Explosive detection is a non-destructive inspection

Inspection

An inspection is, most generally, an organized examination or formal evaluation exercise. In engineering activities inspection involves the measurements, tests, and gauges applied to certain characteristics in regard to an object or activity...

 process to determine whether a container contains explosive material

Explosive material

An explosive material, also called an explosive, is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure...

. Explosive detection is commonly used at airport

Airport

An airport is a location where aircraft such as fixed-wing aircraft, helicopters, and blimps take off and land. Aircraft may be stored or maintained at an airport...

s, port

Port

A port is a location on a coast or shore containing one or more harbors where ships can dock and transfer people or cargo to or from land....

s and for border control

Border control

Border controls are measures used by a country to monitor or regulate its borders.The control of the flow of many people, animals and goods across a border may be controlled by government Customs services. Security is enforced by various kinds of Border Guards and Coast Guards...

.

Dogs

Specially trained dog

Dog

The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...

s can be used to detect explosives using their noses which are very sensitive to scents. While very effective, their usefulness becomes degraded as a dog becomes tired or bored.

These dogs are trained by specially trained handlers to identify the scents of several common explosive materials and notify their handler when they detect one of these scents. The dogs indicate a 'hit' by taking an action they are trained to provide, generally a passive response.

The explosive detection canine was originated at the Metropolitan Police Department in Washington, D.C. in 1970, by then trainer Charles R. Kirchner.

Honey bees

This approach couples trained honey bee

Honey bee

Honey bees are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis...

s with advanced video computer software

Computer vision

Computer vision is a field that includes methods for acquiring, processing, analysing, and understanding images and, in general, high-dimensional data from the real world in order to produce numerical or symbolic information, e.g., in the forms of decisions...

 to monitor the bee for the strategic reaction. Trained bees serve for 2 days, after which they are returned to their hive. This proven system is not yet commercially available. Biotechnology firm Inscentinel claim that bees are more effective than sniffer dogs.

Mechanical scent detection

Several types of machines have been developed to detect trace signatures for various explosive materials. The most common technology for this application, as seen in US airports, is ion mobility spectrometry (IMS). This method is similar to mass spectrometry

Mass spectrometry

Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...

 (MS), where molecules are ionized and then moved in an electric field in a vacuum, except that IMS operates at atmospheric pressure. The time that it takes for an ion, in IMS, to move a specified distance in an electric field is indicative of that 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.

Gas chromatography (GC) is often coupled to the detection methods discussed above in order to separate molecules before detection. This not only improves the performance of the detector, but also adds another dimension of data, as the time it takes for a molecule to pass through the GC may be used as an indicator of its identity. Unfortunately, GC normally requires a bottled gas, which creates a consumable and ease of use issue for the system. GC columns operated in the field are prone to degradation from atmospheric gases and oxidation, as well as bleeding of the stationary phase. Columns must be very fast, as well, since many of the applications demand that the complete analysis be completed in less than a minute.

Spectrometry

Technologies based on ion mobility spectrometer

Ion mobility spectrometer

Ion-mobility spectrometry is an analytical technique used to separate and identify ionized molecules in the gas phase based on their mobility in a carrier buffer gas...

 (IMS) include ion trap mobility spectrometry (ITMS), and differential mobility spectrometry (DMS). Amplifying fluorescent polymers (AFP) use a molecular recognition to "turn off" or quench the fluorescence

Fluorescence

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation of a different wavelength. It is a form of luminescence. In most cases, emitted light has a longer wavelength, and therefore lower energy, than the absorbed radiation...

 of a polymer. Chemiluminescence was used frequently in the 1990s, but is less common than the ubiquitous IMS. Several attempts are being made to miniaturize, ruggedize and make MS affordable for field applications; such as an aerosol

Aerosol

Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...

 polymer that fluoresces blue under UV but is colorless when it reacts with nitrogen groups.

One technique compares reflected ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

, infrared

Infrared

Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 and visible light measurements on multiple areas of the suspect material. This has an advantage over olfactory methods in that a sample does not need to be prepared. A patent exists for a portable explosive detector using this method.

X-ray machines

Specially designed X-ray machine

X-ray machine

An X-ray generator is a device used to generate X-rays. These devices are commonly used by radiographers to acquire an x-ray image of the inside of an object but they are also used in sterilization or fluorescence....

s can detect explosives by looking at the density of the items being examined. They use Computed axial tomography based systems that are enhanced with dedicated software, containing an explosives threat library and false - color coding, to assist operators with their dedicated threat resolution protocols. X-ray detection is also used to detect related components such as detonator

Detonator

A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....

s, but this can be foiled if such devices are hidden inside other electronic equipment.

