2-l8. TYPE OF RESPIRATORS
Industrial respiratory protective devices have been designed, tested, and
approved for protection against specific industrial exposures. These devices have been
grouped for convenience into two general classifications according to mode of
operation. The two basic groups are the atmospheres supplying respirators and the air
purifying respirators. The choice of respirator for a given situation will depend upon a
number of factors, which will be discussed in paragraph 2-22. Detailed information on
these general classes of respirators is provided in succeeding paragraphs.
2-19. AIR-PURIFYING RESPIRATORS
a. General Description. Air-purifying respirators can be half mask, quarter
mask, full-face piece, or mouthpiece styles equipped with air purifying units to remove
gases, vapors, and particulate matter from the ambient air prior to its inhalation (see
Figure 2-11). Some air purifying respirators are "breathing assisted" (blower operated)
and provide respirable air to the face piece (or hood) under a light positive pressure.
These are often referred to as "powered air-purifying respirators" or "PAPR."
b. General Limitations. Air-purifying respirators do not protect against oxygen
deficient atmospheres or against skin irritation by, or absorption through the skin of,
airborne contaminants. The designed efficiency and capacity of the cartridge, canister,
or filter for the contaminant and the measured concentration of the contaminant at the
work site determine the maximum contaminant concentration, against which an air-
purifying respirator will protect. Since air-purifying respirators may not have an end of