Comparison of Simulated Respirator Fit Factors Using Aerosol and Vapor Challenges

Abstract

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.

Total Inward Leakage of Nanoparticles Through Filtering Facepiece Respirators

“…Based on these results, the authors suggested that fit test utilizing a vapor or gaseous agent may be a more critical test in terms of penetration than fit tests using an aerosol. Another study indicated that the lower apparent fit factors measured with acetone vapor may be due to the vapor permeation through the filter media to increase the concentration inside the respirator (Gardner et al, 2004). Further studies showed that the simulated fit factors measured with a gaseous challenge agent sulfur hexafluoride (SF 6 ) was $25% higher than those measured for PSL aerosol challenge with no significant difference between the two test agents (Gardner et al, 2004).…”

“…Another study indicated that the lower apparent fit factors measured with acetone vapor may be due to the vapor permeation through the filter media to increase the concentration inside the respirator (Gardner et al, 2004). Further studies showed that the simulated fit factors measured with a gaseous challenge agent sulfur hexafluoride (SF 6 ) was $25% higher than those measured for PSL aerosol challenge with no significant difference between the two test agents (Gardner et al, 2004). However, the simulated fit factor values measured using isoamyl acetate (IAA) vapor showed a significant decrease at sealed conditions and an increase at larger leak sizes than the values obtained with PSL particles.…”