dumpsterDiver:
This is great information. So you can blow past the NDL at a recereational depth of say 130 feet and stay for 5 more minutes on the bottom and your computer will not give you more than 10 minutes of total deco time and you can probably blow it all off and be "fine".
Have you really done this? Do you really have experiece with diving in this manner? This "advice" is potentially very dangerous. I do 2-3 light deco dives per day and sometime a few more non-deco dives during a typical day while diving between 190 and 90 feet.
I can pretty much assure you that if you stay 5 minutes extra past the NDL limit at 130 feet on, say your third dive of the day, your computer will "spank you hard" and I would be very hesitant to blow off the deco. I have made this "discovery" the hard way. The situation is totally different (and you may be correct) if you stay an extra 5 minutes at 80 feet on the first dive of the day.
Your general statement could really get someone in trouble. I dive with a single computer and almost never look at tables. I follow my computer, do deep stops (that my old oceanic does not call for) and have a lot of faith in the deco information it gives. I have done so many similar dives however, that I pretty much know what my deco status is just by looking at my depth and gas supply. People can follow their computers, but they need to have the EXPERIENCE to know what the computer is going to tell them, "before the computer does".
You are ignoring the most important point of the sentence I wrote which is if the "absolute" worst case happens that your relative risk will not be high. I'm trying to address the fact that the poster does not have formal decompression training and may not be able to handle decompression at the level which is expected of someone who is doing profiles of, say, 20 minutes at 240 fsw where there simply is no room to **** up and blow off any of your deco. At the same time we're not talking about the relative risk of doing that kind of dive and we're talking about the relative risk of a few minutes of mandatory deco at recreational depths.
And I thought I carefully qualified my answer in that this kind of diving still requires people with some introductory training/mentoring in technical diving who were on the road to viewing diving the way technical divers do where problems encountered underwater should be solved underwater. The average recreational diver who doesn't have a clue about all of this and is diving Al80s with no knowledge at all of gas management or any redundancy is completely out of scope for everything I wrote. I don't know how I can be more clear about this. Did you just followup to the first paragraph that I wrote without reading down to the end of it?
I also was careful to mention that I was discussing Suunto computers which I know from experience are very conservative. So going a few minutes into deco on a Suunto computer is really no different from people who push other computers right up the NDL edge. The risk there is the same.
And again, I'm taking a worst-case analysis approach in trying to weight the worst possible outcome against the relative inexperience in decompression diving of the poster. And in the regime we're talking about just about anything works in terms of decompression and its reasonably difficult to mess up. The CESA directly from 130 is very unlikely to happen in someone with a technical mindset who practices basic gas management. The more realistic circumstances (worst case) or a 3 minute stop on a dive 5 minutes over the NDL. And what you're dealing with there is not the certainty of getting bent, but an increased rate of risk compared to the risk of ascending at the NDL time. For divers who do this consistently every dive its a horrible practice and a sure way to get yourself bent. For a diver with the correct outlook on doing decomprssion who is merely inexperienced, they might run something like a 1 in 100 chance of the worst cast happening and a 1 in 100 chance of getting bent in the worst case. That makes for a combined 1 in 10,000 chance of getting bent on any dive which I would consider acceptable risk and on par with the risk of DCS on any recreational dive.
And basically what I'm saying is that decompression risks and training exist on a grey scale continuum which is very poorly captured by lines like "NDL" and by "formal technical training".
Do I think you need formal technical training for 5 minutes of mandatory deco on a Suunto computer at 100 fsw? No. Do I think you need formal technical training for a 20 minute bottom time at 150? Yes. I'm trying to describe the qualitative differences in the risk between those two profiles.
I'm also aware that there's a large qualitative difference between 20 minute bottom times at 150 fsw and 20 minute bottom times at 240 fsw. The 20 minute bottom time at 150 fsw does actually give the diver a lot of leeway to screw up their deco (generally this would be doing way too much rather than too little though) on the way up and still get out fine. When you start talking 240 fsw dives, though, with significant decompression the need to hit the curve precisely starts to become much more important.
