Planned deco on a recreational dive?

[Rusty Roo]

A 25% increase in the risk of getting decompression sickness. It's not worth it.

a 25% increase? so what's the increase between 0- 4 mintues? 100% you're going to get dci?

hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

 

[RainPilot]

Wow another instructor who thinks that the loss of gas at a deco stop is worse than loss of gas on the bottom during a recreational, unplanned deco dive which is conducted without a redundant gas supply.

Have you ever done a CESA with zero air from 100 or 125 feet? Just curious if you have actual experience in something similar.

Who said anything of the kind? I never once said anything about my gas supplies at the time. Nor did John. The ENTIRE point we have both made was that those dives were not necessarily deco dives at all, just illustrating the grey area that can arise depending on computer settings etc.

FYI as a team we had done rock bottom planning, there were 3 of us each with enough reserve gas to take a buddy up WITH the safety stop, in addition I was diving twin sidemount but gas calculation was done for a single tank so I was carrying an additional 80cf of unplanned reserve gas.

The gas planning has never been a point in this thread, I know it's one of your hobby horses but please don't make unwarranted assumptions about my diving practices. I have no intention of being a vendetta target for you like you have been trying to do with @boulderjohn

 

[boulderjohn]

I have no intention of being a vendetta target for you like you have been trying to do with @boulderjohn

Explanation...

I am sure some of you know this already, but dumpsterDiver stalks me. He looks for any opportunity to twist my words, exaggerate statements, and do whatever he can to make me look bad. This is the third thread in which he has done it since January. He also did it to Pete (NetDOc in a thread a week or two ago. This has been going on for many years. I normally ignore what he writes, but I have lately decided to speak out against it. It gets very, very old.

 

[Patoux01]

A 25% increase in the risk of getting decompression sickness. It's not worth it.

Wow, care to cite your sources for this?

Because then I'd have gotten bent about 30 times already in my (short) dive career.

 

[RainPilot]

Oh, @dumpsterDiver in my whole career I have never managed to end up in real deco with no buddy and 500 psi at 100'. I'm quite sure John hasn't either.

Glass houses have a great view but...

Depth: 95 ft, In Deco, 500 psi, No Buddy

 

[Diver0001]

The problem with “lite” decompression diving is not carrying enough gas or being able to control buoyancy to some rudimentary degree, but the ability to survive a loss of gas -at the worst possible time.

I agree and I think this is one of the big risk factors involved in any kind over overhead diving, whether it's a virtual or a real overhead.

I suspect that John would agree with that. I also suspect that he was trying to explain in his post that a "decompression" requirement is a grey line, not a black-and-white line and you jumped on it from a different (black-and-white) perspective. It seems to me that you're both right if you consider the perspective from which the post was written/intended.

gr,
Rob

 

[boulderjohn]

Just to give people an an idea about what I am talking about in terms of the differences in algorithms....

If a diver goes to 100 feet on air for 20 minutes, that diver is within NDLs (barely) according to the PADI tables. That diver has a "required" safety stop on the way to the surface.

If a diver goes to 100 feet on air for 20 minutes, that diver is well into deco according to the Buhlmann ZHL-16-C algorithm with GFs of 50/80 on a Shearwater computer. In fact, the computer will call for nearly a minute at 30 feet, a minute at 20 feet, and 5 minutes at 10 feet.

If those two divers go to 100 feet on air together on air, the diver using the PADI tables has 20 minutes before exceeding NDLs. The diver with the Shearwater will require a 1 minute deco stop after only 9 minutes.

The Buhlmann calculations were done using Multi-deco.

 

[tech_diver]

I believe it was Confucius who said in 500 BC, "a man with two different dive computers never really knows his true deco status"

I think it was Confucius....

 

[wbatten1]

a 25% increase? so what's the increase between 0- 4 mintues? 100% you're going to get dci?

hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm

Wow, care to cite your sources for this?

Because then I'd have gotten bent about 30 times already in my (short) dive career.

Probability and statistics... By saying a 25% increase in the risk of getting DCS, I do not mean an additional 25% chance of DCS occurring. To clarify, if you have a 10% chance of getting DCS, and you increase that risk by 25%, you're adding 2.5% to the chance, giving you a 12.5% chance of getting DCS. If you have a 50% chance of getting DCS and you increase that risk by 25%, you're adding 12.5% chance, giving you a 62.5% chance of getting DCS. My apologies if my phrasing wasn't clear enough.

That 25% is a worst case scenario, but an accurate one based on Buhlmann's ZHL-16 algorithm. However, determining the risk before adding those extra two minutes is quite complicated. That's something not worth 'diving' into right now. (See what I did there?)

More importantly, why has this become a thread in talking about differences in algorithms and who's spent some time in deco / who's ignored stops and came out just fine? My understanding is, the original question was along the lines of, "Is it okay to ignore the limits of my recreational certification and pretend I'm a tech diver without getting any additional training?" Diving to 150ft is well beyond any recreational limit and firmly in the technical world. Proper planning of decompression stops (and understanding of the algorithms in use) is beyond any recreational limit and firmly within the technical world. The answer to the OPs question should be, "Walk away from the dive and do a different one within the limits of your training. There's nothing you'd see on that dive that's worth risking your life."

 

[luscioman]

I find your comments about the dangers of decompression diving to be off the mark. It is surprising to me that a technical dive instructor would promote this kind of attitude (“I don’t worry about it” ) for a recreational dive situation where the diver is accruing 3 minutes of required decompression penalty.

More specifically, you are claiming that should you go a little into deco (without any redundancy which is required by agency standards, it seems), the worst that could happen is that you might run low on air at a shallow stop and have to blow off a minute or so of deco.

The sort of grossly simplistic thinking you put forth is something I would expect from an open water student, not from a tech instructor.

As I have mentioned before, I have no technical training, but it is quite obvious to me that a much, much more serious problem which MIGHT arise on a decompression dive - would occur AT DEPTH not at 10 feet. This is something that I WORRY ABOUT. In other words, the WORST CASE SCENARIO IS NOT A PROBLEM AT 10 FEET!

If a recreational diver (who has entered into the required decompression “zone) is carrying no redundant gas supply (something you have no problem with) and has an air supply failure (at depth) and is unable to secure an alternative breathing gas source, then the only remedy is going to be a rapid ascent – with zero air. The ability to maintain a safe ascent rate of 30 feet per minute (let alone the deco or safety stop) is going to be compromised or eliminated for just about everyone.

The problem with “lite” decompression diving is not carrying enough gas or being able to control buoyancy to some rudimentary degree, but the ability to survive a loss of gas -at the worst possible time.

Once the diver has completed a normal (slow and careful) ascent and has reached the deco stop depth of 10 or so feet, the consequences of (the loss of a gas supply) resulting in the blowing off a minute (or 3) of deco are much less troubling.

If the same thing happens at 125 feet.. The situation is drastically (and obviously) very different.

Since this is the “BASIC SCUBA” section of the forum, I think the weakness in your argument should be explicitly addressed.

DumpsterDiver though we have never met I like your posts and what you offer the board. But just a few weeks ago you posted this thread Depth: 95 ft, In Deco, 500 psi, No Buddy in the video you were at 97 feet with 500 and in deco. You were very clear that this is not recommended and not planned but it did happen and you dealt with it. I think that is important that everyone learns how to deal with deco to some extent. I have been on many boats that a diver comes up with their computer beeping. Crew goes to check it and they have a violation and were in deco. They could have cleared it out if they had some idea how it works but most dont understand what they are looking at in the first place. Understanding how to deal with it if it happens is important for peoples safety and not coming up if they hae 5 mins to do.