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Introduction: Psychophysical measures of wet-suit hood sound attenuation are needed to provide the diving community with guidance on protection from underwater sound., Methods: Underwater hearing thresholds were obtained from 15 male and 5 female recreational divers with and without a 3-mm thick wet-suit hood. Dives were conducted at a depth of 1 m in a large quiet anechoic pool. Thresholds were determined using a two-interval forced-choice procedure with a 0.71 probability of positive response at convergence. A 1-s pure tone was presented with a 20-ms rise and fall time at 100, 200, 250, 300, 400, and 500 Hz., Results: Without a wet-suit hood, mean thresholds decreased from 99 dB re 1 microPa at 100 Hz to 85 dB at 500 Hz. Thresholds were statistically similar at 100 to 300 Hz with and without the wet-suit hood, but were significantly increased at 400 and 500 Hz with the hood (p < 0.001)., Conclusions: In conclusion, at shallow depths, a 3-mm neoprene wet-suit hood attenuates underwater sound by approximately 10 dB for frequencies between 400 Hz and 500 Hz. At frequencies below 400 Hz, a 3-mm neoprene wet-suit hood offers no sound protection.

Increasing use of active low-frequency sonar by submarines and ships raises the risk of accidental exposure of recreational divers to low-frequency underwater sound (LFS). This study aimed to characterize the subjective responses of recreational scuba divers to LFS to ascertain the extent to which LFS may impact their enjoyment, comfort, or time spent underwater. Seventeen male and nine female recreational scuba divers participated. Diving was conducted in an acoustically transparent tank located within a larger anechoic pool. Subjects wore scuba gear and were positioned I m below the surface in a prone position. The sound transducer was located 4 m directly below the diver's head. Sound exposures consisted of three signal types (pure tone, 30 Hz hyperbolic sweep up, and 30 Hz hyperbolic sweep down) each presented at six center frequencies from 100 to 500 Hz and six sound pressure levels(SPL) ranging from 130 to 157 dB re 1 microPa. The duration of each sound exposure was 7 s. Subjects responded via an underwater console to rate aversion to LFS on a category-ratio scale, and to indicate the presence or absence of vibration of any body part. Aversion to LFS and the percent incidence of vibration increased as the SPL increased. The percent incidence of vibration decreased linearly with increasing frequency. At the highest SPL the probability that an aversion rating would exceed Very Severe (7 on the category-ratio scale) was predicted to be 19%. There was no significant difference in aversion among signal types. The 100 Hz frequency was the most aversive frequency (P < 0.05). A plot of aversion vs. frequency showed a U-shaped function with minimum aversion at 250 Hz. In conclusion, diver aversion to LFS is dependent upon SPL and center frequency. The highest aversion rating was given for 100 Hz, this frequency corresponded with the greatest probability of detecting vibration. Factors other than vibration seem to account for aversion to the highest frequencies. Our data suggest that LFS exposures up to 145 dB re 1 microPa at frequencies between 100 and 500 Hz will have minimal impact on the recreational diver.

Performance and physiology of five operators of the one-atmosphere diving system JIM were assessed when diving JIM in mild (20 degrees C) and warm (30 degrees C) water. Each operator completed a minimum of 3 dives at each water temperature; during each dive 5 walks of 18 m and 3 step maneuvers were accomplished. At the conclusion of 40-min dives in water at 30 degrees C, operator heart rate averaged 151 beats/min, system interior temperature averaged 32.6 degrees C, and the mean respiration rate of operators was 28 breaths/min. Task completion times were faster in warm water. Thermal considerations in the deployment of the JIM system are discussed in relation to these data.

The noise inside the U.S. Navy MK 12 SSDS helmet was measured and its effect on the hearing of divers assessed. Seven male divers completed 20 dives while breathing air at simulated depths ranging from 1.8 to 30.5 msw with dive durations ranging from 40 to 120 min. Microphones recorded sound pressure levels inside the helmet while the diver was in the water and exercising. Average corrected sound intensity levels in the helmet ranged from 90.5 dB(A) at 1.8 msw to 97.3 dB(A) at 30.5 msw. Diver hearing threshold level shifts were recorded as a function of helmet noise exposure; moderate threshold shifts were observed at depths of 9.1 msw or deeper after 120-min dives. The hearing of all divers completing dives up to 120 min returned to predive levels within 24 h after noise exposure. However, dive durations in excess of 120 min at 9.1 and 20.1 msw resulted in substantial auditory shifts in 1 diver, which required 2-3 d to recover to predive levels. These results suggest that the impact of helmet noise on diver hearing should be included in planning operations using the MK 12 SSDS.

The visual reaction time performance of divers experiencing CNS oxygen toxicity was assessed during the development of closed-circuit 100% oxygen breathing diving schedules at the U.S. Navy Experimental Diving Unit. Divers repeatedly performed the visual reaction time test of the Performance Measurement System (PMS) during multiple excursion dives. Each diver wore a Draeger LAR V UBA and performed moderate work on an underwater bicycle ergometer while engaged in the reaction time test. A single subject, repeated measures design was used. Six divers experienced 7 episodes of CNS oxygen toxicity while engaged in the visual reaction time test. Two episodes were preceded by a slowing and increase in variability of reaction time. Five episodes were not preceded by changes in reaction time performance. Other objective and subjective symptoms of toxicity experienced by the divers did not appear to be correlated with reaction time performance. Thus, the PMS visual reaction time test was not reliable method of detecting CNS oxygen toxicity in this study.

The neuropsychologic status of 25 male U.S. Navy saturation divers was assessed before and after saturation dives conducted at the Navy Experimental Diving Unit. Between 1982 and 1986, 5 dives to simulated depths of 198 to 335 msw were accomplished. Eighteen divers completed 1 dive, and 7 divers completed 2 saturation dives during this period. Dive durations ranged from 26 to 31 d, with helium-oxygen used as the breathing medium. On each dive the men engaged in strenuous, meaningful, in-water work on the bottom. Comparison of neuropsychologic assessment battery results pre- and postdives did not reveal permanent changes in neuropsychologic status. Transient alterations in affect, visual focusing, and physical activity level presented upon surfacing but resolved within 10 d.