Explosives trace detectors (ETD) are security equipment able to detect explosives of small magnitude. The detection can be done by sniffing vapors as in an explosive vapor detector or by sampling traces of particulates or by utilizing both methods depending on the scenario. Most explosive detectors in the market today can detect both vapors and particles of explosives. Devices similar to ETDs are also used to detect narcotic

Narcotic

The term narcotic originally referred medically to any psychoactive compound with any sleep-inducing properties. In the United States of America it has since become associated with opioids, commonly morphine and heroin and their derivatives, such as hydrocodone. The term is, today, imprecisely...

s. The equipment is used mainly in 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 and other vulnerable areas considered susceptible to acts of unlawful interference.

Sensitivity

Sensitivity is defined as the lowest amount of explosive matter a detector can detect reliably. It is expressed in terms of nano-grams (ng), pico-grams (pg) or femto-grams (fg) with fg being better than pg better than ng. It can also be expressed in terms of parts per billion (ppb), parts per trillion (ppt) or parts per quadrillion (ppq).

Sensitivity is important because most explosives have a very low vapor pressure and give out very little vapor. The detector with the highest sensitivity will be the best in detecting vapors of explosives reliably.

Light weight

Portable explosive detectors need to be as light weight as possible to allow users to not fatigue when holding them. Also, light weight detectors can easily be placed on top of Robots.

Size

Portable explosive detectors need to be as small as possible to allow for sensing of explosives in hard to reach places like under a car or an inside a trash bin.

Cold start up time and analysis time

The start up time should not be a parameter for evaluation of an explosive detector. Start up time only indicates the time required by the detector to reach the optimized temperature for detection of contraband substances.

Ion mobility spectrometry

Explosive detection using Ion mobility spectrometry (IMS) is based on velocities of ions in a uniform electric field. More information on IMS is found here IMS
There are some variant to IMS such as Ion trap mobility spectrometry (ITMS) or Non-linear dependence on Ion Mobility (NLDM) which are based on IMS principle. The sensitivity of devices using this technology is limited to pg levels. The technology also requires the ionization of sample explosives which is accomplished by a radioactive source such as Nickel-63 or Americium-241. This technology is found in most commercially available explosive detectors like the GE VaporTracer, Smith Sabre 4000 and Russian built MO-2M and MO-8. The presence of radioactive materials in these equipments cause regulatory hassles and requires special permissions at customs ports. These detectors cannot be field serviced and may pose radiation hazard to the operator if the casing of the detector cracks due to mishandling. Bi-yearly checks are mandatory on such equipment in most countries by regulating agencies to ensure that there are no radiation leaks. Disposal of these equipments is also controlled owing to the high half-life of the radioactive material used.

Photonic nonradioactive ionization is used for the Quantum Sniffer QS-H150 Portable Explosives Detector, manufactured in the USA by Implant Sciences Corp.

Thermo redox

This technology is based on decomposition of explosive substance followed by the reduction of the NO2 groups. Most military grade explosives have an abundance of NO2 groups on them. Explosive vapors are pulled into an adsorber at a high rate and then pyrolized. The presence of NO2 groups in the pyrolized products is then detected. This technology has significantly more false alarms because many other harmless compounds also have an abundance of NO2 groups. For example most fertilizers have NO2 groups which are falsely identified as explosives, and the sensitivity of this technology is also fairly low. A popular detector using this technology is Scientrex EVD 3000.

Chemiluminescence

This technology is based on the luminescence of certain compounds when they attach to explosive particles. This is mostly used in non-electronic equipment such as sprays and test papers. The sensitivity is pretty low in the order of ng.

Amplifying fluroscent polymer

Amplifying fluroscent polymer is a promising new technology and is based on synthesized polymers which bind to explosive molecules and give an amplified signal upon detection.
The sensitivity is in the order of fg.