Covid and ventilation

"Because the coronavirus is thought to spread primarily through tiny, airborne droplets, employers should upgrade their ventilation and filtration systems before bringing workers back, experts said.
“One thing you can do before you go back to work is simply ask them what they’ve done,” Dr. Allen said. “And if you hear things like, ‘Yes, we’re meeting code,’ then that’s a flag that something’s not right. They should be going above and beyond the bare minimum ventilation and filtration rates.”
Although the ideal ventilation rate varies, in general, employers should maximize the amount of fresh air coming in from outdoors, he said. 

In a relatively small space — say, the size of a typical school classroom — employers should aim for four to six air changes per hour, meaning that the air inside the space is being completely refreshed every 10 to 15 minutes. 

Opening windows can also improve air flow. 

High-quality air filters, like those that are rated as MERV 13 or higher, can trap a majority of airborne viral particles. Some commercial buildings are not equipped for these heavy-duty filters; in those offices, portable air purifiers, equipped with HEPA filters, can be effective, experts said.

“These types of portable units can do a great job of taking particles out of the room,” Dr. Huffman said. “And the next level is even a desktop level HEPA filter, where you have a really small unit that provides clean air into your direct breathing zone.”
These personal units may be particularly helpful in poorly ventilated offices, although experts stressed that employers, not employees, should bear the burden of improving indoor air quality."