Decompression from He-N2-O2 (trimix) bounce dives is not more efficient than from He-O2 (heliox) bounce dives.

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Decompression from He-N2-O2 (trimix) bounce dives is not more efficient than from He-O2 (heliox) bounce dives.

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Title: Decompression from He-N2-O2 (trimix) bounce dives is not more efficient than from He-O2 (heliox) bounce dives.
Author: Doolette, DJ; Gault, KA; Gerth, WA
Abstract: 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.
Description: Citation Status: Active; Citation Classification: Unclassified; Title Classification: Unclassified; Report Classification: Unclassified; Identifier Classification: Unclassified; Abstract Classification: Unclassified; Distribution Limitation(s): 01 - APPROVED FOR PUBLIC RELEASE; Information provided by the Department of Defense and the Defense Technical Information Center (http://www.dtic.mil/) is considered public information and may be distributed or copied unless otherwise specified. Use of appropriate byline/photo/image credits is requested.
URI: http://archive.rubicon-foundation.org/10576
Date: 2015

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