An Evaluation of Explosive Odor Signature Persistence on Training Aid Substrates

Explosives threaten the well-being and lives of civilians, fire service, law-enforcement, and military personnel daily, with injury and fatality reports from the United States Bomb Data Center (USBDC) totaling 127 in the year 2021.The need for detection of these explosives is imperative, with canines being most utilized as bio-detectors for their ability to locate and signal target explosive odors. However, certain explosives are not available to canine handlers for training due to safety regulations, transportation protocols, and other restrictions related to budget or resources, so other training methods are required. One such option is a non-pseudo alternative. Non-pseudo alternatives include encapsulating the true (pure) material, diluting the true material, or impregnating a material by adsorbing the true material’s VOCs from its headspace. The advantage of impregnating a material via headspace of a true material is ease in transportation and handling of the adsorbent, therefore bypassing any risk of detonation or safety restrictions. Getxent polymer tubes is a recently developed impregnation alternative available to handlers, as the tubes are an impregnable material, previously cited in peer reviewed research as collection substrates for substances such as triacetone triperoxide (TATP), smokeless powder, and biomedical matrices. However, to date, no research has been openly disclosed studying their ability to retain primary VOCs of sample matrices of interest as a function of material mass or validating shelf-life perspectives. With this research gap in mind, the goal of this study is to use a common plastic explosive, Composition C-4 (C-4) bulk material to monitor the ability of Getxent tube technology to impregnate key explosive odor markers of interest for biological detection training, and more so, evaluate the persistence of key odor volatile retention across time on this targeted substrate. The objectives of this research are to 1) evaluate target VOC concentration absorption by Getxent tubes following variations in bulk C-4 mass and time impregnation, and 2) monitor its odor persistence over a period of up to 3 - months. Before Getxent impregnation, the bulk C-4 material headspace was analyzed with a PDMS SPME fiber chemistry for 24 hours. The three selected primary odor volatiles used for monitoring impregnation and shelf life were 2 – ethyl, 1 – hexanol (2E1H), cyclohexanone, and 2,3–dimethyl – 2,3–dinitrobutane (DMNB) given their importance within the literature as odor markers for this explosive type. The three mass variations selected were 1 g, 10 g, and 20 g of C-4 explosive, with time impregnation variations of 24 – hour, 72 – hour, and 1 – week. In total, 54 replicates of Getxent tubes were impregnated using the differing mass and time impregnations. A statistical analysis (using mass and time impregnation factors resulted in statistically significant differences in absorption concentrations of C-4 VOCs within Getxent tubes, resulting in 1 g 24 – hour yielding the lowest VOC concentration and 10 g 1 – week yielding the highest. A longitudinal study of the VOCs over a period of three months found that DMNB was detected in higher concentrations across all samples with a range of concentration between 0.8 g/mL and 32 g/mL, while 2E1H and cyclohexanone had a lower consistent concentration over time (average of 0.42 g/mL for 2E1H and 1.23 g/mL for cyclohexanone), with some replicates losing detection levels of the two VOCs after a period of 2 months. The study demonstrated the capability of the Getxent tube technology in the impregnation of target odor volatiles from the C-4 explosive, while exhibiting differences in concentration and shelf life across the distinctive odor volatiles monitored. The results suggest that while the Getxent tube technology does provide an impregnation substrate for explosive odor targets, it is crucial to understand the behavior of individual odor chemicals as a function of time given its potential impact on canine detection and performance.