X-ray display of pipe bomb. Reprinted, with permission, from the Federal Aviation Administration (FAA). Copyright 1998 by the FAA. Photo courtesy of Security Training and Technical Resources.



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--> X-ray display of pipe bomb. Reprinted, with permission, from the Federal Aviation Administration (FAA). Copyright 1998 by the FAA. Photo courtesy of Security Training and Technical Resources.

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--> 2 Detection of Black and Smokeless Powder Devices Introduction Of all the approaches to reducing bombing incidents, detecting 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. Fixed, portal bomb detection systems are already used to screen bags and packages coming into some highly vulnerable locations, such as airports and federal buildings. Portable x-ray detection systems and specially trained dogs are also used in responses to reports of suspicious packages or bomb threats. As mentioned in Chapter 1, however, the majority of the bombs that cause casualties or significant property damage each year in the United States explode in locations where detectors are unlikely to be deployed.1 Since the 1970s, researchers have investigated the possibility that special ''markers" might be added to explosive materials to facilitate the detection of bombs that use these materials. This research took on a special urgency after a small quantity of plastic explosive was used to bring down a Pan American airliner over Lockerbie, Scotland, in 1989 (NRC, 1998). Plastic and sheet explosives concealed in luggage or electronic devices are difficult to detect by x-ray systems. In addition, they typically have such a low vapor pressure that they 1   According to ATF data for 1992 to 1994, a total of 26 of 27 deaths and 167 of 199 injuries from propellant and pyrotechnic bombs occurred in locations where installation of detectors was deemed unlikely (see Table 1.4).

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--> cannot be detected in a suitcase by current vapor detector technology (NRC, 1998). As a result of the Pan American tragedy, four candidate vapor markers were developed for incorporation into plastic and sheet explosives under the auspices of the U.N. International Civil Aviation Organization (ICAO) (NRC, 1998). The ICAO Convention on the Marking of Plastic Explosives for the Purpose of Detection, which was signed in 1991, was recently ratified by more than the required 35 nations and is now in effect.2 The convention requires that all plastic and sheet explosives manufactured in the signatory nations be marked with one of the four vapor markers. These markers make the plastic and sheet explosives approximately one million times easier to detect with vapor detectors (Elias, 1991).3 The Committee on Smokeless and Black Powder was asked (see Appendix B) to assess the feasibility and desirability of adding markers to black and smokeless powders to enhance the likelihood of detecting explosive devices that use these powders. To evaluate the potential value of adding markers to smokeless or black powders, however, it is first important to understand the current capabilities for detecting explosive devices that use unmarked powders. The NRC report Containing the Threat from Illegal Bombings (NRC, 1998) reviews the relevant technologies and their application to high explosives. Rather than repeat that discussion, this report focuses only on the general classes of detection systems and their application to smokeless and black powders. An important characteristic of bombs that use black or smokeless powders is that these powders require containment to produce an effective explosion. As discussed in Chapter 1, the purpose of the container is to confine the gases produced during the burning of the explosive powder. The resulting pressure then explodes the container, and the fragments of the container are propelled outward at high speeds to cause deaths, injuries, and property damage. The need for containment is important in detection because the containers are more easily detectable by some technologies—such as x-ray systems—than are the powder fillers themselves.4 Thus, there are two ways to find a black or smokeless powder device: either detection of the container or detection of the powder itself. Improvised explosive devices are usually concealed in various ways, such as within 2   The convention entered into force for the 38 ratifying nations on June 21, 1998. Eleven nations are capable of producing these plastic explosives, and all or most have chosen 2,3-dimethyl-2,3-dinitrobutane (DMNB) as their marking agent. James P. Rubin, State Department, press release, June 22, 1998; personal communication with Tung-ho Chen, U.S. Army, Picatinny Arsenal, Dover, N.J. 3   The United States has mandated the addition of DMNB to all plastic and sheet explosives following the ICAO convention of 1991. Following U.S. Senate ratification of the convention in 1993, the U.S. military added DMNB to plastic explosives in 1995. 4   By contrast, plastic explosive devices, for instance, are much harder to detect because they can cause a devastating explosion without any container. To detect these devices, it is generally necessary to detect the plastic explosive itself.

