Occupational Noise Exposure Guidelines: Protecting Workers' Hearing
Almost all noise-induced hearing loss (NIHL) is preventable. However, once acquired, NIHL is permanent and irreversible. In addition to hearing loss, evidence shows that prolonged or repeated exposure to high levels of noise is associated with other health effects, such as heart disease, hypertension, and insomnia.
The World Health Organization (WHO) and the United Nations Environmental Programme (UNEP) attest that exposure to loud sounds (noises) adversely affects the lives of millions of people at home, at work, and in the community. Several recommendations for limiting noise exposure to avoid adverse effects have been developed over the years.
However, noise exposure guidelines vary. In this article, we describe how these factors, and other considerations, make developing and applying noise exposure guidelines difficult. First, let’s look at definitions of exposure.
Defining Noise Exposure
The criteria used to define noise limits are complicated by the intrinsic complexities and nuances of sound measurement. Generally, exposure to continuous noise is measured using the frequency dependent A-weighted decibel scale (dB[A]). However, using the C-weighted scale (dB[C]) or unweighted (sound pressure level) scale may be appropriate for noise sources with a large proportion of low-frequency components, very intense levels, and/or high intensity impulse noise.
Few exposures are constant and unvarying; therefore, most exposure limits are based on a Time Weighted Average (TWA) which sums energy over time. This involves specifying an exchange rate. An exchange rate is the increase in allowable exposure level with each halving of exposure duration. Most guidance specifies a 3-dB exchange rate based on the “equal energy” principle (i.e., sound energy doubles with every 3 dB increase in level). Some noise limits use a higher exchange rate (e.g., 5-dB) to allow for intermittency which reduces risk. The exchange rate substantially influences measured exposure and risk.
Other exposure characteristics may also be used to quantify exposure. Differences in exposure definitions explain some of the variability across the noise criteria above. All are measured on the dB(A) scale and use a 3-dB exchange rate. However, the EPA 70 dB(A) exposure limit is set to cover a 24-hour time period (Leq(24)), the 80 dB(A) recommended by the WHO is for a maximum of 40 hours per week, and the 85 dB(A) NIOSH REL is based on an 8-hour workday. The 100 dB(A) WHO limit for venues and events is averaged over only 15 minutes.
Health Outcomes and Target Groups
Noise exposure limits may be set to protect against auditory outcomes, such as hearing loss and tinnitus, or to prevent adverse non-auditory effects (e.g., heart attack, stroke, sleep disturbance, and injury avoidance). The EPA 70 dB(A), WHO 80 dB(A), and the NIOSH 85 dB(A) REL exposure limits were established to prevent hearing loss. However, the definition of “hearing loss” is very different across the guidelines. The NIOSH REL aims to protect workers from developing a material hearing impairment (i.e., hearing loss substantial enough to impact understanding speech) over their working lifetime (assumed to be 40 years).
The EPA limit seeks to protect against a hearing change of more than 5 dB at 4K Hz-a much more stringent hearing loss criterion, which results in a lower recommended exposure limit. The WHO 80 dB(A) guideline was set at a level to avoid any increased risk of permanent hearing impairment due to environmental noise exposures. In contrast to these recommendations, the WHO 100 dB(A) Leq(15min) limit aims to prevent hearing loss only indirectly by reducing “unnecessarily hazardous sound levels” at venues and events. The WHO acknowledges that this 100 dB(A) limit “does not, and cannot, eliminate all risk of an individual audience member suffering sound-induced hearing injury.” Interestingly, some noise exposure guidelines are set to avoid annoyance.
The NIOSH REL is clearly targeted toward workers, whose exposures typically last 8 hours a day, 5 days per week. The EPA 70 dB(A) and WHO 80 dB(A) recommendations target the general population, whose exposures can occur 24 hours a day, 7 days per week, but with more presumed intermittency. The WHO venue and event guidelines are targeted toward adults attending concerts and other loud events. Nearly all current noise exposure recommendations were developed for adults.
Acceptable Risk and Enforcement
Lower noise limits generally protect more people; however, individuals differ in their susceptibility to noise. The 70 dB(A) EPA limit was set to protect 96% of the population. At exposures equivalent to the REL, NIOSH estimates that 92% of workers exposed 240 days/year for 40 years would be protected from developing a material hearing impairment. The WHO 80 dB(A) maximum of 40 hours per week is presumed to protect 100% of the population. As noted previously, the WHO venues and events guidelines acknowledge that some participants may acquire hearing damage even at venues meeting the criterion.
