Decompression limits and long safety stops

[Blackcrusader]

Running 46min at 33m at GF 50/80 gives me deco of 76 minutes. My SAC had to be 8/4 lpm to get numbers he gave us.

OP, just because you had 50 dives in last 2 years doesn't mean a lot. The fact that you didn't even realize that your computer is giving you mandatory deco stop supports this.
Anyway, kudos to you for coming here to get the answers and learn. Learn how to plan your dives and stick to it, or at least pay attention at your DC and go up as you run out of NDL.

Or go the next step and take the TDI Advanced Nitrox and Deco Procedures course?

 

[dmaziuk]

I don’t get this attitude. Cheapo rec computers seem to have crappy black on gray displays. No backlight unless you press a button. So a computer with a colorful easy to read display and nice user interface is only for tech divers?

Works just fine in the Caribbean sun, in fact: better than many colourful displays, and lasts 2 years on a watch battery. For diving in black muck they're suboptimal, but some consider diving in black muck suboptimal in itself.

 

[dberry]

I'm not saying OW or AOW students should spend hours leaning tables, but some sort of basic "sanity check" should be mentioned. I'm sure I'll get slammed for even mentioning the "120 rule", but the OP's first post set off some flags in my mind without consulting tables or a planner... 30 min @ 36m? 57 min @ 33m? OK, maybe these weren't square profile dives, and no, I wouldn't plan my NDL dives around "120", but newer divers need to have some rough idea of where the NDL limits should be before they jump in the pool.

And I agree the OP should be congratulated for being open minded for feedback. Too many folks post a "question" or describe a situation, but really just get defensive and try to justify themselves when offered feedback.

 

[Ahmedben]

As others have said, you appeared to go into deco on your second dive and had a mandatory decompression stop. It is hard to be sure because we do not have enough information on your dives. They were clearly multilevel dives, or else you would have been in deco on the first dive as well.

I quoted part of your post above because it is really not totally the fault of the dive center's crew. It is your dive and your computer. It is important that you understand and monitor what your computer is telling you. If you are in danger of going into deco and do not want to do that, you need to adjust your dive accordingly. You should have ascended to shallower depths, probably on both dives, to stay out of deco. The divemaster cannot force you to stay too deep when you know you should be getting shallower.

helo,
I have bought the IR connector to my PC and I hav downloaded the dive data, both dives were on deco, I would like to hear feed back from a professional people about what could be improved on those dives and mistakes have encountered. i know the simple answer is follow my DC but i was wondering about the Ascent rate was above 12m/minute recommended values 30ft/mn.
P.S.

i have dived 6 deep dives after that deco ones and i followed my DC and all is fine.

 

[scubadada]

Hi @Ahmedben

Thanks for posting the follow up. I assume the red line at the top of the graph is your deco. So, on dive 37, you were in deco from 16 min until 26 min and your deco cleared just before your safety stop. On dive 38, you were in deco from 30 min until just before you surfaced at 56 min.

I bet you have learned some new, valuable information regarding your dive computer, good for you. Going back to your original post is quite interesting now

 

[boulderjohn]

Hi @Ahmedben

Thanks for posting the follow up. I assume the red line at the top of the graph is your deco. So, on dive 37, you were in deco from 16 min until 26 min and your deco cleared just before your safety stop. On dive 38, you were in deco from 30 min until just before you surfaced at 56 min.

I bet you have learned some new, valuable information regarding your dive computer, good for you. Going back to your original post is quite interesting now

Just following up on this...

You did two fairly serious deco dives without deco training or equipment. I want to take a minute to explain the importance of this.

A very general and simplistic way of explaining the difference between a deco dive and an NDL dive is that in an NDL dive, if you encounter an emergency, you should be able to go to the surface immediately, but in a deco dive you can't. That is because of the likelihood of decompression sickness. Decompression divers carry gear (including redundant breathing gases) and have training that allow them to solve problems without going to the surface. In your case, if you had had some sort of an emergency (like a free flow) that forced you to the surface, you would have likely suffered DCS. It could even have been fatal.

