Occupational hearing loss

Exposure to noise can cause vibrations able to cause permanent damage to the ear. Both the volume of the noise and the duration of exposure can influence the likelihood of damage. Sound is measured in units called decibels, which is a logarithmic scale of sound levels that corresponds to the level of loudness that an individual's ear would perceive. Because it is a logarithmic scale, even small incremental increases in decibels correlate to large increases in loudness, and an increase in the risk of hearing loss.

Sounds above 80 dB have the potential to cause permanent hearing loss. The intensity of sound is considered too great and hazardous if someone must yell in order to be heard. Ringing in the ears upon leaving work is also indicative of noise that is at a dangerous level. Farming, machinery work, and construction are some of the many occupations that put workers at risk of hearing loss.

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. NIOSH established the REL for occupational noise exposures to be 85 decibels, A-weighted (dB[A]) as an 8-hour time-weighted average.[16] Occupational noise exposure 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. 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.

OSHA's current permissible exposure limit (PEL) for workers is an average of 90 dB over an 8-hour work day. Unlike NIOSH, OSHA uses a 5-dB exchange rate, where an increase in 5-dB for a sound corresponds to the amount of time workers may be exposed to that particular source of sound being halved. For example, workers cannot be exposed to a sound level of 95 dB for more than 4 hours per day, or to sounds at 100 dB for more than 2 hours per day. Employers who expose workers to 85 dB or more for 8 hour shifts are required to provide hearing exams and protection, monitor noise levels, and provide training.

The NIOSH Sound Level Meter app

Sound level meters and dosimeters are two types of devices that are used to measure sound levels in the workplace. Dosimeters are typically worn by the employee to measure their own personal sound exposure. Other sound level meters can be used to double check dosimeter measurements, or used when dosimeters cannot be worn by the employees. They can also be used to evaluate engineering controls aimed at reducing noise levels.

Some recent studies suggest that some smartphone applications may be able to measure noise as precisely as a Type 2 SLM.[17][18] Although most smartphone sound measurement apps are not accurate enough to be used for legally required measurements, the NIOSH Sound Level Meter app met the requirements of IEC 61672/ANSI S1.4 Sound Level Meter Standards (Electroacoustics - Sound Level Meters - Part 3: Periodic Tests).[19]

Chemically induced hearing loss (CIHL) is a potential result of occupational exposures. Certain chemical compounds may have ototoxic effects. Exposure to organic solvents, heavy metals, and asphyxiants such as carbon monoxide can all cause hearing loss.[20][21] These chemicals can be inhaled, ingested, or absorbed through the skin. Damage can occur to either the inner ear or the auditory nerve. Certain medications may also have the potential to cause hearing loss.[22]

Both noise and chemical exposures are common in many industries, and can both contribute to hearing loss simultaneously.[23] Damage may be more likely or more severe if both are present, in particular if noise is impulsive.[24][25] Industries in which combinations of exposures may exist include construction, fiberglass, metal manufacturing, and many more.[22]

It is estimated that over 22 million workers are exposed to dangerous noise levels, and 10 million are exposed to solvents that could potentially cause hearing loss every year, with an unknown number exposed to other ototoxic chemicals.[21] A 2018 informational bulletin by the US Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) introduces the issue, provides examples of ototoxic chemicals, lists the industries and occupations at risk and provides prevention information.

NIOSH Hierarchy of Controls

The hierarchy of controls provides a visual guide to the effectiveness of the various workplace controls set in place to eliminate or reduce exposure to occupational hazards, including noise or ototoxic chemicals. The hierarchy includes the following from most effective to least effective:

• Elimination: complete removal of the hazard
• Substitution: replacement that offers a smaller risk
• Engineering controls: physical changes to reduce exposure
• Administrative controls: changes in work procedures or training
• Personal protective equipment (PPE): individual equipment to reduce exposure, e.g. earplugs [27][28]

Engineering controls is the next highest in the hierarchy of risk reduction methods when elimination and substitution of the hazard are not possible. These types of controls typically involve making changes in equipment or other changes to minimize the level of noise that reaches a worker's ear. They may also involve measures such as barriers between the worker and the source of the noise, mufflers, regular maintenance of the machinery, or substituting quieter equipment.[29][30]

The OSHA Technical Manual (OTM) on noise provides technical information about workplace hazards and controls to OSHA's Compliance Safety and Health Officers (CSHOs).[31] The content of the OTM is based on currently available research publications, OSHA standards, and consensus standards. The OTM is available to the public for use by other health and safety professionals, employers, and anyone involved in developing or implementing an effective workplace safety and health program.Examples of noise control strategies adopted in the workplace can be seen among the winners of the Safe-in-Sound Excellence in Hearing Loss Prevention Awards.

Administrative control, behind engineering control, is the next best form of prevention of noise exposure.[29] They can either reduce the exposure to noise, or reduce the decibel level of the noise itself. Limiting the amount of time a worker is allowed to be around an unsafe level of noise exposure, and creating procedures for operation of equipment that could produce harmful levels of noise are both examples of administrative controls.[30]

Elimination or reduction of the source of noise or chemical exposure is ideal, but when that is not possible or adequate, wearing personal protective equipment (PPE) such as earplugs or earmuffs can help reduce the risk of hearing loss due to noise exposure. PPE should be a last resort and not be used in substitution for engineering or administrative controls. It is important that workers are properly trained on the use of PPE to ensure proper protection.[30] A personal attenuation rating can be objectively measured through a hearing protection fit-testing system.

In addition to the hierarchy of controls, other programs have been created to promote the prevention of hearing loss in the workplace. For example, the Buy Quiet program was created to encourage the purchase of quieter tools and machinery in the workplace.[32] Additionally, the Safe-n-Sound Award was created to recognize organizations that excel in preventing occupational hearing loss.[33]