Few threats in the world are deadlier and more dynamic than those posed by explosives. More than a millennium after the invention of gunpowder, and nearly 150 years since the invention of TNT, the world’s chemists, physicists, and forensic scientists struggle to stay one step ahead of bomb makers.

Ideally, intelligence collection and emerging techniques like behavioral threat assessment will enable law enforcement to thwart many bombing plots. But for the times when incidents are not stopped in the planning stage, technology can help governments and private enterprises to detect explosives in transit, at entry points, or where they have been planted but before they have been detonated. Security Management looked at progress being made in research labs and in the field.

Trace Detection

In recent years, some of the most fruitful research and development of products to thwart terrorist use of explosives has come in the area of explosives trace detection (ETD), which helps authorities find bombs as well as persons manufacturing or carrying them by spotting miniscule amounts of explosive material on objects or people. Most devices—some of them handheld—rely on either ion mobility spectrometry (IMS) or chemiluminescence.

With IMS, test samples are heated to make them vaporize. IMS machines then pass the vapors through an electrical field. The machine identifies explosive substances based on the speed at which its ions travel. Many IMS units can “sniff” the air around a suspect surface or test an inserted surface swab.

In chemiluminescence, a machine exposes a sample to its own luminescent chemicals that will only bond to explosive molecules. If the machine detects luminescence in the sample, the machine has found an explosive match.

Both technologies are in use by the U.S. Transportation Security Administration (TSA) and by the U.S. military in Iraq and Afghanistan.

While highly effective in detecting small traces, most of these devices have a major limitation: They can only test for roughly a dozen predetermined threat materials. But that is changing as new capabilities are developed.

One trace detector—American Innovations’ XD-2i—offers a broader range, for example. It is able to detect at least 160 explosive compounds, 21 precursor substances, 18 common fillers and forensic taggants, plus five common chemical “confusants,” or inert materials used to mask the presence of threat materials.

Slightly larger than a hand-held two-way police radio, the XD-2i uses flat fabric test swabs, which the user first wipes on the surface being tested. The swab is then inserted into a frame on the face of the device. When cued by the machine, the user applies a series of three separate chemical drops to the swab. Between each drop, the device exposes the sample and reagents to various levels of heat to incite the necessary reactions.

By sight, the user compares the color changes on the swab to a reference card that shows results for specific threat materials. The device is fast and easy to use. The process takes no more than a minute, and one swab can indicate the presence of multiple threat substances in one test, says Chris Boylan, American Innovations’ vice president for homeland security and defense.

The U.S. Army’s Armament Research, Development and Engineering Center tested the XD-2i and found it nearly 95 percent accurate.

Other Chemical Diagnostics

The XD-2i isn’t the only device able to test a broad range of substances. Miniaturization of two complex processes for chemical diagnostics—Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR)—allows rapid identification of thousands of chemicals in the field, with one new device that may soon be in the hands of airport security screeners.

While traditional spectroscopy measures the light emitted from elements when they combust, such as in stars, Raman spectroscopy measures the light refracted from a substance when illuminated with a laser. Conversely, FTIR measures the light absorbed by a substance. The processes are named for the scientists whose work made them possible, 20th Century Indian physicist Sir Chandrasekhara Venkata Raman and 19th Century French mathematician and physicist Joseph Fourier.

While both methods are common in the laboratory, the devices used to conduct them were too large for field use until Ahura Scientific of Wilmington, Massachusetts, fielded the FirstDefender hand-held Raman spectrometer in 2007 and the TruDefender FT FTIR system in 2008. Both products were developed primarily for use by the industrial and hazmat response markets but have found use in explosive ordnance disposal (EOD).

With FirstDefender, the user need only hold the device’s sensor to a suspect substance to see a list of the substance’s chemical components. Because the Raman phenomenon is optical, the sensor can detect material through any membrane that is transparent or translucent—such as a dark glass bottle or a tinted pharmaceutical container. With darker membranes, a test takes longer but only about a minute, says Ahura Vice President of Marketing Duane Sword.

