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Did You Hear That? Dual Hearing Protection – Part II

- November 13, 2017 by Mike Pettit (View all posts by Mike)

In Part 1 of this series, I addressed the use of single hearing protective devices (HPDs) and the effects HPDs have on noise attenuation (weakening of noise levels). In Part 2, I’ll address the use of dual HPDs, and their effects on reducing noise exposure.

Overview

According to OSHA, “Hearing protector attenuation must be sufficient to reduce employee exposure to a TWA (time-weighted average) of 85dBA.”

HPDs are considered the last option for controlling noise exposures, and their effectiveness depends on the protectors being properly fitted and worn.

Dual HPDs
HPDs come in several forms, most commonly ear plugs and ear muffs. Some may argue which is better than the other in regards to reducing noise levels, comfort, etc.

Some also believe using both forms of HPDs at the same time will result in the protection equaling the noise reduction rating (NRR) when the intended protection levels are added together.

Per OSHA, the actual NRR achieved by dual HPDs, when properly fitted and worn, includes the following calculation:

      • Noise Exposure – 104 dBA
      • Higher-rated HPD – 25 dB
      • Subtract 7dB = 18dB
      • Add 5dB for second HPD = 23 dBA

Taking the above into consideration, the anticipated 23dBA reduction would be considered sufficient protection for noise levels at or below 107dBA (but, not for noise levels at 108dBA).

However, due to OSHA’s experience and published scientific literature showing laboratory-obtained real ear attenuation for HPDs seldom being achieved in the workplace, they strongly recommend applying 50% correction factor. Again, this is due to relying on the HPDs being properly fitted and worn during the exposures.

Using the above-recommended calculation method, the following would result:

      • Noise Exposure – 104 dBA
      • Higher-rated HPD – 25 dB
      • Subtract 7dB = 18 dB
      • Divide by 2 = 9 dB
      • Add 5dB for second HPD = 14 dBA

Taking the above into consideration, the anticipated 14 dBA reduction would be considered sufficient protection for noise levels at or below 98dBA, and not for noise levels at 108 dBA.

Summary

Sounds can damage sensitive structures in the inner ear and cause noise-induced hearing loss, which can be immediate or take a long time to be noticed. It can also be temporary or permanent, and can affect one or both ears.

Please remember, the best way to prevent hearing loss is to reduce noise at the source by engineering a noise control solution – an example would include isolating the noise source with an enclosure. Unfortunately, engineering out the noise is not always realistic or feasible.

In both parts of this series, I addressed the use of single and double hearing protective devices once all engineering controls are implemented, and the methods needing to be used to calculate the anticipated noise reduction ratings.

Did you hear that? We hope so!

 

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