What is it about?

COVID-19 spreads through droplets in the air, which contain the virus that causes the disease. Face masks prevent these droplets from getting released into the environment. The N95 respirator is one such protective mask. Some N95 masks contain an exhalation valve. This valve allows exhaled air to pass outside without getting filtered. It closes during inhalation. This implies that an infected person with an N95 mask can release virus-carrying droplets into the air. This possibility has led to growing concern regarding the use of these masks. In this study, the author observed how droplets flow through an N95 mask, with and without a valve. To do so, he used a mannequin head and a fog machine that emits fog droplets. The release of fog droplets was made to match the breathing rate of an adult male. Next, he put an N95 mask with and without a valve over the mannequin's mouth. To view the air flow, the author used a method called schlieren imaging. To understand how exactly the droplets left and entered through the mask, the author lit up the fog droplets. For this, he used a method known as backscattered fog illumination. The author found that N95 masks without an exhalation valve blocked most droplets from entering and leaving the mask. Also, masks with valves did not completely stop the droplets from being released outside. This shortcoming can lead to spreading of infected droplets in the environment.

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Why is it important?

This study reveals how the airflow through an N95 mask with a valve can increase the spread of COVID-19. It highlights the usefulness of important imaging methods to visualize air flow. These techniques include schlieren imaging and backscattered fog illumination. The visuals produced from these methods are easy to understand by large audiences. These findings can also help the public make better choices about what kind of masks to wear during a pandemic. KEY TAKEAWAY: Current N95 masks with exhalation valves are not appropriate for use during a pandemic. They may not prevent infected air droplets from traveling outside the mask.

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This page is a summary of: Flow visualization of an N95 respirator with and without an exhalation valve using schlieren imaging and light scattering, Physics of Fluids, November 2020, American Institute of Physics, DOI: 10.1063/5.0031996.
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