Title: Guide for the Selection of Commercial Explosives Detection
Systems for Law Enforcement Applications
Series: Law Enforcement and Corrections Standards and Testing Program
Author: Charles L. Rhykerd, David W. Hannum, Dale W. Murray, and
John E. Parmeter
Published: National Institute of Justice, September 1999
Subject: Technology in law enforcement
111 pages
259,000 bytes
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U.S. Department of Justice
Office of Justice Programs
National Institute of Justice
National Institute of Justice
Law Enforcement and Corrections Standards and Testing Program
Guide for the Selection of Commercial Explosives Detection Systems for
Law Enforcement Applications
NIJ Guide 100-99
-------------------------------
U.S. Department of Justice
Office of Justice Programs
810 Seventh Street N.W.
Washington, DC 20531
Janet Reno
Attorney General
Raymond C. Fisher
Associate Attorney General
Laurie Robinson
Assistant Attorney General
Noel Brennan
Deputy Assistant Attorney General
Jeremy Travis
Director, National Institute of Justice
Office of Justice Programs
World Wide Web Site:
http://www.ojp.usdoj.gov
National Institute of Justice
World Wide Web Site:
http://www.ojp.usdoj.gov/nij
-------------------------------
ABOUT THE LAW ENFORCEMENT AND CORRECTIONS
STANDARDS AND TESTING PROGRAM
The Law Enforcement and Corrections Standards and Testing Program is
sponsored by the Office of Science and Technology of the National
Institute of Justice (NIJ), U.S. Department of Justice. The program
responds to the mandate of the Justice System Improvement Act of 1979,
which created NIJ and directed it to encourage research and development
to improve the criminal justice system and to disseminate the results to
Federal, State, and local agencies.
The Law Enforcement and Corrections Standards and Testing Program is
an applied research effort that determines the technological needs of
justice system agencies, sets minimum performance standards for specific
devices, tests commercially available equipment against those standards,
and disseminates the standards and the test results to criminal justice
agencies nationally and internationally.
The program operates through:
The Law Enforcement and Corrections Technology Advisory Council
(LECTAC) consisting of nationally recognized criminal justice
practitioners from Federal, State, and local agencies, which assesses
technological needs and sets priorities for research programs and items to
be evaluated and tested.
The Office of Law Enforcement Standards (OLES) at the National
Institute of Standards and Technology, which develops voluntary national
performance standards for compliance testing to ensure that individual
items of equipment are suitable for use by criminal justice agencies. The
standards are based upon laboratory testing and evaluation of
representative samples of each item of equipment to determine the key
attributes, develop test methods, and establish minimum performance
requirements for each essential attribute. In addition to the highly technical
standards, OLES also produces technical reports and user guidelines that
explain in nontechnical terms the capabilities of available equipment.
The National Law Enforcement and Corrections Technology Center
(NLECTC), operated by a grantee, which supervises a national compliance
testing program conducted by independent laboratories. The standards
developed by OLES serve as performance benchmarks against which
commercial equipment is measured. The facilities, personnel, and testing
capabilities of the independent laboratories are evaluated by OLES prior to
testing each item of equipment, and OLES helps the NLECTC staff review
and analyze data. Test results are published in Equipment Performance
Reports designed to help justice system procurement officials make
informed purchasing decisions.
Publications are available at no charge through the National Law
Enforcement and Corrections Technology Center. Some documents are
also available online through the Internet/World Wide Web. To request a
document or additional information, call 800-248-2742 or 301-519-5060,
or write:
National Law Enforcement and Corrections Technology Center
P.O. Box 1160
Rockville, MD 20849-1160
E-Mail: asknlectc@nlectc.org
World Wide Web address: http://www.nlectc.org
-------------------------------
The National Institute of Justice is a component of the Office of Justice
Programs, which also includes the Bureau of Justice Assistance, Bureau of
Justice Statistics, Office of Juvenile Justice and Delinquency Prevention,
and the Office for Victims of Crime.
-------------------------------
U.S. Department of Justice
Office of Justice Programs
National Institute of Justice
Guide for the Selection of Commercial Explosives Detection Systems for
Law Enforcement Applications
NIJ Guide 100-99
Dr. Charles L. Rhykerd
David W. Hannum
Dale W. Murray
Dr. John E. Parmeter
Contraband Detection Technologies Department
Sandia National Laboratories
Albuquerque, NM 87185-0782
Coordination by 
Office of Law Enforcement Standards
National Institute of Standards and Technology
Gaithersburg, MD 20899-8102
Prepared for
National Institute of Justice
Office of Science and Technology
Washington, DC 20531
September 1999
NCJ 178913
National Institute of Justice
Jeremy Travis
Director
The technical effort to develop this report was conducted under
Interagency Agreement No. 94-IJ-R-004, Project No. 97-028-CTT.
This guide was prepared with the assistance of the Office of Law
Enforcement Standards (OLES) of the National Institute of Standards and
Technology (NIST) under the direction of Alim A. Fatah, Program
Manager for Chemical Systems and Materials, and Kathleen M. Higgins,
Director of OLES.
This work was sponsored by the National Institute of Justice, David G.
Boyd, Director, Office of Science and Technology.
FOREWORD
The Office of Law Enforcement Standards (OLES) of the National
Institute of Standards and Technology (NIST) furnishes technical support
to the National Institute of Justice (NIJ) program to strengthen law
enforcement and criminal justice in the United States. OLES's function is
to conduct research that will assist law enforcement and criminal justice
agencies in the selection and procurement of quality equipment.
OLES is: (1) Subjecting existing equipment to laboratory testing and
evaluation, and (2) conducting research leading to the development of
several series of documents, including national standards, user guides, and
technical reports.
This document covers research conducted by OLES under the sponsorship
of the National Institute of Justice. Additional reports as well as other
documents are being issued under the OLES program in the areas of
protective clothing and equipment, communications systems, emergency
equipment, investigative aids, security systems, vehicles, weapons, and
analytical techniques and standard reference materials used by the forensic
community.
Technical comments and suggestions concerning this report are invited
from all interested parties. They may be addressed to the Office of Law
Enforcement Standards, National Institute of Standards and Technology,
100 Bureau Drive, Stop 8102, Gaithersburg, MD 20899-8102.
David G. Boyd, Director
Office of Science and Technology
National Institute of Justice
ACKNOWLEDGMENTS
Many police officers and members of bomb squads helped evaluate our
desired characteristics list for trace explosives detection equipment. They
included:
Arapahoe County Sheriff's Office
Inv. Dan Davis, Sgt. Scott Linne, Sgt. R. R. Euchler, and Sgt. Joe
Dempsey
Charleston, S.C. Police Dept., Explosive Devices Team
Cpl. Robert L. Kemp
Eastern Kentucky University, College of Law Enforcement
Prof. John T. Thurman
Miami Dade Police Dept., Bomb Disposal Unit
Lt. Eric Castaner
National Law Enforcement & Corrections Technology Center - Rocky
Mountain, University of Denver Research Institute
Karen Duffala
National Law Enforcement & Corrections Technology Center - Southeast
Region
Bill Nettles, Tommy Sexton
New Mexico State Police
Major Mike Francis, Major Roger Payne, Major Bill Relyea
Prof. Gary Eiceman (New Mexico State University - Dept. of Chemistry)
helped us with the protocol for evaluating explosives detection equipment.
CONTENTS
FOREWORD
1. INTRODUCTION
2. MARKET SURVEY OF COMMERCIALLY AVAILABLE
EXPLOSIVES EQUIPMENT
o 2.1 Portability
o 2.2 Type of Item Being Screened
o 2.3 Cost Range
o 2.4 Throughput Rate
o 2.5 Trace Explosives Detection
o 2.6 X-ray Explosives Detection
o 2.7 Canine Detection
o 2.8 Novel Detection Techniques
3. SUGGESTED TECHNOLOGIES FOR PORTABLE, SEMI-
PORTABLE, AND FIXED-SITE APPLICATIONS
o 3.1 How to Choose Explosives Detection Technology for Specific
Applications (Tables 7-9)
o 3.2 Practical Notes Concerning Tables 7-9
4. DESIRABLE CHARACTERISTICS FOR EXPLOSIVES
DETECTION EQUIPMENT FOR POLICE WORK
o 4.1 Trace Systems
o 4.2 X-ray Systems
o 4.3 A Practical Example of How to Use Tables 7-11
5. CALIBRATION OF EXPLOSIVES DETECTION SYSTEMS
6. PROTOCOL FOR THE EVALUATION OF COMMERCIAL TRACE
DETECTION SYSTEMS
o 6.1 Introduction
o 6.2 The Basics of Instrument Operation
o 6.3 Protocol for Characterizing a Trace Explosives Detector
7. WARNING: DO NOT BUY BOGUS EXPLOSIVES DETECTION
EQUIPMENT
8. CONCLUSION
Appendix A-1 Suggested Readings
Appendix A-2 Glossary of Terms
Appendix A-3 Explosives: Nature, Use, Effects, and Applications
TABLES
Table 1. Cost Ranges for Trace and X-ray Explosive Detection Systems
Table 2. Throughput Rates
Table 3. Trace Detector Technologies and their Acronyms
Table 4. Trace Explosives Detection Systems
Table 5. X-ray Detector Technologies and Their Acronyms
Table 6. X-ray Explosives Detection Systems
Table 7. Matrices for Law Enforcement - Portable: Easily Carried by One
Person
Table 8. Matrices for Law Enforcement - Semi-Portable: Can fit in the
Trunk of a Police Car
Table 9. Matrices for Law Enforcement - Fixed Location, Dedicated
Systems
Table 10. Characterization of Commercial Trace Explosive Detection
Systems
Table 11. Characterization of Commercial X-ray Explosives Detection
Systems
Table 12. An Example of a Logbook Page
FIGURES
Figure 1. Vapor Concentrations of Neat High Explosives in Saturated Air
at 25 degrees C
Figure 2. Schematic of Ion Mobility Spectrometer (IMS) Operation
Figure 3. IMS Spectrum, a Plot of Signal vs. Drift Time
Figure 4. Commercial IMS Explosives Detection System, Barringer
Ionscan 400
Figure 5. Commercial IMS Explosives Deetection System, Graseby
Plastec
Figure 6. Commercial IMS Explosives Detection System, ION Track
Instruments Vapor Trace
Figure 7. Commercial IMS Explosives Detection System, Intelligent
Detection Systems ORION
Figure 8. Schematic Diagram of Operation of an Electron Capture
Detector (ECD)
Figure 9. Commercial Electron Capture Detector (ECD), Ion Track
Instruments Model 97
Figure 10. Photo of a Surface Acoustic Wave Detector, the EST Model
4100
Figure 11. Photo of a Thermo-Redox Detector, Sintrex/IDS EVD-3000
Figure 12. Photo of a Field Ion Spectrometer (FIS) by MSA
Figure 13. Photo of the EXPRAY Field Test Kit for Explosives
Figure 14. X-ray Explosives Detection System for Personnel, AS&E Body
Search
Figure 15. X-ray Explosives Detection System for Personnel, Rapiscan
Secure 1000
Figure 16. Control Chart Using 5 ng of TNT from June 16, 1998 to July
13, 1998
COMMONLY USED SYMBOLS AND ABBREVIATIONS
A ampere
ac alternating current
AM amplitude modulation
cd candela
cm centimeter
CP chemically pure
c/s cycle per second
d day
db decibel
dc direct current
C degree Celsius
F degree Fahrenheit
dia diameter
emf electromotive force
eq equation
F farad
fc footcandle
fig. figure
ft foot
ft/s foot per second
g acceleration
g gram
gr grain
H henry
h hour
hf high frequency
Hz hertz
i.d. inside diameter
in inch
IR infrared
J joule
L lambert
L liter
lb pound
lbf pound-force
lgf-in pound-force inch
lm lumen
ln logarithm (base e)
log logarithm (base 10)
M molar
m meter
min minute
mm millimeter
mph miles per hour
m/s meter per second
N newton
N-m newton meter
nm nanometer
No. number
o.d. outside diameter
ohm (ohm)
p. page
Pa pascal
pe probable error
pp. pages
ppm parts per million
qt quart
rad radian
rf radio frequency
rh relative humidity
s second
SD standard deviation
sec. section
SWR standing wave ratio
uhf ultrahigh frequency
UV ultraviolet
V volt
vhf very high frequency
W watt
wavelength (wavelength)
wt weight
PREFIXES
d deci (10[-1])
da deka (10)
c centi (10[-2])
h hecto (10[2])
m milli (10[-3])
k kilo (10[3])
u micro (10[-6])
M mega (10[6])
n nano (10[-9])
G giga (10[9])
p pico (10[-12])
T tera (10[12])
COMMON CONVERSIONS (See ASTM E380)
0.30480 m =1ft
4.448222 N = lbf
2.54 cm = 1 in
1.355818 J =1 ft-lbf
0.4535924 kg = 1 lb
0.1129848 N m = lbf-in
0.06479891g = 1gr
14.59390 N/m =1 lbf/ft
0.9463529 L = 1 qt
6894.757 Pa = 1 lbf/in[2]
3600000 J = 1 kW-hr
1.609344 km/h = mph
-------------------------------
NIJ GUIDE 100-99
GUIDE FOR THE SELECTION OF COMMERCIAL EXPLOSIVES
DETECTION SYSTEMS FOR LAW ENFORCEMENT
APPLICATIONS*
This document includes a variety of information that is intended to be
useful to the law enforcement community in the selection of explosives
detection techniques and equipment for different applications. It includes a
thorough market survey of all trace and x-ray based commercial detection
systems known to the authors as of October 1998, including company
contact information along with data on each system's cost, size, and uses.
Information is also included on some additional novel detection
technologies, and on such standard techniques as canine and physical
search. Brief technical discussions are presented that consider the
principles of operation of the various technologies. These may be ignored
by readers who find them too technical, while those wanting additional
technical information can obtain it from the extensive list of references
that is included as an appendix. Other sections of the document present
matrices listing the most highly recommended detection techniques for a
variety of scenarios, a list of desirable characteristics for explosives
detection equipment for law enforcement work with charts rating
commercial systems against these criteria, and a standard test protocol for
the evaluation of trace detection equipment. In addition to a reference list,
the appendices include a section providing basic information about
different types of explosives and explosions. Any law enforcement
personnel having comments or questions are encouraged to contact the 
authors at Sandia National Laboratories.
1. Introduction
The primary purpose of this document is to provide law enforcement
agencies with information that should aid them in the selection and
utilization of explosives detection equipment. The document is thus more
practical than technical, emphasizing advice about the capabilities of
different technologies, and what technologies are likely to work best in
various applications. A wide variety of factors are considered that may be
important to purchasers of detection equipment, including cost, sensitivity,
portability, ease of use, etc. Some technical information is included in
sections describing how the various detection technologies work, but the
level of detail is not great. Readers finding this material too technical can
skip it while still making use of the rest of the document, and readers
desiring more technical detail can obtain it from the suggested readings in
Appendix A-1.
The remainder of this document is divided into several sections as follows: 
Section 2 presents a market survey of currently available explosives
detection equipment. In tables 4 and 6, specific information is listed on 26
trace detection systems and 90 x-ray based detection systems. To the
knowledge of the authors, this information is complete as of October 1998.
The information in these tables includes the type of detector or detection
technology used in each system, cost, recommended uses, system size and
weight, and vendor contact information. In the case of x-ray based
systems, the cost information can only be approximate, because most
vendors are hesitant to quote a specific price for these (usually expensive)
systems. The table on trace detection systems also includes sensitivity
information as provided by the manufacturer, but it must be remembered
that this information comes from the manufacturer and is not based on
independent tests by a third party. Some independent test data exist for a
few systems, and in the experience of the authors, the claims made by the
manufacturers are usually not out of line with the system's true
performance. However, all independent test results known to the authors
are either classified or unclassified controlled nuclear information, so these
results are not included in this document, which is intended for public
release. Parties interested in what independent test data exist should
contact the authors. Also included in section 2 are definitions of
commonly used terms such as throughput rate and portability, a discussion
of explosive vapor pressures and the issue of vapor sampling versus swipe
(particulate) sampling in trace detection, and information on how the
different trace and x-ray systems operate and what their general
capabilities are. Finally, other techniques are discussed, including canine
detection (already familiar to most law enforcement agencies, for drugs if
not for explosives) and a few novel (though usually expensive and not
always fully developed) detection technologies that have appeared in 
recent years.
Section 3 presents three matrices that give recommendations about what
technologies and systems to use for a variety of applications. These
matrices provide a quick reference point for anyone having a specific
application in mind, and wanting to know what sort of detection system he
or she should consider purchasing. Five factors are included in defining
the applications in these matrices: system portability, presence or absence
of an explosives background in the area where screening will be
performed, throughput rate, the type of item to be screened (people,
packages, vehicles, etc.), and system cost. As a general rule, these matrices
do not point to a single system or technique that is considered "best" in
each circumstance, but rather point to several options that may meet the
user's needs. Needless to say, in some cases there may be several detection
systems that can do the desired job, while under other circumstances there
may be no system that does everything the potential purchaser would like
it to do. The latter is unfortunately most often true when severe cost
restraints are placed on the system to be purchased, as is usually the case
in this era of rapidly advancing technology but extremely limited budgets
for technology in law enforcement. It must be stressed that the matrices in
section 3 are intended to point the reader in the right direction, and they
are a starting point rather than a solution in choosing a detection system.
They are not a substitute for detailed discussions with both the vendor(s)
and a knowledgeable third party.
Section 4 discusses various characteristics and performance parameters
that could be used to judge both trace and x-ray based detection systems,
and defines ideal and nominal capabilities or characteristics for these
systems. Defining these parameters is to some degree arbitrary since the
"ideal" will of course depend upon the specific application. The definitions
used are based on the best judgment of the authors and some feedback
received from several law enforcement agencies, but it is really up to each
potential purchaser to determine what the requirements are for his or her
application. Tables 10 and 11 rate various commercial detection systems
as ideal, nominal, or subnominal for the different parameters considered,
and this allows the reader to focus on those parameters that are most
important to him/her and to make rapid comparisons. Once again, these
tables serve as a starting point for obtaining information and should
supplement but not replace detailed discussions with the vendor(s) and
outside experts.
Section 5 briefly discusses the issue of system calibration. Since
calibration is very system specific, little can be said in general about this
topic. The best advice is to discuss the calibration procedure thoroughly
with the vendor of the equipment, and if possible learn it hands-on from
the vendor at an onsite installation and training visit.
Section 6 provides a protocol for the testing and evaluation of trace
detection systems. Such testing is also rather system specific, but this
protocol has been made as generic as possible. The protocol should be of
interest to users wanting to determine performance parameters for the
specific unit they have purchased, and to those wanting to monitor the
performance of the system over an extended period of time. The protocol
also includes some basic information about sampling, ensuring a detector
is free of contamination, etc. For some users in the law enforcement
community, the protocol may be of little interest, and these users can skip
section 6 without losing any content that is crucial to understanding the
rest of the document.
Section 7 contains a brief warning about buying equipment that may not
be based on sound scientific principles. Briefly stated, detectors that
appear to make unprecedented claims about detection capabilities may be
based on faulty science, and in extreme cases could prove to be fraudulent.
When dealing with technologies that appear to be new and report exciting
new capabilities, it is especially important to discuss the purchase with an
outside expert before making a final decision. 
Section 8 provides a brief summary and conclusions section.
Appendix A-1 provides a list of suggested readings relating to the topic of
explosives detection. 
Appendix A-2 provides a glossary of terms used in explosives detection,
many of which may not be familiar to the average reader. 
Finally, Appendix A-3 contains an introduction to different types of
explosives, their uses, and their properties.
Any law enforcement agencies desiring more information about this
document or explosives detection in general are invited to contact the
authors[1] of this document. The contact points are as follows:
2. Market Survey of Commercially Available Explosives Detection
Equipment
In this section four different divisions of explosive detection technology
are discussed. Covered in the greatest detail are (1) trace detection
technologies and (2) x-ray based detection systems, since these are by far
the most widely developed technologies. Canine detection, which is really
a form of trace detection already very familiar to most law enforcement
agencies, is discussed more briefly. Finally, some novel detection
technologies are briefly discussed. Most of these novel technologies are
not fully commercially developed, but they are mentioned here for the
sake of completeness. Readers should note that they might become more
readily available and also cheaper in the near future.
Before the specific technologies are discussed, four key characteristics that
help describe explosive detection systems and applications are defined and
addressed. These characteristics are portability, the type of item being
screened, system cost, and throughput rate. Some of this material is
covered further in section 4, but a brief introduction is necessary at this
point.
2.1 Portability
Portability simply refers to the ease with which a detection system can be
moved from one location to another. Depending on the application,
portability may or may not be important. If a system needs to be carried by
a detective who is screening a room for explosives, portability is clearly
important. On the other hand, if it is only to be used as a dedicated system
for screening people at a single entrance to a courthouse, portability is not
important. In general, systems are divided into three categories: portable,
semiportable, and fixed site. A system is considered portable if it weighs
less than 9.1 kg (20 lb) and can be easily carried by one person (or, in the
case of a canine, led by one person). It is considered semiportable if it does
not meet these definitions, but can be moved easily by two people, fit in
no more than two boxes, and be easily stored in the trunk of a police car.
Systems that are too large or too heavy to meet the definition of
semiportable are considered fixed-site systems. These can be very large
and heavy, and include personnel portals and many baggage screening
systems.
2.2 Type of Item Being Screened
Explosives detection can be used in a variety of applications. Two major
categories are search applications and screening of individual items.
Search applications involve situations where a bomb is suspected of being
in a general area, but the exact location is unknown. This would include,
for example, searching a building or property grounds for a bomb, once a
bomb threat has been communicated. In most search applications, canine
detection will be the detection method of choice because of the dog's rapid
mobility and its ability to follow the scent to its source.
For screening of individual items, a wide variety of technologies can be
useful in different situations. In general, the type of item screened will fall
into one of four categories: people, hand-carried items, mailed or shipped
items, and vehicles. Personnel screening involves detecting bombs or
explosive material that is usually hidden under clothing. It can occur in
many circumstances, ranging from suspect apprehension to screening large
numbers of people entering a courthouse or some other facility. Screening
of hand-carried items will usually occur alongside personnel screening.
Specific items in this category include briefcases, backpacks, purses, hand-
carried bags and packages, etc. Mailed and shipped items are used
increasingly to transport bombs; these items can include letters, small
packages, and large shipping crates. Vehicle screening can involve both
single vehicles (e.g., suspect apprehension) and large numbers of vehicles
at checkpoints. The vehicles involved can range from the smallest cars to
fully loaded tractor-trailers.
2.3 Cost Range
Cost is one of the few characteristics associated with a detection system
that can be fully quantified, and hence it is one of the easiest to get a
handle on when comparing different systems. Obviously, a purchaser will
want to know the exact cost of any system he or she is thinking about
buying. Nevertheless, it is convenient when starting to look at different
systems to divide them into low-, medium-, and high-cost ranges. The
definitions of these ranges are given in table 1; note that they differ for
trace systems and x-ray systems. Cost ranges are used when discussing x-
ray systems. Often x-ray manufacturers are reluctant to quote an exact
price until they have talked to the potential buyer. 
Note that most trace systems cost less than $75K (several less than $30K),
while most x-ray systems cost more than $100K. The authors realize that
all of these numbers may seem staggeringly high to most police
departments, and that cost will usually be one of the most limiting factors
in making a procurement decision. Nevertheless, the ranges listed are
convenient reflections of current costs in state-of-the-art explosives
detection equipment.
2.4 Throughput Rate
When screening individual items, throughput rate refers to the number of
items that can be screened per unit time. It can also be expressed in terms
of the time required to screen a single item. For example, if personnel are
being screened at a checkpoint using a personnel portal that processes five
people every minute, the throughput rate can be expressed as 5
persons/min, 300 persons/h, etc. Alternatively, the screening time can be
expressed as 12 s per person. Throughput rate is typically an issue only
when large numbers of items need to be screened rapidly. Table 2
quantifies high, medium, and low throughput rates for the items discussed 
in section 2.2.
2.5 Trace Explosives Detection
Explosive detection techniques can be divided generally into two
categories: bulk detection and trace detection. In bulk detection, a
macroscopic mass of explosive material is detected directly, usually by
viewing images made by x-ray scanners or similar equipment. In trace
detection, the explosive is detected by chemical identification of
microscopic residues of the explosive compound. These residues can be in
either or both of two forms: vapor and particulate. Vapor refers to the gas-
phase molecules that are emitted from a solid or liquid explosive because
of its finite vapor pressure. Particulate contamination refers to microscopic
particles of solid material that adhere to surfaces that have, directly or
indirectly, come into contact with an explosive material. Explosive vapor
pressures and their implications for detection are discussed in the next
subsection, while the following subsection considers particulate
contamination. Thereafter, several additional subsections are included on
the different trace detection technologies that are currently available for
explosive detection. Note that one consequence of using trace detection is
that a valid alarm may be recorded for the object (person, package,
vehicle, etc.) being screened, even if the object does not contain a
concealed bomb. This can happen if the object has been contaminated with
trace explosive material for any number of reasons, legitimate or
otherwise. For example, when screening people it is possible to record a
positive alarm for nitroglycerin from a heart patient using nitroglycerin
tablets for medication purposes. For this reason, alarm resolution is always
a key issue when utilizing trace detection technologies.
2.5.1 Vapor Pressures of Explosives
To have a good understanding of the trace detection of explosives, it is
important to understand the concept of vapor pressure. The vapor pressure
of a solid or liquid substance at a given temperature is the gas phase
pressure of the substance that exists at equilibrium above the surface of the
solid or liquid. All solids and liquids emit a certain amount of vapor at all
temperatures above absolute zero (-273 degrees C), and at a given
temperature the amount of vapor emitted is characteristic of the particular
substance. As an illustrative example, consider a piece of solid (2,4,6-
trinitrotoluene (TNT)) placed in a jar with the lid closed. Before the TNT
is placed in the jar, there is no TNT vapor present in the jar, but once the
TNT is inside with the lid shut, the pressure of gas-phase TNT in the jar
will increase as vapor molecules are emitted by the solid. Eventually, a
state of dynamic equilibrium will be reached, where the number of vapor
molecules emitted by the solid per unit time is the same as the number per
unit time readsorbed by the solid and the walls of the jar. There will then
be a constant pressure of TNT gas in the jar, and the quantitative value of
this pressure is the vapor pressure of TNT at the prevailing temperature.