Raman functions best with light-colored or clear test materials, and FTIR, since it is testing absorption, does better with dark substances.

With both the Raman and FTIR processes, however, there are limitations. While they can detect explosive chemicals with a high degree of accuracy, they lack the sensitivity of ETD methods, thus requiring a larger, or more concentrated, chemical presence to produce a result.

Ahura maintains libraries of roughly 9,000 chemicals for its Raman devices and 4,000 for the TruDefender FT. Updates are sent to customers on memory cards that are inserted into the device for upload.

Det. Jake Bohi of the Phoenix Police Department Bomb Squad says his unit relies heavily on FirstDefender during an increasingly common type of call: incidents involving suspicious substances. The device rules out harmful materials rather than detecting them, but in doing so, it saves vast amounts of time.

Phoenix’s Bomb Squad recently used its FirstDefender for an unexpected but critical activity: a sweep through all the materials in the department’s property bureau, essentially the department’s evidence locker. The reason for the exercise was that during a specific analysis of materials belonging to a criminal defendant, Bohi’s unit unexpectedly found an explosive substance using the FirstDefender.

The item was removed and destroyed. Given the discovery, the bomb squad proceeded to check the department’s remaining evidence using the device, Bohi says.

A new Ahura device, the TruScreen, simplifies the FirstDefender’s user interface to suit the needs of security checkpoint operators, such as those in the aviation sector. Instead of a list of chemical components, the device offers an alternative mode in which the user will simply receive a result of “clear,” if there is no positive reading, or “threat,” indicating the presence of a designated threat material.

Secondary screening may include a second analysis with the TruScan device in its full diagnostic mode that identifies component chemicals by name. The device is currently in testing with major transportation security agencies, Sword says.

Organic versus Inorganic

The greatest explosive threats— including TNT, plastic explosives, and peroxide-based explosives like TATP and HMTD—are organic, meaning they contain carbon. Thus, differentiating between the organic and inorganic contents brings screeners a long way toward identifying objects that might bear an explosive threat.

Just as medical x-rays help doctors to differentiate between bone and soft tissue by density, advanced technology (AT) and explosives detection system (EDS) machines can help screeners to differentiate between organic and inorganic substances by determining their density and atomic weight.

The AT x-ray machines fielded at most TSA airport checkpoints offer two separate readings of bags from different perspectives,  while EDS, which functions the same as computed tomography, or CT medical scanners, use x-ray diodes that rotate around baggage. The dual perspectives and use of dual x-ray signal strengths improve scanning.

Separate views help the machines generate a visual perspective for screeners while, use of “dual energy” scanning allows the machines to compare the nature of the x-ray radiation’s transmission through an object and, thus, determine density and atomic weight, explains Michael Willenbogen, CEO of Reveal Imaging Technologies, which supplies EDS machines for TSA checkpoints.

AT and EDS machines’ improved sensitivity stems in part from their ability to pull more and more data from the sensors that “read” energy passed through scanned objects and in part from their computers, which handle the added data with ever-increasing speed. The computers run scanner data through algorithms to determine whether a threat is present or not, adds Peter Kant, vice president of global government affairs for Rapiscan, which provides AT machines for the TSA.

After an AT machine scans data, the machine displays color-coded objects and components by substance type and highlights potential threats. The software is updated based on evolving threats.

Liquids, gels, and aerosols. The x-ray machines and their algorithms struggle with one group of substances—liquids, gels, and aerosols—which the perpetrators of the 2006 transatlantic aircraft plot allegedly planned to use as a medium for the highly unstable explosives TATP and HMTD. Since the plot came to light, airline travelers have only been allowed to carry liquids up to three ounces, and they must be placed in transduct them were too large for field use until Ahura Scientific of Wilmington, Massachusetts, fielded the FirstDefender hand-held Raman spectrometer in 2007 and the TruDefender FT FTIR system in 2008. Both products were developed primarily for use by the industrial and hazmat response markets but have found use in explosive ordnance disposal (EOD).