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--> luggage or gift boxes, so that they will not be detected before they explode. Therefore, the ability of the available detection technologies to function despite this concealment must be considered. Detection Scenarios Three scenarios for the detection of bombs containing black and smokeless powders are considered in this report:5 The portal scenario applies in locations where all people or packages entering an area must pass through a few, well-monitored checkpoints. The typical example is the security checkpoint at airports. The suspicious package scenario involves the discovery of a suspicious package in which an explosive device may or may not be concealed. An example is a box making ticking noises placed at the door of a women's health care clinic. In the bomb threat scenario, there is reason to believe that an explosive device is somewhere within a large expanse, but the location is uncertain. For example, a person may have phoned the police to report that a bomb has been planted in a large office building. If a suspicious box or bag is located by security personnel searching the building, then the situation becomes the package scenario. This occurred in the case of the Centennial Park bombing in Atlanta in July 1996. Note that the detection problem is not equivalent in each of the three scenarios. The portal scenario represents the classic detection problem in which a bomb must be detected with high reliability and a low false-alarm rate in the midst of a large volume of innocent items. In the suspicious package and bomb threat scenarios, attention is already directed to a specific item or area, and the challenge is to determine if that particular item or area contains a bomb. This situation would also occur in the portal scenario if the initial screening detector indicated that a particular package might contain a bomb. These scenarios impose different requirements on detection systems. Portal systems are stationary; thus, large system size and high capital cost may be tolerable if the system has a high throughput and a low false-alarm rate. In the suspicious package and bomb threat scenarios, system portability and low cost are more important. In some locations, such as airports and federal buildings, detection equipment is already in place to monitor incoming packages routinely for the presence 5   A truck bomb or car bomb detection scenario was considered in the recent NRC report dealing with high explosives (NRC, 1998). Such a scenario is not considered relevant to black and smokeless powder bombs because of the higher cost and the containment requirements.

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--> of bombs and other dangerous items. The available data suggest that this screening for explosives has been an effective deterrent against bombings in those areas. The presence of such equipment also acts to improve perceived public safety in these areas. If similar monitoring could be done cost-effectively and portably at all potential bombing locations, the deterrent effect could be expanded and the likelihood of bombings could be significantly reduced. However, as discussed in Chapter 1, a large number of deaths and injuries from black and smokeless powder bombs has occurred in locations for which regular screening would be technologically or practically infeasible (see Table 1.4). While much progress has been made in improving the detection of explosive materials with new technologies, current equipment can be expensive and is not always sensitive enough or appropriately configured to detect all types of devices that use the powders that are the focus of this study. This chapter summarizes the generic classes of detection equipment and comments on their applicability to detection of various powder devices in the three scenarios described above. Potential markers are then considered in light of how they could enhance detectability in the situations in which detection of unmarked explosive devices containing black or smokeless powder is difficult. Potential problems with the markers are also discussed. The technologies commented on in this chapter are discussed in greater detail in the recent NRC report, Containing the Threat from Illegal Bombings (NRC, 1998). The same terminology is used in this chapter as in that study. Detecting Improvised Explosive Devices Containing Unmarked Powders Assessing the desirability of adding markers to black and smokeless powders requires an understanding of current capabilities for detecting devices that use unmarked powders. Further, since large stocks of unmarked powders are available in commerce, then even if a marking program were to be initiated, it would still be important to be able to detect devices using these powders. As discussed above, the two basic ways to find a black or smokeless powder bomb are to detect the container or other bomb hardware, or to detect the black or smokeless powder within the container. The performance of current detection technologies in the scenarios of interest is summarized in Table 2.1 . Portal Scenario A wide variety of equipment is available to detect explosives in the portal scenario, including metal detectors, x-ray machines having various levels of sophistication, and vapor/particle detection systems (NRC, 1998). In some cases, the equipment is both costly and immobile. For example, an x-ray computed tomography detector can cost as much as $900,000 and is approximately the size

