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The Noise Reduction Rating (NRR) has been the standard measure of HPD attenuation for decades—and it has been widely criticized for overestimating real-world protection. The personal attenuation rating (PAR) and ANSI S12.71 represent the evolution toward individual-specific measures. Understanding these three systems is essential for making defensible HPD selection decisions and explaining your program to OSHA compliance officers.
Soundtrace produces PAR results through quantitative fit testing as part of its hearing conservation services, giving employers the most accurate measure of each worker’s real-world HPD protection.
The NRR is determined using trained, motivated subjects inserting the HPD under supervised conditions. It is a population average—it tells you what highly proficient users achieved under ideal conditions, not what your workers will achieve on the production floor after 6 hours on shift.
ANSI S12.71 tests HPDs using naive subjects who self-fit the device with minimal instruction—closer to real workplace conditions. It produces two values: an 80th percentile attenuation (what 80% of users will exceed) and a 20th percentile value (the lower bound). These are a much better predictor of real-world performance than the labeled NRR.
Lab panel, expert fitting. High but unrealistic. Required on packaging by EPA.
Naive subjects, self-fit. More realistic population-level estimate. Two values: 80th and 20th percentile.
Individual measure for this worker with this device. Most accurate of the three.
A personal attenuation rating is produced by quantitative fit testing and measures the actual attenuation a specific worker achieves with a specific HPD using their own technique. Unlike NRR or S12.71 values, a PAR is not a population estimate—it is an individual measurement, making it the most legally defensible measure for OSHA 1910.95(i)(4) compliance.
Using the labeled NRR to determine if a worker’s HPD provides adequate protection, then being unable to explain the attenuation calculation during an OSHA inspection. If the NRR is 29 and the worker is at 102 dBA TWA, the OSHA-derated estimate of 11 dB brings exposure to 91 dBA—still above the PEL. A PAR result is the only way to confirm actual adequacy.
For OSHA compliance purposes, a PAR from quantitative fit testing is always more defensible than a derated NRR. A PAR tells you what is actually happening in each worker’s ears.
See: Hearing Protection & Fit Testing: The Complete Employer Guide
Soundtrace fit testing produces PAR results per employee—documented evidence of actual protection, not a derated guess.
Book a DemoGet a quote →The NRR is a laboratory measurement using expert subjects under ideal conditions. It is a population average that significantly overestimates real-world protection. The PAR is produced by quantitative fit testing of an individual worker with a specific device using their own technique—measuring actual attenuation for that person.
ANSI S12.71 uses naive, uninstructed subjects to self-fit hearing protection devices, producing a more realistic estimate of real-world population-level attenuation. It reports two values: an 80th percentile attenuation and a 20th percentile lower bound, accounting for typical technique variation rather than expert fitting.
For individual compliance decisions, a PAR from quantitative fit testing is always more accurate and more defensible than a derated NRR. A PAR tells you specifically whether that worker, with that device, is receiving adequate protection at their actual exposure level.