HEARING PROTECTION Hearing Protection Ratings: NRR vs. SNR – What’s the Difference? 27 Hearing Protection Ratings: NRR vs. SNR – What’s the Difference? When noise levels exceed 85dBA for an 8-hour period, a hearing conservation program is required. However, hearing protection should be used anytime exposure to loud or persistent noise occurs. Earplug ratings help determine the appropriate level of noise protection. Higher ratings indicate greater noise reduction. Two common ratings are SNR and NRR are both measured in decibels (dB). While similar, SNR is generally about 3dB higher than NRR. SNR (Single Number Rating) The EU standard, SNR measures noise attenuation across frequencies from 63 to 8000 Hz. It provides a general estimate of noise reduction, such as an SNR of 20 equating to a 20dB reduction under ideal conditions. Actual protection may vary based on fit and realworld use. SNR is often paired with an HML rating to indicate noise reduction at high, medium, and low frequencies, making it useful for specific noise environments. NRR (Noise Reduction Rating) NRR, the U.S. standard, is measured under controlled conditions following ANSI S 3.19. An NRR of 30dB should reduce noise by 30dB in ideal conditions. However, real-world factors like improper fit can significantly reduce effectiveness. For instance, a 3dB noise increase doubles the intensity, making under-protection dangerous. NRR is often de-rated to reflect actual performance. Derating NRR Ratings To calculate a de-rated NRR, subtract 7 from the given NRR, divide by 2, and subtract the result from the environmental noise level: Estimated Exposure (dBA) = TWA (dBA) – [(NRR – 7)/2] For example, with an NRR of 33 and noise level of 100dB: (33 – 7)/2 = 13; 100 – 13 = 87dB This adjusted value highlights the importance of erring on the side of safety by selecting higher-rated protection or adding layers of protection when necessary.
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