Decompression limits and long safety stops

[ginti]

@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 of the dive wasn't spent on safety/deco stops? The first one is what is usually meant by the question, but unless I've screwed up the math, you'd have to have a pretty impressive SAC rate to spend anywhere near 46 minutes at anywhere near 33m and only use 170 bar.

Agree.

Also, I'm not a tech diver, but for those in the thread who are: wouldn't that kind of profile on air incur a lot more than 11 minutes of deco? My Teric's deco planner says that after 45 minutes at 33m/100 feet on air, I'd need 4 stops totaling 49 minutes, and that's with no residual nitrogen. Obviously coming up even just a little helps a lot in that regard, but even if I drop it down to a max depth of 80 feet (24m) for 45 minutes, I get 3 stops totaling 24 minutes. I'm thinking most of the dive had to be spent at a much shallower depth.

More than 11min for sure. Diving nitrox32 at 30m for 45min would give roughly 15min of deco on backgas. Now, the total deco time takes into account part of the ascent too, but here the OP was diving air and was deeper. Your numbers look realistic.

However, I don't believe he was doing a square profile with a single 12l tank... He probably touched 33m and spent the other time shallower, and this profile would drastically change the mandatory deco time.

@Ahmedben, do you have your diving profile saved on your computer? Would you share it?

 

[formernuke]

You definitely went into deco. Very dangerous for a new diver.

As stated above this is totally your responsibility. It is up to you to understand what your computer is telling you.

The only other thing I can say is I've been on some boats where you would not be allowed back on after doing a unplanned, untrained, unbriefed deco dive.

 

[ginti]

Last question, does the deco. Stop eliminate any DCS risk ?

As mentioned, nothing eliminate DCS risks. However:
1 - Longer safety stop, within the boundaries of rec diving, help mitigating the risks.
2 - Don't be scared of DCS. It is by far one of the least concerning issues in rec diving. Bad physical shape, heart troubles, panicking, inadequate equipment, mechanical barotrauma etc are way more concerning. DCS is an issue, but a very little one.

 

[Ahmedben]

First I would like to thank everybody for their input and valid replay and feedback, much appreciated.

second sorry If I couldn't replay on all the questions as I was tired yesterday and I was replaying from my phone, and some replies doesn't show up ...etc.

Today I feel much better as yesterday a lot of things accumulated ( waking up early, 2 hours drive, diving, 2 hours drive back and probably decompression).

so to get this well, i wouldn't consider my self as a fresh diver, as I am a certified rescue diver, and I had over 50 dives in the last 2 years. but this season i have just started and yesterday's 2 dives were second and third this season ( after 8 months off). Where i stay at the moment the diving trips organized by diving centers on different areas, and each diving center does trips over the same diving points all the time, so basically you go to a certain area and locate a diving center and they will just take you on their boat and head for the dive, we don't involve on planing and the majority of them are professional and they have done these dives thousands of times and they mitigate all the risks and generally they are going with the limits.
Yesterday ones were a bit different ( no need to go into details)

My mistake was not following the DC strictly and I was more like following the dive buddy. ( also the second dive was a bit messy, high current, one of the guys has some issues while diving...etc) so I decided to stay in group than just do my own things following the DC ( lesson learnt).

P.S.
my diving computer was set to the most liberal algorithm setting ( default one).
unfortunately I can not take the dive log data as I don't have the IR connection to my DC

Thanks again for all the feedback
Regards
Ahmed

 

[Ahmedben]

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 was telling you, which might mean you didn't actually do all the stops.

tnx, I feel better today

 

[ginti]

second sorry If I couldn't replay on all the questions as I was tired yesterday and I was replaying from my phone, and some replies doesn't show up ...etc.

Don't worry, it's a forum. You aren't obliged to do anything

so to get this well, i wouldn't consider my self as a fresh diver, as I am a certified rescue diver, and I had over 50 dives in the last 2 years. but this season i have just started and yesterday's 2 dives were second and third this season ( after 8 months off).

2 dives after an eight months break and 50 dives under your belt mean that you are basically restarting; 30m is probably close to your limit, and the way you managed your dive suggests I am right.
Keep it easy right now: I strongly suggest you do several shallower dives, in your comfort zone (max 18m? even less?), before going so close to your boundaries again.

P.S. certifications are not an index of experience, but an index of training. And while at 50 dives you aren't a newbie, you aren't an experienced explorer yet Sometimes having a bit of experience gives the wrong feeling of being more experienced than one really is. I am sure this isn't your case, otherwise, you wouldn't be writing here, but it can be useful to highlight this aspect for other people reading the post.

Where i stay at the moment the diving trips organized by diving centers on different areas, and each diving center does trips over the same diving points all the time, so basically you go to a certain area and locate a diving center and they will just take you on their boat and head for the dive, we don't involve on planing and the majority of them are professional and they have done these dives thousands of times and they mitigate all the risks and generally they are going with the limits.

Yesterday ones were a bit different ( no need to go into details)

My mistake was not following the DC strictly and I was more like following the dive buddy. ( also the second dive was a bit messy, high current, one of the guys has some issues while diving...etc) so I decided to stay in group than just do my own things following the DC ( lesson learnt).

We all do mistakes, and that's fine. Just learn from them

P.S.
my diving computer was set to the most liberal algorithm setting ( default one).
unfortunately I can not take the dive log data as I don't have the IR connection to my DC

Can't you even look at the profile on the screen of your DC?

