Model may be at fault if fit-tests are a failure
November 1, 2004 4 minutes read
Model may be at fault if fit-tests are a failure
NIOSH to add criteria for respirator makers
Poorly fitting respirators may cause additional headaches for hospitals as they scramble to fit-test hundreds of employees to comply with U.S. Occupational Safety and Health Administration (OSHA) regulations.
The choice of respirator can make a big difference in how successful you are at fit-testing employees, according to a study by the National Institute for Occupational Safety and Health (NIOSH).1 In fact, concerns over fit characteristics have influenced NIOSH to add new criteria to its respirator certification program.
By setting limits on the total inward leakage of masks the amount of aerosol that comes in through the filter and face seal NIOSH will essentially require better-fitting respirators. "We want to write a standard that is representative of the best technology that is available today. That means some respirators will not make it because we will set the standard at the top," says Rich Metzler, MS, director of NIOSH’s National Personal Protective Technology Laboratory in Pittsburgh.
A study of 18 models by NIOSH found a glaring difference in their basic fit characteristics.
Three models performed well right out of the box, without fit-testing, the study found.1
With some models, only one or two out of 25 test subjects were able to pass a fit-test, says Chris Coffey, PhD, chief of the Laboratory Research Branch in NIOSH’s Division of Respiratory Disease Studies in Morgantown, WV. In fact, combined with a margin of error in fit-testing, even those who passed with poorly fitting respirators may not have adequate protection.
"Fitting characteristic is an important facet," he says. "At one point in time, people thought if you passed the fit-test, you got an adequate level of protection, that fit-tests were basically 100% accurate. We’ve shown that may not be the case. Tied with poor fitting characteristics, you can end up with a respirator that doesn’t protect adequately even if you passed the fit-test."
Yet both Coffey and Metzler emphasize that fit-testing still is important to make sure an individual respirator provides adequate protection for a specific employee.
"Our goal is to improve the fitting characteristics of the respirator so a larger portion of the population will receive a better-fitting respirator, but it does not eliminate the need for the individual to be fit-tested," Metzler says. "Even the good-fitting respirators had an improvement [in fit in the study] when the fit-test was done."
In the study, Coffey and his colleagues tested 18 models on 25 test subjects with varying face sizes. They used Simulated Workplace Protection Factor values a test of total leakage while performing certain exercises to evaluate respirator performance. The researchers also compared the effectiveness of different fit-test protocols, including Bitrex, saccharin, (both qualitative) and the quantitative Portacount.
The small sample size and survey population limits the study’s scope. There are more than 165 models of N95 filtering facepiece respirators. But here are some findings:
• There is no perfect fit-test.
Some employees will pass a fit-test although the mask really doesn’t provide the protection for which the N95 filtering facepiece respirator was designed, and some will fail although they actually fit properly. The amount of "beta" (falsely showing adequate protection) and "alpha" (falsely showing inadequate protection) error differs with different fit-test methods.
• Qualitative fit-testing has a higher error rate.
Because it’s subjective, some employees may simply say, "I think I taste something." You may want to vary the concentrations of the substance you’re using to see how it effects the pass-fail rate, Coffey suggests. Research is needed on how varying the concentrations of the test agent affects the pass/fail rate, he says.
• You can’t tell just by looking at a respirator whether it will fit.
"Some of them looked like they did fit," Coffey points out. "The leaks were small enough that you couldn’t tell just by putting them on someone’s face and saying, This one will do well, and this one will do poorly.’"
• Choosing a better-fitting respirator could make your fit-testing process smoother.
For example, 76% of test subjects passed the Portacount fit-test with the MSA Affinity Ultra, a model that provided almost five times the required level of protection even without fit-testing.
Yet the overall pass rate for all 18 models with the Portacount was 16%. (For a list of the models tested and their performance without fit-testing, see box.)
Reference
1. Coffey CC, Lawrence RB, Campbell DL, et al. Fitting characteristics of eighteen N95 filtering-facepiece respirators. Journal of Occupational and Environmental Hygiene 2004; 1: 262-271.
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