples and attempts to

determine whether the samples are substantially the

same as samples previously submitted under a

previous model name.

Armor certified by NIJ is listed on NIJ’s Consumer Product List, which is maintained by TAPIC.

Consulting NIJs Consumer Product List is the only

sure way to determine whether NIJ has certified

compliance with NIJ Standard 0101.03; this cannot

always be determined from the label. Some martion that identifies a unique ballistic panel construction; i.e., a specific number of layers of one or more

types of ballistic fabric and or ballistic-resistant

material assembled in a specific manner.

A body armor STYLE is a manufacturer designation (number, name, or other descriptive caption)

used to distinguish between different configurations

of a body armor product line each of which includes

the same model of ballistic panel.

The distinctions between body armor model and

style were established to eliminate the necessity of

retesting a given body armor model for compliance

with the NIJ Standard each time a manufacturer

incorporates the model into [a] different style of

armor. [145]

keted armor is certified only by the manufacturer and NIJ certifies the ballistic resistance of a model on

not by NIJ. the basis of ballistic testing of samples of the model

in accordance with the standard; NIJ certifies the

ballistic resistance of a style on the basis of

Models and Styles of Armor inspection of a sample by TAPIC to determine that

NIJ notes that “For the purposes of the . . . body it does indeed contain a model of ballistic panel

armor certification procedures, the following defini- already certified to have the ballistic resistance

tions have been adopted: claimed for the style. Thus all styles of the same

7 we &s@@sh~~=n~~s cert~l~tion tniter@ which require one test according to NLJ Standard 0101.03 and have o~m r~fiements as we~~

and the ballistic test specified by the standard, which maybe performed for NJ certifkation or for other purposes, such as manufacturer’s certification

of compliance or testing samples of certified models for quality assurance (commonly called “retesting”).
Police Body Armor Standards and Testing: Volume I ● 9

Box E—Types of Guns

Firearms are classified according to barrel length as handguns or long guns; the latter include rifles and

shotguns. Handguns and rifles (and some shotgus) are generally designated by their “caliber” and by the nature

of their firing action.

The caliber is the inside diameter of the barrel. Thus .22s have barrels with an inside diameter of 0.22 inch,

and that of “9mm” guns is 9 millimeters. Anomalously, .38 Specials have barrels with the same inside diameter

as that of a .357-caliber revolver: 0.357 inches. While the .38 Special cannot fire the longer or “magnum” .357

ammunition, the .357 revolver can fire .38 ammunition.1 The designation” .380” is used for automatics firing .38

caliber (i.e., .357 -inch) bullets from specialized cartridges. The “+P” designation appended to some .38 Specials

indicates that the gun can withstand the high chamber pressure exerted by +P ammunition.

With the exception of the .410-caliber shotgun, a shotgun is measured by reference to a (now largely

hypothetical) musketball-style lead sphere that just fits in the barrel: the “gauge” of the shotgun is the number of

such balls one could make from a pound of lead. Therefore a smaller gauge number denotes a larger gun. The most

common sizes of shotgun are the 12 and 20 gauges; if measured in inches these would be approximately .80 and

.68 caliber, respectively. If .410 shotguns were measured in terms of their gauge, they would be 90 gauge. There

also exist shotguns of gauges 28,16, and 10.

Other anomalies abound. For example, while the .30-06 and the .30-30 rifles use the same .308-inch diameter

ammunition, the “06” of the former’s designation refers to its year of adoption by the military, while the second

“30” in “.30-30” refers to the (original) weight of the latter’s powder load, in grains.

Actions are often designated “full automatic,” “automatic,” “semi-automatic,” “autoloading,” “double

action,” “ “single action, “ “bolt action,” “ lever action,” and “pump.” These terms divide the weapons according

to what the firer must do to fire repeated shots. “Full automatic” weapons will fire continuously as long as the

trigger is pulled back, until they run out of ammunition (or until they jam). “Semi-automatic,” “double action,”

and “autoloading” weapons require a separate trigger pull for each shot. “Single action” weapons require

“cocking” between shots; “bolt action,” “lever action,” and “pump” rifles and shotguns require operation of

their bolt, lever, or pump between shots.

The terms “automatic” and “semiautomatic” are not always correctly used or understood. Regarding

handguns, “automatic” is used in contradistinction to “revolver”; the Colt .45 M1911al (familiar for decades as

the U.S. military’s sidearm) is an “automatic” whereas the Colt .45 Peacemaker (of cowboy fame) is a revolver.

“Automatic” handguns fire in the manner called “semiautomatic” for other guns: shots can be fired in rapid

succession by repeatedly pulling the trigger, without any other action such as operating a bolt, pump, or cocking

lever—but so do most modern revolvers. (Some products of the Ruger Arms company and the Colt Peacemaker,

which appeared in 1873, do not.) Otherwise, “automatic” is properly used to describe “full automatic” guns, i.e.

machine-guns: guns that will continue to fire as long as the trigger is depressed. (Most such guns have a

“selective-fire switch,” allowing the user to toggle between full automatic and semiautomatic modes of operation.)

A submachinegun is a machine gun that fires pistol ammunition.

A “carbine” is a compact rifle. Attempts to define the term “assault rifle” for legal purposes have met with

great difficulty because these guns differ from other semiautomatic carbines largely through styling, not

functionality.

1 mS ~~ -e it tilc~t to establish What ~ of ammunition was used in an assault which makes reenactment problematical.

SOURCE: OffIce of ‘lMmology Assessment, 1992.

model are assumed to have the same ballistic stitching of ballistic panels (e.g., box stitch versus

resistance. quilt stitch) would make the panels different models.

TAPIC considers garments differing only in color Types of Ballistic Resistance

to be of the same style. Differences ir-the size or cut The .03 standard defines six standard types of

(i.e., shape) of garments would make them different ballistic resistance for which armor may be tested

styles, not different models, even though size and cut and provides for custom testing for “special type”

possibly affect ballistic resistance. Differences in ballistic resistance. Each type is defiied in terms of

327-115 0 - 92 - 2 : QL 3
1O ● Police Body Armor Standards and Testing: Volume I

Box F—ABCs of Ammunition, Bullets, and Cartridges

.

22-cal. KmD

.25-cal. ED

.32-cal. m

.380-cal. D

.38 Special m

.357 Magnumm

9-mm. ED

.44 Magnum u==

.45-cal. (Em

Pistol and rifle ammunition is described in terms of

the diameter of the bullet, the length of the cartridge,

and the shape and composition of the bullet. Shotgun

ammunition is described in terms of the diameter

(gauge or caliber) of the gun barrel for which it is

designed, and by whether it contains a single bulletlike “slug,” or if not, by the size of the shot or pellets

it contains.

Bullet diameters are, of course, the same as the

inside diameters of the gun barrels from which they are

fired. The sizes and nomenclature of these were

discussed in box E.

The length of the cartridge has a direct bearing on

the amount of powder it can contain and thus on the

velocity with which it can propel the bullet. “Magnum’ cartridges are longer than standard cartridges to

contain more powder. Likewise, many handguns are

chambered for .22 Long Rifle cartridges, which

contain more powder than .22 “Shorts.”

Bullets vary in shape, construction, and composition. The shape can range from the relatively pointed

Speer bullet, no longer used in body armor testing, to

the cylindrical “wad cutter” bullet optimized for the

clean punching of circular holes in paper targets. The

‘‘ semi-wadcutter” shape is a compromise between the

wadcutter and the typical domed bullet shape. ‘HollowPoint” bullets feature a small cavity in the nose, to

create mushrooming after impact. Some controversy

surrounds the question of whether nominally identical

bullets differ sufficiently in shape to affect the outcome

of armor tests.

Bullets can have full or partial metal jackets. A

partial jacket, typically found on a hollow point bullet,

leaves the nose of the bullet exposed. The jacket is

typically made of copper, though copper-clad steel

jackets are not unheard of. A “gas check” is a copper

shield on the base of the bullet to keep the burning

gunpowder from melting the base while the bullet is

still in the gun.

Jackets and gas checks aside, bullets are normally

made out of lead. The hardness of this lead is governed

by the degree to which it is alloyed with other metals.

Some bullets contain harder metals, either in the

form of steel balls cast into the lead or, in the extreme

case, machined steel, brass, or even tungsten bullets

coated with copper or Teflon. These bullets are

designated “armor piercing.” “Armor piercing” military rifle bullets, such as those used in testing Type IV

armor, consist of a steel core covered by a full copper

jacket. Some have lead bases or point fillers. The rare

Teflon-coated bullets made of machined steel, brass, or
Police Body Armor Standards and Testing: Volume I ● 11

tungsten have gained notoriety far out of proportion to Shotgun loads range from birdshot loads containing

their number. Originally designed for use by police hundreds of small pellets to the slug load, composed of

officers in shooting through cars, they received their a single bullet-like “slug.” Buckshot lies between

“cop killer” nickname later, when soft body armor these extremes, with a shell containing a dozen or so

was introduced. They will penetrate soft body armor, pellets, depending upon the size of the buckshot. To

but no armor-wearing officer has been killed by one.1 make up for the lack of rifling inmost shotgun barrels,

The Teflon in itself confers no special armor-piercing slugs themselves are typically rifled, i.e., cast with

properties, and is used merely to lessen the extreme slanted grooves on their sides to impart aerodynamibarrel wear that would otherwise be caused by bullets cally the spin needed for stability.

made of such hard materials.

1 TWO offl~ers Waekilledby such bullets in 1967, before the introduction of soft body armor into kv~OrCment use.

SOURCE: Office of ‘lMnology Assessment, 1992.

the type or types of bullets fried at panels of the

armor to test its ballistic resistance (see table 1). Two

types of handgun bullets are fired to test for Tjq?e I,

It-A, II, or III-A ballistic resistance, which soft

armor can provide. One type of rifle bullet is fired to

test for T~e III or IV ballistic resistance, which hard

armor can provides

Each standard type of armor is expected to offer

protection against the threat associated with it as

well as against the threats associated with all other

standard types of armor appearing above it in table 1.

For this reason, the types of armor defined by ND

Std. -OlOl.O3 are often referred to as “levels,” level

Ii-A being presumably superior to level I, for

example. However, a certification test for type II-A

ballistic resistance would not actually test resistance

to type I threats. In addition, an NIJ guide speciiles

other threats against which it expects armor of each

standard ballistic-resistance level to provide protection (see table 2), even though the .03 test does not

actually test resistance to such threats. [145]

Selection of Samples

The NIJ standard specifies that “Four complete

armors, selected at random and sized to fit a 117 cm

(46 in) to 122 cm (48 in) chest circumference, shall

constitute a test sample. (Note: The larger the size,

the more likelihood that all ballistic testing will fit

on just two complete armors.)’ In quality assurance,

Table l—Types of Ballistic Resistance Defined by NIJ

Standard 0101.03 in Terms of Bullets and Velocities

Specified for Testing

Bullet mass lmpactvelocit~

Type Bullet caliber and type (grains) (ft/s)

I .22 long rifle high-velocity

.38 round-nose lead

II-A .357 jacketed soft-point

9-mm full metal jacket

II .357 jacketed soft-point

9-mm full metal jacket

II I-A .44 magnum lead semiwadcutter gas-checked

9-mm full metal jacket

Ill 7.62 mm full metal jacket

Iv .30-06 armor-piercing

Special custom

40

158

158

124

158

124

240

124

150

166

custom

1,050

850

1,250

1,090

1,395

1,175

1,400

1,400

2,750

2,850

custom

%finumum velocity; the maximum velocity for a fair hit is 50 ftls greater.

SOURCE: National Institute of Justice, 1987 [144].

‘‘selected at random’ usually means ‘‘selected at

random with uniform probability’ ‘—i.e., sampling

should insure that all units of the model should have

the same chance of being selected to be tested.

However, this is impossible if samples are selected

for certification testing before production of the

model has been discontinued. Tjq?ically samples are

selected after only a few units have been produced;

consequently, the sampling procedure does not

guarantee that the samples are representative of

8 me test ~roc~we for ~~spec~ ~e$$ b~li~ti~ resis~m is the s~e as for s~@d types of b~istic resis@n&, except the person ordering tbe

testing (e.g., a manufacturer) specifies the type and nominal velocity of the test projectile to be used. For example, a manufacturer could have armor

tested for W certification of Special ~pe ballistic resistance to a .45-caliber bulleq a 12-gauge rifled slug, or buckshot at a specified velocity,

Special-type armor is not necessarily expected to protect against the threat associated with any other type.
12 ● Police Body Armor Standards and Testing: Volume I

Table 2—Types of Ballistic Resistance Defined by NIJ

Standard 0101.03 in Terms of Guns and Ammunition

Against Which Protection Is Expected

Type Threat

I .22, .25 and .32 caliber handguns,

.38 Special lead round-nose

II-A .38 Special high-velocity,

.45s,

low-velocity .357 Magnum & 9-mm,

.22 rifles

II Higher velocity .357 Magnum and 9-mm

III-A .44 Magnum and submachine gun 9-mm

Ill High-power rifle:

5.56mm,

7.62mm FMJ,

.30 carbine,

.30-06 pointed soft point,

12-gauge rifled slug

Iv Armor-piercing rifle bullet, .30 caliber

(1 shot only}.

SOURCE: National Institute of Justice, 1987 [144] and 1989 [145].

yet-to-be-produced units of the model, particularly

of smaller sizes.