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--> TABLE 2.1 Current Detection Techniques for Unmarked Powder Devices Detection Scenario/ Technology Object Detected Comments Portal X-ray Container/device Effective, high throughput; not usable to screen for devices carried by people Metal detector Container/device Effective if device contains metal; can detect devices carried by people Vapor/particle Powder New technology aimed at detecting high explosives; capabilities for detecting powders not fully determined Package X-ray Container/device Portable, lower-cost systems available for use by bomb squads; helpful in identifying presence of bomb, rendering safe, and providing evidence afterward Metal detector Container/device Effective if device contains metal Vapor/particle Powder Lower-cost, portable systems under development; capabilities for detecting powders not fully determined Dogs Powder Effective, though exact chemicals detected by dogs and their sensitivity to powders inside well-sealed devices are not well understood Bomb threat Dogs Powder Uniquely effective owing to both high sensitivity and self-guided searching capability of a minivan.6 Such machines could be used at a few high-risk locations where the portal scenario applies, but would be difficult to use in the package scenario and impossible for the bomb threat scenario. In the case of black and smokeless powder devices, the presence of a container simplifies the detection problem considerably. The most common containers, which may be metal, plastic, glass, or cardboard, must have sufficiently strong walls to enable the buildup of the high internal pressures necessary to yield an effective bomb.7 Thus, container walls, which typically have a higher density than either the powder fillers or the surroundings, are likely to be visible on standard x-ray systems. 6   The CTX-5000 Series computed tomography detectors are roughly 14.5 feet long, 6.7 feet high, and 6.25 feet wide, and weigh approximately 9,350 pounds. Manufacturer's product literature, 1998. 7   Note that bombers have been known to pack nails or tacks around the container to increase the number of dangerous fragments flying around when the bomb explodes. If such additions are metal, then such a device is considered for record-keeping purposes to be in a metal container, even if the powder is actually encased in some other material.

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--> Standard x-ray machines have a high rate of throughput that makes them practical for routine screening. In addition, the effectiveness of such machines is well known publicly. Therefore, they not only serve to detect illegal devices but also merely by their presence can be a deterrent. The drawback to the use of x-ray machines at portals is the fact that they cannot be used to inspect humans because of exposure concerns. Therefore, x-ray equipment is often used in combination with metal detectors. However, while the x-ray detectors are capable of finding all sorts of containers, whether metal, plastic, glass, or cardboard, the metal detectors are limited to detecting a metal device concealed on a person, such as a pipe, nails or tacks, or a metal initiation mechanism. Several detection systems can detect explosive vapors emanating from a device, assuming that an air sample taken near a package containing an explosive device will contain enough vapor from the explosive material to be detectable. Equipment that uses this approach includes thermo-redox detectors8 and electron capture detectors (NRC, 1998). The size of the equipment required for sample capture and analysis is often quite large. The resulting limited mobility of the detection equipment means that such instrumentation could be used in portal and perhaps package scenarios but not in the bomb threat scenario. Other factors that could limit the effectiveness of vapor-based detection systems for devices using black and smokeless powders are the low volatility of some powders and the enclosure of the powders within pipes or other containers. The vapor pressure of single-base smokeless powders, black powders, and black powder substitutes is much lower than that of other smokeless powders,9 and the amount of vapor expected to escape from a typical bomb container has not been established. Several detection systems currently available can use samples obtained from the surface of a package or the handle of a bag. Such equipment includes ionmobility-spectrometry detectors and chemiluminescence detectors (NRC, 1998). These machines are similar to those based on vapor samples except that the reliance on significant volatility of powders is removed. When a sample from the exterior of a case is tested, the assumption is that handling an explosive material or device cleanly is difficult. Very often, bomb makers will get trace elements of the powder on their hands or on the exterior of the package containing the device. Therefore, the success of such detection methods is independent of the type of container used to make the device and of the type of powder, and these detection techniques can be expected to be effective on all types of devices in the portal and package scenarios in which physical sampling of people or items is permitted. One disadvantage is the potential for false-positive alarms attributable to small 8   Manufacturer's literature for the Scintrex EVD-3000. 9   The nitroglycerin in double-and triple-base powder can be readily detected by explosives vapor detectors.

