There are a lot of hazardous airborne contaminants, vapors, fumes, viruses that can make your lungs, and your body, very unhappy. The kind of respirator you choose will depend on what nastiness you find yourself working in. The filtering capacity of respiratory masks varies according to the nature of the hazard. It is recommended that you buy respirators approved by the National Institute for Occupational Safety and Health (NIOSH) for the particular contaminants to which you are exposed. For more details about respirators, check out NIOSH www.cdc.gov/niosh/homepage.html or OSHA www.cdc.gov/niosh/database.html websites.