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Understanding Noise Exposure Limits: Occupational vs. General Environmental Noise

Categories: Hearing Loss

 

Noise-induced hearing loss (NIHL) is 100% preventable; however, once acquired, it is permanent and irreversible [NIOSH 1998]. Understanding and minimizing the risks associated with noise exposures are the keys to preventing noise-related hearing loss.  NIOSH has a long history of leadership in conducting research, advancing control measures, and recommending noise-exposure limits to prevent job-related hearing loss.  Sometimes, observers ask whether our recommended limits for occupational exposure can be applied to exposures in the general environment from sources such as street noise, consumer appliances, and recreational pastimes. 

The answer, as we’ll explain below, is not exactly.

 

What is the NIOSH Recommended Exposure Limit?

 

NIOSH establishes recommended exposure limits (RELs) to protect workers against the health effects of exposure to hazardous substances and agents encountered in the workplace. These NIOSH limits are based on the best available science and practices.  In 1998, NIOSH established the REL for occupational noise exposures to be 85 decibels, A-weighted (dB[A]) as an 8-hour time-weighted average.  Exposures at or above this level are considered hazardous.  The REL is based on exposures at work 5 days per week and assumes that the individual spends the other 16 hours in the day, as well as weekends, in quieter conditions.  Importantly, the NIOSH REL is not a recommendation for noise exposures outside of the workplace in the general environment.

NIOSH also specifies a maximum allowable daily noise dose, expressed in percentages. For example, a person continuously exposed to 85 dB(A) over an 8-hour work shift will reach 100% of their daily noise dose.  This dose limit uses a 3-dB time-intensity tradeoff commonly referred to as the exchange rate or equal-energy rule: for every 3-dB increase in noise level, the allowable exposure time is reduced by half.  For example, if the exposure level increases to 88 dB(A), workers should only be exposed for four hours.  Alternatively, for every 3-dB decrease in noise level, the allowable exposure time is doubled, as shown in the table below.

Average Sound Exposure Levels Needed to Reach the

Maximum Allowable Daily Dose of 100%

Time to reach 100% noise dose Exposure level per NIOSH REL
8 hours 85 dB(A)
4 hours 88 dB(A)
2 hours 91 dB(A)
60 minutes 94 dB(A)
30 minutes 97 dB(A)
15 minutes 100 dB(A)

 

 

When to Apply the NIOSH REL

 

The NIOSH REL is an occupational exposure limit, and was set to protect workers from developing hearing loss –substantial enough to make it difficult to hear or understand speech – over the course of a forty-year working career.  Risk of hearing loss from noise exposure is a complex issue.  Some single, brief intense exposures (such as a gunshot going off near your ear) can cause immediate hearing loss; however, these cases are rare.  Most noise-induced hearing loss is a result of accumulated damage from repeated exposures to hazardous noise.  In addition, the risk of noise damage depends on several factors: how loud the noise is, how long you listen to it, how much rest your ears get between exposures, and your individual susceptibility to noise.

Occupational noise exposure limits are established to simplify the complex question of risk and protect as many workers as possible from the effects of noise. The NIOSH REL is not designed to protect all workers from all hearing damage. When setting this limit, NIOSH acknowledged that approximately 8% of workers could still develop hearing loss.  In order to protect the most sensitive 8% of the population, NIOSH recommends that hearing protection be worn whenever noise levels exceed 85 dB(A) regardless of duration.

 

The Relationship between Occupational and General Environmental Noise Exposures

 

Noise can be found everywhere – restaurants, music and sporting venues, movie theaters, hospitals, and schools. Can the same occupational noise exposure guidelines that apply to workers also apply for assessment of risk to the general public?  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.

What noise recommendations exist for the general public? A 1974 U.S. Environmental Protection Agency report [EPA 1974] recommended a 70 dB(A) over 24-hour (75 dB(A) over 8-hour) average exposure limit for environmental noise (note that the 1974 report was explicit to state that it should not be constituted as a standard, specification, or regulation). The EPA document also specified two other limits for speech interference and annoyance (55 dBA for outdoors activities and 45 dBA for indoor activities)*. The EPA limits were chosen to protect 96% of the general population from developing hearing loss as well as to protect “public health and welfare” (defined as personal comfort and well-being and absence of mental anguish and annoyance).

Both the NIOSH and EPA limits are based on the same scientific evidence and the equal-energy rule (i.e., 3-dB time-intensity tradeoff). However, the NIOSH REL and the EPA limit are designed to protect against different problems – the EPA limits are set to prevent noise that is annoying as well as hearing loss, whereas the NIOSH limit is set solely to protect against hearing loss.  The limit values (85 vs. 70) also differ because the EPA limit is 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.  In addition, the EPA limit includes a 1.6 dB(A)** allowance to protect against exposures for 365 days a year while the NIOSH REL is calculated to protect against work place exposures for 250 working days a year.  Finally, the EPA limit does 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, is required to do under the Occupational Safety and Health Act of 1970.