Conduct of the Test

Armor to be tested is mounted on a flat block of

inelastic backing material-typically modelling clay—

to be shot. The impact velocity of each bullet is

measured using a ballistic chronograph (see figure

2). If the bullet hits an appropriate point on the panel

at an impact velocity within specified limits (see

table 1), the impact is considered a fair hit. The test

requires a fair hit in each of six specified areas on

each panel in a specified sequence (see figure 3).

Each shot must impact at least 3 inches from the

edge of the panel and at least 2 inches from the

closest point of impact of any prior shot.

In tests of Type I, II-A, II, or III-A ballistic

resistance, four complete armors, typically including eight armor panels (four each front and back) are

usually shot. Each ballistic element (front or back

panel) is sprayed with water and then shot with test

bullets of the first type, then another one is sprayed

and shot with test bullets of the second type. This is

repeated with unsprayed, dry samples. This requires

a minimum of 48 shots per test: 2 element types

(front and back) x 6 shots each x 2 types of test

bullets x 2 wetness conditions.

If the velocity of a shot is too low and it does not

penetrate the panel, or if the velocity of a shot is too

high and it does penetrate the panel, the shot is

repeated, aimed at least 2 inches from the closest

point of impact of any prior shot. However, no more

than eight shots (of one caliber) may be fired at any

panel.9 The armor cannot be certified if any fair shot

penetrates.

After the first fair shot at each panel, the panel is

removed from the backing and the depth of the crater

(called the backface signature or BFS) is measured.

If the BFS exeeds 44 mm or if the armor was

penetrated, it fails; if not, the panel is replaced on the

backing without filling the crater or otherwise

reconditioning the backing material, and testing for

penetration is resumed.l0 The standard prohibits

adjusting a panel (e.g., patting it down) thereafter,

unless it is reused for testing with a second type of

bullet.

NIJ Standard 0101.03 specifies that armor be

tested on a block of backing material at least 4 inches

thick “and of sufficient length and width . . . to

completely back the armor part to be tested. ” The

standard does not specify unambiguously that the

backing must be flat, and in fact requires it to be built

up to achieve contact with the armor when testing

female armor with bust cups or when testing rigid

armor for Type III or IV ballistic resistance. However, in practice, a flat surface is used in other cases.

Until recently, the testing of a whole armor

garment with removable ballistic panels (the usual

configuration) was precluded by the requirement

that each ballistic element (e.g., panel) be tested

separately. (Although the standard explicitly allows

testing a whole armor garment if it is made in one

part without removable ballistic panels, this may be

precluded by the provision that requires the backing

to be “of sufficient length and width . . . to

completely back the armor part to be tested.”) In a

letter dated April 27, 1992, NIJ directed H.P. White

Laboratory, Inc., that effective June 1, 1992, it

should test samples for compliance with NIJ Stand-

$J To provide for contingencies, six complete armors (12 panels) must be submitted for a Me I, ~-A, ~ or ~-A test.

10 ~ s~dad 0101.03” specfles tit teS~g s~l be continued titer ~ch BFS m~s~ment if it is no ~eater than 44 mm, md ilftti shoot@ Sk

fti shots per panel if none penetrated. It neither requires nor prohibits continuation of the testing in other cases-i.e., after failures. However, NJ has

directed H.P. White Laboratory, Inc. (HPWLI), the only laboratory authorized to conduct testing for NIJ certiilcation, to complete the testing despite

disquali.tlcation of the armor.
Police Body Armor Standards and Testing: Volume I ● 13

Figure l—Certification That a Model of Armor Complies With the NIJ Standard Is

Based on Inspection and Testing of Samples Submitted by the Manufacturer

 Production Certification testing

u

I

● Its

SOURCE: Office of Technology Assessment, 1992.

ard 0101.03 by mounting the whole armor garment

on a smaller clay block in a curvilinear frame (see

photo)--a highly abstract mannequin.11 The standard itself was not changed.

This summary does not cover all details of the

standard; the interested reader is referred to the

standard itself and to appendix A of this report for

additional details.

Validity of the Test

The standard does not explain the rationale for its

provisions but does refer readers to an NIJ guide that

discusses the origin of the standard briefly and cites

detailed reports of research considered by the

drafters of the standard.

The standard specifies how to conduct a ballistic

test of samples of a model of armor under controlled

conditions, in order to measure properties of the

samples (types of “ballistic resistance”) that can

reasonably be expected to be related to the protection that other samples of the same model will afford

wearers in service. However, the details of the

relationship are uncertain and disputed; no body of

data reliably links performance in the lab with

performance in service. This situation is common in

consumer-product safety testing, but it leaves room

for legitimate questioning of the meaning of passing

the test.

FINDINGS

Benefits of Wearing Armor

Body armor saves lives and could save more if

worn more often by more officers. Wearing armor

has saved about 10 to 30 sworn police officers from

fatal gunshot wounds each year in recent years. The

number saved each year would roughly double if all

officers wore armor at all times. Wearing armor also

saves officers from death or serious injury in other

types of assaults and accidents, especially vehicle

accidents. By industry estimates, armor has saved

over 1,300 police from death or serious injury by

firearms assaults (about 40 percent), other assaults

(about 20 percent), and vehicle and other accidents

(about 40 percent). [18]

 to Standard 0101.03)” is to be done of test 

certification test.
14 ● Police Body Armor Standards and Testing: Volume I

Figure 2—Instrumented Ballistic Test Range for

Testing Armor as Specified in NIJ Standard 0101.03

Line

,flight

B

, / stop

trigger

/ ’ / ’ —-Start

I

Chronograph

A -5 m for type 1, II-A, II, and II I-A armors;

15 m for type Ill and IV armors.

B -2 m minimum

C - Approximately 0.5 to 1.5 m

SOURCE: National Institute of Justice, 1987.

However, even universal wearing of armor would

not save officers from fatal gunshot wounds in

unprotected parts of the body or from some guns and

ammunition more powerful than those the armor was

designed to protect against (see figure 4).12

Factors Influencing Wearing of Armor

Police departments can promote the wearing of

armor by

1.

2.

3.

4.

5.

purchasing and issuing it or reimbursing

officers for purchasing their own armor,

ensuring that it fits,

encouraging or requiring officers to wear

armor when on duty,13

ensuring that chiefs and other supervisory

officers set a good example by wearing

armor, and

instructing officers in the donning and

laundering of armor and in the benefits of

Figure 3-Sequence of Aim Points on Each PaneI,

as Specified in NIJ Standard 0101.03

------- —.- —- —------ —— —---

All shots at least 7.6 cm (3 in) from any edge

and at least 5 cm (2 in) from another shot

SOURCE: National Institute of Justice, 1987.

Figure 4—How Fatal Bullet Wounds in the Torso

Would Decrease if the Wear Rate Increased

Torso wounds and wear rate

100% I

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Wear rate

SOURCE: Office of Technology Assessment, 1991.

wearing armor and the limitations of its

protection.

Discomfort is probably the main reason why some

officers who own armor do not always wear it.

Wearers (and, especially, nonwearers) commonly

describe their armor as “hot, “ “heavy,” “stiff,”

“chafing,” and the like. Complaints about chafing,

 Soft body armor has a good record of protecting wearers against ammunition more powerful than those it was advertised or certi.tied to

protect nevertheless, in some eases rifle bullets and other high-energy bullets have penetrated armor not designed to stop it.

13 off some cases while “moonlighting” as a private security guard.
Police Body Armor Standards and Testing: Volume I ● 15

Figure 5—Wear Rate Versus Temperature-Humidity

Index (THI)

Wear rate

100% 1 — 

Style 1

90% Style II

80% -

 Style II, 10-ply

I — 12-ply

60%

50%

40%

30%

20%

10%

0%vo~

40 50 60 70 80

Temperature-humidity index (THI)

SOURCE: Aerospace Corp., 1977.

and to some degree about stiffness and the impression of great weight, may be the result of a bad fit,

or of strapping the armor on too tightly. Ensuring

good fit can encourage wearing of armor.

Officers’ complaints that armor makes them feel

hot, however, cannot be attributed to improper fit.

Not only is armor material a good thermal insulator,

it also blocks the evaporation needed for the body’s

normal perspirative cooling. A large, year-long

survey conducted by the Aerospace Corporation for

the NILECJ found that the strongest influence on

wear rate (of those considered) was the TemperatureHumidity Index (THI).14 Reported wear rates were

higher at times and locations with lower values of

the THI (See figure 5.), and higher in the winter

months than in the summer. (See figure 6.) [7]

Some officers find they can lessen this blocking

effect of the vest by wearing a special undergarment

having vertical ribs designed to hold the vest away

100%

90%

80%

70%

60%

50%

40%

30%

20%

1 o%

Figure 6-Wear Rate Versus Month

Wear rate

 Style I

‘

- Style II

 Style II, 10-ply

‘1 — 12-ply

 14-ply

-6 18-ply

 24-Ply

0% I I I I I I I

J FM AMJJ ASOND

Month

SOURCE: Aerospace Corp., 1977.

from the body and allow circulation of air under the

vest.

Complaints about the weight of the vest are of

particular concern, because weight—unlike chafing

or heat retention—is directly related to the ballistic

resistance of the vest. Stopping heavier, faster,

harder bullets makes the vest heavier, as does

protecting a greater fraction of the body. Thus,

insofar as weight lessens comfort, there exists a true

comfort-v. -protection tradeoff. However, an analysis of the Aerospace Corporation’s survey data

indicates that wear rate does not decrease markedly

with increasing coverage or armor weight until the

weight of armor material per unit area exceeds about

4.5 kilograms per square meter, which is typical of

models certified to have type II-A ballistic resistance

(see figure 7).15 Lighter armor with less ballistic

resistance was not worn more, but heavier armor

with more ballistic resistance was worn slightly less.

 defined the Temperature-Humidity Index by the formula = 15 + 0.4 x (T + where T = 

@9, and = wet-bulb temperature (?F).

 Officers Participating in to armor; other things being equal, officers not obliged or ordered wear armor might

be less likely to wear it than other officers, and their wear rate might show greater sensitivity to weight per unit although this is speculative.
16 ● Police Body Armor Standards and Testing: Volume I

Figure 7—Wear Rate Versus Areal Density of Armor

Wear rate

(12-month average)

100%

I — Wraparound vests

 Front/back only

80%

I

60%

)

 - +

20% -

o% I

o 1 2 3 4 5 6 7

Areal density (kg/sq m)

SOURCE: Office of Technology Assessment, 1992, based on data from Aerospace Corp., 1977.

Departments that are contemplating purchasing heavier armor should consider that the

greater protection it could provide may be offset

by a lower probability that it will be worn. Details

will depend on region, season, type of duty, and

individual physiology. This is less of an issue for

tactical armor that can be tolerated for limited

periods of high risk, even though uncomfortably

heavy.

Goals of Testing and Certification

Purchasers and wearers of armor want to know

whether a model of armor will protect them against

a specified threat. Unfortunately, testing can only

estimate the probability that the armor will stop a

specified bullet and prevent the impact from injuring

them. The estimate could be wrong, because identical tests of identical samples of armor may yield

different results, and because the validity of the test

(the correlation of its results with performance in

service-see box G) is uncertain. Experiments

designed to gauge the validity of a test can measure

the statistical confidence (see box H) with which one

can conclude that armor that passes the test would

limit probability of injury to whatever level maybe

required. However, the assessment of the validity

of existing or proposed test procedures cannot be

objective or conclusive unless NIJ specifies the

maximum acceptable risks of specific types of

injuries or incapacitation by penetrating and

nonpenetrating bullets, and the statistical confidence with which the validity of the test must be

demonstrated.

A test of ballistic resistance would be called

‘‘valid’ if armor that passes it is adequately safe in

service. Hence, one cannot decide whether a test is

valid unless “adequately safe” has been defined.

Moreover, one cannot decide whether a testis valid

unless “adequately safe’ has been defined probabilistically—i.e., by specifying the maximum acceptable probabilities of specific types of injuries or

incapacitation under specific conditions.

These maximum acceptable probabilities must be

greater than O percent; no armor can be expected to

protect a wearer with certainty, desirable though that

may be. Even if, hypothetically, it could, that could

not be shown “scientifically.” If, however, a

nonzero maximum acceptable probability of each

type of injury to be avoided were specified, then

analyzing medical and ballistic data from shootings

of persons wearing armor (primarily assaults on

police officers) and subjecting the victims’ armor to
Police Body Armor Standards and Testing: Volume I ● 17

Box G—Stringency, Validity, and Reproducibility

In this report, a test of ballistic resistance, such as that specified by NIJ Standard 0101.03, is called “stringent”

if a sample of armor has a high probability of failing it. Of course, the probability varies from sample to sample,

so the term has only relative (not absolute) meaning.1 Nevertheless, no matter what the probability is, certain

changes in the test can increase it; others can decrease it. For example, requiring the sample to withstand more shots

while allowing no more penetrations would increase any sample’s probability of failing the test, hence it would

increase the stringency of the testIncreasing the stringency of a test may not make it better. Whether it does depends in part on the validity of

the test. In this report, a test of ballistic resistance is said to be “valid” if armor that passes it is adequately safe in

service. This term, too, is relative--validity depends on the safety criterion to be met. In any case, if the results of

a ballistic test are completely unrelated to the performance of armor in service, the test would be invalid.. Valid tests

may be have different types and degrees of validity; to describe them precisely and distinguish them requires

statistical terminology (e.g., correlation between test outcome and penetration in service).

Whether increasing the stringency of a test is judged to be an improvement also depends on the judge’s stake

on the outcome. If a mandatory test is invalid, making it more stringent would strengthen whatever restriction it

imposes arbitrarily on the freedom of the producer to sell, and the freedom of the consumer to buy, any armor they

please.

