Inspection system for detecting explosives and narcotics.
In recent years, there has been a continuous increase in the use of explosives (HE) and drug smuggling by terrorists and other criminal elements.
It is almost impossible to detect and prevent such illegal actions.
However, there are areas of increased control taking into account vulnerable places where the presence of explosives and other contraband substances may be detected. Such areas include airports and airplanes.
There are numerous known ways for air passengers to conceal explosives and other contraband substances. Such substances may be hidden under the clothing of airline passengers, in their carry-on baggage, or in checked baggage carried in the cargo holds of aircraft.
Over the years, various methods for detecting explosives and narcotics have been developed and tested in practice — from using specially trained dogs to complex systems that react to the presence of traces of such substances.
Technical devices and systems for detecting explosives and other contraband substances can be divided into two categories according to their operating principle: those using various radiation for detection and those using vapors of explosives and drugs for this purpose.
The first category includes X-ray, gamma and neutron irradiation systems, and nuclear magnetic resonance (NMR) systems. These systems and the methods used in them are most suitable for detecting explosives and narcotics hidden in baggage and carry-on items of air passengers, and are completely safe for them.
The second category of detection systems uses electron capture methods, gas chromatography, mass spectroscopy, plasma chromatography, biosensors and laser photoacoustics.
All of these methods are more applicable to the detection of explosives and drugs hidden in or under the clothing of people, or traces of such substances remaining on the skin, clothing and various objects belonging to persons who have handled these substances, for example, who carried them.
All of the above detection systems and methods are currently in use. Research is also being conducted in the government and private sectors to further improve these systems and develop new methods.
As explosives technology develops and new types of explosives appear, such as plastic explosives, their detection is becoming an increasingly difficult task.
In particular, it is necessary to solve the problem of reliably detecting explosives with very low vapor pressure or low particle emission levels, and reducing search time.
At the 1987 Carnahan Conference, a paper was presented on a study of various integrated explosive detection systems conducted at Sandia National Laboratories in connection with the development of a walk-through inspection system.
The results of this study suggested a three-stage explosive detection process, including the following steps: sampling of explosive vapors, concentration increase, and isolation of specific types of explosive vapors. The paper proposed various vapor sampling devices.
Various configurations of portals and the dynamics of airflows within them were investigated to determine the configuration that provides the best sampling.
The report concluded that a downward semi-laminar airflow over the effective area of the body of the person being searched, in combination with a vacuum suction funnel approximately 30 cm in diameter, placed under a grate in the floor of the portal, is the best method for collecting explosive vapors or corpuscular radiation for analysis.
Various detection instruments have been used to isolate the vapors of specific explosives, including the Phemto-Chem 100 Ion Mobility Spectrometer in combination with a sample enhancer developed by Ion Track Instruments. An ion mobility spectrometer is a plasma chromatograph that uses an atmospheric ion-molecular reactor to produce charged molecules that can be analyzed by ion mobility.
The device for increasing the concentration of vapors of selected samples is a screen in the form of a disk, driven into rotation by an electric motor. The screen coating absorbs vapors emitted by various substances. During subsequent heating of the screen, desorption of these vapors with increased concentration occurs.
The main problem encountered by the developers of walk-through arched explosive detection systems was maintaining the integrity of the air samples taken.
Maintaining sample integrity involves preventing contamination from the environment while allowing screened individuals to pass through the portal at a constant rate, which is essential for the effective operation of any screening system. The report cited above noted that air sample integrity is not maintained in doorless walk-through screening systems.
If there are air flows through the portal, caused, for example, by operating air conditioners or people passing through, the probability of detection can be reduced by 10%. Equipping portals with doors increases reliability and the probability of detection, but at the same time creates a problem associated with an unacceptable reduction in the capacity of the system for airports.
In recent years, several patents have been issued in the United States and a number of other countries for methods and means of detecting contraband substances, including explosives and drugs, in the baggage and carry-on baggage of air passengers or in cargo containers.
These methods and the devices and systems based on them are reduced to the following processes: the inspected object (item of baggage) is passed through an inspection tunnel, controlled along three axes, where it is blown by a circulating air flow.
A sample of air in the tunnel is taken for subsequent analysis. However, none of these patents proposed using the concentration of vapors in the samples taken to increase the sensitivity and selectivity of detection means.
Several subsequent US patents used absorption and desorption of vapor or particle radiation from contraband to detect them, but these patents did not apply to the use of arch-type vapor sampling chambers.
Two patents (1995 and 1996) by Canadian inventors propose an inspection system that overcomes the shortcomings of previously proposed systems and systems.
It is designed to detect explosives, narcotics and controlled chemical reagents by analyzing samples of the vapors or corpuscular radiation they emit. Such substances can be hidden in the baggage and hand luggage of airline passengers, and traces of these substances remain on their clothing or skin.
All operations of the detection process must be carried out unnoticed by airline passengers and without harm to them and sufficiently quickly, without delays or interruptions in the flow of people and baggage.
The installation is an integrated system containing sampling means in the form of the first and second sampling and analysis subsystems, a control and data processing subsystem.
In the first embodiment of the installation, a sampling chamber is used in a passage portal in which an air flow circulates. This flow blows on people or objects passing through the chamber and enters the sampling zone.
The portal and the chamber are designed so that samples can be taken with a concentration of vapors and/or particles of the mentioned substances sufficient for analysis.
A small amount of circulating air during a period called the sampling period is collected by an external air pump or fan and sent to the first and second sampling and analysis subsystems.
In the second embodiment of the sampling system, a probe held in the operator's hand is used to collect samples, which he moves over specific areas of the person or object being inspected and removes vapors or particles of controlled substances.
The probe contains a rotating brush located at its input end.
The vapors and particles of substances collected by the probe are sent to the common sampling and analysis subsystem.
The probe is designed so that it forms an airtight connection when in contact with the inspected object.
In the third embodiment of the inspection unit, an automatic baggage and carry-on baggage inspection chamber for air passengers is used to collect samples.
The chamber has the shape of a rectangular tunnel with an open entrance and exit.
The dimensions of the chamber roughly correspond to the dimensions of a typical X-ray inspection unit used at airports.
The chamber is installed above the conveyor belt that delivers the objects to be inspected. It has at least four sampling heads with rotating brushes that cover all surfaces of the objects and particles of controlled substances.
The collected air samples are sent to the first and second sample collection and analysis subsystems.
In the first of these subsystems, the collected sample with a concentration of vapors or particles of controlled substances in it equal to several trillionths of a share is converted into vapor form.
In this form it is fed to a high-speed chemical analyzer, which may be a gas chromatograph, an electron capture detector, or an ion mobility spectrometer. The latter type of chemical analyzer is preferred.
In the second subsystem, as a result of several successive steps, the sample volume is reduced with an increase in the concentration of vapors or particles in it, and it is sent to a high-speed chemical analyzer (a gas chromatograph with an electron capture detector).
The action of this subsystem consists of absorption of vapors and particles contained in the sample by an absorbent substrate and their subsequent desorption when the substrate is heated.
This process is repeated several times until the degree of purification required for analysis is achieved. Based on the analysis, the class of substances and their quantity in the inspected objects are identified.
The main function of the control and data processing subsystem is to signal the presence of controlled substances in the inspected object and, if required, the level of their concentration.
The subsystem responds to the difference in background concentration levels and concentrations that cause an alarm. This subsystem also controls the state of the entire installation using a microprocessor or computer.
Modular software allows programming the installation to detect specific substances.
The patents contain a detailed description of all subsystems of the installation and more than 20 explanatory diagrams and drawings.