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--> amounts of powders present on people who have had legitimate contact with such powders through reloading or manufacturing activities. Dogs have demonstrated their ability to detect a wide range of smokeless powders, black powders, and black powder substitutes, and currently can be trained to detect devices containing any type of powder (Krauss, 1971; U.S. Department of the Treasury, 1997).10 However, they can quickly become tired and are not well suited to the task of routine screening of large volumes of material, such as would occur in the portal situation. One technology that may hold some promise for the future is the development of an ''artificial dog's nose"—an instrument that would mimic the mechanism of canine olfaction but would not be subject to fatigue. Currently, research is under way on devices that employ the molecular matching techniques thought to be utilized by dogs. While currently still in development, there is some hope that such equipment will provide a relatively low-cost, portable alternative to actual dogs.11 Suspicious Package Scenario Portable standard x-ray systems are currently used to examine suspicious packages. For example, a basic portable model that can fit in the trunk of a large car and costs on the order of $20,000 is capable of providing an image of a suspicious package in real time.12 There are several benefits of using x-ray machines in the package scenario. First, the machine constructs an image of the contents of the suspicious package that can be recorded on film and preserved or analyzed. Such an image provides information about the type of device and the location within the package that will be useful to the people in charge of preventing an incident. In addition, the picture could be used as evidence later, even if the package is destroyed in a render-safe procedure or accidental detonation. Finally, x-ray images are constructed by analyzing variations in density; therefore, x-ray equipment would be capable of detecting any type of powder in any type of container. Vapor or residue detectors are becoming available that might be used to examine a suspicious package, but the results are likely to be less definitive than an x-ray showing the presence of a container, initiator, timer, and so forth. The use of dogs is another detection system known to be effective in examining suspicious packages. Dogs can be trained to detect a variety of black and 10   Also based on personal communications with Lyle Malotky, Federal Aviation Administration, May 12, 1998; Ed Hawkenson, U.S. Secret Service, August 7, 1998; David Kontny, Federal Aviation Administration, July 1998; and Walt Burghardt, Lackland Air Force Base, July 1998. 11   Personal communication from Regina Dugan, Defense Advanced Research Projects Agency, May 29, 1998. 12   Manufacturer's literature for the SAIC RTR-3.

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--> smokeless powders. However, black and smokeless powders emit a bouquet of odors, and it is not understood to which specific chemical compounds the dogs are actually reacting and whether, once trained to detect one kind of powder, they can learn to detect another kind with a different bouquet (Rouhi, 1997). In addition, while researchers contacted by the committee have found that the operational sensitivity of dogs to small concentrations of powder vapors is quite high, their ability to detect powders in well-sealed containers, such as pipe bombs, has not been fully explored.13 As with the portal scenario, the development of an inexpensive, portable vapor detector that would simulate a dog's nose could provide significant benefits. Bomb Threat Scenario At present, the only method available for searching a large-area for the presence of a bomb is canine or human examination. Dogs combine high sensitivity to powders along with independent searching capability, and thus enjoy a major advantage over other detection systems in this scenario. All other systems require close proximity to the device in order to function properly. In the event that an inexpensive electronic detector were developed that would simulate the function of a dog's nose, this might provide a viable alternative. In light of the above discussion, it is clear that of the detection technologies currently available, the standard x-ray imaging systems are the best available method for detecting devices containing unmarked explosives in the portal and package scenarios. Beyond detection, x-ray equipment also provides useful information that can assist in render-safe procedures and evidence gathering, and this equipment, when combined with metal detectors in the portal scenario, seems to be sufficient. In the bomb threat scenario, no current technologies seem to be applicable other than a thorough search by people or dogs. It is to this scenario that markers might bring the most added value. Markers for Black and Smokeless Powders Characteristics of an Ideal Marker The addition of markers to smokeless or black powder is designed to enhance detection, particularly through low-cost, simple systems. In assessing the value of any particular detection marker, it is useful to consider the characteristics of an ideal marker, even though such a marker may not presently be attain- 13   Many pipe bombs have holes in the pipe that allow the fusing or electrical wires to be accessible to the bomber. If the holes are not completely sealed, vapor exiting such holes may facilitate canine detection of these devices.

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--> able in practice. These criteria are not of equal importance. If the occasion for adding markers arises, choices will have to be made about which criteria are the most significant, based on the data then available. No real or perceived health or safety risks. The ideal marker would not adversely affect safety in any way. This implies that not only would it avoid changing the performance parameters of the powders, but it would also not adversely affect the health or safety of powder workers, powder users, or the general public. The ideal detection marker system would be fully accepted by the public. In addition to having no real risks, the ideal system would also have no perceived risks. The ideal system would be unobtrusive and, when implemented, would not cause significant delays or inconvenience to the public. Wide applicability and utility for law enforcement. The ideal detection marker would be applicable to all smokeless and black powder threats. It would be versatile and could be used in a wide variety of configurations and scenarios. For example, the detection marker system could be used in airports to screen passengers, carry-on items, and checked baggage. It could be used to screen vehicles passing through checkpoints such as building entrances, parking garage entrances, stadium entrances, and through freeway exits. It could be used by the U.S. Postal Service for nonintrusive scanning of mailed packages. An ideal marker system also would allow remote interrogation of suspicious packages or vehicles. Chemical and physical compatibility with black and smokeless powder . The ideal marker would be compatible with all black and smokeless powders and have no measurable effect on powder characteristics. That is, presence of the marker would have no effect on performance, safety, sensitivity, stability, shelf life, or ballistic properties. In all respects, the powder, either with or without the ideal marker, would behave in exactly the same way. See Appendix G for a discussion on the types of tests necessary for investigating chemical and physical compatibility and for a representative listing of organizations capable of conducting such tests. No adverse environmental impact or contamination. The ideal detection marker would not adversely affect the environment in any way. It would have no negative impact on the atmosphere, the soil, the water, or the food chain. The lifetime of the ideal marker would be comparable to the shelf life of black and smokeless powders; the marker would biodegrade or spontaneously disintegrate and, consequently, would not build up in the environment. Low costs to various links in the chain of commerce. The ideal marker would be inexpensive, a small fraction of the total cost of the black or smokeless powder. This low cost would include the cost of the marker itself, as well as all manufacturing, distribution, and tracking costs associated with its addition. It would be safe and simple to incorporate the marker into production of the powder and would have minimal impact on the production process. In addition, corre-

