AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Bacillus Spore Filtration Efficiency of HEPA Filters
JACKY ANN ROSATI ROWE, April Corbett, Alfred Eisner, US EPA
Abstract Number: 579 Working Group: Homeland Security
Abstract When anthrax contaminated buildings are decontaminated, air is typically removed from the building with high flow vacuum systems using HEPA filters. There is concern, in the clean up/responder community because of the toxicity of the removed agent, and because of the high flow rates used in these systems, that spore collection efficiency may not be as needed. To this end, we conducted research to investigate the spore breakthrough/bypass of HEPA filters at high flow.
Because of physical similarities, Bacillus thuringiensis Var. kurstaki (Btk) was used as a simulant for Bacillus anthracis. A Dash 5 portable air cleaner was used with Magna 1000 series HEPA filters (rated 99.97% efficiency). Aerosol was generated, using a BGI Three-Jet Collison nebulizer, with varying spore concentration levels. Aerosol size distributions and concentrations were measured both prior and post filtration by an Aerodynamic Particle Sizer 3321. Samples of surfaces upstream and downstream of the HEPA filters were collected using microbial swabs and analyzed.
Duplicate runs were performed at four different experimental conditions: high spore concentration/high flow, high concentration/low flow, low concentration/high flow, low concentration/low flow. Generated aerosol size distributions were bimodal, with peaks at 0.65 and 1.2 micron aerodynamic diameters. These peaks were consistent throughout all experiments, with the lower peak being determined via UV APS to be water droplets, and the higher peak being determined to be biological materials. At all experimental conditions, filtration efficiency was 99.99% + or - 0.29. The lowest filtration efficiency occurred at the high spore concentration/high flow conditions.