If a mandatory testis valid, making it more stringent would increase the degree or the certainty of the protection

it provides a wearer, which would be good for the wearer, other things being equal. But, depending on how it is done,

increasing the stringency of the test might also fail the only armor that some would-be purchasers consider

affordable (this would decrease sales), or the only an-nor that some potential wearers find comfortable enough to

wear routinely (this would decrease wearing and might decrease lives saved). Others might find armor passing the

more stringent test less comfortable, even though they tolerate and wear it. Clearly, different stakeholders will weigh

the advantages and disadvantages of increasing the stringency differently. If the test is voluntary rather than

mandatory, the effects would be less stark but more complicated to assess.

A test’s validity is distinct from its realism. A test that shot each sample of armor with one bullet, fired from

a gun (and a cartridge) drawn at random from those confiscated by police would be more realistic than the

NIJ-specified test. The result of one such test would not be a reliable indicator of how armor like the sample tested

would protect a wearer in service, nor could the same result be expected to be obtained in another test of a similar

sample of armor. Conversely, tests designed to predict protection reliably would use many shots by a more limited

variety of bullets than assailants use and would test several samples of armor.

A major concern of producers and purchasers alike is the reproducibility of a test, which could be defined as

the probability that successive tests of “identical” samples will yield the same results (if the testis a pass/fail test)

or results within specified limits (if the result of the test is a score). However, it is impossible to determine the

reproducibility of a test, according to either of these definitions, because one cannot measure either probability.

A more practical but more complicated approach is to define the reproducibility of a pass/fail test in terms of

lower confidence limits (corresponding to various confidence levels) on the probability that a sample will pass a

test, given that an identical sample passed an identical test. Similarly, the reproducibility of a test that results in a

score may be defined in terms of confidence limits on the probability of obtaining a score within specified limits,

given that an identical sample attained a score within the same limits.

Actually, no two samples will ever be identical, nor will a test be conducted in exactly the same manner each

time. Even if identical samples were tested in exactly the same way, the results could differ because of fundamental

physical reasons. This makes it difficult, if not impossible, to scientifically test whether an observed variation in

test results should be attributed to a variation of test procedure or, alternatively, to a variation of armor samples.

In some cases, subsequent investigation has found a variation of either test procedure or armor samples that might

have influenced the test results, but this does not prove that the variation was the sole cause of the differing results.

1 F~~oro, ~ pro~bi~ty that a partic&u S-plc will fail a test cannot be determined even after testing-it a o~y b esmt~+

SOURCE: OffIce of lkchnology Assessment, 1992.

327-115 0 - 92 - 3 : QL 3
18 ● Police Body Armor Standards and Testing: Volume I

Box H—Statistical Confidence

The idea of “probability” is clear to most of us: we understand the statement that “vest X has a 91 percent

probability of stopping bullet Y going Z feet per second.” Yet many statements about these probabilities are

couched in terms of “statistical confidence,” as in “90 percent confidence that vest X has at least a 91 percent

probability of stopping bullet Y going Z feet per second.” This sounds like an extra layer of waffling. Why is it

needed?

It is needed because we can never test enough vests to be sure that the stopping probability is exactly 91 percent.

After 100 shots and 9 penetrations, 91 percent would be a best guess (a “maximum-likelihood estimate”: the

probability that would have made the test results more likely than any other probability would). However, the true

value could be 90 percent or 92 percent. Even after 1,000 shots with 90 penetrations, we can’t be sure that we haven’t

been a little lucky or a little unlucky in our shooting.

For this reason, we need to express probabilities in terms of a level of confidence (such as 90 percent) that the

true value lies in some range, called a confidence interval, that depends on the test results. For example, 100 shots

with 9 penetrations gives 90 percent confidence that the stopping probability is at least 86 percent and 99 percent

confidence that it at least 82 percent. This means if the stopping probability were no greater than 86 percent, there

would have been a 90 percent probability of getting more penetrations than we did (9), and if the stopping probability

were no greater than 82 percent, there would have been a 99 percent probability of getting more penetrations.

Conducting more tests narrows the range of probabilities (the confidence interval) that corresponds to some

confidence level. For example, a total of 1,000 shots with 90 penetrations (the same fraction) gives 90 percent

confidence that the stopping probability is at least 90 percent and 99 percent confidence that it is at least 89 percent.

SOURCE: Office of Technology Assessment, 1992.

the ballistic test in question, using bullets of the type confidence or decreasing the significance required

with which it was shot (this is called a “reenactment”— increases the number of reenactments required to

of the test to which the armor might have been decide validity.

subjected before being used) would allow the

validity to be decided “scientiilcally”—i.e., with an Once validity is decided, the issue of appropriate

appropriate level of statistical confidence, if the test stringency will be clarified:

is accepted as valid,16 or with an appropriate level of

statistical signficance, if the test is rejected as ●

invalid. 17

What levels of statistical confidence and statistical significance are appropriate? The former must be ●

less than 100 percent and the latter greater than O

percent, otherwise an infinite number of reenactments would have to be performed. Aside from this,

the choice is entirely subjective—a matter of acceptable risk. To avoid future controversy over such

matters, NIJ should specify the levels of statistical

confidence and statistical significance it deems

appropriate for deciding validity.

It may, however, take months or years to collect

enough data to decide the validity of a test with the

confidence or significance required. Increasing the

Invalidity is rejected with the statistical significance required by NIJ, the test should be

changed.

If validity is accepted with much more statistical confidence than the minimum required by

NLJ, then it could also be concluded, with the

minimum confidence required by NIJ, that to

pass the test, armor must provide greater safety

than required by NH-equivalently, that some

adequately safe armor would fail, which would

be unfair to its manufacturer. This would also

argue for changing the test. However, no matter

what the test, there is always some chance that

adequately safe armor will fail. To preempt

debate on this issue, NIJ should specify a

maximum acceptable probability that safe armor

16 Here “statistical confiden~” refers to the probability that the test would have been rejected as invalid erroneously, if the probability of m fijq

to be avoided were as great as the maximum acceptable probability of injury, which in this context is called the upper contldence limit on the probability

of injmy.

17 “Statistic significan~’ refers to the maximum probability that the test has been rejected as invalid erroneously, i.e., the probability that the test

would have been judged invalid if the probability of an injury to be avoided were as great as the maximum acceptable probability of injury.
Police Body Armor Standards and Testing: Volume I ● 19

will fail-a maximum acceptable producer’s

risk, in the parlance of quality control.

● If validity is accepted with little more statistical

confidence than the minimum required by NIJ,

it cannot be argued that the testis (much) more

stringent than necessary to meet the safety

goals. To charge excessive stringency would be

to charge that NIJ requires greater safety for

wearers than the critic deems appropriate. It

should be recognized that this is an essentially

political issue, not a scientific one.

In 1976, NILECJ specified the maximum acceptable risk of death or serious injury by nonpenetrating

bullets, 18 but did not specify the statistical confidence with which acceptable risk must be demonstrated. [106] The safety goals, which were proposed

in a 1973 Army study for NILECJ, [104] have been

phrased differently in different reports by those

associated with NILECJ’S Lightweight Soft Body

Armor Program. [74, 106, 145] This has caused

some confusion about the precise meaning of the

goals; clarification will be necessary in order to test

the validity of the standard scientifically.

Moreover, NILECJ did not specify any maximum

acceptable risk of penetration; it said only that armor

“should prevent penetration by the bullet into the

chest, abdomen, or back. ’ If this means that no risk

of penetration is acceptable, no test could determine

whether armor satisfies this criterion: no matter how

many tests resulted in no penetration, there would be

no guarantee that the next shot would be stopped. A

realistic goal would specify some nonzero maximum acceptable risk, and some statistical confidence with which it must be demonstrated.

Much of the current controversy over armor

standards and testing arose and persists because

the certification procedure does not quantify the

risks, and the uncertainties in the risks, to

manufacturers, purchasers, and wearers.

A risk for the manufacturer is that samples of a

model will be tested and certified, and that samples

produced later will be retested and fail. This has

happened a few times. In some cases, no visible

difference between the retest sample and the sample

tested for certification was found.

Concerning one such case, TAPIC wrote, “It is

apparent that when a marginal vest is submitted for

multiple tests, it is to be expected that some will pass

and some will fail. ” [32] OTA concurs, but notes

that marginal design or variations in production are

not the only possible causes of variation in test

results. Part of the variance of test results might be

caused by subtle variations in test procedure.19

Although experiments can be designed to estimate the effect of deliberately controlled variations

in samples or test procedure on the variance of test

results, OTA knows of no way to attribute fractions

of the unexplained variance of test results to (1)

variations in samples, (2) variations in test procedure, and (3) irreducible randomness. Probably all

contribute in some unknown proportion.

Apart from the problem of assigning blame for

variation in test results to various hypothesized

causes, there are fundamental limits to the amount of

information that the passing of a certification

test—any certification test--can provide about the

probability that identical samples would pass an

identical retest. Statisticians describe the limits in

terms of the statistical confidence with which one

can conclude that the probability of passing a retest

is greater than some number called a lower confidence limit. “Statistical confidence” refers to the

probability that the test would have been failed if the

probability of passing it, or an identical retest, were

as low as the lower confidence limit. The greater the

lower confidence limit, the lower the statistical

confidence with which one can draw such a conclusion. 20

18 Btilets stopped by -or often bruise or lacerate the skin behind the armor. Usually such injuries are fior; they do not ficapacibte the victim

(they often go unnoticed!) and require no surgery. However, a fast or heavy projectile stopped by light armor may bruise or rupture vital organs; this

is called blunt trauma if unaccompanied by severe skin laceration. However, a bullet may even push armor into the skirL producing not only laceration

but what surgeons call a penetrating wound, even though the armor is not penetrated.

19 AII ines~bl~possibly very small-part is caused by the irreducible, quantum-mechanical randomness of physical phenomem.

20~ tie pmbabdi~ of Pmsfig a ~fiation test or ~ identi~ retest wme 1/2, the probability tit the ce~lcation test WOW k ftdd wotid k

1/2. Thus cemj5cation provides only 50 percent statistical confidence that the probability of similar samples passing a retest is at least 1/2. It provides

only 40 percent confidence that similar samples will pass a retest with a probability of at least 60 percent, 30 percent con.tldence that similar samples

will pass a retest with a probability of at least 70 percent etc.—no matter howmuchcare is taken to make the samples of armor and test procedure uniform.

Certification likewise provides only 50 percent confidence that similar samples will pass both of two retests with a probability of at least 1/4, or three

of three retests with a probability of at least 1/8, etc.
20 ● Police Body Armor Standards and Testing: Volume 1

Details of the test, such as whether armor is

repositioned between shots, may affect the probability with which samples will pass a test, and if they

are known to differ from test to test in a systematic

way, such tests would not be ‘‘identical.”21 Steps

can be taken to eliminate some possible sources of

systematic test-to-test differences (see below), but it

is doubtful all possible sources could be eliminated,

and it is certain they could not be proven to be

eliminated. Even if they were eliminated, one test

could provide only limited statistical confidence

(see fh. 21) in the corresponding confidence limits.

This is not widely recognized; NIJ’s criteria for

certification and recertification should recognize

such uncertainties explicitly and should advise

manufacturers, purchasers, and wearers.22

It is not essential that the ballistic resistance of

armor be tested under rare, extreme environmental conditions, provided customers understand the limitations of the testing. It would be

reasonable for NIJ to specify optional tests for

ballistic resistance under such conditions and to

certify compliance of armor passing such tests at an

approved testing laboratory. Such tests would increase the cost and stringency of tests while providing diminishing returns in terms of risk reduction,

because shootings of officers under such conditions

are rare.

It would be reasonable to require ballistic testing

only under those conditions that research shows

affect ballistic resistance substantially and occur at

least 10 percent of the time when armor is worn.

Allowing ballistic testing under less common conditions to be optional would permit (but not require)

consumers to accept the risk that the actual ballistic

resistance of armor could be less than the certified

ballistic resistance up to 10 percent of the time. This

does not mean the armor would be penetrated, or the

wearer killed, by 10 percent of all bullets that hit

armor; that would be the worst possible case. Even

so, the risk, although unknown, could be significant,

and NIJ might be unwilling to allow consumers who

would accept it to buy armor certified by NIJ to

provide a level of ballistic resistance only 90 percent

of the time.

Nevertheless, there are arguments for accommodating such consumers:

●

●

●

●

●

●

Designing armor to have rated ballistic resistance under some rare conditions may make it

uncomfortable and decrease the probability it

will be worn under all conditions.

The validity of a test of ballistic resistance

under a rare condition may not be demonstrable

with reasonable confidence (at least, for several

years) because few or no cases suitable for

reenactment may occur.

The costs of the extra testing required, which

would be passed on to consumers, would be

avoided.

Consumers could (and should) be told of the

conditions for which the rated ballistic resistance is certified, and of the most commonly

occurring conditions known or believed to be

detrimental and for which ballistic resistance is

not certified. Consumers, thus informed, could

decide to accept the risk.

Optional standard tests for ballistic resistance

under the more common rare conditions (e.g.,

wetting) should be specified for the benefit of

purchasers who demand it and are willing to

pay the passed-on share of the cost of the extra

testing.

There are precedents for accepting comparable

or greater risks in return for economy, comfort,

and other benefits. For example, in 1976

NILECJ stated the following goal for lightweight body armor: ‘‘Any blunt trauma effects

requiring surgical repair should have a mortality risk of 10% or less. ’ ’23 [106] As another

example, police officers rarely wear (and few

possess) helmets providing ballistic protection,

even though more than half of the officers

killed wearing armor were killed by head

wounds. 24

21 me c~c~atiom above assume the probability of passing a test or retest rem constan~ although unknown. However, a systematic change in test

conditions, such as might be caused by a corrupt tester bribed to influence the outcome of retests, could cause the probability of passing retests to differ

horn the probability of passing the original test.

