This calculator has been added to show the student how selection of different frequencies can give widely different results 



In 1997 NIOSH defined "material hearing impairment as an average of the HTLs for both ears that exceeds 25 dB at 1000, 2000, 3000, and 4000 Hz".    Because of this we offer a calculator which uses these frequencies coupled with the AMA formula for high and low fences and weighting between ears.  The Federal Employee Compensation Act (FECA) uses a similar methodology of coupling the 1972 NIOSH frequencies with the AMA formula for calculating hearing impairment.   

FECA may someday revise their formula to use the 1997 NIOSH frequencies.  The 1997 NIOSH frequencies are weighted towards the maximum area of audiometric loss for noise exposure.  (In noise induced hearing loss, the high-frequencies are effected more than the low and the loss is often maximum at 4000 Hz.)  In my opinion all three of the pure-tone-average  frequencies of 500 Hz, 1000 Hz and 2000 Hz, which are correlated with speech reception should be used in determining hearing handicaps.   The "impairment" as determined by the 1997 NIOSH calculator verses the AAO-79 calculator will be expected to be much more severe.   In some of my patients, the difference is as much as 25%.  Thus, if the 1997 NIOSH calculator is adopted, disability payments and total body handicap calculations should be modified.

The Following are excerpts from DHHS (NIOSH) Publication No. 98-126 (Published in 1997)

Prince et al. [1997] (reprinted in the Appendix of this document) derived a new set of excess risk estimates using the ONHS data with a model referred to as the "1997-NIOSH model," which differed from the 1972-NIOSH model [NIOSH 1972]. A noteworthy difference between the two models is that Prince et al. [1997] considered the possibility of nonlinear effects of noise in the 1997-NIOSH model, whereas the 1972-NIOSH model was based solely on a linear assumption for the effects of noise. Table 3-2 provides an overview of the differences between the 1997- and the 1972-NIOSH models. Prince et al. [1997] found that nonlinear models fit the data well and that the linear models similar to the 1972-NIOSH model did not fit as well. In addition to using the 0.5-1-2-kHz and the 1-2-3-kHz definitions of material hearing impairment to assess the risk of occupational NIHL, Prince et al. [1997] used the definition of hearing handicap* proposed by the American Speech-Language-Hearing Association (ASHA) Task Force on the Definition of Hearing Handicap. Prince et al. [1997] found the ASHA Task Force definition (average of HTLs at 1000, 2000, 3000, and 4000 Hz) [ASHA 1981] useful because it was geared toward excess risk of hearing loss rather than compensation. Phaneuf et al. [1985] also found that the audiometric average of 1000, 2000, 3000, and 4000 Hz provided "a superior prediction of hearing disability in terms of specificity, sensitivity, and overall accuracy." The ASHA Task Force definition is also referred to as the 1-2-3-4-kHz definition in this criteria document. Table 3-3 presents the excess risk estimates for this definition and associated 95% confidence intervals.

As mentioned earlier in this section, the protection goal incorporated in the definitions of material hearing impairment has been to preserve hearing for speech discrimation. The 4000-Hz audiometric frequency is recognized as being both sensitive to noise and important for hearing and understanding speech in unfavorable or noisy listening conditions [Kuzniarz 1973; Aniansson 1974; Suter 1978; Smoorenburg 1990]. In recognition of the fact that listening conditions are not always ideal in everyday life, and in concurrence with the ASHA [1981] Task Force proposal, NIOSH has modified its definition of material hearing impairment to include 4000-Hz when assessing the risk of occupational NIHL. Therefore, with this modification, NIOSH defines material hearing impairment as an average of the HTLs for both ears that exceeds 25 dB at 1000, 2000, 3000, and 4000 Hz. Based on this definition, the excess risk is 8% for workers exposed to an average daily noise level of 85 dBA over a 40-year working lifetime. NIOSH continues to recommend the REL of 85 dBA as an 8-hr TWA on the basis of (1)analyses supporting the 1972 REL of 85 dBA as an 8-hr TWA, (2) reanalyses of the ONHS data, (3) ASHA Task Force positions on preservation of speech discrimination, and (4) analyses of excess risk of ISO, EPA, and NIOSH databases.

Noise Induced Hearing Loss References:  Go To NIOSH References

Go To Power Point Occupational Hearing Loss Lecture

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