7. What is the unit measurement of noise?

It is calculated in Decibel (dB) For every 5 dl increase, the noise is louder by double

NRR-Noise Reduction Rating. It is a laboratory-derived numerical estimate of the attenuation that is provided by the protector.

Attenuation – Attenuation refers to the damping or decrease of noise levels as a result of wearing Hearing Protector Devices (HPDS)

Suitable Hearing Protector -The term “suitable hearing protectors” as used in the provision means protectors that are comfortable to wear and that offer sufficient attenuation to prevent hearing loss.

How to find out the attenuation As per OSHA 1910.95 app B

For Single Protection

When using a sound level meter set on the weighting network

A. Obtain a representative sample of the C-weighted sound levels in the employee’s environment

B. Subtract the NRR from the C-weighted average sound level to obtain the estimated A-weighted TWA under the ear protector Estimated Exposure (dBA) = TWA (dBC) – NRR

Single Protection Example:

1. C-weighted TWA = 108 dBC, ear plug NRR = 32

2. Estimated Exposure = 108-32 = 76 dBA

This hearing protection is considered adequate, as it is below the 85 dBA threshold

For dual protection (ear muffs and plugs are used simultaneously) use the following:

A. Determine the laboratory-based for the higher rated protector (NRRh).

B. Add 5 dB to the field-adjusted NRR to account for the use of the second hearing protector

C. Subtract the remainder from the TWA as follows: Estimated Exposure (dBA) TWA (dBC)-(NRR + 5)

Dual Protection Example

1. TWA=110 dBC, plug NRR=29, and muff NRR=19 dB

2. Estimated Exposure = 110 (29+5)=76dBA

This hearing protection is considered adequate, as it is below the 85 dBA threshold.

Note: If A weighted TWA is set in the sound level meter then deduct value of 7 from NRR Hearing Protection.