22 ~ptiom descn~d blow cm 1~t t. my “due desired the probabfity with which s~ples of a model titMe acay typical wodd be judged

erroneously, on the basis of retests, to be so atypical as to be unacceptable. Such options require several initial tests to characterize armor deemed typical

and acceptable and would be more efficient (requiring less testing) if the testis one that results in a score rather than a pass or failure.

23 See ~so next Ffi~g, ad app. D (esp. bOX D-1) ~ VO1. 2 of this WWII.

~From 1980 ~ou@ 1990, of 170 us, law e~orcment Offlcem ~U~w--or, 104 (61 percent) Were killed by head wo~ds. [140]
Police Body Armor Standards and Testing: Volume I . 21

The 10 percent occurrence criterion discussed

here for illustration is arbitrary. It would also be

reasonable to require ballistic testing only under

those conditions that research shows affect ballistic

resistance substantially and occur at least, for

example, 5 percent of the time. Deciding where to

draw the line is a policy choice for NIJ, but requiring

testing under conditions that occur no more than 1

percent of the time would be unnecessarily costly

and the marginal benefit might not be measurable.

Two extreme conditions that have been the

subject of recent controversy are exposure of armor

to blistering heat and the heavy wetting of armor as

a result of immersion, sweating, or rain. Although

these conditions apparently are rare, lesser wetting

of armor by sweat or rain is common. However, no

one knows how frequently untreated fabric armor

is wetted enough to degrade its ballistic resistance

to some unacceptable level.

Test Procedures

This section describes OTA’S findings regarding

controversial aspects of the test procedure specified

by NIJ Standard 0101.03:

the BFS test (for protection against injury by a

stopped bullet),

the number of shots required per panel,

what non-penetration in testing says about risk

of penetration in an assault,

the test fixture on which armor is shot, and

the prohibition on patting down bulges in the

armor caused by previous shots in the test

sequence .

Validity is at issue in all cases; the correspondence

of test results to risk in service is uncertain. In some

cases, the controversy is compounded by the lack of

a clear specification of maximum acceptable risk, as

noted above.

The impact of a bullet stopped by armor can

kill or injure the wearer. Bruising and minor

laceration is to be expected, but some test of the

ability of armor to protect its wearer from critical

injury is needed. The NIJ test, which is based on

the depth of the crater made in clay behind the

armor when it is hit, serves this purpose. Of the

armors that have stopped bullets in assaults,

those that would have passed the NIJ test (for

protection from a stopped bullet of the type it

stopped in an assault impacting at the same speed

as in the assault) limited the chance of death or

life-threatening injury to about 1 in 300, which is

much smaller than the maximum risk acceptable to

NILECJ in 1976: 1 in 10.

Armor fails the NIJ test if the depth of the crater

(called the backface signature, or BFS) made in the

clay behind the armor exceeds 44 mm. The 44 mm

limit was based in part on NILECJ-sponsored

experiments in which animals wearing one type of

armor were shot with one type of bullet at a specified

nominal velocity.

2526 No Werner of NIJ-certified

armor has suffered a type of injury that this test was

designed to prevent, even though it was not intended

to prevent such injuries with certainty. However,

critics in the armor industry contend that soft armor

designed to protect wearers from high-energy handgun bullets (type III-A) could be made lighter, more

flexible, and more comfortable if the BFS limit were

increased or if a resilient backing material were

used, and they hypothesize that this could be done

without exceeding the NILECJ-specified maximum

acceptable risk.

Now that hundreds of officers have been shot on

their armor and a few thereby injured, it is possible

to compare injuries sustained (or lack thereof) to the

backface signatures produced in clay behind armor

of the type worn, using weapons and cartridges of

the types used by their assailants. Such measurements are called reenactments; they are reenactments not of the assault, but of a ballistic test the

armor might have been subjected to (see figure 8).

Reenactments are a uniquely valuable, ethical tool

for investigating the safety guaranteed by the

existing NIJ test and for assessing alternative tests.

In particular, they could provide the data required to

estimate whether the 44-mm BFS limit is more

stringent than required to meet the 1976 NILECJ

25 me ~e~emh ~dicat~ 44- ~a~ ~~ppropfiate, if not ~omemative, BFS limit for .qg.speci~ led round-nose bullets impacting at about 8(X)

feet per second (a type I threat) on 7-ply Kevlar armor. NILECJ Standard 0101.01 extrapolated the limit to all armors at all ballistic-resistance levels,

assuming the BFS limit that would limit the risk from a high-energy bullet stopped by any armor to 10 percent would be no greater, and might be smaller,

than the BFS limit for .38-Special bullets on 7-ply Kevlar armor @ster Shubiq pers. comrn., 13 Nov. 1991]. This was a reasonable conjecture at the

time.

26 me NJJJ77J ~so ~d~ ~y ~xpefien~ ~ ~hi~h -~r~d goats ~ere. shot with .357 Magnum ~d g-mm b~le~, as Wa armor on clay backing,

but the research was not completed or published.
22 • Police Body Armor Standards and Testing: Volume I

Figure 8—” Reenactment” of a Ballistic Test That Armor Shot in an Assault Could Have Been Subjected To

 assessment

— . . .

Reenactment

Anal ysis v

. . . . .

Assessment of risk

- of armor passing test

- of armor failing test

SOURCE: Office of Technology Assessment, 1992.

safety goals or any other goal NIJ might consider.

DuPont had an independent laboratory perform

several such reenactments in October 1991. OTA’s

analysis (appendix D) of the results (and the fact that

only 2 to 4 of the roughly 600 shots stopped by armor

caused serious injury) is the basis for the finding

above.

OTA’s analysis shed little light on the discrimination of the test—i.e., on whether the risk to wearers

of armor that would have failed the test was

substantially greater than the risk to wearers of

armor that would have passed the test (see figure 9).

To assess the discrimination of the test more

accurately, more reenactments would have to be

performed.

Although ND’s 44-mm BFS limit has been a topic

of considerable controversy, it has not been a major

cause of certification-test failures: as of October 31,

1991, less than 3 percent of the models of armor

submitted for an NIJ certification test failed solely

because of excessive backface signature.27

The relationship between the probability of

armor penetration on human wearers and the

probability of armor penetration in a NIJ test is

not known.

The probability that a panel of armor will stop a

bullet may vary from one location on the panel to

another. It may depend on the number of shots that

have previously hit the same panel. It may also

depend on whether the panel is wet. The fact that

each of four panels has stopped six fair shots in a test

only provides information about the geometric mean

(a kind of average28) of stopping probabilities

averaged over all shot locations and wet/dry conditions. In particular, it allows one to calculate the

statistical confidence with which the geometricmean stopping probability exceeds any confidence

 is for submitted to and tested for certification of model compliance 

 geometric of 24 probabilities is calculated by multiplying them and raising the result (the product) to Power 
Police Body Armor Standard and Testing: Volume I ● 23

100%

1 o%

1%

o. 1%

Figure 9—Discrimination of the NIJ Test for Protection

From the Impact of Stopped Bullets

 given FAIL)

Perfect

Discrimination

Confidence

o 0.001 0.002 0.003

 given PASS)

None

0.004

Reenactment data provide 90-percent conf idence that the risk of trauma to wearers of armor that would

have passed the test (Pr{trauma, given PASS}) and the risk of trauma to wearers of armor that would

have failed the test (Pr{trauma, given FAIL}) are in the shaded region shown. If they were at the upper

left-hand corner of the region, the test would have perfect discrimination; if they were at the lower

right-hand corner of the region, the test would have no discrimination. This result indicates that

Pr{trauma, given PASS} is less than about 0.0025 unless the test has little discrimination.

Whatever the value of Pr{trauma, given FAIL}, if Pr{trauma, given PASS} were at the right-hand

boundary of the region, there would have been a 90-percent probability that the reenactment results

would have led to a greater maximum-likelihood estimate of Pr{trauma, given PASS} than the one

actually obtained (0). This is what “90-percent confidence” means.

SOURCE: Office of Technology Assessment, 1992.

limit of interest.29 30 This information is important

for characterizing the reproducibility of test results,

but it says nothing about the mean stopping probability on human wearers averaged over shot locations and conditions of assaults.31 That is an issue of

validity.

The DuPont-sponsored reenactments showed that,

in an assault, armor may stop a projectile of a type

it is unlikely to stop in a test. Physical reasoning, and

ballistic tests sponsored by Allied-Signal, suggest

that part of the reason for this apparent discrepancy

is that most types of projectiles are more likely to

penetrate typical armor if they hit it broadside, as in

most shots of the NIJ test, than if they impact at an

angle, as often happens in assaults. The backing

material used in the test may also make a difference.

Performance and analysis of the additional reenactments would yield more information about the

 For stopping probability were 90 percent, there would be a 92 percent chance that one or more 

have occurred; thus the geometric-mean stopping probability (on clay) is at least 90 percent with 92 confidence. By the same reasoning, it is

at least 95 percent with 71 percent confidence, at least 99 with 21 percent confidence, and at least 99.9 percent with 2 percent confidence.

30 shot shots therefore 

probability is as high as most would want. It provides 75 percent confidence that the stopping probability is at least 50 but only 51 

confidence that it is at least 90 and only 2 percent confidence that it is at least 99 percent.

31 of 

1,o79 on one sample of clay, on another sample of clay, on goat on goat abdomen. 

data, not yet analyzed, for .357 and .45-caliber threats N. comm., Jan. 10, 1992], but none for human wearers.
24 • Police Body Armor Standards and Testing: Volume I

400

300

200

100

0

Figure 10—Shots Per Panel in Actual Assaults Assaults

2 5

20

15

10

5

0

 Saves

 Slayings

2 3 4 5

1 2 345

Shots per Panel

SOURCE: DuPont, 1991, based on DuPont and FBI records.

correlation of armor penetration on clay with armor

penetration on human wearers. This information

could be used to determine the number of shots a

certification test must have to infer whether the

armor limits the probability of penetration to whatever level may be required by policy, with the

confidence required. (The probabilities of penetration on clay and in service need not be equal for the

test to be valid, but the relationship between them

must be known, at least statistically.)

Neither the six-shot per panel NIJ .03 test nor

the five-shot per panel NIJ .02 or PPAA tests

reflect expected assault conditions: in a typical

shooting in which an officer’s armor is hit, only

one panel is hit, and by only one shot. The .02, .03,

and PPAA tests for soft armor specify five or six

shots per panel partly for conservatism (i.e., to

simulate a worse-than-expected multi-shot assault)

and partly for economy (i.e., they require additional

shots on a panel in lieu of shooting them at separate

panels, which would increase the cost of testing).

In over 90 percent of 440 felonious shootings of

armor wearers, only one shot hit the armor. In only

two cases—less than 0.5 percent-did five shots hit

a panel. In no case did six shots hit a panel (see figure

10). [16]32 To simulate these assaults in terms of

shots per panel, a realistic 48-shot test33 would

require shooting 23 complete armors,34 about six

times as many as the .03 standard requires: two to six

(nominally four) complete armors.

The realism of NIJ-compliant testing would be

improved if the NIJ standard were revised to

allow testing of a whole armor garment on a test

fixture, such as a mannequin, to which the armor

could be affixed by the strapping or fasteners a

wearer would use. Such a revision would also

create an incentive for technological innovation. For

example, stitching elastic strapping directly to the

32‘r’hese based on FBI of slayings of armored officers from 1980 through 1989 (’‘fatal wounds occurred outside 

426 saves from 1973 through 1989 recorded by Club In there were five saves with an unspecified

nurnberofbullets stopped by one panel and one or two bullets stopped by the opposite panel. Furthermore, of 

were non-fatally hit on unarmored areas of the body.

 of shots would the amount of information the test would provide about the ballistic resistance 

 A 48-shot test shots on of panels and one shot on each of 44 panels, requiring and hence 23 

armors to be shot.
Police Body Armor Standard and Testing: Volume I ● 25

ballistic panels might reduce ply separation of some

armor in an assault as well as in testing, which would

improve the reproducibility of test results.

NIJ has considered alternatives to the fixture

specified in the .03 standard and has had the National

Institute of Standards and Technology’s Office of

Law-Enforcement Standards (NIST/OLES) conduct

tests of three alternative fixtures: (1) the clay block

specified by NIJ Std. -0l0l.03 in a square frame, (2)

a mannequin as specified by PPAA STD-1989-05,

[113] and (3) an experimental curvilinear test fixture

(called “the curv”) consisting of a rectangular frame

holding a clay block but with semicylindrical sides

facilitating the attachment of a complete armor by

means of its own strapping and fasteners (see photo).

NIJ found the curv to be superior to the .03 block,

partly on the grounds that ballistic tests of identical

armor showed greater consistency on the curv than

on the block. [149] Other advantages of the curve,

relative to the clay block, are: (1) the greater realism

of testing whole armor attached by its own strapping

and fasteners; and (2) the practical necessity of doing

so to test an integral armor garment (e.g., one made

with a single, -wrap-around, non-removable ballistic

element). A mannequin of the type specified by

PPAA would also have these advantages.35

As noted above, NIJ recently directed H.P. White

Laboratory, Inc., to use the curvilinear test fixture for

tests of model compliance withNIJ Standard O101.03.

However, the standard itself was not changed, so

other testers may continue to use the clay block

specified by the standard.

