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Facts on noise levels:

Decibels measure sound pressure and are logarithmic, a 3db increase almost doubles sound pressure, a 6db increase quadruples sound pressure.

Gradual hearing loss may occur after prolonged exposure to 90 decibels or above.

Exposure to 100 decibels for more than 15 minutes can cause hearing loss.

Exposure to 110 decibels for more than a minute can cause permanent hearing loss.

Here are some examples of noise levels:

Video arcades - (110 dB).

Firecrackers - (125-155 dB at a distance of 10 feet).

Live music concerts - (120 dB and above).

Movie theatres - (118 dB).

Health clubs and aerobic studios (120 dB).

Sporting events (127 dB).

Motorboats - (85-115 dB).

Motorcycles - (95-120 dB).

Snowmobiles - (99 dB).

"Boom cars" - (140 dB and above).

Here are noise levels of firearms:

.223, 55GR. Commercial load 18" barrel 155.5dB

.243 in 22" barrel 155.9dB

.30-30 in 20" barrel 156.0dB.

7mm Magnum in 20" barrel 157.5dB.

.308 in 24" barrel 156.2dB.

.30-06 in 24" barrel 158.5dB. In 18" barrel 163.2dB.

.375 18" barrel with muzzle brake 170 dB.

.410 Bore 28" barrel 150dB. 26" barrel 150.25dB. 18" barrel 156.30dB.

20 Gauge 28" barrel 152.50dB. 22" barrel 154.75dB.

12 Gauge 28" barrel 151.50dB. 26" barrel 156.10dB. 18" barrel 161.50dB.

.25 ACP 155.0 dB.

.32 LONG 152.4 dB.

.32 ACP 153.5 dB.

.380 157.7 dB.

9mm 159.8 dB.

.38 S&W 153.5 dB.

.38 Spl 156.3 dB.

.357 Magnum 164.3 dB.

.41 Magnum 163.2 dB.

.44 Spl 155.9 dB.

.45 ACP 157.0 dB.

.45 COLT 154.7 dB.

Properly fitted earplugs or muffs reduce noise 15 to 30 dB. The better earplugs and muffs are approximately equal in sound reductions, although earplugs are better for low frequency noise and earmuffs for high frequency noise.

All of us should be trying to get the greatest Noise Reduction Rating (NRR) that can be put together. NRR 30 plugs with NRR 20 muffs will give you an effective NRR 45 (add plugs and muffs, then subtract 5). If noise levels are 160 dB this gives you an exposure with plugs and muffs of 115 dB. The acceptable exposure time for this is 15 minutes total for the day. If the noise levels are 150 dB the resultant acceptable exposure time with the given plugs and muffs is 1 hour and 4 hours if the noise level is 140 dB. You're not going to find unsuppressed noise levels below 140dB with gunfire.

If you are shooting by yourself, roughly 100 rounds of 140 dB instantaneous noise in a day should not produce hearing damage. Put your plugs and muffs on and you get to shoot up to a thousand rounds without damage (louder ammo/gun and the allowable drops by a factor of 5). Shoot with other people and you have to add all the rounds shot cumulatively (10 people shoot 100 rounds and everybody's done for the day; toss a handcannon or 30 cal rifle in and you're back down to 200 rounds cumulative). If you shoot on an indoor range then all the rounds fired while you are on the range go into your total. So you can see that it doesn't take very long on a range to have a thousand rounds popped off around you.

If you want to know what the noise level you are exposed to is you can rent noise dosimeters that you can wear. They will record the total noise exposure and present the information to you as dB. You can then subtract the adjusted combined NRR of your hearing protection to determine if you're getting too much exposure.