I am not sure what happened to my question so I will leave a abbreviated version. The term "negative pressure room" is generally reserved for reference to Class N or Class Q. My dentist recently added 2 to his dental facility. He says being treated in the room will decrease my risk. I understand that it might decrease risk from someone who is infected who was  treated in the same chair compared to following an infected patient in a room with out good air circulation. I don't understand how it would lower risk if an infected person were being treated in a plain (not negative pressure room) room say, down the hall. Or if there were viral particles in the facility air but outside the negative pressure room. Seems like viral particles would be swept into the room, making the negative pressure room the dirtiest rather than the cleanest room in the facility. For the patient in the chair, the negative pressure room seems the least protective. But obviously if the patient was infectious treating the patient in that room would offer other patients in the facility and maybe the dentist the least risk possible. Seems like the negative pressure room protects others fin the facility rom the patient while the positive pressure rooms protect the patient from others who may be infected who are in the facility. Have I missed something? Any clarification would be appreciated.