# Optimum amount of hearing protection?

Wood-working tools can be very loud. Noise levels of 104 - 110 dB have been measured in real-world use. (Theoretically, the noise levels are supposed to be measured one meter away from the source of the noise. One meter is 3' 3 3/8".)

There are a few forms of hearing protection available. For example:

• Squishy ear-plugs for putting in one's ear canals. Typical earplugs are rated for about 32 dB of noise reduction.
• Headset-like earmuffs. Typical earmuffs are rated for about 29 dB of noise protection.

Is it considered best practice to wear both ear-plugs and earmuffs when working with power tools? Or does the combined noise reduction make it so hard to hear non-tool noise that you will not hear other potential dangers?

• I like this question and I eagerly await knowledgeable answers! Otherwise I'll have to go and do some research to find out... :) Mar 18 '15 at 16:51

OSHA defines what noise levels warrant hearing protection to assure safe working conditions. Excessive noise is generally defined as exposure to 85 or more decibels of sound over an 8 hour period. But if the ambient noise exceeds those levels, the amount of time until damage can occur will decrease.

Hearing protectors must be tested and approved by the American National Standards (ANSI), and all devices must be labeled with a noise reduction rating (NRR) to quantify their effectiveness. The higher the NRR number, the greater the capacity for noise reduction.

Even though NRR is expressed in decibels (dB), it is important to understand that hearing protectors DO NOT reduce the surrounding levels by that amount.

To calculate the actual noise reduction, take the NRR rating, subtract 7, and then divide by two. So if you have a piece of machinery operating at 110 dB with hearing protection rated at 33 NRR, the reduction would look like this:

110 dB - (33 - 7) / 2
110 dB - 13
= 97 dB

You can then use the chart above to determine if addition noise protection is necessary.

There's obviously little downside to being overly conservative when it comes to protecting your hearing. I tend to use it even if I don't absolutely need it; it's just a good habit.

If you are occasionally working with something particularly loud, you can double up the methods of protection… but if you do this often, it is best to just buy one, convenient piece of protection that will handle those levels.

But if you are layering, it is important to understand that layering noise protection is not additive (i.e. 33 dB + 29 dB ≠ 62 dB reduction). At these ANSI-rated levels, you typically just take the higher level and add an additional 5 dB of noise reduction. In the case above, you'd end up with an effective rating of about 38 dB NRR.

If you are concerned about blocking out the "normal" noises as a matter of safety (communicating with people, hearing alarms, etc), then you might want to consider investing in some electronic ear protection (search). Devices like these will provide an effective reduction of loud noises while allowing (or even amplifying) the normals sounds you might want to hear. That's pretty cool.

I use electronic hearing protection almost exclusively. When I am working with loud equipment (or things that go <boom>), I want to be able to hear the things going on around me. When the equipment goes off, I don't have to remove my hearing protection or remember to put it back on again. When it starts to get noisy, it's just there. And I like to assure that I can continue to communicate normally with the people or things around me.

• This is interesting. I had heard about subtracting some number from the NRR but not the part about dividing by 2. Why are these extra calculations necessary to arrive at the actual noise reduction? Is this just a rough estimate that happens to be "close enough" in the typical noise range without doing any logarithmic calculations?
– rob
Mar 18 '15 at 22:49

When in the shop, it is wise to use hearing protection. I prefer to use earmuffs rather than plugs but that is more of a comfort concern than having any scientific proof behind its efficacy.

Ultimately I think the answer becomes "if it is loud enough that you're reluctant to turn it on at night" then you should absolutely have ear protection.

I would find using two forms of hearing protection onerous, so I prefer to use just one good set of earmuffs which I also use at the rifle range. Muffs designed to dampen the sound of gunshots are also perfect for power tools! Just make sure that you purchase normal, low-tech earmuffs. Some earmuffs sold for the rifle range will only block sudden loud noises (like a gunshot) while the constant whine of a power tool will pass through unimpeded. You want universal sound suppression!

• Just a note of clarification for those who may happen to see your post, then see some shooter's ear plugs at the local sporting goods store. Some of the shooter's ear plugs have flaps that close automatically under the concussive force of a gunshot, but are otherwise open to allow conversation/listening for the wild life to wander by. They do a great job of cutting out the sharp gunshot, but will do nothing about the steady whine of power tools. (Yes, I know you said "muffs", but some people skip little details like that.) Mar 19 '15 at 2:09
• Very good point! I'll edit my answer to make this more apparent. Mar 19 '15 at 2:10