With FirstDefender, the user need only hold the device’s sensor to a suspect substance to see a list of the substance’s chemical components. Because the Raman phenomenon is optical, the sensor can detect material through any membrane that is transparent or translucent—such as a dark glass bottle or a tinted pharmaceutical container. With darker membranes, a test takes longer but only about a minute, says Ahura Vice President of Marketing Duane Sword.

Raman functions best with light-colored or clear test materials, and FTIR, since it is testing absorption, does better with dark substances.

With both the Raman and FTIR processes, however, there are limitations. While they can detect explosive chemicals with a high degree of accuracy, they lack the sensitivity of ETD methods, thus requiring a larger, or more concentrated, chemical presence to produce a result.

Ahura maintains libraries of roughly 9,000 chemicals for its Raman devices and 4,000 for the TruDefender FT. Updates are sent to customers on memory cards that are inserted into the device for upload.

Det. Jake Bohi of the Phoenix Police Department Bomb Squad says his unit relies heavily on FirstDefender during an increasingly common type of call: incidents involving suspicious substances. The device rules out harmful materials rather than detecting them, but in doing so, it saves vast amounts of time.

Phoenix’s Bomb Squad recently used its FirstDefender for an unexpected but critical activity: a sweep through all the materials in the department’s property bureau, essentially the department’s evidence locker. The reason for the exercise was that during a specific analysis of materials belonging to a criminal defendant, Bohi’s unit unexpectedly found an explosive substance using the FirstDefender.

The item was removed and destroyed. Given the discovery, the bomb squad proceeded to check the department’s remaining evidence using the device, Bohi says.

A new Ahura device, the TruScreen, simplifies the FirstDefender’s user interface to suit the needs of security checkpoint operators, such as those in the aviation sector. Instead of a list of chemical components, the device offers an alternative mode in which the user will simply receive a result of “clear,” if there is no positive reading, or “threat,” indicating the presence of a designated threat material.

Secondary screening may include a second analysis with the TruScan device in its full diagnostic mode that identifies component chemicals by name. The device is currently in testing with major transportation security agencies, Sword says.

Organic versus Inorganic

The greatest explosive threats— including TNT, plastic explosives, and peroxide-based explosives like TATP and HMTD—are organic, meaning they contain carbon. Thus, differentiating between the organic and inorganic contents brings screeners a long way toward identifying objects that might bear an explosive threat.

Just as medical x-rays help doctors to differentiate between bone and soft tissue by density, advanced technology (AT) and explosives detection system (EDS) machines can help screeners to differentiate between organic and inorganic substances by determining their density and atomic weight.

The AT x-ray machines fielded at most TSA airport checkpoints offer two separate readings of bags from different perspectives, while EDS, which functions the same as computed tomography, or CT medical scanners, use x-ray diodes that rotate around baggage. The dual perspectives and use of dual x-ray signal strengths improve scanning.

Separate views help the machines generate a visual perspective for screeners while, use of “dual energy” scanning allows the machines to compare the nature of the x-ray radiation’s transmission through an object and, thus, determine density and atomic weight, explains Michael Willenbogen, CEO of Reveal Imaging Technologies, which supplies EDS machines for TSA checkpoints.

AT and EDS machines’ improved sensitivity stems in part from their ability to pull more and more data from the sensors that “read” energy passed through scanned objects and in part from their computers, which handle the added data with ever-increasing speed. The computers run scanner data through algorithms to determine whether a threat is present or not, adds Peter Kant, vice president of global government affairs for Rapiscan, which provides AT machines for the TSA.

After an AT machine scans data, the machine displays color-coded objects and components by substance type and highlights potential threats. The software is updated based on evolving threats.