 

[scubadada]

Your Cressi computer, running Cressi RGBM would be considered conservative. It is possible that your DM and other divers were diving computers with more liberal decompression algorithms...

Thanks, a good point, never though that the difference in algorithm can lead to big difference between them.

@Ahmedben

Hi Ahmed,

This is particularly true of the RGBM computers (Cressi, Mares, Suunto) on repetitive dives. The first dive on RGBM computers is generally fairly liberal, most would consider them moderate or middle of the road in the spectrum between conservative and liberal.

Repetitive dives are shortened by a number of factors that are incorporated into the RGBM algorithms and can end up with relatively short NDL times. The factors that may shorten repetitive dives are generally not explicitly discussed in owner's manuals for the computers, that is true for your Leonardo. Factors that are frequently discussed are fast ascent, short surface interval (yours was not short at 1:50), reverse profile, sawtooth profile, and perhaps others. I don't know what being close to deco or doing deco might do. Remember, you can always check your expected NDL before a dive by using your dive planner function.

Your owner's manual only mentions a safety stop of 3 min, I do not see that it is adjustable. Perhaps your 1st dive also had a short deco stop?

Your computer gives you a warning when your NDL reaches 3 min

It warns you again when you go into deco and has a deco symbol. This must be where you saw your deco time on the 2nd dive.

You can verify whether you went into deco or not on the primary screen of your onboard log. Go back and look at the 1st and 2nd dive for this day and check the deco status

If you omit a deco stop on your computer, you will be locked out for 48 hours.

I dive frequently off boats in SE Florida. Several times every year someone asks why their computers are not working correctly. The most common answer is that they are locked out due to a missed deco stop. This happens almost exclusively with RGBM computers. Many divers are not familiar enough with how their computers work and with what their computer is telling them.

You appear to have a good attitude toward your diving and a willingness to learn. Best of luck in your future diving.

 

[Aquaviolator]

This thread should be a topic covered in basic open water. Instead its just use the computer and the dive tables are just barely mentioned, much less fully comprehended.

 

[Esprise Me]

Can't you even look at the profile on the screen of your DC?

Not an option on the Cressi Leonardo, unfortunately. You can't even get your average depth without buying that stupid cable and downloading the dive to your PC. I used to have one of those, and I was so thrilled with all the bells and whistles when I upgraded to a Shearwater Teric.

My mistake was not following the DC strictly and I was more like following the dive buddy. ( also the second dive was a bit messy, high current, one of the guys has some issues while diving...etc) so I decided to stay in group than just do my own things following the DC ( lesson learnt).

I think the scenario you describe is actually really common. Diving requires that you pay attention to a lot of things at once. When you're following a guide and trying to keep an eye on your buddy while also looking at fish, it's hard enough to remember to keep checking your gauge. Trying to also periodically check your remaining NDL on your computer and keep a mental tally of those numbers without losing sight of the guide, buddy, and stuff you came to see in the first place, is more than many people can manage unless they dive frequently for some time. And if you do realize your air or NDL is running low, it's not always easy to get your guide's attention and get them to bring the whole group up, so you're faced with an unenviable choice between risking running out of air/NDL, and leaving the group. I've said before that's a topic I wished they covered in OW, because while it seems clear enough in retrospect that the scary second option is the right one, I don't think many divers who haven't thought it through in advance are capable of coming to that decision underwater. And if you've been following a guide and not checking your compass or making note of features you could use to navigate, and you don't have a DSMB or don't know how to use it, leaving the group could be problematic. I dive without a guide all the time, but I too am susceptible to turning off my brain when I'm following someone. I think that's a big part of why so many vacation divers end up going into unplanned deco, with many not even doing the deco stops their computer tells them to do.

Anyway, we all make mistakes, but only some of us take the time to learn from them. Glad you're one of us!

 

[scubadada]

Not an option on the Cressi Leonardo, unfortunately. You can't even get your average depth without buying that stupid cable and downloading the dive to your PC. I used to have one of those, and I was so thrilled with all the bells and whistles when I upgraded to a Shearwater Teric.

I am unable to see my average depth or starting and ending gas pressure on my 12 year old AI Oceanic VT3 without downloading the computer. Fortunately, it came with the download cable and Oceanic had a free, more than adequate, download application. Both the computer and download app work to this day and I still dive the computer (1764 dives, 1862 hours0.

I have dived a number of second/backup computers since 2006, a Cochran EMC-14 for its liberal algorithm, an Oceanic Geo 2 to match the DSAT deco algorithm of my VT3, a Dive Rite Nitek Q to learn Buhlmann, and a Shearwater Teric since 2019.

Computers have come a long way, even for those of us that do mostly no-stop or light deco dives. My Teric gives me average depth, a dive profile, water temperature, starting and ending gas pressure, SAC, and starting and ending CNS O2 exposure, all off the onboard log. Downloading by Bluetooth to the Shearwater Cloud apps gives considerably more information. The Buhlmann ZH-L16C with GFs deco algorithm is infinity flexible to meet my personal requirements. The SurfGF function allows me to surface from my safety stop or deco stop with the safety margin I choose.

For recreational diving or light technical activity, with the major exception being air integration, the Shearwater Peregrine offers many of the same features of the Teric at less than half the price for the computer alone, not even considering the extra cost of a transmitter