A comparison of facemask and respirator filtration test methods

Abstract

NIOSH published a Federal Register Notice to explore the possibility of incorporating FDA required filtration tests for surgical masks (SMs) in the 42 CFR Part 84 respirator certification process. There have been no published studies comparing the filtration efficiency test methods used for NIOSH certification of N95 filtering facepiece respirators (N95 FFRs) with those used by the FDA for clearance of SMs. To address this issue, filtration efficiencies of "N95 FFRs" including six N95 FFR models and three surgical N95 FFR models, and three SM models were measured using the NIOSH NaCl aerosol test method, and FDA required particulate filtration efficiency (PFE) and bacterial filtration efficiency (BFE) methods, and viral filtration efficiency (VFE) method. Five samples of each model were tested using each method. Both PFE and BFE tests were done using unneutralized particles as per FDA guidance document. PFE was measured using 0.1 µm size polystyrene latex particles and BFE with ∼3.0 µm size particles containing Staphylococcus aureus bacteria. VFE was obtained using ∼3.0 µm size particles containing phiX 174 as the challenge virus and Escherichia coli as the host. Results showed that the efficiencies measured by the NIOSH NaCl method for "N95 FFRs" were from 98.15-99.68% compared to 99.74-99.99% for PFE, 99.62-99.9% for BFE, and 99.8-99.9% for VFE methods. Efficiencies by the NIOSH NaCl method were significantly (p = <0.05) lower than the other methods. SMs showed lower efficiencies (54.72-88.40%) than "N95 FFRs" measured by the NIOSH NaCl method, while PFE, BFE, and VFE methods produced no significant difference. The above results show that the NIOSH NaCl method is relatively conservative and is able to identify poorly performing filtration devices. The higher efficiencies obtained using PFE, BFE and VFE methods show that adding these supplemental particle penetration methods will not improve respirator certification.

SARS-CoV-2: the emergence of a viral pathogen causing havoc on human existence

“…Social distancing, on the other hand, will help in limiting the spread of virus from carriers who are yet to develop symptoms but have already contracted the virus. N95 filtering facepiece respirators (N95 FFRs), which are being widely used as a precautionary measure, are efficient (99.8%) in filtering particulate matter of size up to 0.1 lm (Rengasamy et al 2017). Since the size of SARS-CoV-2 is 0.1 lm in diameter, N95 FFRs can almost competently filter them out.…”

Current understanding on the Effectiveness of Face Masks and Respirators to Prevent the Spread of Respiratory Viruses

“…Performance of a filtering device is measured in terms of filtering efficiency (E) or assigned protection factor (APF) which are defined as [56,57] :…”

“…The other technical details for NIOSH NaCl aerosol method are: a) pre-conditioning of the filtering device at ~85% relative humidity and ~38 °C for 24 hours, b) 2% (wt/vol) aerosolized NaCl solution should be charge neutralized and then passed through the convex side of filtering device. The filtering device should be properly sealed on the sample holder or mannequin [56] . The flow rate of 80 Lmin -1 simulates the breathing volume during a heavy work load.…”

“…A summary of filtration efficiency of different face masks and respirators along with few test parameters is summarized in table 1. [59] ≥99.2% H1N1 viable virus, flow rate 85 L min -1 and perfect sealing [68] 97.1-97.8% bacteriophage phiX174, 28.3 L min -1 and perfect sealing [56] Surgical mask (3 ply/SMS type)…”

Fast and simple assessment of surface contamination in operations involving nanomaterials

“…To this end, a common particulate mask filter was fitted to a mannequin head with a backside exit to draw a continuous air stream. Respiration mask filters with different characteristics [32] are commonly used to protect personnel from particle aerosols in workplaces and several guidelines have been issued for their use and disposal [33]. Nevertheless, the outside of mask filters may become contaminated during use.…”