The Evolution of Explosives Simulants

The Evolotion Of Explosives Simulants

Explosives simulants were initially developed when the need to train security personnel to detect explosives first arose. The introduction of the first technological explosives detection systems motivated further development, which continued and expanded in parallel to the upgrading of these technologies.

First generation simulants replicated properties important for detection by humans, such as color, texture and typical external appearance. In the absence of technological solutions, these properties served as the basis for the identification of explosives.

Subsequently, with the production of the first generation X-ray based explosives detection scanners, second generation simulants were developed to meet the specific requirements of technological detection systems. These new simulants replicated X-ray absorption properties as interpreted by the screener's eyes.

The added possibility of developing calibration tools and databases of concealed IEDS, to be used for training, testing and quality assurance purposes, further broadened the potential uses of explosive simulants.

However, the complexity involved in the development of second generation simulants, replicating actual explosives in a broader range of characteristics, presented a dilemma. While there was logic behind the use of two separate lines of simulants – one intended for manual searches and the other for technological detection, innovative security concepts integrating the human element and advanced technologies supported the use of one set of simulants meeting both needs, despite the greater challenge presented by their production.

The choice of simulants was therefore dependent on the application: where detection was based solely on X-ray images, with no human contact – texture and color were meaningless. However, in integrated security operations, all properties (first- and second generation) were necessary to increase detection rates.

The later development of dual energy X-ray scanners capable of distinguishing between organic and inorganic materials led to the deployment of a new type of automatic detection systems, requiring third generation simulants. These upgraded versions offered enhanced detection based on Z effective properties, and not on density alone. This also presented the opportunity of new applications, such as pre-certification and training on the proper implementation of integrated security procedures when using automatic explosives detection scanners.

However, the deployment of these dual energy scanners – both automatic and operator decision – presented a major obstacle: false alarms, as well as certain detection limitations. The development of multi-view CT explosives scanners effectively overcame these challenges, as the CT scanners enabled advanced analysis without interference from other layers, such as exist in one view scanners. This led to the determination of a precise CT# scale enabling to accurately distinguish between inert materials and explosives.

Further scanner upgrading necessitated the development of fourth generation simulants, providing highly selective detection windows and typical computed tomography properties for accurate CT#, while preserving all other X-ray properties. The challenge was to unify the sophisticated algorithms based on real explosives' properties and cover all the detection parameters. The new detection thresholds required enhancing the simulants' performance level in relation to previous applications, as well as new ones, above all – calibration and verification.