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SUMMARY With the current high level of security awareness in the transit environment and the considerable proportion of bomb threats that are hoaxes, law-enforcement and transit- security officials need decision-making tools to investigate threats before taking actions such as an evacuation order. The use of technology is one option for safely investigat- ing bomb threats. In addition to the traditional practice of using trained dogs, state-of-the-art tools are available for detecting the presence of explosives, including portable explosive trace- vapor detection devices. Some transit agencies deploy bomb-sniffing canine units, but the dogs can only work a short period of time before they are fatigued. Many of the technology-based detection devices are not subject to fatigue, but they have not been used on a routine basis in transit systems. This report addresses the need to determine the usefulness of existing portable explosive detection devices (EDDs) in a transit environment. The audience of this report includes transit agency general managers, middle- to upper-level managers, transit-security and/or law-enforcement officials, and local or state law-enforcement representatives. The Federal Aviation Administration (FAA) is the first transportation agency that has deployed EDDs (for use at airports). The technology is predicated on trace-vapor detection of explosive residues using ion mobility spectrometry. The methodology for this research included selecting commercially available portable EDDs and testing them in the laboratory as well as in field tests in actual transit agency environments such subway stations and platforms, bus stations, tunnels, and repair facilities. The test method for the field tests was semi-quantitative and reproducible, and it tested the full cycle of detection capabilities from sample collection to identifi- cation. The test strategy was based on methods used by the Transportation Security Administration (TSA) Howard Center (formerly the FAA Technical Center), but was adapted to the needs of the study. There are a number of explosive detection systems that are designed around vapor and trace detection. Unfortunately, the majority of modern explosive compounds dis- play an extremely low vapor pressure and make vapor-based detection difficult. The vapor pressure is the gas phase pressure due to the material that is found in the air APPLICABILITY OF PORTABLE EXPLOSIVE DETECTION DEVICES IN TRANSIT ENVIRONMENTS
above the explosive. Materials that are volatile have a very high vapor pressure and are inherently easier to detect. Materials that have a very low vapor pressure (like most explosives) are inherently harder to detect. For the purposes of this study, vapor detection capabilities were not tested. This report investigated a number of currently available and emerging technologies that are suitable for portable instrumentation for explosives detection. Many of these technologies are based on trace or vapor detection and would include Ion Mobility Spectrometry (IMS), Surface Acoustic Wave (SAW) detection, electrochemical detec- tion, and fluorescent polymers. One of the key parameters to be compared is the rela- tive sensitivity of the equipment. The amount of material available in the gas phase or as a trace contaminant in typical applications is very small and makes detection very challenging. IMS is one of the leading technologies for field portable trace detection and was the type of technology used in this study. It is used in a number of security-related appli- cations to detect contraband items such as drugs, explosives, and chemical warfare agents (CWAs). A comparison between the portable EDDs and canine units was made under this study. The canine nose is able to spatially locate the source of a scent, allowing the rapid search of a large area. In addition, canines are able to distinguish the presence of explosives in complex environments and are much less susceptible to the problems of masking interferents. The disadvantages of using dogs are the extensive training requirements and their inability to work for extended periods. Costs are approximately $10,000 to purchase a trained animal and a $2,000 annual cost for care and feeding. For information on using dogs for explosive detection, see TCRP Report 86: Public Trans- portation SecurityâK9 Units in Public Transportation: A Guide for Decision Makers. In the decision-making process for transit agencies who are considering deploying portable EDDs, the acquisition, installation, training, operations, and maintenance costs associated with these devices are important factors. These costs will undoubtedly vary depending on the conditions and circumstances of the application. For example, screen- ing vehicles entering tunnels or underground garages and screening packages or other possessions of transit riders on the platform are two different applications of the devices. Another consideration is comparing the costs of using portable EDDs to the costs of using intensive hand searches or dogs trained to detect explosive residues. The onsite testing was undertaken at three major transit locations within the United States. The criteria for the transit site selection included system age, location, climate, and types of available systems. Collectively, the transit sites used to test portable EDDs were representative of the range of potential applications and reflected the nature of the perceived threat to transit systems. Specifically, the selected sites included diesel and compressed-natural-gas bus maintenance yards; diesel and electric rail (including commuter rail, subway, light rail, and street trolley); parking facilities (including garage and underground facilities); access points to transit operations (e.g., turnstiles, escalators, tunnels, and platforms); and other areas where suspicious packages may potentially be found. The portable EDD used for testing was relatively simple to handle and operate. It was proven reliable in detecting trace explosives while operating under a wide range of con- ditions. The devices are lightweight and very transportable. They proved to be reliable (no systematic failures) and to be able to operate for extended periods. On average, it took an operator less than 2 minutes to complete each test. One of the aims of this study was to uncover conditions that may affect these devices adversely, such as the existence of external fumes near cleaning closets, copy shops, hairdressers, restaurants, or around combusted diesel fuel. None of the external factors 2
3in these places seemed to significantly affect the outcome of tests. This report addresses a number of potential scenarios in the transit environment. In many of these situations, the trace detection equipment could offer meaningful aid. In others, the current tech- nology is problematic. Some of the scenarios addressed in the report are listed below: Abandoned or Lost Articles. In cases of suspicious packages, transit officials typi- cally call explosive ordnance disposal (EOD) units to evaluate the package, but it would be very desirable to be able to perform a screening prior to calling officials. The equip- ment used in this study appears to be reliable and sensitive enough to be used as a screen- ing tool, but it has some limitations. The portability, ease of operation, short setup time and sensitivity of the system makes it attractive for this application. However, taking swab samples is an issue when examining abandoned/lost articles because, in the case of a suspicious abandoned package, the operator may decide not to handle the package for safety reasons. In this case, the trace detection equipment provides little utility. Screening. Passenger screening does not seem to be a feasible use for this type of system. Lining up passengers for screening, as is done in airports, would cause mas- sive delays in commuter travel. In addition, a single station may have multiple entry points, leaving an attacker with the option to bypass the screening point. Post-Blast Analysis. An application of the EDD is the use of the device to evaluate post-blast residue. The EDD may be a tool to aid in collection of evidence in the field. Information collected from interviews with transit officials suggested that this tech- nology could provide significant help in investigating bomb crime sites. After a blast, railcar parts can be investigated for residues of explosives.
