Excellent question! At first glance, it would appear that you will still be exposed to 120 dB of noise, even with a 30 dB ear plug properly inserted (150-30=120), and because 120 dB is far above the 85 dB beginning threshold of NIHL (noise induced hearing loss,) it would seem that NIHL from shooting is unavoidable, and yet, shooters routinely are undamaged by their shooting experiences. What is going on here?
To understand how shooters can be exposed to 120 dB of noise without damaged hearing the result, consider the first principle in hearing protection: For noise below 140 dB, which can cause instant damage, NIHL results from the weighted average cumulative noise exposure. (The below table illustrates that principle nicely.)
How Loud and How Long
One way that noise can permanently damage your hearing is by a single brief exposure to a high noise level, such as a firecracker going off near your ear. But hearing damage can also occur gradually at much lower levels of noise, if there is enough exposure over time. To protect your hearing, you'll want to limit your exposure to these moderately high noise levels and give your ears a chance to recover after any period of noise exposure.
Safe Exposure Times
|Instantaneous permanent damage||140+||Shotgun, rifle, jetplane takeoff|
|Less than one second||130||jackhammer, heavy industry|
|Less than ten seconds
Threshold of pain
|1.5 minutes||110||Power tools, snowmobile|
|15 minutes||100||Chainsaw, motorcycle|
|2.5 hours||90||Lawn mower|
|8 hours||85||Beginning of Danger Zone|
|Prolonged exposure to noise levels 85dB and higher can result in permanent hearing loss.||80||City Traffic|
|70||Vacuum cleaner, hair dryer|
|60||Office, sewing machine|
|Common noise levels (dB), and their effect upon hearing.||10||Breathing|
|0||Threshold of normal hearing|
So, let’s assume your shotgun produces 150 dB. Most likely, that number is based on measurements taken at a point close to the weapon, and a point that is closer to the source of the sound than will be your ears. As a result, you will most likely experience a lower exposure level than the maximum the gun can produce. It is also true that a shotgun blast is quite short-lived, resulting in a lower cumulative exposure level than you might expect. All that said, better to overestimate the danger than underestimate it, but stay with me as I continue our example.
NIOSH (The National Institute for Occupational Safety and Health, a division of the US CDC, the Centers for Disease Control and Prevention) says that one should never allow exposure over 140 dB lest you suffer instant and irreversible hearing damage. So, assuming you can wear a protector that reduces the maximum noise level at your ear by 30 dB, when shooting a shotgun that produces 140 dB at your ear, you would experience just 110 dB (140-30=110) (this assumes you had the hearing protector fitted properly, which is vitally important…) According to the table above, you could stand such an impact for a total of 90 seconds in a 24 hour period without harm.
Now, assume the duration of the muzzle blast is 500 milliseconds (a severely conservative estimate given that a muzzle blast actually lasts 3-5 milliseconds.) Of course you are exposed to more sound as the muzzle blast noise bounces back to you after being reflected off the ground, walls if there are any, nearby vehicles, trees, and the like. Even so, the total exposure you experience will be far less than our conservative estimate of 500 milliseconds.
Using this very conservative 500 millisecond number, according to the table, you could be exposed to 180 such muzzle blast noise events within a 24 hour period without harm as long as you were wearing the 30 dB protector (90 seconds per day/500 milliseconds per event = 180 events per day.) As you increase the noise level, of course you would need more protection, and/or you could stand fewer blasts without damage.
So that is how as a shooter, you can be exposed to numerous 140 dB noise events with just a 30 dB hearing protector, and suffer no hearing damage.
SNR, NRR, and IPIL Rating
NRR and SNR ratings are based on a single noise level, usually set at 100 dB, but it turns out that most hearing protectors act differently as the noise level increases, giving you more protection than the NRR alone suggests. The appropriate metric for rating hearing protectors used against impulse noise is called the IPIL rating (Impulsive Peak Insertion Loss) which considers the non-linear noise blocking properties of the specific hearing protector. At present very few devices have an IPIL rating though, so the NRR will have to do for now. In all cases of which I am aware, the IPIL will be greater than the NRR, so using the NRR is a good conservative approach. For more on IPIL, see the report here.
Another recommendation of NIOSH is to use dual protection (ear muffs worn over ear plugs) any time you will be exposed to noise levels exceeding a time-weighted 8 hour exposure of 100 dB or more. Computing that exposure level would be difficult, so my simplifying suggestion is to use dual protection any time you are in the following situations:
- You are going to spend significant time in a constant noise environment at or above 100 dB.
- You are planning to shoot indoors with any caliber of weapon.
- You are planning to shoot any guns larger than a .22 caliber when target shooting outdoors.
- You are shooting a large caliber weapon when hunting alone.
- You are hunting with others close by, as in a duck blind. It can get really loud with three guys all repeatedly firing their shotguns next to each other.
When using a dual protection system, you can estimate the total protection you are getting by adding 6 to the higher NRR rating of the two devices you are wearing. For instance, if you are using a 30 NRR ear plug under a 25 NRR ear muff, you should experience about a 36 effective NRR rating. This assumes you are getting the full rated performance from both devices. The trouble with wearing dual protection is that you cannot hear the range officer or your buddies calling to you out in the field when hunting. A highly recommended solution is to use an electronic shooting ear muff rather than a passive ear muff. The electronic muff will amplify the sounds you hear so that you can more easily hear the range officer through the ear plugs, and when someone fires near you, the electronic ear muffs will instantly shut down the amplifier, and you will enjoy the full rated protection of the muffs.
Recommendations for shooters and others using dual protection
Most users of dual protection choose ordinary foam ear plugs worn under passive ear muffs. As stated above, any time you need the ability to hear what is going on around you, we suggest electronic shooting ear muffs which will enable you to hear amplified voices even through your ear plugs. We offer many different models starting in the mid $20 range. If you have never tried electronic shooting ear muffs, a great model to begin with is the Bilsom Impact Sport. At under $50, these nice slim, well-made ear muffs are one of the best value options available.
In addition to ordinary foam ear plugs, you may want to consider some of the more sophisticated shooting ear plugs which have non-linear acoustic filters that let you hear low sounds but then give you more protection automatically, against dangerously loud sounds. Some of these also include a valve you can open to let sound flow through the filter, or close to give full block noise protection.
Those with filters and valves to open and close a sound vent include:
Shooting ear plugs with just the nonlinear filters include:
I invite you to explore the world of shooting and hunting protection products here and do not hesitate to get in touch. We are here to help any way we can.
Until next time, be safe and do the right thing.
Tom Bergman, Vice President
Ear Plug Superstore