 

[Nemrod]

I might be misreading the second graph but it looks like you surfaced still in deco obligation? The first graph you cleared.

As Mr. John says, both of these dives exceed your equipment and training level and had you encountered a problem you might have been seriously hurt (DCS).

Many divers may push their dive such that they ride the computer knowing from previous experience that as they ascend the deco obligation will continue to clear. I am guilty of that. I justify it in my mind though it is a poor practice in general because I have my computer set for a high safety factor.

Those two dives justify full redundant equipment because simply ascending would not have cleared your obligation, you had a deco ceiling. This is why divers who do caves, wrecks and deliberate deco dives carry fully redundant equipment.

The simple answer is not to just follow your computer but to plan your dives sufficiently that know about how much BT you have for your mix and anticipated depths and times and surface intervals and then monitor your computer to remain in compliance for any deviations from the plan.

You are cutting it too close there .

James

 

[MrBlenny]

Mark Powell wrote an entire book on decompression theory (Deco for Divers), going well beyond the basics, and he never once felt compelled to teach how to use tables. Decompression theory is one thing. Managing decompression is another.

I second this: Deco for Divers is an excellent book that I have read and re-read. Definitely worth the $35 USD.

 

[scubadada]

Hi @Ahmedben

To expand on my previous post a little, following the additional replies from @boulderjohn and @Nemrod

Can you drag your cursor over the dive profiles to find out how much deco you had during the dives? That would help us better understand the magnitude of your errors. On both dives the text below the graphs states that you did not have a deco stop violation. That is why I earlier stated that it appeared that you had just cleared deco on dive 38 before surfacing. Apparently, your computer did not go into violation gauge mode.

On dive 37 you went into deco after you had started your slow ascent and cleared a little before your safety stop. I would imagine that the deco obligation for this dive was quite short, a few minutes. This type of profile was mentioned by @Nemrod

Dive 38 is a different story. You went into deco at about 20 meters and stayed at that depth or a little deeper for about 5 min, before starting your ascent. When you got to your stop depth, and as per your initial post, it appears that you had 8 min of deco obligation, not trivial.

Does the red flag next to the dive number in your log indicate a deco dive? If that is the case, it appears that dives 33 and 42 also had deco obligations.

Your Cressi computer is relatively conservative, especially on repetitive dives

Decompression limits and long safety stops

If you did all the stops your computer told you to do, chances are you won't suffer DCS this time. But I would encourage you to rest, drink water, pay attention to how you feel, and seek medical attention if anything feels off. It sounds like you might be a little unsure about what your computer...

scubaboard.com

Decompression limits and long safety stops

@Alaskan Scuba Dude, post #5 said the SI was 1 hour and 50 minutes. He is a bot, he doesn't really care of what was said - he just wants to say stuff. @Ahmedben, when you say the second dive was "mostly at depth," do you mean it was mostly at a depth of close to 33 meters, or just that most...

scubaboard.com

Despite that, you are putting yourself at risk with your training and equipment deficiencies. I hope you are doing better.

 

[MrBlenny]

helo,
I have bought the IR connector to my PC and I hav downloaded the dive data, both dives were on deco, I would like to hear feed back from a professional people about what could be improved on those dives and mistakes have encountered. i know the simple answer is follow my DC but i was wondering about the Ascent rate was above 12m/minute recommended values 30ft/mn.
P.S.

i have dived 6 deep dives after that deco ones and i followed my DC and all is fine.

It's great that you got the IR connector so you can fully review your dives. Like many other here, I find this to be an invaluable tool for all dives, deco or not.

Also, as you indicate above that you are continuing to do deep dives (what do you consider deep?), I would highly suggest getting a second computer. At 30+ meters it's really easy for an issue to eat into your NDL (narcosis doesn't help with rapid problem solving, either), and suddenly being without a computer is less than comforting. As a real-world example, during a training exercise for my AN/DP I had my computer battery nearly die while I was at 40m (lithium battery + cold water). This would have been stress inducing at a minimum had I not had a second computer. For the sort of depths you seem to enjoy, a Perdix or similar computer would be advantageous, but anything is better than no computer. Just my two cents

Cheers!