Requiring adjustment (“patting down”) of

armor between shots would control shot-to-shot

and test-to-test variability of test conditions. For

armor susceptible to ply separation, this would

decrease the stringency of the test but would

more realistically simulate typical assaults, in

which one panel of armor is hit by only one bullet.

It might simulate assaults with multiple hits per

panel less realistically.

Ballistic tests of identica136 armor panels indicate

that ply separation contributes to the penetration

probability of some types of armor, especially

unquilted fabric armor. Patting the armor down

between successive shots (to reduce or eliminate ply

separation, push the armor against the backing, and

smooth the backing) reduced the penetration probability and hence also the stringency of the test and

the variance in penetrations (a measure of shot-toshot differences) .37

Some critics of the NIJ standard argue that ply

separation (“bunching” or “balling”) does not

occur in actual assaults and that it should therefore

be corrected in certification tests by patting the

armor down between shots. Most of the evidence

adduced consists of statements by survivors of

shootings, who claim their armor did not bunch up,

or that they recall that their armor did not bunch up,

or that they do not recall their armor bunching up.38

Some critics theorize that the dynamic, elastic

human torso oscillates after being shot and pats the

armor down from the inside. Clearly the chest or

abdomen, after being indented by a stopped bullet,

does return to its pre-impact position (unless the

stopped bullet fractures a bone or the armor penetrates the skin). However, biomechanical research

35 w~so fo~d the Cm to be superior to the PPAA mannequin. In these tests, the face of the clay in tie mannequin’s box was planed to facilitate

accurate measurement of the baclcface signature. When armor was mounted on the clay, it arched over the clay in the box, and was not “in intimate

contact’ with the clay as required by both NIJ Std. 0101.03 and PPAL4 STD-1989-05. NIST noted this may have contributed to ply separation, hence

to penetration and variance in results. OTA believes this is not an appropriate compariso~ nor is it consistent with provisions in NIJ Std. 0101.03 for

testing of type III or IV ballistic resistance or female models of armor; those provisions, like PPAA STD-1989-05, require clay to be mounded behind

the armor panel to assure the panel is in intimate contact with the clay. BFS measurement would be most accurate if the first shot impacts a flat area

of the clay, but this need not include the whole face of the clay block.

36 That is, -or pmels made to be as nearly identical as the manufacturing and quality-assurances processes permitt~.

ST Here we assume the probability of penehation on any shot is less than one-half, as it is with high cotildence in dlllost ~c~lcation tests.

Otherwise, reducing the penetration probability would increase the variance.

38 The reliabfity of such assertions is doubti. We do not doubt the integrity and conviction of those who make such statements, but considerable

psychological research shows that recollection of inconsequential circumstances surrounding a threatening or traumatic event is frequently mistaken.

For example, “research. . . with Air Force flight-crew members confirms that even highly-trained people become poor observers under stress. The actual

threat that brought on the stress response, having been highly significant at the time, can be remembered; but memory for other details such as clothing

and colors is not as clear . . . .“ [30]
26 ● Police Body Armor Standards and Testing: Volume I

Mounting Fixtures for Ballistic Tests of Body Armor

Top left: Clay block specified by NIJ Std. 0101.03 in rectangular

frame.

SOURCE: El. du Pent de Neymours & Co., Inc., 1992.

Top right: Mannequin with clay-filled cavity specified by PPAA

STD-1989-05.

SOURCE: Office of Technology Assessment, 1991.

Bottom right: Experimental curvilinear frame tested at HPWLI

by NIST/OLES for NIJ.

SOURCE: Office of Technology Assessment, 1991.
Police Body Armor Standards and Testing: Volume I ● 27

suggests that the sternum (breast bone) would do so

slowly and would not rebound outward.39

On balance, this is too little information to

decide conclusively how common and marked ply

separation is in multi-shot assaults. Worse, we

know of no ethical means of finding out, so the

controversy may continue indefinitely. Even so, it

would be reasonable to revise the standard to

require patting, with the rationale that the

revised test would more realistically simulate the

most common type of assault—assaults with one

impact per panel—but would fire several such

shots at each panel in the interest of economy.

Whether to trade off conservatism about rare

assaults for greater realism in simulating typical

assaults is a policy choice for NIJ. There is no

technical reason not to.

Assuring Quality

NIJ’s certification procedure certifies adequacy of design. It does not assure product

quality, nor does it prevent fraud in the marketplace. It attests that a few samples of each NIJcertified model did pass a test specified by the NIJ

standard and implies other samples could also pass

the test if constructed in the same manner as the

original samples. But certification provides no

assurance that they are so constructed.

Clearly, assuring product quality would require

selecting samples of production armor periodically

and testing the samples. It would also require using

statistical methods to estimate the probability that

the units not tested would pass the test; if it is too

low, certification would be denied, suspended, or

revoked.

OTA has considered two approaches in detail: (1)

lot sampling and acceptance testing and (2) statistical process control. These are described below,

under Options for the Department of Justice, and

in greater detail in appendix E.

UNRESOLVED ISSUES

More research will be needed to assess the

discrimination of NIJ’s test for protection from

the impact of a stopped bullet, to estimate the BFS

limit appropriate for whatever safety goal NIJ

may specify, or to identify a test with better

discrimination between reliable and unreliable

armor. Clearly (see Findings) armor that would

have passed the test has limited the chance of injury

by a stopped bullet of the type, and at the velocity,

used in the test, to less than 1 in 300-but so has

armor that would have failed the test. Possibly the

test discriminates poorly—i.e., the risk of trauma to

wearers of armor that would have failed the test may

differ little from the risk of trauma to wearers of

armor that would have passed the test; if so, the

allegation of some manufacturers that the test has

little discrimination would be borne out. To decide

whether this is so would require performance and

analysis of additional reenactments.

Data from additional reenactments could shed

light on other issues related to protection from

stopped bullets. They could be used to estimate (1)

how risk (in aggregate and by threat) would vary if

the BFS limit were varied and (2) the BFS limit

appropriate for whatever safety goal NIJ may

specify. If additional reenactments are conducted, it

would be convenient to measure, at the same time,

quantities other than crater depth (e.g., crater diameter); this could allow a test with better discrimination

to be identified (see next option).

Tests based on crater depth and other measurements (e.g., crater diameter or deformation

velocity or pressure) should predict acceptable

protection from stopped bullets more reliably

than does the current test, which is based on

crater depth alone. More measurements would

provide more information; further research could

compare the cost-effectiveness of tests based on

different sets of measurements. For example, the

Army developed (for NILECJ) a method to predict

the lethality of a stopped bullet based on the bullet’s

mass and velocity, the armor’s weight per unit area,

the wearer’s weight and body-wall thickness, and

the diameter of the crater made by the armor in clay

backing. With some adjustment (and, ideally, validation by reenactments), the method could be used

to gauge protection from a stopped bullet for armor

certification. Very likely, other models based on the

same or additional measurements would be even

39A bi~~eC~c~mOdel &SCfi~d ~ ~pp. c ~re~cts tit he stem~ (br~st bone) wo~d not rebo~d outw~d ~ycmd its prt3-klpaCt dkfUlCt2 flDIIl

the spine, and it would take about 50 milliseconds-the interval between successive shotsofaMAC-11 submachine gun-for the compression caused

by a stopped bullet to subside to 37 percent of the maximum compression. The abdomen would probably take longer.
28 • Police Body Armor Standards and Testing: Volume I

more reliable, but research would be needed to

confirm this.40

Untreated fabric armor without waterproof

covers is apparently rarely wetted in service (by

perspiration, precipitation, or immersion) to the

extent that its ballistic resistance is clearly degraded; however, the frequency of such wetting is

not known. Hence, if the NIJ standard were

amended to make wet-testing optional (as critics

propose), we do not know how much greater risk

an officer would face wearing dry-certified armor

than wearing wet-certified armor. Nor do we

know how much more frequently the officer

would wear dry-certified armor than wetcertified armor. We suspect the answers to both

questions depend on climate, type of duty, and

individual physiology, and we expect individuals

or departments could answer them as well as

OTA or NIJ could. They could measure wetting of

their armor by weighing it. However, they would

require assistance-training, instructional materials,

or worksheets—to estimate the probabilities of

wearing and wetting and to understand the uncertainties in the estimates.

The status qu0--certification of armor only if

samples pass the test after being sprayed—guards

against the possibility that armor may become

dangerously wetted. However, critics of the NIJ

standard question the need for the wet testing,

arguing that “waterproofing causes more trouble

than it’s worth, because it gives the wearer a

rubber-sheet effect, making the body armor too

uncomfortable to wear.”41 [120]

Defenders of the standard point to the profuse

sweating that wearing any vest can cause in hot

weather, and to the possibility of immersion, as

exemplified by an assault in which an officer42 was

held underwater by an assailant who attempted to

drown him and then shot him twice in the back, on

his armor, with his own revolver.43 Even in this case,

it is not known whether the armor was wet, or how

wet it was, where the bullets hit.

If such wetting occurred as much as 5 percent or

10 percent of the time, it would very likely have

caused penetrations, in assaults, of uncertified,

non-wet-tested armor, which in fact has saved

hundreds of police officers and not once been

penetrated by a bullet it was advertised to stop.44

No one denies that fabric armor not treated to

repel water loses some ballistic resistance as its

water content increases.45 However, it fully recovers

its resistance after drying. Soaking such armor may

degrade ballistic resistance dramatically; spraying it

with salt water to simulate sweating had a negligible

effect in one series of tests; [105, 106, 8] we do not

know how spraying as spectified by NIJ Standard

0101.03 affects the ballistic resistance of various

armors.

Tests conducted for NIJ by MST’s Law Enforcement Standards Laboratory in 1990 showed the V5O

(the velocity at which bullets have a 50 percent

chance of penetrating) of KevlarR panels decreased

with increasing water content as shown in figure 11.

[62]

To use this information (or similar information

about other bullets or armor) to assess the risk of

unacceptable degradation of ballistic resistance, one

would have to know the statistics of moisture pickup

by armor worn by the wearer or wearers of interest.

In an experiment conducted at the FBI Academy,

untreated KevlarR armor worn by an instructor

performing prolonged strenuous activity (on a‘ ‘hot,

humid day” [62]) absorbed and retained perspira40 See appen~ E for further details.

41 FabriC -or tit pasSa a teSt @ cm ~ made t. pass it wet by treating @ b~istic fabric or the fiber from which it is woveQ by eIICIOSklg the

ballistic element ina waterproof cover, or by using more layers of untreated fabric. Some treatments may make the armor more costly or less comfortable.

42 Ohio State Trooper Cardinal.

43 Theme I 8.ply Kevl~ b~k p~el of the officer’s Point Blank armor (which had a ~W frOnt pRUel) stopped ~th shots> even fiough ‘m

impacted close to the edge of the ballistic panel, where armor is not tested for ballistic resistance. The shots made a hole extending horn 13/d inch to

33/A inch from the edge of the c~er g~ent’s pocket for the ballistic panel. The ammunition ww Cm 125-gK JSp .38 SP1 +P.

44 Unmrtified armor not designed to provide rated performance when soaked is credited with more “saves” per vest sold than comparable certifkd

(wet-tested) armor is. Mr. ClintonE. Davis, Executive Vice-President, Second Chance Body Armor, Inc., wrote, “Ourrecords show over the last eighteen

(18) years that 10 percent of the non-waterproofed vests in the field have accounted for 40 percent of the saves. This means that a non-waterproof

concealable vest is six (6) times more likely to be worn. ” [46] OTA is not persuaded of the last poin~ because non-wet-tested armor has been on the

market and in service about six years longer than wet-tested armor has, allowing more opportunities for more saves. However, it is plausible that a

non-waterproof concealable vest is more likely to be worn.

45 Sowg does not cause ~or~de from nonwoven Spectra Shie@ composite mtefi to lose bd.listic resistance.
Police Body Armor Standard and Testing: Volume I ● 29

Figure 1 l—Effect of Wetness on Ballistic Resistance

of KevlarR Armor

v 50 (ft/s) 1,600

1,400

1,200

1,000

800

600

400

200

0

— 20-ply panel

+ 12-ply panel

0% 5% 10% 15% 20% 25% 30% 35% 40%

Water content (o/o of dry weight)

124-gr 9mm FMJ

SOURCE: Office of Technology Assessment, 1992, based on data from

NIST/LESL, 1990.

tion equalling 22 percent of its weight, which could

cause a considerable loss of ballistic resistance (see

fig. 11). [8] If ballistic resistance is to be certified

even for such conditions of heavy and prolonged

perspiration, spraying or immersing the armor before ballistic testing is necessary. However, some—

perhaps most-duties will not cause enough perspiration to significantly degrade the ballistic resistance

of untreated fabric armor,46 and moisture pickup

may depend on fabric47 and individual physiology.

By wearing and weighing untreated fabric armor,

an individual could estimate how often it becomes

dangerously wet. By alternately wearing waterproof

armor, he or she could decide whether it is less

comfortable; if not, there would be no reason to wear

the untreated armor. However, we doubt many

officers would conduct such an experiment at their

own expense, and what they learn would not help

others.

NIJ could solicit volunteers for a similar nationwide experiment and provide them with armor. For

the results to be useful in various jurisdictions, NIJ

would have to determine how wetting and wear rate

(or comfort) depend on various factors, such as the

ambient (outdoor) Temperature-Humidity Index and

whether the wearer spends most of the time in a

climate-controlled environment. One of the problems of such a study would be reliance on volunteers; those who do not volunteer may be the ones

most sensitive to comfort-the ones hypothetically

most benefited by untreated armor.