 

Noise Level versus Time-Weighted Average Noise Exposure

 

It is important to differentiate between noise level and time-weighted average noise exposure.  While noise levels describe the intensity of sounds at a given point in time, the NIOSH and EPA exposure limits are set as time-weighted average exposures over periods of time.  While few people are able to measure their average noise exposures outside of work; , sound levels can be measured with a sound level meter or a smartphone sound measurement app.  Suppose you are at a restaurant, a concert hall, or a sporting event and you are able to measure the sound levels… how do you know whether your hearing is at risk?  The sound level at a given point in time can be higher than the exposure limit without creating risk, provided it is balanced out by enough time at lower levels during the day.  Even without knowing your time-weighted average, if the readout shows a level of 85 dB(A) or higher, NIOSH recommends that you take precautions to protect your hearing by reducing the noise when possible, limiting your exposure time, and/or using appropriate hearing protection.

Hopefully, the many considerations involved in setting and using noise exposure limits are clearer now. In a nutshell, while the NIOSH REL only applies to the workplace, protecting your hearing whenever sounds reach 85 dB(A) or more is a good health practice no matter where your ears are!

 

Chuck Kardous, MS, PE, is a research engineer with the NIOSH Division of Applied Research and Technology.

Christa L. Themann, MA, CCC-A, is an audiologist with the NIOSH Division of Applied Research and Technology.

Thais C. Morata, Ph.D., is a research audiologist with the NIOSH Division of Applied Research and Technology and the Coordinator of the NORA Manufacturing Sector Council.

W. Gregory Lotz, Ph.D., Captain, USPHS; is the Division Director of the Division of Applied Research and Technology (DART) and the manager of the NORA Manufacturing Sector Council.

 

For more information on about protecting your hearing and noise at work, including free materials, videos and tools, please visit the Noise and Hearing Loss Prevention Topic Page or send us your comments or questions in the comments section below.

 

* Text added to include additional EPA limits per reader comments.

** Typo corrected changing 1.4 to 1.6 dB (A).

References

EPA [1974]. Information on levels of environmental noise requisite to protect public health and welfare with adequate margin of safety. EPA/ONAC 550/9-74-004. http://nepis.epa.gov/Exe/ZyPDF.cgi/2000L3LN.PDF?Dockey=2000L3LN.PDF

NIOSH [1998]. Criteria for a recommended standard: occupational noise exposure. DHHS (NIOSH) Publication Number 98-126.  http://www.cdc.gov/niosh/docs/98-126/

Public Comments

Comments listed below are posted by individuals not associated with CDC, unless otherwise stated. These comments do not represent the official views of CDC, and CDC does not guarantee that any information posted by individuals on this site is correct, and disclaims any liability for any loss or damage resulting from reliance on any such information. Read more about our comment policy ».

  1. February 9, 2016 at 4:17 am ET  -   Daniel Fink MD

    This blog post points out an important difference between a recommended occupational noise exposure level and what constitutes a safe noise exposure level for the general public. Noise levels appropriate for truck drivers, miners, or construction workers are too loud for children’s tender ears, which have to last them a lifetime, and their parents and grandparents. As society has gotten louder- with noise levels of 80-100 dB being reported in restaurants, bars, clubs, gym, movie theaters (100-125 dB in action movies), and sports events (world record stadium noise level 142.2 dB set i 2014 at Kansas City’s Arrowhead Stadium, exceeding the OSHA maximum noise exposure level of 140 dB), with elimination of the nighttime quiet period in many American cities, we are all at risk of hearing loss. Daniel Fink MD

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    • AUTHOR COMMENT February 10, 2016 at 8:28 am ET  -   Chuck Kardous, Christa Themann, Thais Morata and Gregory Lotz

      Dr. Fink, Thank you for your comments and commitment to hearing loss prevention in the general environment.

      Link to this comment

  2. February 10, 2016 at 1:38 pm ET  -   Paul Landsbergis

    Great explanation. I’m still curious, however, whether there is any legitimate scientific reason for OSHA’s 5-dB exchange rate for its PEL as opposed to the 3-dB exchange rate used by NIOSH for its REL? Or, is OSHA’s PEL exchange rate based also on “cost and feasibility”? Thanks.

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    • AUTHOR COMMENT February 16, 2016 at 10:47 am ET  -   Chuck Kardous, Christa Themann, Thais Morata and Gregory Lotz

      Thank you for your comment, Dr. Landsbergis. After the OSH Act passed, OSHA had the authority to adopt existing standards as PELs under the new OSH Act for 24-months after passage. The OSHA PEL was set in a Federal Register notice (39 FR 23502) based on prevailing consensus standards at that time, mainly the 1966 CHABA and 1968 Walsh-Haley noise standards. Although those noise standards had varying exchange rates (2-3 dB for long durations of noises of moderate levels and 6-7 dB for short duration of noise, high intensity bursts), it is understood that the final regulation adopted a 5-dB exchange rate for simplification purposes.

      And yes, OSHA must consider technical and economic feasibility under the OSH Act.

