I’m sorry, you do still need to wear a mask. Why?
For the same reasons Health Care Workers continue to get infected in hospitals which have excellent ventilation with 6 Air Changes Per Hour.
Ventilation cleans up far-field aerosols (>6 feet away), but cannot clean the air of aerosols that have just been emitted by the infected person (near-field aerosols < 6 feet away).
An example to help explain – you are in a room with someone smoking a cigarette and an air cleaner. You can see the smoke being removed from the air by the air cleaner. But if the smoker blows smoke in your face, the air cleaner cannot clean it in time.
“We put a HEPA air cleaner in our classroom. Do I have to wear a mask in the classroom? Yes. Think about a used diaper in a room. What is the best way to keep the room from stinking? It is not to open a window or put in a filter. It is to remove the diaper from the room. This is one of the fundamental pillars of indoor air quality: source reduction.
Wearing a mask, even a cloth mask that isn’t perfectly fitted, will reduce the number of aerosols that get into the air from a contagious individual. When we talk, we expel more particles that are airborne than when we are just breathing. When we talk loud or sing, we expel even more. Hence, even the teacher should wear a mask. Masks with clear mouth shields should be sought if people who need to lip read are present.
The goal is a layered risk reduction. We need to take as many actions as we can (increase ventilation, HEPA air cleaner, masks, etc.) to reduce the risk as none will completely eliminate it. Wearing masks will reduce average airborne particle load (1 micron) in the classroom by roughly 30%.” Source.
Here’s a video that shows aerosols in general – and how plexiglass does NOT stop aerosols.