October 2006 - Volume 8 - Number 4

Research and Technology

Adee Schoon
Research Scientist
Leiden University
Leiden, the Netherlands

Canine Unit
Netherlands National Police Agency
Nunspeet, the Netherlands

Sebastian Götz
Doctoral Candidate
Chemical Analysis Group
Faculty of Science and Technology and MESA+ Research Institute for Nanotechnology
University of Twente
Enschede, the Netherlands

Martijn Heuven
Engineer
Chemical Analysis Group
Faculty of Science and Technology and MESA+ Research Institute for Nanotechnology
University of Twente
Enschede, the Netherlands

Martin Vogel
Assistant Professor
Chemical Analysis Group
Faculty of Science and Technology and MESA+ Research Institute for Nanotechnology
University of Twente
Enschede, the Netherlands

Uwe Karst
Professor
Chemical Analysis Group
Faculty of Science and Technology and MESA+ Research Institute for Nanotechnology
University of Twente
Enschede, the Netherlands

Abstract | Introduction | Materials | Methods | Results | Discussion | Acknowledgment | References

Abstract

Improvised explosive mixtures such as triacetone triperoxide (TATP) are a new challenge in combating terrorism and crime. Traditionally trained bomb dogs need to be trained on these products, but the dangers in synthesizing and storing these products create difficulties. In this study, training aids were developed based on TATP produced in very small amounts using pure base compounds. Both experienced and new dogs were trained using these aids. The dogs were subsequently tested on detecting solid crystalline TATP synthesized using different base compounds and production methods. Dogs trained to respond to the training aids demonstrated a sufficient response to different kinds of crystalline TATP, whereas no systematic false alerts on either acetone or hydrogen peroxide were noted.

Introduction

In today’s world, improvised explosive devices and homemade explosives are a major threat to public safety. Often, these explosives are easy to make. Base components are readily available, and the production methods can be found on the Internet. However, because many of these homemade explosives are extremely sensitive to impact, friction, and electrostatic discharge, the synthesis as well as the storage can be extremely dangerous (Dubnikova et al. 2005). The friction sensitivity of triacetone triperoxide (TATP) is 0.3 Nm (nitroglycerin has a friction sensitivity of 0.2 Nm), and its explosive power is close to that of TNT (trinitrotoluene). It is classified as a primary high explosive. Incidents have been reported in which TATP has exploded without external stimulus. The known sensitivity of TATP creates a danger to those handling or storing even small amounts. TATP has been described as a common terrorist bomb by Hayden (2004), and it achieved notoriety through Shoe Bomber Richard Reid, who planned to use it on an American Airlines flight in December 2001.

Because TATP is highly volatile, it should be easy for dogs trained on its odor to locate it. However, TATP is extremely dangerous to synthesize and work with. It is therefore necessary to develop a training aid that can be produced in a safe manner. Using such an aid to train explosive detection dogs should enable them to find solid TATP—indeed, not only the TATP on which they were trained but also TATP produced in different manners, that is, by using different base components in different degrees of purity.

For example, acetone is a known degradation product of TATP (Oxley et al. 2002). This fact currently provides the basis for the training method used by some agencies in Israel, where dogs are trained to detect acetone. Based on this training method, the dogs are said to detect TATP (Gluk, personal communication, April 7, 2005). This can be a useful method depending on the operational use of the dogs. When working outdoors checking for car bombs, a dog is unlikely to come across acetone, which would create an unwanted alert. But in many countries, the same dogs that detect TATP are also used to conduct house searches, where they are likely to come across products containing acetone, such as nail polish remover. Thus, in the Netherlands, training with acetone was not considered an option.

Oxley et al. (2004) used trace amounts of solid TATP and TATP-vapor-saturated cotton balls to train and test dogs. They showed that two dogs trained on the vapor-saturated cotton balls responded directly to solid TATP both in a training-wheel situation and in a room search, after which they gradually increased the difficulty of the training-wheel tests. The tests were conducted blind, and in the room search, a non-TATP-trained bomb dog also searched the rooms as a control.

Two points of criticism can be made of this study.  First, a proper test should contain distractors that have been placed at the same time as the target odor. This is necessary to prevent the dogs from using any cue other than the target odor itself. This protocol was not systematically followed. Second, only one kind of TATP was used (high grade), and no test was done that included TATP made from different base components or synthesized in a different manner. For example, TATP can be made using either sulfuric acid or hydrochloric acid, and it can be made from high-purity components or from less pure so-called technical chemicals that could leave traces that influence the final odor signature of the product. Thus, the question of whether dogs trained on a single kind of TATP also would find the kinds of variations found in operational settings still needs to be answered.

