Detecting Explosives: Airport Security's Advanced Methods

Detecting explosives in airports is a critical aspect of aviation security, with the primary goal of preventing terrorist attacks and ensuring the safety of passengers and staff. Airports employ a range of technologies and methods to detect explosives, including X-ray scanning, explosive trace detection (ETD), ion mobility spectrometry (IMS), canine units, and advanced imaging technology (AIT). These methods aim to identify explosive materials or residue and play a crucial role in maintaining security at airports worldwide.

Ion mobility spectrometry

The process involves vaporizing and ionizing a sample, which can be collected by wiping an individual's hands, clothes, or belongings with a swab. This gives the molecules a positive or negative charge. Each type of molecule travels at a different speed when ionized, and IMS measures the time it takes for an ion to move a specified distance in an electric field. This is indicative of the ion's size-to-charge ratio. Ions with a larger cross-section will collide with more gas at atmospheric pressure and will, therefore, be slower. By measuring the exact speeds of the ionized particles, IMS can identify the types of molecules present and detect the presence of explosives.

IMS has become a prominent trace detection method for explosives due to its portability, efficiency, and low detection limits. The use of pre-concentrators, which collect explosive vapours and particles dislodged by air pulses, has enhanced the effectiveness of IMS. Additionally, IMS is well-suited for forensic investigations, as it can detect post-blast residue from explosives on items of forensic and evidentiary value.

Recent advancements in IMS include a better understanding of reagent gas chemistries, the influence of temperature on ion stability, and improved sampling methods. Commercial instruments have also been refined to provide faster and more reliable measurements for on-site detection of explosives.

X-ray scanning

X-ray radiography, or projection imaging, is a common imaging method that collects X-ray attenuation line integrals in two dimensions. This technique does not resolve the third dimension along the incident X-ray direction, which is where computed tomography (CT) comes in. CT provides visual, three-dimensional displays of the scanned materials, allowing for the identification of certain shapes or patterns associated with explosives, such as wires, batteries, or detonators. CT can also provide information about the physical density and effective atomic number of a material, aiding in the discrimination of explosive materials.

X-ray diffraction imaging (XDI) is another imaging technique that complements X-ray radiography. It is similar to magnetic resonance imaging (MRI) in that it provides additional security applications beyond what X-ray radiography can offer.

In recent years, there has been a push for automation in X-ray screening to improve detection capabilities and reduce the workload on airport security staff. Automated explosive detection systems for cabin baggage screening (EDSCB) have been developed and implemented in some airports, but not yet on a wide scale. Research has shown that while experienced screeners are adept at detecting improvised explosive devices, EDSCB can enhance their detection of bare explosives. Additionally, less experienced screeners benefit significantly from EDSCB in detecting both improvised explosive devices and bare explosives.

Overall, X-ray scanning plays a crucial role in airport security by providing a non-destructive method for detecting explosives in baggage and carry-on items.

Sniffer dogs

The use of sniffer dogs to detect explosives was first pioneered in 1959 in Algeria under the command of General Constantine. However, it was in 1974 at JFK Airport in New York that a sniffer dog first identified a bomb in a passenger's luggage, potentially saving hundreds of lives. Since then, sniffer dogs have become a common sight at airports around the world.

In addition to explosives, sniffer dogs can also detect firearms by searching for the scent of gunpowder, which lingers on a gun for weeks after it has been fired. The dogs search luggage and passengers for firearms in a similar manner to how they detect explosives, and it is imperative that they operate covertly to avoid alerting potential shooters.

The Australian Federal Police (AFP) is an example of a law enforcement agency that utilizes sniffer dogs at airports. The AFP has a team of Firearms and Explosives Detector Dogs (FEDD) that are primarily involved in screening incoming and outgoing passengers, searching incoming baggage and cargo, and are even called upon for operational activity in the community. The AFP's detector dog training is based on repetition and reward, and the success of the program is largely due to the handlers, who ensure the dogs are well-looked after and not bored with performing the same duties every day.

Chemical reaction swabbing

Swabbing is a standard method of identifying concealed explosive devices in security-conscious locations like airports. This method involves taking swabs from the surface of a suspicious object.

One such swabbing method is the use of chemically modified swabs. These swabs are coated with an acidic polymer that is activated by exposure to humidity. The moisture activates the acidic coating, turning low-vapor pressure salts into highly volatile chloric and perchloric acid vapors, which are easily detected. The swab is then inserted into an instrument for analysis. The results, produced within seconds, indicate the presence of vapors of suspect compounds and may also identify the general types of compounds detected.

Another swabbing method is demonstrated in a paper by James M. E. Glackin et al. of the University of St Andrews and the Swedish EOD and Demining Centre-SWEDEC. The paper outlines a method of using swabs coated with a commercial fluoropolymer to collect material from the surface of a suspicious object. The swabs are then heated to thermally desorb the explosives, causing the quenching of light emission from a thin-film luminescent sensor. This method has been shown to be up to three orders of magnitude more sensitive than standard colorimetric tests.

In addition to these methods, there are also colorimetric test kits that are widely used for explosive detection. These tests involve applying a chemical reagent to an unknown material or sample and observing a color reaction. Common color reactions are known and indicate whether an explosive material is present and, in many cases, the group of explosives from which the material is derived.

Mass spectrometric vapor analysis

The process of vaporizing the sample is often done through gas chromatography, which separates the compounds within the sample. However, this method has limitations, as different compounds can have the same retention times, making it challenging to definitively identify a specific compound. This is where mass spectrometry comes in as a more precise tool.

Mass spectrometry is considered the world's most accurate set of scales, capable of measuring the mass of single molecules. It measures the mass-to-charge ratio of ions (M/Z) within a sample, allowing for the identification of specific molecules based on their unique mass. This technique can identify a wide range of molecules, from metal ions to small organic molecules and even proteins.

The process of mass spectrometric vapor analysis typically involves several steps to ensure accuracy and reduce the likelihood of false positives. For example, a positive test result usually requires the collected compound to match several known characteristics of a controlled substance, such as gas chromatography retention time, molecular mass, and fragment masses.

The sensitivity of mass spectrometry is impressive, requiring only low nanogram to picogram quantities of material for detection. This makes it an invaluable tool for enhancing airport security and improving the accuracy of explosive detection, working in tandem with canine units to ensure a comprehensive screening process.

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