Note that the vapor pressure of a chemical at a specific temperature is the
maximum pressure of the gas that may exist above a solid or liquid. If the
system has not yet reached equilibrium, the actual pressure of the vapor
may be less than the vapor pressure, but never more.
For convenience, vapor pressures are often expressed not in true pressure
units but as relative concentrations in saturated air. Such concentrations
are proportional to the true vapor pressure, and they often provide a clearer
picture of the amounts of vapor that are involved. Figure 1 shows the
vapor concentrations in saturated air of several high explosives at room
temperature (25 degrees C or 77 degrees F). 
Note that the vertical axis of figure 1 has an increasing logarithmic scale,
so that each higher mark corresponds to a factor-of-ten increase in vapor
pressure. The horizontal axis displays the molecular weights of the various
compounds, and is not important in the following discussion. It can be
seen that the vapor pressures of the explosives shown vary widely. For
example, the vapor pressure of ethylene glycol dinitrate (EGDN) is about
10(9) times (or one billion times) higher than the vapor pressure of HMX
(homocyclonite, or octogen). In general, the explosives can be broken into
three groups based on their vapor pressures. The high vapor pressure
explosives include EGDN, nitroglycerin (NG), and 2,4-dinitrotoluene
(DNT). These explosives have saturated vapor concentrations in air close
to or greater than one part per million (1 ppm), which means that at
equilibrium there will be roughly one molecule of explosive vapor per
every million air molecules. The medium vapor pressure explosives have
saturated vapor concentrations in air near one part per billion (1 ppb), a
factor of about 1,000 lower than the high-vapor-pressure explosives. The
medium-vapor-pressure group includes TNT and NH(4)NO(3)
(ammonium nitrate). Finally, the low-vapor-pressure explosives have
saturated vapor concentrations in air near or below the one part per trillion
(1 ppt) level, approximately an additional factor of 1,000 lower than the
medium-vapor-pressure explosives. The low-vapor-pressure group
includes HMX, RDX (cyclotrimethylenetrinitramine or cyclonite), and
pentaerythritol tetranitrate (PETN). These vapor pressures are for pure
materials. Vapor pressures for mixtures containing these explosives may
be even lower.
The relative values of the vapor pressures mentioned above have important
implications for the trace detection of explosives. The high-vapor-pressure
explosives are relatively easy to detect from their vapor using detectors
such as ion mobility spectrometers or electron capture detectors. Thus
dynamites, which usually contain EGDN and/or NG as an explosive
ingredient, can usually be detected from their vapor. Detecting these
compounds by swiping surfaces for particle contamination (see next
section) is also possible in some cases, but it may be less effective than
with lower-vapor-pressure explosives, because the high-vapor pressures
cause small particles to evaporate rapidly. In other words, in the case of
particle sampling, the evidence may not be present long enough to make a
detection. The medium-vapor-pressure explosives can sometimes be
detected from their vapor, but in many cases this will test the limits of
sensitivity for gas- phase detection, and particle detection based on surface
swiping is usually preferred. Ammonium nitrate is a somewhat special
case because it is almost always used in quantities of hundreds or even
thousands of pounds in devices such as car bombs, and not in small bombs
that could be carried on a person or shipped through the mail. Thus when
ammonium nitrate is used, there is likely to be lots of contamination
present to make a swipe-based detection, and various bulk detection
techniques (e.g., x-ray) should also be effective. The low-vapor-pressure
explosives do not produce enough vapor to be detected from their vapor in
any but the most exceptional circumstances, and efforts to detect these
compounds using trace technology must focus on swipe collection of
particulate material. This makes swiping the preferred collection technique
when dealing with plastic explosives such as C-4, semtex, and detasheet,
which contain RDX and/or PETN as the explosive ingredient.
The vapor pressure of a substance can be expressed as:
where P(v) is the vapor pressure, P(0) is a constant with the same units as
P(v), DG is the free energy of sublimation (for a solid) or vaporization (for
a liquid) in units of J/mole, R is the gas constant in units of J/K x mole and
T is the temperature in degrees K. An important point that can be gleaned
from this equation is that P(v) depends upon the temperature as discussed
above, and in fact the value of P(v) will increase exponentially with
increasing temperature. Because of this exponential dependence, the effect
of temperature on vapor pressure is quite dramatic. For example, for solid
TNT near room temperature, the vapor pressure approximately doubles
with every 5 degrees C (9 degrees F) increase in the temperature of the
solid. Thus one cubic centimeter of air that is saturated with TNT vapor
will contain about 0.096 ng of TNT at 25 degrees C, 0.19 ng of TNT at 30
degrees C, and 0.38 ng of TNT at 35 degrees C (1 ng = 10(-9) g = one
billionth of 1 g). This means that one possible way to increase the chances
of a successful vapor detection if a package or suitcase is suspected of
containing a bomb is to heat the object. However, this is not always
possible, and it can lead to interference problems if the object also
contains another material that is more vaporous than the explosive. It
should be pointed out that the numbers given for TNT vapor are very
small compared to the amount of TNT contained in a typical particle in a
fingerprint, which might contain several micrograms of TNT (1 ug = 1,000
ng). For a high-vapor-pressure explosive such as NG, the vapor
concentration in air will be about 1,000 times higher than in the case of
TNT. Therefore, the amount of NG vapor in a cubic centimeter (ccm) of
saturated air will start to approach the amount present in a typical piece of
particle contamination.
A detailed report on the vapor pressures of several common high
explosives has been published by Dionne et al. (Ref. 57 in App. 1). This
study investigated the vapor pressures of TNT, RDX, PETN, NG, and
NH(4)NO(3) over a wide range of temperatures. In each case, an empirical
formula was derived for the vapor pressure over a certain temperature
range. For example, in the case of TNT, it was found that the vapor
pressure could be calculated from:
where Log P(v)(ppt) is the base ten logarithm of the vapor pressure in
units of parts per trillion (ppt), and T is the temperature in degrees K. This
equation is valid for temperatures between approximately 21 degrees C
and 144 degrees C. Similar equations for the other explosives, referred to
collectively as the Dionne equations, provide a convenient means for
estimating the vapor pressures of these explosives at different
temperatures.
A final important point about vapor pressures and vapor detection of
explosives involves the low-vapor-pressure plastic explosives based on
RDX and PETN. It has already been pointed out that RDX and PETN
have extremely low vapor pressures, and the vapor pressures of the plastic
explosives containing these compounds are even lower, due to the
presence of oils and plasticizing agents that give the plastic explosive its
form and consistency. When these explosives are manufactured, they are
often spiked with a high-vapor-pressure nitro-compound called a taggant.
Common taggants include ortho-mononitrotoluene (o-MNT), para-
mononitrotoluene (p-MNT), and dimethyldinitrobutane (DMDNB). These
taggants have vapor pressures similar to NG or EGDN, and their presence
makes vapor detection of plastic explosives possible. However, relying on
vapor detection with plastic explosives is still very risky, because old or
homemade samples of plastic explosives will not contain the taggant.
Nevertheless, detection of one of the taggants using gas-phase sampling
with a trace detection system should be interpreted as possibly indicating
the presence of a plastic explosive.
2.5.2 Particulate Contamination
Particulate contamination, which can also be referred to simply as particle
contamination, consists of microscopic solid particles, often with masses
on the order of a few micrograms. Explosives in general tend to be rather
sticky, and a person handling a macroscopic piece of the solid material
will quickly transfer large amounts of such contamination to his or her
hands. This material will then be transferred to any additional surfaces that
are touched by the hands, which will likely include parts of the person's
clothing as well as doorknobs, tabletops, and other objects he/she contacts.
While it is hard to make generalizations, a typical fingerprint will contain
many particles, often with a total mass on the order of 100 ug. For low-
and medium- vapor-pressure explosives at room temperature, this amounts
to more material than would be present in a liter of air saturated with vapor
by a factor of 1,000 to 1,000,000. Thus, for these explosives, the ability to
make detections based on particulate contamination is crucial, as was
alluded to in the preceding section.
Particulate contamination is usually sampled by wiping the surface to be
screened with a swipe pad provided by the manufacturer of the trace
detection system being used. Once this is done, the swipe pad can be
inserted into a sampling port on the instrument, and in a matter of seconds
it can be analyzed for the presence of explosives. This works best with
briefcases and similar small packages. When screening people, this sort of
surface swiping will necessitate physical contact with the test subject, and
in some situations this may be considered excessively invasive. It should
be noted that while careful handling of the explosive and the proper use of
disposable gloves can greatly reduce the spread of particulate
contamination, reducing it to zero is extremely difficult. Most bomb
builders and carriers will not have the expertise required to do a clean job,
so this method of sampling has very wide applications.
2.5.3 Trace Technologies
The following subsections discuss specific trace detection technologies. A
listing of different trace technologies and their acronyms is given in table
3.
2.5.3.1 Ion Mobility Spectrometry
Ion mobility spectrometry (IMS) is one of the most widely used
techniques for the trace detection of explosives and other contraband
materials. The principle of operation of an IMS is shown in figure 2. The
spectrometer consists of two main sections: the ionization region and the
drift region. In a typical IMS, ambient air is drawn into an inlet port at the
rate of a few hundred cubic centimeters per minute (ccm/min). The
purpose of the instrument is to analyze this air for explosives or other
compounds of interest, which may be present in the air in the form of
vapor or airborne particulate matter. The air first enters the ionization
region, where electrons interact with the incoming molecules to form
positive or negative ions. In the case of explosives, it is negative ions that
are formed. The source of the ionizing electrons is a small, sealed piece of
metal that has been coated with a radioactive material, usually nickel-63
(63Ni{28}). Once ions are formed, they are periodically admitted into the
drift region through an electronically shuttered gate. The ions are drawn
through the gate by a static electric field, which pulls them towards a
metal collection plate at the far end of the drift region. This "drift" of the
ions from one end of the drift region to the other occurs at atmospheric
pressure, with many collisions between the ions and the various molecules
present. The time that it takes the ions to travel the length of the drift
region is called the drift time, and is a complex function of the charge,
mass, and size of the ion. Typical drift times are on the order of a few
milliseconds (1 ms = 0.001 s). The current collected at the metal plate is
measured as a function of time, and an IMS spectrum is a plot of ion
current versus time, with different peaks representing different specific
ions. An IMS spectrum of an air sample containing two types of
explosives is shown in figure 3. Sometimes an additional gas called the
dopant or carrier gas is admitted into the IMS to aid in the ionization
process; very commonly methylene chloride or some other gas that easily
forms chloride ions is used. Ions from this gas usually form the largest
peak in the IMS spectrum, commonly known as the reactant ion peak or
RIP, which serves as a reference peak.
There are a number of features of IMS that make it attractive for the trace
detection of explosives. This technique has probably been more widely
developed for commercial applications of trace explosives detection than
any other. A number of companies market IMS systems, including
Barringer, Graseby, and Ion Track Instruments (see table 4). By the
standards of most technology-based explosives detectors, IMS systems are
moderately priced, with several systems in the $30K to $50K range.
Upkeep costs vary from system to system, but are moderate in most cases.
Most IMS systems are small and portable enough to be moved around in
the trunk of a police cruiser, and can be operated by a person with only a
few hours of training. These instruments have response times of only a
few seconds, the proven ability to detect a number of key explosives,
subparts per billion sensitivity in some cases, and audio and visual alarms
that tell the operator when an explosive has been detected, and what type.
The most effective means for collecting a sample for presentation to one of
these systems is surface swiping, but vacuum collection of samples is also
possible with many systems. Figures 4-7 show photos of some commercial
IMS systems. 
Like all detection techniques, IMS also has certain weaknesses and
drawbacks. As mentioned above, a radioactive material is used as the
source of ionizing electrons in the ionization region. This source typically
has a strength of about 10 mCi and does not pose any health risks if the
system is operated properly, but simply having such a source may lead to
some extra paperwork and regulatory oversight. Several attempts have
been made to develop an IMS with a non-radioactive electron source such
as a plasma discharge, but to date no such systems are commercially
available. Most IMS systems do not run off batteries but rather require an
electrical outlet, and this limits some field applications. There is a
nontrivial warmup time, usually on the order of 10 min, associated with
these systems. The drift time associated with a given ion is dependent on
atmospheric pressure and can thus change during inclement weather or
when the spectrometer is moved more than a few hundred feet in
elevation. This requires little more than routine, periodic recalibration, but
users need to be aware of this potential problem. Like other technology-
based trace detection techniques, IMS systems cannot yet compete with
canines in their ability to follow a scent to its source.
Another drawback of IMS in some applications is that the peak resolution
is not outstanding, and two different ions of similar size and mass may
appear to give only a single peak rather than two distinct peaks in an IMS
spectrum. One method of attacking this problem is to prefraction the
molecules entering the IMS by first passing the incoming gas through a
gas chromatograph (GC). A GC column is essentially a hollow tube,
usually packed with beads that are coated with a special chemical
substance, referred to as the stationary phase. This coating interacts more
strongly with some molecules than with others, so if a gas flow containing
different types of molecules is admitted into the GC, molecules that
interact more strongly with the stationary phase will take longer to pass
through the column. This means that an originally random mixture of
different molecules can be sorted by type, with each species exiting the
GC at a different time. The time it takes a certain molecule to travel
through the length of the GC column is referred to as the retention time. If
two molecules have identical drift times in an IMS, they will almost
certainly have different retention times in the GC, and their peaks can thus
be temporally resolved because they will enter the IMS at different times.
A combined system of this type is referred to as GC/IMS, and such
instruments are marketed by Intelligent Detection Systems (see table 4) for
approximately $75K.
2.5.3.2 Chemiluminescence
Most explosive compounds, including all of those shown in the preceding
chart of gas phase concentrations in saturated air, contain either nitro
(NO(2)) or nitrate (NO(3)) groups. The compounds commonly used as
taggants in plastic explosives also contain NO(2) groups. Detectors based
on chemiluminescence take advantage of this common property of most
explosives by detecting infrared light that is emitted from electronically
excited NO(2) molecules, denoted as NO(2)*. In a chemiluminescence
system, explosive molecules are first pyrolyzed to produce nitric oxide
(NO). The NO molecules are then reacted with ozone (O(3)) in an
evacuated reaction chamber maintained at a pressure of about 3 torr = 0.4
kPa. This reaction produces the excited state molecules, NO(2)*. A
photomultiplier situated behind a red light filter is used to detect the
infrared photons of a characteristic frequency that are emitted when the
NO(2)* molecules decay to form unexcited NO(2). The signal output
measured by the photomultiplier is directly proportional to the amount of
NO present in the reaction chamber, and this signal is thus used to detect
the presence of explosives in a chemiluminescence system. The overall
sequence of reactions can be summarized as follows (where the chemical
equations have not been balanced):
Used alone, chemiluminescence is not capable of identifying what type of
explosive molecule is present. Indeed, all that can be said is that a
molecule must initially have been present that decomposed to yield NO
molecules, and such molecules include not only explosives and taggants
but also species found in fertilizers, some perfumes, and other potential
interferents. For this reason, chemiluminescence detectors are not used
alone but are fitted with a front-end gas chromatograph (GC), as described
in the section on ion mobility spectrometry. The GC allows different
molecules that are detected with the chemiluminescence detector to be
specifically identified based on their GC retention times, and the resulting
system is referred to as a GC/chemiluminescence (GC/CL) detector.
Systems of this type are marketed by Thermedics (see table 4).
The best-known GC/chemiluminescence system is the Thermedics Egis. It
is capable of analyzing samples in 18 s, and because of its high sensitivity
and excellent selectivity it is a popular system with laboratory researchers
and forensic analysts. However, its cost of approximately $150K is 2 to 3
times the cost of a typical IMS system. One nice feature of
chemiluminescence detectors is that they do not utilize a radioactive
ionization source, and thus avoid some of the paperwork and regulatory
oversight that may be associated with IMS detectors. A drawback of
chemiluminescence systems is their inability to detect explosives that are
not nitro-based.
2.5.3.3 Electron Capture Detectors
An electron capture detector or ECD detects explosives and other types of
molecules having high electron affinities. A schematic diagram of a
typical ECD detector is shown in figure 8. In an ECD, a vapor sample is
drawn into an inlet port, and this vapor mixes with a stream of inert carrier
gas (usually helium or argon). The gas flow then travels through an
ionization region to an exhaust line. In transit, the gas flow passes through
a chamber with a radioactive material that acts as an electron source, as in
an IMS. The source material is usually either nickel-63 (63Ni{28}) or
tritium. The emitted electrons become thermalized through collisions with
the gas in the chamber, and eventually are collected at an anode. Under
equilibrium conditions, there is thus a constant standing current at the
anode. The basic principle behind an ECD is that this standing current is
characteristic of the gas mixture being drawn into the system. If the gas
mixture originally consists, e.g., of helium and room air, the standing
current will be reduced if the vapor of an explosive enters the chamber.
This happens because the explosive molecules have a high electron
affinity and thus a tendency to capture free electrons and form stable
negative ions, leaving fewer electrons to reach the anode. Thus, a
reduction of the measured standing current is evidence that an explosive or
some similar species is present. As with a chemiluminescence detector, the
ECD by itself cannot distinguish individual types of explosives from each
other or certain interferents, so a gas chromatograph is placed on the front
end to allow temporal identification of different explosives. Several
companies market detectors of this type (see table 4), referred to as
GC/ECD detectors. A photo of a commercially available GC/ECD device
is displayed in figure 9.
This type of detector has a rapid response and typical sensitivities of about
1 ppb for most electron-capturing compounds. This sensitivity is
somewhat less than the sensitivity of a typical IMS or chemiluminescence
system, but it is still adequate for some applications. However, GC/ECD
detectors usually cost less than IMS or chemiluminescence systems, with
several systems available for $20K or less. These systems also tend to be
smaller, lighter, and more easily portable. As with an IMS, the fact that the
instrument has a radioactive ionization source can lead to some extra
regulatory oversight. Another problem with ECD systems is that they
require an ultrapure carrier gas, usually contained in a small cylinder, and
the availability of this carrier gas can put limits on field applications.
2.5.3.4 Surface Acoustic Wave Sensors
Surface acoustic wave (SAW) sensors are usually coupled with a front end
GC, as is the case with ECD and chemiluminescence detectors. The
principal component of a SAW sensor is a piezoelectric crystal that
resonates at a specific, measurable frequency. When molecules condense
on the surface of this crystal, the resonant frequency shifts in proportion to
the mass of material condensed. The frequency shift also depends upon the
properties of the material being deposited, the surface temperature, and the
chemical nature of the crystal surface.
In a typical system, the exit gas from the GC is focussed onto the SAW
resonator crystal using a carefully positioned and temperature controlled
nozzle. A thermoelectric cooler maintains the SAW surface at sufficiently
low temperatures to ensure efficient trapping of the molecules of interest.
The crystal surface can also be heated in order to desorb vapors and thus
clean the surface. The temperature of the surface allows control of sensor
specificity, by preventing adsorption of species with vapor pressures above
a certain level. This feature is useful in distinguishing between high and
low vapor pressure explosives. During sampling, vapors are concentrated
in a cryo-trap before being desorbed into the GC for temporal separation.
SAW sensors are marketed by Electronic Sensor Technology, Inc. (see
Table 4). Pictured in figure 10 is EST's Model 4100. Total analysis time,
including sample concentration in the cryo-trap, is typically 10 s to15 s.
The system is advertised to have parts per billion sensitivity to certain
types of explosives. It is about the size of a large briefcase, and is
operational within 10 min of startup. The cost is about $25K, similar to
some GC/ECD systems.
2.5.3.5 Thermo-Redox Detectors
Thermo-redox technology is based on the thermal decomposition of
explosive molecules and the subsequent reduction of NO(2) groups. Air
containing the explosive sample is drawn into a system inlet at a rate of
approximately 1.5 L/min. The air is next passed through a concentrator
tube, which selectively adsorbs explosive vapor using a proprietary
coating on the tube's coils. The sample is then pyrolyzed to liberate NO(2)
molecules, and these molecules are detected using proprietary technology.
Those interested in additional information on this technology should
contact Intelligent Detection Systems (see table 4), which now markets the
thermo-redox based equipment formerly marketed by Scintrex.
The thermo-redox system currently marketed, the EVD-3000, is a hand-
held unit that costs approximately $23K, pictured in figure 11. It can
analyze both vapor and particle samples, and contains no radioactive
source. Since only the presence of NO(2) groups is detected, this
technology cannot distinguish among different explosives and potential
interferences that contain NO(2) groups. Thus, the system identifies the
presence of an "explosive-like" material, without identifying a specific
explosive. Furthermore, the technology cannot detect explosives that do
not contain NO(2) groups.
2.5.3.6 Field Ion Spectrometry
Field ion spectrometry (FIS) is a relatively new trace detection technology
(1994) that is related to IMS. It incorporates a unique ion filter using dual
transverse fields, which allows interferences to be eliminated
electronically, without the use of GC columns, membranes, or other
physical separation methods. FIS is similar to IMS in that it involves
separating and quantifying ions while they are carried in a gas at
atmospheric pressure. Furthermore, both systems utilize soft ionization
methods that yield spectra where the species of interest produce the main
features (i.e., under proper conditions there is little decomposition of the
analyte).
In FIS, ions enter an analytical volume defined by a pair of parallel
conducting plates where they execute two motions. The first is a
longitudinal drift between the plates due to the bulk motion of a clean, dry
carrier stream of air. The second is an oscillating motion transverse to the
bulk flow velocity that occurs as the ions respond to an asymmetric, time-
varying electric field imposed between the two plates. In response to the
asymmetric field, the ions tend to migrate towards one of the plates where
they will be neutralized. A second DC field is simultaneously established
across the plates and can be used to balance or compensate for the drift
introduced by the primary field. The DC field intensity needed to
compensate for the AC field induced drift depends on the mobility of the
particular ion under investigation, so that only specific ions can pass
completely through the analytical volume and into the collection area for
detection. Therefore, the device can be tuned to selectively pass only the
ions of interest. Scanning the DC field intensity produces a spectrum of
ion current versus field intensity that is known as an ionogram. 
The sole manufacturer of FIS sensors is Mine Safety Applications (MSA)
--see table 4. Their system, pictured in figure 12, can currently be
purchased for about $30K. The sensor has no moving parts except for a
small recirculation fan and no consumables except a replaceable calibrator
and gas purification filters. The size of the system is 0.022.66 m3 (0.8 ft3),
excluding a computer for control and display. The manufacturer has
reported detection limits for explosives such as TNT, RDX, and PETN in
the low picogram range. To our knowledge, there have not yet been any
independent tests to verify this. A response time of 2 s for a single target
molecule plus another 5 s for each additional target molecule has been
reported. Like an IMS, an FIS uses a small radioactive source for
ionization. Because of the newness of this technique, the current systems
may be better adapted to laboratory research than to routine field
applications, but this could change in the future.
2.5.3.7 Mass Spectrometry
Mass spectrometry (MS) has long been one of the most powerful
techniques available for laboratory chemical analysis. Although it is rarely
used in routine field applications and may thus be of little interest to law
enforcement agencies doing explosive detection, it is discussed briefly
here for completeness and because of this widespread laboratory use.
While there are different types of mass spectrometers, this is basically a
magnetic filtering technique. Molecules are first ionized and then passed
through a magnetic filter, which allows ions to be identified based on their
charge-to-mass ratio. In some systems, the MS is connected to a front-end
GC. Mass spectrometers have excellent specificity for identifying different
ions, and some systems have sub-picogram sensitivity. Mass
spectrometers tend to be expensive. Table 4 lists one mass spectrometer
system that costs $70K, with an advertised sensitivity in the low parts per
billion range for some analytes.
2.5.3.8 EXPRAY Field Test Kit
EXPRAY is a unique, aerosol-based field test kit for the detection of what
the manufacturer refers to as Group A explosives (TNT, DNT, picric acid,
etc.), Group B explosives (Semtex H, RDX, PETN, NG, smokeless
powder, etc.), and compounds that contain nitrates that are used in
improvised explosives. Detection of explosive residue is made by
observing a color change of the test paper. EXPRAY can be used in a
variety of applications, and although in some aspects it does not perform
as well as many of the other trace detectors discussed in this section, it
costs only $250. This very low cost, coupled with simplicity and ease of
use, may make it of interest to many law enforcement agencies (see the
EXPRAY kit in fig. 13).
The EXPRAY field kit[2] is comprised of the following items:
o one can of EXPRAY-1 for Group A explosives,
o one can of EXPRAY-2 for Group B explosives,
o one can of EXPRAY-3 for nitrate-based explosives (ANFO, black
powder, and commercial and improvised explosives based on inorganic
nitrates),
o special test papers which prevent cross contamination.
Initially, a suspected surface (of a package, a person's clothing, etc.) is
wiped with the special test paper. The paper is then sprayed with
EXPRAY-1. The appearance of a dark violet-brown color indicates the
presence of TNT, a blue-green color indicates the presence of DNT, and
an orange color indicates the presence of other Group A explosives. If
there is no reaction, the same piece of test paper is then sprayed with
EXPRAY-2. The appearance of a pink color indicates the presence of
Group B explosives, a group which includes most plastic explosives. If
there is still no reaction, the same paper is then sprayed with EXPRAY-3.
The appearance of pink then indicates the presence of nitrates, which
could be part of an improvised explosive. If EXPRAY-2 is applied after a
positive result with EXPRAY-1, a change to pink color indicates a double
or triple base explosive. The chemistry associated with these color changes
is proprietary. Note that the order of spraying is critical, and all three
sprays should be used in order to perform a complete test. 
The EXPRAY system has certain limitations. Obviously, it is not always
possible to identify the specific type of explosive present when a positive
result occurs. Sampling is entirely by surface swiping; there is no method
for obtaining a vapor sample. Furthermore, not all types of explosives can
be detected. Some nitrate esters and the chlorate group give a negative
result. These include mixtures of potassium chlorate, sodium chlorate, and
potassium nitrate with sugar, sulfur, and/or carbon. In addition, only the
specific colors mentioned above can be judged a positive detection. Other
discoloration is possible, but should be judged negative.
The manufacturer claims that EXPRAY can detect particles as small as 20
ng. However, tests performed at Sandia National Laboratories show limits
of detection for TNT that are 10 to 20 times greater than this.
Nevertheless, this kit is still sensitive enough to make detections in many
real world situations.
2.5.4 Table on Commercial Trace Detectors
Table 4 gives information on various commercially available trace
explosives detection systems. It must be emphasized that all information is
subject to change, and the potential buyer should always check with the
manufacturing company to obtain the most up-to-date information,
including information on new systems. Companies can also provide advice
on the suitability of their products for specific applications, though such
advice will clearly not be disinterested. Bear in mind that all costs are
approximate, and will depend to some degree on the exact options and
accessories purchased.