Some noise limits have the force of law. Regulatory agencies such as OSHA and EPA create legally enforceable noise regulations and standards which set limits on exposure to hazardous noise. The EPA Office of Noise Abatement and Control was phased out in 1982 leaving noise control to state and local governments without the presence of a federal program. State and local governments may pass legislation to regulate noise exposure. Legislation may include noise level limits, zoning laws, time of day restrictions, and nuisance ordinances.
In contrast, other governmental, professional, or standards organizations propose voluntary guidelines and recommendations on noise exposure limits. Recommendations do not carry the force of law.
Recent Guidelines and Recommendations
New or updated noise limits have been published periodically and vary due to differences we have described. In 1999, the WHO recommended community noise limits of 55 dB(A) Leq for outdoor living areas to prevent serious annoyance. They also recommended a limit of 70 dB(A) Leq for industrial, commercial shopping, and traffic areas (indoors and outdoors) to prevent hearing loss. In 2018, the WHO Regional Office for Europe strongly recommended that noise levels produced by road traffic be reduced to < 53 dBA Lden to prevent adverse health effects.
Noise exposure guidelines, recommendations, and regulations need to be based on sound, ethical science and include high-quality, relevant information. Guidelines and recommendations need to be clear, valid, and transparent and based on the highest level of scientific evidence obtained through a systematic review of the literature.
An intra-agency workgroup formed within the National Center for Environmental Health (NCEH) in the Centers for Disease Control and Prevention (CDC) endeavors to assist in this effort by conducting research and providing public health education materials. The workgroup is comprised of CDC staff members from NCEH, the National Center for Chronic Disease Prevention and Health Promotion, the National Center on Birth Defects and Developmental Disabilities, and NIOSH. In addition, staff from the National Institute on Deafness and Other Communication Disorders in the National Institutes of Health collaborate with the workgroup on activities of mutual interest. Workgroup members collaborate to address the risks of exposure to hazardous noise levels.
Practical Steps for Noise Management in the Workplace
Here are practical steps for effective noise management in the workplace:
- Measure Noise Levels: Use sound level meters (SLM) or noise dosimeters to assess noise levels in different areas of the workplace. If an SLM is not available, sound measurement apps can provide a measure of area noise but may not comply with regulatory requirements.
- Create Noise Maps: Develop a noise map of facility areas to identify the loudest zones and the equipment contributing to high noise levels. A simple example of a noise map. It can be hand-drawn in practice.
- Monitor Individual Worker Exposure: Measure individual worker noise exposures using a personal dosimeter in areas with high noise. Attach the microphone to the top of the worker's shoulder on the side that is likely to have the highest exposure. If the device does not have a separate microphone this may not be necessary.
- Implement Controls: When employees are subjected to sound levels exceeding 85 dBA TWA, feasible administrative or engineering controls are to be utilized. Types of administrative controls are rotation of employees, limiting time of certain operations, or restricting areas or work operations. If feasible engineering or administrative controls cannot be accomplished personal hearing protective devices must be provided and used to reduce sound levels in areas above 85 dBA.
- Provide Hearing Protection: The hearing protection used will depend on the operation, employee preference and attenuation required. Employees are given the opportunity to select their hearing protectors from a variety of suitable hearing protectors.
- Conduct Audiometric Testing: NIOSH recommends annual audiometric testing for workers exposed to noise above the REL. Conduct testing on workers when they are first enrolled in a hearing loss prevention program. This is called baseline testing. NIOSH recommends that employers obtain baseline tests within 30 days of initial exposure for newly exposed workers. Unlike baseline testing, annual hearing tests should be done as close to the end of a worker's shift as possible (no preceding quiet period).
- Analyze Audiogram Results: Results of annual hearing tests should be compared to results from the baseline hearing test to check for significant threshold shift (STS). NIOSH considers a 15 dB change in hearing threshold at any frequency to represent an STS. If an STS is noted during an annual hearing test, the worker should be retested within 30 days to confirm.
