Respirators (respiratory personal protective devices) are widely used for protection against inhaled toxins. The two major categories of respirators are air-purifying devices and atmosphere-supplying devices. Air-purifying respirators function by partially “cleaning” the inhaled the air (filtering out hazardous agents), whereas atmosphere-supplying respirators provide an independent source of air. The 1994 CDC guidelines established performance criteria for respirators employed to prevent transmission of M. tuberculosis.
Currently, the National Institute for Occupational Safety and Health (NIOSH) lists four types of personal respirators for use as protection against tuberculosis. The devices are listed below in appropriate order of common use, convenience, and cost.
N95 and other disposable particulate respirators: These respirators are relatively simple, disposable devices and are now widely used for protection against occupational tuberculosis. Although they look like surgical masks, these devices are fundamentally different in construction and function.
Powered air-purifying respirators (PAPR): The powered air-purifying respirator provides a greater degree of protection than the N95 respirator. It consists of a tight-fitting face mask or a loose-fitting hood or helmet that is attached by a hose to a battery-operated fan that blows filtered air into the mask.
Replaceable particulate filter respirators: External air-filtering cartridges are attached externally to the mask device itself. These devices are widely used in chemical industry and other settings and come with either half-masks or full facepiece masks.
Postive-pressure supplied-air respirators: These respirators use compressed air delivered to a half or full facepiece mask through a hose from a fixed source.
Other types of devices have been used in the past. Dust-mist (DM) and dust-mist-fume (DMF) respirators have been widely used in industry and were used for tuberculosis protection during hospital outbreaks in the late 1980s and early 1990s. High-efficiency particulate air respirators (HEPA) are effective at removing smaller particles than the DM and DMF devices and began to supplant the DM and DMF respirators for tuberculosis protection before being largely replaced by N95 devices and, infrequently, PAPRs.
The mask type for a respirator is constructed to meet the specific application needs. For tuberculosis control and a number of other uses, the mask itself generally contains the filtration medium. This contrasts with devices commonly used for many chemical exposures, in which the