Researchers at the Thermal Hydraulics Research Laboratory have conducted experiments studying the efficacy of homemade and mass-produced masks. Supplies of mass-produced masks have decreased as the COVID-19 pandemic has progressed, necessitating the use of homemade masks.
Face masks are an important component of personal protection equipment employed in preventing the spread of diseases such as COVID-19. As supply of mass-produced masks has decreased, the use of homemade masks has become more prevalent. It is important to quantify the effectiveness of different types of materials to provide useful information, which should be considered for homemade masks.
Filtration effects of different types of common materials were studied by measuring the aerosol droplet concentrations in the upstream and downstream regions. Flow-field characteristics of surrounding regions of tested materials were investigated using a laser-diagnostics technique, i.e., particle image velocimetry. Pressure difference across the tested materials were measured.
Figure 1: Experimental setup to measure the flow-fields, aerosol droplet concentrations, and pressure difference across the materials.
Figure 2: (Top) High-resolution images of tested materials, i.e., cotton, fabric 1, micro fiber, coffee filter, HVAC filter, shower curtain, and vacuum bag. (Bottom) Images of commercial surgical mask (3 layers) and R95 mask (5 layers).
Measured aerosol concentrations indicated a breakup of large-size particles into smaller particles. Tested materials had higher filtration efficiency for large particles. Single-layer materials were less efficient but they had a low pressure drop. Multi-layer materials could produce greater filtering efficiency with an increased pressure drop, which is an indicator of comfort level and breathability. The obtained flow-fields indicated a flow disruption downstream of the tested materials as the velocity magnitude noticeably decreased.
Figure 3: A concept to characterize the filtration efficiency of masks’ materials.
Animations (top-bottom) illustrate the filtration effect of materials using aerosol droplet and laser diagnostics.
The obtained results provide an insight to flow-field characteristics and filtration efficiency of different types of household materials commonly used for homemade masks. This study allows comparison to mass-produced masks under consistent test conditions while employing several well-established techniques.