Respirator Leak Detection by Ultrafine Aerosols: A Predictive Model and Experimental Study

Abstract

The leak performance of half-mask, maintenance-free respirators was studied theoretically and experimentally. A predictive model for the theoretical protection factor and leakage flow has been developed that uses the equation of particle conservation inside and outside the respirator. An experimental study was conducted using NaCl particles of 10 nm in diameter and a condensation nucleus counter as the particle detector. A respirator fitted with controlled leak holes of 20-3000 p m in diameter was tested at steady flow rates of 10, 32, and 100 L/min. Results showed that the aerosol penetration into a respirator was strongly influenced by the filter efficiency, leak hole size, and flow rate through the respirator. The results are in good agreement with theory, but some discrepancy bas been noted at lower flow rates and smaller leak hole sizes. For the dnst/mist respirators, the experimental protection factor for ultrafine 0.01-pm NaCl particles ranged from 3145 to as low as 3. For the high efficiency dust/mist/ fume/radionuclide respirator, a protection factor as high as 4.1 X lo9 was measured on the ultrafine aerosol. For all respirators, the protection factors decreased rapidly with increasing leak hole size and increased as flow rate decreased.The result of the study shows that with ultrafine aerosols, the particle penetration through the respirator filter can be reduced to a small, and in some instances, negligible value. The resulting protection factor is then due almost entirely to aerosol penetration through the leak hole. The ultrafine aerosol test can thus be used to study the characteristics of the face seal leakage, without the complication of the aerosol penetration through the respirator filter.

Respirator Performance against Nanoparticles under Simulated Workplace Activities

“…exhalation valves). The filter penetration of particles is dependent on particle diameter, particle charge state, filter fiber charge, fiber packing density, and filtration velocity, while FSL is dependent on the fit of the respirator to the face and work activity (Liu et al , 1993; Han et al , 2005; Grinshpun et al , 2009). …”

Simulation and Evaluation of Respirator Faceseal Leaks Using Computational Fluid Dynamics and Infrared Imaging

“…The N95 filtering facepiece respirator (FFR) is widely used in workplace environments to prevent exposure to hazardous aerosols. The protection provided by an FFR is a function of leakage between the respirator and the face (Liu et al, 1993) as well as particle penetration through the filter medium (Grinshpun et al, 2009). Quantitative fit tests can determine the overall performance of a respirator but cannot identify the specific location of facepiece leaks.…”

Penetration of nanoparticles through fibrous filters perforated with defined pinholes

“…In the case of nanoparticles, could diffusion within the leak be the cause of their higher collection efficiency than for larger particles? Liu, Lee, Mullins, and Danisch (1993) define a criterion, which allows us to characterise respiratory mask protection against NaCl nanometric particles in the presence of a calibrated leak. Their measurements indicate large decreases in this protection coefficient, when the mask is perforated.…”