When I see prominent audiologists quoted in media reports implying that 85 decibels (dB) is safe for hearing, I wonder, “Is this what they learn in audiology training programs? Don't they understand the basic science of noise-induced hearing loss?”
A Google search using the terms “audiologist 85 dB” returned 351,000 results in 0.41 seconds, while a search using the terms “American Academy of Audiology 85 dB” and “American Speech-Hearing-Language Association 85 dB” returned a list of resources associated with professional groups that use 85 dB as the safe noise exposure level.
For example, “85 dBA is considered the cut off between safe and potentially unsafe loudness levels,” said Sharon A. Sandridge, PhD, the director of the audiology clinical services at Cleveland Clinic (https://cbsn.ws/2FFCDK2). In a Q&A with NBC News on how to determine if a sound is too loud for children and how to teach your kids about safe listening, Julie Hauser, an audiologist and amplification coordinator at the Children's Hospital of Pittsburgh, referred to the standards set by the Occupational Safety and Health Administration (OSHA) on how loud noise can be in the workplace (https://nbcnews.to/2RNwsW3). “OSHA determined that you can safely listen to noise—or music—at 85 decibels for eight hours,” she said. “Those standards can be a good guideline for parents.”
In another article published in Baylor College of Medicine News, Michaela Stapp, AuD, an audiologist at Baylor's department of otolaryngology, underscored the growing concern surrounding the dangers of using earbuds and headphones (http://bit.ly/2QZwVEm). “Loud noise exposure through these devices can cause noise-induced hearing loss for students if not monitored properly… Experts typically consider anything at or above 85 decibels dangerous at an extended period of time,” she said. However, since most people don't have a sound level meter, Stapp said that if other people can hear what is playing in your headphones, you should definitely turn it down.
WHERE DOES THE 85 dB NUMBER COME FROM?
I think I know where audiologists get this misinformation. Hauser clearly referenced OSHA, while others probably relied on the National Institute on Deafness and Other Communication Disorders (NIDCD), which states: “Long or repeated exposure to sound at or above 85 decibels can cause hearing loss” (http://bit.ly/2PHHvTy). The NIDCD statement is factually correct, but it is about as useful as a warning from the National Cancer Institute that might say: “Long or repeated exposure to the sun can cause skin cancer.” That's not particularly helpful information.
Auditory damage from noise is a function of sound level and total exposure time. The sound level is defined in dB, which is a logarithmic scale and a proportional, not an absolute, measurement referenced to a baseline. Because of the mathematics of logarithms, a 3 dB increment indicates a doubling of the sound intensity. An 85 dB sound has 31.6 times more intensity than a 70 dB sound, not 21 percent more, as is commonly thought (http://bit.ly/2Q0j6Jb).
The auditory injury threshold is only 75 to 78 dBA, and auditory injury may begin at sound levels lower than these values (Int J Audiol. 2012 Feb; 51(0 1): S3). The NIOSH occupational noise exposure criteria specify 85 dBA as the recommended exposure level (REL) for occupational noise (http://bit.ly/2jvoyRr). That's only for noise when at work. A NIOSH Science Blog post on Feb. 8, 2016, discussed the difference between an occupational noise exposure standard and a safe noise exposure standard for the public (http://bit.ly/2PHqM30). I also wrote about this in the American Journal of Public Health in 2017 (http://bit.ly/2PDyISK)
The NIOSH REL is A-weighted, for occupational safety and health purposes, to reflect the frequencies heard in human speech. The decision to use A-weighting, rather than C-weighting or unweighted decibels, appears to have been made because hearing loss or “material hearing impairment” was the compensable injury workers were presenting with after occupational noise exposure. A-weighting may not be appropriate for auditory health and certainly not for the non-auditory health effects of noise. The causal factor for sound damage is the total energy of the sound, with some evidence showing that higher-frequency sound damages cochlear hair cells needed for hearing while lower-frequency sound damages vestibular hair cell involved in balance. A-weighting reduces measured sound levels by approximately 5 to 7 dB. C-weighting emphasizes lower-frequency sounds below 200 Hz.
SAFE LEVEL IS ONLY 70 dBA
Those citing the NIOSH standard of 85 dBA as safe for the public clearly don't understand that noise is different from other occupational exposures, e.g., ionizing radiation or toxic solvents, because exposure continues outside the workplace, all day long, all year long, for one's entire lifetime. In 1974 the U.S. Environmental Protection Agency (EPA) adjusted the NIOSH 85 dBA REL for the additional time exposure—24 hours a day instead of eight hours a day and 365 days a year instead of 250 days—to calculate that a 70 dB time-weighted average for 24 hours was the safe noise exposure level to prevent noise-induced hearing loss in 99 percent of the public (by convention, time-weighted averages are presented as dB, not dBA or dBC).
The actual safe noise exposure level to prevent hearing loss is probably even lower than 70 dB time-weighted average for a day. The EPA did not adjust for lifetime noise exposure, using only the 40-year occupational exposure, perhaps because the life expectancy of a man was only 67 years in 1974. With today's average life expectancy of about 80 years in the United States and many living even longer, a 40-year exposure history is insufficient. The additional years of exposure may explain why hearing loss is so common in older Americans.
An important concept to consider is the total daily noise dose. How much noise is a person exposed to in a day? Any occupational noise exposure calculator will show that if a person has two hours of noise exposure at 85 dB, it is mathematically impossible to average 70 dB for the day even if the other 22 hours are at zero dB. As shown by Flamme, et. al, in Kalamazoo County, MI, most adults receive total daily noise doses exceeding the EPA and WHO safe noise exposure thresholds for preventing noise-induced hearing loss (Int J Audiol. 2012).
The problem of non-occupational noise exposure causing hearing loss is unfortunately not merely a theoretical concern. In 2017 the Centers for Disease Control and Prevention reported that approximately 25 percent of American adults between 20 to 69 years old had noise-induced hearing loss (NIHL), known to be caused by noise and not by other causes from the characteristic audiometric notch (http://bit.ly/2lZxpNr). Most concerning was the finding that almost 20 percent of the people with NIHL had no loud occupational noise exposure.
In the absence of a federal noise exposure recommendation, guideline, or standard for non-occupational noise exposure, the NIDCD's 85 dB standard seems to have become the de facto federal noise exposure standard for the public. It's even used as the volume limit for headphones marketed as “safe” even for children as young as 3 years old. But 85 dB is not a safe noise exposure level to prevent hearing loss, certainly not without a time limit. If anyone has any scientific evidence showing that 85 dB without time limit is safe for hearing, let me know. Otherwise, dear audiologists, please stop citing 85 dB as a safe noise level for the public. It isn't.
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