Aerosol and Air Quality Research, 16: 2428–2437, 2016 Copyright © Taiwan Association for Aerosol Research ISSN: 1680-8584 print / 2071-1409 online doi: 10.4209/aaqr.2015.07.0466 Assessing the Protection Provided by Facepiece Filtering Respirator: New Model Involving Spherical Porous Layer with Annular Peripheral Opening Ilnar T. Mukhametzanov 1 , Sergey A. Grinshpun 2* , Shamil K. Zaripov 1* , Artur K. Gilfanov 1 1 Kazan Federal University, Kazan 420008, Russia 2 Center for Health-Related Aerosol Studies, University of Cincinnati, Ohio 45267-0056, USA ABSTRACT The penetration of aerosol particles inside a facepiece filtering respirator (FFR) was investigated using a novel model, which involved a spherical porous layer representing a filter and an annular peripheral opening representing a faceseal leakage. The model utilized a two-dimensional laminar incompressible flow in a free space and porous zones that are numerically solved by a computational fluid dynamic code FLUENT. Following the model validation, the efficiency of an FFR with an annular faceseal leakage opening was investigated as a function of the inhalation flow rate, particle size, and the ratio of the leak-to-filter areas. The filter material permeability was determined for a conventional N95 filter medium. It was found – for two inhalation flow rates (Q i = 30 and 85 L min –1 ) and three particle diameters (d p = 50 nm, 100 nm and 1 µm) – that once the faceseal leakage area exceeded 0.1% of the total surface of an N95 facepiece, the respirator was unable to offer the 95% protection – the minimum level that should be provided by its filter. It was demonstrated that under certain leakage condition (partially determined by the inhalation flow rate), the respirator protection level becomes independent on the particle size; furthermore, it is not anymore affected by the efficiency of its filter, and is only influenced by the size of the faceseal leakage. Keywords: Respiratory protection; Penetration; Filter; Faceseal leakage; CFD. INTRODUCTION Facepiece filtering respirators (FFRs) are widely used for protecting the human respiratory system from various aerosol hazards. Inhalation of ultrafine/nano-scale (< 0.1 µm) and fine (< 2.5 µm) particles is of significant concern because these particles can penetrate to the lower sections of the respiratory tract and cause health problems. The protection offered by an FFR is often determined by measuring the efficiency of a respirator filter. E.g., the National Institute for Occupational Safety and Health (NIOSH) grants a respiratory protection device an N95/R95/P95 certification if the collection efficiency of its filter is at least 95%. However, the respirator performance also depends on the fit, which involves the respirator peripheral area because – beyond the filter media – the particles may readily penetrate through the faceseal leakage (Fig. 1(a)). Experimental studies, e.g., Chen and Willeke (1992) and Grinshpun et al. (2009), have demonstrated that even small * Corresponding author. Tel.: 1-513-558-0504; Fax: 1-513-558-2263 E-mail address: sergey.grinshpun@uc.edu; shamil.zaripov@kpfu.ru faceseal leakage can considerably decrease the protection level offered by a facemask. The particle flux through a leak depends on factors such as the breathing flow rate, particle size, leak size, and filter air permeability. The manikin-based performance evaluation of faceseal filtering respirators and masks with artificial leaks (both peripheral and in-filter ones) was conducted by several investigators, including Hinds and Kraske (1987), Chen and Willeke (1992), Lee et al. (2005), Rengasamy and Eimer (2011) and Rengasamy and Eimer (2012). The effect of the faceseal leakage on the particle penetration inside a respiratory protection device was discussed by Grinshpun et al. (2009), Cho et al. (2010), He et al. (2014) and others. Modeling of the protection offered by a non-perfectly fit FFR is important for predicting the actual aerosol exposure for a wearer and optimizing the design of respirators. A 3D computational fluid dynamic (CFD) model developed by Lei et al. (2013) for a human head geometry demonstrated that faceseal leaks are primarily formed in the nose area as well as under the chin; however, the contributions of the particle penetrations through the filter and the faceseal leakage remain insufficiently characterized. A parametric study utilizing a user-friendly mathematical model would be useful for predicting the protection of respirator as a function the breathing regime, particles size, leak size, filter material permeability, and other variables.