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--> sponding detection equipment costs would be low enough to be affordable for a variety of applications (e.g., local law enforcement, train stations, building entrances). Ideally, a single marker should be used for all smokeless and black powders. A single marker simplifies detection, lowers marker cost, and lowers detection system cost. This scheme also reduces liability risks since all manufacturers mark with the same material. Unique signature impossible to mask or contaminate. The ideal detection marker would be impossible to remove or shield and would be impervious to countermeasures. With unenhanced human senses, the marked black or smokeless powder would look and smell exactly like unmarked powder. The presence of the marker would only be discernible with state-of-the-art detection technology. The marker should not be common in nature or industrial use in order to ensure that the natural background is low or nonexistent. Unique information that is easy to detect. The ideal marker would ensure that black or smokeless powder detection is straightforward and unambiguous, requiring little or no operator training or subjective evaluation. It would have sufficient signal strength (and/or background suppression) to be rapidly detected, permitting high throughput of screened objects (people or things) passing through the detection system in any orientation. The false-alarm rate would be zero, and the probability of black and smokeless powder detection would be 100 percent. Detection equipment would be portable, compact, robust, and would require little maintenance. Appropriate lifetime. In addition, the lifetime of the ideal marker would be comparable to the shelf life of the marked material. Black and smokeless powders are designed to remain functional for several decades, and, if stored properly, will last a good deal longer. Approaches to Marking The two basic approaches to marking powders are active marking and passive marking. Both require adding some substance or material to the powder. An active marker continuously emits some kind of signal that announces its presence; such a signal could be a chemical vapor, light, sound, radiowaves, or radioactive emissions, such as x-rays or gamma rays. An example of an active marker is an unstable atom that spontaneously decays by emitting detectable particles and/or radiation. In contrast, a passive marker must be "probed" before its presence can be detected. An example of a passive marker is a dye particle that produces visible fluorescent light when ultraviolet light is shined on the material. There are three classes of markers discussed here: active chemical vapor markers, active radiation-emitting markers, and passive markers. None of the current marking schemes are without potential difficulties. However, the various technologies are worth discussing in the context of marking powders and of enhanced detection for building or large-area searches. A more extensive

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--> description of the various marking technologies can be found in the previous NRC report (NRC, 1998). Vapor Markers The most obviously useful markers in the bomb threat scenario are vapor markers. Because ICAO adopted this technique for use in plastic and sheet explosives, vapor markers are the markers about which there is the most information. Double-base propellants can be readily detected by vapor detectors owing to the presence of volatile nitro compounds, such as nitroglycerin. However, the minimum amount of black powder, single-base smokeless powder, and composite propellant detectable by various detection technologies focused on powder, rather than devices, would be much lower if the powder contained an active vapor marker than if the powder were unmarked. Unlike detectors based on interrogation of powders by nuclear or x-ray radiation, vapor marker detection is applicable to all scenarios, including detection of explosives concealed on people. The effective detection of powders through detection of vapor markers could only be prevented by complex countermeasures. Of the four markers approved for use in plastic and sheet explosives under the ICAO convention—2,3-dimethyl-2,3-dinitrobutane (DMNB), ethylene glycol dinitrate (EGDN), ortho-mononitrotoluene (o-MNT), and para-mononitro-toluene (p-MNT)—DMNB best meets the overall criteria for a suitable detection marker for high explosives, and has been added to plastic explosives in the United States since 1995.14 DMNB is unique and apparently has no known industrial applications. There is little likelihood that this compound will be present in the background.15 Also, relatively low levels of DMNB are readily detectable with a commercial explosive-vapor detector that is portable and low cost, coupled with the use of a proper sampling interface (ICAO, 1991). However, in considering the incorporation of DMNB into powders, there are two areas of potential concern. The first is the lifetime of DMNB, which is relatively short in comparison to the typical shelf lives of smokeless and black powders which can easily extend past 20 years. The second is introducing a substance with the toxicity level of DMNB into a commonly used material.16 14   James P. Rubin, State Department, press release, June 22, 1998. 15   If DMNB were to be used to mark smokeless or black powders, this might cause an increase in false alarms at bomb detection checkpoints owing to traces of the marker adhering to the millions of people who use these powders legally. 16   The toxicity level of DMNB was a less pressing issue when it was considered for use in high explosives, which, even unmarked, have a toxicity level comparable to that of DMNB.

