Page:NIOSH DM DFM respirator evaluation draft.pdf/92

This page needs to be proofread.

84

Performance Evaluation of DM and DFM Filter Respirators—WORKING DRAFT 9.15.92

100 L/min/mask through their filter(s) with peak volumetric rates of about 200 to 250 L/min/mask. Similarly, Johnson et al. defined heavy work as that with an average respiratory ventilation of 80 L/min/mask with a peak flow of 192 L/min/mask. Also on the subject of respirator work rates, two respirator experts commented in 1984:

The breathing rate at a moderate to heavy work rate would be greater than the rate at rest. Typical rates may be 60 LPM (L/min) at work versus 6 LPM at rest. Higher breathing rates may affect a respirator's efficiency.^[1]

Therefore for filter testing, a range of volumetric flow rates from about 35 to 100 L/min/mask are most relevant to actual workplace usage of filter masks for use at medium (moderate) to heavy work rates.
Filter loading can also have a marked effect on filter leakage values. In general, leakage decreases as filter loading increases. That is, clean filters are generally the least protective. This effect applies to "mechanical" (non-electrostatic) filter media. For "electrostatic" filter media the loading effect can be reversed, with increasing leakage resulting from increased loading.^[2]^[3] Wilmes stated in the early 1980s: The current [30 CFR Part 11] certification tests only give an integrated value throughout the time period and provide little information on how much penetration occurs at any particular time. This element is important in that many of the filter media in existence today and in use in respirators have either good initial filter efficiency but the efficiency "degrades" when the filter begins to load with particulates due to the masking or loss of electrostatic charge or alternately other types have poor initial filter efficiency but the efficiency increases as filter becomes load (sic) or clogged.

133 Wilmes, D.: Recommendations to NIOSH for Revision of 30 CFR Part 11, memorandum from chairman of the Ad Hoc Air-Purifying Committee of the ANSI Z88 Committee for Respiratory Protec-

tion, St. Paul, MN (undated, ca. early 1980s), p. 2.

↑ Dixon, S.W. and T. J. Nelson: Workplace Protection Factors for Negative Pressure Half-Mask Facepiece Respirators, J. Int. Soc. Respir. Prot. 2(4): 347-361 (1984), p. 357.
↑ Hyatt E. C. et al.: Respirator R and D Related to Quality Control; LASL Project P-37, Los Alamos Scientific Laboratory, Quarterly Report July 1 thru September 30, 1971, No. LA-4908-PR (March 1972), pp. 15-16.
↑ Douglas, D. D. et al.: Respirator Studies for the National Institute for Occupational Safety and Health—July 1, 1974-June 30, 1975, Los Alamos Scientific Laboratory, Progress Report, No. LA-6386-PR (August 1976), pp. 17-19.

[1] Dixon, S.W. and T. J. Nelson: Workplace Protection Factors for Negative Pressure Half-Mask Facepiece Respirators, J. Int. Soc. Respir. Prot. 2(4): 347-361 (1984), p. 357.

[2] Hyatt E. C. et al.: Respirator R and D Related to Quality Control; LASL Project P-37, Los Alamos Scientific Laboratory, Quarterly Report July 1 thru September 30, 1971, No. LA-4908-PR (March 1972), pp. 15-16.

[3] Douglas, D. D. et al.: Respirator Studies for the National Institute for Occupational Safety and Health—July 1, 1974-June 30, 1975, Los Alamos Scientific Laboratory, Progress Report, No. LA-6386-PR (August 1976), pp. 17-19.

[1]

[2]

[3]