# Presentation: 673176

## Comparison of the Regulatory Noise Reduction Rating (NRR) and the Required ANSI S3.19 Test Method With Real-World Outcomes and Results From Testing With the New ANSI S12.6B Method 

- John R. Franks, Ph.D.
- Chief, Hearing Loss Prevention Section

**Notes:**
Dr. Suter covered the history of ASA and ANSI standards for testing hearing protectors as well as the development of the rating system and it’s application by OSHA, including derating schemes used by OSHA and recommended by OSHA.  She also covered the work of the NHCA Task Force on Hearing Protector Effectiveness. What I will address are the issues of the present testing method required by the EPA and the potential offered by changing to a newer subject-fit method as defined in ANSI S12.6-1997.  I will address only linear passive hearing protectors, since Dr. Casali will discuss the many issues related to non-linear devices later this morning.  I will also not address the rating system directly, since Dr. Murphy will discuss that matter following my presentation. 

## ANSI S3.19-1974

**Notes:**
ANSI S3.19-1974 (R-1979) is a legacy standard that was adopted by the EPA in the labeling rule.  The standard has since been rescinded by ANSI, but lives on in the regulation.  

## ANSI S3.19-1974

**Two methods for psychoacoustic testing of hearing protectors**
**Experimenter Fit**
**Subject Fit**
**Measure: **
**Real Ear Attenuation at Threshold (REAT)**

**Notes:**
S3.19 provided two psychoacoustic methods for testing hearing protectors: Experimenter fit and subject fit.  The psychoacoustic procedure is auditory threshold testing for noise bands (diffuse sound field noise-band audiometry) with ears open and with ears occluded.  In experimenter fit, the experimenter is responsible for determining how well the protector is fitted for testing.  In subject fit, the subject is responsible for that determination. 

The difference between the noise-band thresholds with ears open and ears occluded is Real Ear Attenuation at Threshold (REAT)

## ANSI S3.19-1974

- In **40CFR211**.**102, SubPart B**  the U.S. EPA adopted the experimenter-fit version of S3.19
- Experimenter fit interpreted to mean that the test subjects did not participate in fitting
- Experimenter worked to obtain best possible fit with no consideration of comfort or wearability

**Notes:**
In 40 CFR211.102, SubPart B, the U.S. EPA adopted the experimenter fit version of S3.19.  A justification was that the experimenter fit would be what well trained, well-motivated hearing protector wearers could achieve.  

The experimenter fit was interpreted to mean that the test subjects did not participate in the fitting.  The experimenter might use a fitting noise and ask the subjects to engage in such tasks as covering their occluded ears with their hands to see if there were differences between the ears, but the subjects did not touch the protectors once they were fit nor at all during the ears-occluded audiometry sessions.

The experimenter worked to obtain the best possible fit with no consideration of comfort or long-term wearability. In effect, during the fitting process, the subject became an acoustic test fixture.

## ANSI S3.19-1974

- Results were
- Employ of highly trained subject panels willing to endure uncomfortable protector fittings
- Extremely consistent REATs from fit-to-fit within a subject
- Combined with calculation method, treating **3** REATs per subject for **10** subjects as **30** independent observations, standard deviations were extremely small

**Notes:**
The results were:

Testing laboratories recruited subjects who were willing to endure uncomfortable protector fittings and willing to perform the noise-band audiometry diligently.  Given the requirements of the standard that test subjects have hearing within normal limits, subject panels were often made of college students who could be panel members for a period of a few years.

Because of the experience of the experimenter, REATs were extremely consistent from fit-to-fit within a subject and the REATs were also very high.  When I performed such testing in the early 1980s, we would often create a test panel by screening potential subjects with another protector to get the best panel for the actual test.

For the correct statistical treatment of the data, 3 REATs from the test subjects would have been to use the mean REAT for each subjects, and these means would have been used to calculate a grand mean and a standard deviation of the subject means.  S3.19, however, called for treating each REAT as a separate observation, and thus the mean REAT was based on the 30 observations (it would have been no different from the grand mean) and the standard deviation was for the 30 observations.  A standard deviation calculated with an N of 30 will always be smaller than a standard deviation calculated with an N of 30.  So the final result was high REATs and small standard deviations.

