# How Loud Is Too Loud? How Long Is Too Long?

Noise-induced hearing loss (NIHL) occurs when tiny sensory hair cells in our inner ears are damaged by noises that are too loud and that last for too long. But how loud is too loud, and how much time is too long? The answers are related: the louder the sound, the shorter the time before damage can occur. Read on to learn more about the mathematics of NIHL.

## Why do decibel levels count?

The intensity, or loudness, of sound is measured in decibels. Decibel levels begin at zero, which is near total silence and the weakest sound our ears can hear. By comparison, a whisper is 30 decibels and a normal conversation is 60 decibels.

To determine the decibel level, the intensity of each sound is compared with that of near total silence. Decibel levels increase by a factor of 10. That means that sounds that are 10 times more intense than near total silence are 10 decibels. A sound that is 100 times more intense is 20 decibels. A sound 1,000 times more intense is 30 decibels. The sound of an ambulance siren at 120 decibels is about 1 trillion times more intense than the weakest sound our ears can hear. Sounds that reach 120 decibels are painful to our ears at close distances.

Scientists believe that, depending upon the type of noise, the pure force of vibrations from loud sounds can cause hearing loss. Recent studies also show that exposure to harmful noise levels triggers the formation of molecules inside the ear that contribute to hair cell damage and NIHL. These destructive molecules play an important role in hearing loss in children and adults who listen to loud noise for too long.

## How does time multiply the danger of NIHL?

NIHL is related both to the decibel level of a sound and to the amount of time you are exposed to it. The distance you are from the sound also matters. A sound gets louder as you move closer to the source and softer as you move away from it. If you are far away from the sound, its intensity and its potential to cause damage are much lower. In addition, the impact of noise adds up over a lifetime. If you are exposed to loud sounds on a regular basis, your risk for permanent damage adds up as you age.

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NIHL is also related to a person’s genes. Some people are more likely than others to develop NIHL when they listen to certain sounds. Scientists are working to determine which people are more at risk for NIHL and which are less at risk. For this reason, we all need to protect our hearing when we are exposed to loud noise.

Researchers who study hearing loss in the workplace have found that a person who is exposed to noise levels at 85 decibel or higher for a prolonged period of time is at risk for hearing loss. For this reason, these workers are required to wear hearing protectors, such as earplugs or earmuffs, while they are on the job. Many devices that children use today have noise levels much higher than 85 decibels. For example, an MP3 player at maximum level is roughly 105 decibels. That’s 100 times more intense than 85 decibels! Scientists say that sounds at 100 decibels can cause damage after 15 minutes of unprotected exposure. Sounds at 110 decibels can cause permanent hearing loss after just one minute of exposure.

## How can I reduce the possibility of NIHL?

Your ears can be your warning system for potentially dangerous noises. The noise is too loud when:

• You have to raise your voice to be understood by someone standing nearby.
• The noise hurts your ears.
• You develop a buzzing or ringing sound in your ears, even temporarily.
• You don't hear as well as you normally do until several hours after you get away from the noise.

If you are around noises at this level, take protective action. To avoid NIHL,

• Block the noise (wear earplugs or earmuffs).
• Avoid the noise (walk away).
• Turn down the sound.

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