On assessing the possibility of detecting explosives and devices containing them.
PETROV Sergey Ivanovich
ON ASSESSING THE POSSIBILITY OF DETECTING EXPLOSIVES AND DEVICES CONTAINING THEM
Explosives (EV) exist both in solid (condensed), liquid and gaseous states, representing consistencies of the widest range of colors and transparency.
Explosives for drilling and blasting operations in industry and for military purposes are produced in industrial conditions.
A whole range of explosives can be produced by handicraft methods using publicly available materials, naturally inferior to industrially produced substances both in terms of efficiency and reliability and safety of use.
Nevertheless, the possibility of the appearance of such explosives during attempts to carry out terrorist acts or in areas of local armed conflicts cannot be ruled out.
In addition, explosive mixtures may be formed periodically or randomly during the implementation of certain technological and production processes based on substances that are not traditionally classified as components of explosives.
In particular, volumetric explosive compositions (volume-detonating mixtures or VDM) may be formed as a result of mixing finely dispersed metal particles, organic-based particles or gaseous hydrocarbons with atmospheric oxygen in certain proportions.
Most often, such compounds can be formed during the production of explosives and pyrotechnic products, during the loading of ammunition, during the processing and storage of grain legumes (corn, peas, sunflower, etc.), during the production of complex organo-compounds of various types and chemical fertilizers (paints and varnishes, ether compounds), during the extraction and transportation of certain minerals (coal, gas and gas condensate, oil), in metallurgical production, during the production of sugar and in the woodworking industry.
Moreover, the sensitivity of such compositions to external influences that initiate the development of detonation processes in them sometimes significantly exceeds the corresponding indicator for industrially produced explosives.
Another issue is that the concentrations of substances in the composition, at which the development of detonation processes in it is possible, are usually within very narrow limits and in practice occur quite rarely.
However, given the large masses of the resulting mixtures (up to several tons) and the high levels of heat of explosive transformation, one can conclude that such substances pose a serious danger in some situations.
In these conditions, with all the variety of forms and types of explosives, it is obvious that the human ability to visually identify explosives and explosive mixtures is sharply limited, although in some cases a good knowledge of their external features and technical parameters played a decisive role in the search for and disposal of explosive devices and other explosive objects (EOE).
In practice, both in drilling and blasting operations in industry and in military affairs, mainly solid explosives are used due to their greater ease of use. The most well-known of them are TNT (TNT, trinitrotoluene, TOL) and hexogen.
Recently, plastic (plasticine-like) and elastic (rubber-like) explosives, commonly called “plastic” explosives, have become increasingly widespread.
They are mixtures of high-power powdered explosives (hexogen, TENA) with a binder (synthetic rubber, mineral and essential oils, paraffin, stearin, suspension fluoroplastic) and, in some compositions, with aluminum powder.
Such plastic and elastic explosives are used both in military affairs and in industry (in metalworking using explosions). According to their explosive properties, such explosives are classified as high explosives of normal power, but are more convenient to use due to the possibility of giving the charge any shape.
Currently, the opinion about the very high power of plastic explosives is widely spread through the media: supposedly “plastic” explosives are 5 or even 10 times more powerful than TNT.
In reality, plastic explosives do not exceed TNT in terms of explosive transformation energy, however, the local (high explosive) effect of the explosion of their charge, due to the possibility of more tightly pressing it to the surface of the object being destroyed, somewhat exceeds the high explosive effect of the explosion of TNT blocks, which have flat edges that do not ensure their tight fit to uneven surfaces.
High explosives are divided into:
- High-power explosives (RDX, TEN, TNT-RDX alloys, HMX, tetryl);
- Normal-power explosives (TNT, TNT-xylitol alloys, dynamites, pyroxylin, plastic and elastic explosives);
- Low-power explosives (ammonium nitrate, mixtures of ammonium nitrate with flammable or explosive substances).
For comparative evaluation of explosive properties of different explosives, the TNT equivalent can be used, numerically equal to the ratio of the heat of explosive transformation of the compared explosive with the similar characteristics of TNT.
The most powerful explosive is octogen, the TNT equivalent of which is 1.8.
