Criteria For a Recommended Standard Occupational Noise Exposure
Revised Criteria 1996
*United States Codes. See USC in references.
*Any exposure time above the ceiling limit of 115 dBA shall be included in the calculation of the 8-hour time-weighted-average exposure.
*TWA = 10 x Log(D/100) + 85
1Standard Industry Classification (SIC) (Source: Anonymous )
2Numbers not available from NOES are extracted from unpublished data from the following sources: NIOSH Farm Family Health Hazard Survey (agricultural services), Mine Safety and Health Administration (mining), and U.S. Army Center for Health Promotion and Preventive Medicine (government civilian work force).
3Source: Bureau of Census 
% of Noise-Exposed Worker) x (Number of Production Workers in 1992)
*For purposes of comparison in this table, hearing impairment is defined as an average of the hearing threshold levels at 500, 1000, and 2000 Hz that exceeds 25 dB.
**Adapted from 39 Fed. Reg. 43,802 [1974b].
***Percentage with hearing impairment in an occupational-noise-exposed population after subtracting the percentage who would normally incur such impairment from other causes in an unexposed population.
1The American Speech-Language-Hearing Association makes a distribution between the terms "hearing impairment" and "hearing handicap," but for the purpose of the subsequent discussion in this criteria document, only the term "hearing impairment" is used.
2Prince et al.  found that the
excess risk estimates at exposure levels below 85 dBA were not well
defined. Insufficient data for workers with average daily exposures below
85dBA led to considerable variability in the estimation, depending on the
statistical assumptions used in the modeling.
*Adapted from ANSI .
3The selection of one-half the exposure limit as the trigger level for the HLPP has precedence in other occupational health standards, and is necessary to ensure the coverage of those workers whose time-weighted-average exposure levels may exceed the exposure limit on any given day but not everyday [NIOSH 1977; NIOSH 1978].
*Adapted from Royster .
*Adapted from Royster .
4The OSHA methods are a simplication of "NIOSH Method #2" [NIOSH 1975; Lempert 1984; NIOSH 1994].
*Adapted from Berger et al. 
N = size of test population
NRR = labelled Noise Reduction Rating
Wght = weighted on the basis of test population size