Personal Exposure Limits

In the workplace, the allowable personal noise limits are based upon an 8 hour exposure. The personal exposure limit (PEL) is 90 dBA for 8 continuous hours. At 85 dBA for 8 continuous hours, staff must be included in the University of Minnesota Hearing Conservation program.

In the community, noise may be considered a pollutant. The Minnesota Pollution Control Agency (MPCA)enforces noise pollution rules based upon a statistical calculations of samples taken over a one-hour period. There are two descriptive statistical:

  • L10 is the noise level that is exceeded for 10 percent, or six minutes, of the hour
  • L50 is the noise level that is exceeded for 50 percent, or 30 minutes, of the hour

There is not a limit on maximum amount of noise. The L10 and L50 levels limits also change from day to night, and according to the land use where the noise is heard. Additionally, municipalities may enforce local ordinances as well.

In classrooms, offices, clinics, and lecture halls, sound is measured without occupants to determine the ambient noise inherent to the space. These levels are compared to noise criterion curves that are specific to the occupancy classification of an ideal space. Noise criterion curves are the levels at several frequencies within the 1/1 octave band, that should not interfere with person-to-person communication with the space during occupancy. These levels are not enforceable limits. They are recommendations based upon professional recommendations. 

To prevent adverse outcomes of noise exposure, noise levels should be reduced to acceptable levels. The best method of noise reduction is to use engineering modifications to the noise source itself, or to the workplace environment. Where technology cannot adequately control the problem, personal hearing protection (such as ear muffs or plugs) can be used. Personal protection, however, should be considered as an interim measure while other means of reducing workplace noise are being explored and implemented.