Hearing protection - Is there a Doctor in the house?

[PinnedAndRecessed]

This is no longer the accepted approach and fell out of favor over 2 years ago. You no longer add the NRR of the plugs and muffs and subtract 5 dB. Instead you take the higher of the two and add 5 dB to that. 30 plug with 20 muff gives an effective NRR of 35 not 45.

Source, please.

Your first link does not work.

 

[hso]

http://www.osha.gov/dts/osta/otm/noise/hcp/attenuation_estimation.html
http://www.e-a-r.com/pdf/hearingcons/earlog13.pdf
http://www.e-a-r.com/pdf/hearingcons/FAQdualHPD.pdf

Following OSHA's guidance you would subtract 7 dB from the highest protective device if you are measuring the noise on the A scale instead of the C scale. You then add 5 dB for the lower of the two protective devices.

Use the following formulas to estimate the attenuation afforded to a noise-exposed employee in a work environment by muffs, plugs, or a combination of both.


* A common method used for single protection (either muffs or plugs) is as follows

1. Determine the laboratory-based noise attenuation provided by the HPD. This is referred to as the Noise Reduction Rating (NRR) and is listed on the packaging.

2. Subtract the NRR from the C-weighted TWA workplace noise level, as follows:

Estimated Exposure (dBA) = TWA (dBC) - NRR

If C-weighted noise level data is not available, A-weighted data can be used by subtracting a 7 dB correction factor from the NRR, as follows:

Estimated Exposure (dBA) = TWA (dBA) - (NRR - 7)

Example:

TWA=100 dBA, muff NRR=19 dB

Estimated Exposure = 100 - (19-7) = 88 dBA

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

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

2. Subtract 7 dB from NRRh if using A-weighted sound level data.

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

4. Subtract the remainder from the TWA as follows:

Estimated Exposure (dBA) = TWA (dBC) - (NRRh + 5) , or

Estimated Exposure (dBA) = TWA (dBA) - [(NRRh- 7) + 5]

Example:

TWA=110 dBA, plug NRR=29, and muff NRR=25 dB

Estimated Exposure = 110 - [(29 - 7) + 5] = 83 dBA

I always read about the dB reduction with a "properly fitted" ear muffs. Realisticly speaking how well do they work while wearing safety glasses?

The rule of thumb is to subtract 5 dB for the earpieces breaking the seal the muffs make (effectively halving the protection).

So, if you're wearing shooting glasses (like you're supposed to) and you've put your NRR 30 plugs in properly and have your NRR 20 muffs on properly you would have an effective protection of between 30 + (20 - 5 = 15 defined as 5) = 35 and 28 = 30-7 + defined as 5

So our example 157 dB gunshot with the shooter wearing plugs and muffs will expose the shooter to ~ 122 to 149 dB hazardous noise.

 

[Sidewinder6]

Over 20 years ago I was involved in a shooting incident where a 12 ga was discharged inches from my unprotected ear. (Growing up in the rock and roll world and also a period where safety equipment was not the highest priority didnt help.) That said, I have permanent ringing which is rather loud and I frequently ask people to repeat something before I can understand it. The ear drum was perforated and my doctor tells me there is a scar on it. When I go to the range, I use molded ear plugs because I prefer not to have the large outside the ear protectors. They get annoying after wearing them a couple hours. I found those various brands of sonic ear valves are basically not enough protection for range shooting unless you dont worry about long term damage. Be careful with your ears, you may live to regret shrugging it off.

 

[quatin]

db = decibels. It's a logarithmic unit, not a linear unit. 32 db + 32 db is not 64 db. It's 35 db.

 

[pastaman]

I know that in the Air Force when standing within 20 feet of a running jet engine, foamies and muffs (double protection) are considered good enough. They should definitely be good enough for short durations like a gunshot.