Hearing protector attenuation methods

Use the C-weighted dosimeter method in 1910.95 App B: obtain the employee's C-weighted dose for the full workshift, convert it to a TWA, and subtract the hearing protector's NRR from that C-weighted TWA to estimate the A‑weighted TWA under the protector.

• Steps: (1) Measure C-weighted dose over the shift and convert to TWA (see appendix A references in the standard); (2) Subtract the NRR shown on the hearing protector packaging from the C‑weighted TWA; (3) The result is the estimated A‑weighted TWA under the protector.
• Remember: calculated attenuation is realistic only if the protector is properly fitted and worn, as stated in 1910.95 App B.

If your dosimeter cannot measure C-weighting, use the non-C dosimeter method in 1910.95 App B: convert the A-weighted dose to a TWA, subtract 7 dB from the NRR, and then subtract that reduced NRR from the A-weighted TWA to estimate the A-weighted TWA under the protector.

• Steps: (1) Convert the A‑weighted dose to a TWA (see Appendix A referenced in the standard); (2) Reduce the NRR by 7 dB (NRR - 7 dB); (3) Subtract the result from the A‑weighted TWA to get the estimated protected TWA.
• Note: The appendix explains the 7 dB adjustment is required when starting from A‑weighted measurements (1910.95 App B).

When using a sound level meter on the A-weighting network, follow the 1910.95 App B A-weighted method: obtain the employee's A-weighted TWA, subtract 7 dB from the NRR, and subtract that value from the A-weighted TWA to estimate the A-weighted TWA under the protector.

• Steps: (1) Measure representative A‑weighted levels and compute the TWA for the employee; (2) Reduce the NRR by 7 dB; (3) Subtract this adjusted NRR from the A‑weighted TWA to get the protected TWA.
• Reminder: The calculation assumes proper fit and consistent wear of the hearing protector (1910.95 App B).

Use the C-weighted sound level meter method in 1910.95 App B: obtain a representative sample of the C-weighted levels (or C-weighted average), then subtract the NRR from that C-weighted level to estimate the A-weighted TWA under the protector.

• Steps: (1) Measure representative C‑weighted levels for the employee's environment; (2) Compute the C‑weighted average or dose and convert to the equivalent TWA if needed; (3) Subtract the full NRR (no 7 dB reduction) from the C‑weighted result to estimate the protected A‑weighted TWA.
• Note: The appendix treats subtraction from C-weighted measurements differently than from A‑weighted ones; follow the specified approach in 1910.95 App B.

When using area monitoring with an A-weighted meter, 1910.95 App B directs you to obtain a representative area A-weighted sound level, subtract 7 dB from the NRR, and then subtract that adjusted NRR from the area A-weighted level to estimate the A‑weighted TWA under the protector.

• Steps: (1) Take representative area A‑weighted measurements that reflect the employee's exposure; (2) Subtract 7 dB from the NRR; (3) Subtract the adjusted NRR from the measured A‑weighted level to estimate the protected TWA.
• Caution: Area measurements may not reflect an individual worker's exposure as accurately as personal dosimetry; 1910.95 App B emphasizes taking representative samples for each time segment.

The correct adjustment is to subtract 7 dB from the NRR before applying it to A-weighted measurements, per 1910.95 App B; this compensates for the difference between the laboratory-based NRR (which is C-weighted or broadband-based) and workplace A-weighted measurements.

• Practical effect: Use (NRR - 7 dB) when subtracting from A‑weighted TWA or area A‑weighted levels.
• Reminder: No 7 dB reduction is applied when you start from C‑weighted measurements—there you subtract the full NRR (1910.95 App B).

An employer may use one of the NIOSH methods (#1B1, #1B2, or #1B3) as an alternative to the EPA NRR when they prefer those procedures: the appendix states employers may evaluate attenuation using the NIOSH methods described in HEW Publication No. 76-120 rather than the NRR (1910.95 App B).

