Understanding Noise Exposure Limits: Occupational vs. General Environmental Noise

Posted on by Chuck Kardous, MS, PE; Christa L. Themann, MA, CCC-A; Thais C. Morata, Ph.D. and W. Gregory Lotz, Ph.D.

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).


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.  https://www.cdc.gov/niosh/docs/98-126/

Posted on by Chuck Kardous, MS, PE; Christa L. Themann, MA, CCC-A; Thais C. Morata, Ph.D. and W. Gregory Lotz, Ph.D.

50 comments on “Understanding Noise Exposure Limits: Occupational vs. General Environmental Noise”

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 ».

    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

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

    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.

    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.

    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?

    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).

    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.)

    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.

    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.

    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).

    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.

    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

    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 .

    I really enjoyed reading your blog, you have lots of great content. I look forward to reading more posts from you.

    Thanks for the excellent article and discussion. I am currently working on research which sets out to examine the differences between European and USA legislation and procedures in workplace noise assessment.

    My data concludes that the exchange rate issue has far reaching consequences and it means that workers in the US can be exposed to much higher levels of noise for much longer periods than their European counterparts. Furthermore in Europe statutory obligations on employers to protect workers’ hearing are triggered at an LEX, 8h (equivalent to the USA’s 8 hour TWA) of 80 dBA .

    I am finding it particularly difficult to source suitable peer-reviewed publications (other than Alice H. Suter’s ) which address the key issues of my research – i.e. the 5 dB exchange rate and the 85 dBA PEL and how they can be detrimental to US workers’ hearing.

    Could you please let me know of any relevant publications I may have overlooked. Alternatively would it be possible to copy this email to any of your colleagues who in turn may be able to direct me to some suitable publications.

    I would be pleased to issue the findings of my research to anyone who may have an interest.

    Thanking you in anticipation.

    Kind regards,
    Dermot Moloney, MSc, BSc, MIOA, MIEnvSc, CSci.

    Thank you for your comment and email, Dermot. We agree that the different exchange rates used in the U.S. have far reaching consequences on the hearing health of the American worker and that is why NIOSH has advocated for a recommended exposure limit (REL) of 85 dBA and the use of the 3-dB exchange rate since 1998. The present OSHA permissible exposure limit (PEL) is 90 dBA for an 8 hour day. The OSHA standard uses a 5 dBA exchange rate. We present the rationale for using the 3-dB exchange rate in chapter 3 of our criteria document https://www.cdc.gov/niosh/docs/98-126/pdfs/98-126.pdf. We have additional information in a white paper we published in Seminars in Hearing [“National Research Agenda for the Prevention of Occupational Hearing Loss – Parts 1 & 2” Sem. Hear. 34(3):141-251 (2013)]. Dr. Suter has in fact led most of the efforts jointly with NIOSH to make the case for the 3-dB exchange rate. We are also in the process of publishing additional information on this specific subject, possibly in the form of another white paper, we’ll keep you updated. Hopefully others reading the blog could chime in as well if they know of other efforts on the subject. Please follow us on @NIOSHNoise on twitter for the latest updates.

    Hi panel of experts,

    I just moved to my new house and there are two water fountains in the middle of the apartments which is operating from 8.30am to 9.30pm, 13 hours continuous. When I measure it with an industry sound meter, it is showing 75dbA at the balcony, and around 68dbA inside my living room. Do you have any international guide for acceptable residential noise level relating to my situation? Is there any articles you could point me to suggest the risk of long-term exposure to such unhealthy environmental noise, especially to children? I just looked at WHO guide which is quite general and does not specifically address the readings recorded.

    Thank you for your kind reply as I am really concern about long term exposure of 68-75dbA noise.

