Outputs and Transfer - Research Goal 1.3:
Achieve a better understanding of the combined effects of continuous and impulsive noise exposures
Partly as a result of the field research at Ford, the HLR program cosponsored a workshop, “Impulsive Noise: A NORA Hearing Loss Team Best Practice Workshop” in 2003. At the workshop, there was consensus that 1) impulsive noise is more hazardous than continuous noise, 2) there are presently no instruments that can accurately calculate a person’s exposure in an impulsive-noise environment, and 3) simple integration of impulsive and continuous noises below 140 dB SPL will understate the true noise burden of an environment in which both impulsive and continuous noises are present.[7]
Since the workshop, the HLR program developed a computer program for measuring the relative contributions of impulsive and continuous noise to a person’s exposure that reflects all of the methods discussed at the workshop.[8]
Partly in response to requests from Ford industrial hygienists for suggestions about how to improve the problems in their overall hearing loss prevention program, we developed “A Practical Guide to Effective Hearing Conservation Programs in the Workplace”1 that provided a template for a program that would go beyond mere compliance with OSHA regulations and establish “best practices” that would be more effective in preventing occupational hearing loss.
Within a year, Ford implemented this program. In addition to the purchase of new audiometers and new hearing conservation database management software, the new Ford hearing loss prevention program included:
- Biennial task-based noise exposure assessment at each work station.
- Pre-employment audiometry.
- Annual audiograms administered during work period instead of before work.
- Evaluation of audiogram for threshold shift at time of test.
- Scheduled retest at time of original test if there was threshold shift.
- Explanation results of at time of test, not later and not by form letter.
- Provision of a wide choice of hearing protectors and training for workers in their use.
- Provision of an educational brochure at time of test.
- Development of a plan to engineer noise out of new Ford plants, thus reducing the number of noise-exposed workers.
Further, the HLR program entered a Cooperative Research and Development Agreement (CRADA) with Larson-Davis Inc. (a noise measurement equipment manufacturer) to incorporate the algorithms into a new generation of dosimeters and integrating sound level meters. These instruments are expected to better quantify salient variables associated with impulsive noises.
Intermediate Outcomes
Partly in response to NIOSH recommendations, the international (ISO-1999) and U.S. (ANSI S3.44-1996) standards on noise exposure and noise-induced hearing loss have incorporated special procedures which may be used when impulsive noise is present. These procedures permit adding a 5-dB allowance to the measured Leq (equivalent sound level)values when impulsive noises are a substantial component of an exposure event.
Presently, the best metric of a hearing loss prevention program’s success is the annual incidence rate of Standard Threshold Shift (STS). A truly effective program would have an STS rate no higher than would be expected for the non-noise exposed general population (2.3%), based on calculations from database A of ISO-1999[9] that has since been incorporated into ANSI S3.44-1996.[10] Over the course of seven years, the STS rate at Ford was reduced from 6.8% to 3.4% (50%) as shown in Figure 3.1 below. Due to changes in staffing of Ford’s industrial hygiene and medical departments, data beyond 1997 are not available, although they may be in the future.
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[7] Kardous K, Murphy WJ (2005). New System for monitoring exposure to impulsive noise. Internoise 2005/ 34th International Congress and Exposition on Noise Control Engineering. Rio de Janeiro, Brazil, August 6-10, 2005.
[8] Kardous CA, Franks JR, Davis RR. [2005] NIOSH/NHCA Best-Practices Workshop on impulsive noise. Noise Control Eng. J. 53 (2): 53-60.
[9] International Organization for Standardization [1990]. Acoustics—determination of occupational noise exposure and estimation of noise-induced hearing impairment. 2nd ed. Geneva, Switzerland: Reference No. ISO 1999 1990.
[10] ANSI [1996]. American national standard: Determination of Occupational Noise Exposure and Estimation of Noise-Induced Hearing Impairment. New York: American National Standards Institute, Inc., ANSI S3.44-1996.