As COVID cases drop in the U.S. and vaccinations increase, many companies are bringing their employees back to office buildings. And lots of those workers are worried: Will shared spaces remain safe as restrictions are lifted and viral variants spread? Avoid spraying disinfectants in the air, Marr says, because they can be harmful when inhaled. “You’re looking for at least three to four air changes per hour—meaning that every 15 to 20 minutes, the indoor air is replaced with outdoor air,” Marr says. So if the level is high, it means that there’s a lot of exhaled breath hanging around in the air,” Marr says.