DCS due to reading computer wrong (I think)

[RJP]

No one is saying is saying an AI computer is the panacea to safe diving. It's just an instrument to assist in making a safer dive, and I prefaced my comment that a deco dive should be preceded by making a dive plan. And by the way, no matter how well trained you are and how well you plan, I can always come up with a scenario that will kill you -- the point is one can make a dive safer but not foolproof.

I don't disagree with your general point, but rather with the idea that providing a diver with a piece of information which is effectively meaningless provides any benefit. Since the information is meaningless the ability for that information to help is zero. On the other hand, the potential for a diver who relies on that information to come to some harm because of that reliance is unacceptably high. Not because it will happen often, but because the outcome could be very serious if it does happen.

I dive an AI computer on recreational dives, and simple tech dives. It tells me my NDL and my remaining air time. It's easy enough to look at those two numbers and completely understand the situation I'm in. If I only had one number - a projection of how much longer I could stay in the water based on combination of current depth and remaining NDL and gas... I'd actually be at a disadvantage as now I don't really have enough information to understand what that number REALLY means for the rest of my dive. Can I stay five more minutes to try to get that lobster? I don't really know how to answer that question in a way that makes me comfortable.

 

[flots am]

Originally Posted by Hatul "the newer Uwatec Sol/Luna provide another safety net with AI. They display the Remaining Bottom Time, that still allows enough gas to made a safe ascent with all the required stops."

I actually own one of these, and while it will do what you say, it's sort of a "deal with the devil" because the algorithm is based on you immediately starting your ascent and ascending at the "ideal ascent rate".

Unfortunately, it's difficult to start ascending "when it beeps" because there's generally an up-line you would need to go find, and it only works when ascending at "the ideal rate." The only way to know "the ideal rate" is to stare at the computer the entire time and watch the ascent indicator, since it's not a fixed rate, but is calculated on the fly based on pressure gradients.

It's a really nice computer and I like it a lot for no-deco dives, but riding it during a deco dive scares the crap out of me and I won't do it. On deco dives I use in gauge mode along with my watch and extra depth gauge in my pocket, and the plan I got from vPlanner, taped to my wrist slate.

While they're both computers, the printed plan has several advantages:

• I can give it a sanity check before the dive. If it says "60 minutes of deco", I'm likely to modify the dive plan and re-run it.
• Paper stuck to a wrist slate with clear packing tape can't crash or say "E7" or "Switching to gauge mode" at an inopportune moment.
• I know whether I have enough gas or not before the first drop of water hits my mask.

Also, I especially liked this section of the Uwatec manual: "Always dive with back-up instruments. Make sure that you always use back-upinstrumentation including a depth gauge, submersible pressure gauge, digital bottomtimer or dive watch, and have access to decompression tables whenever diving witha dive computer."

If the computer craps out, what percentage of divers will say "Oh ****! What do I do now?!!", and what percentage have backup equipment and tables and know how deep they were and for how long?

Since the backup plan is tremendously more reliable than the computer, I just go with that from the beginning.

flots

 

[DandyDon]

Secondly, I have already decided to retire from diving in September 2015. I'll be 2 months short of my 60th birthday by then and maybe less than 3 years away from job retirement. There are quite a few land based holidays that my wife and I want to do while we still can afford to do so and my diving has taken too much vacation time in the last 6 years. I made a promise to my wife that after I retire from diving we will cover those overland places and I intend to keep that promise.

Blah!

Do that if you want to, but I just cut back on number of trips per year.

 

[clownfishsydney]

I think that most people on this forum do not understand how often the San Francisco Maru is dived and how the conditions are generally as perfect as a deep dive can have. As I early said, I have been to Chuuk six times and dived the SFM seven times.

• There is virtually never any current on or above the wreck (I have never had any at all)
• Visibility is in the range of 30 to 50 metres
• The surface conditions are generally millpond, at worse, perhaps half a metre slop
• The dive masters for Blue Lagoon have dived it hundreds of time
• The DMs leave a spare tank at the anchor
• They sometimes carry a spare one as well
• There is generally another spare tank and/or nitrox hanging off the dive boats
• Every diver would have done multiple days diving and multiple dives each day before doing the SFM

I would estimate that probably an average of 10 divers a day (not week) most days of the year. Say 3,000 dives a year. I have never heard of any real problems of Australian divers getting bent on this wreck.

In my view, this is a dive only for experienced divers, but any competent experienced recreational diver could do it without running into any problems.

And yes, I have seen incompetent divers do it, including some who appeared to be tech trained and who dived with up to four tanks and banged and bashed their way around the wreck. Just because someone has done a tech course does not mean they are a competent diver!

 

[Quero]

Pfft, it won't happen to me.

:rofl4:

---------- Post added February 24th, 2013 at 04:28 PM ----------

Exactly. Because the operation allows and even encourages recreational divers to do this dive (remember that the OP believed that the dive plan had been discussed in depth during the briefing),

Either you are misquoting the OP (I don't feel like re-reading the thread) or the OP doesn't understand what a dive plan is.

You wouldn't have to read far. This is from the first post in the thread:

The dive was over the wreck of San Francisco Maru, the so-called "Million Dollar Wreck". It was a deep dive just beyond the 50m mark and since we were all diving on single tank 24% nitrox, the dive plan was very carefully discussed. For a start, we were required to miss the night dive the previous evening to increase the surface interval. The divers would go down in 2 groups of 8 divers each and each group was supervised by 2 divemasters who hovered just above the top deck where they could keep all their charges in sight.

