Fluorescence Lights the Way Toward Improved Protective Garments

Courtesy Photo | An array of blue light-emitting diodes (LED) and a time-gated specialized camera are used to collect whole body image data from a test mannequin. (Image courtesy of Howard J. Walls, Ph.D., Aerosol Control Group Lead, RTI International)  

FORT BELVOIR, VA, UNITED STATES

12.17.2018

Courtesy Story

Defense Threat Reduction Agency's Chemical and Biological Technologies Department

Fluorescence isn’t a new concept. It’s widely found throughout nature, and fluorescent light bulbs have been around for more than a century. Even though fluorescence has long been known of, researchers with the Defense Threat Reduction Agency’s Chemical and Biological Technologies Department are using fluorescence in novel ways to improve protective garment testing. The result will provide warfighters with enhanced capabilities and improved reliability of this vital layer of agent protection.

Chemical and biological agents can be delivered in aerosol, vapor or liquid form, requiring a distinct test as each type attacks protective equipment in different ways. The current Aerosol Systems Test (AST) uses the protocol, commonly referred to as the Man-in- Simulant Test, or MIST. This procedure places a test participant into a closed recirculation chamber where they are exposed to a fluorescently tagged silica aerosol. This consists of a fine powder and simulates a chemical warfare agent (CWA) in order to replicate an aerosol-based threat.

After a test participant is exposed to the CWA simulant, pre-defined locations are analyzed by sampling the test participant’s skin. The skin is rinsed, and the amount of fluorescent tag in the rinse is measured. These measurements are combined, and with the use of a computational tool, the degree of aerosol penetration is determined and the garment system is given a rating. However, this approach involves significant time, labor and cost due to the wet chemistry methods used for analysis. Also, the site sampling limits the ability to determine points of high aerosol deposition as the method averages the amount of fluorescence.

To create a more efficient and effective test, researchers Howard Walls, Ph.D., with RTI International, Chris D. Geddes, Ph.D., with the University of Maryland, Baltimore County, and Salvatore Clementi with DTRA CB, are testing improvements that use a camera and imaging system to capture whole-body fluorescence. The imaging system includes an array of blue light emitting diodes (LEDs) that causes the fluorescently-tagged silica aerosol to glow. Using this advancement, researchers can take pictures of the whole body aerosol deposition and computationally analyze the data.

However, skin is primarily composed of protein and is naturally fluorescent. Researchers quickly discovered that the background fluorescence of human skin outshone that from deposited silica aerosol material, thereby reducing test sensitivity.

To overcome this obstacle, the team employed a specialized, time-gated camera similar to one used by NASA for measurements on aircraft. Geddes also provided a new long-life fluorescent tag that is approved for human use. After a brief light pulse from the LED array, skin fluorescence rapidly loses intensity in nanoseconds; in contrast, the long-life fluorescence tags emit light over periods of milliseconds. By waiting until the background skin had extinguished before collecting image data, the team eliminated skin fluorescence and improved test sensitivity.

The time-gated camera takes 1,000 consecutive exposures of a given position on the subject to create one image. It then moves to the next body position and repeats the process until 16 images, collected at various heights and angles, are produced. The images are used to generate composite full-body images, which are then quantified and displayed by the computer. Where the current AST procedures required multiple hours to collect and analyze data, the improved AST procedures significantly shortened the imaging, data processing and full analysis time to as little as 25 minutes, for less than half the current cost.

An additional advancement provided by the improved AST capability is the ability to gather quantitative test data that is not available through other test methods. Data is visualized in a 360-degree, whole-body image that clearly shows aerosol deposition locations and concentrations by the intensity of colored light patterns, overlaid on a grayscale body shape. A computational data visualization tool in development will provide an accurate means for displaying the specific locations and patterns of the deposited aerosol that can be viewed and manipulated by the operator.

While the current skin sampling AST provided only an average exposure of a test subject’s entire body, the improved test identifies regional “hot spots” of aerosol deposition. Re-engineering garment systems to mitigate these hotspots will allow a more rapid and cost-effective approach to performance improvement. Garment system configurations that provide a range of aerosol protection will be used to define the test’s measurement range.

Designed to realistically test protective garments and equipment, the improved AST is undergoing further optimization to better understand the potential for warfighter exposure to CWA aerosols in a simulated operational environment. The addition of a time-gated camera, long-life fluorescence tag and whole-body imaging methodology reduces the time and cost of data collection, which translates to a reduced burden on the test subject and operator.

Importantly, this enhanced approach supports the collection of quantitative data as part of a historical data library that will support future standardized testing, promote greater accuracy and reduce knowledge gaps through operationally-relevant testing. This evolving combination of testing improvements represents a significant advancement over the current methodology as it allows direct comparison of next-generation protective garments with enhanced capabilities and reliability to better protect the warfighter.

DTRA CB POC: Kendra McCoy, Ph.D.; [e-mail]

• Date Taken: 12.17.2018
• Date Posted: 12.19.2018 08:17
• Story ID: 303867
• Location: FORT BELVOIR, VA, US