Pressure-demand type respirators

Combination Type C supplied-air respirator [see below], pressure demand type, with full or half facepiece, and auxiliary self-contained air supply or (2) Combination type continuous-flow supplied-air respirator with full or half facepiece and auxiliary self-contained air supply. 

There are two basic designs, one in which the supply of air is from a source outside the contaminated area, while in the other, the wearer of the respirator unit carries the air supply in a tank. There are also subdivisions within these two majortypes. A majorsubdivision,common to both, is whether the units operate as demand or pressure demand units. For the former, the demand valve permits the flow of air only during inhalation, and a negative pressure exists at that time within the facepiece, which may allow inward leakage from the contaminated atmosphere. The pressure-demand type maintains a positive pressure within the facepiece at all times and is unlikely to allow leakage of outside air into the respirator Pressure demand units are much more desirable and should be used in most applications. Demand units are not approved for IDLH atmospheres. 

The pressure-demand type is an apparatus in which the pressure inside the facepiece in relation to the immediate eiiviromnent is positive during both inhalation and exhalation. Tliis style would allow no outside atmospheric contaminants into the respirator s facepiece. 

RESPIRATORY PROTECTION CONCENTRATION RESPIRATORY PROTECTIVE EQUIPMENT < 5.2 (as mixture i.e., 3.7 mg/m3 DETA and 1.5 mg/m3 EGME)NIOSH approved full face piece respirators with an organic vapor canister will be on hand for escape. (M9, M17, M40 series gas masks are acceptable for this purpose. Other masks certified as equivalent maybe used.) NIOSH approved escape type SCBA can also be used >5.2 or concentration unknownNIOSH approved full face piece pressure demand SCBA. Or NIOSH approved full-face piece positive pressure, supplied-air respirators with auxiliary SCBA... 

Self-contained breathing apparatus with a full facepiece operated in pressure-demand or other positive-pressure mode or (2) Supplied-air respirator with a full facepiece operated in pressure-demand or other positive-pressure mode and equipped with an auxiliary escape-type self-contained breathing apparatus operated in pressure-demand mode. 

Type C supplied-air respirator [see page 360] operated in pressure-demand or continuous-flow mode (2) Powered air-purifying particulate filter respirator for dust and mist or (3) Powered air-purifying particulate filter respirator or combination chemical cartridge and particulate filter respirator for coke oven emissions. 

Escape (1) Self-contained breathing apparatus in demand or pressure-demand mode or (2) Full-face mask respirator with chin-style or front- or back-mounted type industrial size canister specifically approved for protection against formaldehyde. 

Type C Respirator An airline respirator, for entry into and escape from atmospheres not immediately dangerous to life or health, which consists of a source of respirable breathing air, a hose, a detachable coupling, a control valve, orifice, a demand valve or pressure demand valve, and arrangement for attaching the hose to the wearer and a facepiece, hood, or helmet. 

Both continuous-flow and pressure demand respirators are of this type. 

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