2.6 X-ray Explosives Detection
X-ray technologies are used to search for explosives in a variety of
situations. X-ray systems are most often used for screening luggage,
packages, mail, and other relatively small items. All of the systems
involve irradiation of a target item with x-rays, followed by detection of an
image created by x-rays that are either transmitted or backscattered by the
item. The process of personnel screening is problematic because of
privacy concerns and the perceived health problems associated with x-
rays, but there are currently two different x-ray based personnel scanners
on the market in the U.S. Vehicle screening systems are also available,
though these are large, expensive, and require passengers to exit the
vehicle while it is being screened. 
2.6.1 X-ray Technologies
The capabilities of x-ray systems range from those that produce a black
and white picture to those that measure the effective atomic number (Z) of
the screened items. The black and white images must be viewed and
subjectively interpreted by an operator. Systems measuring effective Z can
automatically alarm in the presence of materials that have an effective Z
that is in the correct range for explosives. For most x-ray systems on the
market, detection of a suspicious object is not automatic, and suspicious
objects need to be identified by the person viewing the images. Two
commercial x-ray systems for personnel screening (soft x-ray) are shown
in figures 14-15. Many baggage-screening systems are also available and
are similar to systems deployed at airport checkpoints. Such airport
systems are undoubtedly familiar to the reader and are not pictured here.
X-ray imaging systems can be divided into two broad types of categories:
o systems that simply produce an image
o systems that detect explosive-like materials and may generate automatic
alarms.
The simple black and white images from fluoroscopic imaging, image
storage panel, and standard transmission systems cannot identify the actual
explosive material, but do allow the operator to see wires, batteries,
detonators and other bomb components. Fluoroscopic imaging refers to a
transmission x-ray system, where the transmitted x-rays form an image of
the objects investigated on a fluorescent screen. This is the simplest type
of system, exposing the entire object with a cone of x-ray energy, often for
extended periods. The fluorescent screen can be viewed in real time using
a 45  mirror (to avoid standing in direct line with the x-rays), or can be
used in conjunction with a video camera and a video image storage panel.
Use of the camera and image storage panel minimizes the x-ray dose to the
object being viewed, by allowing the image to be captured during a brief
exposure. Even with a camera and storage device, this type of system is
not film safe. The main reasons for the continued use of fluoroscopic
imaging and image-storage panel systems are low cost and portability.
A higher level of technology is the standard transmission x-ray. These
systems use a fan or flying-spot of x-rays to scan the object as it is carried
past the scanner by a conveyor belt. A black and white image is produced
directly with a linear array of sensing diodes. The resulting image is stored
in digital memory and displayed on a TV or computer screen for operator
viewing. These systems are often found at airport checkpoints, where
carry-on bags are screened. While standard transmission systems deliver a
smaller x-ray dose to the object being screened (they are film safe), they
produce black and white transmission images similar to the fluoroscopic
systems and are subject to the same detection limitations. Specifically,
standard transmission systems cannot identify the actual explosive
material, but do allow the operator to see wires, batteries, detonators and
other bomb components. In order to provide an operator with
identification of explosives-like (low-Z) materials, other x-ray
technologies like backscatter, dual energy, or computed tomography may
be employed. Backscatter systems produce an image from x-rays that are
scattered from the screened object. Because low-Z materials are more
efficient at scattering x-rays, explosive-like materials are imaged as bright
in the backscatter image, while they are barely visible in the transmitted
image. The backscatter system produces two images and both the
backscatter and transmission images are displayed. The backscatter image
is usually most effective for the detection of low-Z materials such as
explosives, narcotics, and plastic handguns while the transmission image
is most useful for viewing metals. Backscatter systems cannot discriminate
between various low-Z materials (e.g., between C-4 military plastic
explosive and harmless plastic).
In order to specifically distinguish explosive-like materials from common
low-Z materials, other technologies are employed. Dual energy x-ray
systems yield superior material discrimination through comparison of the
attenuation of x-ray beams at two energies. Thus, identification of low-Z
materials can be achieved by using incident x-ray beams of two distinct
energies. Materials of specific Z numbers (the same effective Z as
explosives) can be clearly highlighted for the operator by adding color to
the image. A material that has a high Z number (metals) is often colored
green, while low-Z materials are colored orange, and materials with the
same Z as explosives are red. 
Some standard transmission systems may have color instead of black and
white displays. Do not confuse dual-energy systems with colorized single
energy transmission systems, which do not color the image on the basis of
Z number, but rather color the image based on the level of x-ray energy
that is transmitted. These simple single-energy colorized systems have
never been proven more effective than the single-energy black and white 
systems, although their displays may look similar to a dual-energy display.
Computed tomography (CT) is an even more sophisticated x-ray technique
in which two-dimensional images ("slices") through an object are added
together to produce a three dimensional image. Along with the three-
dimensional image, the effective Z number is calculated and materials
with the same Z number as explosives can be identified. This is essentially
the same technique that may be familiar to the reader from medical CAT
scans. Development of a dual-energy CT scanner is underway. This
system may be capable of detection with lower false alarms than the
single-energy CT scanners.
Any system that can determine that low-Z materials are present can have
an automated alarm function added. Systems that have been converted into
automated detection systems include backscatter, dual energy, and the CT.
In fact, CT systems are most useful as automated detection systems
because the image they produce may be difficult for the operator to
interpret (the image is often heavily distorted).
2.6.2 Table on Commercial X-ray Detectors
Table 6 lists commercially available x-ray detection systems that can be
used to detect explosives. Note that most of these systems are not easily
portable, and are intended for screening at fixed checkpoints rather than
for field use. Since costs vary widely depending on options and
accessories selected, specific prices are not quoted, but rather the price
category of each system is listed. Low cost is defined as less than $70K,
medium cost as $70K to $300K, and high cost as greater than $300K.
Again, it is very important to have thorough discussions with the vendors
before making a purchase decision.
2.7 Canine Detection
Trained canines provide a reliable and time-proven method for detecting
concealed explosives. There is in principle no explosive compound that
dogs cannot be trained to sniff out, and dogs used in the U.S. military are
typically trained to detect nine different explosives. Compared to
technology-based "sniffer" systems, dogs have the advantages of (1)
superior mobility and (2) the ability to rapidly follow a scent directly to its
source. Because of these advantages, canines are an excellent choice for
explosives detection applications that involve a significant search
component. Such applications include the search of vehicles, warehouses,
luggage and cargo, aircraft, buildings, offices, and areas exterior to
buildings such as parking lots, property perimeters, etc. Dogs are not
usually used to search people because of the liability issues involved
should a dog bite someone. Disadvantages of canines compared to trace
technologies include: limited duty cycle (i.e., a dog works about 1 h before
requiring a break), the need for regular retraining, and the inability to
communicate to the handler the type of explosive that is detected.
Law enforcement agencies can obtain canines from various civilian
contractors. The best contact point is probably a law enforcement agency
in the same area that already utilizes canines. The purchase cost is
typically $5K to $10K per dog, and the initial training usually costs an
additional $6K to $12K. This training typically involves two people and
lasts up to three months. Once a dog has been procured, monthly training
sessions are required. These are often performed in-house, so that the main
cost is the time of the personnel involved. Feeding and caring for a dog
(veterinary bills, etc.) typically costs approximately $1.6K per year.
2.8 Novel Detection Techniques
This section lists several additional explosives detection techniques that
have received at least some commercial development. Since most of these
techniques are still in the process of development, it is especially
important to contact the companies involved to obtain the latest
information.
(1) Thermal Neutron Activation (TNA): This technique is based on the
interaction of neutrons with the nitrogen atoms contained in an explosive
compound. A system of this type is produced by Science Applications
International Corporation (SAIC), phone: (800)962-1632, fax: (619)646-
9718. The system is capable of detecting a number of explosives and has
been used to screen check luggage in airports. However, it is very large
1363.6 kg (3,000 lb) and costs approximately $900K. Smaller and cheaper
systems may be developed in the future, as the technology progresses.
(2) Pulsed Fast Neutron Analysis (PFNA): This new and promising
technique is also being developed by SAIC, which should be contacted if
additional information is desired. It is also based on the interaction of
neutrons with the explosive material, which results in the emission of
gamma rays with characteristics that are indicative of the specific material.
Preliminary testing has shown that many materials, including but not
limited to explosives, yield unique signatures when this technique is
applied. It has been used primarily for luggage screening.
(3) Quadrupole Resonance: This is a promising new technology that has
been extensively developed by Quantum Magnetics, Inc., phone:
(619)566-9200. This technique uses pulses of radio-frequency energy to
excite nitrogen nuclei within an explosive material, which then
(4) emits photons of characteristic frequency when they relax. A number
of systems are available for screening mail, packages, boxes, etc. Cost
varies from $65K to $400K depending on the system selected.
(5) Portable Isotopic Neutron Spectroscopy (PINS) Chemical Assay
System: This system has been jointly developed by EG&G Ortec (phone:
(423)482-4411) and the Idaho National Engineering and Environmental
Laboratory. It is also based on irradiation of the explosive material with
neutrons to produce gamma rays of a characteristic energy. It is designed
primarily for field use in military applications, where it identifies
explosives, nerve agents, and blister agents associated with firing ranges
and munitions burial sites.
3. SUGGESTED TECHNOLOGIES FOR PORTABLE, SEMI-
PORTABLE, AND FIXED-SITE APPLICATIONS
This section presents three matrices (tables 7-9) that provide suggestions
on which explosives detection technologies are likely to work best in a
variety of different circumstances and applications. The emphasis is on
what methods will work best in general, and not on what specific system
should be purchased from a specific manufacturer. When two or more
technologies will work equally well, all are listed. Note that high
technology solutions are not always the best solutions. In a number of
cases, canine detection or physical search (manual search) by police
officers or security guards may prove more effective.
3.1 How to Choose Explosives Detection Technology for Specific
Applications (Tables 7-9)
The three matrices consider five factors that law enforcement personnel
will want to weigh in making a procurement decision:
o Degree of Portability: Table 7 is for portable applications, table 8 for
semiportable applications, and table 9 for fixed-site applications. The
definitions of portable, semi-portable, and fixed-site are as given in section
2.1.
o Presence or Absence of an Explosives Background: For some
applications that are primarily at a fixed site, the presence of background
explosives contamination at the site could present problems. For example,
if a detector is to be deployed near a bunker where explosives are stored,
there will probably be a considerable amount of particulate contamination
in the general area, transported by wind, people's feet, etc. In such cases, it
may be undesirable to use trace detection and perhaps also canine
detection in the area, because the contamination will lead to many
nuisance alarms that need to be resolved. Bulk detection technologies or
physical search are often preferable in such situations.
o Item to be Screened: There are four categories of items - people, hand-
carried items, mailed items, and vehicles, as discussed in section 2.2.
o Throughput Rate: Alternatives are provided for low, medium, and high
throughput rates, as defined in section 2.4.
o System cost: Low-, medium- and high-cost range alternatives are
considered, with the cost ranges defined as in section 2.3. Recall that the
cost ranges are defined differently for trace and x-ray systems, in order to
reflect the realities of the current market. 
3.2 Practical Notes Concerning Tables 7-9
o If a low-cost option is listed, it can also be used in principle for the
situation defined by the medium-cost and high-cost boxes just below it.
However, it is sometimes the case that there is a trade-off between cost
and performance, and sensitivity or some other performance characteristic
may suffer if the cheapest possible system is chosen.
o In some checkpoint screening applications, a high throughput rate may
make it impossible to uniformly screen all items passing through the
checkpoint. In these cases, a possible option is random screening. Random
screening means that only a randomly chosen fraction of the passing items
will be screened for explosives. For example, with a personnel portal,
every fifth person passing the checkpoint might be screened, rather than all
persons. The advantage of random screening is that it can reduce a high
throughput situation to a medium or low throughput situation and thus
provide more time to screen the individual items that are screened, while
still retaining some deterrent effect. The disadvantage, obviously, is that it
becomes possible for a bomb to pass through the checkpoint in an item
that is not screened. In general, uniform screening is to be preferred to
random screening whenever possible, but random screening is always an
alternative. In tables 7-9, random screening is recommended only in cases
where uniform screening would almost certainly be too slow.
o Shaded boxes in the three matrices represent combinations of cost and
throughput rate where it is difficult or impossible to perform uniform
screening with current technologies. In many cases, these combinations
are also unlikely to occur. For example, it will probably never be
necessary to screen people with a high throughput rate using a portable
system. A portable system for personnel screening is needed only for
applications such as searching an apprehended suspect in the field, and in
such an application a high throughput rate is not needed. The officers
involved can, within reason, take as much time as they need to search the
suspect.
o Metal detection is listed in a few places in these matrices where options
are rather limited, but it must be remembered that metal detection is of
limited value in searching for explosives. It can find primers and metallic
bomb components, but not the explosives themselves.
o In the matrices, the range of recommended trace or x-ray systems in a
particular situation is given by using the numbers assigned to detection
systems in tables 4 and 6. Thus, for example, "Trace 1-7" indicates that
any of the first seven systems listed in table 4 might be a satisfactory
choice for the given situation.
Readers of this document are encouraged to study tables 7-9, and focus on
those circumstances they believe will be most important to their intended
applications. Once again, it must be emphasized that these matrices serve
as a starting point, and not an endpoint, in choosing an appropriate
detection system. Obtaining product literature, speaking with the
vendor(s), and holding discussions with an outside expert are still
necessary to make the best-informed decision possible.
4. DESIRABLE CHARACTERISTICS FOR EXPLOSIVES
DETECTION EQUIPMENT FOR POLICE WORK
Sections 4.1 and 4.2 present tables and discussion dealing with desirable
characteristics for trace and x-ray explosives detection equipment that
might be used in law enforcement work. In the case of trace detection
systems, 22 different characteristics are discussed in table 10. A much
smaller number of defining characteristics for x-ray systems is in table 11.
4.1 Trace Systems
In looking at desirable characteristics for detection systems, a useful
approach is to define "ideal" and "nominal" characteristics, and then to
classify each detector (when possible) as ideal, nominal, or subnominal
with regards to that particular characteristic. While the definitions of ideal
and nominal are necessarily somewhat arbitrary and application
dependent, this categorization allows comparisons to be made easily and
rapidly. However, it must be remembered that a law enforcement agency
needs to procure a system based on the characteristics that are most
important to it, and these will vary widely. In other words, there is no "one
size fits all" method of choosing detection equipment for law enforcement
work. For some applications, it may be crucial that a system meet the
"ideal" standard for one or more characteristics, while for other
characteristics a subnominal rating may be perfectly acceptable. Note that
no system in table 10 meets all of our ideal characteristics, and it is very
likely that no system will meet any other set of "ideal" specifications that
might be defined. The enumeration of "ideal" and "nominal"
characteristics in this section should not be construed as providing a list of
requirements; it is intended only to provide information. As with the
matrices in section 3, this table should serve only as a starting point in
making a procurement decision. Furthermore, it must be remembered that
some of the characteristics considered are not fully quantifiable, and in
such cases the associated "ratings" (ideal, nominal, subnominal) are
necessarily subjective and could be open to debate. With these caveats in
mind, the following characteristics are considered:
(1) System Size: Ideal capability: The system can be easily carried by one
person. Nominal capability: The system fits easily in the trunk of a
standard police car. Comments: At present, few commercial systems meet
the ideal capability. The two that do are the Scintrex/IDS EVD-3000 and
the ITI Vapor Tracer. Most commercial trace detection systems meet the
nominal capability, though a few of the larger ones such as the Thermedics
EGIS do not. Obviously, personnel portals also do not meet the nominal
capability.
(2) System Weight: Ideal capability: The system consists of one piece that
weighs less than  9.1 kg (20 lb), so it can easily be hand-carried by a single
operator. Nominal capability: The system can be contained within two
crates or packages, each with a weight of 
22.73 kg (50 lb) or less. Comments: Only a few commercial trace
detection systems meet the ideal capability, but most meet the nominal
capability.
(3) Cost: Ideal capability: The system costs less than $30K. Nominal
capability: The system costs less than $100K. Comments: Most of the
commercial systems now available cost $75K or less. Few are less than
$25K, although some like the Scintrex/IDS EVD-3000 and the ITI Vixen
are. These two systems are based on thermo-redox and ECD technology.
Those technologies are typically less sensitive compared to systems
employing chemiluminescence or IMS technology. The typical cost for
IMS systems is $40K to $75K.
(4) Explosives Detected: Ideal capability: The system can detect TNT,
RDX, PETN, NG, EGDN, DNT, ANFO (ammonium nitrate), double base
smokeless and black powders, and common taggants such as DMDNB and
mononitrotoluenes. Nominal capability: The system can detect TNT,
RDX, PETN, NG, and black powder. Comments: These are the common
high explosives that police officers are likely to encounter in everyday
situations. Some less common explosives that are likely to be very rare in
real-life situations are not considered here. Little emphasis is placed on
chemical taggants because (a) there is lots of untagged plastic explosive
material around (C-4, semtex), and (b) it is assumed that most sample
collection will utilize surface swiping, in which case the explosives are
easily detected without taggants. Most commercial systems do not detect
all explosives equally well in practice. For example, IMS systems can
detect nitrate-based explosives such as ANFO and black powder, but not
as effectively as they detect TNT, RDX, etc. All of the commercial
systems that the authors are familiar with can detect the nominal list; most
can detect the ideal list.
(5) Ruggedness: Ideal capability: The system is encased and protected to
withstand wind, dust, and rain. It must also withstand the routine shocks
and vibration associated with transporting it. Nominal capability: The
system is generally rugged for field applications, but will not be operated
during inclement weather (and thus exposure to dust, rain, and severe
winds will be minimized). It must also withstand the routine shocks and
vibration associated with transporting it. Comments: All current systems
meet the nominal capability. Some testing would be needed to determine
which systems meet the ideal capability.
(6) Field Operation (Power): Ideal capability: The system can operate on
batteries. Nominal capability: The system can operate from a standard 110
V AC power outlet. Comments: While battery operation is ideal, many
commercial systems do not offer this option. All systems meet the nominal
capability.
(7) Maintenance: Ideal capability: Nominal maintenance required, perhaps
every six months, and can be performed by a law enforcement officer.
Nominal capability: Monthly replacement of consumable chemicals,
filters, etc. Comments: Most systems will meet the nominal capability.
(8) System Calibration: Ideal capability: A simple calibration procedure
should be provided by the manufacturer and well documented in a manual.
Under normal weather conditions, not more than one recalibration should
be required per day, assuming continual operation of the equipment.
Nominal capability: As for the ideal case, except that recalibration up to
once per hour is permissible, assuming continual operation of the
equipment. Comments: Most current systems meet the ideal capability
under normal weather conditions. However, pressure changes during
storms can rapidly change peak positions in IMS spectra, resulting in the
need for frequent recalibration during inclement weather. This may be a
problem with some other technologies as well. Police departments may
wish to consider questions such as "How many days a year are there
severe storms in this region?" before purchasing a system. Note also that
moving an IMS system to a new elevation may also require recalibration,
due to the pressure change involved. For most systems, this will not be an
issue if the elevation change is less than plus/minus 91.44 m (plus/minus
300 ft).
(9) Start-up Time: Ideal capability: Less than 10 min from a warm start,
and less than 20 min from a cold start. Normal capability: Less than 1 h
from a cold or warm start. Comments: For most systems, the start-up time
will be considerably less if the system has been turned off briefly after
running for a long time (warm start) than if it has been turned off for a
long time (cold start). Thus, it may be desirable to have a system running
continually at headquarters, and turn it off only when it needs to be
transported to a nearby locale. This would certainly result in quicker start-
ups in field applications.
(10) Sample Collection Mode: Ideal capability: All target explosives can
be detected using vapor (vacuum) collection. Nominal capability: All
target explosives can be detected using swipe collection. Comments: It has
been our general experience that IMS and chemiluminescence systems
have the sensitivity to detect all the target explosives in a vapor collection
mode (though the authors have relatively little experience with ANFO and
black powder). The ECD and thermo-redox systems fail to detect at least
some of the explosives in this collection mode. Data concerning vapor
collection with GC/SAW systems and some less commonly used
technologies was not reviewed. All systems should be adequate when
collecting samples via swiping surfaces. For most applications, surface
swiping should be permissible. However, there are a few applications
where vacuum collection may be preferable. For example, obtaining
samples from a suspect's clothing is perhaps best done by vacuuming,
since physical contact with the suspect (swiping his clothing) might be
considered excessively invasive (i.e., a violation of his right to privacy, or
unreasonable search without probable cause, etc.). Surface swiping will
also lead to greater concern about cross contamination of samples.
(11) Sample Collection Time: Ideal capability: Ten seconds to 5 min
(variable depending upon how the sample is obtained). Nominal
capability: One minute to 5 min (variable depending upon how the sample
is obtained). Comments: All systems known to the authors can meet the
ideal capability.
(12) Sample Analysis Time: Ideal capability: The system gives an
"answer" less than 30 s after a sample is inserted into the instrument.
Nominal capability: The system gives an "answer" less than 2 min after
the sample is inserted into the instrument. Comments: Most if not all
commercial trace detection systems meet the ideal capability. In general,
this means that sample collection rather than sample analysis will usually
be the rate limiting step.
(13) Limits of Detection: Ideal capability: Can detect 100 ug of each target
explosive in the vapor collection mode at least 95 percent of the time.
Nominal capability: Can detect ug of each tarrget explosive in the swipe
collection mode at least 95 percent of the time. Comments: The 100 ug
figure is chosen because this is approximately the amount of particle
residue contained in a typical fingerprint. Some current systems meet the
ideal capability for all target explosives, while virtually all of them meet
the nominal capability. For swipe collection, the true detection limit will
depend to at least some degree on the surface the explosive is deposited
on. Note that for ANFO the detection limit is likely to be less important
than for the other explosives, because ANFO is almost always used in very
large quantities.
(14) Alarm and User Notification of Detection: Ideal capability: The
system has both an audio and a visual alarm, and tells the user what type
of explosive has been detected. A spectrum may be displayed, but the
system must not require the user to interpret the spectrum in any way.
Nominal capability: The system should have an audio alarm or a visual
alarm. It will tell the operator that an explosive or explosive-like material
has been detected, but will not identify the type (in this sense, it will be
similar to an explosives sniffing canine). Comments: Most trace detection
systems meet the ideal capability. A few, like the Scintrex/IDS EVD-3000,
meet only the nominal capability.
(15) False Positive Rate: Ideal capability: Less than 1 percent in laboratory
tests. Nominal capability: Less than 5 percent in laboratory tests.
Comments: These numbers should be based on laboratory tests because it
ought to be possible to obtain clear-cut answers by doing the proper
studies. Until such studies are performed, no definite answers can be
given. However, all systems can meet the nominal capability, and many
will probably meet the ideal capability. 
(16) Nuisance Alarm Rate: Ideal capability: Less than 1 percent when
handled by police officers that are reasonably clean but may have had
recent contact with firearms and ammunition. Nominal capability: Less
than 5 percent when handled by police officers that are reasonably clean
but may have had recent contact with firearms and ammunition.
Comments: Nuisance alarms are alarms caused by true detections, but
where the material detected is only innocuous contamination that does not
result from the presence or handling of an illegal bomb or any other threat
item. Some systems could give nuisance alarms when handled by law
enforcement personnel that have been in contact with weapons.
(17) Probability of Detection: Ideal capability: Greater than 99 percent for
a swiped fingerprint. Nominal capability: Greater than 95 percent for a
swiped fingerprint. Comments: Testing needs to be done to determine
these values, but all systems should meet the nominal capability and
several will meet the ideal capability. A swipe-friendly (smooth and hard)
surface with deposited explosive is assumed. Note that this capability sets
the false negative rate, since the false negative rate is simply one minus the
probability of detection.
(18) Data Storage: Ideal capability: The data obtained can be stored in the
system and printed out later. Nominal capability: Data can be saved if the
system is connected to a computer at the time of data collection.
Comments: Most current trace detection systems meet the nominal
capability.
(19) Ease of Use: Ideal capability: No factory training required. Could be
operated by an average police officer with one day of training. Nominal
capability: No factory training required. Could be operated by an average
police officer with no more than three days of training. Comments: This is
a very important criterion, but it is also subjective and difficult to define.
Most current trace detection systems probably meet the ideal capability as
defined here.
(20) Legal Issues: Ideal capability: The system should be certified to meet
certain judicial standards, such as the Dow and Frye standards. There
should be a proven history of data obtained with the system standing up in
court. Nominal capability: There must be a reasonable expectation that the
data obtained with the system can stand up in court, based on the record of
similar instruments. Comments: Some detectors, such as the Barringer
Ionscan, have undergone certain forms of legal certification. Probably all
of the detectors considered could get such certification. Determination of
the current legal status of each instrument should be based on up-to-date
conversations with the vendor.
(21) Drug Detection: Ideal capability: The system can also detect key
illegal drugs such as cocaine, heroine, marijuana, and methamphetamine
when operated in the proper mode. Nominal capability: No drug detection
capability. Comments: It is up to each law enforcement agency that
procures a detector to decide if they would like to use it as both an
explosives detector and a drug detector. Most IMS-based systems can
perform drug detection, but only when operated in a mode where
explosives cannot be detected. Thus, these systems can detect drugs and
explosives, but not at the same time. The chemiluminescence, ECD, and
thermo-redox systems cannot detect drugs.
(22) Radioactivity: Ideal capability: The system contains no radioactive
source. Nominal capability: The system can contain a sealed radioactive
ionization source with a strength of less than 50 mCi. Comments:
Chemiluminescence detectors contain no radioactive source and hence
meet the ideal capability. GC/SAW and thermo-redox detectors also
contain no radioactive source. On the other hand, IMS and ECD detectors
have a radioactive source. Several companies are doing research to
develop nonradioactive IMS sources (Corona Discharge IMS), but none
are commercially available yet and it is not certain how soon these will be
available for reliable field use. The potential problem with these
radioactive sources is one of paperwork and convenience, than one relating
to human health, because the low energy electrons emitted are easily
stopped by skin. Police departments need to be sure that if they purchase a
detector with a radioactive source, they can transport it freely within their
area of operation. Keeping a logbook of where the system goes each day is
probably reasonable and even desirable, but any paperwork that is required
beyond this would be a burden and could inhibit rapid field deployment.
Most commercial detectors will be acceptable for police use with regards
to this issue.
