Respirators are masks used to protect people from inhaling dust or gases. Usually in the workplace but do-it-yourselfers sometimes need them for the same reasons.
It's a common mistake made in television and movies to call a ventilator, a respirator. Ventilators are the devices used in hospitals, extended care facilities, and in some homes to support patients who either can't breathe on their own. Or have difficulty breathing due to some injury, or disease process.