overview

The following are the different ways that the Noise Reduction Rating (NRR) can be used. This document provides a brief summary and several examples of these evaluation methods. An employee may not be exposed to noise levels exceeding 90dBA as an 8 hour Time Weighted Average (TWA). A comprehensive hearing conservation program must be implemented when noise level exceeds 85dBA as an 8 hour TWA.

When noise is measured and attenuation estimated using EPA Ratings:  http://www.access.gpo.gov/nara/cfr/waisidx_02/40cfr211_02.html
Noise Level – NRR = Attenuated Noise Level

Example: 97-23 = 74

In a working environment with a noise level of 97, an earplug with an NRR of 23 gives an Attenuated Noise Level of 74.

Earplug	Noise Level	NRR Rating	Attenuated Noise Level
Pura-Fit®/SparkPlugs®	122	33	90
Pura-Cones®	119	29	90
Traffic Cones®	113	23	90

When noise is measured and attenuation estimated using OSHA C Weighted: http://www.osha.gov/dts/osta/otm/noise/hcp/attenuation_estimation.html

Noise Level – 50% of NRR = Attenuated Noise Level

Example: 97-11.5 = 85.5

(23/2) = 11.5

Earplug	Noise Level	Attenuation	Attenuated Noise Level
Pura-Fit®/SparkPlugs®	106	16	90
Pura-Cones®	104.5	14.5	90
Traffic Cones®	101.5	11.5	90

When noise is measured and attenuation estimated using OSHA A Weighted: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=9737&p_table=STANDARDS

Noise Level – (NRR – 7dBA)/2 = Attenuated Noise Level

Example: 97-8 = 89

(23-7)/2 = 8

Earplug	Noise Level	Attenuation	Attenuated Noise Level
Pura-Fit®/SparkPlugs®	102.5	12.5	90
Pura-Cones®	101	11	90
Traffic Cones®	98	8	90

Caution: Use this information only as a guide to the different ways NRR data is utilized in the field. These should not be used by the end-user to indicate the actual amount of attenuation attained by an end-user in a specific situation.

WARNING: The information contained in this Tech Brief is dated and was accurate to the best of Moldex's knowledge, on the date above. It is not meant to be comprehensive, nor is it intended to be used in place of the warning/use instructions that accompany Moldex respirators. Outside of the USA, check with all applicable and local government regulations.

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