Dive Computer No Deco Computations Question

[David Carron]

How about providing a profile that does not immediately violate good diving practices? If you get DCS from that ascent (which is likely), then what is the purpose of talking about the later parts of the dive?

A diving computer displays little more than "the later parts of the dive" (the ascent profile, specifically). If you consider that in this case there is no purpose in that (displaying an ascent profile) then what do you think the computer should display?

Some manufacturers agree with you and stop displaying an ascent profile, some disagree and continue displaying an ascent profile as if the violation hadn't happened, others disagree and try to take the violation into account, presumably according to some extensions to the model.

I've been professionally involved in discussions around this precise problem for years haven't really found a credible solution.

 

[GreggS]

Isn't this whole part of the thread about what the computers do when violating good diving practices?

Yes it is.

I think the vast majority of people that are Scubaboard members are well practiced with their computers. Whether it be Shearwater or Suunto, if you follow what the DC is telling you, you will not lock it out. I started out diving Suuntos and did so for about 5 years. Not once did I get locked out. I did go into a light deco once and had to do a stop at 45 fsw for 7 minutes. No biggie. At other times, I have been shown a ceiling while on a dive, but that was no big deal, either. Just stayed below the ceiling until it cleared. But I knew what my computer was telling me and followed what it was saying to me.

The problem arises when people buy a computer and, regardless of the brand, don't take the time set up the DC properly or to understand what the display is telling them. My wife and I were at AKR in Roatan in 2021. There was couple there that joined our boat about mid-week. Lovely couple that were decent divers. However, they only had one computer that he wore and, of course, it was a Suunto Zoop Novo. We got to chatting on our way in from a dive and he started asking me about something on the display. I had to explain to him what all the different numbers were telling him and how he could scroll thru the button presses to see other information if he wanted. I also explained to him why it was important why each one of them needed a computer.

It's these type of people that are going to get locked out. They don't know what they're looking at when they look at the computer nor know why they're now locked out if it happens. Honestly, if they can't be bothered to read the manual and at least try to understand their DC, it is more or less useless to them, much like the couple in the example earlier in the thread. As I said, I also think there are very few people on Scubaboard that pertains to.

But as has been mentioned earlier by others, unless there is a glitch or malfunction going on in the computer, none of them are going to randomly lock you out without being in violation. It still isn't a great design that it locks you out during a dive, but post-dive I can understand.

 

[Nemrod]

Yeah. I’m clear that many do that. I’m not a fan of the practice of using air settings while diving Nitrox, but I do get why some do. As long as you don’t exceed MOD, it provides a safety buffer. Though that buffer may be purely theoretical.

What I can’t wrap my head around is people who do that, then proceed to ignore the warnings/alerts on the computer.

I know it can happen and has happened, but have any of you guys had or know of a O2 hit due to exceeding the MOD, once or repeatedly? I have exceeded MOD numerous times but only briefly, it is easy to do in some places where you are on a wall. I do not mean by accident in my case but with intention in that I knew I would be below MOD briefly on 32%, example, Devil's Throat, 130 feet +/-, for maybe a couple of minutes before going shallower quickly. This instead of incurring deco on a single tank precluding direct to surface ascent.

I encounter DMs and Instructors recommending to their students or clients to set an air profile in their computer despite being on 32% mix and this on dives where flirting with MOD is a real possibility if not for certain. Intentionally going beyond MOD briefly and knowingly doing so, well, but to dive numerous deeper dives pushing MOD over the course of a trip diving an air profile on the computer and 32% in the tank. I think it is bad advice.

 

[Bento.Box]

I got a computer to provide information throughout the dive. My computer should not throw a tantrum and give me the silent treatment while in the water. I'm not a fan of -dive lockouts either, but I understand that a little more.

It provides useful information as long as it can. It‘s not „throwing a tantrum“ afterwards.

It’s really not a big deal, since we are in a rare emergency situation and probably unable to follow any recommendations anyway.

