Daniel Fink – email@example.com
Board Chair, The Quiet Coalition, 60 Thoreau Street Suite 261, Concord, MA, 01742, United States
The Quiet Coalition is a program of Quiet Communities, Inc.
Popular version of 3pNS1-What is the safe noise level to prevent noise-induced hearing loss?, presented at the 183rd ASA Meeting.
Ear structures including outer, middle, and inner ear. Image courtesy of CDC
If something sounds loud, it’s too loud, and your auditory health is at risk. Why? The safe noise exposure level to protect your hearing- to prevent noise-induced hearing loss (NIHL) and other auditory disorders like tinnitus, also known as ringing in the ears, might be lower than you think. Noise damages delicate structures in the inner ear (cochlea). These include minuscule hair cells that actually perceive sound waves, transmitted from the air to the ear drum, then from bones to the fluid in the cochlea.
Figure 1. Normal hair cells (left) and hair cells damaged by noise (right). Image courtesy of CDC
[A little detail about sound and its measurement. Sound is defined as vibrations that travel through the air and can be heard when they reach the ear. The terms sound and noise are used interchangeably, although noise usually has a connation of being unpleasant or unwanted. Sound is measured in decibels. The decibel scale is logarithmic, meaning that an increase in sound or noise levels from 50 to 60 decibels (dB) indicates a 10-times increase in sound energy, not just a 20% increase as might be thought. A-weighting (dBA) is often used to adjust unweighted sound measurement to reflect the frequencies heard in human speech. This is used in occupational safety because the inability to understand speech after workplace noise exposure is the compensable industrial injury.]
Many audiologists still use the industrial-strength 85 dB noise level as the level at which auditory damage begins. This is incorrect. The 85 dBA noise level is the National Institute for Occupational Safety and Health (NIOSH) recommended occupational noise exposure level (REL). This does not protect all exposed workers from hearing loss. It is certainly not a safe noise level for the public. Because of the logarithmic decibel scale, 85 decibel sound has approximately 30 times more sound energy than the Environmental Protection Agency’s 70 decibel safe sound level, not about 20% as might be thought.
The EPA adjusted the NIOSH REL for additional exposure time- 24 hours a day instead of only 8 hours at work, 365 days a year instead of 240 days- to calculate that 70 dB average noise exposure for a day would prevent noise-induced hearing loss. This is the only evidence-based safe noise level I have been able to find.
But the real safe noise level to prevent NIHL must be lower than 70 dB. Why? EPA used the 40-year occupational exposure in its calculations. It didn’t adjust for lifetime exposure (approaching 80 years in the United States before the COVID pandemic). NIHL comes from cumulative noise exposure. This probably explains why so many older people have trouble hearing, the same way additional years of sun exposure explains the pigmentation changes and wrinkles in older people.
My paper explains that the NIOSH REL, from which EPA calculated the safe noise level, was based on studies of workers using limited frequency audiometry (hearing tests), only up to 4000 or 6000 Hertz (cycles per second). More sensitive tests of hearing, such as extended-range audiometry up to 20,000 Hertz, shows auditory damage in people with normal hearing on standard audiometry. Tests of speech in noise- how well someone can hear when background noise is added to the hearing test- also show problems understanding speech, even if standard audiometry is normal.
The actual noise level to prevent hearing loss may be as low as 55 dBA. This is the noise level needed for the human ear to recover from noise-induced temporary threshold shift, the muffling of sound one has after exposure to loud noise. If you’ve ever attended a rock concert or NASCAR race and found your hearing muffled the next morning, that’s what I’m talking about. (By the way, there is no such thing as temporary hearing loss. The muffling of sound, or temporary ringing in the ears after loud noise exposure, indicates that permanent auditory damage has occurred.)
55 dB is pretty quiet and would be difficult to achieve in everyday life in a modern industrialized society, where average daily noise exposures are near 75 dB. But I hope that if people know the real safe noise level to prevent hearing loss, they will avoid loud noise or use hearing protection if they can’t.