Decompression limits and long safety stops

[ginti]

Cressis are twitchy. I have my profiles peppered with "momentary ascent rate warnings" (they come up as yellow triangles in subsurface) where I know there was no audible alarm. Those red dots mean nothing.

@Ahmedben download subsurface, import your logs, and see what it says about your deco at different GF-Hi settings. I expect you'll see the similar ceiling on the first dive at GF 75-ish, not so sure about the second.

Given his experience, I imagine GF are a bit complicated for the OP and might add confusion at this stage...

 

[Ahmedben]

@Ahmedben thank you for sharing your experience here, and it's good to see that you are making the effort to understand what happened, and improve as a diver. You've already gotten plenty of analysis and advice about the dives as reported from smarter people than me, so I won't try to give any more at this time.

But looking at the dive log photo, I did notice something strange. The screenshot is a little grainy and hard to read, but it appears that your dive has 3 logs from that date, not just 2:
- dive 36 at 11:35m to 28.7m for 6 minutes
- dive 37 at 11:45 to 36.4m for 30 minutes
- dive 48 a4 14:12 to 33.2m for 56 minutes

View attachment 737127

From the logs, it appears that for dive 36, you descended down to 28m, briefly looked around, maybe encountered a problem, and then returned to the surface. You solved whatever the problem was at the surface, and then descended once again (dive #37 to 36m), where you eventually bumped into the deco obligation, as discussed upthread.

Maybe I have read that wrong. But if I'm reading this right, two things come to mind:

1) If the computer thinks that this is two separate dives, then you would have had a very brief (maybe 3-4 minute) surface interval between them. It sounds like the Cressi algorithm penalizes for a number of things, I wonder if a tiny dive, followed by a tiny SI, followed by a regular dive is one of these circumstances? @scubadada may have some insight here, since he seems to understand the ins and outs of the RGBM algorithm well. By the way, if there is such a penalty here, that may partly explain the gap between what your computer said (mandatory deco stop) and what others on the dive said (safety stop only).

2) From the Cressi dive software, is it possible to merge dives #36 and #37 into one dive? If so, this may give you a clearer picture of the entire dive. Also, you may want to configure the end-of-dive delay on your dive computer, if Cressi supports this -- I personally have mine set to 10 minutes.

Hi Brett. Thanks for your input. Actually it is true 36 and 37 are one dive and we dive into cave ( bat cave) and inside this cave at the top it has air and we went out to see the bats at the top of the cafe. We stayed like 2 minutes roughly. And then we continued our dive. Good observation. So BC things they are two dives with no surface time

 

[Ahmedben]

Given his experience, I imagine GF are a bit complicated for the OP and might add confusion at this stage...

I will check and give a try. I am a fast learner

 

[Ahmedben]

Yea

@Ahmedben thank you for sharing your experience here, and it's good to see that you are making the effort to understand what happened, and improve as a diver. You've already gotten plenty of analysis and advice about the dives as reported from smarter people than me, so I won't try to give any more at this time.

But looking at the dive log photo, I did notice something strange. The screenshot is a little grainy and hard to read, but it appears that your dive has 3 logs from that date, not just 2:
- dive 36 at 11:35m to 28.7m for 6 minutes
- dive 37 at 11:45 to 36.4m for 30 minutes
- dive 48 a4 14:12 to 33.2m for 56 minutes

View attachment 737127

From the logs, it appears that for dive 36, you descended down to 28m, briefly looked around, maybe encountered a problem, and then returned to the surface. You solved whatever the problem was at the surface, and then descended once again (dive #37 to 36m), where you eventually bumped into the deco obligation, as discussed upthread.

Maybe I have read that wrong. But if I'm reading this right, two things come to mind:

1) If the computer thinks that this is two separate dives, then you would have had a very brief (maybe 3-4 minute) surface interval between them. It sounds like the Cressi algorithm penalizes for a number of things, I wonder if a tiny dive, followed by a tiny SI, followed by a regular dive is one of these circumstances? @scubadada may have some insight here, since he seems to understand the ins and outs of the RGBM algorithm well. By the way, if there is such a penalty here, that may partly explain the gap between what your computer said (mandatory deco stop) and what others on the dive said (safety stop only).

2) From the Cressi dive software, is it possible to merge dives #36 and #37 into one dive? If so, this may give you a clearer picture of the entire dive. Also, you may want to configure the end-of-dive delay on your dive computer, if Cressi supports this -- I personally have mine set to 10 minutes.

this is the log of 36

 

[dmaziuk]

I will check and give a try. I am a fast learner

Don't worry: "gradient factors" is basically a conservatism setting, subsurface is using 75% by default but you can play with it and see what your decompression obligation would have been at different conservatism level as per Buhlmann model, and how that compares with Cressi RGBM.

Here's a profile similar to your first dive (4m shallower) and you can see the ceiling calculated at GF Hi 75 roughly similar to the red line in your picture.

 

[ginti]

I will check and give a try. I am a fast learner

Well in this case.... Deco for divers from mark Powell. Good luck

 

[ginti]

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.

I cite my post again to highlight an important point. DCS is one of the least concerning issues in rec diving when diving according to the accepted safety rules. If you break the rules (for instance: doing deco dives without the appropriate training), DCS becomes a more significant risk.

Good that the OP is trying to understand what happened.

 

[Ahmedben]

I cite my post again to highlight an important point. DCS is one of the least concerning issues in rec diving when diving according to the accepted safety rules. If you break the rules (for instance: doing deco dives without the appropriate training), DCS becomes a more significant risk.

Good that the OP is trying to understand what happened.

What’s does the op means. You made me feel you own this world. And I am just a snoop. Very strange behavior from a diver.

 

[Belzelbub]

Hi Brett. Thanks for your input. Actually it is true 36 and 37 are one dive and we dive into cave ( bat cave) and inside this cave at the top it has air and we went out to see the bats at the top of the cafe. We stayed like 2 minutes roughly. And then we continued our dive. Good observation. So BC things they are two dives with no surface time

That makes sense. Not sure if it's possible with your computer, but see if you can increase the end dive delay. I have the delay set for 10 minutes on my computers. I can still manually end it earlier if I want to. This would group those two dives together as one. In some logging software, you can also do this after the fact.

this is the log of 36

I'm not sure if it's something with the computer, or the way that it displays on the screen, but this is the second dive where it appears that the dive ends at depth. Are you able to scroll to the right on the logging software, or does the profile really end at depth.

 

[Belzelbub]

What’s does the op means. You made me feel you own this world. And I am just a snoop. Very strange behavior from a diver.

That's you. Original Poster, whoever started the thread is the OP.