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I can't speak for the NOAA manual, but the Navy Diving Manual says: - No planned deco diving in SCUBA, except for MK16 Closed circuit UBA in which case there are no gas changes made normally. - When diving surface supplied, either use air or HeO2 with no N2. And below is an excerpt from the manual with respect to surface supplied HeO2 diving: "14-3.3 Procedures for Shifting to 60 Percent Helium/40 Percent Oxygen at 100 fsw. For dives deeper than 200 fsw in which the bottom mixture contains less than 16 percent oxygen, it is necessary to shift from the bottom mixture to 60 percent helium/40 percent oxygen at 100 fsw during decompression or the next shallower stop if there is no 100-fsw decompression stop. Ventilate each MK 21 MOD 1 diver using the following procedures. 1. Ventilate each diver and listen for the gas-flow change over the communications. 2. Once a gas-flow change is heard, continue to vent for an additional 10 seconds. If a gas-flow change cannot be heard, ventilate for a minimum of 20 seconds. The time required to effect the shift over to 40 percent oxygen is not critical. 14-3.4 Procedures for Shifting to 100 Percent Oxygen at the First Oxygen Stop. All dives except no-decompression dives require a shift to 100 percent oxygen at the 50-fsw stop, or at the 40-fsw stop if there is no 50-fsw stop. Upon arrival at the stop, ventilate each MK 21 MOD 1 diver with oxygen following these steps: 1. Ventilate each diver and listen for the gas-flow change over the communications. 2. Once a gas-flow change is heard, continue to vent for an additional 10 seconds. If a gas-flow change cannot be heard, ventilate for a minimum of 20 seconds. Verify the diver's voice change. Time at the stop begins when the diver is confirmed to be on oxygen. When 50 fsw is the first oxygen stop, the ascent time from 50 fsw to 40 fsw is included in the time of the 40-fsw stop." What this doesn't say in these paragraphs, but is shown in the tables, is that for dives with 16% O2 or more, the procedure is bottom gas all the way to 50fsw and then shift to 100% O2. The deepest table for which this procedure is shown is the 200fsw. Before you reflexively flame Navy use of O2 at 50fsw, consider that there is a world of difference between a SCUBA diver and a surface supplied diver. In particular, if the SS diver has an O2 problem he will not lose his gas source and drown. The surface team controls the gas and can immediately switch gas at the first indication of a problem. The role of the Navy diver during deco is to relax and breathe. Topside runs the operation with tables open and a written dive chart. Additionally there will always be a chamber on site for air dives below 130fsw and all HeO2 dives. So, short answer - IMHO the Navy Diving Manual doesn't give you a whole lot of really applicable advice for this case. B.L. Flank -----Original Message----- From: Kent R. Frazier [mailto:kd5aes@ar*.ne*] Sent: Monday, August 28, 2000 2:58 PM To: techdiver@aquanaut.com Subject: Re: 80/20 deco First, let me qualify my question by stating that I have been inactive for a couple of years and I am not a "Technical" diver. Just someone who would like to expand his knowledge base. I'm perfectly happy diving within the "recreational" limits. Feel free to flame me all you like. Just curious, what does the NOAA Manual and or the U.S. Navy Manual say about this subject, if anything? Kent R. Frazier, KD5AES -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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