X. Miscellaneous
J. Body Armor Information
3. Summary of Technical Aspects
by Julius Chang (p00302@psilink.com)
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).
Every year, about 60 sworn police officers are shot to death
in the line of duty (1, 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).
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"
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 asute 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 of armor had certain types of ballistic
resistance 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, meed 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 based on a
quantitative safety criterion and biomedical experiments (shootings
of animals) intended to demonstrate that samples of armor *like those
passing the test* would perform as required in service.
The current method, like its predecessors, is necessarily the
result of an implicit trade-off among simplicity, economy, realism,
reproducibility, risk to the consumer, and risk to the 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 revision 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 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 101st 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 0101.01, or any superseding standard issued by NIJ. H.R.
322, a bill introduced in the current (102nd) 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 Subcommittee on Crime
and on Economic and Commercial Law.
The purpose of the study was to clarify the issues of whether
NIJ Standard 0101.03 should be revised and if so, what actions
Congress might take. Congress would like to know wheter the standard
is informative and fair to purchasers and wearers or 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. Manufacturersare justified in demanding that the
standard not discriminate unfairly against their products. Principal
points of uncertainly 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 charactersitics 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.
* 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.
FOOTNOTES
1. Most lethal shootings are felonious; a few are accidental.
2. Many unsworn police officers, such as private security guards, are
also shot to death.
3. See Findings, below.
4. The rationale for each revision is discussed in detail in appendix
A of this report.
5. Those involved have later pointed out that the poor record-keeping
of the .02 era precludes definite knowledge of which vests passed, or
indeed of which were tested. The issue is further clouded by the
fact that NIJ permitted the manufacturers of vests 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 chould choose what vest
to test.
REFERENCES
13. Bachner, [Thomas E.] Ed, "The History of NIJ's Test Problems,"
section 9 of The DuPont Mid-West Body Armor Symposium, sponsored by
Missouri Police Chiefs, Inc., and the International Association of
Chiefs of Police, Chesterfield, Missouri, August 29-31, 1990
(Wilmington, DE: The DuPont Company, 1990).
15. Bachner, Thomas E. (ed) Jr., Brierly, William, and Slavin, Helen
A., "Casualties vs. Casualty Reduction -- Lessons Learned From the
Eighties," section 7 of The DuPont Mid-West Body Armor Symposium,
sponsored by Missouri Police Chiefs, Inc., and the International
Association of Chiefs of Police, Chesterfield, Missouri, August
29-31, 1990 (Wilmington, DE: The DuPont Company, 1990).
102. Michaels, Maureen (Strategy Polling Corporation), Rowan, Michael
(Strategy Polling Corporation), and Curran, Jim (John Jay College of
Criminal Justice), National Body Armor Survey (New York, NY: City
University of New York, John Jay College of Criminal Justice, March
1991).
151. U.S. Department of Justice, Office of Justice Programs, National
Institute of Justice, Office of the Director, The NIJ Body Armor
Program, enclosed with letter of Charles B. DeWitt (Director, NIJ) to
Michael B. Callaham (Senior Analyst, OTA), July 30, 1991.
Soft body armor works by catching the bullet in 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 Presiden 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, Kevlar(R) (26 g/d)
and Spectra(TM) (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 marked under the
names Kevlar(R) (by the DuPont de Nemours co., Inc.) and Twaron(R)
(by Akzo, Inc.). This 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 Kevlar(R) 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 Spectra(TM), has greater tenacity and slightly
less elongation than Kevlar(TM). Although, some Spectra(TM) fiber is
woven into Spectra(TM) fabric for armor, Spectra(TM) is also used by
Allied-Signal in the manufacture of Spectra-Shield(R), a nonwoven
composite material used in soft as well as rigid armor (see Box C).
A single, thin flexible sheet of Spectra Shield(R) is made by (1)
bonding a single layer of closely spaced parallel fibers together
with Kraton(TM) 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 Shield(R) between layers of Spectra(TM) or Kevlar(R)
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
Shield(R) non-woven composite material is unaffected by wetness.
