Rapid identification of suspect substances is important to the operation of the entire criminal justice system. For police, it often means the difference between retaining a suspect in custody and being forced to let him go because evidence is not yet available. For prosecutors it means having more time to prepare the case. For the scientists in the forensic laboratory it saves time and personnel and increases the accuracy of their work. Forensic laboratories frequently have insufficient staff to meet the high demand for their services. Furthermore, since explosives analysis is not a routine request, each case requires extra time to prepare for it.
During the last few decades, advances in electronics have made analytical instrumentation better, cheaper and smaller. Today, most forensic laboratories have several types of analytical instrumentation and often multiple instruments, such as GC/MS (gas chromatography with a mass selective detector), which has become a standard in drug analysis. The questions these various instruments address are “What is this material? Is it a bomb?, a chemical agent?, a drug?, or perhaps a hoax?”
The identification of common chemicals is relatively straightforward. For decades there have been handbooks tabulating their various physical properties, and in recent years, methods for sample identification have improved with the availability of commercial computer databases. For example, a GC/MS run of a suspected narcotic compared to the available drug library allows tentative identification within 30 minutes. These data libraries are available for such properties as mass (MS), infrared (IR), Raman, and nuclear magnetic resonance (NMR) spectra and are often part of the software packages that come with the purchase of new instrumentation. Alternatively, they may be obtained from independent companies specializing in such databases.
Unfortunately, there are only a handful of useful reference books of the properties of explosives, propellants, and improvised explosives.1-10 Furthermore, many are multi-volume series, which are difficult and expensive to acquire and lack actual analytical data spectra, chromatograms, thermograms or photographs for comparison.1-6 The adage “one picture is worth a thousand words” is never more true than in discussing analytical data, and there exists a need for a compendium of explosive properties, one in which actual data can be viewed and compared. The focus and purpose of this work was to create a centralized database of explosive properties, published in hard copy and as a computer searchable reference, to meet this need.
A group of people working in the field of fire and explosion debris analysis, organized as the Technical Working Group for Fire and Explosion (TWGFEX), sets standards for the investigation of fires and explosions. The Laboratory Explosives Group, a committee of that organization made up of scientists who work in state and federal forensic laboratories and chaired by heads of the bureau of Alcohol, Tobacco and Firearms (ATF) and Federal Bureau of Investigation (FBI) forensic explosives laboratories, published a document of guidelines for good forensic laboratory practices in the analysis of unconsumed intact explosives. The guidelines set out a number of analytical techniques that are potentially applicable to the analysis of explosives. This information has been compiled in a matrix of minimum analysis requirements for the identification of intact explosives. It was recognized that the correct characterization and/or identification of an explosive depends on the use of acceptable analytical methods and the expertise of the analyst. The TWGFEX guidelines do not discourage the use of any particular method and recommend the use of multiple techniques based on different principles to confirm identification. The guidelines categorize the analytical techniques for explosives as (A) those that provide structural and/or elemental information (i.e. mass spectrometry, energy dispersive x-ray spectroscopy), (B) those that provide a high degree of selectivity (i.e. infrared spectroscopy), and (C) those that are useful for corroborating identification (i.e. solubility). For example, a white powder is soluble in water. If it is an explosive, it is likely an inorganic salt such as ammonium nitrate or chlorate. However, further information is necessary; it could be table salt.
The TWGFEX guidelines also provide a list of the most commonly encountered explosives. It includes military (TNT, PETN, RDX, HMX, picric acid, tetryl, EGDN, nitromethane) and commercial (ammonium nitrate (AN), ANFO, water gel, emulsion) explosives, gun propellants (black powder, Pyrodex, smokeless (double-base & single), nitroglycerin, nitrocellulose), improvised explosives (TATP, HMTD), and components of explosives (potassium and sodium nitrate, sulfur, carbon, potassium perchlorate, sodium benzoate, dicyanodiamide, ascorbic acid, nitroguanidine, metriol trinitrate, DEGDN, DMNB). The multitude of plasticized explosives, dynamites, and other composite formulations require careful selection of a representative data set. A survey of each material would be extremely time-consuming and necessitate acquisition of large quantities of these explosives. Further, it is anticipated there would be little significant differences in properties among samples in each category. Thus, for plastic bonded military explosives, dynamites, the myriad of smokeless powders, and ammonium nitrate formulations we have depended on the Rhode Island State Crime Lab and other forensic labs throughout the country to provide a list of the prevalent formulations.
Though the guidelines suggest possible techniques for examining exemplary explosives and a list of the most commonly encountered explosives in forensic laboratories across the country, no actual analytical data was presented. Careful attention was paid to follow the matrix of techniques found in the TWGFEX guideline in the compilation of this manual, allowing it to serve multiple purposes. It will provide a database of actual analytical data for known energetic materials as an aid for identifying unknown materials as explosives. As such it will be useful to any laboratory working with explosives, especially forensic and national laboratories and explosives and explosive detection equipment manufacturers. In addition, this manual serves as a companion piece to the TWGFEX document, which is available to all forensic laboratories. Indeed, it is not feasible to apply every technique to each material. In compiling this database, the most feasible techniques were used for each material. Materials with poor volatility or poor solubility were somewhat difficult to characterize and were given special attention to investigate possible modes of characterization, such as thermal analysis and MS using a direct insertion probe.
