DCI and the perils of diving in a mixed EAN/Air Group

[dmaziuk]

If the case is being made for knowing what information the computer will display under deco obligation and how to interpret and act on this information, I agree. However I do not agree that the first time this should experienced for real is by an untrained diver and without appropriate guidance from an instructor.

ZH-L with silly GF presets aside, you would expect that when you "just" overstay the NDL, you
1) get a deco stop "just" under the surface, which means at 3 msw because that's what they're traditionally rounded to, and
2) it will be controlled by your "fastest" tissue compartment whose half-time is typically between 2.5 and 5 minutes. One half-time drops half of its gas loading so the duration you should get is between 3 and 5 minutes.

They train new divers how to act at 3 metres for 3 minutes at the end of the dive already, computer or no computer.

 

[Graeme Fraser]

ZH-L with silly GF presets aside, you would expect that when you "just" overstay the NDL, you
1) get a deco stop "just" under the surface, which means at 3 msw because that's what they're traditionally rounded to, and
2) it will be controlled by your "fastest" tissue compartment whose half-time is typically between 2.5 and 5 minutes. One half-time drops half of its gas loading so the duration you should get is between 3 and 5 minutes.

They train new divers how to act at 3 metres for 3 minutes at the end of the dive already, computer or no computer.

Yes, and the ceiling may well disappear during ascent, which to the untrained eye could be confusing. What next, push it to 5-10 minutes deco to force a stop?

What about other algorithms like the Suunto fused, which gives a curve hug and no displayed time at stop. Dived with a tech diver not long ago who'd recently taken ownership of an Eon Steel but looked totally perplexed on his deco.

 

[Bob DBF]

(Going back to this thread - it does concern me greatly that there are suggestions being made about how to hide accidentally going into 'computer deco'. This is what happens when a 'line' is created and is not healthy. Mistakes and minor deviations from accepted practice must be allowed, accepted, discussed and learned from - as the OP has initiated with his post. Expecting arbitrary humans to bow down to the wisdom of the diving gods on the principal of 'cause I said so' is not rea

The problem is that the training is done more by catchphrase than by giving a new diver an understanding of deco theory, to put in context NDL, and why and how you put strategies togather to first stay within NDL, and then how to mitigate the dangers should one screw up and go into deco without proper training.

Saying "follow your computer" is not a good solution. I'm pretty good about reading and understanding technical manuals, and I got supprised by mine. Without giving any other indication that I saw on the dive, it started flashing deco when I surfaced. I yelled to my buddy and we went to the safety stop to see what I did wrong. The computer looked as normal as it always did, so we burned the rest of our air and went back up to the flashing deco. The computer log showed I went into deco for less than a minute I didn't see, and was letting me know after the fact. I probably thought this was less important than recognizing a deco screen and how to read the screen and get out of deco, then forgot about it. Now I reread the manual at least once a year, and before a big trip, also I carry the paper copy with me.

Now imagine a new diver, confused by the screens, flashing deco. Another rule is have 500# in your tank when you surface. The diver has not been given the Information to make an informed decision.

If every dive is a deco dive, the training should reflect that. My initial SCUBA training did, as did my OW.


Bob

 

[dmaziuk]

Yes, and the ceiling may well disappear during ascent, which to the untrained eye could be confusing. What next, push it to 5-10 minutes deco to force a stop?

You do a 3-5 minute stop at 3-5 metres, what's confusing about it? My point is, you need to overstay your no-stop time for more than "just over NDL" in order to generate a deeper and/or longer stop. From the description, this was not the case here. To me all this blowing on "normalizing decoviance" "unable to interpret the computer" trumpet seems misplaced.

What about other algorithms like the Suunto fused, which gives a curve hug and no displayed time at stop. Dived with a tech diver not long ago who'd recently taken ownership of an Eon Steel but looked totally perplexed on his deco.

Not displaying time at a stop would be a seriously drain-bramaged user interface design, but having never dived a fused Suunto myself I'll take your word for it.

 

[Kay Dee]

And I know a number of tech divers with access to O2 who will use 40% for that purpose, instead of 50%, because you don’t have to maintain that tank and reg as O2 clean.