    Hi Dickson. NIOSH does not provide guidance on environmental or non-occupational noise exposures. However, you can consult the EPA reference that we cited in the blog for the information you’re looking for, or for a quick summary, this link https://www.epa.gov/aboutepa/epa-identifies-noise-levels-affecting-health-and-welfare which states that 70 dBA measured over 24 hours as the noise exposure level that would prevent any measurable hearing loss over a lifetime, 55 dBA for outdoor noise exposure levels to prevent interference and annoyance. The link above indicates that the EPA has transferred the primary responsibility of regulating noise to state and local governments.

    A couple of questions: when you discuss 45dB interior and 55dB exterior is that measured from the source of the sound? And about OSHA accepting a NIOSH finding, am I correct that a private individual not part of a business can not make a complaint? Thanks.

    Thanks for your questions, Mark. In the EPA’s noise levels document we cited above, it states that annoyance due to noise (the 45 dB for indoors and 55 dB for outdoors you mentioned) is measured by community surveys.

    As for your second question, any worker can file a complaint with OSHA if they believe their working conditions are unsafe or unhealthful (https://www.osha.gov/workers/index.html), but if you’re talking about a private individual experiencing noise annoyance problems, then that individual must check with his local community to see if there are any specific noise ordinances in place.

    Hey panel of experts,

    How does NIOSH chart of Permissible Noise Exposures (PNE) go hand in hand with hearing protecting companies’ unwavering claim that they manufactured products, that protect your hearing in loud environments, for example night clubs with probably music louder than 100dB, while still allowing you to make conversations without too much muffling? Their NRR is not fit, according to this chart, but rather slightly attenuate the noise.

    Known products include: Eytmotic, Downbeats, Eargasms and many more…

    What are your thoughts on this ?

    Best regards,

    Hello, I would be interested to know the upper frequency that the limits in your blog apply for? 8 kHz? 10 kHz?

    Thank you for your question and hope we understood it correctly. NIOSH’s recommended exposure limit of 85 dBA over 8 hours is based on the A-weighting frequency response, and thus the use of the term dBA. Both OSHA and NIOSH state that noise should be measured with a Type 2 (or better) sound level meter. The different types are described in the American National Standard Specification for Sound Level Meters (ANSI S1.4). A Type 2 sound level meter will only measure accurately up to 8000 Hz, so that is essentially the upper frequency limit. However, it should be noted that hearing protection devices are typically far more effective in the high frequencies than they are at lower frequencies. Thus, the protection achieved at 8000 Hz can be assumed to be as much — if not more — when extended to higher frequencies.

    I am not an engineer or a physician, i was an air traffic controller for 36 yrs. I was exposed to acoustic shock trauma from a loud high pitched tone. It was a maintenance tone used to test repairs on landlines. I wore a headset with ear bud. The headset allows up to 113db peak audio. According to my research, I was listening to voice audio at 75db. That volume increased up to 103db. It felt like a needle was jammed in my ear.
    I suffered hearing loss at 4000 hz. Follow on diagnosis includes, bruxism, TMD, hyperacusis. According to my audiogram 3 weeks prior to my injury, I had normal hearing.

    With so much data on TWA free field noise levels, why is there so little compared to headsets/earbuds? With the NIHL in the younger generation, using earbuds, growing at an alarming rate, you would think more would be done to prevent hearing loss.

    NIOSH recommends peak audio not to exceed 85db(headset), yet OSHA does not address this in 29 cfr 1910.95?

    Most all headsets( call centers, dispatchers, ATC etc) have some type of limiter, so the expense is already there.
    Standard MP3 and smart phone type ear buds generally allow up to 105db.
    Why is money more valuable than health?

    !am interested in any available data on Emergency Medical Technicians noise exposure due to sirens and helicopter noise.

