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Lori wrote: >It seems to me that the technicial used her computer and ignored what >was learned in basic open water. i.e. may deepest dive first, followed >by next deepest... So following a 21 ft. dive, even if it was sort of >like decompression, with a 87 ft. dive was not a good profile. I was >taught in my first open water class the a computer will allow this, but >it still shouldn't be done. Robert Mullins quoted from Discover Diving: >"That morning I had done a 100 foot+ dive, surfacing with plenty of time >allowed by the computer. My second dive of the morning was a mere 21 >foot dive, so I actually spent that time decompressing from the first. >After lunch I went back out and made a third dive to 87 feet. After >each of the deeper dives, I had ascended to much shallower depths for >the last fifteen minutes as a safety stop. When I surfaced after my >last dive, the computer said I still had approximately fifteen to twenty >minutes of bottom time left. According to the computer's information, I >thought I was being careful. Yet I still got bent!" We can determine very little from the given scenario. If this statement was an exact quote (i.e. unedited) we can determine that their "explanation" of the situation most likely belies a very poor understanding of computers and how they work. The statement "When I surfaced after my last dive the computer said I still had approximately fifteen to twenty minutes of bottom time left" is so poorly constructed that it's laughable. Anyone on this list knows that remaining "bottom time" depends on the depth (e.g. many computers will scroll the NDL times for each of the depths from 30 to 150'). I would *assume* that they meant that they had about 15-20 minutes of NDL time at their "shallow safety stop", which most likely means that they were indeed fairly heavily loaded, but this may be a bad assumption. We don't know the profiles or the surface intervals and, possibly even more importantly, we don't know the physiological state of the diver at the time this occured (i.e. how dehydrated, how tired, any alcohol remaining, any other drugs, etc). We don't even know what the symptoms were that this person had (i.e. if they *really* were bent or if it was something else). I'm not trying to trivialize the situation, just saying that, as stated we as divers cannot learn anything from this (except to describe your situation more exactly using facts, profiles, times, etc). Personally I have done much more aggressive diving than this with no problem. There is always the real possibility that this diver is one of those with PFO. I know that we went over this here a couple months back, but, I wonder if it wouldn't be a good idea to include a description of PFO, what it is, how you can be tested, possible consequences, in *every* first level of scuba class, especially since it's quite likely that there are a percentage of divers out there for whom the tables as currently used are NOT safe because of this. Lori listened well in her basic open water class. The thing that I have not seen ANY open water class teach is... How long to wait before you can dive deep again!!! Do you wait until you're "totally clear", do you wait until you're an "A" diver, or what? Computer won't tell you this, but, neither will the tables, AND, if you're diving square profiles, computers are quite often more conservative than the tables! An interesting discussion recently came up on rec.scuba regarding the algorithms of some computers, in particular the Cochran Nemesis. I thought I'd mention it here in case others are interested. It seems that the Nemesis penalizes you (i.e. reduces your NDL times) for subsequent dives done during the same "dive day", where a dive day only ends when you're totally clear (thus a dive day could be a week or more long!). The penalty increases on the 2nd, 3rd, and 4th dives, then stays constant. The 4+ penalty reduces NDLs on all dives in the 75+' range. I don't have the information as to HOW much it reduces them for the 3rd and 4th (and subsequent dives), but the *1st level* of compensation only starts at 140 ft and is reduced as follows No comp 1st level comp 140ft. 9 min 8 min 150ft. 8 min 5 min 160ft. 7 min 2 min Now, while this seems pretty innocuous (after all, 140' is pretty deep to begin with), remember, that the 4+ dive penalty affects all dives at the 75'+ level. -Carl-
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