Help needed analyzing a dive

[Dody]

One of my friends, a diver with about 100 dives over 5 years called me today saying that he had been in deco for the first time in his life but the circumstances are strange. He told me that he dived at 39 m and surfaced when the NDL was at 2 minutes. He said that after a while, the NDL rose to 3 minutes. He also claimed that his computer never gave any alarm. At some time, he got a serious buoyancy problem and told me that releasing air from LPI or valves did not work but this is not what triggered the deco, right.
We checked together and he rose from 24m to 4 meters in 2 minutes so the rapid ascent was not that severe. To make a long story short, he was not alerted of any deco, he did not know he was in deco, he did not do any deco stop, continued his dive and made a safety stop at the end. After the dive, he was shocked to see deco dive in the DC log although the computer is not locked. To add to the puzzle even though he did not do a deco stop, it seems that the deco disappeared a few minutes before the end of the dive (see attached pictures). What has happened?

 

[J-Vo]

I have no idea what those screen shots are telling me, but I would guess the PDC is calculating ascent rates into "deco"/"No deco" while the log software is showing any time there is a deco ceiling. So your under a deco ceiling, but as long as you ascend at 10m/s you will not exceed it.

As for deco clearing while at the safety stop/shallow portion, that's just how deco works.

 

[Blackcrusader]

With many dive computers even if you went into a slight deco the deco will clear itself as you ascend. My shearwater will do this and show DECO CLEAR in top right hand corner when you also complete the safety stop.

Strange your friend thinks he needs to surface when NDL increases as he ascends and no need to rush to the safety stop level as his DC would show increased NDL even at a slow ascent rate. See the video a very slow ascent but NDL increased.

 

[Gareth J]

I am not familiar with the computer or the plot.
I am assuming the Red section is the dive requiring decompression. The Blue the No-stop dive.
Most dive software allows you to step through the dive, showing the computer display as the dive progresses, i. depth, dive time, no-stop/decompression time, alarms, ascent rates etc.
If your software allows you to do this, then it may provide more information.

Looking at the pictures you posted, the initial impression is that the no-stop dive time reached zero, at or about the deepest point of the dive. What your friend may then have seen, as he initially started his ascent, was not the No-Stop time increasing as he got shallower, BUT, the decompression stop time increasing as he started his ascent. (Even though he was getting shallower, he was still on gassing, this would cause the decompression penalty to progressively increase! )
If my assumption is that BLUE is no-stop and RED is decompression, then it would appear that the decompression time was missed during the ascent / rapid ascent. The subsequent re-descent, was potentially within the 'window' the computer allowed for the diver to re-descend below the stop ceiling. Eventually the decompression was completed and the computer switched back to no-stop (Blue).
In the top left of the picture there is an arrow down with 3.4m. This I suspect is the ceiling depth. Which again would indicate that the computer had transitioned from no-stop to decompression stop dive.

This may will be an issue of lack of familiarity with the computer display when it switched from no-stop to stop time.
If there is a simulation facility on the computer, I would suggest running it, and getting the computer to transition from no-stop to stop time to make you familiar with the computer display.
Assuming there is an alarm when the no-stop time reaches may well be wrong. I know on some of the Suuntos they give a 'beep' when you transition from no-stop to stop time. I have seldom registered the beep!
My OSTC and the CCR don't produce any audible alarm when you transition from no-stop to decompression.

There are three issues.
1. The loss of buoyancy control is of significant concern, especially when the dive depth is taken into account.
2. The fact that the diver transitioned from no-stop to stop time and was unaware of the fact.
3. The fact that the diver re-descended after surfacing and missing compulsory decompression stops.
All three of these are red flags.

This is not intended as a direct criticism of the individual. Just observations.

 

[Dody]

I am not familiar with the computer or the plot.
I am assuming the Red section is the dive requiring decompression. The Blue the No-stop dive.
Most dive software allows you to step through the dive, showing the computer display as the dive progresses, i. depth, dive time, no-stop/decompression time, alarms, ascent rates etc.
If your software allows you to do this, then it may provide more information.

Looking at the pictures you posted, the initial impression is that the no-stop dive time reached zero, at or about the deepest point of the dive. What your friend may then have seen, as he initially started his ascent, was not the No-Stop time increasing as he got shallower, BUT, the decompression stop time increasing as he started his ascent. (Even though he was getting shallower, he was still on gassing, this would cause the decompression penalty to progressively increase! )
If my assumption is that BLUE is no-stop and RED is decompression, then it would appear that the decompression time was missed during the ascent / rapid ascent. The subsequent re-descent, was potentially within the 'window' the computer allowed for the diver to re-descend below the stop ceiling. Eventually the decompression was completed and the computer switched back to no-stop (Blue).
In the top left of the picture there is an arrow down with 3.4m. This I suspect is the ceiling depth. Which again would indicate that the computer had transitioned from no-stop to decompression stop dive.

