Efficacy of 3-Layer Felt Masks Containing Polypropylene Membranes in Particle Filtration with SARS-CoV-2 Size Range

Background and Aim: The use of a mask is an effective measure to reduce the transmission of Covid-19. Today, due to the lack of N95 masks and medical masks with good performance, felt masks are widely used due to their ease of manufacture and low cost. The aim of this study was to determine the effectiveness of 3-layer felt masks containing polypropylene membranes in filtering particle size in the SARS-CoV-2 range. Methods: In this study, a 3-layer felt mask was designed. For production, materials were selected that are currently available in the market and are used by manufacturers for the bulk production of the mask. Polypropylene fabric was used as the first and third layers of the outer part of the mask and the middle layer was made of felt with a pore size of about 400 nm. The efficiency of the mask in the filtration of particles of different sizes was measured according to BS EN149 standard at a flow rate of 30 liters per minute. Results: The efficiency of the felt mask for particle filtration with a size of 300 nm, which is approximately equal to the size of the SARS-CoV-2, is in the range of 11 to 25%. While the efficiency of the mask in the filtration of particles with a size of 500 nm is about 13 to 32%. The efficiency of this mask in filtering particles with a diameter of 10 microns increased by an average of 83%. The average efficiency of the mask in particle filtration with sizes of 0.3, 0.5, 1, 2.5, 5 and 10 micrometers is equal to 18, 22, 33, 50, 66 and 83%, respectively, and the average pressure drop is equal to 4 Pascal. Conclusion: The findings of the present study showed that the use of a felt mask with such a design and structure to prevent Covid-19 is not effective enough and may even increase the prevalence of the disease by creating false confidence in individuals. Due to the widespread use of felt masks in the community, improving the filtration capability of this mask for particles smaller than 500 nm and also modifying the surface and structure of the mask by hydrophilizing polypropylene fibers inside the mask can play an important role in reducing the prevalence of Covid-19.