For the protection of public health, the Environmental Protection Agency proposed these levels:


Neighborhoods - During waking hours 55 dB
Neighborhoods - During sleeping hours 45 dB
Classrooms - during teaching sessions 35 dB
Hospitals - during waking hours 45 dB
Hospitals - during sleeping hours 35 dB


For the workplace, the Occupational Safety and Health Administration (OSHA) proposed these permissible noise exposure times (I have included examples of sounds at various levels for easier understanding):


85 dB and higher - prolonged exposure will result in hearing loss
90 dBA - no more than 8 hours per day (examples - lawn mower, truck traffic, hair dryer)
95 dBA - no more than 4 hours per day
100 dBA - no more than 2 hours per day (example - chain saw)
105 dBA - no more than 1 hour per day
110 dBA - no more than ½ hour per day
115 dBA - no more than ¼ hour per day (preferably less)
140 dBA - NO EXPOSURE TO IMPACT OR IMPULSE NOISE ABOVE THIS LEVEL (examples - gunshot blast, jet plane at takeoff)


The Academy of Pediatrics and the National Campaign for Hearing Health states 85 dB is the threshold for dangerous levels of noise.


The National Campaign for Hearing Health's Toxic Noise Guidelines (exposure times and decibel levels that cause hearing loss)


85 dB 8-hour period
85 - 90 dB 2-hour period
90 - 100 dB 1 to 2-hour period
100 - 110 between 2 and 15 minutes
110 - 120 less than 30 seconds
130 dB ANY EXPOSURE WILL RESULT IN PERMANENT HEARING LOSS


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