The study presented here was conducted to investigate if the common Dutch method of making training aids (impregnating stainless steel tubes or other objects with the odor of an explosive by storing them for a minimum of 24 hours in a glass jar with solid explosives but without direct contact with the explosives) could be used to train the dogs to reliably detect different kinds of solid TATP. An analysis of the training aids was also made.

Materials

Explosive Detection Dogs

The dogs that were used in this study (crossbred Malinois shepherds and one Labrador retriever) were fully trained and certified Dutch explosive detection dogs. These dogs are trained to alert to 12 basic odors from the different explosive groups described by Furton and Meyers (2001) and are also trained to find different military and civil explosive compounds that contain one or more of these chemicals. They are also trained to detect firearms. All dogs were operationally active during the study period.

Test Material

The TATP used in the tests was synthesized as described by Wolffenstein in 1895. For this work, the synthesis was carried out to obtain 100 mg of TATP in case of quantitative yield of the product. For both the synthesis and handling of TATP, appropriate safety precautions must be taken: reinforced goggles and gloves, splinter-proof vessels, and protective shields. All chemicals were purchased from Aldrich Chemie (Steinheim, Germany), Merck (Darmstadt, Germany), Sigma (Deisenhofen, Germany), and Fluka (Neu-Ulm, Germany) in the highest purity available except where explicitly mentioned otherwise. Eight different batches of TATP were synthesized during the study (Table 1). For the tests, less than 50 mg of each TATP batch was put into a petri dish.

Table 1: Description of TATP batches used. Batch A type was used for training purposes.

H₂SO₄: sulfuric acid; HCl: hydrochloric acid; analytical grade: highest purity available for chemical analysis or synthesis; technical grade: purity related to commercially available product for everyday use.

Control odors were objects impregnated with the odor of nitroglycerin or black powder (common training odors for the dogs used). Approximately 20 g of nitroglycerin or 33 g of black powder was put into a glass jar, under a grid. The objects were placed on top of the grid and left there for 24–48 hours before use.

Distractor odors used were a small amount (less than 50 mg) of HMTD (hexamethylene triperoxide diamine) in a petri dish, a child’s marble, a pebble from outdoors, a cork from a wine bottle opened two days earlier, an empty petri dish, a wooden ice-cream stick, a cinnamon stick, an empty paper box, and a number of small objects contaminated in the same way as the control odors but with the odor of caraway seed, firelighter, cleaning detergent containing an unspecified mixture of acids (Antikal brand, manufactured by Procter & Gamble), DEET mosquito repellent, coffee creamer, dishwasher detergents, white spirit, iodine, orange-flavored and Earl Gray tea, glue, laundry detergent, hydrogen peroxide, acetone, dill seed, olive oil, lavender oil, furniture wax, vanilla oil, and lemongrass oil.

Training Aids

As training aids, stainless steel tubes (cleaned in a dishwasher and subsequently boiled for 1 hour) and pieces of untreated Kings Cotton (cotton bandage material) were impregnated with the odor of TATP. This was done in the way that Dutch training aids are commonly made, and the tubes had been used as training aids before. Cleaned tubes are not responded to by the dogs.

The explosive material (in this case, 5 mg of batch A-type TATP) was put into a glass jar and covered with a grid. Stainless steel tubes or pieces of Kings Cotton were placed on top of the grid, and the jar was closed. After 4–7 days they were removed from the glass jar containing the TATP and put into clean glass jars with twist-off lids. These aids were subsequently used for training, usually within a few days but occasionally after a longer period (up to 21 days). After use, the training aids were discarded. (Tubes were cleaned and used again. The Kings Cotton was discarded.)

The dogs in the first test group were trained by their own handlers using both the tubes and the pieces of cotton as training aids. They were trained intermittently in an operationally busy period that lasted 6–7 months. During the training they were also accidentally exposed a few times to batch B-type TATP as a result of an insufficient rinsing of the TATP synthesized for training purposes.

The dogs in the second test group were trained by their own handlers using as training aids only the stainless steel tubes impregnated with the odor of TATP. The dogs were exposed to approximately 50 of these tubes over a period of a few months prior to the test. The third test was conducted with dogs that had been trained on the impregnated tubes 4 months before the test but that had not been subjected to regular reinforcement training during the months before the test. In the fourth test, two of the dogs that had participated in the third test were retested. In the 2 weeks between the two tests, they had been given reinforcement training using the impregnated tubes as training aids. The other four dogs that participated in the fourth test had been trained recently using the impregnated tubes, but not as extensively as the dogs that participated in the second test.