While it's true that he doesn't say "the dive plan was discussed by the staff very carefully, the mention that the staff required them to skip the night dive and supervised from above certainly makes one think that the OP interpreted the briefing as being the plan. I do agree with you that a briefing is not a plan, which was essentially why I said that "the OP believed that the dive plan had been discussed in depth during the briefing".

 

[RJP]

In my view, this is a dive only for experienced divers, but any competent experienced recreational diver could do it without running into any problems.

Per the OP, the opposite is also true.

 

[halocline]

No one is saying is saying an AI computer is the panacea to safe diving. It's just an instrument to assist in making a safer dive, and I prefaced my comment that a deco dive should be preceded by making a dive plan. And by the way, no matter how well trained you are and how well you plan, I can always come up with a scenario that will kill you -- the point is one can make a dive safer but not foolproof.

The only way an AI recreational dive computer, even an absurdly overpriced one with everything but the kitchen sink, could make this dive safer for an un-trained deco diver with a single tank would be to have a pre-dive alarm that screams "DONT DO IT"

Jeez, you'd really think this would be obvious....

---------- Post added February 24th, 2013 at 08:56 AM ----------

The captain and the crew of the Odyssey provide exquisitely detailed DIVE SITE BRIEFINGS prior to every dive. They do not, however, discuss a DIVE PLAN in any way. In fact they are very clear that they will NOT engage in any aspect of dive planning with or for passengers.

Still, I believe they have an obligation to take reasonable measures to ensure that the divers on their boat are following generally accepted safe diving practices. They are leading dives, sending DMs into the water, essentially sanctioning the divers' behavior on their charter. This is de-facto dive 'planning', or at least dive 'supervision.'

---------- Post added February 24th, 2013 at 09:17 AM ----------

I would estimate that probably an average of 10 divers a day (not week) most days of the year. Say 3,000 dives a year. I have never heard of any real problems of Australian divers getting bent on this wreck.

Well, you have heard of one British diver getting bent, the subject of this thread. Just quickly nosing around DAN's site, it appears that total DCI incidence in recreational diving, including un-reported and non-emergency cases of all types of DCI, is estimated at 2-4 cases per 10000 dives. If the diver who started this thread is the only case of any DCI-related problem on this wreck for an entire year, then it would still be on the high side with your estimate of 3000 dives/year. However, as I mentioned before, if thousands of recreational divers, un-trained and un-equipped for deco diving, are in fact doing this dive, I'd be happy to wager that eventually the statistics will show DCI incidence far above the norm for recreational diving. It's simply too deep.

It's nice that you and everyone you know are fine and comfy with this type of diving, but it's so far off the accepted norms set by every training agency that you can't reasonably argue that it's safe.

I totally understand how the conditions make it 'seem' easier to execute a dive like this, but it's still 170 feet of water.

 

[Bonuss]

If the diver who started this thread is the only case of any DCI-related problem on this wreck for an entire year, then it would still be on the high side with your estimate of 3000 dives/year. However, as I mentioned before, if thousands of recreational divers, un-trained and un-equipped for deco diving, are in fact doing this dive, I'd be happy to wager that eventually the statistics will show DCI incidence far above the norm for recreational diving. It's simply too deep.

I think youv'e made some great points; although some of the thinking is somewhat "black and white". I don't assume EVERY diver in this theoretical year prepaired (ill prepared) like the OP; nor do I assume everyone with a computer on this dive are relying soley on a computer. I think without your statement above it is still logical to assume that the occurance of DCS will be more significant on this and similar popular deep dives. The interesting data would be if we actually knew how say 100 or 1000 divers prepaired, planned, trained. Your points are well warrented! You demoted my computer in my mind to a "nice additional source of info" (haven't really pushed rec limits yet).

I have made the joke to freinds before that if I die and they reccover my body, the computer will provide a very nice profile of what happened (and or didn't happen) for them to discuss. (I'll sign a release to Scuba Board tonght)

Bob in CO

 

[halocline]

I think youv'e made some great points; although some of the thinking is somewhat "black and white". I don't assume EVERY diver in this theoretical year prepaired (ill prepared) like the OP; nor do I assume everyone with a computer on this dive are relying soley on a computer.

Bob in CO

Yes you're right, but in fact it would tilt the scale in the direction of increased DCI incidence if you only counted recreational, single tank divers on this dive, excluding the properly trained and equipped divers. Maybe there's only 2000 dives/year done in this manner, or maybe fewer. So a single incidence in a year would be above the norm.

Statistics are difficult in this situation because overall scuba diving is very safe and the risk of DCS in recreational diving is very very low. So you need lots and lots of numbers. If accurate records were kept for years, a decent statistical study might be possible.

 

[Lorenzoid]

I wonder how many incidents go unreported in which customers of this liveaboard or similar ones experienced DCS to one degree or another, an out-of-gas situation, or some other potentially life-threatening event? If a diver doesn't go to the chamber, phone DAN, or seek hospital care, is it ever going to make it into the statistics? I did not go and re-read all the OP's comments, but if I recall, somewhere he mentioned that the crew warned the divers that there had been incidents of DCS.