    Hello Ellen and thanks for your question. The only information NIOSH collected on siren noise inside medical emergency vehicles was through a health hazard evaluation (HHE) back in the 1980’s that found noise levels exceeded our recommended exposure limit for drivers and patients https://www.cdc.gov/niosh/nioshtic-2/00130563.html. In that report, NIOSH made some recommendations about placement of the siren that reduced noise levels. NIOSH also conducted several assessments on firefighters’ exposure to siren noise that offer additional (and somewhat similar exposure information) that could be of interest. Those studies can be accessed through a search of terms such as “Firefighter and Noise” on our website: https://www2a.cdc.gov/nioshtic-2/advsearch2.asp. There are several studies and published reports from non-NIOSH researchers available, but most of those are also dated back to the 80’s and 90’s and before advances to reduce noise levels inside the cabins of emergency vehicles and before optimal siren placement.

    As far as occupational noise exposure to helicopter noise, we do not have any specific information on medical helicopters but we have conducted an HHE to measure noise levels for helicopter pilots used in law enforcement https://www.cdc.gov/niosh/nioshtic-2/20044072.html that can also offer a glimpse of the levels inside the cabin of a helicopter, though medical helicopter may be better equipped to block unwanted noise. If you have a specific concern about your hearing, we recommend you contact the NIOSH Health Hazard Evaluation program https://www.cdc.gov/niosh/hhe/request.html and request that NIOSH conduct an evaluation in your workplace.

    I am an Occupational (Industrial) Hygienist in the UK. Congratulations on an an outstanding piece of work.

    Firstly, where can external microphones be obtained and secondly is the app now available for android phones?

    I would like to make a couple of comments; measuring noise is easy – but measuring noise exposures is difficult! You must ensure that all noise exposures are captured in your assessment. Because of the logarithmic nature of noise, short duration exposures to high levels of noise can have a very significant effect. Remember to consider not only normal operations such as setup, routine running and end of shift activities, but also unplanned events such as blockages, stoppages and breakdowns; machine adjustments, tool change-overs, machine malfunction, maintenance and cleaning; and air and steam leaks or venting, and use of air lines for cleaning and drying activities. A noise level of 105 dBA for 1% of the day, could double the noise exposure from 85 to 88 dBA as an 8-hr Leq. In essence consider the routine planned and unplanned events that take place each and every day.

    With regard to 3, 4 or 5 dB exchange rates; all are approximations – The 3 dB exchange rate is based on the use of a simple equal energy principle whilst the 4 and 5 dB exchange rates assume that there is some recovery in the hearing system between exposures. Whilst, all have some merits the general consensus is now that the simple equal energy principle is preferred as it is the most protective.

    However, it should be remembered that it is an approximation and that where noise is presented as an impact or as an impulse the 3 dB exchange rate appears to under-estimate the risk of hearing loss. It should be further noted that chemical exposures can have an additive or synergistic affect so if the noise risk is from impact noise or from combined chemical and noise exposures you should obtain specialist advise.

    Hello Adrian and thanks for the comments, very well-thought through. It’s always wonderful to hear from a practicing professional, thank you for taking the time to share your thoughts. We think our readers will find them valuable. In response to your comment about the exchange rate and impulse noise, you may be interested in a recent science blog we posted on this specific subject: How can we measure impulse noise correctly?

    As for the NIOSH SLM app, your questions (and our response) may be more helpful to our readers on the NIOSH SLM blog. External microphones are available from several online outlets or directly from the manufacturers. We tested the MicW i436 and Dayton Audio iMM6 in our study https://asa.scitation.org/doi/full/10.1121/1.4964639, both performed well, though only MicW now offers external microphones that can directly connect to the lightning port (MicW i437L).