Departments that order and enforce the wearing of

armor would be in a position to randomly select

subjects and order them to participate. However, the

department would face an ethical dilemma: could it

justify ordering an officer to stop wearing wet-tested

armor and instead wear untreated armor for the

duration of the experiment, knowing there is a

possibility it might be wetted enough to be degraded

and then shot in that condition? The risk appears

low, but such an experiment must be performed to

measure it. It may happen that the risk is more than

offset by the increase in wear rate. A decision to do

so would be analogous to a common one: deciding

to issue type II or II-A armor rather than type III-A

armor, because of comfort, economy, or expected

wear rate; the type III-A armor promises better

protection.

In summary, there is an apparently small but

unquantified risk that non-wet-tested armor might

be wetted enough to be degraded and then shot.

However, wet-tested armor might be worn less often

than non-wet-tested armor. There is no compelling

evidence that requiring wet-testing costs more lives

than it saves, but neither is there a compelling

rationale for continuing to require armor to be tested

wet, as the current NIJ standard does. Revising the

NIJ standard to allow armor to be tested wet or dry

would allow purchasers to choose armor that they

believe offers the most protection, considering wear

rate as well as ballistic resistance, and considering

local and personal factors, such as climate and type

of duty. They might err, and more research would be

needed to give them better guidance.

OPTIONS FOR THE

DEPARTMENT OF JUSTICE

Some have questioned the need for a Federal role

in the formulation of standards for body armor

intended for use by State and local police officers,

yet no serious contention has surrounded the assignment of that role-given that it should exist—to the

46 Up percent 

 fabric holds less water than does saturated 
30 • Police Body Armor Standards and Testing: Volume I

Department of Justice.48 Within the Department of

Justice, the role again finds a natural home: the

National Institute of Justice, created in 1979 by the

Justice System Improvement Act. NIJ’s mission is

‘‘to encourage research and development to improve

the criminal justice system and to disseminate the

results to Federal, State, and local agencies. ’ [144]

A major part of NIJ’s effort to assist lawenforcement agencies with the acquisition of new

technology is the issuance of voluntary standards for

a variety of police equipment, including radios,

weapons, automobile tires, and body armor. The

Office of Law-Enforcement Standards (OLES) of

the National Institute of Standards and Technology

(NIST) assists NIJ in developing and revising

standards, including the standard for ballistic resistance of body armor.

Although no significant body of opinion holds

that the body armor question lies outside of NIJ’s

mandate or purview, many have expressed the

feeling that NIJ has become unduly wedded to the

existing standard. They feel that long-standing

conflict over the body-armor issue among persons

whose strong personalities and knowledgeable minds

are driven by the earnest desire to save the lives of

as many police officers as possible has solidified

positions, especially those in NIJ, to a degree beyond

that justifiable on purely scientific or technical

grounds. This perception constitutes a public relations problem for NIJ.

It is clear the standard should be revised—

eventually. It could be revised now to reduce the

latitude in test procedures permitted by the standard.

This would limit lab-to-lab and test-to-test variations in test conditions, which might be partly

responsible for variations in test results. Minor

variation in test conditions occurs in normal testing;

its influence may be minor or insignificant. However, it is possible a tester may have some incentive

to conduct a test “by the book” but in a manner

intended to maximize (or, depending on the incentive, to minimize) the probability that the armor will

pass the test. Minor revisions in the standard could

limit the latitude of such inadvertent or operatorcontrolled variation in test conditions. The section

Revise NIJ Standard 0101.03 (below) describes

several such revisions; they include specifications of

bullets and backing material, reducing the range of

allowed backing-material temperature, measuring

backing-material temperature and consistency more

frequently, and patting down armor between test

shots. Revising the standard to specify a number of

specific procedures already used at H.P. White

Laboratory, Inc. would further limit possible lab-tolab variations in test conditions. (Recall that any

individual with two guns, modelling clay, a thermometer, a steel ball, and a ballistic chronograph

can test samples of armor and certify the model’s

compliance with the NIJ standard on the labels of

other units of the model.)

Moreover, as discussed above in Findings, the

validity of the current test has not been demonstratednor can it be until acceptable risks are specified. This

lack of demonstrated validity does not require

revising the current standard. But if NIJ wishes to

assure purchasers and wearers of the protection

afforded by a unit of certified armor, it must (1)

specify its safety goals so the validity of the current

test or a proposed revision maybe tested; (2) test the

validity of the test specified by the standard; (3)

revise the standard, if required for validity, and (4)

implement a quality-assurance program to ensure

that certifiled armor offered for sale is as safe as the

samples that passed the (valid) test of ballistic

resistance. All the items on this list are discussed in

the next four subsections: Specify Acceptable Risks,

Revise NIJ Standard 0101.03, Assure Quality, and

Sponsor Research.

Specify Acceptable Risks

Specifying acceptable risks would allow the

validity of the current test to be decided scientifically and would give NIJ a yardstick for assessing

options for revising its test and its certification

process. NIJ should specify the types and degrees of

injuries and incapacitation by penetrating and nonpenetrating bullets that the armor is to prevent and

the maximum acceptable risks of such injuries and

incapacitation (as well as the statistical confidence

with which acceptable risk must be demonstrated).

Illustrative options for doing so are listed below.

Safety goals should be weighed carefully, bearing

in mind they benefit only those who wear certified

armor. Making the goals extremely stringent

could decrease the number of such officers and

increase the ranks of those who wear uncertified

~ See, however, Other Policy options, below, regarding the jurisdictions of the Federal Trade Commission (FTC) md the OCCupatiOMl safeW and

Health Administration (OSHA).
Police Body Armor Standards and Testing: Volume I ● 31

armor or none. Requiring very high confidence

that the test limits the probability of whatever

type of injury is to be avoided to a very small

number will make the cost of testing the validity

of the test very high and will increase the cost of

compliance testing and of producing certified

armor. It may also require armor to be thick, stiff,

and heavy in order to have a reasonable chance of

passing the test. Such armor would probably be worn

less, which could cost lives, on balance.

A statement of goals could be of the following

generic form:

Certified armor should:

(1) Stop each shot, up to n per panel, with

probability ps or greater.

(2) Leave wearer ambulatory with no injury rated

higher than ion the Abbreviated Injury Scale49 [88]

after each stopped shot, with probability pa or

greater.

Reenactments or other tests should:

(3) Demonstrate that armor meeting the certification criteria will accomplish goal (1) with at least

Cl-percent confidence and goal (2) with at least

C2-percent confidence.

Customizing this statement requires choosing

values of n, ps

, i, pa, and C. The parameters n and ps

specify the required protection from penetration in

an assault by whatever projectile may be specified:

n is the number of shots the ballistic element (e.g.,

panel) is to withstand, and ps is the minimum

reliability with which each of them is to be stopped.

Thus if a panel is to stop each of six shots (n = 6) with

97 percent reliability (ps= 0.97), then it should stop

all six shots with 83 percent reliability (0.976 =

0.83).

A ballistic test used or proposed for certification

of armor’s ballistic resistance may require more or

fewer than n shots per panel. Whether it provides the

protection required by this safety criterion (viz.,

from n shots per panel) is a question of validity that

can only be settled (ethically) by reenactments

designed to test the validity of the test. If the safety

criterion requires the armor to withstand more

impacts of the specified bullet per panel than have

ever hit a panel of armor in service, the validity of the

test cannot be tested scientifically. If there are

enough assaults of the appropriate type to perform

reenactments and test validity, the conclusion may

depend on the required reliability, and will depend

on the confidence (C1

) with which validity is to be

demonstrated. Requiring extreme reliability and

confidence will ensure that any ballistic test will fail

a test of validity. If NIJ wants a demonstrably valid

test, it must not require that a panel withstand more

than a few shots, nor that it withstand them with 100

percent reliability, nor that this be demonstrated

with 100 percent confidence.

The parameters i and pa 

specify the required

protection from stopped projectiles in an assault.

The parameter i designates the maximum tolerable

severity of injury, on the following scale:

Abbreviated Injury Scale

6: fatal

5: critical-survival uncertain

4: severe, life-threatening-survival probable

3: severe, not life-threatening

O-2: not severe

Protection from incapacitation may also be specified-for example: “Leave wearer ambulatory. . . .“

It is tempting to specify “Leave wearer ambulatory

and able to hit a man-sized target in a vital area with

at least one round from service weapon (etc. ),” but

it would be difficult or impossible to demonstrate

scientifically that a ballistic test meets such a

requirement. The ability to walk away—a useful

capability in itself-is more easily tested and can be

considered a “proxy” (a plausible substitute) for

other desirable capabilities, the validity of which

may be impossible to confirm.

The parameter, is, again, a kind of reliability—

the reliability of protection from severe injury or

incapacitation by a stopped bullet. More of it is

better, but the higher the value specified, the lower

the confidence with which reenactments can confirm

validity. Requiring extreme reliability (pa) and

confidence (C2 ) will ensure that any ballistic test

will fail a test of validity.

The illustrative generic safety goals are necessarily technical in order to make it possible to test their

validity scientifically. Even if realistic parameter

values are chosen, it may take years before a test of

49we expect ~~~~d ~mt -or t. ~mvent ~jfies ~~ MS rafigs of 6 (fa@), 5 (criti~: surviv~ uncertain), and 4 (severe, life-~atellirlg:

survival probable) with a high probability. NIJ could allow injuries rated 3 (severe, not life-threatening) or below on the AIS, on the grounds that requiring

armor to prevent them may have a negative, but as yet unquantiiled, effect on wear rate.
32 . Police Body Armor Standards and Testing: Volume I

Table 3—Choices for Safety Goals

Option Psi Pa c1 C2 Rationale

1 6 0.97 3’ 0.99 50 99 Goals defined implicitly by NIJ

Standard 0101 .03@ c

2 6 0.95 3 0.95 95 95 NIST hypothesized ps

,

-d to balance risks, pa, C1/1 OO, and

C2/100 assumed equal.e

3 6 0.90 3 0.95 95 95 Less than half of penetrating

torso wounds are fatal.f

Notes:

 not higher injury rating, 4, which is to be avoided, means “severe, life-threatening;

surviva! probable.”

bNIJ requires, 

probability day at least 97 percent, for soft armor. The calculation, based on the test of 24 fair shots per caliber

with no penetrations, is: 1- thus 0.50= 1-0.971524. The standard is also consistent with (Cl = 

 - 0.71), and other combinations. However, the refers to the 

probability on wearers, in service. This is tacitly assumed to be comparable to the stopping probability on clay, but

additional research would be needed to test the hypothesis.

 implicitly required safety from stopped bullets is greater than required by the as discussed above in

Findings.

 illustrative boundary between bad and marginai armor (see appendix forthe fact that the of increased 

O percent to 5 percent, the acceptable risk of life-threatening injury from a stopped bullet has been decreased from

10 percent (the to 5 percent.

fThe ailowed risk (1- of penetration is twice the risk (1- of iife-threatening injury by a stopped bullet,

because fewer than half of penetrating torso wounds are This may risks more than option 2.

SOURCE: Office of Technology Assessment, 1992.

the validity of a ballistic test with respect to the goals

may be completed. They will have to be explained

in terms familiar to police officers. The present

question for NIJ is whether to specify safety goals

explicitly and realistically enough so they can be

used as a standard against which the validity of

ballistic tests of armor can be assessed.

Table 3 shows three possible combinations of

parameters for the generic statement of safety goals

and provides a brief rationale for each option. All are

realistic and, we believe, comparable in some ways

to what NIJ Standard 0101.03 was intended to

require. However, these options are more rigorous in

that they specify confidence levels with which

validity is to be demonstrated. It is harder to

demonstrate that a ballistic test meets a safety goal

requiring only 97 percent reliability in stopping each

shot and 50 percent confidence that the reliability is

that high than to demonstrate that the test meets a

different safety goal requiring 100 percent reliability

in stopping each shot but no specific confidence that

the reliability is that high.

Revise NIJ Standard 0101.03

This section describes the most important options

for revising NIJ Standard 0101.03. Appendix E

discusses these (and others) in greater detail.

Whatever other changes are made, some of the

latitude in test procedures permitted by the standard

should be reduced to limit lab-to-lab and test-to-test

variations in test conditions, which might be partly

responsible for variations in test results. Since NIJ

Standard 0101.03 was issued in 1987, the 

White Laboratory, Inc. (HPWLI), which currently is

the only ballistic test laboratory authorized by NIJ to

do testing for certification by NIJof compliance with

the standard, has adopted particular ways of conducting the test in the interest of reproducibility. NIJ

has also issued directives instructing the H.P. White

Laboratory to perform parts of the test in particular

ways that are not the only ways allowed by the

standard. Other laboratories attempting to conduct a

test in accordance with the standard+. g., for

developmental testing of a new model—might

conduct their testing in accordance with the standard

but not exactly in accordance with the procedures

H.P. White Laboratory would use for certification

testing of the model.

The lab-to-lab variations in test conditions might

cause lab-to-lab variations in test results. To preclude this, when NIJ does revise NIJ Standard

0101.03, the many de facto requirements that have

been specified by letters, telephone calls, or established practice at H.P. White Laboratory should be

incorporated explicitly into the revised standard.

This would limit the ways in which test conditions
Police Body Armor Standard and Testing: Volume I ● 33

could differ from laboratory to laboratory, and, at

laboratories other than H.P. White, from test to test.

Revise the Backface Signature Limit

The backface signature limit specified by the

standard could be revised based on the maximum

risk of injury NIJ will accept and the statistical

confidence it requires in the validity of the BFS test.

