Explosives Simulants for Trace Detection

Explosives Simulants for Trace Detection

TDS systems identify the presence of explosives by implementing a different approach. Instead of trying to analyze the IED through its internal components, residue of explosives molecules remaining on the IED's surface during its assembly or through particles migration processes are collected using a vacuum device or swabs. This residue is then analyzed by sensitive analytical equipment that investigates its chemical and physical properties.

When evaluating the effectiveness of the trace detection approach, we must consider both stages: not only the analysis, but also the sampling. Understanding the importance of each stage to detection accuracy enables to optimally train operators and validate biosensors (in case of canines and other animals) and technological sensors.

Analysis

The first trace detectors comprised color reagents, which produce a change in color when they come into contact with explosives. These kits are suitable mainly for trace amounts that can be seen with the naked eye. Two basic types of simulants were developed for these reagents. The first involves the use of a non-explosive compound that reacts with the reagent to provide a color indication. The second type, which is also easier to produce, involves mixing a trace amount of real explosives with an inert chemical, producing a substance that will not detonate at trace detectors' detection levels and will therefore not be categorized as a hazardous material by the authorities.

The dilution method became widespread with the deployment of a second major trace technology: the mass spectrometer (MS), which detects trace molecules according to specific parameters of molecular weight and drifting time. MS technology enabled upgrading calibration and validation using diluted explosives.

The use of diluted explosives also facilitates the training of canines to detect explosives. Since the precise way dogs sense various chemicals is complex and not fully understood, the dilution method is preferable, as it ensures the canines are indeed being trained to detect the real explosive material, focusing on its unique active elements.

Sampling

Sampling efficiency is dependent on explosives' surface adhesion properties; it is not always a simple case of sampling a powder. For example, plastic bonded explosives like C4 contain a very "sticky" binder, which binds the RDX explosives powder inside. When this explosive comes into contact with a surface, a thick layer of the binder with the RDX powder remains attached to the sampled surface. Sampling in this case is different than sampling free powder, such as TNT, which has much lower adhesive forces to the surface.

Improved sampling tools are currently under development, and are expected to be available in the near future.