This is not neccesarily correct for the cylinder and valve. Only so if an 'up to 40%' mix is being filled by a membrane system or continuous flow blend system. If your filling by the so-called partial pressure blending method then the cylinder and valve should be O2 clean. Obviously not an issue for the reg though, no mater what method was used to fill the cylinder (up to 40%).

 

[Kay Dee]

A question for AlanS if your stll reading this.

You said in your first post that you were on a liveabord and this was your third dive of the day and "........I signalled to the guide/leader that time was up and did the usual safety stop",

If I may ask, how many days had you been diving (on the liveaboard) and what time and depth is your 'usual' saftey stop?

As an aside, that is not directed at AlanS in any way, IMO a safety to stop is simply that, for saftey, and yes they should be done. On the other hand, a deco stop is oblgatory and must be done.

 

[Mike Walker]

I'm pretty good about reading and understanding technical manuals, and I got supprised by mine. Without giving any other indication that I saw on the dive, it started flashing deco when I surfaced. I yelled to my buddy and we went to the safety stop to see what I did wrong. The computer looked as normal as it always did, so we burned the rest of our air and went back up to the flashing deco. The computer log showed I went into deco for less than a minute I didn't see, and was letting me know after the fact. I probably thought this was less important than recognizing a deco screen and how to read the screen and get out of deco, then forgot about it. Now I reread the manual at least once a year, and before a big trip, also I carry the paper copy with me.

Now imagine a new diver, confused by the screens, flashing deco. Another rule is have 500# in your tank when you surface. The diver has not been given the Information to make an informed decision.

Thanks Bob - this closely aligns with what prompted me to write this in the first place.

Very few people can simply read a manual for something as potentially complex as a modern dive computer and remember enough about the 'obscure' functions (those they don't use regularly) to be able to effectively interpret them at some indeterminate point in the future (perhaps years after they bought the thing and read the manual... if they read the manual...). Going through the practical steps at least once will get a much much higher rate of retention - particularly if it is underwater and not simulated.

My initial encounter with this was 'accidental' - I was intentionally trying to ride the NDL curve up for the dive (last dive of trip, long time before flying) and went a bit slow. Suddenly my computer was doing things it hadn't done before. Having some knowledge of deco principals/procedures and the benefit of one of the more verbose computers (Perdix) it was not difficult to safely ascend following the computers instructions. But it did cause me to think/reflect on how this could have played out differently for someone with only the knowledge contained in typical OW/AOW courses (or someone less technologically inclined or more prone to panic).

Anyways, I've said my bit and I'll stop derailing this thread now

 

[Steelyeyes]

My wife and I were diving a mixed group of Ean 32 and air on the east side of Cozumel a couple of years ago. The other couple was from Germany just hadn't seen the need to get Nitrox certified. We did three dives. The German lady got seasick after the first one and opted out of the 30 minutes at 20 feet in a crowd of people looking at the wrecked Spanish galleon. We made a mid day break on shore and left her with a few people at a restaurant and then went south for the last dive. We were cruising around at 60 FSW and about half way through our dive the DM signaled that he was taking the German guy up to a shallower position and for us to finish our dive (so much for all Aldora groups sticking together but whatever). At about an hour I was getting chilly and we were still good on gas and NDL but it was time to go. I gave my wife the thumbs up, we caught up to the DM and the German at 30 FSW and ascended the rest of the way together. On the boat ride back I explained the charms of getting a Nitrox card. The guy was an MD and I told him he could blow through the course work in the time it took to have a couple of cocktails that night and he'd be good to go on Nitrox the next day.

We ran into the DM and Adrienne our previous DM that week at the Cerveceria Punta Sur that night. I guess since the guy's wife wasn't much on boats and waves he didn't think the Nitrox card would help him out unless he found another buddy and that wasn't going to happen.

 

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[crofrog]

The real issue is that every single thing is a speciality these days. Nitrox should be included in open water vs a ******** 200 extra dollars to get shown how to use an analyzer, but the scuba police aren’t incentivized to create competent divers in ow.