pressure is measured in
decibels (dB). Like a temperature scale, the decibel scale goes
below zero. The average person can hear sounds down to about 0 dB, the level
of rustling leaves. Some people with very good hearing can hear sounds down
to -15 dB. If a sound reaches 85 dB or stronger, it can cause permanent
damage to your hearing. The amount of time you listen to a sound affects how
much damage it will cause. The quieter the sound, the longer you can listen
to it safely.
A typical conversation occurs at 60 dB – not loud
enough to cause damage.
A bulldozer that's idling is loud enough at 85 dB
that it can cause permanent damage after only 8 hours!
When listening to music on earphones at a standard
volume level 5, the sound generated reaches a level of 100 dB, loud enough to
cause permanent damage after just 15 minutes per day!