Hearing Health Risk in a Population of Aircraft Carrier Flight Deck Personnel

Military Medicine, Jun 2004 by Rovig, Glen W, Bohnker, Bruce K, Page, John C

This study evaluated the risk to hearing health associated with duty on the flight deck of a Nimitz class aircraft carrier. Descriptive data includes time-weighted average noise exposure and an evaluation of temporary threshold shift for a group of nonaviator flight deck personnel (FD), and a comparison of accrued permanent threshold shift among three shipboard occupational groups that had been matched for years of military service. The study participants included 76 FD personnel in a high-exposure group, 77 engineers in a moderate-exposure group, and 52 administrative personnel who were considered to have low occupational noise exposure. The study found a mean FD time weighted average of 109 dBA over workdays averaging 11.5 hours. Only 2 (4%) of 52 administrative personnel had any appreciable hearing loss (defined as worse than 20 dB at any frequency 1,000 through 4,000 Hz), whereas FD and engineers demonstrated 17% and 27% hearing impairment, respectively.

Introduction

Occupational noise exposure is a pervasive health risk within the Navy and Marine Corps, with an estimated 350,000 military and civilian personnel routinely exposed to hazardous workplace noise. In 1995, Wolgemuth et al.1 noted a 29% incidence of hearing threshold shift among more than 12,492 file audiograms from Atlantic Fleet Sailors. We previously reported that 18% of 54,057 file audiograms demonstrated significant threshold shift and that Navy male sailors developed hearing loss at a faster rate than civilians in similar age groups.2,3 Exposure to hazardous noise has been associated with a variety of military-specific occupations. An aircraft carrier flight deck during flight operations is perhaps the single most noise-hazardous work environment in the Department of the Navy. Dozens of personnel work in close proximity to multiple aircraft generating 140 dBA or more of recurring noise during workdays that may exceed 14 hours. There has been no focused evaluation of hearing health risk among flight deck personnel (FD), although a 1973 Technical Memorandum reported that the flight helmet (with incorporated earmuffs) provided adequate protection against aircraft noise of that era.4

Background

The purpose of this study was to determine whether FD are at greater risk of developing a hearing loss than selected other occupational groups aboard a Nimitz Class aircraft carrier. All FD wear headgear called "cranials," which include earmuffs with a noise reduction rating of 23.5 Current occupational health and safety policy for Navy Forces Afloat requires double hearing protection when noise environments exceed 104 dBA.6 Navy Medical Department policy estimates 30 dB of protection from double protection, suggesting the probability of overexposure in sustained 140 dBA environments. The combination of extended workdays and persistent overexposures predicts a high incidence of hearing loss among FD.

Methods

all data were collected during two at-sea periods of carrier qualifications in the summer of 2000 using a protocol approved by the Institutional Review Board from the Naval Medical Center Portsmouth Virginia. The carrier qualification operations for new and requalifying pilots provided a robust noise environment for study, with more than 200 launches and recoveries of aircraft daily. FD volunteers were solicited with outstanding cooperation from the ship's Air, Medical, and Safety Departments. Participants were typically aircraft handlers, aviation weapons handlers, aircraft catapult launch crew members, and aircraft refuelers. Participation was limited to those with at least 2 years of service to facilitate identification of possible accrued hearing loss. Each FD volunteer completed a questionnaire and signed a release before participation. The questionnaire solicited information about hearing-related complaints and off-duty noise exposure (e.g., personal listening devices and shooting). Other than four engineering personnel (ENG) who contributed dosimetry and temporary threshold shift (TTS) data, ENG and administrative personnel (ADMIN) were passive participants whose health records provided hearing threshold data for comparison. The study size was limited by the number of experienced FD available. As such, statistical significance was rarely achieved and is not reported.

Dosimetry Data

Ten Larson-Davis model 705 dosimeters were used, limiting daily participants to that number. FD and ENG volunteers presented at the ship's Medical Department before flight operations began on the day they were to be monitored/tested.

Dosimeters were clipped on each subject's belt, with the microphone (windscreen attached) clipped to the collar at approximately ear level. Participants were cautioned to leave the dosimeter in place all day, including meal breaks, and to report back to Medical immediately after being released from their work stations at the end of the duty day. Dosimeters were turned off at that time, and data were uploaded for later analysis. Seventy-two sets of FD dosimetry data and four sets of ENG data were collected. Data analyzed for the study included the 8-hour time-weighted average (TWA), total minutes the dosimeter was in place (inclusive of breaks), and the approximate interval between noise exposure and post-test. Dosimetry results are presented using the Department of Defense (DoD) standard of an 85 dBA allowable exposure during an 8-hour workday, with a 3-dB time-intensity exchange.7 Unless otherwise described, data represent environmental readings (unprotected) as opposed to at the plane of the eardrum (protected).