Opportunities to Improve Airport Passenger Screening with Mass Spectrometry (2004)

Explosive trace detectors have become a part of the layered, system-of-systems aviation security structure in use at various airport locations. Dogs are used to screen a number of items, from foodstuffs to bombs; IMS systems are used to screen carry-on bags; and metal detectors and x-ray systems screen for concealed weapons. Each detection technique has strengths and weaknesses, and, as discussed in Chapter 2, the committee believes that mass spectrometry will find use as an adjunct for many of these detection systems. Again, the key advantages of mass spectrometry are the improvement in chemical specificity (enabling a lower alarm threshold while maintaining a low false alarm rate) and its applicability to a variety of threat substances. Security advantages accrue directly from these features, including faster diagnosis of potential threats, greater capability for detecting new threat species, and improved instrument performance—especially under unfavorable background conditions. MS also offers a standard against which to evaluate the performance of existing IMS instruments.

Chapter 2 explored the potential advantages of MS-based trace detection systems in detail. This chapter offers one plausible scenario for integrating MS instruments into an airport security system, as part of an overall effort to improve trace detection capabilities. It envisions a phased introduction process that involves several generations of MS-based systems, adaptations that will be necessary for these systems to function in an airport checkpoint and screening context, and future technological developments that might allow the instruments to address broader security issues, such as monitoring of the air handling system.

Below, the committee describes an evolution of various generations of mass spectrometers that would provide increasingly capable trace detection systems and at the same time decrease costs and improve functionality. The deployment is assumed to take place in a large urban airport; the estimates provided for instrument costs are rough, based on committee members’ experience with the research, development, and commercialization of analytical instruments.

As noted in Chapter 2, current sampling methods that involve wiping selected carry-on baggage are time consuming, prone to operator error, and incomplete in coverage. There have been proposals to automate this process using lasers or other methods of safely dislodging material from the entire bag. If these efforts are successful, they would greatly enhance trace detection utilizing any technology. Development of engineering prototypes and agreement on specifications for the final product might take

1 to 2 years, with deployment not likely before year 3. This development should be concurrent with any existing and new trace technology efforts and coordinated with them.

The rationale for current trace detection systems is to screen passengers for the presence of explosive residues or vapors. However, for reasons of safety and respect for personal privacy, sampling is limited to the wiping of hard objects (computers, briefcases, and carry-ons) that the passenger has touched—passengers themselves may not be subjected to radiation, have their skin or clothing wiped, or be otherwise touched by an operator. Thus, current sampling methods might fail to detect traces of a bomb or other threat substance that adhere to a terrorist’s skin or clothing.

One option for sampling the passenger directly without raising safety or privacy issues is to introduce portals in which the passenger walking through is subjected to a puff of air intended to dislodge particles of threat materials from skin or clothing and to collect and concentrate the resulting air sample. Research and development already conducted by the TSA, the national laboratories, and private industry have resulted in several portal prototypes, and models of the portals that use IMS or MS-based detection have been tested by the TSA. Issues that remain to be resolved include the appropriate limit of detection, the acceptable rate of false positives, and especially, passenger acceptance and restrictions on passenger flow. These issues need to be resolved by testing in an actual airport environment.

Operational tests of these units in selected airports could begin within 1 year. Testing could likely be completed in an additional 6 months to 1 year, with final specifications and testing protocols formulated in the second or third year. While the IMS-based detectors in these portal systems are essentially the same as those currently deployed for bag screening, the MS version would require additional development and testing to make it more rugged and suitable for installation in a concourse environment. The MS equipment must be designed in accordance with human factors principles for both interface design and operator training. Addressing these issues might delay wider deployment of these first-generation MS-based systems for an additional year. It would be very important that the specifications for the MS system include lower limits of detection, and the design should anticipate that future models will be programmed for analysis of additional threat materials. This dual deployment would allow comparison of MS and IMS technology in terms of false positives and probability of detection at a lower detection limit. With a simple coupon inlet, this machine could also be configured to help resolve alarms from existing ETDs, as well as any other unresolved alarms from suspicious materials that are not covered by ETDs or dogs.

These portals are expected to be deployed at a limited number of security checkpoints. For a large urban airport, between 5 and 10 MS-based portals might be deployed at a cost of $100,000 to $150,000 per portal, an increment of $25,000 to $50,000 in initial costs over the comparable IMS portal. Operating costs for the MS-based portal are expected to be $2,000 to $5,000 higher per year than those for the IMS portal.

