Occupational Noise: Definition, Standards, and Prevention
Occupational noise refers to undesired sound present in the workplace [1]. Exposure to occupational noise is a significant concern for workers across various industries. It can lead to auditory and non-auditory health effects, where examples of auditory health effects are tinnitus and occupational hearing loss, while examples of non-auditory health effects include annoyance, sleep disturbance, impaired attention, communication impairment and cardiovascular disease. Undesired noise, especially one-time exposure to impulse noise, such as from gunshots, can lead to hearing loss [2]. If not prevented, this can further develop into a permanent and irreversible condition, noise-induced hearing loss (NIHL).Noise-induced auditory symptoms (NIASs) refer to the symptoms that develop after exposure to loud noise in excess of 85 dB, typically at the temporary-threshold shift (TTS) stage when the condition of the ears’ sensory cells in the cochlea becomes fatigued [3]. Occupational noise, if experienced repeatedly, at high intensity, for an extended period of time, can cause noise-induced hearing loss (NIHL)[14] which is then classified as occupational hearing loss. Noise, in the context of industrial noise, is hazardous to a person's hearing because of its loud intensity through repeated long-term exposure. In order for noise to cause hearing impairment for the worker, the noise has to be close enough, loud enough, and sustained long enough to damage the hair cells in the auditory system.
Modern thinking in occupational safety and health further identifies noise as hazardous to workers' safety and health. Noise can also affect the safety of the employee and others. Noise can be a causal factor in work accidents as it may mask hazards and warning signals and impede concentration. Noise may also act synergistically with other hazards to increase the risk of harm to workers.
A simple example of a noise map. It can be hand-drawn in practice. After completing a noise map, identify the loudest areas on the map and the equipment in those areas.
Each industry is different, as workers' tasks and equipment differ, but most regulations agree that noise becomes hazardous when it exceeds 85 decibels, for an 8-hour time exposure (typical work shift). This relationship between allotted noise level and exposure time is known as an exposure action value (EAV) or permissible exposure limit (PEL). The EAV or PEL can be seen as equations which manipulate the allotted exposure time according to the intensity of the industrial noise. As the industrial noise intensity increases, the allotted exposure time, to still remain safe, decreases. Thus, a worker exposed to a noise level of 100 decibels for 15 minutes would be at the same risk level as a worker exposed to 85 decibels for 8 hours.[2] Using this mathematical relationship, an employer can calculate whether or not their employees are being overexposed to noise.
The Significance of Noise Measurement
Measuring noise exposure is essential to protect workers’ hearing health and ensure workplace compliance with safety regulations. Regular monitoring identifies areas where noise exceeds safe thresholds, such as the 85 dBA action level set by organizations like OSHA and NIOSH. This data helps employers implement effective controls, such as reducing noise at the source, providing hearing protection, and ensuring proper work schedules to limit workplace noise exposure duration.
Additionally, measuring sound exposure enables organizations to comply with legal and industry standards, avoiding potential fines or litigation. Noise exposure measurement also helps detect risks early, preventing occupational hearing loss among workers and promoting a safer, more productive workplace environment.
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.
Noise Exposure Limits and Action Values
The noise exposure limits are associated action values based on decibel levels outlined by standards such as the European Union’s Directive on Noise. The Noise Directive outlines three primary daily noise exposure levels and corresponding actions:
- Lower action value (80 dBA): When daily or weekly noise dose reaches this level, employers must inform and train workers about the risks and provide preventive audiometric testing. If noise risks can’t be avoided by other means, suitable individual hearing protectors should be made available.
- Upper action value (85 dBA): At this level, employers must take specific actions to reduce noise levels over time, such as implementing noise-reducing programs and marking noisy areas with signs. Employees also have the right to consult with medical professionals regarding their hearing health. Moreover, suitable individual hearing protectors should not only be available but also used by workers.