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  3. February 14, 2016 at 9:59 pm ET  -   Deanna Meinke, PhD

    I would appreciate clarification regarding this blogs reference to the consideration of “annoyance” in the EPA noise exposure limits related to noise-induced hearing loss. I am aware of “annoyance” as a factor which was integrated as part of the EPA community noise standards that were designed to consider the non-auditory effects of noise. However, aren’t the EPA 24 hour noise exposure limits referenced in this blog specifically related to the risk of auditory damage and not annoyance?

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    • AUTHOR COMMENT February 17, 2016 at 12:03 pm ET  -   Chuck Kardous, Christa Themann, Thais Morata and Gregory Lotz

      Thank you for your excellent question, Dr. Meinke. The Noise Control Act of 1972 was established “to promote an environment for all Americans free from noise that jeopardizes their public health and welfare.” In the 1974 EPA document that we reference in the blog, they define public health and welfare as “complete physical, mental and social well-being and not merely the absence of disease and infirmity.” This definition would take into account sub-clinical and subjective responses (e.g., annoyance and other adverse psychological reactions) of the individual and the public. The phrase “health and welfare” also includes personal comfort and well-being and the absence of mental anguish and annoyance.”

      So while the EPA limit of 70 dBA over 24 hour referenced in the blog does specifically relate to the risk of auditory damage, there are 2 other limits that the EPA specified in the document (55 dBA for outdoor interference and annoyance and 45 dBA for indoor interference and annoyance) that we didn’t include to keep the blog clear and simple. We are simply trying to draw a distinction between occupational standards (that protect workers against material hearing impairment) and the EPA limit(s) that protect against hearing loss as well as to protect “public health and welfare” (which include personal comfort, absence of mental anguish, and annoyance).

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  4. February 15, 2016 at 11:22 am ET  -   Peter Zavon

    I can’t speak for OSHA, but I believe their use of a 5dB exchange rate is based on the practicalities of calculating time-weighted averages in the days before integrating sound level meters and hand-held computing devices. When all you could do was take spot sound level measurements and manually integrate them into an estimated average, a 5 dB exchange was easier to calculate with, and was thought (or hoped) to incorporate lunch and other break periods that were without significant sound exposure but were not generally measured – because the person taking the measurements was also taking lunch, etc. (At least, that is what I remember being told in graduate school in the mid-1970s.)

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  5. February 16, 2016 at 1:01 pm ET  -   Rick Neitzel, PhD

    Just adding a note for clarification. Annoyance does *not* factor in to the EPA’s 70 dBA 24-hour recommended exposure limit – that applies for the other limits recommended by the EPA (i.e., 55 dBA outdoors, 45 dBA indoors), but not the 70 dBA recommendation, which is focused solely on preventing any measurable NIHL (i.e., <5 dB among even the most susceptible individuals). The EPA recommended limit does indeed average over 24 hours, while the NIOSH recommended limit is averaged over 8 and assumes effective quiet (i.e., below 70 dBA) for the other 16 hours in a workday. It might be useful to amend the blog post to note that EPA has several recommended limits, not just the 70 dBA limit designed to prevent any noise-induced hearing loss, and that the growing body of evidence with regards to non-auditory health effects from noise exposure <70 dBA makes the 55 and 45 dBA limits important enough to explain.

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    • AUTHOR COMMENT February 18, 2016 at 1:48 pm ET  -   Chuck Kardous, Christa Themann, Thais Morata and Gregory Lotz

      Thank you for the clarification, Dr. Neitzel. Our main intent in relation to the issue of annoyance was to explain the rationale that lead to our REL (hearing loss) vs. the EPA limit(s) (hearing loss + public health and welfare). We thought introducing the two other EPA limits (interference and annoyance limits for indoor and outdoor activities) would distract our readers from the main point of the blog, but since it has been brought up by you and Dr. Meinke above, we made the appropriate changes to the blog.

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  6. February 19, 2016 at 8:30 am ET  -   Tim Kelsall

    Good article, but you made a mistake in transcribing. You quoted an adjustment for weekends, etc. as follows: ”In addition, the EPA limit includes a 1.4 dB(A) allowance to protect against exposures for 365 days a year while the NIOSH REL is calculated to protect against work place exposures for 250 working days a year.” However if you look in the EPA levels document they actually used 1.6 dB, which is simply 10 log(365/250).

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    • AUTHOR COMMENT February 19, 2016 at 12:43 pm ET  -   Chuck Kardous, Christa Themann, Thais Morata and Gregory Lotz

      You are correct. The text should read 1.6 dB (A). Thank you for pointing out the typo. We have fixed it in the blog text above.

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  7. March 9, 2016 at 3:36 am ET  -   Easter

    Awesome question, this is the major these day in many parts of the world, for all occassions folks use dj with high volume which lead to total deaf. UNO has to take a step to stop this. thanks

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  8. June 1, 2016 at 7:55 am ET  -   Hoang Minh Triet

    The I for Really Never Thought the About Loud Noise Exposure in at The First Long Time to have have AN Impact like that . Because Sound IS One Essential Part of Life , SO that We See IT AS Self-Evident . Thanks for at The Reminder of the this .

    Link to this comment

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