20 adults in one classroom from 18:30 to 19:30. Someone left half-way through the parent-teacher conference, so that's the little dip in the middle. The air purifier (the height and width of one grown-up, with the depth of a fridge) stood in the back of the room and was switched off.
One person was coughing.
One person was wearing a respirator. It was not the coughing person.