In addition to instrumental analysis, several modes of chemical analysis were investigated for use in the field identification of explosive compounds. One such field identification technique is a series of chemical spot color-change tests. Many common military grade explosives can be classified, if not identified, by observation of the chemical reaction with a set of standard reagents. In many cases, several spot tests are applicable to a single compound. In the use of these tests as a primary means of identification, it is advisable to use as many applicable tests as possible to increase the certainty of identification.
This database is intended to serve as a comprehensive reference containing physical and spectral properties of a wide variety of energetic materials. The presented data includes actual spectra and traces from MS, IR, Raman, NMR, and differential scanning calorimetry (DSC). Other techniques that are identified in the TWGFEX guideline were investigated for their potential application to the characterization and identification of explosives, but were dismissed from this collection based on the practicality of their use in a forensic laboratory with standard equipment. Energy dispersive x-ray spectroscopy (EDS), which is commonly found in the well-funded laboratories and is used primarily in the investigation of gunshot residues, is one such technique. Though the potential of easily determining elemental composition by EDS is promising, in a comparison of five pure organic explosives (TNT, RDX, HMX PETN, and Tetryl) the elemental compositions reported by the EDS data were incorrect. In addition, the variance noted between the data and the expected values was not standard across the different compounds, making mathematical adjustment and calibration of the instrument for this purpose difficult. Another promising technique is x-ray powder diffraction spectroscopy (XRD), which gives information about the crystal structure of a sample, which in turn is highly characteristic of a particular compound. This technique was dismissed because of the amount of sample required to perform the analysis. Though commercially available instruments may vary in the amount of sample required for analysis, the instrument available for this study required approximately one half gram of pure compound to collect data of sufficient quality and resolution, an amount that is in great excess of the available sample amount for most of the compounds analyzed. Finally, traditional microscopic techniques such as polarized light microscopy (PLM) and conventional or stereo-microscopy (MCR) were dismissed based on the sharp learning curve and operator skill required to accurately use these techniques for identification. Though some analysts with many years experience claim to be capable of identifying pure intact organic explosives on the basis of PLM alone, such an analysis requires the calculation of the samples birefringence based on the observations noted when examined through the microscope. Successful analysis by these methods, though possible, is not practical in the standard forensic laboratory when other more objective techniques such as IR and MS are available.
The data is organized by both compound name and analytical technique. Overviews of the technology employed and the basic principles upon which each technique is based as well as the technique’s specific application in the field of explosives analysis are also available. Information as to the conditions under which such data were obtained is included along with melting points, flame/burn characteristics, solubilities, reactivities, and synthetic procedures. Where important for characterization, individual portions of spectral data are magnified (such as to exhibit important MS peaks). In the interest of consistency, most of the spectra were generated on instruments at the University of Rhode Island in a facility that has an ATF license and magazine for storage of small quantities of energetic materials and is equipped with the appropriate analytical instrumentation.
- "Encyclopedia of Explosives and Related Items," U.S. Army Armament Research & Develop. Command; PATR-2700, Dover; 1960-78.
- Urbanski, T. "Chemistry & Technology of Explosives," Vols1-4; Pergamon, NY; 1964, 65, 67, 84.
- Dobratz, B.M. "LLNL Explosives Handbook Properties of Chemical Explosives and Explosive Simulants," Lawrence Livermore Laboratory UCRL-52997; March 1981.
- Brinkley, S.R.; Gordon, W.E. ?AMC Engineering Design Handbook: Principles of Explosives Behavior", U.S. Army Material Command, 1978.
- Gibbs, T.R.; Popolato, A. (eds.) "LASL Explosive Property Data," U. California Press; 1980.
- Meyer, R. "Explosives," 3rd ed. VCH, Essen, Germany; 1987.
- Cooper, PW; Kurowski, SR “Introduction to the Technology of Explosives,” VCH, NY; 1996.
- Oxley, J The Chemistry of Explosives, in "Explosives Effects & Applications" Walters & Zukas, ed. Springer, NY 1998.
- Yinon, J.; Zitrin, S. “Modern Methods & Applications in Analysis of Explosives,” Wiley, NY, 1993.
- Yinon, J.; Zitrin, S “The Analysis of Explosives,” Pergamon Press, Oxford, 1981.
- Nam, Sae-Im, "On-Site Analysis of Explosives in Soil; Evaluation of Thin-Layer Chromatography for Confirmation of Analyte Identity," CRREL Special Report, August 1997.
- Baytos, John F., "Field Spot-Test Kit for Explosives," LA-12071-MS, Los Alamos National Laboratory, University of California, United States Department of Energy, contract W-7405-ENG-36, issued July 1991.