To plan for any future rescue of personnel in a disabled and pressurized submarine, the US Navy needs a method for predicting risk of decompression sickness under possible scenarios for crew recovery. Such scenarios include direct ascent from compressed air exposures with risks too high for ethical human experiments. Animal data, however, with their extensive range of exposure pressures and incidence of decompression sickness, could improve prediction of high-risk human exposures. Hill equation dose-response models were fit, by using maximum likelihood, to 898 air-saturation, direct-ascent dives from humans, pigs, and rats, both individually and combined. Combining the species allowed estimation of one, more precise Hill equation exponent (steepness parameter), thus increasing the precision associated with human risk predictions. These predictions agreed more closely with the observed data at 2 ATA, compared with a current, more general, US Navy model, although the confidence limits of both models overlapped those of the data. However, the greatest benefit of adding animal data was observed after removal of the highest risk human exposures, requiring the models to extrapolate.

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POTENTIAL BENEFITS OF NAVY DIVE COMPUTER USE IN SHIPS HUSBANDRY DIVING: ANALYSIS OF DIVES CONDUCTED ON THE USS RONALD REAGAN (CVN-76) Navy Experimental Dng Unit

The USN N2-O2 primary data set is a collection of dive profiles that the U.S. Navy uses to calibrate probabilistic decompression models for air and N2-O2 diving. Each dive profile describes the depth/time/breathing gas history,number of participating divers, and decompression outcome of experimental dives.Original research reports, research protocols, databases, and diving logs describing the experimental dives were searched for work and temperature information. A subset of the USN N2-O2 primary data set was augmented so that dive profiles included diver whole body oxygen consumption (estimated from descriptions of work performed), work type, posture, water temperature, and diving dress. Two additional data files describing experimental dives that compared working and resting dives were also augmented

Heliox (He-O2) enables diving deeper than limits imposed by breathing N2-O2, but heliox has some costs, and several navies have pursued a trimix (He-N2-O2) diving capability as an alternative to heliox. It is widely believed that trimix bounce dives can be conducted with substantially reduced decompression times than corresponding heliox dives. If this were true, trimix would be an attractive alternative to heliox for U. S. Navy MK 16 MOD 1 underwater breathing apparatus (UBA) diving. However, there is no direct evidence of greater decompression efficiency of trimix than of heliox. Decompression efficiency was assessed by comparing the incidence of decompression sickness (DCS) following decompression dives using MK 16 MOD 1 UBAs (1.3 atm PO2 set point) with either heliox (88% He / 12% O2) or trimix (44% He / 44% N2 / 12% O2) diluent. Both trimix and heliox dives followed the identical depth/time schedule (200 fsw for 40 minutes bottom time followed by 119 minutes of decompression stops). This schedule was selected for having the largest difference in estimated probabilities of DCS between trimix and heliox among a range of candidate schedules that were practicable to man-test and operationally relevant. The trial ended at an interim stopping criterion with fifty man-dives completed on the heliox schedule with no diagnosed incidents of DCS, and forty-six man dives completed on the trimix schedule with two diagnosed incidents of DCS. The null hypothesis was retained: decompression from trimix bounce dives is not more efficient than decompression from heliox bounce dives. Potential disadvantages of heliox with respect to cost, thermal balance, and voice communications are of limited relevance to MK 16 MOD 1 diving. In the absence of any decompression advantage, trimix is not an attractive alternative to heliox for U. S. Navy MK 16 MOD 1 or other closed-circuit, self-contained diving. 15. SUBJECT TERMS Decompression Sickness; Decompression Schedules; Heliox; Trimix 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON NEDU Librarian a. REPORT