The real bacterial filtration efficiency to evaluate the effective protection of facemasks used for the prevention of respiratory diseases

The real protection offered by facemasks to control the transmission of respiratory viruses is still undetermined. Most of the manufacturing regulations, as well as scientific studies, have focused on studying the filtration capacity of the fabrics from which they are made, ignoring the air that escapes through the facial misalignments, and which depends on the respiratory frequencies and volumes. The objective of this work was to define a Real Bacterial Filtration Efficiency for each type of facemask, considering the bacterial filtration efficiency of the manufacturers and the air that passes through them. Nine different facemasks were tested on a mannequin with three gas analyzers (measuring inlet, outlet, and leak volumes) inside a polymethylmethacrylate box. In addition, the differential pressure was measured to determine the resistance offered by the facemasks during the inhalation and exhalation processes. Air was introduced with a manual syringe for 180 s simulating inhalations and exhalations at rest, light, moderate and vigorous activities (10, 60, 80 and 120 L/ min, respectively). Statistical analysis showed that practically half of the air entering to the system is not filtered by the facemasks in all intensities (p < 0.001,eta p(2) = 0.971). They also showed that the hygienic facemasks filter more than 70% of the air, and their filtration does not depend on the simulated intensity, while the rest of the facemasks show an evidently different response, influenced by the amount of air mobilized. Therefore, the Real Bacterial Filtration Efficiency can be calculated as a modulation of the Bacterial Filtration Efficiencies that depends on the type of facemask. The real filtration capacity of the facemasks has been overestimated during last years since the filtration of the fabrics is not the real filtration when the facemask is worn.

Automated summary

The real protection offered by facemasks for respiratory virus transmission is still unknown. Current regulations and studies focus on the filtration capacity of mask fabrics, ignoring the air that escapes through facial misalignments. This study aimed to determine the Real Bacterial Filtration Efficiency of different masks by considering both the manufacturers' filtration efficiency and the air that passes through them. Testing was conducted on nine masks using gas analyzers and a mannequin, demonstrating that around half of the air entering the system is not filtered by the masks. Results also showed that hygienic masks consistently filter over 70% of the air, regardless of intensity, while other masks had varying responses depending on the amount of air mobilized. Therefore, the real filtration capacity of masks has been overestimated, as fabric filtration does not accurately represent filtration when masks are worn.