The 0.3-micrometer diameter used in the certification testing is approximately the most penetrating particle size for particulate filters. Although it seems contrary to expectation, smaller particles do not penetrate as readily as 0.3-micrometer particles. Therefore, these respirators will filter all other particle sizes at least as well as the certified efficiency level.

2. How effective are the Part 84 filter respirators against asbestos fibers or other rod-shaped particles?

Although fibers or rod-shaped particles may have very small cross-sectional diameters relative to their lengths, the Part 84 particulate filter respirators will be at least as efficient against this particle shape as the certified efficiency level.

3. How do I tell a new Part 84 particulate filter from the Part 11 predecessors?

There are several labeling changes for Part 84 filter respirators that should enable users to distinguish between the Part 11 and Part 84 respirators. These are as follows:

• NIOSH and DHHS emblems on Part 84 labels replace NIOSH and MSHA logos on Part 11 labels.
• The approval number will be in the format of TC-84A-xxxx for Part 84 devices rather than TC-21C-xxxx or TC-23C-xxxx for Part 11 devices (except for particulate PAPRs, which will continue to be numbered with the sequence TC-21C-xxxx or TC-23C-xxxx).
• The certification filter series and efficiency levels (e.g., N95, P100, etc.) are included on the Part 84 filter approval label.

4. How long can I use my particulate respirator for TB exposures before I discard it?

In the health care setting, the filter material used in respirators may remain functional for weeks to months [CDC 1994]. As long as there is no oil mist, reuse is limited only by considerations of hygiene, damage, and breathing resistance. Respirators with replaceable filters are designed for reuse, and a respirator classified as disposable may be reused by the same health care worker as long as it remains functional.

Before each use, the filter material should be inspected. If the filter material is physically damaged or soiled, the filter should be changed (in the case of respirators with replaceable filters) or the respirator should be discarded (in the case of disposable respirators). Your employer should develop standard operating procedures for storing, reusing, and disposing of respirators designated as disposable and for disposing of replaceable filters.

5. Is it always necessary to fit-check a respirator before each use?

Fit-checking your respirator before each use is important to minimize contaminant leakage into the facepiece. Your respirator manufacturer has recommended fit-checking procedures that should be followed by the user each time the respirator is worn.