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--> Radiation-emitting Markers Among active marking alternatives to vapor markers, radiation-emitting markers—coincident gamma-ray emitters specifically—were identified as the most promising technology for marking high explosives in the 1998 NRC report. When considering the marking of smokeless and black powders, an optimal radioactive marker would emit a readily detected characteristic signature, emit sufficiently penetrating radiation to reach the detector, be detectable at levels below the natural radioactive background, have a half-life comparable to powder shelf life (which can be greater than 20 years), and be inexpensive to implement. A gamma emitter would be necessary to ensure sufficiently penetrating radiation, and the gamma rays would need to have an energy of 0.5 MeV or greater to prevent countermeasures such as shielding.17 Certain radioactive isotopes decay by emitting two or more gamma rays simultaneously. These isotopes are detectable at extremely low concentrations; the detectors only count events in which two gamma rays arrive within a narrow time window. Thus, isotope concentrations can be used that are actually below the natural radioactive background. Within this category of isotopes, the three possible candidates for use as radioactive markers are the isotopes of cobalt (60Co), bismuth (207Bi), and sodium (22Na). The 1998 NRC report noted that, of the three, 60Co has the best set of characteristics for explosives marking. The isotope is available and relatively inexpensive because hospitals use sizable quantities (kilocurie amounts) as a radiation source. Also, the isotope emits a pair of nearly isotropic gamma rays with energies of 1.2 MeV and 1.3 MeV that would simplify the technical requirements for detection equipment. An important issue for marking of powders, however, is that the half-life of this isotope is 5.3 years, distinctly shorter than the expected shelf life of smokeless and black powders.18 The half-life of 207Bi (30 years) would be more suitable for powder marking; on the other hand, this isotope emits a pair of mismatched gamma rays (0.57 MeV and 1.06 MeV) that would require a pair of energy windows for each detector. Currently, the amount of research and extent of demonstrations for the 207Bi marking scheme are not nearly as extensive as the work done on the 60Co scheme (JASON, 1994). Note that the half-life of the positron-gamma-emitting 22Na (2.6 years) is probably too short for either explosives or powder marking. 17   At these energies, the amount of metal required to shield the signal becomes prohibitively large. 18   To some extent this problem could be countered by simply adding a higher concentration of isotope to the powders. However, higher concentrations might raise health, safety, and environmental concerns.

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--> The radiation levels caused by marking of explosive materials with radioactive isotopes would be very low—comparable to or below background.19 However, it is worth considering not only the actual potential health impacts but also the perceived risks. The public's negative perception about radioactivity may make it exceedingly difficult to introduce such markers into a widely available commercial product. Other Marking Approaches Passive markers for explosives detection have been discussed in great detail in several JASON reports, although powder detection was not specifically considered (JASON, 1986, 1987, 1988, 1994). None of the passive markers that have been proposed are currently close to meeting the characteristics of the ideal marker, and the problems inherent in the majority of concepts make implementation either impossible or totally unacceptable. When discussing the potential value and difficulties involved in adding markers to smokeless and black powders, it is important to focus on the situations in which current detection of unmarked powders is insufficient or costly. Such situations include detection in the bomb threat scenario of any powder-based device, particularly one containing black or single-base smokeless powder. In this situation, portability and ease and speed of operation are of paramount importance. Therefore, for many of the passive markers the cost and size of the detection equipment preclude their usefulness. The marking techniques with expensive and unwieldy equipment include high-Z x-ray fluorescence markers, high-Z x-ray absorption edge markers, thermal neutron absorbers, and rare element nuclear magnetic resonance markers. Other passive markers—such as dipole or diode markers—are physically incompatible with powders and easily susceptible to countermeasures (JASON, 1994). Finally, a third class of passive markers—thermal neutron or deuterium markers—are so costly to purchase or to add to the powders that their consideration at this time is not practical.20 Discussion The committee focused its attention primarily on the applicability of vapor markers to black and smokeless powders. This choice was owing in part to the 19   It has been estimated that pound for pound, bananas have three times the radioactivity (owing to naturally occurring radioactive potassium, 40K) as would bulk explosives marked with 60Co (JASON, 1994). 20   Note that more details on the difficulties in all of the passive marking techniques mentioned above are given in the report Containing the Threat from Illegal Bombings (NRC, 1998).

