Ed Nykaza - etn106@psu.edu
Tom Frank
Dept. of Acoustics
Penn State
University Park, PA 16802
Popular version of paper 2aPP8
Presented Tuesday Morning, November 11, 2003
146th ASA Meeting, Austin, TX
Hazardous workplace noise is a major problem for industries in the United States. Besides causing stress and anxiety, arousing the nervous system, and lowering work performance, hazardous noise can cause temporary and permanent hearing loss (Gelfund, 1997). Noise-induced hearing loss (NIHL) from long-term hazardous noise exposure is a permanent and irreversible hearing loss due to damaged or destroyed inner ear hair cells (Melnick, 1991). Further, the hearing loss worsens due to continued hazardous noise exposures.
In the US there are over 30 million workers exposed to hazardous noise daily, another 10 million already having a NIHL, and approximately 9 million more that are at risk of developing a NIHL (NIOSH, 1998). NIHL is the most common occupational disease in the US, and over $39 million are spent annually on worker compensation claims for NIHL (Dept. of Labor, Workers Compensation Costs Charged to Federal Employing Agencies for Hearing Loss Costs for Period July 1, 2001-June 30, 2002).
A new approach to eliminating or preventing the progression of NIHL is the Exposure Smart Hearing Protector (ESP), developed by doseBusters USA, Inc. (www.dosebusters.com). The ESP consists of left and right microphone-implanted earplugs and a dual-channel dosimeter. There are various types of earplugs that can be attached to the microphones and also an earmuff version.
The dual-channel dosimeter allows simultaneous measurement of sound pressure level from each earplug. Every second, the ESP accumulates noise dose data using the higher of the two microphone measurements. This ensures that the noise dose is not underestimated, unlike typical dosimeters that only have microphone located on one side of the body. For example, if a directional source is located on the left side of a worker and the microphone to the dosimeter is attached to the workers right shoulder, the recorded noise levels can be underestimated due to a head-shadowing effect.
In practice, the worker wears the earplug-mounted microphones in either the primary or secondary position. In the primary position, with the plugs inserted into the ear canals, the microphones measure the noise levels impinging the worker's eardrums. In the secondary position, with the earplug-mounted microphones hanging around the neck area, the microphones accumulate ambient noise levels, which have been documented to be essentially equivalent to the levels reaching the open ear. Obviously, the primary position is preferred when ambient noise levels are high, and the secondary position is preferred when ambient noise levels are low.
At the end of the work shift the cumulative microphone measurements account for protected periods and unprotected periods. This is the real innovation of the ESP: the dose measurement at the end of the work shift is actual protected dose. The ESP measurements take into account the quality of the hearing protector fit and the actual wearing time of the protector. The actual protected dose is the only quantity that is directly related to the potential of occupational noise-induced hearing loss, and the ESP is the first device capable of this measurement ("A New Approach to Hearing Conservation: The Exposure Smart Protector (ESP)," presented at Noise-Con, Cleveland, OH, 2003).
The pager-sized ESP dosimeter, typically worn in a shirt pocket, has two warning lights. When the measured noise level exceeds 85 dBA in either of the microphones, a red warning light flashes, indicating a potentially hazardous instantaneous noise level. If the plugs are in the secondary position, this indicates that the plugs should be inserted into the ears. If the plugs are in the primary position, the warning light indicates that more attenuation is required to reduce the exposure to a safe level. This can be achieved by adjusting the hearing protection for a better fit or by using a different type of hearing protector. A yellow warning light flashes when the accumulated dose equals 40%, indicating that the user is approaching the allowable dose for the shift. This instructs the worker to wear the ESP earplugs in the primary position for the rest of the shift in order to prevent the worker's exposure from exceeding a 50% dose or 85 dBA TWA. The literature indicates that there is little potential for noise-induced hearing loss for exposures under 85 dBA TWA (MSHA, 1999).
At the end of the work shift, data from each worker's ESP unit is downloaded into a personal computer via serial infrared transmission and stored in a database. Immediately following a successful download the worker's name and full-shift noise dose appear on the computer screen. These measurements should be performed daily, thereby establishing a complete noise exposure history for the worker.
The ESP methodology provides the worker with daily, immediate feedback on actual personal noise exposure. Ideally, with this information the workers will adjust their hearing protector wearing habits and lower their personal noise exposure to a safe level. Not surprisingly, initial studies show that in some cases, management intervention with the employees is required to ensure that safe exposures are maintained. Therefore, in order to increase the efficiency of using the ESP for preventing NIHL, a new ESP Supplemental Software Program (ESSP) has been developed. This program not only records workers' daily NELs, but also determines if intervention is required to ensure workers' exposures are maintained at safe levels.
The ESSP is to be used in conjunction with the ESP and was designed to assist health and safety personnel by monitoring the NELS of workers using ESPs. The ESP data management system provides a mechanism for readout, archiving, and analysis of all worker exposure information. The purpose of the ESSP is to make this approach even more user friendly, and to establish a higher level of accountability. Basically, the ESSP generates a list of workers who have either been over-exposed to noise, have failed to download data on a daily basis, or have not worn the ESP for an entire work shift. After reviewing the list of workers in violation, the safety director talks to the worker (intervenes) to find out why the worker was placed on the list. Following intervention, the safety director then enters a text explanation into the database. This provides a permanent record and establishes accountability. More importantly, solutions to these problems can be sought out quickly and efficiently, leading to the ultimate goal of eliminating or reducing the progression of NIHL.
Together, the ESP and ESSP have the potential to revolutionize occupational hearing conservation and eliminate work-related NIHL. For the first time, a distinction between occupational and non-occupational noise exposure can be made, ultimately lowering worker's compensation claims. Secondly, because noise measurements are to be taken each day, long-term studies can be performed to establish a better relationship between noise level, duration of exposure, and the risk of inducing noise damage or hearing loss. Lastly, new more stringent noise regulations can be passed, which would provide protection to all workers instead of only a percentage.
Gelfund, S.A. (1997). Essentials in Audiology, Thieme Medical Publishers, Inc., New York, NY.
Melnick, W. (1991). Hearing Loss from Noise Exposure, Chapter 18 in Handbook of Acoustical Measurements and Noise Control, edited by Harris, C.M., McGraw-Hill,Inc., New York, NY.
MSHA (1999). Health Standards for Occupational Noise Exposure; Final Rule. Mine Safety and Health Administration. 30CFR Federal Register, 49549-49634.
NIOSH (1998). Criteria for a recommended standard: Occupational noise exposure, revised criteria 1998. National Institute for Occupational Safety and Health. DHHS (NIOSH). Pub. No. 96-115, Cincinnati, OH.