- Inform and Train Workers: You should tell workers they are having their noise exposure monitored and provide them with an explanation of the results. Involve workers in the noise monitoring process. They can provide important information about the work environment, machinery operation, and specific job tasks. Encourage workers to tell you when changes in equipment or production occur.
- Maintain Records: Employee exposure measurements and assessments are maintained at the office of Environment, Health and Safety. Employee audiometric test records are kept at the University Employee Occupational Health Clinic.
Remember: Noise levels are likely hazardous if a person must raise their voice to speak with someone is an arm's length away.
This figure shows the relationship between exposure level and exposure duration under the NIOSH REL. As sounds become louder than 85 dBA, the length of a daily exposure must be reduced. For each 3 dBA increase in noise level, NIOSH recommends reducing the exposure duration by half. This is called the exchange rate. Similarly, if the daily exposure is longer than 8 hours, the allowable noise level is lower.
Understanding Audiometric Testing
An audiogram is a graph of hearing thresholds at various frequencies in each ear. Thresholds which are 25 dB HL (hearing level) or better (lower) are considered normal for adults. This audiogram shows normal hearing thresholds in the right ear. Frequency refers to how low or high the "pitch" of the sound is.
Example of an audiogram showing normal hearing thresholds.
Workers who develop an STS - whether temporary or permanent - should be notified. Steps should be taken to prevent further change in hearing.
University Hearing Conservation Programs
All University employees whose noise exposures equal or exceeds an eight-hour time weighted average (TWA) of 85 decibels are enrolled in a hearing conservation program. When information indicates that any employee’s exposure may equal or exceed an 8-hour time-weighted average of 85 decibels, the department is to notify the Health and Safety Office to implement a monitoring program.
The noise survey is performed using a sound level meter (A-scale, slow response) and/or noise dosimeter for evaluation of personal exposures. The employee is to be notified when he/she is exposed at or above an 8-hour time-weighted average of 85 decibels. Annual audiometric testing is performed by a licensed or certified audiologist, at UNC School of Medicine’s Speech and Hearing department.
A baseline audiogram is obtained within 6 months of an employee’s first exposure at or above the action level. The baseline audiogram is established to compare against subsequent audiograms. Audiometric tests are to be pure tone, air conduction, hearing threshold examinations, with test frequencies including as a minimum 500, 1000, 2000, 3000, 4000 and 6000 Hz. Employees are to be notified, in writing, of the results of exams.
When employees are subjected to sound levels exceeding 85 dBA TWA, feasible administrative or engineering controls are to be utilized. The University strongly encourages the use of hearing protection devices while working around noisy equipment. For employees who have experienced a standard threshold shift, hearing protectors must attenuate employee exposure to an 8-hour time-weighted average of 85 decibels or below.
Signs are to be posted in areas where noise levels are above 85 dBA stating that hearing protection is required. An annual training program is provided for each employee included in the hearing conservation program.
OSHA Regulations
Protection against the effects of noise exposure shall be provided when the sound levels exceed those shown in Table G-16 when measured on the A scale of a standard sound level meter at slow response.
OSHA Table G-16: Permissible Noise Exposures
When employees are subjected to sound exceeding those listed in Table G-16, feasible administrative or engineering controls shall be utilized. When the daily noise exposure is composed of two or more periods of noise exposure of different levels, their combined effect should be considered, rather than the individual effect of each. If the sum of the following fractions: C1/T1 + C2/T2Cn/Tn exceeds unity, then, the mixed exposure should be considered to exceed the limit value.
The employer shall administer a continuing, effective hearing conservation program, as described in paragraphs (c) through (o) of this section, whenever employee noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels measured on the A scale (slow response) or, equivalently, a dose of fifty percent.
Audiometric tests shall be performed by a licensed or certified audiologist, otolaryngologist, or other physician, or by a technician who is certified by the Council of Accreditation in Occupational Hearing Conservation, or who has satisfactorily demonstrated competence in administering audiometric examinations, obtaining valid audiograms, and properly using, maintaining and checking calibration and proper functioning of the audiometers being used. A technician who operates microprocessor audiometers does not need to be certified.
Where mobile test vans are used to meet the audiometric testing obligation, the employer shall obtain a valid baseline audiogram within 1 year of an employee's first exposure at or above the action level. Testing to establish a baseline audiogram shall be preceded by at least 14 hours without exposure to workplace noise.
