Feature Article, January 2007
This month's article was originally published in the April,
2002 Forensic Science Communications, and is reprinted here with permission
of the author.
The Manufacture of
Smokeless Powders and their
Forensic Analysis: A Brief Review
Robert M. Heramb
Graduate Student
Bruce R. McCord
Associate Professor of Analytical and Forensic Chemistry
Department of Chemistry
Ohio University
Athens, Ohio
Introduction
Smokeless powders are a class of propellants
that were developed in the late 19th century to replace black powder. The term
smokeless refers to the minimal residue left in the gun barrel following the use
of smokeless powder. In forensic analysis, smokeless powders are often
encountered as organic gunshot residue or as the explosive charge in improvised
explosive devices.
All smokeless powders can be placed into one of
three different classes according to the chemical composition of their primary
energetic ingredients. A single-base powder contains nitrocellulose, whereas a
double-base powder contains nitrocellulose and nitroglycerine. The energetic
ingredients in triple-base powders are nitrocellulose, nitroglycerine, and
nitroguanidine, but because triple-base powders are primarily used in large
caliber munitions, they are difficult to obtain on the open market.
Composition and Manufacturing
The major classes of compounds in smokeless
propellants include energetics, stabilizers, plasticizers, flash suppressants,
deterrents, opacifiers, and dyes (Bender 1998; Radford Army Ammunition Plant
1987).
-
Energetics facilitate the explosion. The base charge is nitrocellulose, a
polymer that gives body to the powder and allows extrudability. The addition
of nitroglycerine softens the propellant, raises the energy content, and
reduces hygroscopicity. Adding nitroguanidine reduces flame temperature,
embrittles the mixture at high concentration, and improves energy-flame
temperature relationship.
-
Stabilizers prevent the nitrocellulose and nitroglycerine from decomposing
by neutralizing nitric and nitrous acids that are produced during
decomposition. If the acids are not neutralized, they can catalyze further
decomposition. Some of the more common stabilizers used to extend the safe
life of the energetics are diphenylamine, methyl centralite, and ethyl
centralite.
-
Plasticizers reduce the need for volatile solvents necessary to colloid
nitrocellulose, soften the propellant, and reduce hygroscopicity. Examples
of plasticizers include nitroglycerine, dibutyl phthalate, dinitrotoluene,
ethyl centralite, and triacetin.
-
Flash suppressants interrupt free-radical chain reaction in muzzle gases and
work against secondary flash. They are typically alkali or alkaline earth
salts that either are contained in the formulation of the propellant or
exist as separate granules.
-
Deterrents coat the exterior of the propellant granules to reduce the
initial burning rate on the surface as well as to reduce initial flame
temperature and ignitability. The coating also broadens the pressure peak
and increases efficiency. Deterrents may be a penetrating type such as
Herkoteâ,
dibutyl phthalate, dinitrotoluene, ethyl centralite, methyl centralite, or
dioctyl phthalate; or an inhibitor type such as Vinsolâ
resin.
-
Opacifiers enhance reproducibility primarily in large grains and keep
radiant heat from penetrating the surface. They may also enhance the burning
rate. The most common opacifier is carbon black.
-
Dyes are added mainly for identification purposes.
-
Other ingredients may be one of the following:
-
A graphite glaze used to coat the powder
to improve flow and packing density as well as to reduce static
sensitivity and increase conductivity
-
Bore erosion coatings applied as a glaze
to reduce heat transfer to the barrel, but uncommon in small-arms
propellants
-
Ignition aid coatings that are most
commonly used in ball powders to improve surface oxygen balance
|
Figure 1-
Common smokeless powder morphologies |
Chemical composition is one important
characteristic defining smokeless propellants; however, another important
characteristic is its morphology. Shape and size have a profound effect on the
burning rate and power generation of a powder (Meyer 1987). Common particle
shapes of smokeless propellants include balls, discs, perforated discs, tubes,
perforated tubes, and aggregates (Bureau of Alcohol, Tobacco and Firearms 1994;
Selavka et al. 1989). A few common types of smokeless powder morphologies can be
seen in Figure 1 (Bender 1998).
Morphology also lends clues to whether a powder
is single- or double-base (Bender 1998). Most tube and cylindrical powders are
single-base, with the exception of the Hercules Reloaderâseries.