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--> availability of ICAO markers, specifically DMNB, which is currently in use in the United States for the marking of plastic and sheet explosives. In addition, in contrast to some of the other marker technologies, the committee felt that vapor markers would be applicable to each of the detection scenarios discussed in this report (see Table 2.1). The vapor markers were viewed as a possible enhancement to the capability of current systems, such as the use of dogs, to detect the more volatile components or impurities in black and smokeless powders. The cost of marking plastic and sheet explosives with DMNB is expected to reach $0.20 per pound of explosive for marking at the 1 percent by weight level (NRC, 1998). If this same cost were applicable to powders, it would add between 1 and 2 percent to the retail cost of the powders. As noted in Table 2.1, current portal detection systems, especially x-ray systems, are likely to be effective in detecting the containers of black and smokeless powder devices in this scenario. Accordingly, vapor markers would likely add little to detection capabilities for these devices in the portal scenario. In the suspicious package scenario, portable x-ray systems are considered effective in detecting the device containers, and dogs are considered effective in detecting black and smokeless powders in the devices. However, the ability of dogs to detect a wide variety of different powders and their sensitivity to powders contained in well-sealed devices is not well understood. If their detection capabilities turn out to be limited in this regard, it is possible that a vapor marker could address some of these limitations. Before a marker such as DMNB could be used, however, issues relating to its loss of effectiveness over time owing to volatility, its toxicity compared to that of the powder itself, and the sensitivity of dogs to this marker would have to be addressed. A marker would also make possible the use of a vapor detector tuned to detect that specific marker. In the bomb threat scenario, the only detection options currently available are searches by humans or dogs. Canine searches are likely to be effective, subject to the potential limitations discussed above in the package scenario. The presence of a marker might enhance the speed with which a canine could locate a bomb, or in the future make possible the use of a vapor-sniffer device (artificial dog's nose) that could facilitate the search by following a concentration gradient of the vapor marker to the device's location. The benefits of a marking program are limited by bombers' ability to obtain unmarked powders, either from existing stockpiles, or by manufacturing the powders themselves from precursor chemicals. Given the large volumes of commercial and military surplus powders available and their long shelf life (at least 20 years), even if a full-scale marking program were implemented today by powder manufacturers, potential bombers would have access to unmarked powders for many years to come. Clandestine manufacture of black powder from its constituent chemicals would provide another way of evading a marking program.

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--> Findings and Recommendations The detection of improvised explosive devices that contain black and smokeless powders must be considered in the context of the materials that are used to make the devices and the situations in which the devices are used. Finding: Pipe bombs and similar explosive devices that use black and smokeless powders can be detected by exploiting both the properties of the powder itself and those of the container. Finding: Current x-ray systems are capable of detecting explosive devices containing black and smokeless powders and are effective when placed at a portal or when used in portable equipment to examine a suspicious package. Current x-ray technologies are not suitable for quickly screening large numbers of packages or for performing large-area searches. This method of detection has the advantages that the x-ray image provides information about the construction of the device that can be useful in render-safe procedures, and the image can be preserved on film to be used as evidence in an investigation or prosecution. Thus, x-ray systems are very useful in portal scenarios, such as for examination of the packages that come into a company mailroom or that are carried onto a plane.21 Portable x-ray machines can also be carried to the location of a suspicious package and used to determine its contents. The limitations of x-ray equipment relate to its weight and method of analysis. Because the current portable x-ray detectors are roughly double the size of a large suitcase and must be set up around a specific package, x-ray technology is of limited use when searching large open areas or buildings in response to a bomb threat. Also, x-ray images must be examined by trained personnel or require the use of complex pattern recognition software to determine if the contents of the package resemble an explosive device. That is, this technology cannot be effective for screening large numbers of packages, as would be needed for example, to examine all baggage or mail shipped by airlines or all packages transported by a commercial delivery service. Finding: Both black and smokeless powders contain volatile compounds that are detectable by dogs. Canine searches are the only viable means of conducting large-area searches for hidden explosive devices. Dogs are used by the U.S. 21   For health reasons, x-ray equipment cannot be used to screen people entering through a portal; instead, metal detectors are used for this purpose. However, unlike x-ray systems that enable security personnel to view an image of the interior of a package and therefore detect a wide array of devices, metal detectors can only indicate metal objects concealed on a person and therefore are only able to detect devices that utilize metal containers or include other metallic components. Thus, metal detectors are more easily circumvented than x-ray systems.