The amount of each demanded is a policy choice for

NIJ (see Specify Acceptable Risks, above). Of all

possible limits that would satisfy the safety goals,

NIJ could choose the one that maximizes discrimination—i.e., that minimizes the estimated probability of misclassification of acceptably safe armor as

unacceptable or vice versa.50

The maximum allowable BFS might be calculable

from existing reenactment results, depending on the

safety goals. For example, if NIJ chooses to allow at

most a 1 percent probability of life-threatening

injury from a stopped bullet (even if survival is

probable), then permitting any BFS but prohibiting

penetration would accomplish this with better than

99 percent confidence, if armor designs and the

firearms threat change no more than they did in the

past two decades. Additional research would be

necessary to determine BFS limits appropriate for

some safety goals NIH might specify (e.g., if NIJ

undertakes to protect wearers against injuries rated

3 or lower on the Abbreviated Injury Scale).

Require Patting Down of Armor Between Shots

The standard could be revised to require patting

down of armor between shots. This would simulate

typical assaults (those that cause only one impact per

panel) more realistically than does the current test.

However, it might simulate assaults causing multiple impacts per panel less realistically. It would limit

inadvertent shot-to-shot and test-to-test variability

of test conditions, and would limit opportunities for

any operator (tester) to deliberately influence the

probability of passing by aiming either at or between

the “hills” caused by the bunching effects of

previous shots. It would decrease the stringency of

the test in that it would give armor of models

susceptible to ply separation in testing an increased

probability of passing.

Specify Standard Bullets

The bullets to be used in the test could be specified

more precisely. The probability with which a

commercially available bullet of specified mass and

caliber will penetrate armor at a specified velocity

depends on the bullet’s construction and composition. [28] A bullet that deforms may be stopped by

relatively few layers of armor; many more layers

may be needed to stop sharp fragments of a hard or

steel-jacketed bullet.

Specifying more precisely the bullets to be used

in the test could increase reproducibility of test

results. It would not simulate the diversity of the

threat faced by police officers (neither does the

current set of test bullets), but reenactments could

assess the reliability with which armor tested with

standard bullets stops bullets that hit wearers.

Specify Standard Backing Material

The backing material to be used could be specified. Specifying the backing material to be used for

the test might improve its reproducibility. In practice, only one backing material, Roma Plastilina No.

1 modeling clay, is used by HPWLI for NIJ

certification tests. However, NIJ Standard 0101.03

does not require it; a tester may use any material that

passes the “drop test” specified to check the

consistency of the backing material.

Some backing materials conditioned to pass the

drop test yield different backface signatures at the

much higher deformation velocities typical of a

ballistic test conducted in accordance with NIJ

Standard 0101.03.51 Thus the drop test does not

assure that backface signatures produced in different

backing materials behind similar armors by similar

bullets impacting at similar velocities will be the

same. Some materials are known to yield different

results; others, not yet tested by NIJ or NIST, could

differ more dramatically. Specification of a backing

material would eliminate this potential source of

50 ~temtively, ND could choose the one that minimizes its expected utility, [9] but this would involve assessing the value of a life saved in monettuy

or other terms to which the values of other possible benefits and losses may be compared. This has proven controversial in other fields, such as automotive

safety engineering. [76]

51 For exmple, ~ teSt5 conducted by the British police Scientific Development Branc& under otherwise simih COnditiOKIS the average (Vk fitt@

backface signatures produced in U.S.-made Plastilioa and U.K.-made Plasticize were similar at impact velocities of 350 Ws but differed by about 4.4

mm for each 100 m/s above or below 350 m/s. [29] Cf. [28, 84].
34 ● Police Body Armor Standards and Testing: Volume I

variation in-or operator influence on—test conditions. 52

Reduce Tolerances on Backing Material

Properties

The allowable range of backing material temperature could be reduced, and the temperature or

consistency of the backing material (or both) could

he required to be measured at specified time

intervals or stages of ballistic testing.

The consistency (flowability) of clays commonly

used for backing has been shown to be very sensitive

to clay temperature. Variation in the temperature of

clay backing material could make the difference

between passing and failing NIJ’s test for protection

from stopped bullets. In 1977, the Aerospace Corporation recommended that, for adequate reproducibility, backing material be maintained at 70° plus or

minus 2°F.

NIJ Standard 0101.03 allows backing material to

have a temperature between 15 and 30°C (59 and

86°F) during testing. It requires the consistency of

the material to be tested three times by dropping a

specified weight from a specified height and measuring the depth of the crater it makes. In practice (at the

H.P. White Laboratory), all three drop tests are

conducted before—not during or after-testing.

Possibly the consistency may change during testing,

e.g., as a result of bullet impacts or as the material’s

temperature approaches ambient temperature (which

is required to be in a narrower range than the

material’s temperature). In tests observed by OTA,

the backing material cooled during testing.53 Possibly this happens in a uniform way at H.P. White, but

it could vary from lab to lab. Moreover, the latitude

permitted by the standard could be exploited to

influence test results.

Reducing the allowable range of backing material

temperature, and requiring temperature to be measured and consistency to be tested at specified time

intervals or stages of ballistic testing would limit the

latitude for deliberate or inadvertent variation of test

conditions, even within the bounds allowed by the

standard, or inadvertent transgression of the bounds.

It may improve the reproducibility of backface

signature measurements, especially of crater diameter, which could be used in assessing protection from

blunt trauma. It might also improve reproducibility

of penetration tests.

Certify Wet and Dry Ballistic Resistance

Separately

The wet test could be mandatory or optional.

Some purchasers or wearers may prefer armor with

inadequate wet ballistic resistance because of cost or

comfort. They may suspect the risk of its becoming

dangerously wet is so low they would accept it. But

to learn what the risk is, they would have to weigh

their armor regularly to measure and record water

retention and analyze the records to calculate

frequency with which retention exceeds dangerous

levels. In compensation, wear rate might be increased among those who find armor with inadequate wet ballistic resistance more affordable or

comfortable but who also value NIJ’s certification.

Subjecting armor only to the dry testing specified

in the NIJ standard would reduce the stringency of

the test, even for armor that performs as well wet as

dry. If NIJ wished to compensate for this and

maintain the stringency of the test, it could offer a

choice of the current wet-dry test or a double-dry test

with the same number of fair shots required.

To halve the cost of testing, one industry source

has proposed testing and certifying dry ballistic

resistance or wet ballistic resistance, but not requiring both tests. This is based on the premise that no

conceivable type of armor has less ballistic resistance when dry than when wet. This is plausible, but

even if true, armor would have a higher probability

of passing a wet-only test than a wet-dry test with

twice as many shots.

Rate the Ballistic Resistance of Each Certified

Model With a Score

The standard could specify a way to rate the

ballistic resistance of each certified model with a

score, such as the V50 ballistic limit-the velocity at

which test bullets have a 50 percent chance of

penetrating.

The present certification test is a pass/fail test,

although armor may be tested for resistance to any

type of bullet at any velocity. Nevertheless, knowing

52 ~~ou@ ~~y ~ompoSition d~ons~ably ~=. me r~~ts of the deformation test (for protection from nollpenetrating blllle~), it k IIOt ~~

that it affects the results of the penetration test. More research would be needed to fmd out whether it does.

53 However, after the last shot at each panel, craters were filled with clay warmer than the rest of the face of the clay block.
Police Body Armor Standards and Testing: Volume I ● 35

Figure 12—Estimates of V5O and V1O Obtained by Logistic Regression

Penetration probability

1

0.9 — Logistic Model

 Data (stop) 0.8

 Data (penetration)

0.7

0.6 V50 estimation

0.5

‘ -- 

0.4

0.3

0.2

V 10 estimation 

0.1 ———— — — — — — — — — — — — — —

0 ‘

— 

600 700 800 900 1,000 1,100 1,200 1,300 1,400

Impact velocity (ft/s)

1,500 1,600

.357 Magnum at 30° incidence v. panel on clay, smoothed between shots.

SOURCE: Office of Technology Assessment, 1991.

only that a model has passed does not indicate the

velocity at which the test bullets would be expected

to penetrate it. Indeed, that velocity cannot be

estimated unless the test requires some test bullets to

impact at a velocity high enough to penetrate the

armor samples.

A test developed by the Department of Defense

[138] for estimating the V5Oof (unbacked) armor

could replace NIJ’s current test of resistance to

penetration. 54 A model could be certified to have a

specified type or level of ballistic resistance if the

V50 for each type of test bullet equals or exceeds a

specified minimum value, and if samples also pass

a test for protection from blunt trauma. But the

model would be rated as well as certified, to let

purchasers know the model exceeds minimum NIJ

standards-and by how much.

An alternative score is the V1O, the velocity at

which test bullets have a 10 percent chance of

penetrating-i.e., at which armor stops a bullet with

90 percent reliability. It could be estimated by

logistic regression [91] based on velocities and

penetrations measured in a DoD-like test (see figure

12). For purchasers who demand 90 percent, rather

than 50 percent, reliability in stopping, the V1O would

be more appropriate for comparing to typical or

conservative threat velocities than would the V50.

However, probability of penetration in service may

differ from probability of penetration in the test.

A sample’s V05 or V01 could likewise be estimated

by logistic regression, and certification could be

based on them. However, there would be more

uncertainty in these estimates than in estimates of

Vl0 or V50; achieving comparable accuracy would

require firing more shots than would be needed to

estimate V10 or (esp.) V50.

Use Anthropomorphic Test Fixture

The standard could be revised to allow or require

testing of a whole armor garment on an anthropomorphic test fixture to which the armor could be

affixed by the strapping or fasteners a wearer would

use. This would improve the realism of the test and

would be necessary to test integral armor-armor

made from a single panel of ballistic material

stitched so that it can not be spread flat on a clay

block. The curvilinear frame developed and tested

by NIST for NIJ would be a suitable fixture; so

 DOD as backing material, but NIJ could that clay or some other backing material be used. Regardless 

used, calibration of penetration probability in the test with penetration probability in assaults would be an issue.
36 ● Police Body Armor Standards and Testing: Volume I

would the mannequin specified by the PPAA. For

either fixture-but especially for the mannequin-it

would be prudent to require aim points to be at least

2 inches from the frame or clay box walls, to limit

whatever effects their proximity may have on

penetration probability or deformation.

The standard should continue to require that the

armor be placed in intimate contact with the backing

material. This may require mounding the backing

material behind some parts of some armors. However, the standard could require the backing surface

to be flat within a specified (perhaps threatdependent) radius about the first aim point, to permit

backface signature to be measured to the current

standard of accuracy.

The standard could specify test fixtures of various

sizes to accommodate armors of various sizes. NIJ

Standard 0101.03 specifies that samples be sized for

46- to 48-inch chests, explaining that ‘the larger the

size, the more likelihood that all ballistic testing will

fit on just two complete armors.” However, it may

be that smaller armor is less likely to pass the test,

other things being equal—that is, size may be

ballistically significant. We do not know whether it

is, and we do not know that it is not, but qualitative

physical arguments suggest that it might be.55 Hence

a more conservative provision would require separate certification, and hence testing, of each size,

which might require fixtures of several different

sizes. This would be costly—it would increase the

nonrecurring cost to the test lab, which would have

to stock several fixtures, and the recurring cost to

manufacturers, who would have to conduct more

testing.

A simpler, less costly, and even more conservative option would be to require the samples to be the

smallest size in which the model is offered.

Certification of lots (rather than models) as

described below would require the test lab to have

fixtures of various sizes to accommodate samples of

various sizes. However, it would not require each

size of each model represented in a lot to be tested;

two tests per lot would suffice in some cases.

Assure Quality

OTA found (see Findings above) “NJ’s certification procedure. . . does not assure product quality,

nor does it prevent fraud in the marketplace. ’ This

section describes briefly two options, either or both

of which NIJ could implement if it wants to assure

buyers and wearers that each unit of armor certified

to comply with the current NIJ standard (or a

successor) and offered for sale has been subjected to

sampling for inspection and ballistic testing to

confirm its adequacy or its similarity to samples

previously found to be adequate.

Many variants of these illustrative options maybe

invented; they would provide different types of

guarantees-some statistical, others non-quantitative. They would assure product quality and provide

assurance against some imaginable types of fraud in

the marketplace. Preventing false or deceptive

labeling or advertising is discussed below, under

Other Policy Options.

Certify Lots

NIJ could certify lots, rather than models, of

armor. This would certify acceptability of product

quality, not just acceptability of model design. If

intentional or inadvertent changes in manufacturing

caused the ballistic resistance of units (nominally) of

a certain model to degrade, this option would keep

lots with unacceptably low ballistic resistance off

the market, with a probability that can be made as

high as desired by testing a sufficient number of

samples per lot. Either the ballistic test specified in

NIJ Standard 0101.03 or a different one could be

used.

To exercise this option, NIJ would have to

1.

2.

3.

Define a lot.

Specify a sampling plan--i.e., the number of

samples from each lot to be tested, and criteria

for acceptance and rejection based on test

results.

Ensure the samples to be tested are selected

randomly from each lot.

55 men -or stops a btile~ tie armor is bent stretched, and often cut or tomnea the point of impact. A second shot may be more Wely to Penetrate

ifit impacts in the damaged area than if it impacts eLsewhere. The standard’s requirement that each test shot impact at least 2 away inches from any point

of prior impact is intended to prevent this influence. However, the radius of weakening might extend farther than 2 inches from a point of impact; the

extent of weakening would depend on the bullet its velocity, the armor, and the backing material.
Police Body Armor Standard and Testing: Volume I ● 37

Figure 13—Notional Control Chart for Sequential Lot-Acceptance Testing

Failures

7 I /

4 --

3 -

2 -

1 -

Consumers’ risk

if accepted

 lot

-. >----

Producer’s risk

if rejected

 lot

2 3 4 6 7 8 9 10

Tests

SOURCE: Office of Technology Assessment, 1992.