## 40CFR211.102 SubPart B

- Equation for Noise Reduction Rating is:
-           8000
- NRR = 107.9 dBC - 10 log 10 0.1(L*Af** *-AP*V**f *98 ) - 3 dB.
-             *f*=125  Hz
- Where
- L*Af** *is the A-weighted octave band level at frequency *f *of a pink noise spectrum with an overall level of 107.9 dBC, and AP*V*f98 is the mean REAT value minus 2 standard deviations at frequency *f  *
-     (2 standard deviations accounts for 98% of the variance in a normal distribution), and – 3 dB is the uncertainty function.

**Notes:**
The equation for the noise reduction rating (NRR) is:

     8000
NRR = 107.9 dBC - 10 log 10 0.1(LAf -APVf 98 ) - 3 dB.
            f=125  Hz

This equation is similar to that used for any single number rating.  What it expresses is that the log summed A-weighted REATs minus some allowance for variance in the data, in this case 2 standard deviations, are subtracted from a log summed pink noise.  In the case of the NRR, the pink noises are 1/3 octave bands centered at 125, 250, 500, 1000, 2000, 3150, 4000, 6300, and 8000 Hz, so they total 107.9 dB.Then 3 dB is subtracted to allow for spectra uncertainty – the uncertainty that the protector will be used in a noise with a spectrum that is not flat.  The NRR is intended to be subtracted from the user’s C-weighted noise exposure level to determine the A-weighted protected exposure level.  If the exposure level is measured in A-weighted decibels, 7 dB is subtracted from the NRR in an effort to universally account for differences in C and A-weighted noise measurements.  In theory, if users wore the protector as it was tested, 98% would receive the labeled amount or more.

## 40CFR211.102 SubPart B

- The use of the experimenter fit of S3.19 with high REATs and small standard deviations resulted in large
- NRRs

**Notes:**
However, the use of the experimenter fit with experience subject panels resulted in high REATs and small standard deviations.  

That, in turn, resulted in large, over predictive NRRs.

## Real-World Studies

- In 1976 Padilla reported at 500 Hz a mean REAT of 5.5 dB with a standard deviation of 9.1 dB for the V51-R earplug for 183 subjects with 1 repetition each.
- The manufacturer’s S3.19 REAT at
-    500 Hz was 24 dB with a standard deviation of 2 dB for 10 subjects with 3 repetitions each.

**Notes:**
In 1976 Padilla reported the first real-world study of the attenuation of an earplug, the V51-R that has been around for many years.  It is a mushroom-shaped, single-flange premolded vinyl earplug.  Only one frequency was tested, 500 Hz. The mean REAT was found to be 5.5 dB and the standard deviation for 183 subjects was 9.1 dB.  There was one measurement per subject.  This was a spontaneous test in that workers were taken off the production line, given a plaque to hold as they walked to the testing facility so that they couldn’t touch the earplugs before the test, and then tested with the protectors in.  Then, they removed the protectors for the ear-open portion.

The manufacturer’s S3.19 REAT at 500 Hz was 24 dB with a standard deviation of 2 dB for a 10-subject panel with three repetitions each. Conclusion? Padilla’s workers weren’t wearing the protector correctly.

## Real-World Studies

- In 1980, Fleming reported the following for the same earplug:

**Notes:**
In 1980, Fleming studied the same earplug and found the following:

At 500 Hz, the mean REAT was 11.4 dB with a standard deviation of 8.7 dB (not statistically different from Padilla’s 5.5 dB mean REAT and standard deviation of 9.1 dB).  Fleming’s data were statistically different from the manufacturer’s S3.19 data at each test frequency.  Fleming used 9 subjects.

## Real-World Studies

- By 1994 there were 22 real-world studies of various earplugs and earmuffs
- None showed agreement with the manufacturers’ data collected in accordance with S3.19.

**Notes:**
By 1994 there were 22 real-world studies of various earplugs and earmuffs.  Some of these were spontaneous studies, as with Padilla and Fleming, and some of these were scheduled. In a scheduled study, the test subject appears at the test site, dons the hearing protector as he or she wears it normally, and is tested in a controlled environment that meets the diffuse sound-field requirements of the standard.  S3.19 and S12.6 have essentially the same requirements, except that S3.19 requires a reverberant sound field with maximum and minimum reverberation times at each test frequency while S12.6 has only a maximum reverberation time for each test frequency. In spite of the face validity of the spontaneous test – prohibiting the test subject from touching the hearing protector from the time of leaving the work area until being tested in the ears-occluded condition - there is no statistical difference between data collected in spontaneous and scheduled tests.  This puts paid, for at least this situation, to the notion that the test subject will fit protectors better under supervision than during normal day-in and day-out use.