 

[Belzelbub]

It provides useful information as long as it can. It‘s not „throwing a tantrum“ afterwards.

If every other dive computer manufacturer behaved that way, then I'd agree with you.

As it stands, I'm only aware of 2 different computer manufacturers that do an in-water lockout. Suunto and the AWU/Oceanic+ are the only ones that seem to do that.

The rest seem to continue to provide guidance to the best of their ability at least until you get to the surface. Then some will lock out, others won't.

It’s really not a big deal, since we are in a rare emergency situation and probably unable to follow any recommendations anyway.

Sure. It's not really a big deal. Until it is.

And as I said before, dive computers should really not be designed for the divers that ignore the recommendations.

 

[boulderjohn]

I know it can happen and has happened, but have any of you guys had or know of a O2 hit due to exceeding the MOD, once or repeatedly?

I encounter DMs and Instructors recommending to their students or clients to set an air profile in their computer despite being on 32% mix and this on dives where flirting with MOD is a real possibility if not for certain. Intentionally going beyond MOD briefly and knowingly doing so, well, but to dive numerous deeper dives pushing MOD over the course of a trip diving an air profile on the computer and 32% in the tank. I think it is bad advice.

I have never heard of a DM recommending this. In fact, in my experience, it is quite the opposite. I have seen DMs absolutely anal about the MODs--sometimes absurdly so. A DM in Bali panicked if we took 32% below 60 feet. A DM in Cozumel would not let me use 32% on a dive planned to 80 feet because he was afraid I might momentarily lose buoyancy control and plummet below the 111 foot MOD.

As for getting O2 toxicity on a NDL dive using an AL 80, I recently ran into an older document (can't remember where) that expressed the opinion that you can't get toxed using a standard nitrox mix in an AL80 because you can't exceed MODs long enough to get a hit. You don't tox just by straying below the MOD--it takes a while. All the cases I know of are on technical dives, and the violations were significant.

 

[Bento.Box]

Sure. It's not really a big deal. Until it is.

And when would that be the case?

 

[tursiops]

I recently ran into an older document (can't remember where) that expressed the opinion that you can't get toxed using a standard nitrox mix in an AL80 because you can't exceed MODs long enough to get a hit.

I think this is nonsense. I just played with MultiDeco a bit; 150 ft for 12 mins using 32%. You hit PPO2 of 1.77 for about 10 mins, get a slight deco obligation, CNS total 252%, and use less than 42 cuft (assuming RMV of 0.5 cuft/min). If you backed off to 140 ft but for 20 mins, you get more deco, only hit PPO2 of 1.67, CNS 111%, and still only used 63 cuft. Going the other way, to 160 ft on 32%, for 20 mins, you get 12 mins of deco, hit PPO2 of 1.97, CNS of 910%, and just barely can do it on an AL80.

 

[Belzelbub]

And when would that be the case?

Whenever you've messed up and check your dive computer for ascent guidance and find out that it's checked out.

I agree, it's a rare occurrence. My comment was to imply that while it's not a a frequent occurrence, it's important when it's needed.

 

[Nemrod]

I have never heard of a DM recommending this. In fact, in my experience, it is quite the opposite. I have seen DMs absolutely anal about the MODs--sometimes absurdly so. A DM in Bali panicked if we took 32% below 60 feet. A DM in Cozumel would not let me use 32% on a dive planned to 80 feet because he was afraid I might momentarily lose buoyancy control and plummet below the 111 foot MOD.

As for getting O2 toxicity on a NDL dive using an AL 80, I recently ran into an older document (can't remember where) that expressed the opinion that you can't get toxed using a standard nitrox mix in an AL80 because you can't exceed MODs long enough to get a hit. You don't tox just by straying below the MOD--it takes a while. All the cases I know of are on technical dives, and the violations were significant.

I can only say what I know and what I have seen more than once, in fact, routinely in some places. It makes my OCD meter peg.