24 hr noise exposure aboard US navy aircraft carriers

Background: Personnel assigned to aircraft carriers are exposed to a variety of noise sources from equipment and flight deck operations for durations >12 h. Personnel work and live in environments where hazardous noise areas and hearing recovery spaces such as sleeping and relaxation areas are in proximity to one another which provides little recovery time from hazardous noise. This investigation describes noise levels measured over a 24-h period on a US Navy aircraft carrier during flight operations for different populations of aircraft carrier personnel. Methods: Personal noise monitoring occurred from 23 to 28 January 2014 aboard a US Navy Nimitz-class aircraft carrier during a routine at-sea period. Fifty-nine study volunteers were assigned to similar exposure groups (SEGs). The SEGs were compared to determine which groups were at greatest risk of hazardous noise exposure. Statistical analysis was conducted with SPSS version 24 using an alpha level of 0.05. Results: Mean 24-h equivalent continuous sound levels Leq(24-h) and on-duty time weighted averages (TWA(on-duty)) ranged from 71 to 127 decibels A weighted (dBA). The 80 dBA American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) for 24-h noise exposure was exceeded by 93% of the study volunteers. The 85 dBA ACGIH TLV and Department of defense Occupational exposure limit for 8-h noise exposures was exceeded by 68% of the population. Leq(off-duty) ranged from 38 to 102 dBA with 61% of the population exceeding the 70 dBA ACGIH TLV classified as effective quiet to allow for temporary threshold shift recovery. SEG 2 Flight Deck Launch and Recovery had significantly higher 24-h noise exposures than SEG 3 Damage Control Maintenance and Repair (P = 0.01), SEG 5 Supply (P = 0.01), and SEG 7 Administrative/Professional (P = 0.009). Similar results were found for TWA(on-duty) noise exposures. Median TWA(on-duty) and Leq(24-h) for SEG 2 were 16–21 dB higher than SEG 3, 5, and 7. There were no significant differences between off-duty Leq noise exposures according to SEG. Discussion/Conclusions: SEGs located on the flight deck (SEGs 1 and 2) and SEGs responsible for maintenance and repair activities (SEGs 3 and 4) supporting flight operations had the highest TWA(on- duty) and Leq(24-h). These findings raise serious concerns because high noise exposures both on- and off-duty may result in immediate acoustic trauma and development of temporary threshold shifts, which, if unresolved with auditory rest, may lead to permanent hearing loss.