Liquids, gels, and aerosols. The x-ray machines and their algorithms struggle with one group of substances—liquids, gels, and aerosols—which the perpetrators of the 2006 transatlantic aircraft plot allegedly planned to use as a medium for the highly unstable explosives TATP and HMTD. Since the plot came to light, airline travelers have only been allowed to carry liquids up to three ounces, and they must be placed in transparent bags and removed from carry-on luggage at security checkpoints. Those restrictions are expected to be lifted with ever-improving AT machine analysis and processing, but the timetable for the change is uncertain.

In the fall of 2008, former TSA administrator Kip Hawley wrote on an agency blog that his agency expected to eliminate volume restrictions for carry-on liquids in the fall of 2009 and to eliminate all requirements, including the need to remove liquids from carry-on bags at checkpoints, by the end of 2010. Recently, however, TSA spokeswoman Lauren Gaches told Security Management that the TSA will not stick to any fixed schedule, adding that “changes are dependent upon industry-driven developments.”

By contrast, European authorities expect to make changes soon. Ben Clifton, a spokesman for the U.K. Department for Transport, says that his agency may approve AT technology that allows relaxed liquid policies on a trial basis in 2010; the European Union has indicated that it may do likewise.

Vehicle Scanning

In high-risk environments requiring vehicle access, security staffs typically detect threats through visual inspection and the most effective explosive detection tool available: a dog’s nose.

Technologies, however, offer alternatives for situations where dogs are not available or practical. Radiation-based scanning methods for vehicles include traditional transmission x-rays and backscatter x-ray. Unlike transmission x-rays, which pass through the subject, backscatter radiation is ultra-high frequency energy that is transmitted onto a subject and reflected back and read by the device. Different materials—including metal and organic substances, such as explosives or people—reflect back varying amounts of energy, producing black-and-white display images that reveal organic objects in lighter shades.

Security screening vendor Spectrum San Diego recently debuted a vehicle scanning system that offers full-vehicle scanning on a par with that of the aviation sector’s AT machine, using the dual-energy method. The company’s CarScan requires only a standard wall outlet for power and offers an 11-foot by-11-foot scanning portal. For scans, vehicles simply drive through. Like airport AT machines, the scanner produces a display image with different substances color-coded for the screener. Metals are black, less dense organic substances are yellow, and denser ones are rust-colored.

According to Spectrum San Diego, the CarScan exposes a vehicle’s occupants to 10 microRem of radiation per scan, equivalent to less than an hour of natural background radiation.

The company plans to make the CarScan available for commercial sale later this year at a cost of $1 million each. By contrast, the life-cycle cost of an explosives detection canine team is about $570,000, says Hank Nolin, CPP, president of Florida’s Sun State Specialty K-9s.

Spectrum San Diego claims that CarScan can complete a full vehicle scan in seven seconds, where a canine team requires roughly a minute.

Portable X-ray Technology

Military EOD units and police bomb squads rely increasingly on portable x-ray technology to help them determine what’s inside a suspect package or an improvised explosive device without disturbing it.

Most current portable x-ray sets consist of two pieces: one is a transmission element or diode, often about the size of a hand-held circular saw; the other is a rigid, poster-sized film panel. Common systems include ALLPRO Imaging’s ScanX 12, originally developed for large-animal veterinary medicine, and Science Applications International Corp.’s (SAIC) RTR-4.

When an EOD unit or bomb squad wants to scan an object, a technician or robot must carry the device to the object, position it, and activate it. Then the ScanX 12’s films must be retrieved for viewing. SAIC’s plate device is far larger, but does offer a wireless connection for viewing images on a computer at a distance.

Lt. Richard Puschel, of the Union County, New Jersey, Police Department Bomb Squad, says he’s most interested in a new self-contained, real-time x-ray device called OpenVision LT, manufactured by Envision Product Design of Anchorage, Alaska. The relatively compact device mounts on opposite ends of an adjustable bracket that can be carried by a technician or mounted on a robot’s arm.

On one end is the device’s diode; at the other end is its sensor. Either manually or via remote control, a bomb technician sweeps the device over and around the sides of an IED or suspect package. The unit transmits a real-time video image of the scan wirelessly, which can be viewed on a hand-held wireless receiver, a heads-up display, or on a remote computer.

