Decompression Stop Guidelines - What we have to do if got deco alert?

[Diver-Drex]

@The Chairman and @boulderjohn, agree 100%. Lead by example and make the important things important.
I would add to explain why things are important. It's not just to pass the class. Too often what was seen and done in class is quickly over written by what is seen on "real dives" and in an effort to not look like a newb. If people understand why they are doing something they are more likely to not discard it.

 

[The Chairman]

I would add to explain why things are important.

You can be sure that I often wax long, if not poetic when it comes to why i dive the way I dive! Some have even used the term ad nauseum.

 

[DevonDiver]

We certainly don't and shouldn't plan for "all things go wrong"

Nobody suggests you should.

Contingency planning involves reasonably predictable and foreseeable issues that could arise.

Technical diving courses introduce many of these foreseeable problems.

Experience, prudence, foresight and local diving knowledge will introduce more.

The danger is when people dive in ignorance of risks and consequences. Recreational diving courses typically gloss over these (at best), or absolutely deny them (at worst). Very, very few recreational instructors are actively enlightening divers on risks and consequences.

Jumping into technical (deco, overhead etc) diving, without the change of educational tone that tech-level training enables, can allow recreational divers to persist in a rose-tinted, risk-blind, outlook that can lead them into very unforgiving situations.... where most failures are beyond their capacity to resolve and the consequences are more damaging than they would predict.

This is why technical (all?) divers should progress the scope and challenge of their diving slowly and keep their dives forgiving / survivable until they've had chance to learn the lessons and broaden their experience.

Recreational no-stop diving is inherently safe and forgiving of failures. It's the place to make your mistakes, get away with it, and learn lessons.

Each step above that... into deco, into accelerated deco, into extended range, into mixed gas, into hypoxic gas, to expedition level tech depths.... becomes significantly less forgiving and offers more severe consequences to any failure and not having a practicable contingency measure for any issue that might arise.

Even where divers might be 'risk-educated'... there can also exist situations where those known risks are perceived only as hypothetical. Thereby enabling a "it can't happen to me" mindset. That mindset can be just as bad as being risk-ignorant.

When experience really is at a suitable level, the diver will have no false illusions of the risks they face, the consequences of failing to mitigate those risks with adequate contingencies... and the fact that those risks really do apply to them.

 

[IDCBali]

Hi Guys... I Expected this article has a lot of opinion from people. This is just an information.. if that information is not right or other please corection.. or I will delete this article.. if this information not good..

 

[Gareth J]

The initial post was to my mind a little alarmist. Some of the other post have been amusing.

A couple of points that sprung to mind as I read through the three.

1. New divers have a lot to learn and absorb. As such, they are often given "rules" to follow, which should keep them in the low risk zone. The "rules" are generally to avoid situations where they have yet to learn the whys and the how.
I teach for an training organisation that is no-stop diving max depth 20m (66ft) on the entry qualification.
The next level includes decompression diving.

2. Whilst decompression diving does add some risk. Particularly - once in decompression, you can't make a direct ascent to the surface with out the increased risk of DCI.
There is risk if you surface after a dive to the extreme of the NDL, is the same as when you surface at the end of a dive where you have completed the compulsory decompression incurred on a moderate decompression dive.
The "safe to surface" point that the computer indicates is based on the same M value limits. i.e a mathematical perceived safe limit of nitrogen over pressure in the tissues.

Riding the computer, i.e. ascending and keeping 1 minute or so as the available No Stop Time, is far more aggressive to my mind than getting 5 minutes of deco and adding 3 or four minutes on at the end of the stop as a safety factor.

The main issue is can the diver maintain the stop depth accurately rather than saw toothing up and down on the stop. Can the diver make a controlled ascent with out saw toothing or ascending to quickly.

3. Understanding what is happening with decompression is important. The mistaken impression that you are not doing any decompression if you stay within the NDL is very wrong (as has been pointed out by others).
Any time you ascend you are involved in a decompression phase of the dive. If you ascend too fast, you are outside the decompression profile for the NDL dive (table). It should also be remembered that sitting on the surface after the dive you are doing a decompression stop!

4. In simple terms. If you exceed the NDL on your computer it is not a crisis or emergency - as long as you can ascend slowly and carefully and hold the required stop AND that you have sufficient gas to complete the stop.