Methods

Dog Search Tests

The dog search tests were conducted in a chemical laboratory at the University of Twente (Enschede, the Netherlands). The test material was distributed over a number of cupboards under the laboratory tables. The test material was added to the objects that were already stored in these cupboards. This was done in the absence of the dogs and their handlers, who were not given any information about the location of the different odors.

One by one, each handler and his dog conducted the test. The test consisted of a number of consecutive searches of a set of cupboards. The handler was told which set of cupboards to search. The handlers worked in their usual way: when a dog indicated, the handler would raise his hand to signal that the dog had made an indication. If the dog responded to a target odor, the handler was informed that his dog had chosen correctly and the dog was rewarded. This was labeled a “full response.” If the dog responded to a nontarget odor, the handler was informed of this and the dog was given a verbal correction and/or was stimulated to continue searching. This was labeled a “false-positive response.” If a search ended without an indication, the handler was asked whether his dog had seemed especially interested in an area that, if this had been an operational search, would have led to closer investigation. If this occurred in the area where the target odor was hidden, this was classified as “marked interest.” If this occurred in an area without a target odor, this was classified as a “false-positive response.”

Chemical Analysis of Training Material

The stainless steel tubes that were predominantly used for the training were analyzed for the presence of TATP. The surface of the metal pipe was cleaned using a small piece of filter paper that had been wetted with cetonitrile prior to use. Subsequently, the filter was eluted with 2 mL of acetonitrile, and the obtained solution was investigated applying a rapid photometric test scheme described in the literature based on the use of peroxidase and ABTS [2,2’-azino-bis(3-ethylbenzothiazoline)-6-sulfonate] diammonium salt (Schulte-Ladbeck et al.). The limit of detection for this method for TATP is ~4 × 10^–6 moles/liter (mol/L).

Results

Pretraining tests

Prior to the training, six operational explosives dogs were tested in the laboratory environment. They conducted two searches. The first search was a control search, meant to see if the dogs were capable of working in the laboratory, and was conducted as a nonblind training session in which the handlers were initially told where the target odor was. In this search of five open cupboards, the control odor was in one of the cupboards. Five dogs responded directly to this common training odor. One dog had more difficulty: the control odor had been placed in the back of cupboard, but when it was moved to the front, the dog responded as it had been trained.

The second search was conducted blind as described in the Methods section. In this search, one of the six open cupboards contained a petri dish with less than 50 mg of batch A-type TATP. None of the dogs responded to this odor (see Table 3). None of the dogs responded to any of the five different freshly introduced distractor odors in the other cupboards.

Chemical Analysis of Training Material

The amount of TATP adsorbed on the stainless steel tubes was too low to be determined by the method used.

Posttraining Tests

Table 2 contains a summary of the results of the four posttraining test sessions. Full response and marked interest have been taken together (as positive responses) because both of these reactions would have led to the operational decision of investigating the area further. Of the 46 searches conducted, the dogs responded to the target by indication or marked interest 34 times, of which 17 were full responses and 17 were considered marked interest. Thus, half of the indications were clear, whereas the other half were open to handler interpretation. The dogs completely missed 12 times, thus failing to indicate the target odor in 26.1 percent of the searches. Eight false indications, mostly on introduced distractors, were also noted.

Table 2: Summary of Posttraining Results

Positive responses: dogs fully indicating or so highly interested as to lead to further examination; miss: if no response was seen at all; false responses: full indication elsewhere.

In Table 3, the results are broken down into the different test sessions. For the first test, three dogs that had been trained to detect TATP using the training aids were tested in the same laboratory as in the pretraining test. The dogs conducted four searches; all searches were conducted blind in the manner described in the Methods section. In the first search, the control odor was in one of the four open cupboards. All of the dogs responded to the control odor and ignored the two distractors. In the other three searches, different batches of TATP were used (see Table 2). In the second search, one of the six open cupboards contained batch A-type TATP. All of the dogs responded to this and ignored the two distractors. In the third search, one of the three open cupboards contained batch B-type TATP. Here, two dogs responded fully to the TATP, while one paid a great deal of attention to the TATP but did not make a full response. The dogs ignored the distractor odor. In the fourth search, one of the six open cupboards contained batch C-type TATP. All three dogs responded to the TATP, while ignoring the three distractor odors.