Disc powders, ball powders, and aggregates are double-base, with the exceptions
being the PB and SR series powders manufactured by IMR Powder Company of
Plattsburg, New York.
Except for ball powder, smokeless powder is
manufactured by one of two general methods, differing in whether organic
solvents are used in the process (Meyer 1987; Radford Army Ammunition Plant
1987). A single-base powder typically incorporates the use of organic solvents.
Nitrocellulose of high- and low-nitrogen content are combined with volatile
organic solvents, desired additives are blended with them, and the resulting
mixture is shaped by extrusion and cut into specified lengths. The granules are
screened to ensure consistency, and the solvents are removed. Various coatings,
such as deterrents and graphite, are applied to the surface of the granules. The
powder is dried and screened again, then blended to achieve homogeneity.
The manufacture of double-base powders requires
the addition of nitroglycerine to the nitrocellulose. Two methods can be used.
One method uses organic solvents, the other uses water. The organic solvent
method mixes nitrocellulose and nitroglycerine with solvents and any desired
additives to form a doughy mixture (Meyer 1987; National Research Council 1998;
Radford Army Ammunition Plant 1987). The mixture is then pressed into blocks
that can be fed into the extrusion press and cutting machine. The resulting
granules are screened prior to solvent removal and the application of various
coatings. The powder is dried, screened again, then blended to achieve
homogeneity. The water method adds the nitroglycerine to a nitrocellulose water
suspension to form a paste (Meyer 1987; Radford Army Ammunition Plant 1987). The
water is removed by evaporation on hot rollers, then the dried powder is shaped
by extrusion and cutting.
Triple-base powders use a solvent-based process
similar to the double-base powder process (Meyer 1987; Radford Army Ammunition
Plant 1987). Nitrocellulose and nitroglycerine are premixed with additives prior
to the addition of a nitroguanidine solvent mixture. The nitroguanidine is
incorporated into the overall mass without dissolving in the other materials.
The final mixture is then extruded, cut, and dried.
The manufacture of smokeless ball powder
requires a more specialized procedure (National Research Council 1998).
Nitrocellulose, stabilizers, and solvents are blended into a dough, then
extruded through a pelletizing plate and formed into spheres. The solvent is
removed from the granules, and nitroglycerine is impregnated into the granules.
The spheres are then coated with deterrents and flattened with rollers. Finally,
an additional coating with graphite and flash suppressants is applied, and the
batch is mixed to ensure homogeneity.
In the manufacturing process, smokeless powders
are recycled and reworked (National Research Council 1998). When a powder within
a batch is found to be unsatisfactory, it is removed and returned to the process
for use in another lot. Manufacturers save money by recycling returns by
distributors or the return of surplus or obsolete military powders. Hence,
reworking and recycling the material assures good quality control of the final
product, reduces costs by reusing materials, and reduces pollution by avoiding
destruction by burning.
Distribution
The production of smokeless powders is big
business in the United States, where approximately 10 million pounds of
commercial smokeless powders are produced each year. Most of the powder is sold
to the original-equipment manufacturers to be used for manufacturing ammunition.
A large amount is sold to domestic and foreign militaries (National Research
Council 1998). The rest is sold in individual canisters (ranging from ½-pound
cans to 12- or 20-pound kegs) to gun stores or hunting and shooting clubs for
hunters and target shooters who prefer to hand load their own ammunition.
There are several ways smokeless powders are
distributed within the United States (National Research Council 1998). Some
manufacturers, foreign or domestic, produce, package, and sell their own powders
commercially. They may also sell in bulk to resellers and to original-equipment
manufacturers that repackage and sell it under their own labels. The powder
manufacturers and repackagers may disburse large quantities of canister powders
to distributors who later sell to smaller distributors and wholesalers, who in
turn, supply cans to dealers, gun shops, shooting clubs, and other retailers. At
this point, consumers can purchase a 1-pound canister of powder for
approximately $15 to $20 from a retailer, though the cost per pound can be
cheaper if bought by the keg or acquired through a gun club (National Research
Council 1998).
Manufacturers who produce smokeless powders for
the U.S. military can distribute it either by selling the powder directly to the
military or by selling them the preloaded ammunition. Powders can also be
shipped to U.S. military subcontractors, foreign governments, or foreign loading
companies for loading into military ammunition (National Research Council 1998).
