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| Title: | CHISAT II: EXCURSIONS TO 60 AND 80 MSW WITH HELIOX FROM NITROX SATURATION AT 25 MSW |
| Authors: | Hamilton Jr, RW
Shi, Z
Gerth, WA
Zhuang, Q |
| Keywords: | decompression
helium
heliox
saturation
decompression
narcosis
air
nitrox
chamber
model |
| Issue Date: | 1996 |
| Abstract: | BACKGROUND: Vertical excursions allow divers in seafloor habitats to work at depths deeper than the habitat. Descending excursions from saturation in nitrox have almost all used air as the breathing gas; depth is effectively restricted to less than 60 msw by narcosis and oxygen exposure. Our objective was to investigate use of helium mixtures for excursions, taking counterdiffusion into account. METHODS: In Shanghai, 2 teams of 2 divers were saturated at 25 msw simulated depth in a chamber with 0.32 - 0.35 PO2 in N2, and performed a total of 32 diver-excursions. Each team excursed daily to either 60 msw pressure for 70 min or 80 msw / 40 min. Bottom mix was trimix, 50percent He, 34percent N2, and 16percent O2, giving a PO2 of 112 kPa at 60 msw and 144 kPa at 80 msw. Divers did 3 x 10-min work periods at 60 and 2 x 10-min at 80 msw, on an uncalibrated bicycle ergometer; this increased ventilation on the order of 5 to 15 liters/min. Thus divers were active and exercising their knees but were not doing heavy work. Decompressions breathing bottom mix were 70 and 98 min for the 60 and 80 msw excursions. We calculated these with HRL's DCAP, neo-Haldanian model Tonawanda IIa, with M-values based on Repex (NOAA Undersea Research Rept 88-1B) modified to consider the Nisahex trimix excursions from nitrox saturation at 50 msw (Muren et al, U/W 8, Bachrach and Matsen, UHMS 1984). RESULTS: Doppler bubbles reached Spencer Grade III at times, predominately in one diver. No symptoms were reported nor signs of DCS detected. Saturation decompression using NOAA's Repex procedures was uneventful; Grade II and occasionally III bubbles persisted in 2 of the divers until 24 hours after surfacing. CONCLUSION: We conclude that excursions with heliox and trimix rich in helium can be performed effectively and reliably to as deep as 80 msw using these procedures. [Sponsored by NOAA-NURP and CUTI]. |
| Description: | Undersea and Hyperbaric Medical Society, Inc. (http://www.uhms.org ) |
| URI: | http://archive.rubicon-foundation.org/479 |
| Appears in Collections: | UHMS Meeting Abstracts
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