Abstract
The effectiveness of face masks for preventing airborne transmission has been debated heavily during the COVID-19 pandemic. This paper investigates the filtration efficiency for four different face mask materials, two professional and two homemade, for different airflow conditions using model experiments and artificially generated water droplets. The size range chosen represents particles with the largest volume that can be suspended in air. The particles are detected using double pulsed interferometric particle imaging, from which it is possible to estimate the positions, velocity, and size of individual particles. It is found that all the tested face masks are efficient in preventing particles from transmission through the mask material. In the presence of leakage, particles larger than approximately 100μm are completely removed from the air stream. The filtration efficiency decreases with the decreasing particle size to approximately 80% for 15μm particles. The size dependency in the leakage is mainly due to the momentum of the larger particles. The results show that even simple face mask materials with leakage prevent a large portion of the emitted particles in the 15–150 μm range.
Highlights
Airborne transmissions of particles carrying diseases between humans depend on a number of factors related to the host, the environment between the host and the susceptible, and the susceptible itself.[1]
This paper investigates the filtration efficiency for four different face mask materials, two professional and two homemade, for different airflow conditions using model experiments and artificially generated water droplets
The results show that even simple face mask materials with leakage prevent a large portion of the emitted particles in the 15–150 μm range
Summary
Airborne transmissions of particles carrying diseases between humans depend on a number of factors related to the host, the environment between the host and the susceptible, and the susceptible itself.[1]. During the COVID-19 pandemic, the efficiency of wearing face masks to reduce the spread of airborne viruses has been strongly politicized. Among scientists, there seems to be a consensus that face masks are efficient in reducing the spread of infections aerosols,[4] especially, since there are reports of asymptomatic carriers.[5–7] Since the COVID-19 outbreak, the interest in biological fluid dynamics has increased rapidly. The transportation step can be divided into two different cases: droplet transmission and airborne transmission. The airborne particles (aerosols) tend to follow the airflow, and their trajectories are, mainly dependent on the flow conditions in the space between people. There is a smooth gradient between these cases that depends on the size and shape of the droplets, density differences between the droplet and air, the air viscosity, and the flow conditions in the environment. Recent modeling has shown that respiratory droplets are surrounded by humid puffs that increase the local humidity, increase the lifetime, and can even cause particle growth.[10,11]
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