examined these issues for high explosives in its 1998 report Containing the Threat from Illegal Bombings (NRC, 1998). Black and smokeless powders were explicitly excluded from that study, but a 1997 amendment to the law required that the Treasury Department request a separate study of the technical feasibility of adding markers or taggants to black and smokeless powders. The NRC Committee on Smokeless and Black Powder responded by examining the relevant issues, with the goal of analyzing whether markers and taggants could be added to black and smokeless powders, while considering whether such additions would pose a risk to human life or safety; substantially assist law enforcement officers in their investigative efforts; substantially impair the quality and performance of the powders for their intended lawful use; have a substantial adverse effect on the environment; have costs that outweigh the benefits of their inclusion; and be susceptible to countermeasures.2
From 1979 to 1992 in the United States, the number of reported bombings involving black and smokeless powders approximately doubled (Hoover, 1995). However, between 1992 and 1996 (the most recent year for which data were available to the committee), the number of reported bombings involving these powders leveled off, averaging about 650 per year. From 1992 to 1994 the number of "significant" bombing incidents—defined by the committee as those that resulted in (or, for attempted bombings, had the capability of causing) death or injury or a minimum of $1,000 in property damage—was in the range of 250 to 300 per year.
Two federal agencies gather statistics on bombing incidents in the United States: the Department of the Treasury's Bureau of Alcohol, Tobacco, and Firearms (ATF) and the Department of Justice's Federal Bureau of Investigation (FBI). Each agency maintains separate statistics on bombing incidents, and each distributes its own form for voluntary reporting of incidents by local investigators. Discrepancies between the two data compilations complicate the analysis of the bombing threat.
Of all the approaches to reducing bombing incidents, detection of a bomb prior to explosion is the most attractive, since it provides an opportunity to render the bomb safe before it can cause death, injury, or property damage.
Three scenarios for the detection of bombs were considered by the committee: the portal, in which all people or packages entering an area must pass through a few well-monitored checkpoints (for example, at airports); the suspicious pack-
See Appendix B for a complete statement of task.