You probably already know that sound is vibration. The vibrations are the sound waves. They strike the ear drum to make it move. The ear drum makes the middle ear bones move to send that energy into the cochlea of the inner ear. Within the cochlea are tiny cells called hair cells because of the hair-like structures called hair bundles on the top of them. There are 18,000 hair cells in each ear. The sound moves the hair bundles, which in turn changes the movement into electrical energy stimulating the auditory nerve. The signal travels up the nerve to the brain and the brain recognizes the sound. These tiny hair cells are very important in the process of hearing. They are also very tiny (all 18,000 could fit on the head of a pin), sensitive, and delicate. If too much movement (sound) pushes them over too much or too often, they can break off. If too many of them are damaged, the whole cell dies.

Think of hair cells as you would a patch of grass. You can walk across that patch of grass and the grass bends but comes back up straight. But if you walk over the grass over and over again or you drive a truck over the grass not all the grass will come back up straight, many blades will be broken. The truck is like loud noise. The blades of grass or the hair bundles bend over and are broken off, killing the cell underneath. The death of the cell is permanent. No hair cells will grow back to take its place. Lose enough of those cells and you have lost a whole frequency of sound.

It is the hair cells that we need to protect. They have to last our whole lifetime. Even if you have already lost some of your hearing you should protect what you have left so you don’t lose even more. Hearing aids will only amplify sound, they will not take the place of the hair cells you have lost.

Before and After Loud Sounds - The top electron microscope photo shows the tiny hair bundle on top of a healthy inner ear hair cell. Compare it to the bottom electron microscope photo of a sound-damaged hair bundle again on top of an inner ear hair cell.

Decibels are a measurement of sound just as inches and feet measure distance. According to NIOSH (National Institute for Occupational Safety and Health) 85 decibels (dBA) is safe for up to 8 hours. That is 8 hours over a 24-hour period. That means that you can be working in a factory or other occupation where the noise level is 85dBA for 8 hours and most people will be fine. But if you then go to the shooting range or dancing at loud club, or go into your workshop after work, you add more noise to the equation.

For every additional 3 dBA your safe listening time is cut in half. That means, if the sound is 91 dBA you have just 2 hours of relatively safe listening time per 24 hours. (Don’t worry about the “A”, it just gives a more actuate reading of the sound)

So what is 85dBA anyway? 85dBA is the sound of a busy street corner. Next time you are standing at the busy city street corner, listen to the sound. That is about 85dBA. 91dBA is the sound level of a gas lawn mower. A band saw is about 98dB when measured at the ear drum.