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--> Secret Service, the Bureau of Alcohol, Tobacco, and Firearms, and the Federal Aviation Administration to detect explosive materials. They are also used by bomb-scene technicians to help investigators locate powder evidence that may not be visible to humans. The experience of the agencies that train such dogs and study their abilities has demonstrated that the dogs are capable of recognizing the presence of black and smokeless powders. However, there is not complete understanding of the biochemical mechanism of canine olfaction, the circumstances that can interfere with canine detection of powders, or the exact chemicals and concentration of chemicals that dogs are able to detect. RECOMMENDED ACTION: Further research should be conducted on canine detection of bombs made with black and smokeless powders enclosed in various containers. Research should also be conducted on the development of inexpensive and portable instrumental sensors that mimic canine detection. Better knowledge of how dogs detect devices containing black and smokeless powders would enable more efficient and appropriate use of dogs in examining large-areas and buildings and would assist in the development of instruments capable of mimicking the methods by which dogs detect powders. Depending on their size, cost, and speed, such instruments could be used for large-area searches and for high-throughput, routine screening of packages. Finding: Detection markers added to black and smokeless powders could assist in the detection of explosive devices in several situations: large-area searches, examination of suspicious packages, rapid and routine screening of large numbers of packages, and enhancement of canine ability to detect black and smokeless powder bombs. A detection marker's value to law enforcement for detecting explosive devices containing black and smokeless powder would depend on the properties of the added marker, such as its degree of detectability through a sealed pipe or layers of wrapping, and on the portability and cost of the associated detection equipment, as well as its range and sensitivity. Finding: No current marking system has been demonstrated to be technically feasible for use in black and smokeless powders. While vapor markers have been successfully introduced into plastic and sheet explosives, there has not been a definitive study of how such markers might work in black and smokeless powders. Some issues of concern include the high volatility and the toxicity of vapor markers such as DMNB. In marking techniques that use radiation-emitting isotopes such as cobalt-60, the concentration of isotope required to produce the desired detection sensitivity has not been established. A potential limitation of such a marking system is the public's negative view of radiation, even at low

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--> levels, as well as the technique's suitability for use only in the portal scenario, owing to the costly and nonportable nature of the associated detection equipment. RECOMMENDATION: Detection markers in black and smokeless powder should not be implemented at the present time. X-ray systems and dogs currently provide a strong capability for detecting bomb containers and unmarked black and smokeless powders in the scenarios considered by the committee, and most powder bombings currently take place at locations in which deployment of bomb detection systems is not practicable (see Table 1.4). Therefore, the committee believes that the effectiveness of a marking program would be limited at the present time. Institution of a marking program would incur significant costs. At the current level of fewer than 10 deaths and 100 injuries per year and very few terrorist incidents, the committee believes that the benefits are not sufficient to justify such a marking program. If the threat were to increase substantially in the future, and test data were available, benefits might exceed costs, and a marking program might be warranted. A marking program for black and smokeless powders would be justified only if three criteria were met: the frequency and severity of black and smokeless powder bombs were found to be high enough to justify marking; the markers first were thoroughly tested and found to be safe and effective under conditions likely to be encountered in the legal and illegal uses of the powders; and the social benefits of markers were found to outweigh the costs of their use. RECOMMENDED ACTION: Research should be conducted to develop and test markers that would be technically suitable for inclusion in black and smokeless powders. The marking schemes studied should be those that would assist in large-area searches or rapid screening of a large number of packages. More information and work are needed on marking technologies. Should it become necessary for policymakers to mandate the implementation of more intensive control procedures, the agencies concerned would then have the data necessary to make informed decisions about markers.