Any exposure to noise above 85dB can damage the human hearing; as a rule of thumb, the ambient sound is too loud if you can not carry on a conversation without raising your voice. Occupational noise exposure limits governed by OSHA in the Safety and Health Regulations for Construction define excessive noise levels by the duration of exposure.

 

Hours per Day of Permissible Exposure	Slow Response Sound Level dBA
8	90
6	92
4	95
3	97
2	100
1	102
1	105
½	110
¼	115

 

When the sound level varies for a duration of time, take the duration of each sound level divided by its corresponding Permissible Exposure time from the above chart to find it's factor. The sum of all factors in a day, known as the equivalent noise exposure factor, should not exceed one. Additionally, instantaneous noise like impacts or impulses should not exceed 140 dB sound pressure level.