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

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By choosing this as a 'line' with no exceptions it creates a situation where a recreational diver going to 0.001 minutes NDL on their computer is perfectly acceptable but going 1 minute into decompression (and the few minutes that might add to the ascent) is completely verboten. This results in a lot of sheep standing 1" away from the electric fence at the edge of the field because that's where all the tasty grass is. That is - one has created a situation where a lot of people are operating to 100% of their limit even on a 'typical' dive (because they've been told it's a-ok) and have no idea what happens just beyond. What happens to the sheep that one day finds itself on the other side of the electric fence?

By deliberately pushing just a little bit into deco (in the context of a person's particular computer's assessment of the situation) and then safely making ones way back out now the '100% knowledge capacity' threshold is extended. Any dive undertaken within computer NDL limits now becomes a 90% knowledge capacity activity for that diver with a nice smooth grey transition area up to 100% - no longer a 'line'. I would suggest this probably makes each 'typical' dive now inherently safer but, more importantly, if the threshold (which is now at 90% of capacity) is violated by accident that diver is still operating within their knowledge and training. They know they shouldn't be there - but they've been there before and can safely get back.

Lines are only good for the types of people who colour within them.

I should definitely emphasize that my advocating this experimentation is 100% about 'learning you're computer' and not about 'learning deco procedures'. Doing it once - and only once - in friendly conditions (lots of gas, etc.) for a timespan only long enough to make the computer react is really not adding any risk (certainly less than doing it accidentally and unprepared at some point in the future). Ideally this would be integrated into an AOW type course to allow for supervision/guidance - but that might distract from PADI's latest course development efforts on how to best colour match your fins and weight pockets....

In the context of this thread, I disagree. The problem with pushing a limit is that it increases your decompression stress and risk of DCS, especially with multiple days of diving, even if the magic bracelet says that you are safe. That is the take home message, and it holds for air or nitrox, as mentioned upthread. It should be stressed that the NDL line is a bright line through a grey area - that is, a somewhat arbitrary approximation of safe N2 loading which will keep the vast majority of people from getting bent. But it's no guarantee.

On the other hand, to address the "sheep" issue, the way that you communicate to recreational divers about what lies beyond that line is to tell them that they shouldn't plan on doing it without training, and appropriate redundancy and gas reserves. But you should also tell them that if for whatever reason they find themselves with a deco obligation, just follow the computer and do the deco. You don't need to do "a little bit of deco" to make that point. By suggesting de minimis cases ("what about just ONE MINUTE of deco? Can I do that?"), we normalize variance and make the next person push it a little further.
 
Glad yr ok - but from a beginners diving position , looks like was avoidable - but will say, as everyone is different and no algorithmn or computers will suit all- looks like you found yrs out , K
 
( I dived to 21.5 m on my PADI course Open Water !! Did not die :wink: )
 
( I dived to 21.5 m on my PADI course Open Water !! Did not die :wink: )
But your instructor violated the standards. If he did not follow the standard in one area how can you be sure that your received adequate instruction and he followed them inALL other areas?
Just saying ...
 
Yr right - @fsardone - but at the submerged monument I did get to see a Black Ghost pipefish , so was worth the risk . I do understand people have died to write these tables n limits , but care n a bit of planning will stop horrible things happening. My guy in Red Sea was waaaaay better than guy in UK . K
 
Takeaways - Be very careful about repetitive diving in a mixed air group where you are the only air breather and there is no other check on the performance of your dive computer. Request that the dive guide/leader uses the same gas mix as the most restrictive person in the group (might get some blowback on that). If you have to be the 'tail end charlie' set the P value on your computer to the most conservative value and don't repetitively dive close to limits . If you have more than one computer decide on actions in the event of alarms etc before you get in the water. Get EAN/Nitrox qualified so you always have the option.

Safe Diving. Alan

I'm glad you're OK; that's the important thing.

I dive with a backup and I usually only follow the instructions of my primary unless of course my primary fails. My backup is same or more liberal than my primary. I think ensuring the computers are set properly before you start diving is important. Usually, a more conservative backup doesn't work as you can lock it out and upset it, therefore defeating the purpose of a backup.

I don't think diving a different gas than everyone else was the issue and I don't think what gas the dive guide dives would have affected the outcome. It is on ourselves as divers to be our own "check and balance". The main thing is that you became bent while even diving within NDL on your primary computer which said you still had NDL left. That could mean a possible PFO but it could also mean that you, as an individual, cannot and should not dive as close to NDL as you did. Unfortunately, the way to find that out was having to have skin bends. Everyone is different and PFO aside, it is not an exact science as some folks do get bent within recreational limits while not having a PFO. I am assuming (correct me if I am wrong) that this is a Suunto based on the P0/P2 settings. They are generally known to have a quite conservative algorithm already. Perhaps it is in good order that you dive nitrox in the future (get certified for it!), dive P1 or P2 while on nitrox, don't dive so close to NDL, and maybe also restrict yourself to fewer dives per day and in repetition once you get checked out for a PFO.
 
Yr right - @fsardone - but at the submerged monument I did get to see a Black Ghost pipefish , so was worth the risk . I do understand people have died to write these tables n limits , but care n a bit of planning will stop horrible things happening. My guy in Red Sea was waaaaay better than guy in UK . K

Look I do not want to derail the thread but you just are demonstrating the point of getting close o little bit past the limit because it is worth it. This is the same thing the OP did. Except the OP is seeking not to repeat the mistake you think it was worth it.
It is not. Either you have the training the currency and the equipment to go there or you do not. If you do it anyway you are out of charted territory and after a couple of times doing it and nothing happened you think it is ok. This is normalization of deviance and has killed many.
Please rethink your approach.
 
https://www.shearwater.com/products/teric/

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