Comparing the Current NRR with the Proposed
new NRR
12/21/2008
In the nearly 30 years since the Noise Reduction Rating first appeared, it has been recognized as being an inaccurate predictor of actual field performance (numbers much higher than actually achieved by groups of workers in practice), too difficult to use (correct use requires subtraction from dBC values instead of dBA values), and too finely tuned (the fact that it’s a single number seems to imply great precision, i.e., to within 1 dB). The new approach is intended to address those issues as summarized in the table below.
See the proposed new label.
Feature | Current NRR | Anticipated New NRR |
Noise rating | Single number based on 1976 NIOSH publication | Dual number, high/low values, based on recent ANSI S12.68-2007 standard |
Protection goal | 98% of optimally fitted users should obtain this value | High value possible for 20% of highly trained and motivated users to obtain; low value possible for 80% of individually trained users to obtain |
How to use | Subtract directly from dBC noise measurements to predict dBA exposure; if subtracted from dBA, a 7-dB correction is required (NRR – 7) | Subtract directly from dBA noise measurements |
De-rating | OSHA requires a 50% de-rating for certain applications, NIOSH suggests a more complex scheme | Intention is for no de-rating to be required, but some early data suggest otherwise. Outcome indeterminate at this time. |
Product applicability | Applies to conventional HPDs, and only to the passive and/or non-level-dependent performance of electronic and level-dependent HPDs | Applies to all types of HPDs, with separate indicators for passive, and for electronic and level-dependent performance (see examples) |
Test method (passive mode) | HPDs fit by experimenter per ANSI S3.19-1974 using 10 subjects | HPDs fit by subjects after detailed training per ANSI S12.6-2008, Method A, using 20 subjects for earplugs and 10 for earmuffs |
Test method (active or level-dependent mode) | Not applicable | Includes new tests that are not yet described by ANSI standards but are detailed within the regulation. They involve use of microphone-in-real-ear (MIRE) and acoustical test fixture (ATF) techniques, and for level-dependent devices test signals use an impulse noise with specified peak levels. |
Enforcement and certification | Enforcement and reporting requirements are dormant unless complaints filed with EPA by customers or competitors | Will include requirements for filing data with EPA, for retesting every 5 years, and for enforcement. |
