NIOSH Program Portfolio

Hearing Loss Prevention

Inputs: Occupational Safety and Health Risks

Nonfatal injuries and illnesses

Occupational hearing loss is one of the most common work-related illnesses. Depending on the definition of exposure and impairment, NIOSH estimates that there are between 5 and 30 million workers in the U.S. who are exposed to noise levels at work that put them at risk of hearing loss.  An additional 9 million may be at risk due to exposure to ototoxic chemicals.  There is little data regarding details associated with the number of workers with occupational hearing loss.  This is because there has been no requirement, and hence no mechanism, for recording such data.

However, in the 1998 revised criteria for a recommended standard for occupational noise exposure, NIOSH researchers published risk estimates for hearing loss as a function of years of exposure and noise exposure level.  As shown in Table 1, the 1997 NIOSH analysis of those frequencies likely to be affected by noise (1, 2, 3, and 4 kHz; see highlighted column) demonstrates 1 in 4 workers (25%) will become hearing impaired at exposures to 90 dBA.  By comparison, 1 in 12 workers (8%) are at risk of becoming hearing impaired at exposures to 85 dBA.  The risk does not approach zero until exposures approximate 80 dBA. 

Table 1.  Comparison of models for estimating the excess risk of hearing impairment at age 60 after a 40-year working lifetime of exposure to occupational noise (exchange rate in parentheses).
	.5-1-2 kHz Definition					1-2-3 kHz Definition			1-2-3-4 kHz Definition
Average Exposure Level (dBA)	1971- ISO (3)	1972-NIOSH (5)	1973-EPA (3)	1990-ISO (3)	1997-NIOSH (3)	1972-NIOSH (5)	1990-ISO (3)	1997-NIOSH (3)	1990- ISO (3)	1997-NIOSH (3)
90	21	29	22	3	23	29	14	32	17	25
85	10	15	12	1	10	16	4	14	6	8
80	0	3	5	0	4	3	0	5	1	1

Source: Chapter 2, “Basis for the Exposure Standard", Criteria for a Recommended Standard:  Occupational Noise Exposure – Revised Criteria, 1998

Additionally, as part of the NIOSH Project SENSOR surveillance effort, a limited amount of data on other aspects of occupational hearing loss has also been gathered. In partnership with the Michigan Department of Labor and Economic Growth and Michigan State University  (http://oem.msu.edu/sensor.asp), NIOSH has also published data on the distribution of hearing loss by age and industry (see Figures 1 and 2):

Figure 1. Distribution of noise-induced hearing loss cases in Michigan by age of patient

 

Source: NIOSH Worker Health Chartbook, 2004 DHHS (NIOSH) Publication 2004-146
http://www2.cdc.gov/NIOSH-Chartbook/imagedetail.asp?imgid=72

Figure 2.  Distribution and number of permanent hearing loss cases reported by clinicians in Michigan, by industry, 2000

Source: NIOSH Worker Health Chartbook, 2004 DHHS (NIOSH) Publication 2004-146
http://www2.cdc.gov/NIOSH-Chartbook/imagedetail.asp?imgid=73

Sector

Until recently, there was no requirement to record and track occupational hearing loss. However, in response to NIOSH recommendations, OSHA updated requirements in 2003 for recording occupational illness and injury. A new regulation (29 CFR 1910.04 mandated that beginning in 2004 occupational hearing loss must be recorded on the OSHA Log 300. In November of 2005 the Bureau of Labor Statistics reported the results for this first year of recording occupational hearing loss (Figure 3). Figure 3 depicts the percentage of recordable hearing loss by work sector (2-digit NAICS).

Figure 3.  Percentage of recordable hearing loss for NAICS 2-digit work sector (rounded to nearest percent): mining, 1%; construction, 1%; professional services, 1%; education and health, 1%; manufacturing, 84%; transportation, 11%.

Of the 28,400 cases of occupational hearing loss recorded in 2004, the majority were from the manufacturing sector. The number of recorded cases of hearing loss is likely to be an underestimate of work-related hearing loss cases for several reasons. First, the OSHA criteria for a significant decrease in hearing from a worker’s baseline hearing test, a standard threshold shift (STS), is much lower than the criteria needed to record changes on an OSHA Log 300.  An STS is a change of 10 dB or more averaged across 2, 3, and 4 kHz.  To be recordable, the average change from audiometric zero must be 25 dB.  OSHA provides a more detailed description of these criteria at http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9641. 
Additionally, it should be noted that hearing loss may not be well documented in the construction sector because these workers are not required to be given hearing tests.  Finally, only the small number of workers in the mining sector who are covered by OSHA (rather than MSHA) would have qualifying hearing losses recorded on an OSHA Log 300.  Nevertheless, the new requirement to record work-related hearing loss is a major improvement in our ability to monitor the incidence of occupational hearing loss.

Additional BLS data on work-related hearing loss can be found here:
http://www.bls.gov/iif/oshwc/osh/os/ostb1481.pdf

NIOSH Program:

Hearing Loss Prevention

Program Description
Inputs
• Occupational Risks
• National Research Agenda (NORA)
• NIOSH Strategic Goals
• Emerging Issues
• Partners
• NIOSH Contacts
Activities
• NIOSH Research Projects
Outputs
• Publications
• Topic Pages
• Products
• Research to Practice
• Conferences
Outcomes
Review & Evaluation
• Program Review
• National Academies Evaluation