Indoor Air and COVID-19

Considerations for ventilation in the COVID-19 pandemic

COVID-19, a highly contagious disease spread by respiratory droplets, can be prevented by blocking the exchange of respiratory droplets from person to person and by preventing close person-to-person contact.

What is a respiratory droplet?

A respiratory droplet is a small collection of saliva, mucus and particles from the surfaces of the mouth, nose and lungs. If a person has COVID-19, a respiratory droplet can carry the infectious virus, even if they have no symptoms. Respiratory droplets are made when air moves through the lungs and the nose or mouth, for example when breathing, talking, singing, sneezing, coughing, or playing an instrument using breath, and range in size from 1mm (or about the thickness of a credit card) to a hundred times smaller than the thickness of a human hair. Although some large droplets such as those created when coughing or sneezing can be seen, most are invisible.

How do they get from one person to infect another?

Respiratory droplets are small enough that they can get carried in the air for short distances. While bigger droplets fall to the ground quickly, near the person who is breathing or talking, smaller droplets hang in the air for longer and can travel further, up to an average of about six feet, although the smallest droplets may linger in the air. If someone is talking loudly, singing, shouting, coughing, sneezing or otherwise forcing more air through their lungs quickly, they produce more respiratory droplets into faster-moving air, which can travel much further. Masks help block respiratory droplets from getting into the air and moving far from the person who is breathing, talking or otherwise producing droplets.

What does this mean for ventilation?

Airflow strategies that maximize indoor-outdoor air exchange and that include HEPA filters or other filters such as those rated MERV-13 or higher that filter viruses from the air can help prevent viruses in the air traveling from one person to another. CDC recommends HEPA filters particularly in higher risk areas like a school nurse’s office, as well as making sure that ventilation systems are working well in restrooms and on buses. CDC also recommends using fans strategically to increase the effectiveness of open windows without drawing contaminated air over other people, and disabling demand-control ventilation that reduces air supply based on occupancy or temperature. Adjusting airflow in one room impacts airflow in other rooms, and can also cause challenges for heating and cooling systems. If ventilation with outdoor air cannot be improved, consider decreasing occupancy of the room. Talk with your facilities manager to determine the right strategy for your facility. Ventilation strategies cannot replace other interventions such as masking and maintaining space between people.

What about a portable air filter?

A portable air cleaner or air filter, such as a HEPA filter that is designed for one-room use, can be a useful addition to a facility’s ventilation strategy and may provide added protection. Be sure to direct the airflow so that it does not blow from one person to another. Make sure you understand how the air intake works in the device and what direction it will cause air to flow. Also, most portable air cleaners are rated for use in a certain size of room. Ensure you select a unit of the appropriate size for the room. These strategies cannot replace masking and maintaining space between people but add an extra layer of prevention.

What about UV?

UV, or ultraviolet light, can kill viruses if used at the right intensity for the right amount of time. Some facilities integrate UV into their HVAC systems as an extra layer of protection. UV can be dangerous to humans if used incorrectly so any use of UV sterilization should be carefully considered and part of a larger protection plan. The CDC recommends that UV be used only in addition to other measures such as maximizing outdoor air exchange and good air filtration, rather than relying on it to replace other measures.

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