Evaluation of cold weather decontamination methods.

Most chemical or biological decontamination protocols have been driven by the need for fast and efficient methods that are relatively safe and easy to implement. As such, the focus has primarily been toward "general" environments-those in which water is readily available, and the ambient conditions are amenable to such techniques. Some of these include water showers and/or sprays with chemical decontaminants, eg, soapy water or diluted bleach. However, there exist some scenarios in which water-based decontamination methods are not desirable. These include such operational environments as arid regions (water scarcity), specialized operations (decontamination method must be low volume/weight), and cold weather (freezing risk). This study focuses on the cold weather challenge: identification of common methods for readily available decontamination and evaluation of their respective efficacies. Methods evaluated include wiping (with wet and dry wipes), blotting with moistened wipes, vacuuming, and the application and removal of adhesive tape. Results demonstrate that vacuuming and blotting (without overlapping targeted regions) are generally less effective than other wiping, blotting, and adhesive tape-based measures at removing bacteria from surfaces.

Trace explosives sampling for security applications (TESSA) study: Evaluation of procedures and methodology for contact sampling efficiency.

The detection of trace amounts of explosive materials is critical to the security at mass transit centers (e.g., airports and railway stations). In a typical screening process, a trap is used to probe a surface of interest to collect and transfer particulate residue to a detector for analysis. The collection of residues from the surface being probed is widely viewed as the limiting step in this process. A multi-institutional study was performed to establish a methodology for the evaluation of sampling media collection efficiencies. Dry deposited residues of 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), C-4 (an RDX-based explosive), and pentaerythritol tetranitrate (PETN) were harvested from acrylonitrile butadiene styrene (ABS) plastic, ballistic nylon (NYL), and uncoated aluminum surfaces using muslin, Texwipe cotton, and stainless-steel mesh traps. Transfer and collection efficiencies of the sample media were calculated based on liquid chromatography-mass spectrometry analysis. Dry transfer efficiencies (DTE%) to all tested surfaces were greater than 75%, with transfer to ABS plastic being the lowest. Collection efficiency (CE%) varied significantly across the traps and the surfaces, yet some conclusions can be drawn; nylon had the lowest CE% for all cases (∼10%), and the stainless steel mesh had the lowest CE% for the evaluated traps (∼20%). Though the testing parameters have been standardized among the participants to establish a framework for an independent comparison of contact sampling media and surfaces, substantial variations in the DTE% and the CE% were observed, suggesting that other variables can affect contact sampling.

Contact between traps and surfaces during contact sampling of explosives in security settings.

Realistic descriptions of interfacial contact between rough, deformable surfaces under load are difficult to obtain; however, this contact is of great import in a wide range of applications. Here, we detail, through experiment and computational simulation, the interfacial contact between four common traps and five commonly investigated surfaces encountered in explosives detection applications associated with airport security. The Young's modulus and hardness of four traps and seven substrates were measured using nanoindentation. These properties determine how deformation occurs when traps are applied for contact sampling of explosives. The nanoindentation data were analyzed using the Oliver-Pharr method, and an indenter area function was created using silicon and gold as the reference materials. The Young's moduli of the traps ranged from 0.2 to 8 GPa, while those of the surfaces ranged from 0.5 to 4 GPa. The hardness values of the traps ranged from 0.005 to 0.22 GPa, while those of the surfaces ranged from 0.02 to 0.2 GPa. For each of 20 scenarios (4 traps, 5 surfaces), six contact simulations were performed. In these contact simulations, the Greenwood-Willliamson microcontact model was used to represent the behavior of the asperities on the traps, while the Timoshenko Beam model was used to describe the macroscopic behavior of the bulk trap materials spanning the space between asperities. This combination of feature- and trap-scale modeling provides a more realistic description of the interfacial contact than either model applied individually. The calculated distributions of separation distances between the traps and surfaces when the traps were contacted with the surfaces under a normal load were compared to estimate the relative effectiveness of the traps at interrogating the topography of the surfaces. This method is proposed as a tool to guide the development of trap materials for surface sampling and surface cleaning applications.