An extra-oral dental suction scavenges the air in close proximity to the patient's mouth. Generally we shoot for 6-8 inches. We use it during aerosol producing dental procedures to capture all the  nasty stuff in the patients mouth from getting in our lungs or eyeballs. Seriously though, there are tons of stuff that dental professionals breathe in that we really shouldn't. On the short list: Amalgam vapors, particulate, periodontal bacteria, and viruses such as COVID-19.