If people are exposed to high levels of noise for a long period of time, they may experience hearing loss or constant ringing, buzzing, or even stress and other problems in the ear. The normal human ear can hear sounds with frequencies between 20 and 20 thousand per second. Human voice has an average frequency of three to six thousand and is the most sensitive to the ear. The sound pressure level is measured in decibels and is between zero and 140 decibels. Zero decibel is the hearing threshold, and 140 decibel is a hazardous exposure limit.

Mathematical decibel levels are logarithmic. In other words, increasing the volume of 10 decibels means that the sound is increased ten times. So a seemingly small increase in volume can actually create much higher risks.

For example, the rustling of a leaf 10 decibel, very quiet environment 20 decibel, low voice 30 decibel, quiet office 40 decibel, normal speech 50 decibel, busy office environment 60 decibel, a noisy radio or television 70 decibel, a busy radio street traffic 80 decibels, closely passing heavy vehicle 90 decibels, road drill 100 decibels, chainsaw 110 decibels, closely ventilated jet 140 decibels.

The Regulation on the Protection of Employees from Noise-Related Risks issued by the Ministry of Labor and Social Security in 2013 shows exposure action values ​​and exposure limit values ​​as follows:

• Lowest exposure action values: (LEX, 8h) = 80 decibels
• Highest exposure action values: (LEX, 8h) = 85 decibels
• Exposure limit values: (LEX, 8h) = 87 decibels

If daily noise exposure varies significantly from day to day, then the exposure level is used to apply exposure limit values ​​and exposure action values.