- Limit value (87 dBA): This is the absolute maximum daily or weekly noise excessive exposure level, taking into account the noise reduction provided by hearing protectors.
Occupational Noise-Induced Hearing Loss (NIHL)
Occupational noise-induced hearing loss (NIHL) is a permanent and preventable condition caused by prolonged or sudden exposure to loud noise. It occurs when excessive noise damages the delicate hair cells in the cochlea, a part of the inner ear responsible for transmitting sound signals to the brain. These hair cells do not regenerate, so any damage results in irreversible hearing loss.
NIHL can develop from sustained exposure to loud environments, such as workplaces with heavy machinery, or from a single instance of extremely loud noise, like an explosion. Common symptoms include difficulty understanding speech, especially in noisy environments, and ringing in the ears (tinnitus). NIHL is entirely preventable through proper noise control measures, regular hearing tests, and the use of hearing protection devices like earplugs or earmuffs in high-noise environments.
Noise exceeding 85 dBA over an 8-hour shift is considered a critical threshold because it significantly increases the risk of hearing loss. NIOSH recommends 85 dBA as a threshold, emphasizing that every additional 3 dB effectively halves the safe exposure time. When workers regularly experience sound levels at or above 85 decibels, permanent changes to the inner ear become more likely.
Hearing Conservation Programs
Hearing conservation programs are structured initiatives designed to guard workers against excessive noise exposure. These programs typically specify when hearing protection is required at what decibel level, ensuring that employees receive consistent and clear guidance. Under occupational safety laws, companies must monitor noise levels, provide training, and ensure proper use of earplugs or earmuffs once noise crosses regulated limits.
A fully functioning hearing conservation program involves routine noise checks, provision of adequate hearing protection devices (HPDs), and relevant employee training. This blueprint addresses noise sources comprehensively rather than relying on PPE alone. Recordkeeping, including noise measurements and audiogram data, is essential.
This audiogram shows normal hearing thresholds in the right ear. Frequency refers to how low or high the "pitch" of the sound is.
Methods for Noise Reduction
There are several ways to limit exposure to hazardous occupational noise. The hierarchy of controls[17] is a guideline for reducing hazardous noise. Before starting a noise reduction program, base noise levels should first be recorded.[18] After this the company can start to eliminate the noise source. If the noise source cannot be eliminated, the company must try to reduce the noise with alternative methods.
The hierarchy of controls systematically reduces or eliminates hazardous noise at its source. The approach starts with elimination (removing noisy processes altogether) or substitution (choosing quieter equipment), then moves on to engineering controls (installing barriers or dampening mechanisms) and administrative controls (rotating workers or limiting shift durations). Only at the final stage does it rely on personal protective equipment (PPE), such as earplugs or earmuffs. By adopting this tiered framework, employers strive to mitigate the risks of noise in the workplace before relying on hearing protectors.
Effective prevention starts by identifying hazards and developing systematic hearing programs. This strategy revolves around assessing risks, educating employees about dangers, and deamonstrating why safety is important for both health and productivity. Companies can deploy engineering controls, administrative shifts, and PPE to reduce overall noise exposure.
Engineering Controls
Acoustic quieting is the process of making machinery quieter by damping vibrations to prevent them from reaching the observer. If elimination and substitution are not sufficient in reducing the noise exposure, engineering controls should be put in place by the employer.[a] An engineering control usually changes the physical environment of a workplace. For noise reduction, an engineering control might be as simple as placing barriers between the noise source and the employee to disrupt the transmission path.
An engineering control might also involve changing the machine that produces the noise. Ideally, most machines should be made with noise reduction in mind, but this doesn't always happen.
Administrative Controls
To decrease an employee's exposure to hazardous noise, the company can also take administrative control by limiting the employee's exposure time. This can be done by changing work shifts and switching employees out from the noise exposure area. An employer might also implement a training program so that employees can learn about the hazards of occupational noise. Other administrative controls might include restricting access to noisy areas as well as placing warning signs around those same areas.