None of the studies showed agreement with with manufacturer’s S3.19 data.  In fact all REATS and resultant NRRs were statistically lower for the real-world tests than for the S3.19 tests. 

## S3.19 vs. Field Values

**Real-World**

**S3.19**

**Notes:**
Not only were the real-world NRRs lower than the S3.19 NRRs, there is no correlation between the differences.  That is, it is not possible to develop a formula that would universally allow correction between real-world data and S3.19 data for all devices.  This slide shows the comparison of real-world NRRs to S3.19 NRRs for 9 earplugs and 7 earplugs that werer tested in the 22 studies. 

In spite of the lack of correlation between the two outcomes, OSHA applies a universal 50% derating to the NRR when determining whether a hearing protector would provide adequate attenuation to allow a hearing-protector based hearing conservation program to be implemented in lieu of a program based on control of the noise at the source or in the path.  OSHA does not apply a derating when determining whether a given protector is adequate for a given worker in a given noise.

NIOSH, in an attempt to apply a derating factor that is reflective of the fact that the difference in real-world vs. S3.19 NRRs is smaller for earmuffs and slow recovery foam earplugs, applies a variable derating scheme: 25% for earmuffs, 50% for slow-recovery foam earplugs, and 70% for all other earplugs. The derating is applied to determine whether a given protector should be adequate for a worker in a given noise.  NIOSH does not recommend that hearing protectors be used in lieu of source or path noise control and so does not recommend a derated NRR be used to see if noise control-based interventions can be avoided.

 Presently, NIOSH does not apply a derating for custom earplugs in recognition that they are only as good as the impression and thus can be extremely effective with high noise reduction for a good impression or be essentially ear jewelry offering no noise reduction for a poor impression.  

## Real-World Studies

- Standards Accreditation Committee S12 directed working group S12/WG11 to begin developing a new test method to provide a better predictor of hearing protector performance

**Notes:**
ANSI Standards Accreditation Committee S12 directed working group S12?WG11, chaired by Elliott Berger, to begin development of a new test method tht would provide a better predictor of hearing protector performance in the real-world as one of its tasks.  The working group solicited the cooperation of four laboratories to conduct self-funded studies of various methods.  The laboratories were EarCal at EAR/Cabot which is now Aearo, Virginia Tech, USARL at Ft. Rucker, and NIOSH in Cincinnati.

## S12/WG11 Studies

- Four laboratories set about testing two methods:
- Informed-user fit already incorporated into ANSI S12.6 which had replaced S3.19 - unnoticed by EPA
- Subject fit similar to that in S3.19

**Notes:**
The four laboratories set about testing two methods, the informed-user fit which was already incorporated in ANSI S12.6 as the experimenter-assisted fit, 

and a subject-fit method similar to that in S3.19.  No S3.19 tests were done in this study. A rigorous protocol was developed and each lab followed the protocol carefully.

## S12/WG11 Studies

- Initial study found that
- REATs less than and standard deviations greater than labeled S3.19 experimenter-fit data
- Informed-user fit provided better repeatability
- Subject-fit provided better interlaboratory agreement

**Notes:**
The initial study found that:

For both procedures the REATs were less than and the standard deviations were greater than the S3.19 values reported for the test protectors on the labels.  The protectors where the V51-R, the EP100, the EAR Classic, and the Bilsom UF-1 earmuff.

The informed-user fit provided better repeatability than did the subject-fit.

The subject-fit provided better interlaboratory agreement or reproducibility.  When this series of studies began, the expectation was the the informed user fit would be the better procedure – this was similar to the experimenter-assisted fit of version of S12.6 then current, intended to provide an “optimal” data set.  The fact that the subject-fit procedure provided better interlaboratory reproducibility was a surprise, as was the fact that the subject-fit data was closed to the real-world outcomes reported in the literature. 

