Analysis of test results of mask filtration efficiency
The efficiencies of various configurations of the test mask (masks with operational or nonoperational ventilation fans or masks with sealed Smart Valves) for filtration of pathogens and surrogate air pollutants, including respiratory viruses, bacteria, bacteriophage, and particulates, were determined empirically per the requirements of the relevant Standards (12-15).
Assessment of influenza A virus and rhinovirus penetration
The ability of the test mask to provide user protection against airborne pathogenic viruses was assessed using the human respiratory viruses, influenza A (H1N1) virus and rhinovirus 14 per ASTM F2101-14 (12). The viruses evaluated differ with respect to size and envelope status. Influenza virus is a member of the Orthomyxoviridae family and is a relatively large (80–120 nm) enveloped virus, while the rhinovirus is a member of the Picornaviridae family and is a small (27–30 nm) non-enveloped virus (20). It might be expected, based purely on particle size, that the rhinovirus would represent a greater challenge for a filter mask than the influenza virus, but other considerations apply, as discussed below.
The results of the virus filtration efficiency study (Table 1) indicate that regardless of configuration or surrogate virus evaluated, ≥99.6% (range, 99.6–99.9%) of infectious virus was excluded by the test mask. Filtration efficiency determined by RT-PCR (which determines presence of both infectious and non-infectious virus) was found to range from 98.9% to 100%. In most cases, greater variability was observed in these replicate filtration efficiency measurements based on RT-PCR, compared with the infectivity endpoint (Table 1). No statistically significant differences were observed when these data were analyzed by either influenza virus or rhinovirus for a given mask configuration, or by mask configuration for either one of the viruses.
Assessment of S. aureus and bacteriophage ΦΧ174 penetration
Additional characterization of the ability of the test mask without Micro Ventilator to provide user protection against airborne pathogens was afforded by examination of the filtration efficiency for Staphylococcus aureus and the bacteriophage ΦΧ174 per ASTM F2101-7 (13). These bacterial and viral surrogates differ greatly in size (~2,000×500 nm for S. aureus vs. ~34 nm for the bacteriophage). Due to their differing sizes, it might be expected that the bacteriophage would represent a greater challenge for a filter mask than the bacterium, although other considerations apply, as discussed below.
The result of the virus filtration efficiency and bacteria filtration efficiency studies (Table 2) indicate that regardless of the surrogate pathogen evaluated, ≥99.5% (range, 99.5–99.9%) of microbial agents was excluded by the mask. No statistically significant differences were observed when these data were analyzed by surrogate pathogen for the test mask configuration evaluated.
Assessment of paraffin oil and sodium chloride penetration
The ability of the test mask with operational Smart Valve and Micro Ventilator fan to provide protection against airborne particulates was assessed per EN 149:2001 + A1:2009 (15) using paraffin oil to model liquid particulates and sodium chloride to model solid particulates. The results for various conditioning categories required by the Standard are displayed in Table 3. The efficiency for exclusion of sodium chloride was 99.9%, regardless of the conditioning (“as received”, “simulated wearing”, or “mechanical strength and temperature conditioning”). The efficiency for paraffin oil ranged from 99.3% to 99.7%. Although a statistically significant difference between “as received” and “simulated wearing” testing was identified for both sodium chloride and paraffin oil (P<0.05), the requirements for the Standard were met, including penetration limits as well as breathing resistance (a measure of comfort; data not shown).