Personal Protective Equipment (PPE)
If all other controls fail to decrease the occupational noise exposure to an acceptable level, hearing protection should be used.[34] There are several types of earplugs that can be used to attenuate the noise to a safe level. Some earplug types include: single-use earplugs, multiple-use ear plugs, and banded ear plugs.[35] Depending on the type of work being done and the needs of the employees, earmuffs might also be a good option. While earmuffs might not have as high of a noise reduction rating (NNR) as earplugs, they can be useful if the noise exposure isn't very high, or if an employee cannot wear earplugs.
Noise Measurement Equipments
Noise measurement and testing form the backbone of any effective hearing conservation plan. Employers rely on sound level meters to gauge static areas and dosimeters to record a worker’s noise dose across a full shift. By collecting decibel data, managers can verify hazards. Sound exposure limits guide corrective actions by indicating when to implement new noise controls or strengthen existing measures.
Noise level testing involves measuring sound levels in workplaces to determine if they meet or exceed specific action thresholds, typically set at 80, 85, and 87 decibels (dBA). Employers conduct these tests to assess the noise exposure of employees and ensure compliance with safety limits established by regulatory bodies or standards organizations. The process follows international standards like ISO 1999:1990, which provides guidelines for assessing occupational noise dose and estimating the risk of noise-induced hearing impairment.
Regular noise level testing is particularly important in high-risk industries, such as manufacturing, construction, and entertainment, where elevated noise levels are common. Occupational noise measurement equipment includes:
- Sound level meters (SLMs) are hand-held devices specifically designed to measure noise levels in various environments, including workplaces. They are commonly used to assess hazardous noise levels, identify loud noise sources, and determine compliance with occupational safety standards. SLMs measure sound pressure levels in decibels (dBA), which align closely with human hearing sensitivity.
- Noise dosimeters are small devices designed to be worn by workers throughout their work shifts to measure their personal exposure to noise. These devices calculate the noise dose, which accounts for both the sound levels experienced and the duration of exposure. Unlike standard hand-held meters that measure noise in specific locations, noise dosimeters track the total noise a worker encounters over time, providing a more accurate assessment of their individual risk. Noise dosimeters are especially useful in environments where workers move between areas with varying noise levels, such as construction sites, factories, or event venues.
Regulatory Standards
National Institute for Occupational Safety and Health (NIOSH), Occupational Safety and Health Administration (OSHA), Mine Safety and Health Administration (MSHA), Federal Railroad Administration (FRA) have all set standards on hazardous occupational noise in their respective industries.OSHA regulates workplace noise levels through an action level of 85 dBA (8-hour TWA).
In the United States, noise exposure regulations are established by OSHA 29 CFR 1910.95 1983. This standard is based on the earlier Walsh-Healey Act of 1969. Above 85 dBA, employers are required to develop and implement a hearing conservation program that includes all types of noises between 80 and 130 dB, including impulsive noise. Instruments must be calibrated appropriately and regularly, and workers must be notified of the risks and allowed to observe.
An audiometric program must be undertaken, and records of all results must be retained for 2 years for measurements and for the duration of employment for audiometric records. Above 90 dBA, noise reduction engineering must be undertaken, and the noise output from specific machines or processes must be reduced. NIOSH and the CDC collaborate to research workplace risks and produce guidelines to protect workers’ hearing.
The Control of Noise at Work Regulations 2005 are a set of regulations in the United Kingdom that require employers to prevent or reduce risks to their employee’s health and safety from exposure to hazardous noise. The regulations require employers to carry out risk assessments to determine the level of sound in the workplace, take appropriate action for hearing loss prevention by providing training and information to employees. The regulations set out specific decibel limits and action values, which determine the level of risk and the necessary actions to be taken. The regulations also require employers to take a ‘buy quiet’ approach, where possible, and maintain machinery and noise-control equipment.