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Explosives Detection

An adversary who wants to die trying to carry out a mission is one of the defining elements of the asymmetrical environment in which today’s security professionals must protect society from terrorism. The trend is evidenced by failed suicide attacks such as that attempted on Christmas Day, when authorities say Nigerian Umar Farouk Abdulmutallab tried to kill 289 passengers and crew on a Detroit-bound airliner using a bomb concealed in his underwear. Abdulmutallab’s attack failed due to its lack of sophistication and to the heroism of passengers and crew, but the threat is real and the next attempt may not be as amateurish. The incident highlights the importance of explosives detection technology that could help intercept the next attempt. Security Management looks at the evolving capabilities of such technologies, plus remaining limitations and concerns about privacy implications.

Emerging Technology

The threat of explosives, in particular those that might be directed at commercial aviation, has spurred research into new detection technologies as well as funding of efforts that could help speed commercialization to bring the results to the marketplace. Among the most promising works in progress are the following.

Liquids. Responding to the demand for quick detection of fluid-based explosives in common consumer liquid and gel containers, efforts at Forschungszentrum Jülich GmbH, an interdisciplinary research center in Jülich, Germany, have produced technologies that promise detection of liquid-borne threats through methods that are both rapid and uncomplicated for the end user, developers say.

The first technology, developed by Professor Norbert Klein at the Jülich center, is relatively simple. A liquid container is placed against the detection device, which emits radiation in the radio and microwave ranges. The device senses the test substance’s reaction to determine its conductivity and its dielectric constant, meaning the capability of the substance to hold an electric charge. The test takes less than a second and can detect triacetone triperoxide (TATP), other peroxide-based explosives, as well as alcohol, says Hugo Bibby technical director of Link Microtech, which is marketing the device in Britain for German firm Emisens.

The technology’s primary limitation: when it operates in the microwave range, it cannot test substances in metal containers. The system has undergone two successful airport trials in Europe and is currently under evaluation by the European Civil Aviation Conference, Bibby says.

Vapor trace. The greatest chemical detector in the world is a dog’s nose. Ross Harper, a senior staff scientist with ICx Technologies, lists the various factors that make dogs such effective sensors, whether they’re looking for table scraps or explosives: The surface of a dog’s olfactory membrane is up to four times larger than a human’s, and roughly 40 percent more of a dog’s brain is devoted to detecting scent. As a result, dogs can detect substances even if they are only present at 2 parts per trillion.

Researchers at various universities and the Defense Advanced Research Projects Agency have been working for decades to duplicate what nature has achieved with the canine nose. Those efforts have borne fruit, in particular the ion mobility spectroscopy and chemiluminescence technologies used in today’s explosive trace detection devices, like the hand-held and bench-top machines already in use at airports and security checkpoints around the world.

Other technologies that function at the micro and nano levels have also shown promise at detecting small quantities, and, at least one researcher says that they hold the promise of exceeding the sensitivity of canine olfaction.

Microelectromechanical systems, or MEMS, 1/1000th the width of a human hair can be engineered to bind to only one type of molecule, TATP for example. When that molecule binds to the device, the sensor detects the distortion of the fiber and registers a hit. More recent research conducted by scientists from Germany’s University of Bonn and the Max Planck Institute in Mainz have used “microbalances” made of quartz crystals, which vibrate at a known frequency, to detect contact with TATP with a sensitivity of 1 part per million.

Susan Hallowell, director of the U.S. Department of Homeland Security’s (DHS) Transportation Security Laboratory, acknowledged the promise of quartz microbalances, but noted the challenge of collecting enough air, quickly enough, to produce a high degree of selectivity from a sample.

Another research effort that is making progress is headed by scientist Tom Bruno at the National Institute of Standards and Technology (NIST). That team is developing what Bruno calls “headspace analysis,” meaning simply a sampling of the air over a test substance.

NIST’s technology relies on the attraction of certain molecules of an explosive to specially treated, super-cooled metal coils. A test sample is combined with helium, then passed over the coils. If present in the sample, the targeted molecules will bind to the coils.

The coils are rinsed with a solvent, which can then be tested for the presence of the target substance. The sensitivity of the test, which according to NIST could be adopted for use outside the laboratory, is currently two parts per billion. Bruno, however, tells Security Management that the technology holds the promise of detection at 10 parts per trillion, which would exceed canine sensitivity by a factor of five.

Terahertz scanning. Another technology that has government’s attention is that of Terahertz radiation, a band that is non-ionizing and eye-safe, which means that it could be used safely to scan both liquids and individuals for explosives.