4.2 X-ray Systems
Table 1, dealing with desirable characteristics for x-ray based detection
systems, is somewhat different than table 10. Most significantly, there are
far fewer characteristics that are considered. Two of the most important
are the capability to detect low-Z materials and the presence of an
automatic alarm. For both characteristics, each system has this capability
as a standard feature (+), has it available as an option (=), or does not have
it (-). Mobility is also considered, with each system classified as portable
(P), mobile (M - mounted in a vehicle), or for use at a fixed site (F). Cost
ranges are listed as defined earlier. Note that two cost ranges are listed for
some systems (e.g., Low/Med); this means that the cost range may change
depending upon what options are purchased. Once again, this table is
intended only to provide information, and it can only be a starting point in
making a procurement decision.
4.3 A Practical Example of How to Use Tables 7-11
Consider a law enforcement officer responsible for responding when
suspicious packages are reported. Assume that any technology that the
officer would use must be portable, easily carried by one person. Table 7
(Portable) is selected, because the additional technologies listed in 
table 8 (semiportable) and table 9 (fixed-site) are too cumbersome for this
application. The Hand-Carried Item description fits the suspicious
package, so the second set of three rows of table 7 is selected. In most
cases, there will be No Explosives Background, so the right half of table 7
is used, for that second set of three rows. This area contains nine
combinations: one for each combination of three costs and three
throughputs. In those nine areas in table 7, all the High Throughput boxes
are shaded. These are shaded because it is unlikely that an officer would
have to screen items at a high throughput in a field situation. In this
example of a suspicious package, there is only one suspicious package to
screen, so a relatively Low Throughput rate can be accepted. The Low
Throughput column has now been selected, where it intersects with the
Hand-Carried Item rows in table 7. The only variable left to consider is the
cost of the technology.
In the Low cost ($0K to $30K trace; $1K to $70K x-ray), several Trace (1-
7) and x-ray (1-9) technologies are listed. These numbers refer to table 4
for Trace systems and to table 6 for x-ray systems. (Consider only the
trace systems to simplify this example.) Looking up the name of Trace
system number 6 in table 4, the Scintrex/IDS EVD-3000, pictured in
figure 11 is found. The EVD-3000 costs $23K according to the table, and
it weighs 3.18 kg (7 lb). If there is uncertainty about how it rates against
Trace systems 1-4, table 10, Characterization of Commercial Trace
Explosive Detection Systems, can be consulted.
In table 10, look at the columns labeled Maintenance and Limits of
Detection. The EVD-3000 has subnominal (black) maintenance
characteristics as does Trace system number 3, while numbers 1, 2, and 4
have nominal (blue) maintenance characteristics. But when the Limits of
Detection column is reviewed, the EVD-3000 is the only one of these five
systems that is nominal, while the other systems, numbers 1-4, are rated
sub-nominal. So, a judgment has to be made whether maintenance or
detection is more important to consider. Assume that better limits of
detection are desired. Then the EVD-3000 would be selected over the
other four trace systems. (If the $23K price tag was too high, a department
might choose one of the cheaper systems, 1-5, on that basis.)
What if better limits of detection are needed? What if the EVD-3000 only
rated nominal, while we wanted an ideal rating? Go back to table 7, and
look at the available options. The higher cost selections have not yet been
considered. Trace systems number 8 and 9 are listed in the Medium cost
($30K to $100K) box. Comparing systems 8 and 9 in table 10, system 9
has more pluses, i.e., ideal attributes than 8, and only costs $3K more.
Look at that system for comparison with the EVD-3000.
Trace system number 9 is found in table 4, where it is listed as the Ion
Track Instruments ITMS Vapor Tracer, pictured in figure 6. The Vapor
Tracer costs $38K and weighs 3.18 kg (7 lb) according to that table. Its
characterization from table 10 is that the Vapor Tracer has a nominal
maintenance rating and an ideal limits of detection rating. If the main
consideration is detection limit, and if $38K is an acceptable price for the
organization, then the Vapor Tracer would be selected over the EVD-
3000.
5. CALIBRATION OF EXPLOSIVES DETECTION SYSTEMS
Commercially available explosives detection systems operate using
different principles, and it is difficult to make generalizations about
appropriate calibration procedures. One generalization that can be made is
that all systems made by reputable companies should come with a detailed
user's manual, and this manual should give a recommended procedure for
system calibration. Depending on the system, the recommended
calibration procedure may not be fully quantitative; the emphasis is
usually on ascertaining that the system works at some minimal level. The
manufacturer should normally be questioned about calibration and
maintenance before a system is purchased. In most cases, a company
representative can provide onsite training when the system is first
purchased, giving one or more employees at the purchasing site an
opportunity to receive hands-on training from an expert operator. The
importance of such training can hardly be overstressed.
Commercial trace detection systems use a variety of sample types for
calibration, but all calibration procedures involve challenging the system
with a minute amount of one or more of the target explosives. Several
systems come with sampling pads that have already been spiked with
known amounts of certain explosives. These can be inserted into a
sampling port for analysis, and the lack of a detection from such a pad
would indicate that the system is not working properly. If a detection is
made, the intensity of the signal can provide a semi-quantitative measure
of the system's sensitivity to the explosive involved, though it would be
more accurate to use sampling pads spiked with explosives from freshly
made standard solutions. At least one commercial system comes with a
lipstick-like substance that contains trace quantities of several different
explosives. This system can be tested by challenging it with a sampling
pad onto which a small amount of the "lipstick" has been rubbed. Some
systems that are used primarily for gas phase sampling come with small
vials of material that emit vapors when opened, and can be tested by
holding the open vial up to the system's sampling inlet. Such systems
could perhaps be calibrated more accurately using one of the explosives
vapor generators that have been described in the literature [1-4], but a
calibration of this type would be expensive and time consuming, and is
probably beyond the scope of most law enforcement work.
Bulk detection systems such as x-ray scanners are often calibrated and
tested by challenging them with a threat object hidden in a piece of
luggage or some other type of hand-carried item. This is not always a
straightforward process, because many systems do not alarm automatically
but rather require a person to determine whether a threat item is present on
a displayed screen image. Thus human factors are involved and the
calibration process is not perfectly defined. When looking for explosives,
it is desirable not to work with real explosive materials, because for bulk
testing it would be necessary to work with a macroscopic sample that is
capable of detonation. For this reason, a material called a simulant is often
used in place of the actual explosive. A simulant is simply an innocuous
material that has similar properties to the explosive when probed with the
type of incident radiation the system uses. For example, if a transmission
x-ray system is being used to study detection of detasheet, a good simulant
would be any material that has an x-ray mass absorption coefficient
similar to detasheet. In the past, Vivid Technologies Inc., has sold
simulant materials suitable for the testing of dual-energy transmission x-
ray detection systems. Other manufacturers may also have identified
simulant materials that they would be willing to sell, or provide with the
systems that they sell.
Other calibration measurements for x-ray systems include those using a
step wedge. The step wedge as defined by the American Society of
Testing and Materials (ASTM) is a series of steps of aluminum with a
series of thin wires of various gauges attached beneath. The purpose of
this test device is to determine that the system can produce different
distinct image intensity levels for each step while clearly displaying the
smallest specified wire beneath each step. Typical x-ray systems can
image a minimum of 34AWG solid copper wire through a minimum of 10
steps. Many modern systems can perform at higher levels with 38AWG
and 20 steps are common.
6. PROTOCOL FOR THE EVALUATION OF COMMERCIAL
TRACE DETECTION SYSTEMS
This document describes standard procedures for testing various important
performance benchmarks of commercial, trace explosives detection
systems. These benchmarks include probability of detection, detection
limit, false-negative rate, false-positive rate, nuisance-alarm rate,
interference response, throughput rate, sampling time, analysis time, and
total processing time. Note that other test protocols have been developed
by various agencies and organizations, and interested readers can contact
the authors for further information.
6.1 Introduction
The tests described in this document are intended to be general enough for
application to all or most commercial trace detectors. Consequently,
comparisons between the performance of various detectors and
documentation of existing detectors in service might be made uniform or
convenient. However, these tests are not replacements for user's manuals,
and readers should become thoroughly familiar with the instrument
through reading the user's manual provided by the manufacturer. If any
instructions provided in this protocol contradict instructions given in the
user's manual, operators should follow the instructions given in the user's
manual, or at the very least contact the company marketing the equipment
to discuss the matter.
A procedure not included here, because it is very instrument specific, is
that of instrument calibration, including the setting of alarm levels for
various explosives. All calibrations should follow the procedures given in
the user's manual. When a system is purchased, most vendors will provide
some onsite training so that the calibration procedure can be learned
directly from an expert operator employed by the company.
6.2 The Basics of Instrument Operation
(I) Blank Samples: Verifying Freedom From Contamination
When presenting any chemical detection system with a sample (also
known as "challenging" the system), it is imperative that the system is
clean (free of the substance being detected prior to the challenge). If the
system is contaminated, an apparent detection may result from the
contamination that was already present in the system and not from the
sample being analyzed. Clearly, this could lead to false-positive results.
For example, in a portal system that screens people for explosives, it might
be concluded that a certain person has had contact with explosives, when
in fact he has not.
For this reason, trace detectors must be certified as clean after a positive
response or alarm shows the presence of explosive material. In addition,
the system must be verified as clean before analyzing the first sample.
This is done by challenging the system with blank samples that are known
not to contain explosive material. For example, if swipe pads for sample
collection are being used, pads that have come straight out of the package
supplied by the vendor and have not been exposed to any explosive can be
tested. Thus at the start of each period of use of the instrument and after
the processing of any sample that results in an alarm, challenge the system
with a blank to see whether or not an alarm is recorded. If no alarm is
recorded, proceed to process additional samples. (When doing rigorous
testing, it might be desirable to run as many as three blanks between
samples.) If an alarm is recorded, it almost surely results from
contamination of the system. In this case, keep challenging the system
with blanks until no alarm is recorded. In extreme cases of exposure to
very large explosive masses, it might be necessary to let the system sit for
several hours with the detector at a high temperature in order to purge the
system of all the explosive contamination.
(II) Collecting the Explosive Material: Swipe Versus Vapor Collection
With most commercial trace explosives detection systems, there are two
common means of collecting samples: swipe collection and vapor
collection. In swipe collection, a sampling pad (usually supplied by the
manufacturer) is wiped across a surface suspected of having residue of
explosive material. This surface could be a tabletop, the outside of a
package, a piece of luggage, clothing, and so forth. The sampling pad is
then inserted into a sampling port on the instrument for analysis. In
contrast, vapor collection involves the use of a small hand-held vacuum to
collect airborne vapors or particles. Typically, vacuuming is performed
just above the surface to be investigated. A collection filter is located
inside the inlet of the vacuum, and air is drawn through this filter. The
explosive material will be trapped on the filter. The filter is then removed
and analyzed by the system in a manner similar to the analysis of a swipe
sample. Vapor sampling of this sort is generally less sensitive than swipe
sampling, but it is advantageous for screening people because it is not
necessary to touch the person being screened. Thus, taking samples with
vapor collection is regarded as less invasive than collecting swipe samples.
(III) Explosives Solutions and Proper Handling
Successful work with trace explosives detectors usually requires detection
of explosive residues, amounts of material that are so small that the actual
sample cannot be seen by the human eye. Most trace detectors will show a
positive response to amounts of explosive material on the order of a few
nanograms or less (one nanogram equals one billionth of one gram). Even
in the preparation of solutions of known composition and content
(standardized solutions), only microscopic amounts of material are needed
to perform instrument testing. One benefit of this is that the usual hazards
of working with explosives are obviated, since such tiny amounts of
explosive cannot produce a detonation.
A common method of handling microscopic amounts of explosive material
is to use explosives dissolved in volatile organic solvents. For example, a
typical solution might be TNT dissolved in methanol at a concentration of
1 ng of TNT per microliter of methanol. (Such solutions can often be
purchased directly from commercial chemical suppliers.[3] Once obtained,
the solutions can be used as received, or further diluted to provide lesser
concentrations.) A known amount of explosive can be obtained from such
a solution by withdrawing a known volume of solution (typically
measured in microliters by a syringe) and then depositing this volume onto
a sampling pad. A typical calculation is:
Other terms for mass and volume may be used so long as the units are
consistent throughout the formula. The volatile solvent will evaporate
rapidly at room temperature and the measured amount of explosive
material will remain on the sampling pad. While a thorough discussion of
the proper handling of chemical solutions is beyond the scope of this
document, always make sure that the work area is free of explosive
residues, the syringes and glassware that are used are clean, and in
particular that a syringe used to measure out a dilute solution is not
contaminated with a more concentrated solution.
(IV) Logbook and Record Keeping
An easily overlooked aspect of making trace chemical measurements is
record keeping on a sample and on the instrument used for analysis. In
both laboratory and field use, a record of who, when, where, what, and
why should be kept. This record or logbook is essential for legal purposes
and other uses such as instrument maintenance. 
Notice that consecutive analysis numbers are given for each use of the
instrument and that the sample's identity is recorded elsewhere in the
Description column. Moreover, the table above is an example of minimum
content for a logbook. Other details might include where the data are
stored, a reference to the origin of the standards, etc. In addition, the
results from the calibrations might be maintained elsewhere (see Sec. VII)
in a type of maintenance record to anticipate or schedule routine repair and
upkeep of instruments. Experimental parameters such as temperature and
pressure should be included in the logbook as shown in the fourth column;
these will show only minor changes in laboratory use, but may show wide
variations in field use.
(V) Data Storage and Backup
Trace detectors may be connected to small computers where results of
analyses are processed and findings are displayed. The level of technology
on these detectors may range from hand-held units with on-board
computers without data storage capabilities to laboratory models with
modern computers and large storage capacities. In instances where
analysis results are stored, efforts should be made to copy the results to
another storage medium and the results archived for future use. The
organization and records for such archives should be well maintained and
secure, particularly for legal purposes. The possible corruption of records
through technology failures (copying errors) or other failures (misplace
records or damaged disks) must be avoided. In addition, hardcopy records
might be maintained as the ultimate backup.
(VI) Control Charts and Long-Term Instrument Performance
A routine procedure with trace detectors should be the use of blanks and
standards to guarantee freedom of contamination and proper responses to
known amounts of chemicals. This determines the quantitative response of
the detector and if it changes over time. Often loss in performance for a
detector is seen in the quantitative response and can suggest need of
maintenance. All trace detectors require routine maintenance, so the
frequency and cost of such service should be anticipated. One helpful tool
is the control chart. A control chart is a graph of calibration results of an
instrument on a daily, weekly, or monthly basis. Some control charts may
span years. In the control chart shown in figure 16, the response of an IMS
based detector to 5 ng of TNT was monitored (given a certain amount of
normal variability) from the middle of June until the middle of July. Such
control charts are often created and kept by specialized personnel whose
responsibility is to inventory and maintain field instruments or by regular
laboratory personnel operating the detectors daily. Field or enforcement
personnel should not ordinarily be responsible for this somewhat tedious
aspect of instrumentation use.
(VII) Experimental Parameters
Experimental parameters are those quantities and conditions that define or
describe the conditions under which an analysis or measurement occurred.
When testing a commercial trace detection system, the experimental
parameters will include both system operating parameters (e.g., detector
temperature, alarm level, etc.) and external parameters (ambient
temperature, ambient pressure, etc.). When determining detector
performance, the values of all experimental parameters should be
recorded. Changing any experimental parameter could change the final
value of Probability of Detection [P(d)] or any other experimentally
determined quantity, so the value of the experimentally determined
quantity is only meaningful if all experimental parameters are defined.
Some experimental parameters will have a large impact on the
experimentally measured quantity, while others will have little or no
impact. Minor changes in external parameters such as ambient temperature
usually will have only a small impact. During any testing to characterize a
detector's performance, the experimental parameters should be carefully
monitored.
6.3 Protocol for Characterizing a Trace Explosives Detector
This protocol includes procedures for determining the following
benchmarks, each of which will be described in the sections below:
o Probability of Detection
o Detection Limit
o False-Negative Rate
o False-Positive Rate
o Nuisance-Alarm Rate
o Interference Tests
o Throughput Rate
o Sampling Time
o Analysis Time
o Total Processing Time
6.3.1 Probability of Detection - P(d)
P(d) should be determined or defined for each type of sample collection.
The procedure outlined below concerns the most common method for
explosives screening where a known amount of explosive from a solution
is deposited directly onto a sampling pad. However, a very similar
procedure could be followed to determine a P(d) based on other types of
sampling.
1. See that the system is turned on, calibrated, and that the alarm level is
properly set.
2. Using a syringe, place a known amount of explosive in a solution of a
volatile solvent onto the center of a sampling pad (e.g., 1 ng of TNT in 1
uL of acetonitrile). Use the type of sampling pad recommended by the
manufacturer for that instrument.
3. Wait for the solvent to evaporate.
4. Present the sampling pad to the instrument as appropriate for that
system. For many systems, this will mean inserting the pad into a heated
sample port on the instrument. For others, this may mean rubbing the
sampling pad over an inlet where material is sucked into the system.
5. Observe the system response, and record whether or not an alarm
occurs. You will probably want to save the spectrum produced for future
reference.
6. Present the system with clean pads (a blank), and observe whether or
not an alarm is recorded for the explosive in question. If three consecutive
clean pads produce no alarm, the system can be assumed to be clean and
can again be challenged with a pad containing explosive material.
7. Repeat this procedure for a total of 20 measurements. P(d) is then =
[number of alarms recorded/20].
P(d) can also be measured for the following sampling methods: (i) known
explosive mass deposited onto a designated surface, then swiped; (ii)
known explosive mass deposited onto a surface, then vacuumed; (iii)
known vapor dose directed into sampling pad (perhaps contained in a
vacuum device); and (iv) known vapor dose directed into an instrument
using a vapor generator. Not all of these modes are possible with every
instrument.
6.3.2 Detection Limit (DL)
The DL is defined here as the lowest mass of explosive material with a
P(d) of 0.9 or higher, i.e., the lowest amount that will cause the system to
alarm on > 90 percent of the challenges. Note that this is dependent upon
where the alarm level is set for a particular system.
In principle, it is desirable to test the detection system with a variety of
different masses for a given explosive, and the lowest mass that gives a
P(d) of 90 percent or greater will be the DL. general procedure is outlined
below. Once again the example of known explosive masses deposited
directly onto a sampling pad of the appropriate type is used.
1. See that the system is turned on and properly calibrated, and that the
alarm level is set at the appropriate level.
2. Challenge the system with a blank sample pad to verify that it is clean.
If no alarm is recorded, proceed to the next step. If an alarm is recorded,
repeat this step until no alarm is recorded. To save pads, this step may be
repeated with the same pad initially if desired, but always challenge the
system with at least one new clean pad and obtain a result of "no alarm"
before moving on to the next step.
3. Challenge the system with a sample mass that is suspected of being well
above the DL. This might take some guesswork, but the system manual
and a little experience can be of assistance. If an alarm is recorded, move
to the next step. If no alarm is recorded, the mass chosen was too small.
After running a blank sample to verify system cleanliness, double the
mass, and see if an alarm is recorded. Repeat this procedure until an alarm
is recorded.
4. Perform a P(d) test for the mass where the alarm is recorded, as
described above in the section on Probability of Detection. If P(d) for this
mass is 90 percent or greater, this can serve as the starting point for the test
performed in step (5). If P(d) is less than 90 percent, double the mass and
again perform a P(d) test. Repeat this procedure until a mass is found that
is above the DL, i.e., that has a P(d) of at least 90 percent. 
5. Once such a point above the DL has been found, perform a series of
tests where the system is challenged with ten different masses, ranging
from no explosive to the mass determined in step (4) in equal increments.
For example, if it was determined in step (4) that a mass of  2 ng was
above the DL, the masses tested should be (0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2,
1.4, 1.6, 1.8, and 2.0 ng). Start with the lowest mass (no explosive) and
work upwards, performing two tests for each mass and recording whether
or not alarms are recorded. Make sure that a clean blank sample is run and
that no alarm is recorded following each challenge with explosive
material. 
6. Find from the test in step (5) the lowest mass for which two alarms were
recorded, and run a P(d) test with twenty challenges at this mass. This
mass should be very close to the DL. If P(d) for this mass is found to be
less than 90 percent, perform a P(d) test at the next highest mass, and keep
moving up in mass until a mass is tested where P(d) is greater than 90
percent. If, on the other hand, P(d) is greater than or equal to 90 percent
for the mass chosen initially, move down to the next lowest mass and
perform a P(d) test, and continue to move down until a mass is reached
with P(d) less than 90 percent. Once this procedure is complete, the lowest
mass tested with P(d) > 90 percent can be taken as the DL.
The DL can be determined more precisely by testing at additional
explosive masses between the DL determined above and the mass
immediately below it where P(d) < 90 percent. However, in practice, this
more precise determination will rarely be worth the effort.
6.3.3 False-Negative Rate
For a given set of experimental conditions, the false-negative rate is
simply one minus the probability of detection. Thus, if P(d) = 0.8, the false
negative rate is 0.2, or 20 percent. All experimental parameters must be
identical for this to hold true. If any parameter is changed, determine a
new P(d) before calculating the false negative rate.
6.3.4 False-Positive Test
The following test procedure can be followed for a laboratory test of the
false-positive rate. The example of clean sampling pads, though vapor
tests with clean air could be used in some cases, is used.
1. Make sure the system is turned on, calibrated, and that the alarm level is
set properly.
2. Challenge the system with a clean sample pad. If no alarm is recorded,
the system can be assumed to be clean and the testing can begin. If an
alarm is recorded, continue to challenge the system with clean pads until
no alarm is recorded three consecutive times.
3. Challenge the system with clean sample pads 20 times, and record each
time whether an alarm is recorded and for what explosive. If an alarm is
recorded, interrupt the test by challenging the system with blank pads that
are not counted towards the total of twenty. When three consecutive pads
produce no alarm, the system can be taken to be clean again. At this point,
continue where you left off in the test sequence of twenty pads.
The false-positive rate is then [number of alarms in the test sequence of
twenty pads/20].
A similar and somewhat more useful test could also be performed to
determine the false-positive rate under realistic field conditions. However,
in this case the situation becomes more complicated, because "false
positives" obtained in the field may actually be due to real explosives
contamination. If this is so, they should be classified as "nuisance alarms"
rather than "false alarms." Therefore, some form of alarm resolution
(questioning of people screened or further chemical analysis of samples)
needs to be conducted in order to correctly classify the alarms.
Alternatively, all alarms can simply be classified as "false positives," and
the false-positive rate thus determined will represent an upper limit on the
actual false alarm rate. 
6.3.5 Nuisance-Alarm Rate
Nuisance-alarms are alarms that result from the actual detection of an
explosive, but where the explosive material present originates from an
innocuous source rather than from a threat item. For example, when
screening people for explosives at a checkpoint, a nitroglycerin alarm
could result because the test subject is a heart patient with nitroglycerin
tablets, rather than a terrorist attempting to smuggle a bomb containing
nitroglycerin. Similarly, an alarm for TNT could result from a construction
worker employed at a blasting site, an alarm for black powder or some
related substance could result from anyone having recently handled
firearms for a legitimate reason, etc. In law enforcement applications,
nuisance alarms could result for some explosives detection systems if
these are operated by officers frequently handling firearms, or working in
or visiting areas where there may be explosive contamination.
A nuisance-alarm rate can be determined in the same way as a false-
positive rate, but the tests will need to be performed in a real-world
operating environment rather than in a laboratory. For example, if using a
system to screen persons entering a courthouse, it would be possible to
determine a nuisance-alarm rate by careful examination and questioning of
all persons giving alarms. Based on these followup investigations, the
alarms can be divided into (i) actual detections of bombs or individuals
having handled bombs, (ii) nuisance-alarms, and (iii) false-positives.
6.3.6 Interference Tests
Interferences (or interferents) are chemicals that may interfere with the
detection of explosives using a trace detection system. They can do this by
either masking the presence of explosives when an explosive is present, or
by giving rise to false positives when no explosive is present.
Since interference may produce either false-positives or false-negatives,
two different tests are outlined to check for each of these effects. The
common sampling procedure of placing a known amount of explosive in
solution onto a swipe pad is used as an example, but a similar procedure
could be followed based on other sampling methods.
To check for false-positives caused by interference, follow this procedure:
1. Make sure that the explosives detection system is on, properly
calibrated, and that the alarm level is set as desired.
2. Challenge the system with clean sampling pads until no alarm is
recorded on three consecutive challenges.
3. Place a known amount of the potential interferent onto the center of the
appropriate sampling pad. Use an amount that is at least 100X the DL for
an explosive that has been tested with the system. For most materials, this
step will most easily be accomplished by using a solution of the material
in some volatile solvent. However, for solid materials (e.g., lipstick), this
test could be performed crudely (and nonquantitatively) by simply
smearing the material across the sampling pad.
4. Challenge the system with the sampling pad containing the material
being tested for interference. If no alarm is recorded for explosives, the
material is not an interferent that is capable of producing false-positives.
5. Repeat step (4) with at least two more sample pads containing the
material, to make sure the result is correct. Before each test, challenge the
system with a clean sampling pad to assure that it is not contaminated.
To check whether or not a potential interference can create a false negative
(that is, mask the presence of an explosive), use the following procedure:
1. See that the system is on, properly calibrated, and that the alarm level is
set as desired.
2. Challenge the system with a clean sampling pad to assure that it is not
contaminated.
3. Take a clean sampling pad. Deposit onto the center of this pad a known
amount of the explosive of interest that is approximately twice the DL.
Also deposit into the pad a known amount of the potential interference to
be studied (preferably the same mass as for the explosive).
4. Challenge the system with this pad and see if an explosive alarm is
recorded. If no alarm is recorded, the substance studied is an effective
interferent.
5. After clearing out the system, repeat the test with half as much
interference, and continue this process until the explosive can again be
detected. This gives an idea of how much interference is required to mask
the presence of the explosive.
6. If an alarm is recorded, keep repeating the test while increasing the
amount of interference used, until either the explosive can no longer be
detected or the experiment becomes impractical. If even then the explosive
can be detected, the material present is not an effective interferent.
6.3.7 Throughput Rate
The throughput rate is the number of distinct samples that can be
processed in a given period of time. It is usually expressed in units such as
samples per minute or samples per hour. It needs to be determined by
challenging the system with a large number of samples over a considerable
period of time, in order to obtain an accurate average value. Note that the
throughput rate includes the time needed to collect the samples. Clearly,
the throughput rate will depend upon the sampling process, and will be
different for swipe collection and vapor collection. It can also change for
differing swiping procedures or differing vapor collection procedures,
depending upon how the process is defined. The term "throughput rate"
can refer to any sort of item being screened or processed: people,
packages, vehicles, mail, etc.