Neutron activation

Specially designed machines bombard the suspect explosives with neutrons, and read the gamma radiation decay signatures to determine the chemical composition of the sample. Explosive materials all have similar ratios of carbon, hydrogen, nitrogen and oxygen, which the machine is able to detect.

Detection aids

A detection taggant

Taggant

A taggant can mean a radio frequency microchip used in automated identification and data capture . In such cases, electronic devices use radio waves to track and identify items, such as pharmaceutical products, by assigning individual serial numbers to the containers holding each product...

 can be added when explosives are made to make detection easier. The Montreal Convention 1991 is an international agreement requiring manufacturers of explosives to do this. An example is with Semtex

Semtex

Semtex is a general-purpose plastic explosive containing RDX and PETN. It is used in commercial blasting, demolition, and in certain military applications. Semtex became notoriously popular with terrorists because it was, until recently, extremely difficult to detect, as in the case of Pan Am...

, which now is made with DMDNB

DMDNB

DMDNB, or also DMNB, chemically 2,3-dimethyl-2,3-dinitrobutane, is a volatile organic compound used as a detection taggant for explosives, mostly in the United States where it is virtually the only such taggant in use. Dogs are very sensitive to it and can detect as little as 0.5 parts per billion...

 added as a detection taggant. DMDNB

DMDNB

DMDNB, or also DMNB, chemically 2,3-dimethyl-2,3-dinitrobutane, is a volatile organic compound used as a detection taggant for explosives, mostly in the United States where it is virtually the only such taggant in use. Dogs are very sensitive to it and can detect as little as 0.5 parts per billion...

 is a common taggant as dogs are sensitive to it. In the UK the relevant legislation is the Marking of Plastic Explosives for Detection Regulations 1996.

Bogus Devices

The US Department of Justice warned in a National Institute of Justice publication, "Guide for the Selection of Commercial Explosives Detection Systems for Law Enforcement Applications (NIJ Guide 100-99)," about the ongoing trend of "Bogus" explosives detection equipment being sold to unsuspecting consumers. The report mentions by name the Quadro Tracker, an apparent dowsing rod with a freely pivoting radio antenna rod with no functioning internal components.

"...There is a rather large community of people around the world that believes in dowsing

Dowsing

Dowsing is a type of divination employed in attempts to locate ground water, buried metals or ores, gemstones, oil, gravesites, and many other objects and materials, as well as so-called currents of earth radiation , without the use of scientific apparatus...

: the ancient practice of using forked sticks, swinging rods, and pendulums to look for underground water and other materials. These people believe that many types of materials can be located using a variety of dowsing methods. Dowsers claim that the dowsing device will respond to any buried anomalies, and years of practice are needed to use the device with discrimination (the ability to cause the device to respond to only those materials being sought). Modern dowsers have been developing various new methods to add discrimination to their devices. These new methods include molecular frequency discrimination (MFD) and harmonic induction discrimination (HID). MFD has taken the form of everything from placing a xerox copy of a photograph of the desired material into the handle of the device, to using dowsing rods in conjunction with frequency generation electronics (function generators). None of these attempts to create devices that can detect specific materials such as explosives (or any materials for that matter) have been proven successful in controlled double-blind scientific tests. In fact, all testing of these inventions has shown these devices to perform no better than random chance...."

A number of dowsing rod-style detection devices have been widely used in Iraq

Iraq

Iraq ; officially the Republic of Iraq is a country in Western Asia spanning most of the northwestern end of the Zagros mountain range, the eastern part of the Syrian Desert and the northern part of the Arabian Desert....

 and Thailand

Thailand

Thailand , officially the Kingdom of Thailand , formerly known as Siam , is a country located at the centre of the Indochina peninsula and Southeast Asia. It is bordered to the north by Burma and Laos, to the east by Laos and Cambodia, to the south by the Gulf of Thailand and Malaysia, and to the...

, notably the ADE 651

ADE 651

The ADE 651 is a hand-held device produced by ATSC , which claims the device can detect from a distance the presence and location of various types of explosives, drugs, and other substances. The device has been sold to a number of countries in the Middle and Far East, including Iraq, for as much as...

 and GT200

GT200

The GT200 is a fraudulent "remote substance detector" that is claimed by its manufacturer, UK-based Global Technical Ltd, to be able to detect from a distance various substances including explosives and drugs...

, where they have been reported to have failed to detect bombs that have killed hundreds of people and injured thousands more.