More recent research on liquid-explosives detection at the Jülich center involves radiation at a higher frequency, in from the gigahertz to the terahertz range. Using a newer method of spectroscopy called Hilbert spectroscopy, the technology can measure transmission, reflection, and absorption of substances being tested, which increases accuracy. The test also takes less than a second, according to Jülich researcher Yuri Divin.

Divin and his fellow researchers are working toward development of a compact commercial prototype for the Hilbert spectrometry technology. He thinks it could be fully commercialized within two to four years.

Technology employing terahertz scanning, developed by TeraView Ltd. of Cambridge, England, holds the promise of scanning individuals for either trace or bulk explosives, even those concealed under clothing, according to TeraView CEO Don Arnone.

TeraView’s product, called the TPS Spectra 3000, is housed on a pair of wheeled carts, each about the size of an airline beverage cart. One cart bears a display monitor and the system’s analytic hardware; the other holds the equipment necessary for actual sampling via a sensor placed at the end of a fiber-optic cable.

As with all forms of spectroscopy, the process involves reading radiation. In this case, TeraView’s device emits a beam of radiation that passes unencumbered through clothing. At specific frequencies, however, the energy is absorbed by specific explosive molecules. The technology is already under evaluation at the U.S. Naval Surface Warfare Center at Indian Head, Maryland. It is scheduled for field tests by British aviation security authorities, Arnone tells Security Management.

Integration and Automation

Time and again, investigations by government watchdogs have demonstrated the limitations of human screeners to spot threats when they appear in images on machine monitors. This may be the result of natural shortcomings in human observation and cognition as much as the fault of apathy or distraction after too much time spent staring at the screen.

The Transportation Security Administration (TSA) wants automation that will remove the human element and, thus, the potential for human error. One solution may be what the agency calls automated target recognition (ATR).

Many vendors tout their products as offering ATR, because their software superimposes a box over an anomaly detected on a full body scan or over a large, potentially organic object detected by the dual energy advanced technology (AT) x-ray machines currently used at TSA checkpoints for carry-on baggage. Mitchell Laskey, president and CEO of Brijot Imaging Systems, which sells massive millimeter wave scanners, notes that these capabilities are not truly ATR as much as “automated human assist.”

True ATR could mean an end to the volume restrictions on carry-on liquids, and it might mean an end to the requirement that travelers remove computers from all carry-on bags. But ATR for finding threats on humans is trickier, because of the health and safety issues. Luggage can be screened using relatively high levels of ionizing x-ray radiation, which is most effective at detecting chemical compositions. Human travelers cannot.

The likely solution for scanning people is technology integration, according to Hallowell and Jim Tuttle, director of the explosives division of the Department of Homeland Security’s Science and Technology Directorate. Hallowell acknowledges the potential for an integrated, automated system to provide ATR for that purpose. She notes the prospect of a checkpoint screening device that combines full-body scanning, such as millimeter wave or backscatter, and a sophisticated, non-ionizing and eye-safe explosives detection technology like terahertz radiation (as mentioned earlier). The integrated device could use a full-body scanner to detect an anomaly, then automatically direct a terahertz beam at the highlighted anomaly to determine its composition.

That concept, mated with real-time devices like Smith Detection’s new eqo millimeter wave full-body scanner, could bring security agencies like TSA closer to what some call a “lane of truth,” in which subjects simply pass through an automated screening portal without slowing their gait, let alone stopping and removing articles from bags or shoes from feet.

Another integrated solution would involve mounting terahertz sensors on traditional portal magnetometers, which typically cost less than $5,000 apiece, compared to the $170,000 price tag of the typical full-body scanner, says Arnone.

Mark Laustra, of Smiths Detection, says his firm is collaborating with Analogic, manufacturer of the computed tomography (CT) explosives detection systems used to scan checked airline bags, to develop a belt-fed scanning device for checked baggage that combines both CT and AT technology.

The combined detection capability of the two technologies could mean higher sensitivity and greater speed. That could move aviation security operations closer to another goal: integration of EDS into the existing automated systems used to move checked bags from curb or check-in counter to aircraft. TSA calls the concept “in line” screening of checked bags.

DHS has set a goal of fielding new technologies like terahertz within four years and fielding integrated technology systems within eight years, Tuttle tells Security Management.

Acceptable Risk

Extremists’ activities over the past year have shown they will stop at nothing to beat the screening efforts aimed at detecting explosive threats.

Last August, Abdullah Asieri, one of the most wanted terrorists in Saudi Arabia, secured a personal meeting with the country’s top counterterrorism official, Prince Mohammed bin Nayef, by convincing the government that he was resolved to defect from terrorist ranks. He underwent airport-style security, which reportedly included screening with a magnetometer, and he spent 30 hours in the company of bin Nayef’s security staff, after which he received a personal audience with the prince. At that time, authorities believe a text message sent to Asieri’s cell phone activated a bomb, which may have escaped the screening process because it was hidden within a body cavity. Fortunately, the device killed only the attacker.

