A Framework for Assessing the Health Hazard Posed by Bioaerosols (2008) / Chapter Skim
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4 Implications of BAULA for Detector Test and Evaluation
4 Implications of BAULA for Detector Test and Evaluation
Pages 47-60
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From page 47... ...
This simulant testing is typically done at test chambers and aerosol wind tunnels either at developers' facilities or sometimes at DOD-maintained test facilities (such as Dugway Proving Ground (DPG) in Utah, or Edgewood Chemical and Biological Center (ECBC)
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From page 48... ...
A well-controlled test environment is especially useful in the initial stage of development, when laboratory tests can provide information to modify, redesign, and improve the system. Tests in aerosol wind tunnels provide information about sampling acquisition, including the aspiration efficiency and transmission efficiency as a function of particle size, wind speed, and sampling flow rate.(Cheng et al.
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From page 49... ...
At each of these stages, the biological activity and particle size distribution may be altered. 4.2.1 Sample Preparation An early decision in the T&E procedure is the choice and preparation of the "test material," which includes the BWA itself or a surrogate, possibly along with nonbiological particles and droplets, and interferents.
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From page 50... ...
The information on dry dissemination of biological test material is quite limited. The effects of the aerosol generation technique on the viability of the test material are largely unknown, and aerosols are generated without specific attention to how particle size distribution relates to their behavior within the respiratory tract.
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From page 51... ...
It is possible to produce test aerosols of different particle sizes primarily by adjusting the concentration of the suspended material in the liquid but also by adjusting the nozzle size, driving frequency of the crystal, and the liquid feed rate. Dry Dissemination Techniques A dry dissemination generator usually consists of a mechanism to store, transport, and deliver the test material (a powder)
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From page 52... ...
The referee system is the performance standard to which a device under test is being compared. In order to provide a reference in BAULADae units, it should provide representative and accurate information of the aerosol characteristics of the test material, including, at minimum, aerosol concentration of the active or viable agents, total aerosol concentration of viable and nonviable test material, and particle size distribution.
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From page 53... ...
There are three types of sampling methods. Filtration methods allow collection of different size fractions, can sample large volumes, and can attain 100 percent gas aspiration efficiency; however these require an extraction process that decreases aerosol collection efficiency and can affect sample viability.
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From page 54... ...
The collected liquid sample can be used for PCR, ECL, or other established bio-assays with minimal extraction to determine the level of the specific biological agent of interest. Several liquid impingers have been used to collect biological aerosols.
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From page 55... ...
BOX 4.4 Time-resolved, Continuous Measurement Systems Referee systems that collect samples provide information on biological aerosol concentration and size distribution after time-consuming laboratory assays. On the other hand, real-time measurements provide continuous monitoring of aerosol cloud and may be used to monitor aerosol in the chamber with a feedback loop to control the test aerosol concentration.
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From page 56... ...
For example, during the calibration phase, it will be necessary to verify such measures as: • the proportion of sample that is active depending on different sample preparation techniques; • the amount of sample that remains active following aerosolization; • the size distribution of the particles leaving the entering the air to be transported; • the amount of agent inactivated during transport from aerosol generator to the referee instruments; and • the response function of the different sampling instruments to active and inactive agent. These determinations will not have to be made for every test, but will have to be established for each set of instruments and for each biological agent.
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From page 57... ...
Therefore, it is difficult to assess their measurement accuracy. A standard referee instrument should have near 100 percent gas sampling efficiency, as attained by the isokinetic filter samplers used for the EPA certification of particulate matter samplers or, at least, known sampling efficiencies as a function of particle size, wind speed, and wind direction.
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From page 58... ...
Current candidate detection systems detect both viable and nonviable agent material, but to determine a detector's sensitivity in BAULADae units, evaluators must determine the detector's limit of detection for biologically active units. In order to compare the performance of the detector to the ground truth of the referee system (which will be measuring active agent concentrations)
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From page 59... ...
FIGURE 4.2 Testing requirement for minimum sensitivity. A simple example of the sensitivity bias that can be introduced if the response of a given detector to both active and inactive agent is not taken into account.
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