NIOSH Science Blog clarifies difference between occupational and general noise exposure limits

Many people are confused about what is a safe noise limit for the general public because the only noise limit the public may have heard about is the 85 decibel recommended exposure limit (REL) that National Institute for Occupational Safety and Health (NIOSH) established for occupational noise exposures.  Fortunately, the NIOSH Science Blog has just posted an informative piece* that discusses acceptable RELS for both, titled: Understanding Noise Exposure Limits: Occupational vs. General Environmental Noise.

The authors state that in 1998, NIOSH established the REL for occupational noise exposure to be 85 decibels based on an 8-hour shift for a 5-day work week, adding that the REL “assumes that the individual spends the other 16 hours in the day, as well as weekends, in quieter conditions,” and cautioning that “the NIOSH REL is not a recommendation for noise exposures outside of the workplace in the general environment.”  The difference between the occupational and general environmental noise exposures is that:

The NIOSH REL is not meant to be used to protect against general environmental or recreational noise; it does not account for noisy activities or hobbies outside the workplace (such as hunting, power tool use, listening to music with ear buds, playing music, or attending sporting events, movies and concerts) which may increase the overall risk for hearing loss.

The authors point out that a 1974 Environmental Protection Agency (EPA) report recommended 70 decibels over a 24-hour average exposure limit for general environmental noise (while noting the EPA’s caution that its recommendation was not a standard, specification, or regulation).  This recommendation was determined in a similar manner as the NIOSH REL, but it’s focus was on general environmental noise and not the workplace.  As the EPA report states, their recommendation “was chosen to protect 96% of the general population from developing hearing loss as well as to protect ‘public health and welfare.’”

The authors note that both limits “are based on the same scientific evidence and the equal-energy rule,” but “are designed to protect against different problems.”  As a result, the limit values differ because “the EPA limit was averaged over 24 hours with no rest period while the NIOSH limit is averaged for just 8 hours and includes a rest period between exposures,” and the EPA limit includes an allowance “to protect against exposures for 365 days a year versus the NIOSH REL’s calculation that aims to protect against work place exposures for 250 working days a year.”   The authors add that “the EPA limit did not consider cost or feasibility of implementation as the Occupational Safety and Health Administration (OSHA), in accepting a NIOSH REL as the basis for a mandatory standard, [was] required to do under the Occupational Safety and Health Act of 1970.”

Long and short, the authors conclude that the 85 decibel REL is a work standard that neither mandates nor recommends decibel limits for the general public.  Rather, it is the EPA’s recommendation of 70 decibels that provides the appropriate exposure limits for the public with regard to general environmental noise.

*The post was prepared by NIOSH engineer, Chuck Kardous, MS, PE; NIOSH audiologist, Christa L. Themann, MA; NIOSH research audiologist Thais C. Morata, Ph.D., who is also the Coordinator of the NORA Manufacturing Sector Council; and W. Gregory Lotz, Ph.D, Captain, US Public Health Service, Division Director of the Division of Applied Research and Technology (DART), and the manager of the NORA Manufacturing Sector Council.

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