(Occupational Health and Safety Administration (OSHA) standards discussed within this article reflect General Industry requirements.)
Occupational noise presents a risk in nearly every workplace environment. Excessive sound levels can damage the ear over time and are not reversible. The human ear receives air pressure waves (sound) from the work environment to the outer ear. That sound is then converted into mechanical forces in the middle ear, then converted again in the inner ear into a pressure wave that is converted into an electrical signal interpreted by the brain. Noise can be considered unwanted sound pressure and measured in decibels (dB). “Noise is arguably the most pervasive hazardous agent in the workplace…” (Berger, 2003). The National Institute of Occupational Health and Safety (NIOSH) estimates 22 million workers are exposed to hazardous noise levels annually (NIOSH, 2023).
Occupational Noise-Induced Hearing Loss (NIHL) and Prevention
Occupational noise-induced hearing loss (NIHL) is preventable but requires employers to quantify noise level exposures (i.e., perform an exposure assessment) within their workplace, develop appropriate controls to mitigate any excessive exposure, and may require the development of an OSHA Hearing Conservation Program. Many employers commonly believe that providing earplugs for their workers will fully protect employees; this is often not the case based on data from their work environment. Employers are also known to perform a review of noise in their work environment using a sound level meter to verify noise levels as their only evaluation method. This method often leads the employer to believe they are compliant when a small grouping of instantaneous sound pressure readings is below a certain threshold, which is often inaccurate.
Key Points about Noise Exposure
Generally, noise can be summarized as follows:
- Elevated sound pressure levels are more damaging to the ear than lower sound pressure levels.
- NIHL is a gradual process and may take about a decade of overexposure to reach maximum hearing loss.
- Higher-frequency noise is more damaging to the ear than lower-frequency noise. NIHL generally develops in the 3,000 to 6,000-hertz range. The typical range for the ear is 20 Hz to 20,000 Hz.
- Intermittent exposure to noise is less damaging to the ear than continuous noise.
Quantifying Noise Exposure and Assessing Variability
Quantifying noise exposure is a significant process. OSHA requires all continuous, intermittent, and impulsive (sharp) sound levels from 80-130 decibels (dB) to be integrated into noise measurements. This often cannot be accomplished using a sound level meter. Additionally, occupational exposure variation due to job classifications, routine and non-routine work, task variation, process characteristics, noise sources, etc., must be factored in the exposure assessment. For example, a machinist, a welder, a warehouse worker, an engineer, and a crane operator all working in the same work environment will have significantly different noise exposures, and even the same job classifications can have different exposures performing very similar work.
Importance of Qualified Industrial Hygienists in Noise Exposure Assessment
A qualified Industrial Hygienist should perform noise exposure assessments, given the many factors involved in an exposure assessment and the potential for negative repercussions should the exposure assessment be performed incorrectly. Underestimating noise exposure can lead to hearing loss, workers’ compensation claims, and OSHA compliance violations. In some States, a single workers’ compensation claim related to occupational hearing loss can reach $150,000.
OSHA Permissible Exposure Limits (PEL) and Monitoring
The OSHA permissible exposure limit (PEL) for employees is 90 decibels A-weighted (dBA) as an eight-hour time-weighted average (TWA), meaning the limit is based on both sound pressure level and duration. OSHA requires employers to perform an exposure assessment for sound levels to determine employer exposure relative to the OSHA PEL. As sound levels increase, the duration of allowable exposure time decreases significantly. Table 1 outlines sound pressure level and allowable hours of exposure (OSHA, 2008). When employees are subjected to sound exceeding those in Table 1, employers shall be required to implement feasible engineering or administrative controls. If controls fail to reduce sound levels, personal protective equipment shall be used. OSHA uses a 5 dBA exchange rate (or time intensity exchange rate) that reduces the allowable PEL exposure duration by 50% for every 5 dBA increase. Caution should be exercised for exposure levels exceeding the OSHA PEL, even a few decibels will result in a dramatic decrease in allowable exposure time.
