Detection tagging development has focused on the incorporation of a distinctive vapor taggant into the explosives formulation of blasting caps and gun powders. Subcontracted efforts include sorption of vapor taggants into blasting cap plug closure materials, inclusion of microencapsulated vapor taggants in caps and bulk explosives, and finally, the experimental evaluation of room-temperature sublimable salts. The soption studies have included a wide range of explosives types and have dwelt with more than 150 combinations. Based on criteria developed early in the program, only some 25 candidates are still being investigated. Mircoencapsulated liquids appear to hold substantial promise based on preliminary studies, and an increasing emphasis is being placed in this area. Finally, some preliminary studies have been made on the potential of a coded harmonic radar tagging method, which indicates promise, and a deactivation method using a micromagnetic switch.

Smaller efforts have been initiated in nontagged detection of explosives. The technique of ion-mobility spectrometry is being investigated as a natural vapor detector. (It has also some potential as a vapor tag detector.) The use of the dielectric discontinuity method is being studied as a relatively fast, low cost means of letter-bomb detection. Finally, the technique of dual-energy tomography shows considerable promise as a method of determining the bulk properties (average density and atomic number) of explosives within a larger package.

As part of the technical support task, recommendations regarding fruitful avenues of approach are made, and a number of important developments were studied. The two most important were the detection of explosives (nontagged or vapor tagged) by atmospheric pressure ionization mass spectrometry and olfactory discrimination by the Mongolian gerbil. In either case, the apparent detection limit and specificity surpass known methods by several orders of magnitude, and serious, detailed studies are warranted and recommended.

Nontagged identification of explosives has not been offered the attention it deserves, largely because of the technical difficulty of the area. During this program, several promising technologies were identified and evaluated that suggest that a reassessment of this position should be made. These experimental methods involve comparison (powder matching) and postblast residue analysis (explosive-specific enzymes and chromatographic methods). Such procedures will enhance the forensic chemist's ability to

analyze and identify the type of explosive from blast residue. These methods are suggested out of the realization that identification taggant addition to certain categories of explosives (military explosives, homemade explosives, and explosives in inventory prior to National implementation of the identification tagging concept) represent broad categories of explosives for which only residue analysis can provide investigative support.

The above-described efforts delineate the approach of this program under sponsorship of the Bureau of Alcohol, Tobacco and Firearms. Key program efforts are designed to provide for predetonation detection of illegally used explosives and, in the event of detonation, provide a mechanism of explosives identification thereby giving investigative leads. This duality of concerted efforts is targeted at the ultimate objective toward controlling the illegal use of explosives.

1. INTRODUCTION

The illegal use of explosives has been recognized as a serious threat to the country for a number of years, and several Government agencies have sponsored studies and developments toward countering this threat. However, no substantial gains had been made in achieving a significant impact on the problem until relatively recently. Noting that many bombings were taking place in public areas traditionally considered inviolate, there has developed an element of coordination and cooperation among United States Federal agencies.

Efforts in explosives vapor characterization, identification tagging developments, and initial detection tagging feasibility studies were originated by the Law Enforcement Assistance Administration. The U.S. Postal Service also pioneered studies in explosives vapor characterization, barrier penetration, and detection, as did the U.S. Army Mobility Equipment Research and Development Command (USAMERADCOM). In addition, the Bureau of Mines contributed substantially toward the development of identification tags and an implementation model of a Nationwide explosives identification tagging program.

Under the impetus and coordination of the Advisory Committee on Explosives Tagging of the Bureau of Alcohol, Tobacco and Firearms (ATF), an explosives control program resulted. This report addresses a majority of the technical areas having significant potential for detecting and identifying illegally used explosives.

In addition to ATF, the Federal Aviation Administration (FAA) and the Energy Research and Development Administration (ERDA) currently sponsor the vast majority of ongoing work. Both FAA and ERDA have their own particular operational requirements, which narrowly constrain their objectives and direct their research efforts. As a result, their programs have little impact in the areas of greatest concern to law enforcement personnel, although they may have an effect in the prevention of explosions in public buildings and other controlled areas. The investigations by FAA, and those of the Sandia Corporation (sponsored by ERDA), have been coordinated with ATF efforts to a significant degree, and this cooperative spirit has begun to show results in developing complementary programs. Nevertheless, the ATF program remains the only substantial effort underway which promises to provide the investigator and the analyst improved methods and capabilities for attacking this pernicious problem.

This report describes the work carried out by The Aerospace Corporation and its subcontractors on behalf of the Bureau of Alcohol, Tobacco and Firearms. During Fiscal Year 1977, the major accomplishments dealt with the identification tagging of explosives. This work, of particular importance to investigators and analysts, has no counterpart in other agencies. A substantial effort in detection tagging was begun in conjunction with a smaller-scaled FAA effort. Finally, a limited exploration in untagged detection was initiated to complement the much larger efforts being undertaken by FAA and the Sandia Corporation.