SYSTEM-DESIGN AND TEST METHOD FOR MEASURING RESPIRATOR FILTER EFFICIENCY USING MYCOBACTERIUM AEROSOLS

Recently, the protection of health care workers from tuberculosis-cont aining aerosols has been the subject of considerable debate. An experi mental apparatus and test protocol were developed to measure the colle ction efficiency of surgical mask and respirator filter media using a microbial aerosol challenge. Mycobacterium chelonae (M. chelonae), use d as a surrogate for Mycobacterium tuberculosis, was generated from li quid suspension using a Collison nebulizer. Upstream and downstream co ncentrations of viable aerosol particles were measured using Andersen cascade impactors, while total particle concentrations were measured w ith an aerodynamic particle sizer (APS). A monodisperse polystyrene la tex (PSL) sphere aerosol (0.804 mum) was used in separate experiments to measure filter efficiency; concentrations were determined with the APS. The mycobacterial aerosol ranged in size from 0.65 to 2.2 mum whe n measured with the cascade impactor. A similar size range was found w ith the APS, yielding a count median diameter of about 0.8 mum. Sample s of the mycobacterial aerosol were collected on glass slides; stained M. chelonae, as determined by environmental scanning electron microsc ope, were found to be rod shaped with an average length of 2 mum and a verage width of 0.3 mum. To evaluate the apparatus over a range of fil ter efficiencies (10-100%), different layers of fiberglass filter pape r were tested for penetration using a 0.12 mum dioctyl phthalate (DOP) aerosol measured with a light scattering photometer, in addition to t he mycobacterial and PSL aerosols. For the range of efficiencies teste d it was shown that filter collection of DOP was linearly related to t hat of both mycobacterial and PSL sphere aerosols (r2 = 0.99), demonst rating that an inert aerosol may be used to predict the collection of biological aerosols by such filter media.