Improvised Explosive Devices
An explosion is the result of energy-releasing
reactions, generally accompanied by the creation of heat and gases (a notable
exception is thermites). A distinguishing characteristic of an explosion is the
rate at which the reaction proceeds. There are low-order and high-order
explosives, based on the speed at which the explosives decompose. In low-order
explosives, the process of decomposition, called the speed of deflagration or
burning, produces heat, light, and a subsonic pressure wave. (The reaction speed
of the deflagrating material is less than the speed of sound.) In high-order
explosives, decomposition occurs at the speed of detonation, creating a
supersonic shock wave that causes a virtually instantaneous buildup of heat and
gases. Table 1 shows some differences in low-order and high-order explosives
(Bureau of Alcohol, Tobacco and Firearms 1994; National Research Council 1998;
Saferstein 1998).
|
Propellant Deflagration
|
High Explosive Detonation
|
Initiation Method |
Ignition
|
Shock (from detonator or primary explosive)
|
Reaction Time |
Milliseconds
|
Microseconds
|
|
Pressure at Reaction Front |
3kbar
|
300kbar
|
|
Velocity of Reaction
Front |
0.6 km/sec
|
5-10 km/sec
|
Temperature in Reaction Zone |
2000K
|
5000K
|
Table 1. Energetic Reactions
For low-order explosives, rapid deflagration
causes the production of large volumes of expanding gases at the origin of the
explosion. The heat energy from the explosion also causes the gases to expand.
When the explosive charge is confined in a closed container, the sudden buildup
of expanding pressure exerts high pressure on the container walls causing the
container to stretch, balloon, then burst, releasing fragments of debris to
nearby surroundings. It is this fragmented debris that produces the fatal result
following the deflagration of an improvised explosive device (Saferstein 1998).
The safest and most powerful low-order
explosive is smokeless powder. These powders decompose at rates up to 1,000
meters per second and produce a propelling action that makes them suitable for
use in ammunition. However, the slower burning rate of smokeless powder should
not be underestimated. The explosive power of smokeless powder is extremely
dangerous when confined to a small container. In addition, certain smokeless
powders with a high-nitroglycerine concentration can be induced to detonate. On
the other hand, high-order explosives do not need containment to demonstrate
their explosive effects (Saferstein 1998). These materials detonate at rates
from 1,000 to 8,500 meters per second, producing a shock wave with an outward
rush of gases at supersonic speeds. This effect proves to be more destructive
than the fragmented debris.
The typical smokeless powder improvised
explosive device, a pipe bomb, is roughly 10 inches long and 1 inch wide and
contains approximately ½ pound of powder. The materials used for these devices
are cheap and readily obtainable at commercial establishments. Smokeless powder
is attractive for use in improvised explosive devices, because it is readily
available and has the potential for a powerful explosion when the powder is
placed in a closed container (National Research Council 1998). Larger explosive
devices usually use bulk materials such as ammonium nitrate and fuel oil,
typically purchased in greater quantity at an even cheaper price.
Many types of containers are used in the
construction of smokeless powder bombs (National Research Council 1998). Whereas
metal pipes are most common, plastic pipes, cans, CO2 cartridges, and
glass or plastic bottles have been used. These containers are often placed
within larger packages for ease of transport and concealment.
Another important part of the powder bomb is
the initiation system, which provides the impetus to start the powder burning
within its container (National Research Council 1998). A few examples include
cigarettes, matches, and safety fuses (Scott 1994; Stoffel 1972). Improvised
explosive devices utilizing smokeless powders within a robust container often
include an initiation system, as shown in Figure 2 (Scott 1994).
Using data from the National Research Council
on reported actual and attempted bombings using propellants during the five-year
period from 1992-1996, Table 2 illustrates an average of 653 incidents per year
involving the use of black and smokeless powders. Bombs containing black or
smokeless powders were responsible for an average yearly count of about 10
deaths, 83 injuries, and almost $1 million in property damage for each of the
five years. Using the National Research Council's data involving devices filled
with black and smokeless powders, Table 3 illustrates the number of actual
bombings that caused at least one death, one injury, or a minimum of $1,000 in
property damage, as well as attempted bombings aimed at significant targets
(National Research Council 1998).