    We get the question about the Android version a lot. We addressed it on the NIOSH SLM blog above and we go through the challenges we faced during our studies on Android apps, and more specifically with our app, under the section “Why is the app only available on iOS devices?” here: https://www.cdc.gov/niosh/topics/noise/app.html – It basically has to do with the fragmented Android marketplace and the lack of standardized audio tools and hardware used by the many different manufacturers. For us to release an Android version, we will have to guarantee that the Android version will perform uniformly (and within our accuracy criterion of ± 2dBA) across ALL Android devices and models, and there are hundreds (if not thousands) of different Android devices out there from 400 different manufacturers. Another challenge is that unlike Apple devices that often run the latest OS (~86% of Apple devices run the latest iOS), only 11.5% of Android devices run the latest Android OS so even if we develop and guarantee that an Android version of the app will perform according to our criteria on an Android device, the likelihood that the a user is running the same OS is small and that can create all sorts of unintended consequences. These are really the main reasons that we couldn’t identify a single Android app that met our criteria in our initial studies on smartphone apps, and why the marketplace for Android sound measurement apps is so underdeveloped compared to the iOS marketplace. All these issues may be resolved with the use of an external microphone that can be calibrated with an acoustical calibrator.

    Many cities and jet combat training Military Operations Areas are experiencing 115+ dBA low altitude overflights, with multiple passes over the same location, by F-16s and the new F-35 (117 dBA at 500 feet). Lately, the Air Force and Air National Guard seem to have dropped Lmax data by aircraft, by altitude in their Environmental Assessments and Environmental Impact Statements and replaced it with Sound Exposure Level (SEL). I am unable to find regulations or recommended limits based on SEL. Are there any?

    The EAs and EISs rely on DNL which does not account for cumulative exposure times of multiple individual overflights per 24 hours at well over 100 dBA Lmax.

    In addition, Air Force Instruction 48-127, signed by the Secretary of the Air Force, expressly forbids unprotected hearing exposure above 115 dBA for Air Force personnel, on or off base. Yet the population enduring the noise levels around the air bases and the MOAs have no protection and are clearly having their hearing degraded as well experiencing Speech Interference Levels (SIL) above 103 dBA, where communication is impossible even by shouting to someone 3 feet away from you, multiple times per 24 hours.

    Does the CDC have a position on this?

    Does the medical community have a position on this?

    Thank you for your questions. Please see responses below.

    Are there any regulations based on SEL?
    We are not aware of any “regulations” using SEL. We do recognize the limitations of the continued use of dBA-based metrics in the literature and regulations, and we are trying to move the science towards more appropriate metrics especially when dealing with non-gaussian type of noise (e.g., impulse noise).

    Does the CDC have a position on this?
    NIOSH, as part of the CDC, has an occupational noise criteria document, but CDC as a whole does not have criteria for community noise exposure. These issues were handled by the EPA’s Office of Noise Abatement and Control but that office has been closed since the early 1980’s. The National Center for Environmental Health at CDC is starting a new program to look into environmental and community noise issues https://www.cdc.gov/nceh/hearing_loss/default.html.

    Does the medical community have a position on this?
    Please consult the American Medical Association (AMA) with your question. We are not aware of any guidance from the AMA or the Association of Occupational and Environmental Clinics.

    Please reply to Mr. Stuehmer’s questions above. We live in Michigan’s thumb and the military is proposing making this area a permanent training area for low altitude jet training putting all of our health and hearing in jeopardy.

    As being a USAF flightline worker back in the late 6 0′ s early 70′ s I now have hearing loss. Being turned down by VA.stating the hear loss does not happen years later. If I had a problem it would have developed at the time I was on the flight line.not years later. I’ now appealing the case, but was told not to hold my breath on it

    Thank you for your comment – we sincerely appreciate and understand the difficulties you’ve encountered. Research on noise-induced hearing loss is ongoing, but currently we have no evidence that noise will cause continued changes to an individual’s hearing test results after the noise exposure ends. In addition to occupational noise exposure, many other factors (i.e., genetics, age, ototoxic agents, etc.) can contribute to hearing loss.

    Hopefully your comment will raise awareness among others, including future USAF airmen, about the importance of hearing loss prevention.

    Dear NIOSH colleagues: Thank you again for this bulletin board! Do you know if the EPA, various Acoustic societies, AIHA, ANSI. ASTM, or other organizations have best practice guidance policies for outdoor noise sources that municipalities could refer to? I will of course check with the EPA but you may be aware of consensus bodies that design recommended standards. I’m trying to study what metropolitan areas are doing in 2020 regarding noise and addressing thresholds for compliance.

