Comparison of simulated respirator fit factors using aerosol and vapor challenges

Although not well established, mask leakage measured using submicron aerosol challenges is generally accepted as being representative of vapor challenges. The purpose of this study was to compare simulated respirator fit factors (FFs) measured using vapor challenges to those measured using an aerosol challenge. A full-facepiece respirator was mounted on a headform inside a small enclosure and modified with controlled leaks (laser-drilled orifices) to produce FFs ranging from about 300 to 30,000. A breathing machine was used to simulate breathing conditions of 1.0 L tidal volume and 25 breaths/min. A monodisperse aerosol consisting of 0.72 micron polystyrene latex spheres (PSL) was used for the reference test aerosol, and FFs were measured using a laser aerosol spectrometer. An inert gas, sulfur hexafluoride (SF6), and an organic vapor, isoamyl acetate (IAA), were used as the vapor challenges. The in-mask concentration of SF6 was measured using a gas chromatograph (GC). A GC was also used to quantify in-mask IAA concentration samples actively collected with sorbent tubes. FF measurements made with the PSL aerosol challenge were conducted in sequence with the SF6 and IAA challenges, without disturbing the mask, to yield matched data pairs for regression analysis. FFs measured using the PSL reference aerosol were found to correlate well with those measured with the SF6 (r2 = 0.99) and IAA (r2 = 0.98) vapor challenges. FFs measured using IAA tended to be higher at values below 10,000. The best agreement was observed with the inert gas, SF6. The results of this study suggest that submicron aerosols are suitable as quantitative fit test challenges for assessing the performance of respirators against inert vapors.