This may will be an issue of lack of familiarity with the computer display when it switched from no-stop to stop time.
If there is a simulation facility on the computer, I would suggest running it, and getting the computer to transition from no-stop to stop time to make you familiar with the computer display.
Assuming there is an alarm when the no-stop time reaches may well be wrong. I know on some of the Suuntos they give a 'beep' when you transition from no-stop to stop time. I have seldom registered the beep!
My OSTC and the CCR don't produce any audible alarm when you transition from no-stop to decompression.

There are three issues.
1. The loss of buoyancy control is of significant concern, especially when the dive depth is taken into account.
2. The fact that the diver transitioned from no-stop to stop time and was unaware of the fact.
3. The fact that the diver re-descended after surfacing and missing compulsory decompression stops.
All three of these are red flags.

This is not intended as a direct criticism of the individual. Just observations.

I agree. This is what I told him.
1) I told him to have his BC service. You don’t want to have a BC that can’t deflate.
2) Still no explanation other than he did not look at his DC but there are alarms. I used to have an Aqualung i300c as primary (it is now just a backup) and the alarms are audible enough.
3) He did not surface. He was at 4 meters due to uncontrolled buoyancy. Then he resumed diving oblivious of the deco. He told me his DC only showed fast ascent not deco.
I would have advised him to buy the

I have no idea what those screen shots are telling me, but I would guess the PDC is calculating ascent rates into "deco"/"No deco" while the log software is showing any time there is a deco ceiling. So your under a deco ceiling, but as long as you ascend at 10m/s you will not exceed it.

As for deco clearing while at the safety stop/shallow portion, that's just how deco works.

I have no idea what those screen shots are telling me, but I would guess the PDC is calculating ascent rates into "deco"/"No deco" while the log software is showing any time there is a deco ceiling. So your under a deco ceiling, but as long as you ascend at 10m/s you will not exceed it.

As for deco clearing while at the safety stop/shallow portion, that's just how deco works.

Sorry but I don’t understand the relationship between ascent rate and deco.

 

[Dody]

With many dive computers even if you went into a slight deco the deco will clear itself as you ascend. My shearwater will do this and show DECO CLEAR in top right hand corner when you also complete the safety stop.

Strange your friend thinks he needs to surface when NDL increases as he ascends and no need to rush to the safety stop level as his DC would show increased NDL even at a slow ascent rate. See the video a very slow ascent but NDL increased.

He did not surface on purpose. He just had a buoyancy problem and when fixed at 4 meters, he resumed his dive still oblivious of a deco issue. Can the two issues (fast ascent and deco) be related? I don’t think so. The chart shows that the deco started after the beginning of the ascent and my friend claim that the NDL was increasing.

 

[Dody]

Do you find it realistic to be in deco without knowing it or is it probably a case of not looking at the computer or not understanding the display?
I have never been in deco so I am wondering.

 

[ginti]

Do you find it realistic to be in deco without knowing it or is it probably a case of not looking at the computer or not understanding the display?
I have never been in deco so I am wondering.

You can easily end up in a mandatory deco stop "without knowing It", everything you need to do is to forget looking at the computer and/or at the bottom timer and exceeding the NDL time

P.S. Every dive is a deco dive

 

[ginti]

In the screenshot, I can see a "32 min".

Was it the total dive time? And max depth 39m?

 

[Blackcrusader]

Do you find it realistic to be in deco without knowing it or is it probably a case of not looking at the computer or not understanding the display? I have never been in deco so I am wondering.

You were one minute or less to deco on your first 40.5m dive with a 40m depth limit as a student. You were concerned ou went into deco as your DC had you do a deco stop before the safety stop. Have I been in deco without knowing it? No. Have I gone into deco on an NDL planned dive? Yes. A diver with 100 dives over 5 years may not be fully learned about his DC and NDL and other things. I've had to explain TTS to a number of divers. They have nice computers but fail to know what each thing means. So yes a diver can have a DC and not understand what it tells them.

Most computers will lock you out if you avoid a deco obligation. My Shearwater will not as it is not a baby sitter and no audio alarms as well. Every diver should read their DC manual and not just once only but several times. I've been bored from not diving so I have been sitting around planning dives on air and nitrox some within NDL and some deco dives. I plan with different sac rates to see how many liters of air I need. Different size tanks with different fills taken into account.

I can plan with different GF for deco and get different results for bottom times. What DC is your friend using? I did not look at the graphs yet.