Thus, the range of explosives that can be encountered during operations to search for and neutralize explosive charges is quite specific and quite limited in nomenclature. The only thing left to do is to find these objects.
Currently, a number of means for searching for explosive charges and explosive ordnance have been developed and produced in Russia and abroad, both by direct and indirect signs.
A direct sign is the presence of explosives or their individual components.
Indirect signs of explosive ordnance include: the presence of metal and plastic parts, semiconductor devices (diodes, transistors, integrated circuits), explosive devices, wire lines, antennas, a certain shape of the body (cylinder, parallelepiped), etc.
The most reliable means of detecting explosive ordnance are those that detect direct signs.
Such means include gas analysis devices (or gas analytical devices); devices whose operation is based on the so-called nuclear-physical methods, and special chemical tests.
In addition, dogs specially trained in the mine detection service (MDS) course are widely used to detect explosives.
Gas analytical devices detect vapors or microparticles of explosives in air samples taken using special devices, and according to their operating principle are divided into drift spectrometers and gas chromatographs.
The operation of drift spectrometers is based on the ionization of a continuous gas flow, the separation of the resulting ions of microimpurities by their mobility in an electric field of a special shape, and the registration of the separated ions.
Due to their operating principle, drift spectrometers have a fairly high response speed (from hundredths of a second to several seconds), but at the same time have insufficient resolution.
The insufficient noise immunity of these devices determines their predominant use as indicators of the presence of explosives without identifying their type.
Drift spectrometers show good results in searching for explosives containing TNT and nitroglycerin, which have a fairly high volatility at positive ambient temperatures.
The disadvantage of most drift spectrometers is the limited range of explosives they can detect, since many of them, such as octogen and hexogen, which are part of most plastic and elastic explosives, have low volatility.
Another disadvantage of these devices is that they can only be used at positive air temperatures.
The expansion of the capabilities of drift spectrometers is facilitated by the fact that in real conditions explosives of various types are stored in warehouses and transported together.
In this case, contamination of low-volatility explosives (hexogen- and octogen-containing explosives, PETN, tetryl) with TNT vapors occurs, which significantly expands the capabilities of this search method.
When the temperature of hexogen- and octogen-containing explosive charges increases to 35…40 ° C, it becomes possible to directly detect them without using the effect of “contamination” with TNT vapors.
To quickly create the required temperature on the surface of explosive charges, including at negative ambient temperatures, portable industrial or household hair dryers, other heat generators with an autonomous power source can be used.
The operation of the overwhelming majority of modern portable gas chromatographs is based on the separation of the selected air sample using a special absorbent substance — a sorbent, applied to the surface of capillaries in a polycapillary column.
Further analysis of the separated components is performed using various detectors (for example, electron capture detectors).
Chromatographs have high sensitivity (up to 0.01 μg/m3) and resolution, but the analysis time for one sample is several tens of seconds or more.
The operation of the devices and processing of the analysis results are controlled by built-in microprocessor devices; there is the possibility of interfacing with a computer.
The presence and use of special software for processing signals from detectors provides the possibility of multifunctional use of these devices without any changes in the design.
In this case, if for the operation of drift spectrometers it is sufficient to perform contactless (from a distance of up to 15…25 cm) sampling of air in the area of the suspected explosive charge or device and analysis of the explosive vapors contained in these samples, then for the operation of gas chromatographs it is necessary to directly sample microparticles of the substance, heat them to the evaporation temperature and then analyze them for the presence of explosives.
Naturally, in the second case the volume of information obtained will be significantly greater, which allows in some cases to identify not only the type of explosive, but also some other substances, for example, narcotics.
One of the latest developments in this area is VaporTracer2 (photo 1) by ION TRACK INSTRUMENTS (USA) costing over $ 30,000.
Photo 1. Gas chromatograph VaporTracer2
Unfortunately, in practice, when performing work on searching for and defusing explosive devices of various types, the operator of the device cannot always provide conditions for contact sampling of microparticles of the substance of the object under study, for example, in the case of placing it in an attaché case or other packaging, when there are no traces of explosives on the external surfaces for one reason or another, and the possibility of opening the package is a known danger.
As shown by the world practice of performing work on searching for and defusing explosive devices and other explosive objects, for a specialist conducting such work, in the overwhelming majority of cases, only one piece of information is needed — whether there is an explosive substance or not, that is, whether the device under study can explode or not.
