is essentially that which occurs at a mask's face seal. In marked contrast, with both surgical masks and NIOSH-certified, disposable, particulate-filter respirators (PRs), one must accept the likelihood of some hazardous leakage through the filter that adds to the hazardous leakage at the face seal.
E. Powered, HEPA-Filter Halfmask and Positive-Pressure, Air-Line, Halfmask Respirators—Available NIOSH-certified, powered, HEPA-filter respirators can supply a constant flow of HEPA-purified air under positive pressure for a period of 8 hours with a fully-charged battery pack. This type of filter respirator is also known by the general term powered, air-purifying respirator or PAPR. The specific type of PAPR discussed in these recommendations can be referred to as a "halfmask HEPA PAPR." Two examples of this respirator type are shown in Figures 1 and 2 on pages 34 and 35. NIOSH conservatively estimates that these respirators have less than 2% face-seal leakage under routine conditions (57).
The tight-fitting, elastomeric facepieces and breathing-hose assemblies of these respirators are small and relatively lightweight. The total weight of these devices can go to 5 to 6 pounds, most of which is in the belt-mounted battery, blower, and HEPA-filters assembly. These respirators are designed for continuous use in temperatures ranging from 40°F to 120°F.
The forced, HEPA-filtered airstream flowing into the facepiece of a powered HEPA-filter respirator offers the advantage of a cooling effect in conditions of warm temperatures (this can be a disadvantage for use in cold temperatures). More important, because minimal inhalation effort is needed by the wearer to draw air across the HEPA filters, breathing in a powered respirator is substantially more comfortable than in a non-powered filter respirator (e.g., NIOSH-certified, dust, fume, and mist (DFM) filter respirators).
In use against non-biological aerosols, HEPA filters are routinely replaced only when: (A) airborne materials load them to a point that the flow to the facepiece is not adequate to provide positive pressure or (B) physical damage occurs to a filter. However, in health-care