• Notes on choice: The NRR is a simplification of NIOSH method #1B2, while NIOSH method #1B1 is the most complex and generally the most accurate because it uses more spectral information from the individual's noise environment.
• Requirement: Whichever method is chosen must be applied to the individual's actual noise environment to assess adequacy (1910.95 App B).

Yes. 1910.95 App B requires that the chosen method (NRR or a NIOSH method) be applied to an individual employee's noise environment to assess whether the protector provides adequate attenuation.

• This means assessments should reflect the worker's actual exposure (personal dosimetry or representative area measurements) and not rely only on generic assumptions.
• Also ensure protectors are properly fitted and worn—attenuation estimates are realistic only under those conditions (1910.95 App B).

If an employee has experienced a significant threshold shift, hearing protector attenuation must be sufficient to reduce that employee's noise exposure to an 8‑hour TWA of 85 dB, as required by 1910.95 App B.

• Action steps: (1) Measure the employee's actual noise exposure (use the appropriate method from the appendix); (2) Use the NRR or a NIOSH method to estimate protector attenuation for that individual; (3) Select a protector (or combination of engineering controls and protectors) that brings the estimated protected TWA to ≤ 85 dB.
• Keep in mind: Proper fit and consistent use are essential to achieve the calculated attenuation (1910.95 App B).

1910.95 App B advises employers to take a sufficient number of measurements to achieve a representative sample for each time segment of the employee's exposure; there is no single mandated count—use professional judgment to cover variability in tasks, locations, and time periods.

• Practical guidance: Sample different tasks, work locations, and times of day; use personal dosimetry across full shifts when possible.
• Reason: Inadequate sampling can misrepresent the true exposure and lead to incorrect attenuation estimates; the appendix stresses representativeness and sufficient sampling (1910.95 App B).

Yes, the NRR printed on the hearing protector package can be used—1910.95 App B identifies the EPA NRR as the most convenient method; however, you must apply the NRR using one of the appendix's specified procedures and remember the NRR is a laboratory-derived value that requires workplace adjustment.

• Key points: (1) Use the appendix methods (C‑weighted or A‑weighted approaches) to apply the NRR properly; (2) Adjust the NRR by -7 dB when starting from A‑weighted measurements per the appendix; (3) Ensure protectors are properly fitted—NRR effectiveness is conditional on fit and wear (1910.95 App B).

For complex or highly spectral (frequency‑dependent) noise exposures, the appendix recommends that the more complex NIOSH method #1B1 is likely the most accurate because it uses the largest amount of spectral information from the individual's noise environment (1910.95 App B).

• Guidance: Use NIOSH #1B1 when you have detailed spectral measurements and want greater accuracy; use the NRR (a simplification of NIOSH #1B2) for convenience when spectral detail is limited.
• Requirement: Any selected method still must be applied to the individual worker's noise environment to assess adequacy (1910.95 App B).

While the appendix does not prescribe a specific paperwork form, 1910.95 App B makes clear that employers must select a method and apply it to individuals' noise environments—good practice is to document the method used, the measurements, calculations (including any 7 dB adjustment), and the resulting estimated protected TWA for each employee.

• Documentation to keep: measurement dates and instruments, weighting network used (A or C), the NRR value and any adjustment (e.g., NRR - 7 dB), and the final estimated protected TWA.
• Why: Documentation shows you applied the appendix methods appropriately and supports decisions about protector selection, especially for employees with significant threshold shifts (1910.95 App B).

You must remember that calculated attenuation values are realistic only to the extent that the protectors are properly fitted and worn, per 1910.95 App B.

• Employer responsibilities: provide training on correct fitting and use, conduct fit checks or supervised practice, and verify actual use in the workplace.
• Consequence: Poor fit or inconsistent wear can make the estimated protected TWA overly optimistic; always verify real-world protection through observation or individual fit testing when available (1910.95 App B).