Apart from a few rare events (volcanic eruptions, tsunami, earthquakes), nature does not expose hearing to high intensity sounds. Our ear did not have to develop a system of protection against loud sounds. The ears have no eyelids! This explains why our auditory system is vulnerable to high-intensity sounds that are generated today in industry, entertainment or with amplified music. The ability of our ear to listen to high intensity sounds without danger depends on the duration of these sounds. Thus, the World Health Organization defines safe exposure times according to the loudness:

 

Daily noise exposure limits (1 meter distance from source)
Sound level in dB(A)    Duration of sound exposure
85 8 h
88 4 h
91 2 h
94 1 h
97 30 min
100 15 min
103 7.5 min

It can be noted that the permissible exposure time decreases by half each time the level increases by 3 dB. This is due to the non-linearity of the dB scale. Beyond 130 dB, ear damage is considered to be extremely dangerous, even for very short exposures.