As discussed in Chapter 2, the combination of chromatography and MS has the ability to identify almost all types of organic molecules, and identification of the current list of threat materials covered by IMS in a single C/MS instrument configuration has been demonstrated.¹ However, covering an expanded list of target compounds with a minimum number of configurations of chromatography, ionization, mass

analysis, and detection will require additional development. Selecting the list of probable threat compounds and working out the methods for optimum instrumental configurations will require 1 or 2 years. Once defined, these configurations would then take another 1 or 2 years of instrument development to withstand the rigors of airport use prior to deployment. This second-generation MS detector would be designed to detect multiple threat agents from the beginning and would have to have a lower cost and better reliability than the first-generation systems.

Once developed, the second-generation MS detectors could be compared with the best available IMS devices at passenger checkpoints and portals.² They could be used to probe suspicious carry-on items. If available, dogs are often utilized to resolve this type of threat, which in extreme cases may require evacuation of the terminal to ensure safety. However, dogs are trained on only a small number of specific materials, and chemical and biological threats are not currently in their repertoire.

For a large urban airport, 10 to 20 second-generation instruments might be deployed at an initial cost of $100,000 to $150,000 per instrument. The incremental purchase and operating costs for these instruments relative to IMS instruments would likely be comparable to these costs for first-generation instruments, since there will also be cost reduction efforts with IMS systems.

The committee believes that this second-generation detection system could be deployed in the 4 or 5 years. Even were it not to be widely deployed because of cost or complexity, this system would serve as a gold standard against which to compare alternative technologies.

In this class of third-generation, automated MS instruments, the cost is assumed to be sufficiently low to permit use of a mass spectrometer in every passenger path. With automatic sampling, this device would be an add-on to the x-ray system currently in use for carry-on bags. With additional automatic sampling, this detector could be used in the checked baggage path as well.

A major benefit of this device would be to reduce the need for hand searches. Hand searches are expensive and slow down the overall throughput rate of carry-on and checked baggage. Procedures vary from airport to airport for handling the great variety of packed items, including foodstuffs, that trigger alarms. The success of the hand search requirement is also highly dependent on personnel training, and neither the hit rate nor the false alarm rate has been well established.

Once the advantages of the third-generation MS instruments are demonstrated, it could be decided whether this technology should be widely used in place of IMS. Prior to widespread deployment, the instrument would likely need to be redesigned to achieve a cost reduction of at least 50 percent, with improved reliability to match that of the much less complicated IMS technology. If the portal concept proves to be scientifically, economically, and socially acceptable, it would likely replace all procedures for sampling items the passenger has touched.

At a large urban airport, implementation of this phase would mean deployment of ~50 instruments that are assumed to have an initial cost of no more than $75,000 and an operating cost of less than $5,000 per year. If the superiority of the MS technique is sufficient, the needed R&D effort might well be undertaken by industry and would likely be completed within 2 years.

As future threats emerge, one can imagine attacks on the air handling equipment in either a transportation terminal or in the transportation vehicle. One concept of operations might involve the use of less sophisticated triggering detection devices that would provide immediate emergency rerouting or cessation of air movement and that would then activate the environmental monitoring MS device to identify the species that created the event.

This class of instruments is less well defined than the instruments discussed above and is only at the concept stage. For environmental monitoring, MS operation would feature a data path to a central control point and/or feed-forward warnings to checkpoints or other strategic posts to facilitate airport shutdown and evacuation. This is a scenario in which the false alarm rate must be very low, so that the performance of this mass spectrometer would have to be well established. If biological threats are to be considered, one could expect this device to be two or three times as expensive as the instruments described above owing to the added expense of sample collection and preparation.

In a large urban airport, 5 to 10 instruments might be required, depending on how much remote sampling could be utilized.

Finding 3: The many trace detection tasks that can be envisioned in airports will require MS-based detection systems with various levels of cost and performance; in some cases, years of R&D and testing may be required to produce MS instruments with the necessary specifications.

Technology development schedules depend strongly on government involvement, and the instrument costs and deployment times mentioned here are based on the committee’s best judgment of the difficulty of the detection task and practical issues associated with producing high-quality, field-usable instruments.

Recommendation 3: If TSA wishes to improve its trace detection capabilities, it should deploy MS-based detectors in a phased fashion, with successive generations of instruments addressing lower quantities of an expanded list of threat materials and more sophisticated security tasks. These tasks range from passenger screening at checkpoints to monitoring of the air handling system.

In conclusion, this report has examined the potential of one promising technology—mass spectrometry—to improve trace detection capabilities of explosives as well as chemical and biological threat agents in the aviation environment. Here, the committee has offered just one plausible scenario for deployment of MS systems. Subsequent committee reports will examine additional technologies and defensive strategies for addressing a wide range of terrorist threats.