## S12/WG11 Studies

- Working group convened a second set of studies with three of the original labs and one new lab
- Tighter control of experimenter involvement in subject-fit
- Results were similar

**Notes:**
Consequently, the working group convened a second set of studies.  Virginia Tech was unable to participate and was replaced by the lab at Wright-Patterson Air Force Base.

There was tighter control of the experimenter involvement in the subject-fit method – the experimenter was limited to reading a script and could provide no assistance outside of what was in the script. Thus, the subject-method became a test of the protector and its packaging since the subject was limited to the instructions for fitting provided by the manufacturer.

The test results were similar with the subject fit method providing the lower REATs, larger standard deviations, along with better agreement with real-world data and better interlaboratory reproducibility.

## S12/WG11 Studies

- Data for V51-R

**Notes:**
Here are the data for the interlaboratory study for the V51-R compared to the manufacturer’s reported S3.19 data.  In all cases the differences where statistically significant.

## S12/WG11 Studies

**Notes:**
This graph shows the comparison of the mean REATs from the 5 real-world studies, the mean REATs from the interlaboratory study using the method that is now incorporated in ANSI S12.6 Method B, and the manufacturer’s reported mean S3.19 REATs.  The S3.19 mean REATs are far greater than the others, while the S12.6B REATs fall within those of the real-world studies and are not statistically significant from the real-world mean REATs.

## S12/WG11 Studies

- Data for EP-100

**Notes:**
Here are the data for the interlaboratory study for the EP100 compared to the manufacturer’s reported S3.19 data.  In all cases the differences where statistically significant.

## S12/WG11 Studies

**Notes:**
As with the V51-R, the manufacturer’s reported S3.19 mean REATs are greater than the mean S12.6B REATs and the mean S12.6B REATs are similar to and not statistically different from the mean real-world REATs for the 6 studies, with the except of some frequencies for the second NIOSH study.  The NIOSH studies were conducted with large circumarual earmuffs while the others were conducted in a diffuse sound filed in a laboratory setting.

## S12/WG11 Studies

- Data for EAR Classic

**Notes:**
Here are the data for the interlaboratory study for the EAR Classic compared to the manufacturer’s reported S3.19 data.  In all cases the differences where statistically significant.

## S12/W11 Studies

**Notes:**
As with the V51-R and the EP100, the manufacturer’s reported S3.19 mean REATs for the EAR Classic are greater than the mean S12.6B REATs and the mean S12.6B REATs are similar to and not statistically different from the mean real-world REATs for the 16 studies with a few exceptions for single frequencies.  

## S12/WG11 Studies

- Data for Bilsom UF-1

**Notes:**
Here are the data for the interlaboratory study for the Bilsom UF-1 earmuff compared to the manufacturer’s reported S3.19 data.  In all cases the differences where statistically significant.

## SW12/WG11

**Notes:**
As with the V51-R, the EP100, and the EAR Classic the manufacturer’s reported S3.19 mean REATs for the EAR Classic are greater than the mean S12.6B REATs and the mean S12.6B REATs are similar to and not statistically different from the mean real-world REATs for the 3 studies.  

## S12/WG11 Studies

- Lead to the development of ANSI S12.6-1997 which has two methods
- Method A – Experimenter Supervised Fit
- Method B – Subject Fit
- Subject Fit better predicts Real-World Outcomes

**Notes:**
The working group revised ANSI S12.6 to include two methods. The experimenter-supervised fit remained unchanged from the earlier version of S12.6.  The subject-fit method was added as method B, hence the notation of the method as S12.6B.

The subject-fit method better predicts real-world outcomes and provide data with the best interlaboratory reproducibility. The mean REATs are lower, the standard deviations are higher, and any single=number rating will be lower than for either the experimenter-fit method of S3.19 or the experimenter-assisted fit of S12.6A.

## S3.19 vs S12.6B vs Real-World

**Real-World**

**S3.19**

**S12.6B**

**Notes:**
In terms of real-world data, while the S12.6B mean REATs are generally greater than the real-world data indicate, the S12.6B data are generally not statistically different from the real-world data and they are correlated with the real-world data, whereas the experimenter-fit S3.19 data are statistically different from and not correlated with the real-world data. This graph shows data for a all of the devices tested by the working group interlaboratory study and 8 other protectors as well and a combination fit of the the EAR classic and the Bilsom UF-1.

## ANSI  S12.6-1997

**Notes:**
Thank you, I’ll take any questions now.