Type of Explosive Used |
1992 |
1993 |
1994 |
1995 |
1996 |
Bomb containing smokeless
powder/ black powder/black powder substitutes
|
|
|
|
|
|
Total incidents |
667 |
637 |
696 |
624 |
643 |
Actual |
524 |
498 |
447 |
454 |
405 |
Attempted |
143 |
139 |
249 |
170 |
238 |
Deaths |
9 |
12 |
6 |
8 |
13 |
Injuries |
82 |
68 |
49 |
53 |
162 |
Property damage costs |
780K |
856K |
1.8M |
243K |
896K |
Table 2. All Reported Actual and Attempted
Bombings Using Propellants Between 1992 and 1996
NOTE: Actual and attempted bombings
include incidents in which a device either exploded or was delivered to a
target but did not explode. It does not include unexploded devices that were
recovered by law enforcement personnel but not associated with a target.
|
Number of Incidents
|
Deaths
|
Injuries
|
|
1992
|
1993
|
1994
|
1992-1994
|
1992-1994
|
Total incidents |
260
|
258
|
294
|
27
|
199
|
|
Actual |
166
|
160
|
122
|
27
|
199
|
|
Attempted |
94
|
98
|
172
|
---
|
---
|
Container |
|
|
|
|
|
|
Pipe/metal |
158
|
169
|
158
|
19
|
122
|
|
Pipe/plastic |
28
|
34
|
43
|
0
|
16
|
|
Cardboard/paper |
7
|
3
|
4
|
0
|
2
|
|
Other |
60
|
42
|
72
|
8
|
53
|
|
Unknown |
7
|
10
|
17
|
0
|
6
|
Table 3. Significant Actual and
Attempted Bombings Involving Devices Using Smokeless Powder, Black Powder,
or Black Powder Substitutes
NOTE: Significant bombings represent
actual bombings that caused at least one death, one injury, a minimum of
$1,000 in property damage, or attempted bombings aimed at specified targets.
Analysis
|
Figure 3-
Gradient HPLC analysis of an IMR 700X smokeless powder. Conditions
Restek C-8 Column, 36-80% methanol/water gradient, 1 ml/min, UV
detection at 230 nm. Figure courtesy of Chad Wissinger, Ohio University
|
|
|
Figure 4-
IC Analysis of H414 smokeless powder by Hodgdon. Conditions Nucleosil
Anion
IIÒ
Column, 1mM DCTA pH 5.2, 1.5
ml/min, UV detection at 205 nm. |
Many methods for the analysis of smokeless
powders have appeared over the years. These procedures have been extensively
reviewed in a number of recent texts (Beveridge 1998; National Research Council
1998; Yinon and Zitrin 1993). The initial characterization of the powders is
assessed using powder morphology and spot tests. Various instrumental analytical
techniques allow organic additives such as nitroglycerine, diphenylamine, ethyl
centralite, dinitrotoluene, and various phthalates to be detected and
quantitated. These materials are usually analyzed using gas chromatography-mass
spectrometry (Martz and Lasswell 1983) and liquid chromatography (Bender 1983;
McCord and Bender 1998). Figure 3 illustrates the analysis of an IMR 700X powder
using gradient high performance liquid chromatography (Wissinger and McCord
2002). More recently, methods involving capillary electrophoresis have also been
shown to be effective (Northrop et al. 1991; Smith et al. 1999). Fourier
transform infrared microscopy can be used for the identification of
nitrocellulose (Zitrin 1998).
The process of manufacturing smokeless powders
provides sources of inorganic ions that are present in postblast residue. These
can be analyzed by ion chromatography. Although not unique to propellants, the
presence of these ions can be used in forensic analysis to aid in the
identification of the unknown powder. Potassium sulfate, sodium sulfate,
potassium nitrate, barium nitrate, and other salts may be added during the
processing of the powder. Nitrate, sulfate, hydrogen sulfide, chloride, and
nitrite may appear as a result of the reactions for treating the cellulose to
obtain nitrocellulose (Radford Army Ammunition Plant 1987). Figure 4 illustrates
the analysis of H414 smokeless powder using ion chromatography. Also documented
has been the presence of various cations found in the residue of smokeless
powders after deflagration (Hall and McCord 1993; Miyauchi et al. 1998).