Box B -- Kevlar(R) and Twaron(R)
Kevlar(R) 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 Kevlar(R) and Akzo later (1984) named
Twaron(R). 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
Twaron(R) in the United States until late 1990.
Before Kevlar(R) 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 strength-to-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.
Box C -- Spectra(R) and Spectra Shield(TM)
Spectra(R) is a registered trademark of Allied-Signal, Inc.,
for the high-strength synthetic fibers the company produces from
extended-chain polyethylen (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, moisturem, 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 Shield(TM), introduced in 1988. Thicker, rigid Spectra
Shield (TM) 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 Spectra(R) a tensile strength greater
than aramid fibers. Spectra(R) 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 Shield(TM) is made by aligning Spectra(R) 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 seets
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 Shield(TM)
composite material for use in body armor.[4](1) Thicker, multi-ply
panels for use as structuralk 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 Shield(TM) 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 Shield(TM) is highly water-resistant.
Exposure to water has no effect on its ballistic resistance. Spectra
Shield(TM) is also highly resistant to degradaton by chemicals such
as household bleach.
Another notable characteristic of Spectra Shield(TM) 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. Spectra(R) fabric and Spectra Shield(TM) 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 Shiled(TM) in a carrier garment made of flame-retardant
fabric. Spectra(R) melts at a temperature of 160 F. Armor so hot
would be excruciatingly painful and would burn skim in less than a
second, [128] so ballistic resistance at so high a temperature is
almost irrelevant.
Spectra Shield(R) stored for 90 dyas at 160 F and then
allowed to cool to room temperature regained its room-temperature
ballistic resistance.(2)
FOOTNOTES
1. See also Gary A. Harpell et al., "Ballistic Resistant Composite
Article," U.S. Patent 4,623,574, Nov. 18, 1986.
2. Viz., V50 measured per MIL-STD-662D using a .22-cal., 17-gr
fragment-simulating projectile.
REFERENCES
4. "Biting the Bullet: New Nonwoven Finding Application in Ballistic
Protection," Nonwovens Industry, April 1991, pp. 28 & 30.
47. Davis, Richard C. (Inventor), "Bullet Proof Protective Armor and
Method of Making Same," U.S. Patent 3,783,449, 8 Jan. 1974 (filed 8
May 1972).
48. Davis, Richard C. (Inventor), "Bullet Proof Protective Armor,"
U.S. Patent 3, 829,899, 20 Aug. 1974 (filed 31 Oct. 1973).
49. Davis, Richard C. (Inventor), "Bullet Resistant Under Garment,"
U.S. Patent 3,855,632, 24 Dec. 1974 (filed 7 Jan. 1974).
50. Davis, Richard C. (Inventor), "Bullet Proof Protective Armor,"
U.S. Patent 3,894,472, 15 July 1975 (filed 8 Aug. 1973).
53. Dean, Bashford, Helmets and Body Armor in Modern Warfare, (New
Haven, CT: Yale University Press, 1920).
89. Kaswell, Ernest R., Textile Fibers, Yarns, and Fabrics, (New
York, NY: Reinhold, 1953).
100. Metker, LeRoy W., et al. "A Method for Determining Backface
Signatures of Soft Body Armors," Tech. Rep. EB-TR-75029 (Aberdeen
Proving Ground, MD: U.S. Army Armament Research and Development
Command, May 1975); DTIC AD-A012 797.
128. Stoll, Alice M. and Chianta, Maria A., "Heat Transfer Through
Fabrics as Related to Thermal Injury," Transactions of the New York
Academy of Sciences, vol. 33, no. 7, 1971, pp. 649-670.
162. Vollrath, Fritz, "Spider Webs and Silks," Scientific American,
vol. 266, no. 3, March 1992, pp. 70-76.
-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 t he 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 NIJ-supervised testing
by an NIJ-approved independent laboratory and, if it passes, for
certification 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 NIJ-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 NIJ's 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 marketed armor is certified only by
the manufacturer and not by NIJ.
-Models and Styles of Armor
NIJ notes that "For the purposes of the ... body armor
certification procedures, the following definitions have been adopted:
A body armor MODEL is a manufacturer designation 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]
NIJ certifies the ballistic resistance of a model on 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 inspection of a sample by TAPIC to determine that it
does indeed contain a model of ballistic panel already certified to
have the ballistic resistance claimed for the style. Thus, all
styles of the same model are assumed to have the same ballistic
resistance.
