What’s wrong with NRR (part 2)? Choose A or B

May 9, 2011

With the development of a second method for determining realistic hearing protection “protectiveness”, hearing conservationists now had a method for predicting more closely what would really happen when they supplied hearing protection and training to their work forces. The problem was a lack of support for this standard from industry. ANSI standards are just that – standards. They have no force in law or no effect unless some governing body, empowered to enforce, adopts them into law. So too with ANSI S12.6-1997 (R2008) for Hearing Protection. The only enforcement body using ANSI S12.6-1997 (R2008) is the EPA, the federal agency that has jurisdiction over the laws that invoke ANSI and other standards for labeling hearing protectors for sales in the United States. For Method “B” to gain traction, the EPA would have to mandate its inclusion in the labeling of hearing protectors. Only then would manufacturers be forced to test their protectors under Method “B” and publish/label their results.

Sadly, despite powerful evidence in support of Method B as the most credible, accurate, standardized test method, the EPA chose NOT to endorse this new standard after its promulgation as a standard in 1997. This despite a foundation of bonafide, multi-laboratory, research that supported the validity of Method B over Method A. One reason might be that since the labeling Rule had been in place for years, the EPA was satisfied with its labeling rule for hearing protection and wasn’t ready to revisit it so quickly. There was also a lot of push back from manufacturers. It has been reported that their concerns were the variability in results obtained doing Method “B” tests. (This fact is very telling because hearing conservationists know the variability in using disposable hearing protection). That is part of its problem. Employees need to be carefully trained to use earplugs and muffs or their results are variable and below par compared to the prevailing Standard’s (ANSI S3.19-1974) results. As a result, after S12.6 became an approved ANSI standard, testing protectors under its Method “B” was totally optional and only a few companies actually spent the money to do Method “B” tests. (They are sometimes twice the cost of Method “A” as the panel is double the size).

As if the situation for Method “B” wasn’t bad enough, it is now about to get worse. The EPA is currently finalizing its new hearing protection labeling requirements in light of revisions to ANSI S12.6-1997 (R2008). While this standard maintains Method “B” intact, it offers a revised Method “A” test and reports attenuation with 2 new numbers; NRR20 and NRR80. These numbers describe what 80% of the population can expect to achieve and what 20% of the population can expect to exceed. The EPA has indicated that it is favorably disposed to implementing the 2 number change in its labeling rule. But what should be the basis for calculating these 2 new numbers? And how will a hearing conservationist use these 2 numbers to determine what is safe for any one particular individual? That is still unclear. The EPA’s position has always been to measure “potential” protection not the real world effect. Curiously the EPA had put forward three reasons why they wanted to change the labeling rule. One was repeatability. The EPA’s wording on that subject was

the selected method should provide a reliable and repeatable means for assessing product performance, with minimal influence and impact of non-product outside factors.”

A recent study, conducted by NIOSH over 6 laboratories, comparing Method A and Method B attenuation testing results, showed that Method “B” test results varied less from laboratory to laboratory than did Method A results. In the same Inter-lab study no significant difference in calculating NRR20 resulted from using Method “A” or Method “B” numbers from laboratory to laboratory. Therefore by this measure either Method would be acceptable to capture attenuation data for calculating NRR20.

The EPA’s second concern was that based on the results of the Inter-lab study mentioned above was

significant differences in technique between the 6 testing labs were evident in Method “A” data. However such differences appeared to be masked by large variability between test subjects based on Method “B” data.”

But Method B did not exhibit as high inter-lab variability as Method A did, nor was its between subject variability so high as to cause any differences between using Method A or Method B to collect data for NRR20. What this means simply is that Method B appears to be more repeatable when different labs do the testing because it eliminates the “experimenter influence”.

And finally, the EPA was concerned that

“the true potential effectiveness (NRR) of the HPD, when correctly used, as instructed by the manufacturer, could be understated because of low attenuation measurements that resulted from improper fit by inexperienced subjects; this is particularly important with ear insert HPDs” (earplugs).

So if the EPA’s concern were indeed the case, then the NRR20 values (for at least the earplugs) in the Inter-lab sample would have been lower under Method B than Method A. But they were not. Furthermore, data from field studies show slightly lower attenuation than the lab data using Method B. The real concern is the bias the experimenter supervised fit method, Method A, has when you look at the differences between labs. Method A, with its heavy involvement of the experimenter in supervision, training, and visual determination of fit prior to attenuation testing, is more influenced by the individual lab than Method B, which precludes experimenter involvement.

We made this case to the EPA’s hearings on this matter in January 2010. Nevertheless it appears the EPA has rejected our (John Franks Ph.D., Consultant NIOSH (Ret), John Casali Ph.D., Virginia Tech’s Auditory Systems Lab, Jeffrey M. Goldberg, Custom Protect Ear, Inc., and the National Hearing Conservation Association) pleas for Method B as the basis for labeling. The EPA says it will propose the rule in its final form in May 2011.

By now, if you are still reading this, you are wondering why I’m blogging about such a dry and technical subject. Our mission at CPE is to reduce or eliminate Noise Induced Hearing Loss for our clients. Only by having data that hearing conservationists can use do we have a hope of achieving that end. Our concern is that we are just about to take a giant step backwards.

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