Safe Noise Dose Chart: Noise Exposure Limits for Hearing Safety

Noise Dose Chart: Noise Exposure Limits

The risk to your hearing from noise exposure depends on how loud it is and how long you're exposed to it. This noise dose chart shows the acceptable safety limits.

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 as well, and give your ears a chance to recover after any period of noise exposure.

For example:

At 91 decibels, your ears can tolerate up to two hours of exposure.
At 100 decibels, damage can occur with 15 minutes of exposure.
At 112 decibels, damage can occur with only one minute of exposure.
At 140 decibels, immediate nerve damage can occur.

Firearms, firecrackers, and jet engines taking off are all louder than 140 dB. If you find yourself near any of these without hearing protection, use your fingers and plug your ears! And at the same time, move away from the noise — even a few extra feet can reduce the loudness significantly.

Noise Dose Formula

The generally accepted standard to minimize hearing risk is based on an exposure to 85 dBA for a maximum limit of eight hours per day, followed by at least ten hours of recovery time at 70 dBA or lower (at which the risk of harm to healthy ears is negligible). Then a "3-dB exchange rate" formula is applied, which means that for every 3 dB above 85 dBA, the maximum exposure time is cut in half.

Noise levels above 140 dB are not considered safe for any period of time, however brief. For children, the World Health Organization recommends no exposure above 120 dB.

Maximum Recommended Noise Dose
Exposure Levels

Noise Level (dBA)	Maximum Exposure Time per 24 Hours
85	8 hours
88	4 hours
91	2 hours
94	1 hour
97	30 minutes
100	15 minutes
103	7.5 minutes
106	3.7 minutes
109	112 seconds
112	56 seconds
115	28 seconds
118	14 seconds
121	7 seconds
124	3 seconds
127	1 second
130–140	less than 1 second
140	NO EXPOSURE

Click here for an explanation of dBA, dB, and other sound units.

Using the Chart

* If you want to monitor your total noise exposure without having to keep a time log of readings from a sound level meter, then you want a device called a noise dosimeter. These are normally used only for occupational noise monitoring, since they can be quite expensive and complicated to use. However, Etymotic has developed a noise dosimeter for personal use with a more affordable price. You can buy it at their website or on Amazon.com.

Each line by itself represents 100% of the allowable noise dose per 24-hour day. In other words, if you've already experienced 15 minutes at 100 dBA, you're "done for the day," and the remainder of your 24-hour period should have NO exposure above 85 dBA, and preferably should be below 70 dBA. If you spend a lot of time in environments with varying noise levels above 85 dBA, you can wear a noise dosimeter * and let it monitor the noise levels and exposure times and calculate the noise dose you're getting.

What kinds of sounds do the different decibel levels represent? Check the decibel chart to see examples of sounds across a wide range of decibel levels.

How were these time limits derived? Clearly, it would be unethical to perform controlled experiments on humans to determine what levels of noise and lengths of exposure cause permanent hearing damage. Instead, data have been compiled from cases of hearing loss due to accidental noise exposure, or exposures that occurred before the dangers were well understood, and have been supplemented with known principles of the physics of sound and the physiology of the human ear. Various safety groups and regulatory bodies worldwide have been converging on the above safe noise limits over the past few decades.†

Protecting Your Hearing

Because different people's ears differ in their degree of vulnerability to noise, noise exposure levels that are well tolerated by some people may cause harm in others. If after you've been exposed to noise your ears have a rushing, roaring, or ringing sensation, or you notice that ordinary sounds seem muffled or quieter than normal, you know now that that level of noise is damaging and hearing protection is needed in that situation in the future. If this happens to you, rest your ears (which means no noise above 70 dBA) for 24 hours.

Be aware: Your ears aren't able to "get used to" noise levels. If a certain noise level doesn't seem to bother you as much as it did before, it's not because your ears have toughened up to it; it's because you've lost some of your hearing. In this case, it's all the more critical to protect the hearing you have left.