> an exhaust fan blowing out of an open window to prevent outside air from entering—one of the “negative pressure” rooms that I’d heard about Negative pressure

> an exhaust fan blowing out of an open window to prevent outside air from entering—one of the “negative pressure” rooms that I’d heard about Negative pressure will pull in outside air, which is what you want, instead of letting your contaminated air leak into adjacent rooms. In “clean” rooms you want positive pressure, with a filtered intake, to keep contaminated air out.