In general, the maximum possible throughput rate can be determined by
following this procedure:
1. Collect a large number of the appropriate sampling media (e.g., swipe
pads).
2. See that the detection system is turned on, calibrated, and has the alarm
level properly set.
3. Challenge the system with a clean sampling pad to make sure that it
gives no alarm.
4. Start timing with a stopwatch. Follow the steps listed below for 5 min or
for the time it takes to process ten samples, whichever is greater. Use only
blank samples in this test, to make sure that no time is lost due to detection
system clear down time. The experiment will then give a measure of the
optimum throughput rate for the sampling process chosen.
5. Obtain a sample according to the chosen procedure (e.g., swipe a clean
tabletop), challenge the detector with it, and record the result (alarm or no
alarm).
6. Repeat step (5) until 5 min are up or 10 samples have been processed.
Work deliberately and continuously, but do not rush.
7. Stop the watch and record the finishing time. The throughput rate is the
number of samples processed divided by the total time. For example, if 30
samples are processed in 3 min, the throughput rate is ten samples per
minute.
6.3.8 Sampling Time
The sampling time is the time needed to acquire a sample and to present it
to the explosives detection system for analysis. Like the throughput rate, it
can only be determined accurately by averaging over a large number of
measurements. Since by definition,
total processing time = sampling time + analysis time
the sampling time is perhaps best determined by determining the other two
quantities (see below) and solving the above equation. Obviously, the
sampling time will vary depending on the method of sampling chosen.
6.3.9 Analysis Time
The analysis time is the time required for the system to analyze a sample
with which it has been challenged, including the time needed to produce
an alarm and the corresponding readout. For most trace detection systems,
this time can be determined by continuously challenging the system with
the same sample (e.g., swipe pad) that is either clean or contains explosive
material, waiting for the system to complete the analysis between each
challenge, and then dividing the total time elapsed by the number of
challenges.
6.3.10 Total Processing Time
The total processing time is the time needed to collect and analyze one
sample with the detector in question. It is equal to the sum of the sampling
time and the analysis time. It should also be equal to the reciprocal of the
throughput rate. For example, if the throughput rate is five samples per
minute, the total processing time should be 1/5 min per sample, or 12 s per
sample.
7. WARNING: DO NOT BUY BOGUS EXPLOSIVES DETECTION
EQUIPMENT
From time to time, there are new devices that enter the market. Most
companies make reasonable claims, and their products are based on solid
scientific principles. Claims for some other devices may seem
unreasonable or may not appear to be based on solid scientific principles.
An old truism that continues to offer good advise is "If it sounds too good
to be true, it probably is not true." If there are any questions as to the
validity of a device, caution should be used and thorough research must be
performed before a purchase is made. Money can be wasted and even lives
may be risked. Although there may be other types of nonoperational
devices around, dowsing devices for explosives detection have emerged
during the past couple of years.
There is a rather large community of people around the world that believes
in dowsing: the ancient practice of using forked sticks, swinging rods, and
pendulums to look for underground water and other materials. These
people believe that many types of materials can be located using a variety
of dowsing methods. Dowsers claim that the dowsing device will respond
to any buried anomalies, and years of practice are needed to use the device
with discrimination (the ability to cause the device to respond to only
those materials being sought). Modern dowsers have been developing
various new methods to add discrimination to their devices. These new
methods include molecular frequency discrimination (MFD) and harmonic
induction discrimination (HID). MFD has taken the form of everything
from placing a xerox copy of a Poloroid photograph of the desired material
into the handle of the device, to using dowsing rods in conjunction with
frequency generation electronics (function generators). None of these
attempts to create devices that can detect specific materials such as
explosives (or any materials for that matter) have been proven successful
in controlled double-blind scientific tests. In fact, all testing of these
inventions has shown these devices to perform no better than random
chance.
Mostly these devices are used to locate water and now are used
extensively by treasure hunters looking for gold and silver. In recent years
some makers of these dowsing devices have attempted to cross over from
treasure hunting to the areas of contraband detection, search and rescue,
and law enforcement. The Quadro Tracker is one notable example of this
cross-over attempt. This device was advertised as being a serious
technology with a realistic sounding description of how it worked (close
examination showed serious errors in the scientific sounding description).
Fortunately, the National Institute of Justice investigated this company and
stopped the sale of this device for these purposes, but not before many law
enforcement agencies and school districts wasted public funds on the
purchase of these devices.
Things to look for when dealing with "new technologies" that may well be
a dowsing device are words like molecular frequency discrimination,
harmonic induction discrimination, and claims of detecting small objects
at large distances. Many of these devices require no power to operate
(most real technology requires power). Suspect any device that uses a
swinging rod that is held nearly level, pivots freely and "indicates" the
material being sought by pointing at it. Any device that uses a pendulum
that swings in different shaped paths to indicate its response should also
arouse suspicion. Advertisements that feature several testimonials by
"satisfied users," and statements about pending tests by scientific and
regulatory agencies (but have just not happened yet) may be indications
that the device has not been proven to work. Statements that the device
must be held by a human to operate usually indicate dowsing devices.
Statements that the device requires extensive training by the factory, the
device is difficult to use, and not everyone can use the device, are often
made to allow the manufacturer a way of blaming the operator for the
device's failure to work. Another often used diversion is that scientists and
engineers cannot understand the operation of the device or the device
operates on principles that have been lost or forgotten by the scientific
community.
In general, any legitimate manufacturer of contraband detection equipment
will eagerly seek evaluation of their device's performance by scientific and
engineering laboratories. Any doubt that a device is legitimate can quickly
be dispelled by making a call to any of the known agencies whose
business it is to know about security-related technology.
8. CONCLUSION
Many details regarding commercially available explosives detection
equipment have been included in this document. The reader should first
determine his or her own intended applications, and thus narrow the
problem, to avoid being overwhelmed by the amount of information in this
document and the number of systems from which to choose. Having
decided on the most important application, a decision of which system to
buy can start by consulting table 7, 8, or 9, depending on the desired
system portability. Finding the appropriate boxes in the chosen table based
on the other conditions defining the application and purchase, several
possibly acceptable systems can be chosen in most cases. These systems
can then be looked up in table 4 (trace systems) or table 6 (x-ray systems),
and, if necessary, additional information about the system characteristics
can be obtained from tables 10 and 11. This process should allow the
identification of one or more systems that should be investigated further.
At this point, it would be appropriate to contact the vendor or the authors
of this document for additional information and discussions.
One point that needs to be remembered is that explosives detection
technologies are constantly being improved and expanded, so information
can become dated rather quickly. For this reason, it is especially important
to consult with product vendors and outside experts before making a major
procurement decision. Such discussions are a great aid in making informed
procurement decisions, and can save time, effort, and money.
APPENDIX A-1. SUGGESTED READINGS
General Explosives and Pyrotechnics
1. Kohler, J. and R. Meyer, Explosives, VCH - Verlagsges., Weinheim,
FRG, 1993.
2. Cooper, Paul W. and Stanley R. Kurowski, Introduction to the
Technology of Explosives, VCH Publishers, Inc., 1996.
3. Ellern, H., Military and Civilian Pyrotechnics, Chem. Publishing Co.,
1968.
4. McLain, J., Pyrotechnics, Franklin Institute Press, 1980.
5. Explosives and Rock Blasting, Atlas Powder Co., 1987.
6. Yinon, J. and S. Zitrin, The Analysis of Explosives, Pergamon Press,
1984.
7. Brauer, K., Handbook of Pyrotechnics, Chem. Publishing Co., 1974.
8. Blaster's Handbook, E.I. Dupont de Nemours and Co., 1980.
9. Encyclopedia of Explosives and Related Items, PATR-2700, Picatinny
Arsenal.
10. Journal of Propellants, Explosives, Pyrotechnics (official journal of the
International Pyrotechnics Society), VCH Publishing, Weinheim, FRG.
11. Journal of Energetic Materials, Dowden, Brodman, and Devine
Publishing, Wharton, NJ.
12. Journal of the Society of Explosives Engineers.
13. Cook, M.A., The Science of High Explosives, Reinhold Publications,
1958.
14. Explosive Trains, Army Materiel Command Pamphlet 706-179, March
1965.
15. Principles of Explosive Behavior, Army Materiel Command Pamphlet
706-180, April 1972.
16. Fickett, W. and W.C. Davis, Detonation, University of California
Press, 1979.
17. Fickett, W., Introduction to Detonation Theory, University of
California Press, 1985.
18. Bowden, F.P. and A.D. Yoffe, Initiation and Growth of Explosion in
Liquids and Solids, Cambridge University Press, 1952.
19. Bowden, F.P. and A.D. Yoffe, Fast Reactions in Solids, Butterworths
Scientific Publishing, 1958.
20. Chase, W.G. and H.K. Moore, Exploding Wires, Plenum Press, New
York, 1959.
21. Military Explosives, TM 9-1300-214/TO 11A-1-34, Departments of
the U.S. Army and the U.S. Air Force (Rev. December 1970).
22. Walters, W.P. and J.A. Zukas, Fundamentals of Shaped Charges, John
Wiley and Sons, Inc., 1989.
23. General Information Bulletin 97-1, FBI Explosives Unit-Bomb Data
Center.
24. 1996 Selected Explosives Incidents, Bureau of Alcohol, Tobacco and
Firearms.
Explosives Detection
25. Proceedings from the First International Symposium on Explosives
Detection Technology, Sponsored by the FAA, November 1991.
26. Proceedings from the Second Explosives Detection Technology
Symposium and Aviation Security Technology Conference, Sponsored by
the FAA, November 1996.
27. American Science and Engineering, Inc., Product Sales Literature,
Internet Address: http://www.as-e.com.
28. Nicolet Imaging Systems, Product Sales Literature, Internet Address:
http://http://www.nicing.com/s1000.html.
29. Science Applications International Corporation, Product Sales
Literature, Technical Briefs, Internet address: http://www.saic.com.
30. MinXray, Inc., Product Sales Literature.
31. LIXI Inc., Internet Address: http://www.lixi.com.
32. Rapiscan Security Products, Inc., Product Sales Literature, Internet
Address: http://www.rapiscan.com.
33. XID Corporation, Product Sales Literature.
34. Control Screening, Product Sales Literature, email:csllc@trib.infi.net.
35. Heimann Systems, a Division of Siemans Components, Inc., Product
Sales Literature.
36. EG and G Astrophysics, Product Sales Literature, Internet Address:
http://egginc.com.
37. Vivid Technologies Inc., Product Sales Literature.
38. Invision Technologies, Inc., Product Sales Literature, Internet address:
http://www.invision-tech.com.
39. Ion Track Instruments, Inc., Product Sales Literature.
40. Barringer Instruments, Inc., Product Sales Literature.
41. Thermedics Detection, Inc., Product Sales Literature, Internet Address:
http://thermedics.com, email: sales@thermedics.com.
42. Graseby Security, Product Sales Literature, email:
arhodes@ds5200.gradyn.uk.
43. Intelligent Detection Systems, Product Sales Literature, Internet
Address: http://www.cpadtech.com.
44. Scintrex/IDS, Product Sales Literature, Internet Address:
http://www.scintrexltd.com.
45. Vidisco, Ltd., Product Sales Literature.
46. Proceedings from Sandia National Laboratories Explosives Detection
Workshop, Sponsored by the DOE, March 1997.
47. Proceedings from INMM Annual Meetings, 1996, 1997.
48. Hannum, D.W., Performance Evaluation of Ion Track Instrument's
Vapor Intensifier for Plastic Explosive Recognition (VIPER), Sandia
National Laboratories, SAND93-1058, 1994.
49. Hannum, D.W., Performance Evaluations of Commercial Explosive
Vapor Detectors, Sandia National Laboratories, SAND96-0207, 1996.
50. Hannum, D.W., Performance Evaluations of Commercial Explosives
Vapor/Particulate Detectors, Sandia National Laboratories, 1996.
51. McLuckey, S.A., D.E. Goeringer, and K.G. Asano, Atmospheric
Sampling Glow Discharge Ionization and Triple Quadrupole Tandem
Mass Spectrometry for Explosives Vapor Detection, Oak Ridge National
Laboratory, 1993.
52. Proceedings from The Third Workshop of the International Civil
Aviation Organization (ICAO) Ad Hoc Group of Specialists on the
Detection of Explosives, Sponsored by the FAA, October 1995.
53. Eiceman, G.A. and Z. Karpas, Ion Mobility Spectrometry, CRC Press,
Inc., 1994.
54. Elias, L. and P. Newdorfl, Laboratory Evaluation of Portable and
Walk-Through Explosive Vapor Detectors, Proceedings from the 3rd
Symposium on the Analysis and Detection of Explosives, Mannheim-
Nenostheim, FRG, 1989.
55. Fishbein, R.H., "Pulsed Fast Neutron Analysis," National Defense,
May/June 1997.
56. Entry-Control Systems Technology Transfer Manual, Sandia National
Labs, 1989.
57. Physical Protection Systems Design Methodology, Sandia National
Labs, 1996.
Vapor Pressure and Vapor Generators and Calibration of Explosives
Detection Systems
58. Dionne, B.C., D.P. Rounbehler, E.K. Achter, J.R. Hobbs, and D.H.
Fine, "Vapor Pressure of Explosives," Journal of Energetic Materials, 4
(1986) 447-472.
59. Davies, J.P., L.G. Blackwood, S.G. Davis, L.D. Goodrich, and R.A.
Larson, "Design and Calibration of Pulsed Vapor Generators for 2,4,6-
Trinitrotoluene, Cyclo-1,3,5-trimethylene-2,4,6-trinitramine, and
Pentaerythritol Tetranitrate," Anal. Chem., 65 (1993) 3004-3009.
60. Eiceman, G.A., D. Preston, G. Tiano, J. Rodriguez, and J.E. Parmeter,
"Quantitative Calibration of Vapor Levels of TNT, RDX, and PETN using
a Diffusion Generator with Gravimetry and Ion Mobility Spectrometry,"
Talanta 45 (1997) 57-74.
61. Krzymien, M. and L. Elias, "A Continuous-flow Trace Vapor Source,"
J. Phys. E: Scientific Instruments, 9 (1976) 584-586.
62. Lawrence, A.H. and Pavel Neudorfl, "Detection of Ethylene Glycol
Dinitrate Vapors by Ion Mobility Spectrometry Using Chloride Reagent
Ions," Anal. Chem., 60/2 (1988) 104-109.
APPENDIX A-2. GLOSSARY OF TERMS
Alarm: a signal given by an EDS that indicates to the operator that a
detection of explosive material has been made. For a technological system
such as an IMS the alarm might be either audio (e.g., a buzzer sounds) or
visual (e.g., a message on a computer screen). In the case of a canine, the
alarm is some form of behavior by the dog which the handler interprets as
a detection.
Alarm resolution: the process by which an operator determines whether an
alarm is the result of a threat item being present, or whether in fact there is
no threat item present.
Alarm threshold setting: the signal level above which an EDS is set to
alarm. An EDS may make a detection of an amount of explosive below the
alarm threshold setting, but it will then be assumed that the signal obtained
is either (1) a nuisance alarm or (2) noise.
Ammonia dynamites: a class of dynamites in which a portion of the
nitroglycerin is replaced by ammonium nitrate and nitroglycol. These
dynamites are lower in cost and less sensitive to shock and friction than
straight dynamites.
Ammonia-gelatin dynamites: gelatin dynamites where part of the
nitroglycerin/nitrocellulose gel is replaced by less costly ammonium
nitrate.
Ammonium nitrate: an explosive compound, NH(4)NO(3). It is the main
ingredient of ANFO, and of some water-gel explosives.
Analyte: in analytical chemistry, the compound that is being studied,
analyzed, or identified.
ANFO: a mixture of ammonium nitrate and fuel oil, often used in vehicle
bombs.
Astrolite: a commercially available two-part explosive. One component is
a liquid and the other is a solid.
Attenuation coefficient: a measure of how much an incident probe (e.g.,
electromagnetic radiation) is attenuated as it passes through a given
substance.
Atomic explosion: an explosion caused by the breaking up (fission) or
joining together (fusion) of atomic nuclei. This is the type of explosion
occurring when a nuclear weapon is detonated.
Atomic number: the total number of protons in the nucleus of an atom,
equal to the nuclear charge. Represented by the symbol Z.
Backscatter x-ray system: any x-ray system that detects objects (including
explosives) based on the images produced from reflected x-rays.
Binary explosive: an explosive material containing two different explosive
compounds.
Black powder: a low explosive which is a mixture of potassium nitrate
(KNO(3)), charcoal, and sulfur. It is frequently used in mail bombs and
pipe bombs.
Blasting agent: a chemical composition or mixture, consisting mainly of
ammonium nitrate, which will detonate when initiated by high explosive
primers or boosters. Blasting agents contain no nitroglycerin and are
relatively insensitive to shock and friction.
Blasting cap: a device containing a small amount of primary high
explosive, used for detonating a main charge of secondary high explosive.
Blasting slurries: a blasting agent consisting of NCN mixtures in a gel-like
consistency.
Blast pressure wave: the wave of hot, very high-pressure gases traveling
outward from an explosive detonation. The effect of this wave decreases
as distance from the point of explosion increases.
Bomb: any device containing explosive or incendiary material that is
designed to explode or ignite upon receiving the proper external stimulus.
Bombing: an illegal detonation or ignition of an explosive or incendiary
device.
Bomb detection: the discovery and identification of bombs that are being
smuggled, or used for some illicit purpose. Bomb detection differs from
explosives detection in that the detection may or may not be based on the
detection of the explosive material in the bomb. The detection may be
based on the detection of some other bomb component, such as metal parts
that are identified using metal detection.
Bonding agent: a material that is added to a chemical mixture in order to
help bind the components together.
Boosters: secondary explosives placed between the primary high explosive
(blasting cap) and the main explosive charge, with the purpose of
amplifying the detonation wave from the primary high explosive.
Brisance: the destructive fragmentation effect of a charge on its immediate
vicinity. 
Bulk explosives detection system: any EDS which directly detects a
macroscopic solid mass of explosive material. This is often (but not
always) accomplished using x-ray technology, with the explosive material
being observed as an object on the x-ray image. Bulk detection is in
contrast to trace detection, where the explosive material is detected from
vapor or particulate residue. In contrast to a trace detection system, a bulk
detection system will never detect explosives if only residue is present.
C-3: a military plastic explosive, composed of approximately 80 percent
RDX and 20 percent plasticizer. Also known as composition C-3, it was
the predecessor to C-4.
C-4: a military plastic explosive composed primarily (approximately 90
percent) of RDX. Also known as composition C-4.
Canine detection: the detection of explosives, narcotics, or other types of
chemical compounds through the use of a dog that is trained to sniff out
these substances.
Carrier gas: In IMS technology, the carrier gas (also called dopant) is a gas
which is added to the inlet air flow containing the sample. The purpose of
the carrier gas is to enhance the ionization process, and in some cases to
make the sample molecules easier to detect via the formation of a chemical
adduct (i.e., a species consisting of the sample molecule attached to a
carrier gas molecule or fragment).
Cavity charge: a shaped charge. 
Certification: a process through which an EDS is tested and, if it performs
successfully, is judged to be suitable for certain applications.
Cf: Californium, a radioactive element that emits neutrons and can be used
as a neutron source.
Chemical explosion: an explosion caused by the extremely rapid
conversion of a solid or liquid explosive into gases having a much greater
volume than the original material.
Chemiluminescence: a trace detection technique in which explosives are
detected via light that is emitted from NO molecules in a chemically
excited state. The excited state NO molecules are formed through
deliberately induced decomposition of the nitro (NO(2)) groups in the
original explosive compound.
Combustible: a material capable of igniting or burning.
Commercial explosives detection system: any EDS that can be purchased
on the open market.
Composition B: a plastic explosive that contains approximately equal
amounts of TNT and RDX.
Computer tomography, computed tomography: an x-ray technique in
which transmission images ("slices") taken at many different angles
through an object are put together to produce a three-dimensional image of
the object.
Contraband: any item or material that is smuggled into an area or facility
where it is prohibited. For example, in a prison contraband might include
weapons, explosives, and narcotics.
Conical-shaped charge: a cone-shaped explosive charge, employed to cut
or punch a hole through a target.
Cordeau Detonant: a brand name for detonating cord.
CT: computer tomography.
Deflagration: a subsonic process by which explosives release their energy
through a rapid burning or autocombustion process, this process being
sustained by the energy release from the material. Low explosives explode
via deflagration, and under some circumstances high explosives do also.
The terms explosion and deflagration are sometimes used synonymously,
with both being in contrast to detonation.
Density: the mass of a substance per unit volume, usually expressed in
units of grams per cubic centimeter (gr/cm3).
Detacord: a brand name for detonating cord.
Detasheet: a plastic explosive with a sheet-like structure, containing PETN
as the explosive ingredient.
Detonating cord: a cord-like synthetic explosive product, containing PETN
as the explosive ingredient.
Detonating Fuse: a brand name for detonating cord.
Detonation: the supersonic process by which a high explosive decomposes
and liberates its energy from shock wave compression.
Detonation velocity: the speed at which the shock wave travels through an
explosive material.
Detonator: a device, such as a fuse or blasting cap, used to set off
explosives.
Dielectric constant: the ratio of electric flux density produced by an
electric field in a given material, compared to the density produced by the
same field in vacuum. Also called permittivity.
Ditching dynamite: a form of straight dynamite widely used in commercial
blasting operations. It is characterized by a high detonation velocity of
over 5,185 m/s (17,000 ft/s).
DNT: 2,4-dinitrotoluene, a high explosive compound with a rather high
vapor pressure (near one part per million). Molecular formula
C(7)H(6)N(2)O(4); molecular weight = 182.
Dopant: carrier gas.
Double-beam backscatter x-ray system: a backscatter x-ray system in
which there are two x-ray sources and two detectors, so that both sides of
an investigated article can be looked at simultaneously.
Dual-axis x-ray system: an x-ray system in which the object under
investigation is examined with two x-ray beams coming in at two different
angles.
Dual-energy x-ray system: an x-ray system in which the object under
investigation is simultaneously irradiated with x-ray beams of two
different energies. This allows a wider range of target materials to be
detected than if only one beam of one energy were used.
Dynamite: a solid synthetic explosive material, widely used in blasting
operations. Dynamite usually contains nitroglycerin as a major explosive
component.
ECD: electron capture detector.
Eddy current: a current that is induced around a closed conducting loop by
the application of an external magnetic field. Eddy currents currently form
the basis of most portal metal detectors.
EDS: explosives detection system.
Effective atomic number: for a substance made up of more than one
element, the apparent atomic number that results if the substance is treated
as if it were composed only of a single element. It is closely related to the
weighted average of the atomic numbers of the constituent elements.
EGDN: ethylene glycol dinitrate. This is a high vapor pressure high
explosive that is one of the main explosive ingredients in certain types of
dynamite. Its molecular formula is C(2)H(4)N(2)O(6); molecular weight =
152.
Electric blasting cap: a blasting cap that is initiated by passing electric
current through a bridge wire, thus igniting the primary explosive present
in the cap.
Electroluminescent image panel: a panel that is capable of converting
electric energy into light.
Electron capture detector: a type of explosives detector wherein gas phase
explosives molecules capture electrons from an electron-emitting source to
form negative ions. The presence of an explosive is then deduced by
observing a decrease in the electron current delivered from the emitting
source to a detector.
Electronegativity: the tendency of a molecule to attach an electron.
Explosive bombing: the illegal explosion of a device containing high or
low explosive material.
Explosive mixture: a low explosive material composed of a mixture of a
combustible and an oxidizer.
Explosives: Explosives are compounds or mixtures of compounds which
when subjected to the appropriate stimulus (heat, shock, friction, etc.)
undergo extremely rapid chemical changes that result in the evolution of
large volumes of highly heated gases and exert pressure upon the
surrounding medium. Explosives can be thought of as energy packets that
can release their energy in the microsecond timeframe.
Explosives detection system: any device, person, or animal which serves
the purpose of detecting explosives. Examples include an ion mobility
spectrometer, an x-ray scanner for screening luggage, a trained canine with
a handler, and a security guard conducting manual inspection of backpacks
and briefcases.
Explosive train: a series of explosions specifically arranged to produce a
desired outcome.
EXPRAY: a commercially available, aerosol-based field test kit, able to
detect most explosives. Detection is based on color changes of a special
paper when it is treated with one of three types of aerosol spray.
False alarm: any alarm of an EDS which occurs when no explosive
material or explosive residue is really present. Such alarms may be caused
by chemically similar innocuous compounds, or by system malfunction.
False negative: an indication from an EDS that a person or item being
screened for explosives is free of explosive material, when in fact the
person or item does have/contain explosives.
False positive: an indication from an EDS that a person or item being
screened for explosives has/contains explosive material, when in fact the
person or item does not have/contain explosive material.
Flex-X: a military name for Detasheet.
Fluorophore: material capable of fluorescence.
Fluoroscopic imaging: use of a fluorescent screen to view the contents of
an opaque object, with the contents appearing as shadows formed by
transmission of x-rays through the object.
Forensics: In the sense used herein, the science of trace explosives analysis
as related to criminal investigations or other law enforcement work.
Fragmentation bomb: a bomb such as a pipe bomb where explosive
material is placed inside a metal or other solid casing, with the casing
breaking into fragments that are hurled about the area at high velocity
when the bomb explodes.
Free-running explosives: group of blasting agents consisting of NCN in
small pellet or granular form.
Ft/s: feet per second, the standard unit for detonation velocities.
Gamma rays: high-energy electromagnetic radiation emitted by certain
atoms when they are properly stimulated, as in the technique of TNA.
Gelatin dynamites: a class of dynamites with an explosive base of water-
resistant gel, formed by combining nitrocellulose and nitroglycerin.
Granulation: the grain size of an explosive powder, such as black powder.
Guncotton: nitrocellulose.
Handler: the individual controlling a dog that is trained to sniff out
explosives or narcotics.
HE: high explosive.
High explosives: explosives that are capable of detonation. Common
examples include TNT, RDX, PETN, NG, and EGDN.
High-explosive train: an explosive train involving high explosives.
High-order detonation: complete detonation of an explosive at its highest
possible detonation velocity.
HMX: a high explosive, chemically related to RDX. HMX (Her Majesty's
Explosive) is an eight membered ring of alternating carbon and nitrogen
atoms, with nitro (NO(2)) groups attached to the nitrogens. Molecular
formula C(4)H(8)N(8)O(8), molecular weight = 296. HMX has an
extremely low vapor pressure and hence is very difficult to detect using
any vapor sniffing technique.