Action Level (AL) and Hearing Conservation Program
Employee exposure equal to or exceeding 85 dBA eight-hour TWA (Action Level or AL) will require the employer to implement a monitoring program. Employers must repeat monitoring activities when changes in production, process, equipment, or controls increase any exposure to employees where employees may be exposed above the OSHA AL, or attenuation provided by hearing protection devices may be rendered inadequate. Generally, sound level or noise management is an ongoing effort.
|Duration per day
(dBA slow response)
|0.25 or less
Table 1 – OSHA Permissible Noise Exposure Limits – 1910.95 (OSHA, 2008)
Additionally, employees who are exposed to 85 dBA (AL) or above (not factoring personal protective equipment) are required by OSHA to participate in a Hearing Conservation Program that requires an employer-developed program including annual audiometric testing, baseline audiograms, mitigation controls including personal protective equipment, monitoring, and annual employee training. The Employer Hearing Conservation Program is developed, like many OSHA programs, based on the results of the exposure assessment. Audiometric testing captures the ear’s ability to hear certain frequencies and sound pressure levels. The Hearing Conservation Program requires employers to identify NIHL during an employee’s work history through audiometric testing. Data revealed during audiometric testing is also an indicator of the effectiveness of current workplace controls. Hearing loss associated with the workplace should not occur when proper mitigation controls are in place.
De-rating of Hearing Protection Devices and Instrumentation for Noise Assessment
Employers must provide hearing protection devices to all workers exposed to the 85 dBA (AL) or above, and employers must ensure they are being worn. Hearing protection devices are manufactured with a Noise Reduction Rating (NRR). The NRR represents the attenuation ability of the hearing protection device and rarely reflects the actual noise reduction levels during usage. Employers are responsible for de-rate the effectiveness of hearing protection devices used in their work environment, based on their exposure assessment. This evaluation process is often incorrectly performed by employers. OSHA outlines specific methods of de-rating hearing protection in the Occupational Noise Exposure Standard (OSHA, 2008).
Protecting employee hearing starts with a detailed exposure assessment and using proper instrumentation, often an area where employers struggle. Two primary tools are of significant value when used together are the sound level meter and noise dosimeter. A sound level meter is a direct reading instrument that can be used to collect instantaneous readings from the work environment (Figure 1).
During all parts of the day, sound is propagating at changing levels and a sound level meter will provide instantaneous readings of sound levels, including peak (highest readings) and average reading, among a host of other variables. This tool excels at the beginning stages of noise characterization of the work environment and provides basic information regarding the identification of noise sources, real-time sound pressure levels, area sample data, and provides an expected range of noise levels in a work environment. This tool, however, lacks some critical features, it cannot gather data regarding specific employee noise exposure (dose) and should not be used to determine (in most cases) employee overall exposure.
In many environments where there is high worker mobility, variations in sound level, or where area sampling is infeasible, a noise dosimeter is typically the preferred tool to determine worker exposure to noise. The instrument is worn on the worker as a personal sampling device and collects ongoing data that represents a worker’s noise exposure, including OSHA’s requirements for impact, continuous, and impulsive sounds (Figure 2). Through this method, noise can be collectively captured via data logging throughout a worker’s shift and will provide a TWA of noise exposure to compare against the OSHA PEL, AL, and provide the necessary information for the OSHA Hearing Conservation Program and its various requirements.
Comparison of Standards and Recommendations
OSHA, NIOSH, and the American Conference of Governmental Industrial Hygienists (ACGIH) offer different standards and methods of calculating worker exposure, exposure limits, de-rating of hearing protection devices, requirements for hearing protection, etc. While OSHA standards may be regulatorily required, they are the least conservative standards and may not fully protect workers. Both NIOSH and ACGIH use a 3 dBA exchange rate and 85 dBA occupational exposure limit recommendation for employers that is significantly more conservative than OSHA.
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Berger, E. (2003). Noise Control and Hearing Conservation: Why Do it? In The Noise Manual (5th ed., pp. 1–17). essay, American Industrial Hygiene Association.
National Institute of Occupational Health and Safety (NIOSH). (2023, January 25). Noise and Occupational Hearing Loss. Centers for Disease Control and Prevention. https://www.cdc.gov/niosh/topics/noise/default.html
Occupational Safety and Health Administration (OSHA). (2008, December 12). Occupational Noise Exposure – 1910.95. Occupational Noise Exposure. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.95