TAPIC considers garments differing only in color to be of the
same style. Differences in the size or cut (i.e., shape) of garments
would bake them different styles, not different models, even though
size and cut possibly affect ballistic resistance. Differences in
stitching of ballistic panels (e.g., box stitch versus quilt stitch)
would make the panels different models.
-Types of Ballistic Resistance
The .03 standard defines six standard types of ballistic
resistance for which armor may be tested and provides for custom
testing for "special type" ballistic resistance. Each type is
defined in terms of the type or types of bullets fired at panels of
the armor to test its ballistic resistance (see table 1). Two types
of handgun bullets are fired to test for Type I, II-A, II, or III-A
ballistic resistance, which soft armor can provide. One type of
rifle bullet is fired to test for Type III or IV ballistic
resistance, which hard armor can provide.(8)
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 NIJ
Std.-0101.03 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 specifies 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]
Table 1 -- Types of Ballistic Resistance Defined by NIJ Standard
0101.03 in Terms of Bullets and Velocities Specified for Testing
------------------------------------------------------------------------
Bullet mass Impact velocity(a)
Type Bullet caliber and type (grains) (ft/s)
------------------------------------------------------------------------
I .22 long riflehigh-velocity 40 1,050
.38 round-nose lead 158 850
II-A .357 jacketed soft-point 158 1,250
9-mm full metal jacket 124 1,090
II .357 jacketed soft-point 158 1,395
9-mm full metal jacket 124 1,175
III-A .44 magnum lead semi- 240 1,400
wadcutter gas-checked
9-mm full metal jacket 124 1,400
III 7.62 mm full metal jacket 150 2,750
IV .30-06 armor-piercing 166 2,850
Special custom custom custom
-------------------------------------------------------------------------
(a) Minimum velocity; the maximum velocity for a fair hit is 50 ft/s greater.
SOURCE: National Institute of Justice, 1987 [144].
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
III High-power rifle:
5.56mm, 7.62 mm 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].
-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, "selected
at random" usually means "selected at random with uniform
probability" -- i.e., sampling should ensure 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.
Typically samples are selected after only a few units have been
produced; consequently, the sampling procedure does not guarantee
that the samples are representative of 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 modeling 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.
Figure 3 -- Sequence of Aim Points on Each Panel, as Specified in NIJ
Standard 0101.03
* #1
#4 * * #6 * #5
#2* * #3
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.
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 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,
in 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 exceeds 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.(10) The
standard prohibits adjusting the 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 wdith ... 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 Standard 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 and 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.
FOOTNOTES
7. We distinguish between NIJ's *certification criteria*, which
require one test according to NIJ Standard 0101.03 and have other
requirements as well, and the ballistic *test* specified by the
standard, which may be performed for NIJ certification or for other
purposes, such as manufacturer's certification of compliance or
testing samples of certified models for quality assurance (commonly
called "retesting").
8. The test procedure for "special type" ballistic resistance is the
same as for standard types of ballistic resistance, except the person
ordering the 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 NIJ certification of Special
Type ballistic resistance to a .45-caliber bullet, 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.
9. To provide for contingencies, six complete armors (12 panels) must
be submitted for a Type I, II-A, II, or III-A test.
10. NIJ Standard 0101.03 specifies that testing shall be continued
after each BFS measurement if it is no greater than 44 mm, and after
shooting six fair shots per panel if none penetrated. It neither
requires nor prohibits continuation of the testing in other cases --
i.e., after failures However, NIJ has directed H.P. White Laboratory,
Inc. (HPWLI), the only laboratory authorized to conduct testing for
NIJ certification, to complete the testing despite disqualification
of the armor.
11. "Retesting" (testing samples of a model certified to comply with
NIJ Standard 0101.03) is to be done using the type of test fixture
used in the certification test.
REFERENCES
144. U.S. Department of Justice, National Institute of Justice,
Technology Assessment Program, Ballistic Resistance of Police Body
Armor, NIJ Standard 0101.03 (Washington, DC: National Institute of
Justice, April 1987).