Each employee's annual audiogram shall be compared to that employee's baseline audiogram to determine if the audiogram is valid and if a standard threshold shift as defined in paragraph (g)(10) of this section has occurred. The audiologist, otolaryngologist, or physician shall review problem audiograms and shall determine whether there is a need for further evaluation.
Audiometric tests shall be pure tone, air conduction, hearing threshold examinations, with test frequencies including as a minimum 500, 1000, 2000, 3000, 4000, and 6000 Hz. The functional operation of the audiometer shall be checked before each day's use by testing a person with known, stable hearing thresholds, and by listening to the audiometer's output to make sure that the output is free from distorted or unwanted sounds. Audiometer calibration shall be checked acoustically at least annually in accordance with appendix E: Acoustic Calibration of Audiometers.
Employers shall make hearing protectors available to all employees exposed to an 8-hour time-weighted average of 85 decibels or greater at no cost to the employees. The employer shall evaluate hearing protector attenuation for the specific noise environments in which the protector will be used. The adequacy of hearing protector attenuation shall be re-evaluated whenever employee noise exposures increase to the extent that the hearing protectors provided may no longer provide adequate attenuation.
The employer shall train each employee who is exposed to noise at or above an 8-hour time weighted average of 85 decibels in accordance with the requirements of this section. The training program shall be repeated annually for each employee included in the hearing conservation program.
All records required by this section shall be provided upon request to employees, former employees, representatives designated by the individual employee, and the Assistant Secretary.
Work is one of the most common places you can be exposed to harmful levels of noise, which puts you at risk of noise-induced hearing loss (NIHL). Fortunately, the US Occupational Safety and Hazard Administration (OSHA) has standards and programs aimed at reducing the risk of hearing loss among American workers. This does not mean you have to be exposed to eight continuous hours of loud sound to qualify for help with noise exposure. You can see how this plays out on the chart above.
Within six months of employment in an environment where they are exposed to loud noises, employees must be given a baseline audiogram. Thereafter, they should be provided with a yearly audiogram by a certified audiologist, free-of-charge. Another way to reduce noise is to use administrative controls. This means employers makes adjustments to the work schedule or workplace that don't require much physical modification.
Noise-canceling headphones are great for blocking out ambient noise when you're listening to music or a podcast. Regardless, it is always a good idea to protect your hearing from harmful noise, whether at work and at home. You might be wondering how loud is too loud?
Unfortunately, not all worksite sound is predictable or easily measurable. Sudden blasts at a worksite, for example, may only last seconds but cause severe hearing damage. Or you may not have thought your environment was loud initially, but after awhile you begin to experience symptoms like muffled hearing or ringing in the ears.
Workers have the right to a safe workplace and freedom from being affected by noises loud enough to induce hearing loss. In many situations, workers can file for workers' compensation benefits if they believe their hearing has been damaged on the job. It's important to know you have resources if your employer is not doing enough to protect workers' hearing.
OSHA provides a wealth information for workers on their site. They also provide specific guidance on what to do if you're being exposed to any harmful activities, not just noise. If you've noticed changes to your hearing or are experiencing tinnitus following exposure to loud noise, it's important to get evaluated by a hearing specialist in your area. Noise can cause hearing damage that is permanent and disabling. You may not become aware of the hearing loss until several years have gone by. Long-term exposure to noise in the workplace is also associated with hypertension and other chronic conditions.
Measure your employee’s noise exposures to identify what noise protections need to be in place. L&I’s safety and health consultants can help you do this.
| Noise Level | Action |
|---|---|
| 115 dBA (Measured with the slow setting on a sound level meter) | Take action to reduce noise exposure |
| 140 dBC (Measured with the fast setting on a sound level meter) | Take action to reduce noise exposure |
Eliminating or reducing harmful noise levels is the best way to protect workers. Hearing protection, like earplugs or earmuffs, can protect you from noise if worn correctly. Employees need to be trained on noise and hearing protection. Annual hearing tests help identify hearing loss in your employees. Measure employee noise exposures to determine if it is 85 dBA TWA8 (a-weighted decibels eight-hour time-weighted average) or higher.