logo AMERICAN COLLEGE OF OCCUPATIONAL AND ENVIROMENTAL MEDICINE
logo AMERICAN COLLEGE OF OCCUPATIONAL AND ENVIROMENTAL MEDICINE
Occupational Medicine
A Basic Guide

03: Medical Surveillance

Hearing Conservation
Marco Britton , MD

Noise-induced hearing loss (NIHL) is one of the most common occupational disorders in the United States. The Centers for Disease Control and Prevention estimates that 22 million workers are exposed to unsafe noise levels yearly, and 19% of these workers are hearing impaired.(1) Hearing loss often occurs over a period of time as a result of repeat exposure to high noise levels and is permanent. However, brief exposures to loud noises tend to cause temporary loss that returns to baseline after a period of rest. NIHL is preventable. As such, the Occupational Safety and Health Administration (OSHA) has created the Occupational Noise Exposure standard that guides industries in hearing-conservation efforts.

 

Hearing loss also can be produced by chemicals, drugs, and metals (“ototoxins”) with which people come in contact in the workplace. In many cases, the mechanism of injury is not fully understood by the medical community, and more research needs to be performed. The American Conference of Governmental Industrial Hygienists recommends periodic testing for employees exposed to ototoxins, but currently there is no standard that addresses ototoxic chemicals in the workplace.(2) Federal regulations acknowledge only noise as a risk factor for workplace hearing loss.

 

In addition to identifying work-related causes of hearing loss, medical providers should also consider non-occupational exposures, which can both cause and exacerbate hearing loss.

 

Noise-Induced Hearing Loss

 

Continuous exposure to loud sounds results in NIHL. OSHA considers noise levels at or above 85 dB to be hazardous to hearing and damage structures within the inner ear over time.(2, 3) Due to the gradual nature of NIHL hearing loss, employees may not notice it until several years after the exposure. Thus, proper hearing protection and frequent monitoring is necessary (see below).

 

Brief exposures to intense sound blasts can also lead to NIHL, which may be either temporary or permanent. In the workplace, explosions, which release over-pressurized waves, are a common cause of sound blasts.(4) The impact of the waves ruptures the tympanic membrane, disrupts ossicles, and damages the cochlea. The extent of damage generally depends on the intensity of the sound and the resultant wave produced.

 

Ototoxic Chemicals

 

In the United States, an estimated 10 million workers in diverse industries, from pharmaceuticals to construction, are exposed to ototoxic chemicals that can damage inner-ear structures.(1) Therapeutic agents such as aspirin, diuretics, antibiotics, and chemotherapeutic medications, in addition to heavy metals and various other chemicals, are among them. It is not fully known how these substances cause inner-ear damage, but researchers have proposed possible explanations. For one, antibiotics such as aminoglycosides that are able to cross the blood-labyrinth barrier are thought to induce hair cell death by disrupting intracellular processes. In addition to hair cell damage, these agents also damage the central nervous system, including portions involved in hearing.(5)

 

Non-Occupational Exposures

 

Non-occupational exposures must also be considered as possible causative and contributory factors to hearing loss. Recreational activities such as hunting and target shooting, listening to loud music, and participating in motorsports can also contribute to hearing loss. Medical providers should be aware of their patients’ participation in such activities and take time to counsel patients on wearing hearing protection every time they are engaged in them. When evaluating patients, clinicians should also consider medical conditions that affect hearing, such as infectious diseases, genetic disorders, neurologic disorders, strokes, head injuries, and auditory and central nervous system neoplasm.

 

Occupational Noise Exposure Standard:

 

OSHA addresses hearing conservation in the Occupational Noise Exposure standard (1910.95), which guides employers and providers in assessing noise exposure in the workplace. The standard requires industries to reduce noise levels for workers who are exposed to 85 dB or greater during an eight-hour period. It also outlines various other PELs based on the number of hours the employee is exposed to noise per day.

 

Employees who are constantly exposed to 85 dB of sound over an eight-hour working period (called an eight-hour time-weighted average) must be monitored annually, and employers must provide audiometric testing free of charge. Testing starts with a baseline audiogram, which usually takes place during the preplacement examination, but employers are given up to six months from the employee’s first exposure to an eight-hour time-weighted average of 85dB to provide it.

 

Annual audiograms allow hearing decline to be identified and guides employers to supply employees with proper protection. Each audiogram is compared to baseline to detect whether there has been a standard threshold shift (STS)—an average change in either ear of 10 dB or greater at 2,000, 3,000, and 4,000 hertz.2, 6 If an STS is indicated, then the employer must retrain the worker to use the hearing protection equipment and require the employee to wear it. The employer has 21 days to notify the employee of the STS.

 

In addition to annual audiograms, repeat testing is required when workplace noise exposure levels change, to ensure that adequate hearing protection is provided.

 

Failure to Comply

 

Industries that fail to comply with the Occupational Noise Exposure standard risk accruing fines. Employees who fail to comply with company rules pertaining to hearing conservation are at risk for various repercussions, including disciplinary action and termination. Each company has its own policies thus employees should be encouraged to familiarize themselves with them.

 

Primary care providers play a vital role in employee hearing conservation efforts. At each clinic visit, a brief hearing history should address the duration and types of noises patients are exposed to. Providers should also assess whether protective hearing equipment is required on the job and whether the employee is compliant. Recreational activities, such as hunting, target shooting, and motor sports, should also be explored. Providers can use clinic visits as opportunities for educating patients on the importance of avoiding loud noises when possible and wearing hearing protection when needed.

References:

 

  1. Center for Disease Control and Prevention. Worker Hearing Loss. Available at: https://www.cdc.gov/features/worker-hearing-loss/index.html. Accessed February 20, 2018
  2. Levy B, Wegman D, Baron S, et al. Occupational and Environmental Health: Recognizing and Preventing Disease and Injury, 6th Edition, Oxford University Press 2011, Pages 461-475
  3. Occupational Safety & Health Administration. Occupational Safety and Health Standards: Occupational noise exposure. Available at: https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9735. Accessed February 20, 2018
  4. Center for Disease Control and Prevention. Explosions and Blast Injuries. Available at: https://www.cdc.gov/masstrauma/preparedness/primer.pdf. Accessed March 10, 2018
  5. Kirchner, D, et al. ACOEM Guidance Statement: Occupational Noise-Induced Hearing Loss. JOEM. 2012; 54: 106-108. Available at: https://www.acoem.org/uploadedFiles/Public_Affairs/Policies_And_Position_Statements/Occupational% 20Noise-Induced%20Hearing%20Loss.pdf. Accessed February 27, 2018
  6. Occupational Safety & Health Administration. Hearing Conservation. Available at: https://www.osha.gov/Publications/OSHA3074/osha3074.html. Accessed March 10, 2018