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Aug 4, 2010

Noise-Induced Hearing Loss – Exposure Time Limits


The susceptibility to, and extent of hearing damage caused, by a one-time exposure to loud sound, as well as by repeated exposure to sounds at various loudness levels over an extended period of time, is not always properly appreciated.

Damage occurs very easily to the microscopic hair cells responsible for different frequencies found inside the cochlea, which respond to mechanical sound vibrations by sending an electrical signal to the auditory nerve.

The healthy human ear can hear frequencies ranging from 20Hz to 20,000 Hz. and if a significant number are damaged, noise induced hearing loss results.

The average person can hear sounds down to about 0 decibels (dB) the measure of sound pressure. If a sound reaches 85 dB or stronger, it can cause permanent damage. Many common sounds, often experienced in the workplace may be louder …

A bulldozer that is idling only, and not actively in operation, is loud enough at 85 dB to cause permanent damage after only 1 work day (8 hours), so it’s not too surprising to learn that incidents of industrial deafness are still very much widespread despite of better awareness and legislation.

Noise is probably the most common occupational hazard facing people today. Even outside of work, many people participate in recreational activities that can produce harmful noise (musical concerts, use of power tools, etc.).

The chart below shows most clearly the time limits for exposure to noise levels and the very real dangers of causing real long term damage in a relatively short periods of time.

Decibel Exposure Time Guidelines

Accepted standards for recommended permissible exposure time for continuous time weighted average noise.

For every 3 dBs over 85dB, the permissible exposure time before possible damage can occur reduces by one half.

Continuous dB         Permissible Exposure Time

85                                     8 hours
88                                     4 hours
91                                      2 hours
94                                      1 hour
97                                      30 minutes
100                                   15 minutes
103                                    7.5 minutes
106                                    3.75 min
109                                    1.875 min
112                                     Less than 1 min
115                                     Less than 30 secs