This also means it is preferred to use the "reserve" 50 bar to allow you to complete the stop rather than attempting to avoid breaking "the rule" of ensuring you ascend with the required 50 bar - but have skipped the stop.

The final point - two points

It is far better to be on the boat regretting you cut the dive short or cancelled it than being in the water wishing you where on the boat!

Generally, we have better odds fixing DCI than fixing drowning! Get out of the water BEFORE you run out of gas.

 

[The Chairman]

Riding the computer, i.e. ascending and keeping 1 minute or so as the available No Stop Time, is far more aggressive to my mind than getting 5 minutes of deco and adding 3 or four minutes on at the end of the stop as a safety factor.

I soooo agree with this.

It is far better to be on the boat regretting you cut the dive short or cancelled it than being in the water wishing you where on the boat!

This bears repeating as well.

 

[boulderjohn]

Riding the computer, i.e. ascending and keeping 1 minute or so as the available No Stop Time, is far more aggressive to my mind than getting 5 minutes of deco and adding 3 or four minutes on at the end of the stop as a safety factor.

4. In simple terms. If you exceed the NDL on your computer it is not a crisis or emergency - as long as you can ascend slowly and carefully and hold the required stop AND that you have sufficient gas to complete the stop.

A few months ago I signed up for a dive that was advertised as a double dip (two dives) on a popular wreck at the deeper range of recreational diving. I brought two single LP steel tanks that were seriously overfilled for the experience. They had about 130 cubic feet of gas each. On the boat, there were a number of divers with double tanks. They were planning to do one long deco training dive instead of two NDL dives. Things did not work out, though. When the DM went into the water to try to set the ascent/descent line, she found the current was simply too ripping. She felt we would not be able to pull ourselves down the line. After much discussion, the decision was made to move over to the reef and do a drift dive instead. The boat would drop people off in groups, each group dragging a dive float and flag. I was put in the group with the doubles.

Knowing that I was in a single tank intending an NDL dive and they were planning deco created an obvious problem. The plan was for me to carry the flag, dive as long as I wished, hand the flag off to someone, and follow the line to the surface. The fact that I was diving with a good nitrox mix for the depth and they were on air made it a little more even. As I got to NDL, I still had oodles of gas. I'm pretty sure the doubles people were very surprised I was still with them. I had to make a decision. I probably could have done nearly the entire dive with them with the gas I had, but I did not have redundancy, and I did not have a deco gas. I did stray a bit into deco, but I handed off the flag and made my way up. It would have been extremely unlucky at that point to have a catastrophic gas loss, extremely unlucky, but...but...what would I tell my students they should do in that case, and why should I not do it myself?

 

[scubadada]

...As I got to NDL, I still had oodles of gas. I'm pretty sure the doubles people were very surprised I was still with them. I had to make a decision. I probably could have done nearly the entire dive with them with the gas I had, but I did not have redundancy, and I did not have a deco gas. I did stray a bit into deco, but I handed off the flag and made my way up. It would have been extremely unlucky at that point to have a catastrophic gas loss, extremely unlucky, but...but...what would I tell my students they should do in that case, and why should I not do it myself?

Hi @boulderjohn

What was the duration of your deco obligation? I would assume light deco, whatever your exact definition.

Did you go on to complete a 2nd dive, consistent with the initial plan? I have gone out on many charters that have been a combination of rec and tec, always on a single wreck, never on drift dives. In general, I have always gotten more total bottom time doing 2 rec dives compared to those doing a single tec dive, whether or not I utilized light deco.

Good diving, Craig

 

[boulderjohn]

Hi @boulderjohn

What was the duration of your deco obligation? I would assume light deco, whatever your exact definition.

Did you go on to complete a 2nd dive, consistent with the initial plan? I have gone out on many charters that have been a combination of rec and tec, always on a single wreck, never on drift dives. In general, I have always gotten more total bottom time doing 2 rec dives compared to those doing a single tec dive, whether or not I utilized light deco.

I only did a few minutes of deco. Since i was using ZHL 16C with GFs of 50/80, doing a few minutes of deco was roughly the same as still being within NDLs on some algorithms, so I was pretty safe.

I did do the second dive. The doubles people did not. I did get in much more bottom time than they, but they had a different purpose from mine. They were working on deco skills, so extending bottom time was not their purpose.

 

[RonMurray]

The only time I came really close to running out of air was when I forgot to reset the reserve lever on my "J" valve. Thank goodness air was added as I ascended.

Nice...