Sound Pressure Levels - How much is too much?

Experts agree that continued exposure to sounds pressure levels (SPL) above 85 dBA over time, will cause hearing loss. To know if a sound is loud enough to damage your hearing, it is important to know both the SPL (measured in decibels, dBA) and the length of exposure to the sound. In general, the louder the noise, the less time required before hearing loss will occur.

According to the National Institute for Occupational Safety and Health (1998), the maximum exposure time before hearing damage at 85 dBA is 8 hours. At 110 dBA, the maximum exposure time is one minute and 29 seconds. If you must be exposed to noise, it is recommended that you limit the exposure time and/or wear hearing protection.

The following are decibel levels of common noise sources around us. These are typical levels, however, actual noise levels may vary depending on the particular item. Remember noise levels above 85 dBA will harm hearing over time. Noise levels above 140dBA can cause damage to hearing after just one exposure.

• 0 - The softest sound a person can hear with normal hearing
• 10 - normal breathing
• 20 - whispering at 5 feet
• 30 - soft whisper
• 50 - rainfall
• 60 - normal conversation
• 110 - shouting in ear
• 120 - thunder

Remember that the decibel (dB) is a logarithmic unit, meaning that you cannot add and subtract dB like ordinary numbers. For example, an increase of 3 dB is a doubling of the "strength" of the sound, and an increase of 10 dB means that the sound is 10 times as loud; i.e., 70 dB is 10 times as loud as 60 dB.

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