The most suitable for performing this operation are drift spectrometers, which provide detection of the presence of explosives without identifying their type.
Identification of explosives, including mixed ones, with an accuracy of up to the percentage content of their components, including sensitizers, phlegmatizers, plasticizers and dyes, can be carried out in calmer conditions (for example, in a laboratory) using, for example, gas chromatography devices.
In addition, the developed methods and equipment (for example, the X-ray fluorescence analyzer of the Spectroscan series) allow the identification of the manufacturer and batch based on the qualitative and quantitative composition of microimpurities in explosives for the purpose of carrying out investigative actions.
It should be noted that gas chromatography devices are more complex and expensive and require a fairly high level of operator qualification, especially when working with mixed explosives. Naturally, if an explosive device has a detonator that is switched to the combat position, such identification should only be carried out after disarming this detonator in one way or another.
This article does not analyze the operating features of various gas chromatograph models.
One of the most important characteristics of drift spectrometers that determines the possibility of their use in a specific region of the world to search for specific explosives is the threshold sensitivity — the maximum concentration of explosive vapors in the air that can be detected.
It is known that the ability to detect explosive vapors in air samples using dogs and drift spectrometers depends to a large extent on humidity and, especially, on air temperature.
The threshold sensitivity of domestic explosive detectors “Argus-5”, “Pilot”, “Shelf” (“Shelf-DS”) (photo 2) and MO-02 (MO-02M) for TNT vapors at an air temperature of 20…25 °C and a relative humidity of no more than 95% is at the level of 1*10 -13 g/cm3 of explosives in an air sample and is still significantly inferior to the threshold sensitivity of a specially trained dog — 1*10 -16 g/cm3 of explosives. From the detectors of the MO-02 series, in which an attempt was made to solve the problem of identifying the type of explosive, the devices “Shelf”, “Argus-5” and “Pilot” differ in increased noise immunity, ease of operation and a slightly longer mean time between failures.
The “Argus-5” and “Pilot” detectors differ from the “Shelf” detector by the presence of an LCD display (which displays the set detection threshold level, the alarm signal level when a real explosive is detected, and the battery charge level), improved sensitivity due to the optimization of the design of the sampling part, and the presence of a connector for communication with a PC.
Photo 2. “Shelf” (“Shelf-DS”) explosive vapor detector
Foreign analogues are characterized by a slightly lower threshold sensitivity of 1*10-9…1*10 -11 g/cm3.
At the same time, the threshold sensitivity value specified for domestic models of explosive detectors is of fundamental nature, since for most regions of Russia, due to its geographical location, the effect of relatively low air temperatures is quite long-term, when the volatility of explosives is minimal and, accordingly, the concentration of explosive vapors in the air is minimal.
In these conditions, foreign analogues, regardless of their excellent design, aggressive advertising and success in other countries with a more favorable climate, can give a significant percentage of missed search objects containing explosives, with all the ensuing consequences for the operator of the device and the surrounding space.
Unfortunately, the effective and safe use of drift spectrometers of all models without exception when searching for explosives is hampered by the ability to work from a distance of no more than 15 … 25 cm (under the most favorable conditions).
Accordingly, the detection of explosive devices with tension (scattered), seismic, optical target sensors and explosive devices in a controlled version (via radio or wire) becomes a serious problem.
Naturally, the task of combating such explosive devices must be solved by the comprehensive use of various special equipment, devices and tactical techniques, taking into account the specific situation.
In general, drift spectrometers are quite an effective tool for searching for and defusing explosive charges, explosive devices and other explosive ordnance, provided that the operator of the device has received a sufficient level of special training in this area and the complex use of other technical means and tactical techniques.
Modern drift spectrometers weigh 0.6-7.0 kg, chromatographs — from 1.5 to 50-70 kg. Both drift spectrometers and chromatographs can be powered either from a 220 V, 50 Hz network or from batteries.
Detection of explosives by nuclear-physical instruments is based on the registration of scattered and secondary radiation of neutrons and gamma-quanta obtained as a result of irradiation of the examined medium by a flow of fast neutrons created (in modern instruments) by an isotopic source.