Hydrazine: liquid component of the two-part explosive Astrolite. 
Hydrazine is also used in rocket fuel.
Hygroscopic: readily absorbing moisture, as from the atmosphere.
Immunochemical: relating to antibody-based techniques applied to trace
chemical detection.
Improvised device: a homemade device filled with explosive or incendiary
material and containing the components necessary to initiate the device.
Incendiary device: a device constructed with flammable materials
designed to produce a burning effect.
Incendiary thermal effect: the burning effect of an explosion. It is
relatively insignificant compared to the blast pressure effect.
Infrared radiation: electromagnetic radiation that is less energetic than
visible light and more energetic than microwaves.
Instantaneous combustion: a colloquial term for detonation. Detonation is
in reality not truly instantaneous, but occurs in a matter of microseconds.
Interference, interferent: any chemical compound that serves to mask the
presence of an explosive from a given explosives detection system.
Ion mobility spectrometer (IMS): a trace chemical detector which detects
explosives and other chemical compounds using the technique of ion
mobility spectrometry.
Ion mobility spectrometry: a technique for the trace detection of
explosives and other chemical compounds. In this technique, compounds
are first ionized, then identified based on the time that it takes them to
travel through a region with an applied electric field.
Jet: the extremely hot, swiftly moving bundle of gases and concentrated
power resulting from a directionally directed explosion.
Jet-Axe: a commercially available linear-shaped charge, used to cut
through doors, roofs, and walls to obtain access into a building. 
Kine-Pak: a commercially available two-part explosive, having excellent
shock resistance even after mixture of the two components.
KV: kilovolts, a unit of energy.
KVp: kilovolts potential, x-ray source voltage descriptor.
Lead azide: a primary high-explosive compound, Pb(N(3))(2).
Lead styphnate: a primary high explosive, often used in blasting caps,
C(6)H(3)N(3)O(9)Pb.
Linear-shaped charge: a type of shaped charge used to cut or slice a target. 
Low explosives: explosives which do not detonate, but rather explode via
the process of deflagration.
Low-explosive train: an explosive train employing only low explosives.
Low-order detonation: incomplete detonation of an explosive, or
detonation at less than maximum detonation velocity.
Magnetic moment: a property of the nucleus of atoms that have a non-zero
nuclear spin. These atoms are affected by the application of an external
magnetic field, and can give rise to an NMR spectrum. 
Mail bomb: any bomb that is sent through the postal service in a letter or
package. It is usually designed to detonate when the letter or package is
opened.
Mass spectrometer: an instrument that performs mass spectrometry.
Mass spectrometry: a chemical analysis technique in which the molecules
to be studied are first ionized and then separated and identified based on
their charge-to-mass ratio. Mass spectrometry is performed under
conditions of high vacuum, in contrast to IMS which is performed at
atmospheric pressure.
Mechanical explosion: an explosion caused by the buildup of excessive
pressure inside a solid container, the pressure buildup resulting from the
application of heat and hence vaporization of a material inside the
container.
Mercury fulminate: a primary high-explosive compound, Hg(OCN)(2).
Metal detection: the detection of metals and other conducting materials,
usually based on the detection of eddy currents in an applied magnetic
field.
Microgram: one millionth of one gram, usually written as ug.
Microrem: a unit of radiation dosage, equal to one millionth of a rem.
Microsecond: one millionth of 1 second, usually written as us.
Microwaves: electromagnetic radiation that is less energetic than infrared
radiation but more energetic than radio waves.
Military dynamite: an explosive (not a true dynamite) used in military
construction and demolition work. It is composed of 75 percent RDX, 15
percent TNT, 5 percent motor oil, and 
5 percent cornstarch.
Military explosives: explosives manufactured primarily for military
applications. Examples include TNT, tetrytol, and C-4.
Milking: a dangerous process by which nitroglycerin is extracted from
dynamite.
Milligram: one-thousandth of one gram, usually written as mg.
Millimeter waves: electromagnetic radiation (microwaves) having a
wavelength on the order of a few millimeters.
Mine detection: the detection of land or sea mines that are buried or
submerged. The detection may be made using metal detection, explosives
detection, or some other detection technique.
Nanogram: one-billionth of one gram, usually written as ng.
NCN: nitro-carbo-nitrates.
Negative-pressure phase: the time period following an explosion and after
the passing of the outward-going blast pressure wave, during which the
pressure at a given point is below atmospheric pressure and air is sucked
back into the area. Also called the suction phase. It is less powerful than
the positive-pressure phase, but of longer duration.
Nerve agents: chemical agents that harm humans by attacking the nervous
system.
Neutron: an elementary particle; along with protons and electrons, one of
the three particles that make up atoms. Used as a probe to look for
explosives in the technique of thermal neutron activation. Neutrons are
neutral (i.e., they have no electrostatic charge).
NG: nitroglycerin.
Nitro-carbo-nitrates: a type of blasting agent, composed primarily of
ammonium nitrate and oil.
Nitrocellulose: a cotton-like polymer treated with sulfuric and nitric acids,
and used in the manufacture of certain explosives.
Nitroglycerin, nitroglycerine: a high vapor pressure (vapor pressure
approximately one part per million) high-explosive compound that is the
explosive ingredient in certain types of dynamite. Molecular formula
C(3)H(5)N(3)O(9); molecular weight = 227.
NMR: nuclear magnetic resonance.
Nonelectric blasting cap: a blasting cap in which the primary explosive
material is set off using a flame.
Nuclear detection system: any bulk explosives detection system based on
the properties of the nuclei of the individual atoms within the explosives
material, including TNA, NMR, and QR systems.
Nuclear magnetic resonance: a bulk explosives detection technique based
on the magnetic properties of the hydrogen atoms within the explosive
being detected.
Nuisance alarm: In trace detection, an alarm caused by the detection of
explosive material, but where the detection results not from a bomb or
other contraband explosives but rather from a nonthreat item. For example,
in a portal that screens personnel for explosives, detection of NG on a
heart patient using NG tablets would be a nuisance alarm. A nuisance
alarm is different from a false alarm, since in the case of a false alarm no
explosive material is actually present.
Oxidizer: any substance that chemically reacts with another substance to
increase its oxygen content.
Particulate: contamination in the form of residual particles attached to
clothing, furniture, luggage, skin, or some other surface. 
Parts per billion: a quantitative measure of pressure and certain other
quantities. When used in reference to explosives vapor pressures, one part
per billion means that under equilibrium conditions the air above the
explosive material will contain one molecule of explosive vapor for every
billion molecules in the air itself.
Parts per million: a measure of explosive vapor concentration analogous to
parts per billion, but a thousand times more concentrated. Thus one part
per million of explosives vapor in air means one molecule of explosive
vapor per every million molecules in the air itself.
Parts per trillion: a measure of explosives vapor concentration analogous
to parts per billion, but a factor of one thousand less concentrated. Thus
one part per trillion of explosives vapor in air means one molecule of
explosive vapor per every trillion molecules in the air itself.
Pentolite: a commonly employed booster explosive, composed of 50
percent TNT and 50 percent PETN.
Percussion primer: a primer that converts mechanical energy into a flame,
such as the primer that is set off by the firing pin in a gun.
PETN: pentaerythritol tetranitrate, a common high explosive. It is used in
plastic explosives such as Detasheet and Semtex, and has a low vapor
pressure (a few parts per trillion at room temperature and atmospheric
pressure). Molecular formula C(5)H(8)N(4)O(12); molecular weight =
316.
PFNA: pulsed fast neutron analysis.
Phosphor: any substance that can be stimulated to emit light by incident
radiation.
Picogram: one-trillionth of 1 gram, usually written as pg.
PINS: portable isotopic neutron spectroscopy.
Pipe bomb: a homemade bomb in which explosive material is packed into
a section of (usually metal) pipe. Upon explosion, the pipe may shatter,
and the propelled fragments thus produced can do much damage to people
and property.
Pixel: the smallest resolvable spot on a computer or television screen.
Plastic explosives: high-explosive materials that have the general
consistency of plastic. They are usually composed of RDX and/or PETN,
along with a small amount of oil or plasticizing agent. Examples include
C-4, Detasheet, and Semtex.
Portable isotopic neutron spectroscopy: a portable explosives detection
system based on the emission of gamma rays when a material is
bombarded with neutrons from a Cf source. 
Portal: a walk-through, booth-like structure which serves the purpose of
screening personnel for contraband. Examples include the metal detection
portals currently deployed in airports, and various types of explosives
detection portals that are now on the market or in development.
Positive-pressure phase: the brief time after a detonation in which the local
pressure is much greater than atmospheric pressure, due to the outward-
moving blast pressure wave.
Post-blast analysis: analysis of the site of an explosion to attempt to
identify the type of explosive that was used.
Potassium chlorate: an explosive compound, KClO(3).
Potassium nitrate: a crystalline compound, KNO(3), used in the
manufacture of explosives, pyrotechnics, and propellants. 
Preconcentrator: any mechanical device designed to collect a dilute trace
chemical sample and concentrate it, prior to delivery into a detector.
Prill: the loose, powder form of an explosive (as opposed to gel form) or a
compressed pellet thereof. The readymade ANFO explosive is also
marketed under the name "Prills."
Primacord: a brand name for detonating cord.
Primary explosives: high-explosive compounds or mixtures that, when
present in small quantities, can convert the process of deflagration into
detonation. Primary explosives are used to induce detonation of a
secondary explosive.
Primer: a cap or tube containing a small amount of primary explosive and
used to detonate a secondary main charge.
Primex: a brand name for detonating cord.
Probability of detection - P(d): the probability that a certain EDS can
detect a certain amount of a given type of explosive under a particular set
of conditions. If a positive detection is always made under these
conditions, the probability of detection would be 100 percent. If a
detection is made only half the time, the probability of detection would be
50 percent. In general, a large number of experimental trials need to be
conducted to accurately determine this parameter.
Propellants: explosive compounds or mixtures used for propelling
projectiles or rockets.
Pulsed Fast Neutron Analysis: a nuclear screening technique which
measures the elemental composition of the object being scanned through
neutron interaction with elemental constituents of the object, resulting in
characteristic gamma rays.
Pyrodex: a low-explosive material used as a filler in some improvised
devices. Developed by Hodgdon Powder Company, this propellant is
available in powder or pellet form. Pyrodex has 30 percent more power
than common black powder. 
Pyrotechnics: physical mixtures of fuel and oxidizer powders, used to
produce light (e.g., fireworks), sound, heat, or smoke.
Q: quality factor, electronics-related term defining the selectivity of a
resonant circuit.
QR: quadrupole resonance.
Quadrupole resonance: a bulk explosives detection technique in which the
material under investigation is probed using rf radiation. This results in
excitation of the nuclei of nitrogen atoms, which emit photons of a
characteristic frequency when they relax. The resulting signal is specific
for a certain type of nitrogen-containing compound.
Random screening: performing explosives detection on a randomly chosen
fraction of a large number of people or items. For example, a security
checkpoint might wish to screen every fourth person entering a secure
facility. Random screening has the advantage of providing a deterrent
against the illicit transport of explosives into a given area, while at the
same time being less time consuming than uniform screening.
RDX: a high explosive, cyclotrimethylenetrinitramine, also known as
cyclonite. The abbreviation RDX stands for "research and development
explosive." RDX is the main ingredient of C-4, and is also used in Semtex.
It has a low vapor pressure (low parts per trillion at room temperature and
atmospheric pressure). It consists of a six-membered ring of alternating
carbon and nitrogen atoms, with nitro (NO(2)) groups attached to the
nitrogen atoms. Molecular formula C(3)H(6)N(6)O(6); molecular weight =
222.
RF: radio frequency.
Safety fuse: a flame-producing source used in some nonelectric blasting
caps.
Saltpeter: potassium nitrate.
Secondary explosives: high-explosive compounds or mixtures that are
generally initiated to detonation by intense shock. Secondary explosives
are generally less sensitive than primary explosives, but pack more
explosive power.
Secondary high-explosive boosters: explosives which provide the
detonation link in an explosive train between the very sensitive primary
high explosives and the comparatively insensitive main charge high
explosives.
Secure area, secure facility: any area or facility where access is restricted
by appropriate entry controls. Entry normally involves some form of
identity verification for the entering individual. It may also include
contraband screening.
Security checkpoint: any checkpoint at an entrance to a secure area that
administers some sort of entry control. It may also involve screening for
contraband, including explosives.
Semtex: a type of plastic explosive, normally containing both RDX and
PETN.
Shaped charge: specially shaped explosive charges that are used to cut or
punch holes in solid materials such as steel and concrete.
Shock wave: a sharp discontinuous pressure disturbance traveling faster
than the speed of sound. A shock wave is created when a high explosive
detonates.
Shrapnel: precut or preformed objects (e.g., metal fragments, nails) placed
in or attached to a bomb. When the bomb explodes, these objects are
hurled at high velocity, with much potential damage to people and
property.
Single-energy transmission x-ray scanner: an x-ray scanner using only a
single x-ray beam, in which the portion of the beam that penetrates the
object under investigation is detected and used to produce the x-ray image.
Smokeless powder: an explosive material (double-base propellant) in
powder form, often containing nitroglycerin (typically 40 percent by
weight) as the explosive ingredient.
Sodium chlorate: an explosive compound, NaClO(3).
Sodium nitrate: a chemical compound, NaNO(3). It is sometimes added to
dynamite to increase the oxygen content and hence improve combustion.
Specificity: the ability of a chemical analysis technique to distinguish
similar chemicals from one another. The greater the specificity, the more
certain the identification of a particular compound can be.
Straight dynamites: a class of dynamites containing nitroglycerin as the
explosive base.
Tandem mass spectrometry: a technique of chemical analysis, also referred
to as mass spec/mass spec, or simply MS/MS. Essentially, it involves
sending analyte molecules through two mass spectrometers consecutively,
in order to increase the specificity of the system.
Tetramino nitrate: a highly sensitive primary high explosive, which can be
formed from the reaction of ammonium nitrate with brass or bronze tools.
Tetryl: a high-explosive compound, similar in structure to TNT. Molecular
formula C(7)H(5)N(5)O(8); molecular weight = 287.
Tetrytol: a military explosive composed of approximately 75 percent tetryl
and 25 percent TNT.
Thermal neutron: a neutron having an energy that is typical of neutrons at
room temperature.
Thermal neutron activation: a bulk explosives detection technique, in
which explosives are detected by the emission of characteristic radiation
(gamma rays) that occurs when the explosive material is irradiated with
thermal energy neutrons.
Threat: the event or occurrence which a protective measure is intended to
guard against.
Threat consequence: the results of a particular threat event occurring,
including death or injury to personnel, and damage to property.
Threat item: the item that an EDS is designed to detect, i.e., a bomb or
contraband explosives material.
Threat probability: the likelihood of a particular threat event actually
occurring, on a scale of 0 percent (no probability of occurring) to 100
percent (certainty that the event will occur).
Throughput rate: the rate at which an EDS can process the people or
objects being screened. It is generally expressed in units such as people
per hour for a personnel portal, or bags per hour for an x-ray baggage
scanner.
TNA: thermal neutron activation.
TNT: 2,4,6-trinitrotoluene, a common high explosive with a moderate
vapor pressure (near one part per billion at room temperature and
atmospheric pressure). Molecular formula C(7)H(5)N(3)O(6); molecular
weight= 227.
Tovex: a trade name for certain water-gel based explosives.
Trace explosives detection system: any EDS that detects explosive
materials by collecting and identifying trace residue from the material.
This residue may be in the form of either vapor or particulate. Trace
detection is in contrast to bulk detection.
Two-part explosives: explosives that consist of two separate components,
which are sold together in separate containers and need to be mixed
together prior to detonation.
Ultraviolet light: electromagnetic radiation that is less energetic than x-
rays but more energetic than visible light.
Uniform screening: Performing explosives detection on all persons or
items passing through a given security checkpoint, applying the same
screening process to all of them. Uniform screening is in contrast to
random screening.
Vapor generator: any device designed to produce calibrated amounts of
vapor of a particular compound.
Vapor pressure: the quantity of vapor (usually expressed in terms of a
concentration) of an explosive compound that exists above the compound
in air at equilibrium under a specified set of conditions.
Water-gel explosives: explosive mixtures (slurries) consisting of saturated
aqueous solutions of ammonium nitrates and other nitrates.
Wavelength: a property of electromagnetic radiation that is inversely
proportional to its energy.
Working lifetime: the time period during which a given EDS is useful. For
both a canine and an IMS, a typical working lifetime might be on the order
of 10 years.
X-ray absorption coefficient: the fraction of incident x-rays that is
absorbed by a given material.
X-ray backscatter coefficient: the fraction of incident x-rays that is
backscattered (i.e., reflected) by a given material.
X-rays: high-energy electromagnetic radiation with wavelength in the
approximate range of 0.05 angstroms to 100 angstroms (one angstrom = 1
A = 100 billionths of one centimeter). Less energetic than gamma rays.
X-ray transmission coefficient: the fraction of incident x-rays that pass
through a given material.
Z: symbol for atomic number.
APPENDIX A-3. EXPLOSIVES: NATURE, USE, EFFECTS, AND
APPLICATIONS
The purpose of this appendix is to provide a general understanding of the
nature of explosions and explosives. It is intended not as a textbook or
technical manual, but as a source of background information for police,
security, and other law enforcement officials finding themselves involved
in the prevention and control of the illegal use of explosives.
EXPLOSIONS
TYPES OF EXPLOSIONS
An explosion can be broadly defined as the sudden and rapid escape of
gases from a confined space accompanied by high temperatures, violent
shock, and loud noise. The generation and violent escape of gases is the
primary criterion of an explosion and is present in each of the three basic
types of explosions: 1) mechanical, 2) chemical, and 3) atomic.
Mechanical Explosion
The mechanical explosion is illustrated by the gradual buildup of pressure
in a steam boiler or pressure cooker. As heat is applied to the water inside
the boiler, steam, a form of gas, is generated. If the boiler or pressure
cooker is not equipped with some type of safety valve, the mounting steam
pressure will eventually reach a point when it will overcome the structural
or material resistance of its container and an explosion will occur. Such a
mechanical explosion would be accompanied by high temperatures, a
rapid escape of gases (steam), and a loud noise.
Chemical Explosion
A chemical explosion is caused by the extremely rapid conversion of a
solid or liquid explosive compound into gases having a much greater
volume than the substances from which they were generated. When a
block of explosive detonates, the produced gases will expand into a
volume 10,000 to 15,000 times greater than the original volume of the
explosive. The expansion of these generated gases is very rapid, reaching
velocities of approximately 8.05 km (5 miles) per second. Temperatures
generated by the conversion of a solid into a gas state may reach 3000
degrees C to 4000 degrees C. The entire conversion process takes only
microseconds and is accompanied by shock and loud noise. 
Atomic Explosion 
An atomic explosion may be induced either by fission, the splitting of the
nuclei of atoms, or fusion, the joining together under great force of the
nuclei of atoms. During nuclear fission or fusion, a tremendous release of
energy, heat, gas, and shock takes place. The atomic bombs dropped on
Japan in World War II were rated as equivalent to 18,140 t (20,000 tons
(20 kT), or 18.18 million kg (40 million pounds), of TNT in explosive
power, yet the amount of fissionable material required to produce this
energy weighed approximately 1 kg (2.2 lb). With today's technology,
even greater yields are possible with smaller amounts of fissionable
material. 
NATURE OF CHEMICAL EXPLOSIONS
The explosives normally encountered by law enforcement personnel are
chemical in nature and result in chemical explosions. In all chemical
explosions, the changes which occur are the result of combustion or
burning. Combustion of any type produces several well-known effects:
heat, light, and release of gases. The burning of a log and the detonation of
a stick of dynamite are similar because each changes its form and, in so
doing, produces certain effects through combustion. The real difference
between the burning of the log and the detonation of the dynamite is in the
time duration of the combustion process.
Deflagration (Rapid Combustion)
An example of deflagration or rapid combustion is illustrated by the
internal combustion automobile engine. Inside the cylinder of the engine,
combustible fuel (gasoline) is mixed with a combustion supporter (air),
and the mixture is raised close to its ignition temperature by compression.
When a flame from the spark plug ignites the mixture, rapid combustion or
deflagration occurs. Deflagration is merely a rapid form of combustion,
and ordinary combustion is simply a slow form of deflagration. The speed
of the burning action constitutes the difference between combustion,
deflagration, and detonation.
Detonation (Instantaneous Combustion) 
Detonation can be defined as "instantaneous combustion". However, even
in detonation, the most apid form of combustion, there must be some time
interval in order that the combustion action can be transferred from one
particle of the explosive compound to the next. Therefore, there cannot be
"instantaneous" combustion, but the extreme rapidity of the process, as
compared to that of ordinary combustion and explosion, warrants the use
of the term.
The velocity of this "instantaneous combustion" has been measured for
most explosives and is referred to as the detonation velocity of the
explosive. Detonation velocities of high explosives range from
approximately 2,743 m/s (9,000 ft/s) to over 8,382 m/s (27,500 ft/s). As an
illustration of detonation velocity, if a 8.05 km (5 mile) 80,467 m (26,400
ft) length of garden hose were filled with RDX (detonation velocity 8,382
m/s (27,500 ft/s)) and initiated at one end, the detonation would reach the
other end of the 8.05 km (5 mile) long hose in less than 1 s.
A high-order detonation is a complete detonation of the explosive at its
highest possible velocity. A low-order detonation is either incomplete
detonation or complete detonation at lower than maximum velocity. Low-
order detonations may be caused by any one or a combination of the
following factors: 1) initiator (blasting cap) of inadequate power, 2)
deterioration of the explosive, 3) poor contact between the initiator and the
explosive, and 4) lack of continuity in the explosive (air space).
EFFECTS OF AN EXPLOSION
When an explosive is detonated, the block or stick of chemical explosive
material is instantaneously converted from a solid into a rapidly expanding
mass of gases. The detonation of the explosive will produce three primary
effects and several associated secondary effects which create great damage
in the area surrounding the explosion. The three primary effects produced
are blast pressure, fragmentation, and incendiary or thermal effects.
Blast Pressure Effect
When an explosive charge is detonated, very hot, expanding gases are
formed in a period of approximately 1/10,000 of a second (100 us). These
gases exert pressures of about 635 metric ton (700 tons) per square inch on
the atmosphere surrounding the point of detonation and rush away from
the point of detonation at velocities of up to 11,265 km (7,000 mph),
compressing the surrounding air. This mass of expanding gas rolls
outward in a circular pattern from the point of detonation like a giant
wave, weighing tons, smashing and shattering any object in its path. The
further the pressure wave travels from the point of detonation, the less
power it possesses until, at a great distance from its creation, it dwindles to
nothing. This wave of pressure is usually called the blast pressure wave.
The blast pressure wave has two distinct phases which will exert two
different types of pressures on any object in its path. These phases are the
positive pressure phase and the negative or suction phase. The negative
phase is less powerful, but lasts three times as long as the positive phase.
The entire blast pressure wave, because of its two distinct phases, actually
delivers a one-two punch to any object in its path. The blast pressure effect
is the most powerful and destructive of the explosive effects produced by
the detonation of high explosives.
Secondary Blast Pressure Effects: Reflection, Focusing, and Shielding of
the Pressure Wave. Blast pressure waves, like sound or light waves, will
bounce off reflective surfaces. This reflection may cause either a scattering
or a focusing of the wave. A blast pressure wave will lose its power and
velocity quickly when the detonation takes place in the open. For example,
assume that a block of explosive is detonated in the open, and the blast
wave dissipates at a distance of 30.48 m (100 ft) from the point of
detonation. If the same charge had been placed inside a large diameter
sewer pipe or a long hallway and detonated, the blast pressure wave would
have been still measurable at 6.096 m (200 ft) or more. This is due to the
reflection of the blast wave off the surfaces surrounding it, and the
reflected wave may actually reinforce the original wave by overlapping it
in some places.
Since the reflected wave is a pressure wave, it will exert physical pressure.
Similarly, a blast pressure wave may be focused when it strikes a surface
which acts as a parabolic reflector just as sound waves can be focused and
directed.
Shielding occurs when the blast pressure wave strikes an immovable
object in its path. If a square, solid concrete post 60.96 cm (2 ft) thick is
placed in the path of the blast pressure wave and a wine glass is placed
behind this post, the blast pressure wave will strike the post, and the post
will, in effect, cut a hole in the pressure wave, leaving the wine glass
undamaged. 
When dealing with detonations which have taken place inside buildings,
many unusual effects due to reflection or shielding will be noted. These
effects account for such strange things as the entire wall of the structure
being blown out, but a mirror on the opposite wall remaining intact. 
Secondary Blast Pressure Effects: Earth and Water Shock. When an
explosive charge is buried in the earth or placed underwater and detonated,
the same violent expansion of gases, heat, shock, and loud noise results.
Since earth is more difficult to compress than air, and water is not
compressible at all, the detonation will seem less violent. Nevertheless, the
energy released is exactly the same as would result from a detonation in
the open air. The effect of this violence is, however, manifested in a
different manner. The blast wave is transmitted through the earth or water
in the form of a shock wave, which is comparable to a short, sharp,
powerful earthquake. This shock wave will pass through earth and water
just as it does through air, and when it strikes an object such as a building
foundation, the shock wave will, if of sufficient strength, damage that
structure much as an earthquake would. An explosive charge detonated
underwater will produce damage at greater distances because, unlike earth,
water is not compressible and cannot absorb energy. As a result, it
transmits the shock wave much faster and farther, and consequently
produces greater damage within a larger area.
Fragmentation Effect 
A simple fragmentation bomb is composed of an explosive placed inside a
length of pipe which has the end caps screwed into place. When the
explosive is detonated not only will the blast pressure effect produce
damage, but shattered fragments of the pipe will be hurled outward from
the point of detonation at great velocity. The average fragment produced
by the detonation of a bomb will reach the approximate velocity of a
military rifle bullet 822.96 m/s (2,700 ft/s) a few feet from the point of
detonation. These bomb fragments will travel in a straight line of flight
until they lose velocity and fall to earth or strike an object and either
ricochet or become imbedded. 
