OSHA - Subject-fit

Who We Are Products Reference Search Contacts



NOTE:This is an abridged version of this document.  To read this document in its entirity, please  see the original.

[New Paragraph]


  1. BACKGROUND.   When OSHA promulgated its Hearing Conservation Amendment in 1983, it incorporated the EPA labeling requirements for hearing protectors (40 CFR 211), which required manufacturers to identify the noise reduction capability of all hearing protectors on the hearing protector package. This measure is referred to as the noise reduction rating or NRR. It is a laboratory-derived numerical estimate of the attenuation that is provided by the protector. The standard also prescribes various methods to estimate the adequacy of hearing protection attenuation using the NRR. By December 1983, however, it became evident that the amount of protection users were receiving in the workplace with the prescribed hearing protectors did not correlate with the attenuation indicated by the NRR. OSHA acknowledged that in most cases, this number overstated the protection afforded to workers and issued a change in compliance policy in its compliance instruction CPL 2-2.35A, Appendix A, requiring the application of a safety factor of 50 percent to the NRR, above and beyond the 7 dB subtraction called for when using A-weighted measurements.

    Prompted by the concerns of industry about the inadequacy of the present labeling of hearing protectors, the Industrial Safety Equipment Association (ISEA) convened a meeting of all interested parties and reached a consensus that the high NRR values were misleading users, causing them to assume that they were being adequately protected form noise exposure. This consensus triggered the National Hearing Conservation Association (NHCA) to create a task force on hearing protector effectiveness. The task force was made up of professional organizations, government, industry, and accredited standards working groups. Their task was to develop new guidelines for the proper selection, use and labeling of hearing protectors. In 1997, while the task force was working on their recommended changes, ANSI developed a new test method for measuring the real ear attenuation of hearing protectors (ANSI S12.6-1997), which provides more representative estimates of the real world performance of hearing protectors. This subject-fit method better approximates the protection attained in real workplaces because the untrained subjects in this test method (the only instruction they had was the instruction that comes with the package) closely replicate real world users. With this newly accepted consensus standard, the task force was able to recommend changes in hearing protector labeling and noise reduction rating methodologies, and petitioned the EPA to adopt these changes.

    Manufacturers of hearing protectors are voluntarily adopting these changes. They are testing their hearing protectors according to the subject-fit method, and providing the new label as an insert in the accompanying package. The present label cannot be eliminated because it is still required by EPA as well as by OSHA.
    Note:   Hearing protector packages may contain two labels.

  2. TASK FORCE RECOMMENDED CHANGES. Sample labels and details of the NHCA task force recommendation can be found in Appendix III:5-2 at the end of this chapter. Listed below are the major changes:
    1. The format is very close to the current EPA required label (NRR) but to avoid confusion, this label is distinguished as NRR Subject Fit (SF).
    2. Explicit mention is made on the label that 84% of users can expect to obtain this level of protection. Other considerations should be made when selecting a hearing protector for the individual worker using it, such as ease of use, comfort, compatibility with other safety equipment, work environment, impact of communication, and training on correct use.
    3. The data from which the NRR(SF) is computed is based on lab results from subject-fit data based upon the new ANSI S12.6-1997 standard mentioned above. This method, as opposed to the NRR method which uses highly experienced subject, more closely reflects the actual performance of hearing protectors in real workplaces. Consequently, the new NRR(SF), numbers will be lower than the NRR.
    4. The NRR(SF), has a correction factor built into it, so that the 7dB correction factor does not have to be subtracted from the number for A-weighted measurements as presently required by OSHA.

[Bibliography and Appendix III:5-1 omitted]


The recommendations consist of a proposal to revise the primary and secondary labels for hearing protector packaging, as currently defined by the EPA Hearing Protector Labeling Regulation, as well as the following two administrative issues.


  1. Testing of hearing protector attenuation shall be conducted only in laboratories accredited by the Department of Commerce's National Voluntary Laboratory Accreditation Program (NVLAP).
  2. Mandatory product retesting should occur at least every 10 years, but not more often than every 5 years.


The proposed primary label, including the new single number rating designated the Noise Reduction Rating (Subject Fit) appears below. The secondary label follows.


Rating (SF)

When worn as directed, most users (84%) can obtain at least this much protection. Range of NRR(SF), for existing products is about 0 to 25. (Higher numbers denote greater protection.)

XYZ Corporation
Anytown, USA
Model EXP 579

Federal Law prohibits removal of this label prior to purchase. EPA  LABEL REQUIRED BY U.S. EPA REG. 40 CFR PART 211 Subpart B


Instructions for use (specific to each product)

[NOTE:   This section may contain unlimited text and pictures at the discretion of the manufacturer.]

Selected hearing protectors

The most critical consideration in selecting and dispensing a hearing protector is the ability of the wearer to achieve a comfortable noise-blocking seal which can be consistently maintained during all noise exposures. Additional important issues include:

Hearing protector's noise reduction
Wearer's daily equivalent noise exposure
Variations in noise level
User preference
Communication needs
Hearing ability
Compatibility with other safety equipment
Wearer's physical limitations
Climate and other working conditions
Replacement, care and use requirements

Test Frequency (Hz) 125 250 500 1000 2000 4000 8000 H M L NRR(SF)
Mean Attenuation (dB) 17.9 19.0 21.0 24.7 29.9 35.6 34.6 25 18 14 16
Standard Deviation (dB) 7.3 6.3 7.3 6.4 5.3 5.0 5.4

How to use the Noise Reduction Rating (Subject Fit), [NRR(SF)]

The NRR (SF), may be subtracted from an A frequency-weighted sound pressure level or a time-weighted average noise exposure as follows:

1. The noise level is 92 dB(A).
2. The NRR (SF), is 16 dB.
3. Most users (84%) should be protected to a level 76 dB(A).

Tip:   A better estimate of the protected level can be obtained by adding 5 dB to the NRR (SF), and subtracting it from a noise measurement made using C- instead of A-frequency-weighting.

Applicability of noise-reduction estimates

FAILURE TO FIT THIS HEARING PROTECTOR ACCORDING TO INSTRUCTIONS WILL REDUCE ITS EFFECTIVENESS. When used as directed this hearing protector is expected to provide between 16 and 30 dB of noise reduction for about 66% users. Of those remaining, 17% will be likely to obtain less than 16 dB of protection, and the other 17% will be likely to obtain more than 30 dB.

Differences between hearing protector ratings of less than 3 dB are not important.

Estimating noise reduction for individual users

The labeled values of noise reduction are based on laboratory tests. It is not possible to use these data to reliably predict levels of protection achieved by a given individual in a particular environment. To ensure protection, those wearing hearing protectors for occupational exposures must be enrolled in a hearing conservation program. Non-occupational users should have hearing evaluations by an audiologist, qualified physician, or other qualified professional, on a regular basis.

Impulse noise

Although hearing protectors are useful for protection from impulsive noise, the noise reduction measurements are based on tests in continuous noise and may not be an accurate indicator of the device's performance for impulsive sounds such as gunfire.

Additional information

For additional information call NIOSH at 800-35-NIOSH.

Appendix References

1   These are representative data for a foam earplug. For 2- and 3-position devices such as earmuffs or semi-insert hearing protectors, the data would also have to be provided for the alternative positions, so the above table could contain up to four additional rows.

2   See section on Additional Information to find out more about HML.