Abstract

With the exponential growth of the nano-technological products and their potential impact on the workers’ health and safety, the N95 filtering face-piece respirators (FFRs) are commonly recommended to protect them from the exposure to nano-particles in workplaces. This paper reports the outcomes of a series of experiments carried out to characterize the performance of NIOSH approved N95 filtering face-piece respirators against particles in nano-range: poly-dispersed and mono-dispersed sodium chloride (NaCl) particles were used in this study. In the first experimental set-up, a methodology was developed to test a N95 respirator model, sealed on a manikin head, against 15 to 200 nm poly-dispersed NaCl aerosols as function of flow rate (85, 135, 270 and 360 liters/min), loading time (up to 5 hours), and relative humidity (RH) (10, 30 and 70%). In the second phase, the experimental set-up was adapted to test N95 respirators against mono-dispersed particles (at twelve particle sizes) with a size range between 20 to 200 nm at a constant flow rate of 85 liters/min.

The results from the poly-dispersed aerosol test (PAT) method indicated that the inhalation flow rate had a strong impact on the initial particle penetration; the maximum penetration level through the N95 respirator dramatically exceeded the 5% NIOSH certification criterion at flow rates higher than 85 liters/min. The particle penetrations at the Most Penetrating Particle Size (MPPS), occurring between 30 to 50 nm, were respectively 6.6, 11.7 and 15.3% for the airflow rate of 135, 270 and 360 liters/min. The outcomes of the effect of particle loading on the filter performance showed that, the particle penetration decreased through the N95 respirator for particle sizes below 100 nm.

The mono-dispersed aerosol test (MAT) method was performed at 85 liters/min constant flow rate; the initial particle penetration at the MPPS was below 5% NIOSH certification criterion. Moreover, the initial particle penetration value, measured with (MAT) method was higher than the one measured with (PAT) method at each corresponding particle size.