By Daniel Fink, M.D., Interim Chair, Health Advisory Council
Misrepresentation of 85 decibels as a safe environmental noise level threatens the hearing health of children and the public. Recent statements published by government agencies indicate that 70 decibels is the only safe standard to protect hearing for the public. Our health advisor, Dr. Daniel Fink explains.
One thing that puzzled me when I first became concerned about environmental noise was what constituted a safe noise level for the purpose of hearing protection. The Environmental Protection Agency (EPA) determined in 1974 that a 24-hour average noise exposure level of 70 decibels (dB) or less prevented measurable hearing loss over a lifetime (with substantially lower noise levels required to prevent annoyance and interference with activities.) However, information from the National Institute on Deafness and Other Communication Disorders, American Academy of Audiology or the American Speech-Language-Hearing Association implied that a much louder noise level − anything up to 85 dB − was safe for our ears, with statements such as “Long or repeated exposure to sounds at or above 85 dB can cause hearing loss” or “Sounds that are louder than 85 dB can cause permanent hearing loss”, without specifying the duration of noise exposure. These statements, from authoritative sources, made it difficult to argue that environmental noise exposure below 85 dB damaged hearing.
The decibel scale is logarithmic. Each 10 point increase (e.g., from 70 to 80 dB) represents a tenfold increase in sound energy, even though it is only perceived as twice as loud by humans. And because the decibel scale is logarithmic, 85 dB is not 21% as loud as 70 dB, as might be commonly thought, but 1500% or 15 times as loud.
To learn more, I searched online and eventually wrote to several government agencies trying to understand the apparent disparity (70 vs. 85 dB) in safe noise levels. In December 2015, a communication from the National Institute of Occupational Safety and Health (NIOSH) explained where the 85 dB figure came from. This information was posted in February 2016 in the NIOSH Science Blog. In summary, 1) 85 dB is an occupational noise exposure standard developed to protect workers; 2) at 85 dB noise exposure over a lifetime of work, 8% of workers will suffer hearing loss; 3) the EPA calculated that at 70 dB average noise exposure over 24 hours, 96% of the population would be protected from hearing loss (note that the EPA explicitly stated that this level should not be constituted as a standard, specification, or regulation); and 4) 85 dB is not a safe noise exposure standard for the public.
In occupational settings, workers are protected by federal laws (the Occupational Safety and Health Act) and state laws (e.g., CalOSHA). Hearing protection and training programs are required when workers are exposed to loud noise. Workers are covered by workers compensation insurance, for injury and permanent damage. The 85 dB NIOSH standard assumes occupational noise exposure of 8 hours/day, 250 days/year, for 40 years, with quieter noise levels when not at work.
The public has no such protections. We are exposed to noise 24 hours/day, 365 days/year, for an average lifetime of 78 years. The 70 dB EPA noise level was calculated to account for these factors and protect hearing. The clarification of the difference in these noise exposure levels has important implications for state and local governments, businesses, schools, and all involved in setting public policy and protecting public health.
The occupational noise exposure standard of 85 db is not appropriate outside the workplace. The much lower 70 dB average noise exposure level is the only published safe noise level to protect the public’s hearing.
Legal advisor, Gina Briggs, provides her perspective on the NIOSH clarification.