Pure Tone Audiometry Evaluation Method Effectiveness in Detecting Hearing Changes Due to Workplace Ototoxicant, Continuous Noise, and Impulse Noise Exposures.

OBJECTIVES: The purpose of this retrospective cohort study was to compare the relative risks (RR) of hearing impairment due to co-exposure of continuous noise, impulse noise, metal ototoxicants, and organic solvent ototoxicants using several pure tone audiometry (PTA) evaluation methods. DESIGN: Noise and ototoxicant exposure and PTA records were extracted from a DoD longitudinal repository and were analyzed for U.S. Air Force personnel (n = 2372) at a depot-level aircraft maintenance activity at Tinker Air Force Base, Oklahoma using an historical cohort study design. Eight similar exposure groups based on combinations of ototoxicant and noise exposure were created: (1) Continuous noise (reference group); (2) Continuous noise + Impulse noise; (3) Metal exposure + Continuous noise; (4) Metal exposure + Continuous noise + Impulse noise; (5) Solvent exposure + Continuous noise; (6) Solvent exposure + Continuous noise + Impulse noise; (7) Metal exposure + Solvent exposure + Continuous noise; and (8) Metal exposure + Solvent exposure + Continuous noise + Impulse noise. RR of hearing impairment compared to the Continuous noise-exposed reference group was assessed with five PTA evaluation methods including (1) U.S. Department of Defense (DoD) Significant Threshold Shift (STS), (2) Occupational Safety and Health Administration (OSHA) age-adjusted STS, (3) National Institute for Occupational Safety and Health (NIOSH) STS, (4) NIOSH Material Hearing Impairment, and (5) All Frequency Threshold Average. RESULTS: Hearing impairment was significantly worse for SEG (2) combined exposure to continuous noise and impulse noise only for the PTA evaluation method (2) OSHA Age Adjusted with an RR of 3.11, [95% confidence interval (CI), 1.16-8.31] and was nearly significantly different using PTA evaluation method (4) NIOSH Material Hearing Impairment with an RR of 3.16 (95% CI, 0.99-10.15). Despite no significant differences for SEGs with an ototoxicant exposure, PTA evaluation method (3) NIOSH STS was most sensitive in detecting hearing changes for SEG (8) Metal exposure + Solvent exposure + Continuous noise + Impulse noise as demonstrated by a RR of 1.12 (95% CI, 0.99-1.27). CONCLUSIONS: Results suggest that a single PTA evaluation technique may not be adequate in fully revealing hearing impairment risk due to all stressors and tailoring the PTA evaluation technique to the hazards present in the workplace could better detect hearing impairment. Additionally, results suggest that PTA may not be effective as the sole technique for evaluating hearing impairment due to ototoxicant exposure with continuous noise co-exposure.

Sound Level Measurements in Berthing Areas of an Aircraft Carrier.

BACKGROUND: Personnel assigned to aircraft carriers work and live in environments where hazardous noise areas and hearing recovery spaces such as sleeping areas are in close proximity to one another. Hazardous noise exposure occurring during on-duty time periods and elevated noise levels during off-duty periods in sleeping areas may be prohibiting adequate hearing recovery, thus potentially leading to hearing loss and may lead to adverse effects on sleep, leading to crew-member fatigue. This investigation characterizes Equivalent sound level (Leq) and standardized octave band center frequency noise levels according to berthing (sleeping) area location during flight operation and nonflight operation time periods on a US Navy aircraft carrier. In addition, the investigation compares noise measurements in sleeping areas to noise levels associated with auditory rest and poor sleep quality and quantity. METHODS: Noise levels were measured in berthing areas aboard a US Navy Nimitz-class aircraft carrier during a routine at-sea period. Sixty noise measurements were taken in eight sleeping locations. Leq in decibels 'A' weighted (dBA) and noise levels from 16 to 16 000 Hz in (dB) were measured during flight operations [Leq (flt ops)] and nonflight operations [Leq (nonflt ops)]. Leq was also measured according to sleep area shipboard locations of forward (FWD) Leq (FWD), middle (MID) Leq (MID), and rear (AFT) Leq (AFT). These data were compared to the 70 dBA American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) for effective quiet areas. In addition, these data were compared to noise levels associated with hearing loss and sleep parameters. Statistical analysis was conducted with R version 3.5.2 using an alpha level of 0.05. RESULTS: Leq (flt ops) in sleeping areas was a statistically significant (P < 0.05) 6.4 dBA higher than the Leq (nonflt ops). Leq (FWD) and Leq (MID) in sleeping areas was a statistically significant (P < 0.05) 15.2 and 15.0 dBA higher, respectively, than the Leq (AFT) noise levels. Mean noise levels at standardized center (1/1) octave bands were highest between 500 and 4000 Hz, ranging from 65.2 to 69.8 dB. A total of 72% of all area Leq measurements exceeded the 70 dBA ACGIH TLV classified as effective quiet to allow for temporary threshold shift recovery. All noise measurements exceeded the World Health Organization's noise threshold where adverse effects on sleep begin. DISCUSSION/CONCLUSIONS: Results suggest that sleeping area location in close proximity to relatively high noise sources and activities occurring on an aircraft carrier (i.e. flight operations) increase noise levels in sleeping areas. These findings raise serious concerns since high noise exposures both on duty and during off-duty/sleeping periods may inhibit auditory recovery from hazardous noise exposures. In addition, results suggest noise levels in sleeping areas are high enough to evoke negative sleep effects.

Living at Work: 24-hour 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.

Chemical-Induced Hearing Loss in Shipyard Workers.

OBJECTIVE: The aim of this study was to determine the effect of lead, cadmium, arsenic, toluene, and xylene exposure on hearing compared with noise exposures alone. METHODS: Personnel at a shipyard (n = 1266) were divided into four exposure groups on the basis of concentrations: low metals/low solvents/high noise (reference group), high metals/high solvents/low noise, high metals/low solvents/high noise, and high metals/high solvents/high noise. Hearing changes occurring from the years 2004 to 2015 were analyzed. RESULTS: Hearing changes were significantly worse at 1000 Hz (P = 0.007), averaged across 2000 to 4000 Hz (P = 0.014), and averaged across 500 to 6000 Hz (P = 0.014) for the high metals/high solvent/high noise group compared with the low metals/low solvents/high noise only reference group. CONCLUSION: Simultaneous exposures classified as high for metals/solvents/noise appear to damage hearing more than exposure to noise alone. Hearing conservation programs should take into consideration combined exposures to metals, solvents, and noise, not simply exposure to noise.