OSHA considers a dust mask as a negative pressure particulate respirator with a filter as an integral part of the facepiece or with the entire facepiece composed of the filtering medium. They must be tested and rated by the National Institute of Occupational Safety and Health (NIOSH). Most dust masks have an N95 rating which indicates they are have 95 percent efficiency against particulates but are not rated for oil. Some dust masks are thicker and larger and may have 97 or 100 percent efficiency and may also protect against oil mists. OSHA does not consider surgical masks to meet this standard since they have not been tested by NIOSH.
Dust masks are only effective in controlling particulate matter and mists. They are not meant for use with vapors, fumes, and other hazardous materials. Before providing a dust mask or any type of respirator be sure to evaluate the hazard and provide all necessary training. Manufacturers can provide information on what materials their respirators can best control.