Table 3: Results of the Dogs in Detecting TATP in Relation to Test Session and Different Production Methods  

*No dogs disqualified

In a second test, two of these dogs were tested again on TATP batches of types A, D, and E, and two newly trained dogs were tested on batch A type. The first search was a control search in which the control odor was placed in one of four open cupboards; the other three cupboards contained distractor odors. One of the “old” dogs failed to find this and made a false alert to the odor of coffee creamer. This dog was disqualified for the remaining searches. The other three ignored the distractor odors they came across and responded correctly to the control odor. These dogs were used in the following test (see Table 3).

In the second search, one of five open cupboards contained batch A-type TATP. Two dogs responded fully, and one (a “new” dog) paid a great deal of attention but did not make a full response. The three distractor odors were ignored. In the third search, one of four open cupboards contained batch D-type TATP. The one dog tested here responded fully to this odor and ignored the three distractor odors. In the fourth search, one of the six open cupboards contained batch E-type TATP. The dog paid a great deal of attention to this cupboard and ignored the three distractor odors. This dog had not made the full response to batch B-type TATP in the first posttraining test either.

In the third test, four dogs were tested on TATP batches of types A, C, D, and J. For the first search, the control odor was placed in one of four open cupboards, and the three other cupboards contained distractors. All dogs responded to the acetone distractor odor, and two dogs failed to find the control odor. These two dogs were disqualified, and the remainder of the searches were conducted with two dogs. In the second search, one of six open cupboards contained batch A-type TATP, while three contained distractors. One dog responded fully; the other was markedly interested. The distractors were ignored. In the third search, one of six open cupboards contained batch C-type TATP and two distractors. Here, neither of the dogs responded or showed marked interest in any of the cupboards. This was also the case in the fourth search, in which one of five open cupboards contained batch D-type TATP and three contained distractors. In the fifth search, one of six open cupboards contained batch J-type TATP, and three contained distractors. One dog responded to the TATP, while the other dog responded to a distractor but was not interested in the TATP.

In the fourth test, the two dogs that had been tested in the third search (one had been disqualified; the other had participated fully) were tested again, together with four new dogs. For the first search, a control odor was hidden in one of four open cupboards. Three other cupboards contained distractors. All six dogs gave a full indication on the control odor and ignored the distractors. In the second search, one of the six open cupboards contained batch A-type TATP; two others, distractors. One dog (a retest) indicated fully but also gave a false indication on a hydrogen peroxide distractor. Three other dogs (one retest, two new dogs) showed marked interest for only the TATP; the other dogs missed the target. After these two searches, the remaining three searches were conducted in different sequences by the different dogs. In one search, a batch C-type TATP was hidden in one of six open cupboards; two others contained distractors. Here, one dog (a retest) indicated fully, three others (one retest, two new) showed marked interest, and two missed. There were no false indications.

In another search, a batch H-type TATP was hidden in one of six open cupboards. Three others contained distractors. Again, the same dog (a retest) gave a full indication and no false positives. Four others (one retest, three new) showed marked interest, and one of these also gave a full response to an acetone distractor. The sixth dog missed the target odor but gave no false indications either. For the last search, a batch I-type TATP was hidden in one of five open cupboards; three others contained distractors. The same dog (a retest) gave a full indication on the TATP and no false alerts. Three others (one retest, two new) showed marked interest, one also gave a false indication on an empty box, and another gave a false indication on a cupboard without a distractor. Two dogs missed the target: one of these gave false indications on cupboards without distractors.

The results also can be analyzed by looking at the results obtained by the different dogs. These results are given in Table 4. Here, the variation between the dogs becomes clear: some dogs (1, 2, 3, 4, and 5) seemed to indicate on almost everything, but dogs that missed also did not give full responses (dogs 8, 9, and 10). Dog 6 is of particular interest. The first test in which he participated was the third, and his training had been conducted some time before the test. He missed almost everything. After reinforcement training, he participated again in the fourth test and made full indications on all of the TATP batches.

Table 4: Results obtained per dog per posttraining test session. Two dogs participated in two test sessions.These are labeled A and B.

Discussion

A number of conclusions can be drawn from the test results. First, the commonly used method in the Netherlands to produce training aids can also be used for making TATP training aids, even though the amount of TATP on the training aid is less than 1.8 μg. Because it is possible to produce small amounts of TATP in a safe way, trained scientists in sufficiently equipped laboratories can make these training aids.

Second, the Dutch system of conducting basic training using pure base components leads to a sufficient response of the dogs to low levels (<50 mg) of solid, pure TATP, to TATP synthesized with impure base components, to TATP synthesized with a different kind of acid, and to insufficiently rinsed TATP containing residual components. When incompletely rinsed, the smell of the acid used in the synthesis is discernible even to human noses.

