Classification of Noise

There are various concepts related to decibels, and the question you're asking likely refers to the physical quantity that measures sound intensity. Hearing loss is typically assessed using pure tone audiometry at 500, 1000, and 2000 Hz. The normal hearing range for humans is between 0 and 25 decibels (dB).

According to the World Health Organization's deafness classification criteria:

26-40 dB: Mild hearing loss  
　　 41-55 dB: Moderate hearing loss  
　　 56-70 dB: Moderately severe hearing loss  
　　 71-90 dB: Severe hearing loss

Volume analogy:

　 190 dB Can be fatal
　　 140 dB The highest critical point defined by the EU that can cause complete hearing loss
　　 139 dB The shouts of Schalke fans
　　 130 dB Rocket launch noise
　　 125 dB Jet plane takeoff sound
　　 120 dB Staying in this environment for more than a minute can cause temporary hearing loss.
　　 110 dB Propeller plane takeoff, rock concert sound
　　 105 dB Permanent hearing damage
　　 100 dB Pneumatic drill sound, heavy hammering
　　 90 dB Noisy bar, electric saw sound
　　 85 dB and below Will not damage hair cells in the cochlea
　　 80 dB Noisy office, highway traffic sound
　　 75 dB Human ear comfort limit
　　 70 dB Street environment sound
　　 50 dB Normal conversation sound
　　 20 dB Whispering

Based on average human hearing:

　　 0-20 dB Very quiet and almost imperceptible;
　　 20-40 dB Quiet, like a whisper;
　　 40-60 dB Average, typical indoor conversation;
　　 60-70 dB Noisy and potentially harmful to the nervous system;
　　 70-90 dB Very loud and damaging to nerve cells.  
　　 90-100 dB Increased noise level leading to hearing loss;  
　　 100-120 dB Unbearable, staying for a minute causes temporary hearing issues.
　　 Above 120 dB: Extremely loud or completely deafening

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