SubscribeHistorically, methods for testing components and systems designed to detect and identify aerosolized Biological Warfare Agents (BWAs) primarily involved simulant testing in either the laboratory or at outdoor field trials.
In the laboratory, good control over several important test variables (such as bioaerosol concentrations and durations) can be achieved, though the ambient environment cannot be realistically simulated and can have dramatic effects on biodetection system performance.
Alternatively, outdoor field trials can provide a realistic, high-desert environment, though typically the inherent unpredictable nature of the weather prevents an adequate number of quality tests to be performed in an efficient manner, especially in any type of “developmental” test effort. In parallel with Battelle’s BWA detection system hardware development efforts over the past several years, the need for more effective, more efficient test methodologies was realized.
In response to that dynamic need, Battelle’s Aerosol and Process Technologies (APT) Product Line has developed and implemented several alternative test methodologies designed to “bridge the gap” between laboratory and field bioaerosol testing, and therefore provide biodetection system developers with necessary data upon which to make important system-level decisions.
The demonstrated methodologies allow well-controlled, well-characterized bioaerosols to be presented to the tested systems so that many important system characteristics, such as limits of detection as a function of simulant type, concentration, and particle size, can be characterized. Methods developed by Battelle for testing bioaerosol “point” detection systems include laboratory aerosol wind tunnels, portable “containment boxes”, and the Ambient Breeze Tunnel.
THE AEROSOL WIND TUNNEL APPROACH
APT makes use of a variety of aerosol wind tunnels for numerous applications including filter testing, aerosol characterization, and bioaerosol detection equipment characterization. To test relatively high-volume (50 to 1000 Lair×min-1) aerosol samplers and biodetection systems with both inert and biological aerosols, APT designed and developed a specific bioaerosol wind tunnel – the High Volume Aerosol Delivery System (HVADS).
The HVADS can be combined with numerous bioaerosol generation devices and characterization systems to provide an effective test bed for assessing the performance of biodetection systems and components under well-controlled, repeatable conditions.
It is well suited for bioaerosol collector evaluations (to assess collection efficiencies and concentrating factors as functions of bioaerosol type and size), collector comparisons, and trigger/detector/system evaluations (to assess limits of detection as functions of bioaerosol type and size). Variants of the HVADS have been developed for other specific testing needs as needed.
Figure 1 is a picture of the HVADS being used to test the Joint Biological Point Detection System (JBPDS) system with well-controlled bioaerosols. Since testing with the HVADS allows repeatable tests to be performed efficiently (dozens of high quality tests per day), statistically-significant quantities of data can be obtained in a reasonable timeframe, thus allowing accurate, timely estimates of system performance to be made. Figure 2 shows an HVADS-type test system being used to test a novel bioaerosol collector.
Here, the effects of particle size on collector performance, as functions of collector variables (such as sampling and liquid output rates) can be assessed. The readily obtained performance data can then be used by system developers to optimize system performance, to intelligently conduct system-level tradeoffs, and to assess system-level bioaerosol detection capabilities.
Figure 1. Picture of the HVADS as used to test a bioaerosol detection system in a laboratory setting.
Figure 2. Picture of an HVADS-type test system as used to test a bioaerosol collector.
THE CONTAINMENT BOX APPROACH
In developing the JBPDS, Battelle recognized the need for a test system similar to the HVADS approach, but in a more portable form. APT developed the “containment box” testing approach in which custom chambers are designed specifically to fit the system’s air inlets. As with the HVADS concept, test bioaerosols can be precisely generated and presented to the system on demand, and reference samplers can be used to characterize the test aerosol.
The methodology can be used in almost any environment, as the generated aerosol is contained and does not exhaust from the system due to HEPA filter units designed and constructed for the system air exhausts. Figure 3 shows a picture of a containment box test system being used to verify the performance of a JBPDS system in the laboratory. Since this approach is quite portable and does not allow the generated aerosols to be released into the environment, it can be used in many locations.
Originally, the methodology was developed to assess whether the performance of JBPDS was adversely affected due to integration onto a ship (see Figure 4). On the ship, the air inlet paths were longer and more convoluted than in previously tested versions of JBPDS, therefore potentially adversely affecting the system’s effectiveness.
The containment box approach allowed tests to be performed aboard the ship upon installation, and those results could be compared to previously obtained data to assess whether the system performance was affected. Since that time, Battelle has made use of this approach for other purposes, including “confidence testing” (similar to the original work on the ship) and JBPDS production line testing as part of system acceptance testing.