145. U.S. Department of Justice, National Institute of Justice,
Technology Assessment Program, Selection and Application Guide to
Police Body Armor, NIJ Guide 100-87 (Washington, DC: National
Institute of Justice, February 1989).
(I have summarized this section)
(Italics in the original document are indicated by enclosing the text in
asterisks)
OPTIONS FOR THE DEPARTMENT OF JUSTICE
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. 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 laboratory proceduresalready used at
H.P. White Laboratory, Inc., would further limit possible lab-to-lab
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 demonstrated -- nor can it be until
acceptable risks are specified. This lack of demonstrated vaility
does not require revising the current standard.
Specifying acceptable risks would allow the validity of the
current test to be decided scientifically and would givbe 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 confidenc
with which acceptable risk must be demonstrated).
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
i on the Abbreviated Injury Scale (49)[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 C1-percent confidence
and goal (2) with at least C2-percent confidence.
Revise NIJ Standard 0101.03
Whatever 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 H.P. White Laboratory,
Inc. (HPWLI), which currently is the only ballistic test laboratory
authorized by NIJ to do testing for certification *by NIJ* of
compliance with the standard, has adopted particular ways of
conducting the test in the interest of reproducibility. NIJ has also
issued directives instructing 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 cinduct a test in
accordance with the standard -- e.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.
-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 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 wien 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. (25, 26) No
wearer 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.
OTA's analysis shed little light on the discrimination of the
test -- i.e., 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.
Although NIJ'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 soley because of excessive backface signature.(27)
-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 realistially 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.* 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.
-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 be required to be measured at specified time
intervals or stages of ballistic testing.*
The consistency (flowability) of clays commonly used for
backing has been shouwn 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 degrees 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 chance 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.
-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.
-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 only that model has passed does not
indicate the velocity at which the test bullets would be expected to
penetrate it.
-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.
Assure Quality
-Certify Lots
*NIJ could certify lots, rather than models, of armor.* To
exercise this option, NIJ would have to
1. Define a lot.
2. 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.
3. Ensure the samples to be tested are seleted randomly from
each lot.
-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.
FOOTNOTES
25. The research indicated 44 mm was an appropriate, if not
conservative, BFS limit for .38-Special lead round-nose bullets
impacting at about 800 feet per second (a type I threat) on7-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 [Lester
Shubin, pers. comm., 13 Nov. 1991]. This was a reasonable conjecture
at the time.
26. The NILECJ also funded Army experiments in which armored goats
were shot with .357 magnum and 9-mm bullets, as was armor on clay
backing, but research was not completed or published.
27. This figure is for samples submitted to TAPIC and tested for
certification of model compliance with NIJ Standard 0101.03.
49. We expect NIJ would want armor to prevent injuries with AIs
ratings of 6 (fatal), 5 (critical: survival uncertain), and 4
(severe, life-threatening: 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 prvent them may have a negative, but as yet unquantified,
effect on wear rate.
51. For example, in tests conducted by the British Police Scientific
Development Branch, under otherwise similar conditions the average
(viz., fitted) backface signatures produced in U.S.-made Plastilina
and U.K.-made Plasticine were similar at impact velocities of 350 m/s
but differed by about 4.4 mm for each 100 m/s above or below 350 m/s.
[29] Cf. [28, 84]
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.
REFERENCES
28. Brown, Eric, "Home Office Ballistic Standard," pp. 127-142 in L.
Tobin (ed.), op. cit. infra.
29. Brown, Eric, (Head, Firearms and Armour Programme, U.K. Home
Office Police Scientific Development Branch), personal communication,
29 Nov. 1991.
84. Iremonger, M.J. and Bell, S.J., "Simulation of Behind-Armour
Trauma," pp. 191-204 in L. Tobin (ed.) op. cit. infra.
88. Joint Committe of the American Medical Assoc., American Assoc.
for Automotive Medicine, and the Society of Automotive Engineers,
"The Abbreviated Injury Scale (AIS) -- 1976 Revision," (Morton Grove,
I: American Assoc. for Automotive Medicine, 1976).