Any of several sampling plans could be used.56 A

sequential procedure that OTA finds appropriate

●

●

●

●

●

●

is based on a pass/fail ballistic test for individual units;57

allows a lot to be inhomogeneous;58

defines a unit as “bad” if it has a probability of

passing less than a value pb to be specified by

NIJ;

defines a unit as “good” if it has a probability

of passing greater than a value p G to b e

specified by NIJ;

limits the probability of accepting a lot containing one or more “bad” units to the maximum

consumers’ risk acceptable to NIJ; and

I.i.rNIJs the probability of rejecting a lot containing only ‘‘good’ units to the maximum producer’s risk acceptable to NIJ.59

Samples would be selected randomly from the lot

and tested. Testing could be allowed to continue

until the fraction of tests failed is so great that the lot

must be rejected to limit the consumers’ risk or so

small that the lot must be accepted to limit the

producer’s risk. To decide when a lot must be

accepted or rejected, a “control chart, ” such as the

one shown in figure 13, could be used.60

Establish a Voluntary Quality-Control Program

NIJ could establish and supervise a voluntary

quality control program analogous to the Listing or

Classification programs of Underwriters Laboratories, Inc. (UL). UL Classification of a model of

armor would be based partly on ballistic testing of

samples and partly on inspection of the manufacturer’s manufacturing and quality assurance processes by NIJ or a contractor.

56 However, some Widely used may be inappropriate-for example, those that assume a‘ ‘defective’ unit 

identified as such by inspection or testing.

 .03 test could be used, if armor were only tested wet, so that one unit of would be for each test.

58 whether have some other approaches 

quality control, it is important that a lot be homogeneous, i.e., that units in the lot be alike, at least insofar as can be determined before testing.

59 accomplished the ballistic 

 E of vol. 2 for details.
38 . Police Body Armor Standards and Testing: Volume I

The cost of UL or UL-like procedures for assuring

body armor quality would depend on how samples

are selected, the standard to which they are tested,

and the confidence (if any) with which the tests are

to assure that the samples are identical to the original

test articles or, in any case, provide the ballistic

resistance required.

A simple option would be Classification of a

model of armor as compliant with NIJ Standard

0101.03 or a similar standard. This would require

iNIJial testing of samples in accordance with the

standard. Continuation of Classification would be

contingent on audits of the manufacturer’s production and quality control processes and on selection,

inspection, and ballistic testing of production samples to gauge their similarity to the iNIJial samples.

UL estimates iNIJial testing of a model could be

performed for about $3,000, with each additional

model (from the same manufacturer) tested at the

same time costing about $1,500. Ongoing FollowUp Service would require four annual visits and cost

little more than about $700 to $1,000 per year, if the

manufacturer’s quality control program is in good

order. [112]

However, this option would not provide quantitative estimates of the maximum risk of UL-Classified

armor. Moreover, some manufacturers might hesitate to participate in it because they would perceive

unannounced factory inspections as being intolerably intrusive.

Sponsor Research

Some OTA findings noted gaps in the knowledge

needed for rational standard-setting that could be

filled by additional research. For example, one noted

that “the relationship between the probability of

armor penetration on human wearers and the probability of armor penetration in an NIJ test is not

known.” OTA also noted two Unresolved Issues

that might be resolved by further research:

“More research will be needed to assess the

discrimination of NIJ’s test for protection from the

impact of a stopped bullet, to estimate the BFS limit

appropriate for whatever safety goal NIJ may

specify, or to identify a test with better discrimination between reliable and unreliable armor. ”

“Tests based on crater depth and other measurements . . . should predict acceptable protection from

stopped bullets more reliably than does the current

test, which is based on crater depth alone. . . . Further

research could compare the cost-effectiveness of

tests based on different sets of measurements. ”

The following options for research are aimed at

reducing or eliminating these gaps in knowledge.

NIJ could propose, through the budget process, a

specific program of research for funding by Congress (see Legislative Options, below).

Investigate Resilient Backing Material

NIJ could investigate the use of resilient backing

material for penetration testing. Use of resilient

backing material, such as foam rubber or silicone

rubber, for penetration testing might make ply

separation and penetration probability during testing

comparable to that in an actual assault. However,

there is little objective information about how much

ply separation occurs in any shootings of armored

humans, especially in assaults, and we doubt there is

an ethical way of learning much more about it. The

correlation of penetration in assaults with penetration on resilient backing in tests could be estimated

by conducting reenactments of assaults (see below).

The current BFS measurement on clay backing or

some other test (see below) could be used to estimate

risk of injury from stopped bullets.

Sponsor Additional Reenactments of Assaults

NIJ could sponsor additional reenactments o f

assaults for any or all of several purposes, for

example:

●

●

To estimate the risk, and confidence limits on

the risk, of injury by stopped bullets, as a

function of backface signature depth. Additional reenactments would allow the dependence of risk of injury (especially minor injury)

on backface signature to be inferred with

greater statistical confidence than has been

possible based on the limited number of reenactments performed to date.

To estimate confidence limits on the risk of

injury by stopped bullets, as a function of

backface signature diameter or measurements

other than backface signature. These might

predict serious injury more reliably than does

backface signature diameter. The Army developed a procedure for predicting risk of lethality

as a function of backface signature diameter,

but it is based on animal data and should be

validated, if possible, using human data; we

expect adjustment will be required.
Police Body Armor Standards and Testing: Volume I ● 39

. To infer a relationship between the probability

that armor will be penetrated on clay backing

material in a test and the probability that similar

armor will be penetrated in an actual assault.

. To infer relationships between the probabilities

of armor penetration on backing materials other

than clay and the probability that similar armor

will be penetrated in an assault. Penetration in

assaults may correlate better with penetration

on a resilient backing material such as foam

rubber or silicone rubber than on modeling

clay.

Develop Parametric Models of Mortality and

Morbidity From Stopped Bullets

NIJcould develop parametric models of mortality

and morbidity from stopped bullets—mathematical

formulae or graphs that predict the probabilities that

a single nonpenetrating shot would kill or cause

unacceptable trauma, based on parameters that

describe the threat (bullet mass and velocity), the

armor (areal density), ballistic test results (BFS), and

the wearer (e.g., weight). The model could be fit to

data from reenactments of shootings of armored

humans, or, using a different procedure, to data from

the experimental shooting of animals. Limits on

BFS depth or diameter could be based on the model,

the maximum acceptable risk specified by policy,

and the parameters describing the threat, the armor,

and the wearer.

An advantage of using such models as a basis for

certification is that assessment of the protection new

types of armor provide against various threats would

not require additional biomedical tests (i.e., shooting

large mammals, and killing some); it would only

require additional ballistic tests: shooting the armor

of interest with bullets of interest at velocities of

interest, using a backing such as clay.

This would be more complicated and cumbersome than the current procedure. On the other hand,

it would provide a rationale for certification of

protection against trauma caused by bullets other

than Type I bullets stopped by armor other than

7-ply Kevlar armor. It also would allow armor to be

certified for use only by wearers large enough to face

only an acceptable risk; smaller wearers are probably at greater risk than larger wearers in similar (but

larger) armor.

Sponsor Research on Tests for Protection From

Stopped Bullets

NIJ could sponsor research on the practicality

and validity of tests for protection from stopped

bullets based on measurements other than backface

signatures. Some experts speculate that measurements of pressure in backing material behind armor

during impacts of test bullets might predict serious

blunt trauma more reliably than BFS depths do.

There is a plausible argument-but as yet no

proof—that backing pressure may be a better

predictor of certain functional injuries of the heart

(e.g., ventricular fibrillation or block) that can be

caused by blunt impacts. In experimental animals,

such injuries correlate with backing velocity times

deformation (a “viscous criterion”), which can be

reconstructed from measurements of backing acceleration during impact.

Research on such correlations and on measurement techniques has been conducted, and continues,

at General Motors Research Laboratories and abroad,

in England, France, and Germany (see app. E).

However, more research is needed to correlate

measurements of each type with various types of

injuries to various vital organs. As with the BFS

criterion, validation will ultimately require reenactments of assaults on humans.

Appendix E discusses other options for the

Department of Justice.

OTHER POLICY OPTIONS

The Federal Trade Commission (FTC) and the

Occupational Safety and Health Administration

(OSHA) have jurisdiction in some matters related to

body armor: the FTC has authority to prosecute

cases of false or deceptive advertising or labeling,61

such as the incorrect labeling of armor as an

NIJ-cert~led model, and has done so. OSHA could

protect the occupational safety of police officers by

requiring them to wear approved armor under

specified conditions, but has not done so.

Expand FTC Activities; Involve OSHA

The Administration could direct FTC or OSHA to

expand activities within its jurisdiction related to

body armor. For example, if further complaints of

false or deceptive advertising or labeling are alleged,

61 &-.e tie Feder~ Trade Co~SSion ACt (38 S~t.717, ~~ amended (15 USC. 41.58)); tie Clayton Act (38 stat.730, as amended (15 U.S.C. 27)),

and the Federal Trade Commission Improvements Act of 1980 (94 Stat. 374-397).
40 ● Police Body Armor Standards and Testing: Volume I

investigation and prosecution are within FTC’s

jurisdiction. NIJ must play a role because inspection

of samples for conformance with those submitted for

certification testing will require access to the submitted samples archived by NIJ’s Technology Assessment Program Information Center (TAPIC).

If the Administration desired to mandate the

wearing of approved armor on duty, OSHA has the

authority to do S0.

62 This would require collaboration by OSHA, which has experience in and

infrastructure for regulation, and NIJ and NIST,

which have expertise in the standardization and

testing of body armor.

LEGISLATIVE OPTIONS

Fund NIJ-Sponsored Research

Congress could authorize and appropriate funding for NIJ-sponsored research on topics cited

above in Options for the Department of Justice:

●

●

●

●

●

Investigation of resilient backing for penetration testing.

Reenactments of actual assaults, to test the

validity of the current test for blunt-trauma

protection or help design a new one.

Measurement of backing pressure or acceleration in reenactments, and correlation with blunt

trauma in assaults.

Development of a logistic model that predicts

the incidence and severity of trauma from

stopped bullets, as a function of multiple

measurements, to be used as a basis for armor

certification; also

Periodically updating such a model using data

from reenactments.

Enact H.R. 322, the Police Protection Act of 1991

Congress could enact H.R. 322, the Police

Protection Act of 1991, which would prohibit sale of

armor not certified to comply with the current NIJ

standard or any future revision thereof, and would

authorize NIJ to enforce this ban. Thereafter Congress could fund the mandated program of NIJ

regulation.

This would be a sweeping change. It would give

NIJ more authority and responsibility, the discharge

of which would require more resources-i. e., funding. Authorizing legislation should consider possible conflicts of jurisdiction, especially with OSHA.

If OSHA undertook to require police officers to wear

OSHA-approved armor, and if OSHA-approved

armor were not NIJ-certified, a legal conflict would

arise. However, OSHA has not expressed an intent

to protect police by such a measure.

Enacting H.R. 322 would not settle the standards

controversy and might exacerbate it. We do not

know whether the Act would save more lives than

the current regime of voluntary compliance with the

NIJ standard. Purchasers could have confidence that

armor sold after the law was in force would be very

safe, as NIJ-certified armor is now. The question is

whether it would be purchased and worn as much as

some non-NIJ-certiiled armor, which some customers prefer because of comfort or cost. We do not

know the answer to this question, but it should not

be dismissed; uncertified armor has also performed

well in service and has saved many lives.

Enacting H.R. 322 would require manufacturers

to submit representative samples of certified models

of armor to NIJ periodically to be tested for

continued compliance. That is, H.R. 322 would

create a mandatory quality-control program. It does

not specify details of the sampling and testing; it

leaves that to NIJ. NIJ has not yet proposed or

specified details, so it is not yet possible to assess the

effectiveness of the quality-control provisions of the

bill. Enacting H.R. 322 is not necessary to assure

consumers that production units of NIJ-certified

models conform to the units submitted for certification or have acceptable ballistic resistance. A

voluntary quality-control program would suffice for

that.

Fund Expanded FTC Activity

Congress could fund expanded FTC activity to

investigate complaints of, and prosecute cases of,

false or deceptive advertising or labeling of armor.

This may be necessary if complaints increase--e.g.,

if more vigorous enforcement by NIJ uncovers more

evidence of such malfeasance.

Fund an OSHA program To Standardize Armor

and Mandate Wearing

Congress could fund an OSHA program to

standardize armor and mandate wearing. The Administration could propose such a program, or the

Congress could require the Administration to do so.

@- Occupatio~ Safe@ and Health Act of 1970,29 U.S.C. 651 et seq.
Police Body Armor Standards and Testing: Volume I . 41

OSHA has the authority to specify standards for

armor and require police officers (or others) engaged

in hazardous duty to wear OSHA-approved armor.

OSHA has expressed no intent to do so.

This measure would be even more sweeping than

enacting H.R. 322 (which would not mandate

wearing of armor), and it would probably be more

controversial. However, if enforced vigorously, it

could increase wear rate and save more lives.

1.

2.

3.

4.

5.

6.

7.

8.

9.

10,

11.

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U.S. GOVERNMENT PRINTING OFFICE : 1992 0 - 327–115 : QL 3

ISBN 0-16 -037987-3

79871