Figure 3. Picture of Containment Box approach used to test a bioaerosol detection system in the laboratory.
Figure 4. Picture of Containment Box approach as used to test a shipboard bioaerosol detection system.
THE AMBIENT BREEZE TUNNEL APPROACH
In the past, millions of dollars have been spent for developmental field testing of bioaerosol detection systems. Unfortunately, months of field tests often resulted in limited useful performance data. In response to the need to generate quality performance data on field-ready bioaerosol detection systems in a cost-effective manner, APT developed a concept for a large aerosol wind tunnel – the Ambient Breeze Tunnel (ABT). The first ABT was built and characterized at Battelle’s facility in West Jefferson, Ohio. Figures 5 and 6 show a picture and schematic of the Battelle ABT.
The facility is approximately 150 ft long, has a 20 x 20 ft (center height) cross-section, and provides for wind speeds of up to about 5 miles per hour. Incoming ambient air is effectively mixed with intentionally generated materials for testing (aerosols and vapors); spatial variations have been consistently measured to be less than 5 percent at the sampling region, which is well within the sampling and instrumentation variability associated with the measurements.
Because of its size and operational characteristics, the ABT can be used to test several large items (including HMMWV-mounted systems) simultaneously, allowing for high quality, efficient, head-to-head testing to be performed in a reasonable timeframe.
Figures 7 and 8 show pictures of the ABT being used to test multiple bioaerosol detection systems and an HMMWV-mounted system. Typically, several dozens of high-quality tests can be performed in only a few days, resulting in significant cost savings and an increase in data quantity and quality when compared to historical field testing.
The ABT development effort began in the latter part of 2000, culminating in a first operational test of several biodetection systems in April of 2001. Since that time, additional test objectives for several different programs have been levied onto the ABT approach, and Battelle has continued to develop the specific methodologies to meet each program’s technical objectives.
These include work to repeatedly generate numerous concentration-time profiles, gases and vapors, selected interferants, “dry” simulants, and combinations of these. To further support the Government’s needs for effective field-ready detection system testing, a second ABT was built by Battelle at Dugway Proving Grounds in 2001.
Figure 5. Battelle’s Ambient Breeze Tunnel.
Figure 6. Schematic of Battelle’s Ambient Breeze Tunnel.
Figure 7. Numerous Bioaerosol Detection Systems Being Tested in the ABT.
Figure 8. A HMMWV-mounted Bioaerosol Detection System Being Tested in the ABT.
ADVANTAGES OF THE DEMONSTRATED APPROACHES
The described bioaerosol test approaches are valuable tools that can be used effectively towards developing and optimizing bioaerosol detection systems and their components, and in assessing the performance of these types of systems with respect to other systems and in many different environments. The approaches provide relevant test data with which to assess the performance of bioaerosol systems with several types of bioaerosols, and at a wide range of concentrations and aerosol size distributions.
Further, the approaches are adaptable to be used with nearly any type of system designed to either collect, detect, and/or identify bioaerosols, and in nearly any type of environment. In general, the demonstrated test methodologies offer several advantages over historically used test methodologies:
- They permit reproducible challenge bioaerosols to be presented to any point detection system.
- They greatly reduce the amount of time required to perform significant numbers of tests.
- They increase confidence in the data obtained by controlling the bioaerosol generation rate and ensuring that valid reference data are obtained.
- They eliminate dependence upon weather, thereby reducing downtime.
- They permit testing to be performed in any environment (CONUS, OCONUS, shipboard, etc).
- They save significant amounts of money, time, and effort over the alternative testing methods historically used, and can be adapted to answer many of the questions that current methods do not.
THE NEXT STEP – STANDOFF DETECTION TESTING METHODOLOGIES
Due in large part to the successes demonstrated by Battelle’s test methodology development efforts for the “point” bioaerosol detection test community, the “standoff” test community has embarked on programs designed to develop effective test methodologies for their respective hardware programs. Unlike point systems, standoff systems interrogate large areas from several kilometers for the presence of chemical and biological aerosols.
The primary challenges associated with developing effective test methodologies for these types of sensors include generating well-controlled aerosols along a significant path length (at least dozens of meters), while remaining “invisible” to the standoff detection system and providing reasonable containment of the generated materials.
Battelle has and is currently working these types of methodology development programs, and is having significant success towards developing methodologies with which the standoff detection community can efficiently and effectively test their hardware.