Conclusions
The wide variety of chemical components and the
different morphologies of smokeless powders present a challenge for the forensic
investigator. Physical characteristics of partially burned and unburned powder
as well as the organic and inorganic materials that remain must be considered in
the analysis of postblast residue. Although there are many techniques available
for the determination of components in smokeless powder residue, the various
formulations of powders make it necessary to continue the advancement of
existing analyses and to develop new methods for testing the full range of
available smokeless powders.
References
Bender, E. C. Analysis of low explosives. In:
Forensic Investigation of Explosives. A. Beveridge, ed. Taylor and
Francis, London, 1998, pp. 343-388.
Bender, E. C. Analysis of smokeless powders
using UV/TEA detection. In: Proceedings of the International Symposium on the
Analysis and Detection of Explosives. U.S. Government Printing Office,
Washington, DC, 1983, pp. 309-320.
Beveridge, A., ed. Forensic Investigation of
Explosives. Taylor and Francis, London, 1998.
Bureau of Alcohol, Tobacco and Firearms,
Arson and Explosives Incidents Report (1994). ATF P3320.4, Department of the
Treasury, Washington, DC, 1994.
Hall, K. E. and McCord, B. R. The analysis of
mono- and divalent cations present in explosive residues using ion
chromatography with conductivity detection, Journal of Forensic Sciences
(1993) 38:928-934.
Martz, R. M. and Lasswell, L. D. Identification
of smokeless powders and their residues by capillary column gas
chromatography/mass spectrometry. In: Proceedings of the International
Symposium on the Analysis and Detection of Explosives. U.S. Government
Printing Office, Washington, DC, 1983, pp. 245-254.
McCord, B. and Bender, E. C. Chromatography of
explosives. In: Forensic Investigation of Explosives. A. Beveridge, ed.
Taylor and Francis, London, 1998, pp. 231-265.
Meyer, R. Explosives. 3rd rev., Weinheim,
New York, 1987.
Miyauchi, H., Kumihashi, M., and Shibayama, T.
The contribution of trace elements from smokeless powder to post-firing
residues, Journal of Forensic Sciences (1998) 43:90-96.
National Research Council, Committee on
Smokeless and Black Powder. Black and Smokeless Powders: Technologies for
Finding Bombs and the Bomb Makers. National Academy Press, Washington, DC,
1998.
Northrop, D. M., Martire, D. E., and MacCrehan,
W. A. Separation and identification of organic gunshot and explosive
constituents by micellar electrokinetic capillary electrophoresis, Analytical
Chemistry (1991) 63: 1038-1042.
Radford Army Ammunition Plant. Processing
Manual. Radford, Virginia, 1987.
Saferstein, R. Criminalistics: An
Introduction to Forensic Science. 6th ed., Prentice Hall, Upper Saddle
River, New Jersey, 1998.
Scott, L. Pipe and Fire Bomb Designs: A
Guide for Police Bomb Technicians. Paladin Press, Boulder, Colorado, 1994.
Selavka, C. M., Strobel, R. A., and Tontarski,
R. E. Systematic identification of smokeless powders, an update. In:
Proceedings of the Third Symposium on the Analysis and Detection of Explosives.
Berghausen, Fraunhofer Institute fur Chemische Technologie, 1989, Chapter 3, pp.
1-27.
Smith, K. D., McCord, B. R., MacCrehan, W. A.,
Mount, K., and Rowe, W. F. Detection of smokeless powder residue on pipe bombs
by micellar electrokinetic chromatography, Journal of Forensic Sciences
(1999) 44:789-794.
Stoffel, J. Explosives and Homemade Bombs.
Charles C. Thomas, Springfield, Illinois, 1972.
Wissinger, C. and McCord, B. R. A reversed
phase HPLC procedure for smokeless powder comparison, Journal of Forensic
Sciences (2002) 47:168-174.
Yinon, J. and Zitrin, S. Modern Methods and
Applications in Analysis of Explosives. John Wiley, Chichester, United
Kingdom, 1993.
Zitrin, S. Analysis of explosives by infrared
spectrometry and mass spectrometry. In: Forensic Investigation of Explosives.
A. Beveridge, ed. Taylor and Francis, London, 1998, pp. 267-314.
|