Page 32 - OHS, May 2021

INDUSTRIAL HYGIENE
Evaluating Occupational Noise Exposures
Hearing loss can be amplified by noise and chemicals.
NBY GREGORY BOOTHE, PH.D.
oise induced hearing loss (NIHL) is a fairly common illness. According to statistics reported by OSHA in 2010, NIHL accounted for approximately 12 percent of
1 allrecordableillnessesintheUnitedStates. Thisequated
to approximately 18,748 NIHL cases reported for that year (Figure 1), and may be lower than the number of actual cases.
To identify areas of concern, many safety professionals and industrial hygienists use a sound level meter (SLM) to identify areas in a facility where noise levels exceed 85 dBA. The 85 dBA level is used because it is the action level set by OSHA for an eight- hour shift and the threshold limit value (TLV) set by the American Conference of Governmental Industrial Hygienists (ACGIH). OSH professionals who have worked with noise exposures know the 85 dBA level is just the action level for an eight-hour shift and must be adjusted for extended work shifts to determine the 50 percent dose or the dose where the exposure is 50 percent of the OSHA permissible exposure level (PEL) (90 dBA).
Since sound levels are measured on a logarithmic scale, determining the 50 percent dose is not as simple as dividing an exposure in half. It is complicated further by the use of a 5 dB doubling scale by OSHA and a 3 dB doubling scale by the ACGIH and National Institute for Occupational Safety and Health (NIOSH). Using the OSHA formula, we can determine that the action level for a 10-hour shift is 83.4 dBA and the action level for a 12-hour shift is 82.1 dBA.
Consider Additional Exposures
Once areas of the facility with potential high-noise exposures are identified, most noise evaluations will then include personal sampling using noise dosimeters. Based on the results of the noise dosimetry, individuals are typically included in a formal hearing conservation program if their exposure exceeds the action level. Some facilities will attempt to reduce noise levels if the results exceed the OSHA PEL. Some facilities will simply provide hearing protection and not attempt to reduce noise levels.
In fact, few facilities consider any exposures other than the recorded noise levels when addressing NIHL. There are other
Table 1
potential exposures that should be considered when assessing the risk of NIHLs in a facility, including chemicals. Many chemicals have been identified with the potential to increase the risk of hearing loss even without high-noise exposures. These ototoxic chemicals have the potential to damage parts of the auditory system.2
Acute and chronic exposures to these chemicals can cause temporary or permanent hearing loss. Since this is caused by chemical exposure instead of noise exposure, this would not technically be NIHL. We might call it chemical induced hearing loss (CIHL). Many workplaces contain chemicals that are considered ototoxic. Table 1 is a list of some common ototoxic chemicals published by the National Institute for Occupational Safety and Health (NIOSH, 2018). Per the table, there are several volatile organic compounds (solvents), asphyxiants and metals that are commonly present in industrial operations in the U.S.
Types of Hearing Loss
There are two types of hearing loss: conductive and sensorineural. Conduction loss is the inability of sounds to be conducted from the outer ear to the inner ear where the nerve endings would be stimulated. Conductive hearing loss can be caused by ear infections and physical blockages, including a buildup of ear wax.
Substance Class
Chemicals
Pharmaceuticals
*Ototoxicity at therapeutic doses is limited
Aminoglycosidic antibiotics (e.g., streptomycin, gentamycin) and some other antibiotics (e.g., tetracyclines) Loop diuretics* (e.g., furosemide, ethacrynic acid)
Certain analgesics* and antipyretics* (salicylates, quinine, chloroquine)
Certain antineoplastic agents (e.g., cisplatin, carboplatin, bleomycin).
Solvents
Carbon disulfide, n-hexane, toluene, p-xylene, ethylbenzene, n-propylbenzene, styrene and methylstyrene, trichloroethylene.
Asphyxiants
Carbon monoxide, hydrogen cyanide and its salts, tobacco smoke
Nitriles
3-Butenenitrile, cis-2-pentenenitrile, acrylonitrile, cis-crotononitrile, 3,3’-iminodipropionitrile.
Metals and Compounds
Mercury compounds, germanium dioxide, organic tin compounds, lead.
28 Occupational Health & Safety | MAY 2021
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