Envision President John Pursley says that a separate configuration allows placement of the x-ray sensor at the end of a telescoping pole, whereby bomb technicians or investigators can scan areas such as walls or car doors without risking exposure to the unit’s radiation, which at full power can penetrate two inches of steel. The device retails for $75,000, and costs $58,600 on the federal GSA Schedule.

The system is used by nearly 30 law enforcement organizations around the country, Pursley says, including the Michigan State Police Bomb Squad.

Sgt. Jeff Morton of the Anchorage Police Department Bomb Squad says his unit first used the device this year after someone discovered an abandoned box of mining explosives. The bomb squad needed to determine whether the box contained blasting caps that could detonate the explosives. The OpenVision allowed safe scanning of the explosives. Morton expects to find more uses for the device. “We’re ecstatic about it, because the thing’s just got so much potential,” he said.

Standoff Detection

Most explosives detection options are useless against one of the deadliest threats: the suicide bomber. The best chance of thwarting attacks is detecting bombers before they approach their target.

Standoff Raman spectroscopy remains the stuff of research. The technology already fielded widely for TSA’s controversial full-body scanners could, however, help mitigate the threats posed by suicide bombers and other bad actors.

The full-body scanners used at TSA checkpoints employ active backscatter and millimeter wave radiation, meaning that, like sonar or radar arrays, the devices project radiation onto the subject then detect the energy reflected back. The electrical activity of human bodies includes its own millimeter-wave level radiation which, with the right device, can be detected at a distance. With analytic software, a device can detect an object—like a suicide vest—blocking part of a body’s millimeter wave signature.

The scanners do not require that subjects walk through a choke point, but the technology functions best when individuals are relatively stationary. Its performance is also limited by bright ambient light, such as sunlight.

QinetiQ North America’s SPO-7 can detect large threats, like suicide vests as far as 15 meters away, and smaller concealed objects between four and seven meters away. The larger SPO-20 can screen individuals from up to 65 feet away.

The TSA first piloted standoff millimeter wave technology manufactured by QinetiQ in 2007 at New York City’s St. George Ferry Terminal on Staten Island, and at the Cape May, New Jersey, terminal of the Cape May-Lewes (Delaware) Ferry. This year, TSA launched a new pilot at Boston’s Logan International Airport.

TSA’s full-body millimeter wave and backscatter devices have drawn criticism from civil liberties groups, which liken them to a “virtual strip search” because of their detailed renderings of the body.

QinetiQ’s units, however, do not display such images, according to Wally Miller, QinetiQ’s managing director for transportation security. Instead, they superimpose crosshairs over any potential threats beneath clothing.

A System of Systems

Given the dynamic and deceptive nature of explosive threats, those charged with detecting and protecting against them look for solutions that are scalable and that can have functionality added via software—like AT x-ray and Ahura’s handhelds. “We need to be able to respond quickly as new things come up,” says Greg Holter, staff engineer and co-lead of Pacific Northwest National Laboratories’ (PNNL) Institute for Explosives Detection.

Indeed, despite ongoing advances, technology experts warn that bomb makers remain adaptive. Deadly evidence of that fact was provided in the July attacks on hotels in Jakarta, where terrorists are believed to have checked in as paying guests and assembled the bombs in their rooms.

PNNL’s work to combat all explosive threats runs the gamut from ETD to standoff detection to x-ray solutions. Most of the work is classified. The ultimate goal, according to Holter and PNNL Scientist Jon Young, is a “system of systems” in explosive detection in which the combined parts eliminate each other’s shortcomings.

Such systems already exist, Young says, both on the battlefield, where the military maps human terrain and uses science to detect and make inert improvised explosive devices, and in airports, where behavioral threat detection and technology combine to form tiered security.

In general, however, Holter says, the single most important element is still the human eye, because a technological panacea doesn’t exist.

Joseph Straw is an assistant editor at Security Management.