    The EPA’s Office of Noise Abatement and Control has been unfunded since 1981. Here’s the exact language from their website:
    “In the 1970s, EPA coordinated all federal noise control activities through its Office of Noise Abatement and Control. EPA phased out the office’s funding in 1982 as part of a shift in federal noise control policy to transfer the primary responsibility of regulating noise to state and local governments. However, the Noise Control Act of 1972 and the Quiet Communities Act of 1978 were never rescinded by Congress and remain in effect today, although they are essentially unfunded. ”

    The responsibility for outdoor noise abatement and control today has fallen to local governments. The World Health Organization published some guidelines in the late 1990’s regarding community noise that include information on outdoor noise: https://apps.who.int/iris/handle/10665/66217.

    Also on the EPA’s website, they refer citizens to the Noise Pollution Clearinghouse https://www.epa.gov/clean-air-act-overview/clean-air-act-title-iv-noise-pollution. The Noise Pollution Clearinghouse (www.nonoise.org) has the most updated information regarding laws and ordinances across the United States.

    I spent 12 months (6 months in 1967 and 6 months in 1971 on an east coast lighthouse while serving in the Coast Guard. What would be the deciples of the fog horns and could it cause hearing loss.

    NIOSH has not conducted any assessments of sound levels generated by fog horns. A report by the Navy measured sound level from foghorns at 130 decibels, A-weighted (dBA) at the location of the foghorn. The CDC’s National Center for Environmental Health published the following infographic showing “air horns” can reach 129 dB, a level that can cause immediate hearing damage. However, risk to the individual depends on where the exposed person is in relation to the foghorn (someone standing in the direct path of the horn several feet away may be at more risk than someone standing behind or in an enclosed space 30 feet away). It also depends on how often a person is exposed, once a day, several times a day, how long the foghorn was on when it’s activated. This is also assuming the person is not wearing hearing protection at the time the foghorn is activated.

    Dear experts team; I am looking into noise from multiple gas powered leafblowers being operated at the same time in close proximity and have not found an authoritative source for how to calculate how the noise level increases as more an more leafblowers are operated. As the number of operating leafblowers doubles (from 1 to 2, or 2 to 4, several websites suggests the associated decibels rises by 3.

    Is that right? Is there empirical evidence in support of such a generalization?

    Is there an authoritative source for such an estimate?


    Hi Randall, thanks for the great question. Manufacturers labels are also not always clear, and some “rules of thumb” may be confusing to some, so we thought we’d take the opportunity to provide a detailed explanation, and hopefully it addresses your question(s) and many other similar questions that we often get.

    Decibels (dB) are useful units for talking about sound levels, but are not the most intuitive when it comes to doing math with them because of their logarithmic nature. Most tool manufacturers are likely to report noise generated from their equipment using the term Sound Power Level (dB referencing Watts, sometimes written as dBSWL or Lw).

    The specific empirical evidence you’re searching is governed by the mathematical addition of decibel quantities as described in this common acoustical equation:

    Ltotal (dB)=10 LOG10 (10^(L1/10)+ 10^(L2/10)+ 10^(L3/10)+⋯ 10^(Ln/10)

    If you have two leaf blowers that the manufacturer lists as having Lw = 85 dB, running both of them close together would raise the sound power level output by around 3 dB, here’s how the math works:

    Ltotal (dB)=10 LOG10 (10^(85/10)+ 10^(85/10) ) or 10 LOG10 (10^8.5+ 10^8.5 ) = 88 dB (3 dB higher than a single blower).

    Three blowers would generate 89.8 dB; four blowers ~ 91 dB, eight blowers ~ 94 dB and so on…

    This decibel calculator (https://www.noisemeters.com/apps/db-calculator/) can help you test this concept for adding sound power levels.