Earlier this year, an anonymously sourced article in British tabloid The Sun reported that British domestic intelligence authorities heard “chatter” indicating female terrorist recruits had received breast implants containing liquid-borne explosives. While no one has corroborated the report on the record, medical experts indicated that the process was feasible, and such a ruse could allow a terrorist to pass through existing airport security measures undetected.

That threat has raised the specter of human security scanning that not only penetrates a subject’s clothing but also the subject’s skin to seek out potential threats within the body, as would a traditional medical x-ray. While the former has raised privacy concerns, the latter is likely to create health worries.

Netherlands-based OD Security, a branch of OD Medical, manufactures the Soter RS security body scan. The device is shaped like a large right triangle 12 feet long at the base and roughly 8 feet tall, with a cross-cut recess near its peak. A subject steps onto a small, rail-mounted platform on one side of the recess, grabs two rail handles, and is passed through the machine, which generates a medical-quality x-ray of the individual’s skeleton, internal organs, and any foreign objects. The company claims that the radiation exposure of one scan is equal to that of only one hour at altitude in a jet airliner; the company claims the device is being used—although not necessarily in explosives detection applications—in nations including Mexico, Kuwait, and the United Kingdom.

In the United States, Nesch, LLC, a medical imaging startup based in Crown Point, Indiana, has developed a method to produce high-definition x-ray imaging that uses less radiation than a traditional medical x-ray by producing three separate images displaying x-ray absorption, diffusion, and diffraction. President and CEO Ivan Nesch explains that in a traditional radiograph, absorption of energy by bones clearly shows them on a film; diffusion and diffraction cause the blurring common to medical x-rays. Separating readings for each phenomenon produces clearer images. Nesch hopes that with refinement, he can reduce the radiation required to scan a human to 1/50th that used in a traditional medical x-ray.

Nesch’s technology has been tested twice by the U.S. military for use in “nondestructive” testing (examination of sensitive or dangerous items), he says, but he has not received inquiries from TSA or any other authorities in the traditional security sector.

Legal experts expressed doubt that Western security agencies, in particular TSA, would ever consider “through body” scanning for commercial aviation, regardless of its safety. Dillon Martinson, an attorney and research associate at the Center for Infrastructure Protection at the George Mason University School of Law in Arlingon, Virginia, has studied the privacy debate surrounding full-body scanners. Martinson says that he sees the devices like OD’s as long on legal hurdles and short on risk mitigation.

For example, what if a screener spotted an anomaly on a through-body scan? If not a trained radiologist, how would he or she discern it from a legitimate medical issue or pathology, like a tumor? If passengers have implanted medical devices, would they require a doctor’s note to fly? And if a screener spotted an anomaly that was clearly not a threat but could be disease, would the agency have an obligation to inform the subject? Would the agency be liable if it did not do so? Martinson says these are important questions to resolve.

Acknowledging the persistent question of privacy, Martinson points to the recent incident at Miami International Airport in which a TSA screener who had gone through the full-body scanner in a training exercise was repeatedly taunted by coworkers about his body image. Finally the screener assaulted a fellow worker.

“Confidence in the TSA’s ability to keep these things private and handle them in a delicate way has really been questioned,” Martinson says.

Paul Rosenzweig, also an attorney and the deputy assistant secretary of homeland security for policy from 2005 to 2009, says that any legal precedents governing the technology would likely come from cases based in aviation, as opposed to coming from those involving border security or narcotics enforcement cases. In the latter cases, investigating concealment within the body does not require probable cause but cannot, per case law, “offend the conscience.”

The earliest case law regarding airport screening was decided in connection with the implementation of magnetometers, when a federal appeals court ruled that they do not violate the Fourth Amendment right to privacy because they are a reasonable response to a threat and because the traveler always has the option of taking another mode of transportation, Rosenzweig says.

How the court would rule on a more intrusive screening method is an open question—and one not likely to be tested with regard to through-body scanning. The bigger fight would likely be political. The technology, Rosenzweig says, “would pose significant privacy concerns,” and “DHS will probably never go there.”

The bottom line is that, with or without through-body technology, “we have to accept some level of risk,” says Martinson. Harper agrees, noting, “There is no one solution that’s going to catch everything.”

But that doesn’t mean you can’t go a long way toward making the public safer. Amid the unending cat-and-mouse game of innovation between the security sector and its adversaries, Harper places his faith in a layered approach to detection of explosives threats, which avoids staking too much on any one technology.

Joseph Straw is an assistant editor at Security Management.