When an encased explosive such as a pipe bomb detonates, the rapidly
expanding gases produced by the explosion cause the casing to enlarge to
about one and one-half times its original diameter (material dependent)
before it ruptures and breaks into fragments. Approximately, half the total
energy released by the explosion is expended in rupturing the case and
propelling the broken pieces of the casing outward in the form of
fragments. Fragments resulting from the detonation of a high-explosive
filler have a stretched, torn, and thinned configuration due to the
tremendous heat and pressure produced by the explosion. In contrast, the
detonation of a pipe bomb containing black powder, a low explosive,
would produce fragments that are larger in size than those resulting from a
high-explosive detonation, and they would not have a stretched and
thinned configuration.
Precut or preformed objects such as nails, ball bearings, or fence staples,
which are placed either inside the bomb or attached on the outside are
referred to as shrapnel. Shrapnel serves the same purpose and has the same
effect on personnel, material, and structures as fragmentation. One
advantage of using shrapnel is that part of the energy released by the
explosion, which would normally have been expended in fracturing the
bomb casing into fragments, is used instead in propelling the preformed,
separate pieces of shrapnel. Consequently, the use of shrapnel inside or
attached outside a bomb results in an increase in blast damage by cutting,
slicing, or punching holes in materials near the detonation point.
Incendiary Thermal Effect 
The incendiary thermal effect produced by the detonation of a high or low
explosive varies greatly from one explosive to another. In general, a low
explosive will produce a longer time period of incendiary thermal effect
than will a high explosive. A high explosive will, on the other hand,
produce much higher temperatures. In either case, the duration of the
effect is measured in fractions of seconds. The incendiary thermal effect is
usually seen as a bright flash or fireball at the instant of detonation. If a
high-explosive charge is placed on a section of earth covered by dry grass
and then detonated, only a vacant patch of scorched earth will remain.
However, if a low-explosive charge is placed on the same type of earth
and detonated, more than likely a grass fire will result.
Unless highly combustible materials are involved, the thermal effect plays
an insignificant part in an explosion. Should combustible materials be
present and a fire started, the debris resulting from the explosion may
provide additional fuel and contribute to spreading the fire. When fires are
started inside a structure which has been bombed, they usually are
traceable to broken and shorted electrical circuits and ruptured natural gas
lines rather than to incendiary thermal effects. Incendiary thermal effects
are generally the least damaging of the three primary detonation effects.  
COMPOSITION AND BEHAVIOR OF CHEMICAL EXPLOSIVES
An explosive is a chemically unstable material which produces an
explosion or detonation by means of a very rapid, self-propagating
transformation of the material into more stable substances, always with the
liberation of heat and with the formation of gases. Shock and loud noise
accompany this transformation.
The primary requisite of a chemical explosive is that it contains enough
oxygen to initiate and maintain extremely rapid combustion. Since an
adequate supply cannot be drawn from the air, a source of oxygen must be
incorporated into the combustible elements of the explosive, or added by
including other substances in the mixture. These sources of oxygen are
called oxidizers.
Explosive Mixtures
In the case of deflagrating substances, as contrasted to detonating
substances, the combustible and oxidizer are blended mechanically. The
result of this type of blending is known as an explosive mixture.
Mechanical blending is generally used when manufacturing low
explosives or propellants such as pistol and rifle powders. Propellants are
materials that burn to produce gases used to perform mechanical work,
such as propelling a projectile or pushing a piston. In some cases, a
bonding agent such as water is added to the mixture to form a paste. When
dry, the paste mixture is broken into pieces and ground to produce a finer
mixture than would result from simply blending the separate ingredients.
Explosive Compounds
The first requirement of a detonating substance is that the bond between
the combustible and the oxidizer must be as close as possible. Since
mechanical mixing does not provide a close enough relationship,
detonating explosives must be chemically blended. For example, in
creating the chemical compound nitroglycerin, glycerin is poured slowly
into nitric acid forming a new compound whose elements are bound
tightly together. All high explosives, in contrast to low explosives, are
composed of chemical compounds consisting of tightly bonded
combustibles and oxidizers.
Classification by Velocity
The classification of explosives by the velocity of explosion or detonation
is a convenient and widely used system for distinguishing between two
major groups of explosives.
Low Explosives. Those explosives known as low explosives have rates of
detonation below 999.7 m/s (3,280 ft/s). For example, black powder has a
rate of approximately 399.9 m/s (1,312 ft/s). Low explosives are used
primarily as propellants, because a mechanically mixed explosive charge
minimizes the danger of bursting the weapon in which it is used. In a
mechanical mixture the burning is transmitted from one grain of low
explosive to the next, and the gases produced build up as the powder
burns. This causes low explosives, in terms of performing work, to exert a
rapid pushing effect rather than a shattering effect as do high explosives.
Low-explosives are used in blasting operations and are also frequently the
filler for homemade pipe bombs.
A bomb using low explosives is made by confining pistol, rifle, or black
powder in a length of pipe with end caps. When the confined powder is
ignited, the rapidly produced and confined gases will create increasing
internal pressures until the pipe container bursts and is torn apart by the
pressure. Unlike high explosives, low explosives may be started on the
combustion path by the application of a simple flame or acid/flame
reaction and do not require the shock of a detonating blasting cap. 
High Explosives. This type of explosive is designed to shatter and destroy.
The detonation rate of high explosives is above 999.7 m/s (3,280 ft/s).
There is a wide range in the detonation velocities of high explosives,
extending from some dynamites at 2,743.2 m/s (9,000 ft/s) up to RDX at
8,382 m/s (27,500 ft/s).
High explosives differ from low explosives in that they must, in general,
be initiated by the shock of a blasting cap. When low explosives begin
their combustion, the burning travels from particle to particle because of
the granular form of the explosive. This results in the deflagration of the
material. High explosives detonate, which has been described as
instantaneous combustion. When a blasting cap is detonated in a stick or
block of high explosive, it delivers an extremely sharp shock to the
explosive. This shock breaks the bonds of the molecules of the chemically
bonded explosive material and oxidizers. The disruption of the molecules
is transmitted as a shock wave radiating outward in all directions from the
point of initiation. This internal shock wave is known as a detonation
wave, and it causes each molecule it strikes to rupture. The rupture of each
molecule causes the wave to move faster until, in a very short time and
distance, the explosive material is detonating at its maximum rate. When a
high explosive detonates, the speed at which the detonation wave
progresses through the explosive is called the detonation velocity. It is
usually expressed in feet or meters per second.
Applications of Explosives 
The varying velocities of explosives have a direct relationship to the types
of work they can perform. The differences in velocity determine the type
of power exerted by high or low explosives. Low explosives have pushing
or heaving power and high explosives have, because of the rapid
expansion of their gases, shattering power. Thus, an expert in the use of
explosives will select a high or low explosive depending on the type of
work to be performed. For example, if a large boulder is blocking a dirt
roadway, the experienced blaster might dig a hole under the boulder and
place a black powder 399.9 m/s (1,312 ft/s) charge in the hole. When the
black powder charge is functioned, it will heave the boulder, virtually
intact, off the roadway. If the blaster wishes to reduce the boulder to
rubble so that it may be removed, he might place a TNT 010.4 m/s (23,000
ft/s) charge on or under the boulder. When the TNT charge is functioned,
the boulder will be shattered into many smaller pieces.
Another characteristic of explosives related to work performance is the
fact that the forces created by a detonating explosive will be given off
directionally at a 90 degree angle from the surface of the explosive.
Consequently, if the explosive is cut or shaped to provide 90 degree
surfaces along a predetermined plane, the explosive forces can be focused
directionally, and will produce a greater effect, ounce for ounce, than the
same explosive employed as a mass.
This improved effectiveness is caused by the focusing of the hot gases
released by the detonating explosive. The extremely hot, swiftly moving
bundle of concentrated power is called the "jet" and performs in much the
same manner as the white-hot flame of a cutting torch.
A significant advance in the employment of explosives to accomplish
specific work was achieved with the development of shaped or cavity
charges that focus explosive forces. These specially shaped explosive
charges are employed to cut or punch holes in steel, concrete, and other
materials.
There are two basic types of shaped charges, the conical-shaped charge
and the linear-shaped charge. Conical shaped charges are employed to cut
or punch a hole through the target, while linear shaped charges are used to
cut or slice a target.
Until recent years, the military were the primary users of shaped charges.
Military shaped charges used in military projectiles, rockets, and mines
were employed to destroy tanks and reinforced concrete bunkers. Today
shaped charges are widely used in industry and by public safety personnel.
One of the latest uses of the linear-shaped charge is as an explosive entry
tool employed by fire fighters and public safety officers to cut through
steel fire doors, roofs, and light structural walls. This shaped charge is
manufactured under the name "Jet-Axe," and consists of a linear-shaped
charge contained in a polystyrene box. The box is placed against the target
and the shaped charge is detonated, providing an entry hole to the
building.
Two different sizes of prepackaged shaped charges are utilized by the
armed forces in demolition and breaching operations against steel or
reinforced concrete structures. The 6.82 kg (15-lb) M2A3 shaped charge
and the 18.2 kg (40-lb) M3 shaped charge each contain a 50/50 pentolite/
composition B mixture. The armed forces also use various other shaped
charges, both linear and conical, for special purposes, but these generally
are small hand-packed charges employing composition C-3 or C-4 as the
explosive filler.
EXPLOSIVE TRAINS
An explosive train is a series of explosions specifically arranged to
produce a desired outcome, usually the most effective detonation or
explosion of a particular explosive. The simplest explosive trains require
only two steps, while the more complex trains of military munitions may
have four or more separate steps terminating in detonation. Explosive
trains are classified as either low (propellant) or high, depending upon the
classification of the final material in the train.
Low-Explosive Trains
A round of small arms ammunition is a simple example of a two-step low-
explosive train. The components in this train are a percussion primer and a
propellant charge. The primer converts the mechanical energy of the
weapon's firing pin into a flame. The flame ignites the propellant charge,
and the gases produced by the resulting explosion drive the bullet through
the bore of the weapon.
When low explosives, such as smokeless powder and black powder, are
used in the construction of pipe bombs, a simple two-step explosive train
is again required. A length of safety fuse, which is a slow-burning time
fuse filled with black powder, is inserted into the pipe and the opposite
end of the fuse is ignited with a match. The safety fuse transmits the
flame, after a delay, to the low explosive inside the pipe. When it is
ignited, the low explosive inside the pipe explodes, and the confined gases
produced tear the pipe apart, resulting in both blast and fragmentation. The
majority of low explosives require only a simple two-step train.
High-Explosive Trains 
The nature of high-explosive trains is affected by the broad range of
sensitivity found within the category of high-explosive compounds.
Sensitivity refers to the amount of external force or effect needed to cause
detonation. Some explosives are so sensitive that lightly brushing a small
piece of explosive with a feather will cause it to detonate. On the other
hand, other explosives may be placed on an anvil and struck with a sledge
hammer and will not detonate.
For the sake of safety, the extremely sensitive explosives are always used
in very small quantities, while the comparatively insensitive explosives are
used in bulk quantities. This natural division, by sensitivity, produces two
groups within the category of high explosives. The most sensitive
explosives are referred to as primary high explosives, and the more
insensitive compounds are termed secondary high explosives. 
Primary High Explosives. Explosives known as primary high explosives
are among the most powerful as well as the most sensitive of all chemical
explosives. This combination of power plus sensitivity makes them very
hazardous to handle. The primary high explosives, because of their
sensitivity, may be initiated by applying shock, friction, flame, heat, or
any combination of these conditions. Due to their high detonation
velocities, the primary high explosives are able to create extremely
powerful detonation waves capable of causing complete instantaneous
detonation of other less sensitive explosives. For this reason they are used
as the first step in high-explosive trains and are packaged for this purpose
as blasting caps and military fuse detonators.
When used in both electric and nonelectric blasting caps, the primary high
explosives are detonated by heat or flame. In military fuses, the primary
high explosive is usually initiated by shock of impact or heat-producing
friction. The more commonly used primary high explosives are lead
styphnate, lead azide, mercury fulminate, and diazodinitrophenol, which
have detonation velocities ranging from 5,029 m/s (16,500 ft/s) for
mercury fulminate to 6,614 m/s (21,700 ft/s) for diazodinitrophenol. 
Secondary High Explosives. Compared to the primary high explosives, the
secondary high explosives are relatively insensitive to shock, friction,
flame, or heat and are, therefore, less hazardous to handle and use.
However, as a result of their relative insensitivity, the secondary high
explosives must be initiated or detonated by a very strong explosive wave.
Consequently, primary explosives are used to detonate secondary
explosives.
Secondary explosives comprise the largest single class of explosives and
have detonation velocities ranging from 2,743.2 m/s (9,000 ft/s) for some
dynamites to 7,925 m/s (26,000 ft/s) for military composition C-4.
Boosters. Since there is a wide range of sensitivity found among the
secondary high explosives, some of the more insensitive explosives cannot
be detonated unless the detonation wave of the primary high explosive
blasting cap is amplified or boosted. This amplification is accomplished
through the use of a different and slightly more sensitive secondary
explosive between the primary first step and the main explosive charge. 
The progression of the detonation wave from a small amount of a sensitive
primary high explosive, through a slightly larger amount of a less sensitive
secondary high-explosive booster, to a large amount of very insensitive
secondary high explosive main charge illustrates detonation through a
basic three-step explosive train.
Typical High-Explosive Trains. The explosive train normally used in work
with high explosives is a two- or three-step train. An example of a simple
two-step train is an electric blasting cap containing a primary high
explosive, and a stick of dynamite, as a secondary high explosive. The
blasting cap is detonated by the heat generated by passing an electrical
current through the fine wire imbedded in the primary high explosive
inside the cap. The detonation wave from the blasting cap would cause the
detonation of the dynamite. A simple three-step explosive train could be a
length of safety fuse filled with black powder, a nonelectric blasting cap,
and a stick of dynamite. The burning black powder in the safety fuse
would produce a flame that would detonate the blasting cap, a primary
high explosive, which would in turn detonate the dynamite, a secondary
high explosive.
The number of steps in the explosive train is not always a matter of choice.
As noted previously, some high explosives are so insensitive that the
detonating wave from the blasting cap is not powerful enough to cause
detonation. In such instances, a booster must be employed to amplify and
strengthen the wave from the blasting cap. 
Regardless of how many steps it contains, the firing train is nothing more
than a series of explosions arranged to achieve a desired end result. If the
explosive train is broken or interrupted, detonation of the main charge will
not occur.
Some common explosives likely to be encountered by public safety
personnel will be discussed next with information on the physical
characteristics of the explosive material and its normal use and packaging.
In addition, certain blasting accessories used to detonate the explosives
will be discussed.
Low Explosives
Black Powder. The average composition of black powder is saltpeter
(potassium nitrate), 75 parts by weight; sulfur, 10 parts by weight; and
charcoal, 15 parts by weight. There has been, however, a wide variation in
the black powder formulas that have been used over the years. The black
powder mixture ranges in color from coal black to rusty brown and in
form from a fine powder to granules as large as 1.27 cm (1/2 in) in
diameter. The burning speed of black powder, and therefore to a certain
extent its strength, is controlled by the size of the granulation. Large grains
of powder burn more slowly than fine grains and are consequently less
sudden in their action.
Black powder does not deteriorate with age, even if it has been submerged
in water. Once black powder dries out, it is just as effective and dangerous
an explosive as it was the day it was manufactured. 
Sensitivity to friction, heat, impact, and sparks makes black powder one of
the most dangerous explosives to handle. It is particularly sensitive to both
electrically and nonelectrically generated sparks and should, therefore, be
handled with wooden or plastic tools. As a further precaution, the body
should be grounded before black powder is handled. 
Because of its slow action and consequent heaving or pushing effect, black
powder was for years the sole commercial blasting agent. Though it has
been replaced by dynamite in most blasting applications, black powder is
still used for certain special operations. For this purpose it is manufactured
in varying granulations to enable the customer to match the powder to the
specific application, and packaged in 11.36 kg (25-lb) metal kegs. For
commercial blasting, black powder is also pressed into cylinders
measuring 5.08 cm (2 in) by 3.175 cm (1 1/4 in). Some cylinders have a
0.9525 cm (3/8-in) hole through their center so that an electric squib may
be inserted or so that the cylinders may be laced together on a length of
fuse. In cylinder form, black powder is usually wrapped in paper to form a
stick about 20.32 cm (8 in) in length and packed in 11.36 kg (25 lb) and
22.73 kg (50 lb) cases for sale.
As a blasting charge, black powder has about half the strength of TNT,
and because the basic ingredients can be readily acquired in any
community, it has become the favorite homemade explosive of bombers in
the United States. Black and smokeless powder, whether homemade or
commercial, will probably be the explosives most often encountered in
pipe bombs. When confined inside a pipe and provided with a safety fuse,
no blasting cap is needed to initiate the powder, because the flame from
the end of the fuse is sufficient to cause the explosion of the bomb. It
should be noted that any sparks resulting from an attempt to dismantle a
pipe bomb may produce the same results. Therefore, a discovered pipe
bomb should only be handled by specially trained personnel.
Perhaps the most common use of black powder in routine work with
explosives is in the manufacture of safety fuse. Since its burning rate can
easily be regulated in production, black powder is widely used as the core
burning powder in the safety fuse used commercially, and by the military
to provide a uniform delay time prior to an explosion.
Safety fuse is used for detonating explosives nonelectrically. Normally, its
purpose is to transmit a flame at a continuous and uniform rate to a
nonelectric blasting cap. There are two common burning rates for safety
fuse. The most frequently encountered fuse burns at the rate of 40 s per
0.305 m, while a less common type is designed to burn at the rate of 30 s
per 0.305 m. 
Although safety fuse is designed for use with nonelectric blasting caps, it
may, as previously noted, be used by bombers as a direct means of
initiating a low explosive main charge. A delay element in itself, the safety
fuse can be used to allow the bomber time to leave the scene of the 
incident. When employed in bombings, a portion of the spent fuse will
usually survive the explosion and may be located not far from the point of
detonation. 
o Commercial Safety Fuse. There are numerous brands of commercial
safety fuse, but their only essential difference is in the type of exterior
water proofing materials and color markings. Commercial safety fuse is
approximately 0.508 cm (0.2 in) in diameter, about the size of a lead
pencil, and comes in 15.24 m (50 ft), paper wrapped, rolls or coils. It is
colored orange for general use, black for use in salt mines, and white for
use in coal mines.
o Military Safety Fuse. The U.S. military uses two types of safety fuse,
one called "safety fuse" and the other called "M 700 time fuse." They are
interchangeable in use and similar in construction. 
o Improvised Safety Fuse. Fusing can be made from a common fireworks
fuse, or by saturating ordinary cotton cord with certain liquid chemical
compounds that provide uniform burning when dry. Even the use of rag
wicks in fire bombs such as the "Molotov cocktail" can be considered a
form of improvised fusing. Since most improvised fuses burn at erratic
rates, they can hardly be considered "safety" fuses.
Smokeless Powder. Smokeless powder is the world standard propelling
powder for small arms, cannons, and, in a slightly different form, rockets.
All low explosives currently used as propellants have a nitrocellulose base
and are commonly referred to as smokeless powders. Various organic and
inorganic substances are added to the nitrocellulose base during
manufacture to give improved qualities for special purposes, and these
variations are distinguished by such terms as double-base, flashless, and
smokeless, as well as by various commercial trade names or symbols.
Smokeless powders are produced by dissolving guncotton (nitrocellulose)
in a mixture of ether and alcohol to form a mass called a colloid. The
colloid has the consistency of melted glue, and is squeezed into macaroni-
shaped tubes that are subsequently cut into short lengths. The ether and
alcohol used to dissolve the guncotton are evaporated, leaving a hard
substance. The small cylindrical powder grains resulting from this process
are used as rifle ammunition powders.
Pistol powders, unlike rifle powders, do not generally have cylindrical
grains. Instead, they are manufactured in the form of very fine, thin
wafers, flakes, or balls. These shapes insure the shorter burning time
necessary for full combustion in weapons with short barrels. Shotgun
powders are similar to pistol powders in that they burn more rapidly than
rifle powders. In fact, most shotgun powders are straight nitrocellulose in
composition.
Like black powder, smokeless powders vary widely in both form and
color. The majority of rifle and pistol powders are black in color and are
formed into rods, cylindrical strips, round flakes, or irregular grains.
Shotgun powders may be translucent round or square flakes, orange to
green in color, or may be black irregularly shaped granules. Smokeless
powders of all types are sold in tin flasks, glass jars, plastic containers, and
kegs of varying weights up to 11.36 kg (25 lb).
Unconfined smokeless powder burns with little or no ash or smoke and,
when confined, its rate of burning increases with temperature and pressure.
For this reason, it is frequently used in the construction of pipe bombs. It
should be noted that smokeless powder manufactured for use in small
arms ammunition is usually glazed with graphite to facilitate machine
loading and prevent the accumulation of static electricity. Many of these
powders are as sensitive to friction as black powder, and the precautions
used in handling black powder should be observed for smokeless powders.
Primary High Explosives
Primary high explosives are sensitive, powerful explosives used in
blasting caps, military fuse detonators, and detonating cord to detonate
main charges or secondary high explosives. Blasting Caps. Blasting caps
are used for initiating high explosives and contain small amounts of a
sensitive primary high explosive. Although they are manufactured to
absorb a reasonable amount of abuse under normal conditions, they must
be protected from shock, extreme heat, impact, and rough treatment to
prevent accidental detonation. Blasting caps are functioned either
electrically or nonelectrically.
Electric Blasting Caps. Electric blasting caps are used when a source of
electricity, such as a blasting machine or battery, is available. The electric
cap is constructed from a small metal tube or shell which is closed at one
end. The cap contains a base load of a sensitive high explosive, a pressed
intermediate charge of extremely sensitive explosive, and a loose ignition
charge. The electrical firing element consists of two plastic insulated leg
wires (also called lead wires), an insulated plug which holds the two wires
in place, and a small diameter corrosion-resistant bridge wire attached
across the terminals of the leg wires below the plug. This assembly is
double crimped into the cap shell.
Upon application of electric current, the bridge wire heats to
incandescence and ignites the loose ignition mixture. The resulting heat or
flame sets off the extremely sensitive intermediate charge which, in turn,
detonates the base charge.
Commercial electric blasting caps come in a variety of sizes, with the
Number 6 and Number 8 blasting caps being the most common. Number 6
blasting caps are approximately 2.8575 cm (1 1/8 in) long, with an outside
diameter of 0.635 cm (1/4 in). Number 8 blasting caps have the same
diameter and are about 3.175 cm (1 1/4 in) long. Electric blasting caps
with leg or lead wires 7.315 m (24 ft) long or less are normally packed 50
to a carton and 500 caps to the case. Leg or lead wires, which come in
lengths ranging from 1.22 m to 91.44 m (4 ft to 300 ft), are made of 22
gauge copper wires for lengths up to 7.315 m (24 ft) and 20 gauge copper
for longer lengths. Most commercial blasting caps employ lead wires of
two different colors to facilitate making electrical connections.
Most electric blasting caps have a short circuiting shunt on the exposed
ends of the leg wires to act as a guard against static electricity and to
prevent accidental firing.
Special types of electric blasting caps are manufactured for seismographic
work, open hearth steel furnaces, and other tasks requiring very short
delays. The delays built into these special blasting caps range from 0.5 ms
to 1.5 ms and are indicated by tags attached to each blasting cap.
Nonelectric Blasting Caps. Nonelectric blasting caps are small metal tubes
or shells, closed at one end, which contain a charge of one or more of the
very sensitive primary high explosives. They are designed to detonate
from the flame provided by a safety fuse or other flame-producing device.
Nonelectric blasting caps have a charge of sensitive high explosive in the
base of the cap, with a priming load of extremely sensitive explosive in
front of the base charge, and an ignition load superimposed upon the
priming explosive. In functioning, the burning safety fuse ignites the
ignition charge, which sets off the priming explosive, which, in turn,
detonates the base charge.
The most common commercial nonelectric blasting caps are Number 6 and
Number 8 with aluminum or copper shells. Number 6 caps are 3.4925 cm
(1 3/8 in) long and Number 8 are 3.81 cm (1 1/2 in) long with outside
diameters of approximately 0.635 cm (1/4 in). Some nonelectric caps may
be larger. For example, the standard issue U.S. Army Corps of Engineers
Special Number 8 blasting cap is 5.969 cm (2.35 in) long and 0.612 cm
(0.241 in) in diameter. The larger size must accommodate the larger base
charge required to detonate the less sensitive military explosives.
Nonelectric blasting caps are packaged in a variety of containers,
including metal cans, cardboard boxes, and wooden boxes.
The explosives normally employed in both electric and nonelectric
blasting caps are the following:
o Lead Azide. Lead azide is an excellent initiating agent for high
explosives and is used extensively as the intermediate charge in the
manufacture of blasting caps. It is inferior to mercury fulminate in
detonating the less sensitive main charge explosives like TNT, but is
superior as an initiator for the more sensitive booster explosives such as
tetryl, RDX, and PETN. Lead azide is extremely sensitive to heat, shock,
friction, and static electricity. The form of lead azide normally used in
blasting caps and fuse detonators is dextrinated lead azide. It is white to
buff in color and is manufactured in the form of rounded aggregates
having no visible crystal faces.
o Lead Styphnate. Lead styphnate is a relatively poor initiating explosive,
and is used primarily as an ingredient of priming compositions and as a
cover charge for lead azide to make the lead azide more sensitive to
detonation. It is used as the ignition charge in blasting caps. Lead
styphnate is light orange to reddish-brown in color and its crystals are
rhombic in shape. This explosive is extremely sensitive to heat, shock,
friction, and static electricity.
o RDX or PETN. These secondary explosives are typically used as the
output charge in blasting caps. They are very powerful and have a high
brisance value. 
Detonating Cord. Detonating cord is a round flexible cord containing a
center core of primary high explosive. The explosive core of the
detonating cord is protected by a sheath of various textiles, waterproofing
materials, or plastics.
The function of the protective sheath is to prevent or minimize damage to
the explosive core from abrasion or moisture. Various colorings and textile
patterns are used to identify different strengths and types of detonating
cord. 
While detonating cord has a general resemblance to safety fuse in that it
has the same diameter and is supplied in rolls or coils, detonating cord is
always distinguishable by its white powder core of PETN (pentaerythritol
tetranitrate), an extremely powerful explosive. Pure PETN is white in
color, but the addition of desensitizers may change its color slightly from
pure white to light gray. PETN has no identifiable odor.
Detonating cord is frequently known by a brand name such as Primacord,
Primex, Detacord, Detonating Fuse, or Cordeau Detonant. Most of the
common detonating cords are of the high energy military type, which
contains about 60 gr of PETN per foot. Detonating cords up to 400 gr per
foot are manufactured for special purposes. There are other lower energy
detonating cords designed for specific applications, especially for
operations in developed areas where a diminished noise level is desired.