The presence in the reflected fields of a certain number of neutrons and gamma-quanta, the energy of which lies in certain energy ranges, indicates the presence in the examined volume of hydrogen and nitrogen, which are part of the overwhelming majority of explosives.
Unfortunately, the devices currently being developed for searching for explosives and explosive ordnance in the ground still have low noise immunity, depending on the physical properties of the soil (uneven surface, variable humidity, heterogeneous inclusions), high energy consumption, a fairly large mass (from units to tens of kilograms) and dimensions.
A rather serious problem is the need to protect the surrounding space from ionizing radiation generated by the device.
One of the latest, fairly successful developments in this area is the detector of explosives and other substances based on the nuclear quadrupole resonance method ОВВ-ЯКР-10, designed to work with postal items.
Of the technical means designed to detect and identify explosives, the most widely used in the world at present are chemical express tests in the form of aerosol sprays or droppers (for example, the kits “Antivzryv”, Lakmus-2” and “Poisk-HT”, photos 3 and 4).
Photo 3. A set of express tests for detection and identification of explosives “Antivzryv” (“Lakmus-2”)
Photo 4. A set of express tests for detection and identification of explosives “Poisk-HT”
These express tests provide a solution to the problem of detecting and identifying explosives by their trace amounts on the surfaces of objects, clothing and human hands, including for a long time (up to several months) after the explosives have ceased to come into contact with the surface being examined. The threshold sensitivity of chemical express tests is at the level of 1*10-5 g/cm3.
The research process is fast, visual and does not require additional laboratory equipment.
Personnel using rapid tests do not require special training.
The presence of traces of explosives is determined by the characteristic coloring of the test paper with the sample taken after its treatment with the compounds included in the kits.
In particular, the Anti-Explosion (Latmus-2) kit allows you to detect and visually confirm the presence of traces of the following explosives and mixtures based on them: TNT, picric acid, hexogen (including plastic and elastic explosives based on hexogen, compositions «B», C-4, semtex, RDX), octogen, PETN (PENT), explosives based on nitroglycerin (dynamites, dynamons, etc.), ammonium nitrate explosives (ammonals, ammothols, ammonites), black powder.
The Poisk-HT kit allows you to detect and identify the same range of explosives, with the exception of ammonium nitrate explosives and black powder.
It should be noted that foreign analogues may give gaps when trying to search for domestically produced explosives due to differences raw materials and production technology of explosives in different countries.
The use of specially trained dogs to search for explosives is quite widespread abroad and in Russia. Dogs are highly mobile and can detect explosives of almost any type, but compared to technical means, they have a number of specific disadvantages, which can be a topic for a separate discussion.
When searching for explosives and explosives using dogs and the above technical means, their periodic testing (functionality check) is necessary using standards of various explosives.
The use of real explosives for these purposes is associated with a number of difficulties related to the special conditions of acquisition, transportation and storage of these substances even in small quantities. To solve this problem, explosive simulators were created based on odorologically inert substances with the addition of real explosives in micro quantities.
Such simulators do not have any restrictions on acquisition, transportation and storage: it is impossible to initiate an explosion in them with any external initiating action, and explosives cannot be isolated from them in pure form for the subsequent creation of explosive compositions.
When choosing explosive simulators from the wide variety of available ones, it is necessary to keep in mind that the base of the composition should not contain substances or materials with impurities of household odors, for example, the smell of leather, which can cause false alarms (dog sitting down), i.e. it should be clean in terms of odor.
In addition, it is preferable to use domestically produced explosive simulators, since the explosives they contain in micro quantities, unlike foreign analogues, have the same raw material base, microimpurities and identical technical production conditions as real explosive charges.
The history of the development of explosive device search tools has developed in such a way that at present, both in Russia and abroad, the greatest development has been achieved by tools whose operation is based on the detection of indirect signs.
The widest range is represented by metal detectors (metal detectors, induction mine detectors).
And this is the topic of a separate article.
Thus, at present there is no single universal highly effective tool for searching and identifying explosive and explosive device charges.
An acceptable level of reliability in detecting these objects can only be achieved through the integrated use of various technical means and specially trained dogs, taking into account the safety of operators in conditions of the possible use of real explosive devices.