The incomplete responses in this study can be attributed partly to the character of the dogs involved and partly to insufficient reinforcement training. Some dogs characteristically take a relatively long time to smell the odor thoroughly. It always takes more training before this type of dog makes a full alert, but in the end, they also make very few false alerts. Dogs that fully alert more easily also tend to make more false alerts. This was demonstrated by another young dog that was trained on TATP as part of its basic training. Although not yet fully trained, it readily alerted to all kinds of TATP in the second posttraining session conducted but also false-alerted twice on two of the distractor odors.

Comparing the results of the different tests with different training backgrounds leads to the conclusion that although the dogs learn to recognize the odor quite quickly, they need regular reinforcement training to give clear indications on crystalline TATP.

Third, this training does not lead to systematic false alerts on either acetone or hydrogen peroxide, both of which were present as distractor odors in almost all of the posttraining test sessions. False alerts, although undesirable, are to be expected in studies such as these. In four searches, the dogs came across hydrogen peroxide 12 times: one confrontation led to a false alert. In three other searches, the dogs came across acetone 11 times. Two dogs made false alerts in two different searches, four dogs responded to the same acetone distractor in a control search, and two subsequently failed to find a common training aid. One of these four dogs was retested and did not respond to acetone at all the second time.

These additional observations put this last occurrence into perspective. Not reacting systematically to either acetone or hydrogen peroxide is important in the Dutch operational setting, where the dogs are also used routinely to search for firearms in houses and to check for bombs in hotels and residences, where products containing acetone or hydrogen peroxide may be found. Acetone is apparently not the key element the dogs use to respond, as was also noted by Oxley (2004).

A limitation of this study is the amount of TATP used in the testing. A large amount of TATP may create a problem for the dogs; it is certainly an aspect that is part of correct training procedures on traditional explosives. Here, further chemical analytical work is necessary to see if large amounts can be mimicked, for example, by spreading out a thin layer of TATP over a large area, or if large amounts can be stabilized in some way that does not affect the odor signature of the TATP.

Trained explosives dogs can add TATP to their existing library of target odors quickly. It is a highly volatile product, which makes it very different from the usual low-volatility explosives the dogs are trained to detect. This creates additional training parameters: the dogs need to learn to localize such a volatile odor source from much farther away than they are used to, and the handler needs to recognize the typical “smelling in the air” behavior that the dogs demonstrate prior to localizing the source. The basic training can be done in a week, but the odor needs to be repeated for some weeks to lead to firm indications in different situations. Training always should be concluded with a properly controlled test on different kinds of solid TATP, so the handler can learn to recognize the dog’s behavior in the different scenarios. This testing should be conducted on a regular basis to monitor the dogs. Thus trained and tested, the dogs can provide valuable assistance in combating terrorism.

Acknowledgment

This study was conducted under a contract between the Netherlands National Police Agency and Leiden University.

References

Dubnikova, F., Kosloff, R., Almog, J., Zeiri, Y., Boese, R., Itzhaky, H., Alt, A., and Keinan, E. Decomposition of triacetone triperoxide is an entropic explosion, Journal of the American Chemical Society (2005) 127:1146–1159.

Furton, K. G. and Meyers, L. J. The scientific foundation and efficacy of the use of canines and chemical detectors for explosives, Talanta (2001) 43(3):487–500.

Gluk, Eran, Police Studies Centre, Israel Police, personal communication, April 7, 2005.

Hayden, H. T. Terrorist bombs: Can it happen here? Military.com [Online]. (March 15, 2004). Available: http://www.military.com/NewContent/0,13190,Hayden_031504,00.html.

Oxley, J. C., Smith, J. L., and Chen H. Decomposition of a multi-peroxidic compound: Triacetone triperoxide (TATP), Propellants, Explosives, Pyrotechnics (2002) 27(4):209–216.

Oxley, J. C., Smith, J. L., Moran, J., Nelson, K., and Utley, W. E. Training dogs to detect triacetone triperoxide (TATP). In: Proceedings of SPIE—Volume 5403: Sensors, and Command, Control, Communications, and Intelligence (C3I) Technologies for Homeland Security and Homeland Defense III. E. M. Carapezza, ed. The International Society for Optical Engineering, Orlando, Florida, April 12, 2004, pp. 349–353.

Schulte-Ladbeck, R., Kolla, P., and Karst, U. A field test for the detection of peroxide-based explosives, Analyst (2002) 127(9):1152–1154.

Wolffenstein, R. Über die einwirkung von wasserstoffsuperoxyd auf aceton und mesityloxyd, Chemische Berichte (1895) 28:2265–2269.