For example, one low-energy cord, Detacord, has been developed with a
core of only 18 gr of PETN per foot. Other low-energy cords include Mild
Detonating Fuse and E-Cord, both with reduced core loading per foot.
Detonating cord is used to detonate charges of high explosives in the same
manner as blasting caps and for the same purpose. The detonating cord
with its primary high-explosive core may be tied around, threaded
through, or knotted inside explosives to cause them to detonate. 
Detonating cord is most commonly used when a simultaneous detonation
of a number of explosive charges is planned and when it is not practical to
use electrical circuits for this purpose. For example, to simultaneously
detonate 10 dynamite charges placed 60.96 m (200 ft) apart in a straight
line would require a minimum of about 548.64 m (1,800 ft) of electric
firing wire and a considerable amount of time to prepare and test the
electrical circuit. In contrast, a single line of detonating cord can be laid
out from the firing point in a path that will pass near all of the dynamite
charges. This long line is known as a trunk line. Shorter lengths of
detonating cord, called down lines or branch lines, are attached to the
charges and tied into the trunk lines.
When a blasting cap is attached to one end of the trunk line and detonated,
the detonating wave produced is transmitted through the trunk line and all
the down lines to detonate the dynamite charges simultaneously. The
detonating wave travels at approximately 6,400 m (21,000 ft) or nearly
6.44 km (4 miles) per second.
Secondary High-Explosive Boosters
Secondary high-explosive boosters are explosives that provide the
detonation link in the explosive train between the very sensitive primary
high explosives (blasting caps) and the comparatively insensitive main
charge high explosives, which are also called primer explosives or simply
primers. The explosives packaged for use as boosters are relatively
sensitive and must be handled carefully. Most, for example, will detonate
on sharp impact such as that resulting from a small arms bullet. Due to this
sensitivity, boosters are normally used in small amounts ranging from
several grams up to a 0.5 kg (1 lb) in weight.
Boosters are usually cylindrical in shape with the explosive encased in a
light metal, cardboard, or plastic container. Generally there is an opening
in the end of the booster container to permit the insertion of a blasting cap
or to allow the threading of detonating cord. Boosters packaged in metal
containers are usually employed in wet blasting operations, such as
seismic prospecting or underwater channel cuttings. Cardboard and plastic
encased primers or boosters of varying sizes are generally used in dry
blasting operations, where they are often strung or laced on a length of
detonating cord and lowered into a borehole. After the placing of the
booster, insensitive main charge explosives in prill (loose) or slurry
(liquid-gel mix) form are poured into the borehole. When the charge is
fired, the boosters ensure complete detonation of the main charge
explosives.
Several secondary high explosives are commonly used as primers or
boosters. These explosives are frequently mixed for booster use and, in
some instances, are cast together in a homogeneous mixture or are formed
with one type of explosive cast around or over the other. Common
explosives used in boosters include:
o Pentolite. Pentolite is a very commonly employed booster explosive. It
consists of a homogeneous mixture of 50 percent PETN and 50 percent
TNT. Cast pentolite varies in color from gray to yellow and has a 
detonation velocity of 7,315 m/s (24,500 ft/s).
o RDX. Alone and mixed with other explosives, RDX is used in several
commercial primers and boosters. The Titan Booster 25 is designed
primarily for underwater work. It consists mainly of RDX in a 11.43 cm
by 1.5875 cm (4 1/2 in by 5/8 in) aluminum tube with a cap well located at
one end, giving the appearance of an oversized blasting cap.
o PETN. Described earlier as a filler for detonating cord, PETN is also
used as a booster. It is most commonly used to boost ammonium nitrate
and other cap insensitive explosives.
o Tetryl. Tetryl is the most common military booster. It is yellow in color,
but may appear gray if graphite has been added. Tetryl is a very powerful
explosive with a satisfactory initiating power which is also used in the
manufacture of primary and secondary charges for blasting caps. When
used as a booster, tetryl is usually found in pellet form.
Secondary High-Explosive Main Charges
Dynamite. Dynamite is the explosive most widely used for blasting
operations throughout the world. In the past, dynamite has been relatively
easy to obtain by theft or through legal purchase in the United States.
While dynamites are generally used in earth-moving operations, they
differ widely in their explosive content and, therefore, in their strength and
sensitivity. Commercial dynamites are made of either liquid nitroglycerin,
ammonium nitrate, or nitroglycol (EGDN), along with oxidizers and a
binding material.
The percentage strength of commercial straight dynamite is the gauge by
which the strength of all other commercial dynamite variations are
measured. This measurement is based upon the percentage of nitroglycerin
by weight present in its formula. This percentage value can be misleading,
however, in determining actual blasting power. For example, a 60 percent
dynamite is not necessarily three times as powerful as one marked 20
percent, because the nitroglycerin is not the only energy-producing
ingredient present in the total composition. 
Unless it is packaged loose in boxes or bags for specialized applications,
dynamite will usually be found in cylindrical form, or sticks, wrapped in
colored wax paper. These sticks or cartridges are obtainable in a variety of
lengths and diameters. The most common sizes range from 2.8575 cm (1
1/8 in) to 3.81 cm (1 1/2 in) in diameter and are about 20.32 cm (8 in)
long. In less common larger sizes, dynamite cartridges may be 10.16 cm to
15.24 cm (4 in x 6 in) in diameter and up to 96.52 cm (38 in) in length.
Because of the wide variety of formulas, ingredients, and packaging,
dynamite is not always easy to identify. Consequently, any packaging
materials available should be retained as a means of determining the actual
composition and strength of recovered dynamite.
In addition to its illegal use in bomb construction, dynamite also provides
a source of liquid nitroglycerin for use in safe and vault burglary. Through
a dangerous operation called milking, nitroglycerin is obtained by boiling,
heating, or straining the dynamite through a fine fabric such as silk. The
boiling process is also referred to as sweating, with the separated
nitroglycerin being skimmed from the surface of the pot. In any event, the
resulting nitroglycerin is almost always impure and highly unstable.
Although dynamite is available in an almost unlimited number of sizes,
shapes, strengths, and packages, there are essentially only five basic types
of dynamite in use today.
Straight Dynamites. The explosive base of straight dynamite is liquid
nitroglycerin absorbed in a mixture of various carbonaceous materials,
such as wood pulp or ground meal. Sodium nitrate is added primarily to
supply oxygen for complete combustion of the carbonaceous materials,
thereby increasing the strength of the explosive.
Straight dynamite, because of the nitroglycerin content, has a heavy,
pungent, sweet odor, which is its most outstanding identification feature.
Inhalation of straight dynamite fumes, even for short periods of time, will
usually cause a persistent and severe headache. 
When removed from its wrapper, straight dynamite is light tan to reddish-
brown in color. While they vary in texture, the straight dynamites can be
described as loose, slightly moist, oily mixtures, much like a mixture of
sawdust, clay, and oil. Straight dynamites have been manufactured in
percentage ratings of 10 percent to 60 percent, with the more common
ratings being 30 percent, 40 percent, 50 percent, and 60 percent.
Straight dynamites are rarely used in general blasting work because of
their high sensitivity to shock and friction and their high flammability.
When detonated, they produce toxic fumes, which makes them unsuitable
for use underground or in confined spaces. Because of their high
nitroglycerin content, straight dynamites are the most hazardous of the
dynamites to handle and store. Boxes or sticks of straight dynamite in
storage must be periodically inverted to prevent the nitroglycerin content
from settling to the bottom and leaking out of the stick. Public safety
personnel should be extremely cautious of any dynamite that appears to be
deteriorating or leaking any oily substance. In such cases, the material
should be moved only by trained bomb technicians.
A form of straight dynamite that is widely used in commercial blasting
operations is known as ditching dynamite. Ditching dynamite is
manufactured in a 50 percent grade in sticks 3.175 cm by 20.32 cm (1 1/4
in by 8 in) for use in ditch blasting. The principal characteristic of ditching
dynamite is its high detonation velocity of over 5,181.6 m/s (17,000 ft/s),
which imparts a powerful shock wave and produces a large earth-
shattering effect. 
Ammonia Dynamites. In the manufacture of ammonia dynamites, a
portion of the nitroglycerin content is replaced by ammonium nitrate and
nitroglycol (EGDN). This produces a dynamite which is lower in cost and
less sensitive to shock and friction than straight dynamite. Since it has a
less shattering effect, ammonia dynamite is more suitable for pushing or
heaving kinds of work such as quarry operations, stump or boulder
blasting, and hard pan gravel or frozen earth blasting. Due to these
characteristics, ammonia dynamites are probably the most widely used
explosives of the dynamite family.
Ammonia dynamites are generally manufactured in percentage strengths,
from 20 percent to 60 percent, with detonation velocities in the range of
2,133.6 m to 2,743.2 cm (7,000 ft/s to 9,000 ft/s). However, special
purpose formulas producing velocities from 1,981 m/s to 3,718 m/s (6,500
ft/s to 12,200 ft/s) can be obtained.
When the wrapper is removed, ammonia dynamite will appear light tan to
light brown in color and will have a pulpy, granular, slightly moist, oily
texture. It has the same odor as straight dynamite because of its
nitroglycerin content and may produce severe headaches after short
periods of contact.
Gelatin Dynamites. Gelatin dynamites have a base of water resistant "gel"
made by dissolving or colloiding nitrocellulose with nitroglycerin. The gel
varies from a thick, viscous liquid to a tough, rubbery substance. Gelatin
dynamite avoids two of the disadvantages of straight ammonia dynamite
in that it is neither hydroscopic or desensitized by water. Since it is
insoluble in water and tends to waterproof and bind other ingredients with
which it is mixed, gelatin dynamite is well suited for all types of wet
blasting work. Because of its density, it is also used extensively for
blasting very hard, tough rock or ore.
Gelatin dynamites and semi-gelatin dynamites are manufactured in
percentage strengths from 20 percent to 90 percent. It is an inherent
property of gelatin dynamite to detonate at two velocities. Unconfined, it
will usually detonate at about 2,133.6 m/s (7,000 ft/s), but when confined
gelatin dynamites will detonate in the range of 3,962.4 m/s to 6,705.6 m/s
(13,000 ft/s to 22,000 ft/s), depending upon the strength of the dynamite
employed.
Ammonia-gelatin Dynamites. These dynamites retain most of the
characteristics and qualities of gelatin dynamite, but derive a portion of
their strength from the use of less costly ammonium nitrate. Ammonia-
gelatin dynamites are manufactured in percentage strengths of 25 percent
to 90 percent with detonating velocities ranging from about 3,962.4 m/s
(13,000 ft/s) to 5,181.6 m/s (17,000 ft/s).
Military Dynamites. Military dynamite is not a true dynamite. It is
manufactured with 75 percent RDX, 15 percent TNT, 5 percent SAE 10
motor oil, and 5 percent cornstarch. It is packaged in standard dynamite
cartridges of colored wax paper and is marked either M1, M2, or M3 on
the cartridge. This marking identifies a cartridge size difference only, since
all military dynamite detonates at about 6,096 m/s (20,000 ft/s).
Military dynamite is used as a substitute for commercial dynamites in
military construction, quarry work, and demolitions. It is equivalent in
strength to 60 percent straight dynamite. 
Since it contains no nitroglycerin, military dynamite is safer to store and
transport than true dynamite, and is relatively insensitive to heat, shock,
friction, or bullet impact. These qualities permit safer combat operations
while providing the pushing or heaving action not available from standard
combat demolition explosives. When removed from its wrapper, military
dynamite is yellow-white to tan in color and is a granular substance which
crumbles easily and is slightly oily. It does not have a noticeable
characteristic odor, nor does it cause the headaches typical of the true
dynamites.
Ammonium Nitrate. Ammonium nitrate is one of the least sensitive and
most readily available main charge high explosives. It ranges in color from
white to buff-brown or gray, depending upon its purity, and has a salty
taste. Ammonium nitrate is usually found in the form of small compressed
pellets called prills. While it is extensively used as a blasting agent and by
the military as a cratering charge, it is also an ingredient in the
manufacture of certain dynamites and is widely employed as a fertilizer.
Even a high-explosive grade of ammonium nitrate generally requires the
use of a booster for detonation. For military cratering charges, TNT is used
as the booster, while in commercial applications RDX-filled boosters or
primers are usually employed. The normal detonation velocity of
ammonium nitrate is approximately 3,352.8 m/s (11,000 ft/s). Due to its
hygro-scopicity and the fact that it loses power and sensitivity in direct
proportion to its moisture content, explosive charges composed of
ammonium nitrate are usually packaged in some form of waterproof
container.
Its use as a commercial fertilizer makes ammonium nitrate readily
accessible to anyone. While the grade of ammonium nitrate used as
fertilizer is naturally inferior as an explosive charge, it can be sensitized by
the addition of fuel oil. The mixture is referred to as "prills and oil" or
ANFO (ammonium nitrate and fuel oil), and its use is fairly widespread
because of its low cost and availability.
Ammonium nitrate should be handled with some degree of caution,
because it is a strong oxidizing agent and has the ability to increase the
combustibility of other flammable materials with which it comes in
contact. If it is recovered as the result of a bombing incident, brass or
bronze nonsparking tools should not be employed because they react with
the ammonium nitrate to form tetramino nitrate, which is as sensitive an
explosive as lead azide.
Blasting Agents
A blasting agent is an insensitive chemical composition or mixture,
consisting largely of ammonium nitrate, which will detonate when
initiated by high-explosive primers or boosters. Since they contain no
nitroglycerin, blasting agents are relatively insensitive to shock, friction,
and impact and are, therefore, safer to handle and transport.
One group of blasting agents are called nitro-carbo-nitrates (NCN). NCN
is manufactured mainly of ammonium nitrate and oil, with special
ingredients added to reduce static electricity and prevent hardening of the
agent during storage. It is packaged in sealed waterproof cans, asphalt
laminated paper, and flexible plastic bags which provide water resistance
as long as the containers are not opened or damaged. Container sizes range
from 10.16 cm to 27.94 cm (4 in to 11 in) in diameter, 40.64 cm to 60.96
cm (16 in to 24 in) in length, and weigh from 6.136 kg to 38.636 kg (13.5
lb to 85 lb). NCN is similar to 50 percent or 60 percent blasting gelatin in 
strength, but is much less sensitive. NCN cannot normally be detonated
with a blasting cap or detonating cord alone, but requires a high-explosive
booster.
Free-running explosives consisting of NCN, either with or without the
addition of high explosives, make up another group of blasting agents.
Because of their granular or small pellet form, the free-running agents can
be poured around rigid explosive charges to fill all of the available space
in the borehole. They are also useful for pouring into rough, irregular, or
partially blocked holes, and some free running blasting agents can be
submerged underwater for a period of time without loss of effectiveness.
Sometimes an orange dye is added to the agent to facilitate visibility. 
A final common group of blasting agents are called blasting slurries.
These consist of NCN mixtures, with or without the addition of TNT, in a
gel-like consistency. Some of the blasting slurries have powdered metals,
such as aluminum, added to increase their performance. The blasting
slurries, because of their consistency, can be poured into irregular or wet
boreholes to fill all available space with explosive. Like all of the
previously discussed blasting agents, the blasting slurries require a primer
or booster for detonation. 
Two-Part Explosives 
Kine-Pak and Kine-Stick explosives are two-part explosives, consisting of
ammonium nitrate and nitromethane, which are inert until mixed. When
mixed and detonated with a Number 6 cap, Kine-Pak generates 50 percent
more shock energy than 75 percent dynamite. Following mixture and prior
to detonation, it is some 20 times less shock or impact sensitive than
dynamite. The Kine-Pak and Kine-Stick explosives were developed as a
direct replacement for dynamites and commercial PETN-RDX boosters,
and are manufactured by the Atlas Powder Company.
Liquid Explosive - Astrolite. Astrolite is a liquid explosive developed for
commercial and military applications. Although it is almost twice as
powerful as TNT, Astrolite cannot be detonated until its two separate
components are mixed.
Astrolite comes in two plastic bottles labeled Astropak. The smaller bottle
contains a dry solid component (proprietary, but assumed to be ammonium
nitrate), and the larger bottle contains a liquid-filled can (slightly aqueous
hydrazine) in the bottom. To form the explosive, the contents of the small
bottle are poured into the larger bottle and the top replaced. By pressing
down on the bottle cap, cutters automatically puncture the liquid-filled
can. By inverting and shaking the bottle, the two components are mixed
and are ready for detonation with a standard blasting cap. The liquid can
be detonated in its container or poured into crevices in the ground, cracks
in rocks, or into other containers. Astrolite is clear in color and smells
strongly of ammonia. Additional information on Astrolite may be obtained
from the Explosives Corporation of America, Excca Building, Issaquah,
WA 98027. 
Military Explosives
Explosives made for military use differ from commercial explosives in
several respects. Military explosives, designed to shatter and destroy, must
have high rates of detonation and, because of combat conditions, must be
relatively insensitive to impact, heat, shock, and friction. They must also
possess high power per unit of weight, must be usable underwater, and
must be of a convenient size, shape, and weight for troop use.
Trinitrotoluene (TNT). TNT is probably the most widely used military
explosive in the world. Alone or in combination with other explosives, it is
frequently used as a main charge in artillery projectiles, mortar rounds,
and aerial bombs. As one of the moderately insensitive military
explosives, TNT cannot be detonated by heat, shock, or friction and is, in
fact, safe even when impacted by a bullet. It will usually burn rather than
detonate if consumed by fire.
The TNT most often encountered by public safety personnel will probably
be in the form of the 0.638 cm (1/4-lb), 1.27 cm (1/2-lb), and 0.4545 kg
(1-lb) blocks. These blocks are normally packed in 22.727 kg (50-lb)
wooden boxes for storage or transportation. When TNT is removed from
the cardboard container, it is light yellow to light brown in color and
gradually turns dark brown after several days' exposure to sunlight.
Detonated TNT gives off a dirty gray smoke.
Tetrytol. Tetrytol is used as an alternative to TNT by the armed services
and is composed of about 75 percent tetryl and 25 percent TNT. It is light
tan to buff in color and has a detonation velocity of about 7,315.2 m/s
(24,000 ft/s).
Tetrytol is manufactured for the military both as part of the M1 chain
demolition package and as the M2 demolition block. When the present
stocks are exhausted, no more tetrytol will be procured by the U.S.
military services.
Composition C-3. Composition C-3 is a plastic explosive containing
approximately 80 percent RDX and 20 percent explosive plasticizer. It is a
yellow putty-like substance which has a distinct, heavy, sweet odor. When
molded by hand in cold climates, C-3 is brittle and difficult to shape. In
hot climates it is easy to mold, but tends to stick to the hands. C-3 will
most likely be encountered by public safety personnel in the form of
demolition blocks. 
Composition C-4. Composition C-4 is an improved version of the C-3
explosive. It contains 90 percent RDX and has a greater shattering effect
than the earlier C-3. C-4 is white to light tan in color, has no odor, and 
detonates at about 7,315.2 m/s (24,000 ft/s). 
Sheet PETN (Flex-X). Sheet PETN, called Flex-X by the military and
Detasheet commercially, is a demolition charge consisting of 63 percent
PETN with nitrocellulose and plasticizer added. It comes in the form of
sheets, with each sheet having a pressure-sensitive adhesive backing,
making it possible to apply the sheet to almost any dry surface.
Commercially, sheet PETN is used for explosive forming, cutting, and
metal hardening. The military sheet is supplied only in an olive green
color, but commercial sheets may range from pink to brownish-red.
Improvised Explosives
When manufactured explosives are not available, it is relatively easy to
obtain all of the ingredients necessary to improvise explosive materials.
The list of existing materials and simple chemical compounds which can
be employed to construct homemade bombs is virtually unlimited. The
ingredients required can be obtained at local hardware or drug stores and
are so commonplace that their purchase rarely arouses suspicion.
Starch, flour, sugar, or cellulose materials can be treated to become
effective explosives. Powder from shotgun shells or small arms
ammunition, match heads, firecracker powder, and ammonium nitrate
fertilizers can all be accumulated in sufficient volume to create a
devastating main charge explosive. To explode or detonate the improvised
main charge, some means of initiation is required. The most common
methods of ignition of improvised explosives are summarized below:
o Blasting Caps. Blasting caps, when available, provide the most
successful means of causing the complete detonation of improvised
explosives.
o Percussion Primers. Shotgun, rifle, or pistol ammunition primers have
served as initiators in mechanically functioning bomb assemblies,
particularly with explosives that are sensitive to heat.
o Flashbulbs. Although not explosive by nature, carefully prepared flash
bulbs or light bulbs can be used as initiation devices when placed in
contact with explosive materials that are sensitive to heat and flame. They
can be functioned electrically to provide the necessary heat required to
ignite black powder, smokeless powder, and other heat-sensitive explosive
or incendiary mixtures.
Possible improvised main charge explosives are listed below:
o Match Heads. A main charge explosive consisting of ordinary match
heads confined inside a steel pipe will produce an excellent explosion.
Bombs filled with match heads are extremely sensitive to heat, shock, and
friction, and must be handled with care.
o Smokeless Powder. Smokeless powder, obtained from assembled
cartridges or purchased for hand reloading, is widely employed as a main
charge, particularly in pipe bombs.
o Ammonium Nitrate Fertilizer. Fertilizer grade ammonium nitrate mixed
with fuel oil or potassium nitrate and charcoal makes an excellent main
charge explosive. A booster would be required for detonation.
o Potassium/Sodium Chlorate. Potassium chlorate or sodium chlorate and
sugar mixtures are widely used as incendiary and explosive materials.
Though essentially incendiary compounds, these mixtures will explode
with a violence comparable to 40 percent dynamite when initiated in
confinement.
Nitroglycerin
Although nitroglycerin is not often employed as a main charge either in its
manufactured or improvised state, it is the main explosive component of
straight dynamite and is found in lesser concentrations in a number of
other explosives. Other applications include medical use, oil and gas well
drilling, and the blowing open of safes and vaults by criminals. Liquid
nitroglycerin may also be encountered as leakage from badly deteriorated
dynamite.
Nitroglycerin is an oily liquid which is not mixable with and is about 1.6
times heavier than water. It may be anything from clear and colorless to
amber in color and has been found looking almost milky. Brown fumes in
a bottle of nitroglycerin are due to nitric acid and indicate decomposition
and, thus, increased hazard. It is almost odorless, although there may be an
acrid odor due to the presence of acid.
In a pure state, nitroglycerin is very sensitive to heat, shock, and friction.
Sensitivity increases markedly by the application of heat. When frozen,
nitroglycerin is less sensitive than when it is in a liquid state, but in a
semifrozen state it becomes extremely sensitive due to the internal crystal
stresses brought about by freezing or thawing action. Even under ideal
conditions, nitroglycerin is an extremely dangerous explosive to handle
and can explode from such causes as a slight jarring, overheating, or
chemical reaction with container materials and impurities. In certain cases,
it has been known to detonate for no apparent reason at all.
Footnotes
* Inclusion of specific technologies in this document is not an
endorsement by the authors or by Sandia National Laboratories. This
document includes detectors known to the authors as of October 1998.
Some technologies may not be included in the text due to oversight by the
authors. Some detector characteristics described are not fully quantifiable,
and in such cases, comparisons between detectors are necessarily
subjective.
1. The authors work in the Contraband Detection Technologies
Department 5848, Sandia National Laboratories, P.O. Box 5800, Mail
Stop 0782, Albuquerque, NM 87185-0782.
2. The EXPRAY kit pictured in figure 13 is available from Genesis
Resource as Model M1553. The phone number for Genesis Research is
(602) 838-6420. 
3. An example of this type of supplier is AccuStandard, Inc., 125 Market
Street, New Haven, CT 06513, Phone: (800) 442-5290. 
-------------------------------
About the National Institute of Justice 
The National Institute of Justice (NIJ), a component of the Office of
Justice Programs, is the research agency of the U.S. Department of Justice.
Created by the Omnibus Crime Control and Safe Streets Act of 1968, as
amended, NIJ is authorized to support research, evaluation, and
demonstration programs, development of technology, and both national
and international information dissemination. Specific mandates of the Act
direct NIJ to: 
--Sponsor special projects, and research and development programs, that
will improve and strengthen the criminal justice system and reduce or
prevent crime. 
--Conduct national demonstration projects that employ innovative or
promising approaches for improving criminal justice. 
--Develop new technologies to fight crime and improve criminal justice. 
--Evaluate the effectiveness of criminal justice programs and identify
programs that promise to be successful if continued or repeated. 
--Recommend actions that can be taken by Federal, State, and local
governments as well as by private organizations to improve criminal
justice. 
--Carry out research on criminal behavior. 
--Develop new methods of crime prevention and reduction of crime and
delinquency. 
In recent years, NIJ has greatly expanded its initiatives, the result of the
Violent Crime Control and Law Enforcement Act of 1994 (the Crime
Act), partnerships with other Federal agencies and private foundations,
advances in technology, and a new international focus. Some examples of
these new initiatives: 
--New research and evaluation are exploring key issues in community
policing, violence against women, sentencing reforms, and specialized
courts such as drug courts. 
--Dual-use technologies are being developed to support national defense
and local law enforcement needs. 
--The causes, treatment, and prevention of violence against women and
violence within the family are being investigated in cooperation with 
several agencies of the U.S. Department of Health and Human Services. 
--NIJ's links with the international community are being strengthened
through membership in the United Nations network of criminological
institutes; participation in developing the U.N. Criminal Justice
Information Network; initiation of UNOJUST (U.N. Online Justice
Clearinghouse), which electronically links the institutes to the U.N.
network; and establishment of an NIJ International Center. 
--The NIJ-administered criminal justice information clearinghouse, the
world's largest, has improved its online capability. 
--The Institute's Drug Use Forecasting (DUF) program has been expanded
and enhanced. Renamed ADAM (Arrestee Drug Abuse Monitoring), the
program will increase the number of drug-testing sites, and its role as a
"platform" for studying drug-related crime will grow. 
--NIJ's new Crime Mapping Research Center will provide training in
computer mapping technology, collect and archive geocoded crime data,
and develop analytic software. 
--The Institute's program of intramural research has been expanded and
enhanced. 
The Institute Director, who is appointed by the President and confirmed by
the Senate, establishes the Institute's objectives, guided by the priorities of
the Office of Justice Programs, the Department of Justice, and the needs of 
the criminal justice field. The Institute actively solicits the views of
criminal justice professionals and researchers in the continuing search for
answers that inform public policymaking in crime and justice.
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NCJ 178913