Air velocity refers to how fast the air in the space is moving. Increasing air velocity will move virus particles from the air down onto surfaces, which can be more easily disinfected. Surfaces should be cleaned and disinfected frequently (at least once a day) in the workplace to prevent contact transmission. Workers need to wear masks correctly, and wash their hands with soap and water for at least 20 seconds after touching surfaces. Increasing air velocity also breaks down “vapor clouds” of droplet particles that can form in stagnant indoor air.
Air refresh rate, or exchange rate, is how frequently HVAC systems draw in fresh air from outside into the indoor space. As long as your workplace is in an area with clean outdoor air (ie, no fumes, smoke from fires, or other contaminants), outside air will help reduce the density of virus particles in the air, lowering the risk of infection. This is often called “100% Outside Air” or “High Refresh” mode on HVAC controls.
Humidity is how much water vapor is in the air. Virus particles float in the air longer in very low humidity. In addition, low humidity levels can dry out your nose and eyes and damage the immune system. Therefore, ventilation experts recommend maintaining relative humidity (which changes depending on factors such as air pressure and temperature) between 40%–60%.