The REDON Alternative
OSHA now has accepted a faster respirator fit test protocol that emphasizes mask donning.
- By Andy Coats
- Nov 01, 2004
WHEN performing a quantitative respirator fit test (QNFT), the "way it's always been done" has been to perform several exercises as stated in the accepted protocols listed in the respiratory protection standards of the Federal Register (29 CFR 1910.134). While these exercises are meant to simulate movement in the workplace, the research and rationale for these particular exercises is practically non-existent. There is little information or documentation available that describes the effect or effectiveness of these fit test exercises.
Perhaps the exercises are used because they seem to cause a great deal of variability in test fit factors. But isn't getting the "best fit" the entire purpose of fit testing? If the fundamental fit of the mask is flawed, then the exercises are useless. Studies show that with ambient aerosol technology, the talking exercise consistently creates the greatest amount of leakage during a fit test. (Crutchfield, C: Relationship Between Fit Factors, Penetration, and Mask Leakage. Respiratory Protection Update 7(4):1-9. ISSN 1048-6658, 1995.) But if it's leakage that is being measured, it would be leakage out of the mask as talking creates positive pressure and pushes the air out of the respirator.
In 1997, OSHA accepted a new technology for fit testing. Controlled Negative Pressure (CNP) technology was compared with generated aerosol and ambient aerosol, and the scientific studies consistently showed the CNP measurements were generally more conservative and less variable. CNP measurements can be traced to calibration standards, while aerosol-based systems are not amenable to primary calibration. And because CNP measures direct leak rather than counting particle migration, the time needed to perform a fit test is significantly reduced with Controlled Negative Pressure.
OSHA initially implemented a protocol for Controlled Negative Pressure that was patterned after the original aerosol tests. Analysis of individual fit factors measured by generated aerosol, ambient aerosol, and CNP fit test systems found that significant differences in mask leakage caused by these exercises were generally the exception rather than the rule. (Crutchfield, C., and Van Ert, M.: An Examination of Issues Affecting the Current State of Quantitative Respirator Fit Testing. J. Int. Soc. Resp. Prot. 11(2):5-18, 1993.)
Furthermore, these exercises used with CNP methodology typically showed little or no difference in resulting fit factor measurements.
Mask Donning's Effect on Respirator Fit
The REDON protocol was developed in an attempt to better use the advantages of CNP technology by being more health protective and more efficient in the use of time when performing a fit test. This protocol is described in the preamble to the OSHA standard but was not adopted in the body of the standard because the submission was not judged to have been timely. Instead, OSHA developed a longer protocol to essentially mimic the ambient aerosol protocol. There was no rationale for this longer, untested series of steps.
Studies have been performed and show that donning affects respirator fit to a much greater degree than the test exercises. The REDON protocol actually identified proper-fitting masks to a greater degree than the current lengthy protocol. In one study, the CNP REDON was compared to the OSHA-specified protocol. Based on more than 500 fit tests on firefighter SCBA facepieces in the negative pressure mode, the REDON protocol produced slightly more conservative test results than the OSHA protocol.
OSHA allowed consideration of the acceptance of the REDON protocol in June 2003. Based on information and studies submitted, as well as a public comment period, OSHA has now accepted the CNP REDON as of Aug. 4, 2004.
Advantages of the New Protocol
When fit factors are converted into equivalent leak rates, the real impact of fit test exercises is found to be much less than has been historically assumed. On the other hand, the impact of mask donning on respirator fit has been found to be far greater than fit test exercises. Currently, there is more time spent on performing test exercises than is used trying to determine the best-fitting respirator for each worker.
The CNP REDON fit test protocol is shown to be as effective, if not more effective, than the current standard protocol. And when compared to ambient aerosol systems, CNP has consistently measured much more respirator leakage with less variability.
And because the REDON protocol can be performed three to five times faster than currently specified OSHA protocols, the capability exists for fit test time to be used much more effectively in the future. This win/win situation would allow workers to be more safely tested in a shorter amount of time!
This article originally appeared in the November 2004 issue of Occupational Health & Safety.