    Now, if someone standing several feet away and is interested in what his or her ears are exposed to so they can protect their hearing, that quantity is termed Sound Pressure Level (dB referencing Pascals, sometimes written as dBSPL or Lp) and is usually measured using sound level meters or noise dosimeters. The distinction between sound power levels (what the tool generates) and sound pressure levels (what our ears hear) is critical to understanding the effect of a noise source on hearing since this is what’s we’re more concerned about here at NIOSH – protecting workers against the effects of noise on their hearing health. In the above example, if someone measures the sound level from one leaf blower, say from 10 feet away, and gets a readout of 75 dBSPL on their sound level meter, if you were to add another (exact leaf blower), then the sound level meter is likely to read around 6 dB higher or 81 dBSPL. The same equation above applies but instead of using 10 〖LOG〗_10 we use 20 〖LOG〗_10 to calculate sound pressure levels. This has been a great source of confusion for many over the years. For more information about how sound pressure level and sound power level are different, see http://www.sengpielaudio.com/calculator-soundpower.htm.

    For those interested in protecting their hearing from leaf blowers and other landscaping tools, NIOSH recommends: 1) Using quieter equipment, 2) increasing the distance others are positioned from the leaf blowers and 3) Using appropriate hearing protection. We actually have a specific science blog for landscapers that some may find useful: https://blogs.cdc.gov/niosh-science-blog/2018/08/01/landscape2/.

    I am working on my PhD thesis on this topic. I learned a lot in your article.
    Thank you for your knowledge.

    I recently attended an historic motorsport event in the UK where F1 cars from the 80s and 90s raced. I was close to the start grid and the noise was so extreme I experienced pain in my right ear. I covered my ears at this point. 10 days later I developed tinnitus, which my GP informs me will not heal. Do you have any research on hearing damage caused at motorsport events? I am putting a web site together to highlight the dangers. There was no warning of any kind on the event literature. In the UK there is no legal requirement to even do a risk assessment of noise induced hearing damage for entertainment events.

    Thank you for your comment. Testimonials like yours can contribute to an understanding of the risks. In 2010, NIOSH researchers published “Occupational and recreational noise exposures at stock car racing circuits: An exploratory survey of three professional race tracks” in the Noise Control Engineering Journal

    See also the NIOSH Health Hazard Evaluation on noise in racing, https://www.cdc.gov/niosh/hhe/reports/pdfs/2000-0110-2849.pdf

    We also posted a related blog on noise exposure to workers.
    High Speeds, Higher Decibels

    I want to ask the basic question, that where is the cornerstone ,85dB 8hours per day ,from? could you recommend some published articles about that?
    Thanks a ton!

    Thanks for asking about the basis of the NIOSH Recommended Exposure Limit of 85 dBA averaged over an 8-hour day (85 dBA TWA). NIOSH made this recommendation on the basis of data collected in its Occupational Noise and Hearing Survey, conducted from 1968-1972. Those data aligned well with data previously collected in other studies. A full discussion of the rationale for setting the 85 dBA TWA limit, along with references to earlier studies which were considered, is provided in the original NIOSH criteria document for noise, available here:

    NIOSH re-analyzed the Occupational Noise and Hearing Survey data using more modern statistical techniques when the noise criteria document was revised in 1998. An explanation of that analysis and the rationale for retaining the 85 dBA limit (and the change to using a 3 dB exchange rate) can be found in the 1998 criteria document, available here:

    Can sustained high frequency tonal noise cause hearing damage at “low” or “safe” decibel levels? An example would be an electric motor or inverter.

    Thank you for your question. More details on the exposure would be needed for anyone to give you a definite answer, such as: how low the exposure really is and how long and how often a person is exposed to it. Also, individuals differ in their susceptibility to noise. It is possible for one individual to have a negative effect from an exposure that would be considered safe for most people, but today we cannot identify with certainty who are the more susceptible individuals. This recent paper expands on the issues on risk and different exposure scenarios and limits:

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