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Development of an aerosol system for creating uniform samples of deposited bacteria.

Baron-P; Estill-C; Schnorr-T; Wright-J; Dahlstrom-G; Beard-J; Ward-D
Proceedings of the AAAR 23rd Annual Conference, October 4-8, 2004, Atlanta, Georgia. Mount Laurel, NJ: American Association for Aerosol Research, 2004 Oct; :222
In the aftermath of the anthrax incidents in October 2001, it was apparent that techniques for sampling surfaces for biological agents had not been validated. Several techniques for biological particle removal from surfaces existed but gave varying and uncertain sampling efficiencies, especially at low surface loadings. A project was initiated to develop a system for producing sets of samples having targeted surface concentrations of biological agent-containing particles. Particles aerosolized from a dry powder were to be allowed to settle onto surfaces to simulate the results of the anthrax incidents. A 4' x 4' x 8' test chamber was constructed of static dissipative plastic. Particles were aerosolized using a modified Small Scale Powder Disperser (TSI, Inc.), size selected to less than 5 micrometers using an impactor, and deionized by mixing with air from a bipolar ion source. The aerosol was initially dispersed into the chamber at relatively high air concentrations and monitored using a TSI Aerodynamic Particle Sizer (APS, TSI, Inc.). The aerosol in the chamber was stirred using several fans and the particle concentration in the chamber allowed to decay using stirred settling and dilution (HEPA filter and pump). When the desired air concentration was reached, the sampling surfaces were uncovered and exposed to the (stirred) settling particles. A sample handling and covering system was designed to allow sample manipulation through several glove ports on one side of the chamber as well as sample collection from individual surfaces after exposure. After the desired fraction of particles had settled on the surfaces, the chamber air was flushed clean with HEPA filtered air. Subsequently, the chamber was opened and the surfaces were sampled or removed for evaluation. The APS provided the particle concentration in the chamber, allowing estimation of the number of particles deposited on the surfaces. Four types of surface samples were exposed: agar plates (8), silicon wafers (8), stainless steel rectangles (9), and carpet rectangles (9). The agar plates allowed determination of the colony-forming- unit (CFU) surface concentration. The silicon wafers were evaluated using a light scattering system (Surfscan, KLA-Tencor Inc.) to test for surface deposit uniformity. The stainless steel and carpet surfaces were used to evaluate surface wipe and vacuum sampling techniques. An initial test of the chamber using B. atrophaeus var. globigii (BG) indicated agar surface sample CFU variability of 15% relative standard deviation. Further improvements are planned to reduce this to about 5% and to ensure proper containment of potentially harmful bacteria. Analysis of the samples will be performed by culture techniques and polymerase chain reaction amplification. Tests will be performed with several biological warfare agent simulants. These measurements will allow the estimation of sensitivity, precision, and bias of the surface sampling and analytical methods.
Aerosols; Aerosol-sampling; Aerosol-particles; Bacteria; Bacterial-dusts; Biological-agents; Sampling; Surface-properties; Simulation-methods; Monitoring-systems; Air-monitoring; Air-sampling; Analytical-methods
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Proceedings of the AAAR 23rd Annual Conference, October 4-8, 2004, Atlanta, Georgia
Page last reviewed: May 5, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division