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

[seba76]

I just have a question about this because I was in the middle of a argument between two instructors today and wonder what’s the right behavior.

Context, I’m in a dive center, doing two tanks dive per day with surface interval between 45-60min in warm water. Unfortunately no Nitrox available and the dives are mostly around 20 to 25 m, for 45 min total (incl. safety stop). As a results we are often close to NDL limit (specially on second dive). I always try to ascend when I reach 5min before NDL and was once at 1min, never exceed.

Diving with us is a couple, he is dive instructor (CMAS) he also have PADI dive master, teaching TEC, more than 5k dives. His wife in the other end is level 1 CMAS with around 30 dives I guess.

Today during the second dive her computer (SUNTO) give her a stop of 12 minutes at 5m. It was unclear if she exceed her NDL, but there is a probability. Back to the dive center, the manager ask to see her dive computer and claim that if she exceed the NDL she wouldn’t be able to dive for 48h.

His husband claim that it was a non-sense, the dive together and blame the conservative algorithm of the SUNTO. He also claim that the 48hours out of the water is irrelevant. He also explain that normally you can exceed the NDL by a few minutes, because we will slowly ascent and spend some time at 10m, so computer will clear the deco stop.

I’m a bit confuse, I do not plan to go behind my NDL, but interested to know what happen if you exceed by a few minutes. Does this 48hours no dive time make sense if you follow your computer deco stop? Is it the dive center who is to precautious?

 

[azstinger11]

I just have a question about this because I was in the middle of a argument between two instructors today and wonder what’s the right behavior.

Context, I’m in a dive center, doing two tanks dive per day with surface interval between 45-60min in warm water. Unfortunately no Nitrox available and the dives are mostly around 20 to 25 m, for 45 min total (incl. safety stop). As a results we are often close to NDL limit (specially on second dive). I always try to ascend when I reach 5min before NDL and was once at 1min, never exceed.

Diving with us is a couple, he is dive instructor (CMAS) he also have PADI dive master, teaching TEC, more than 5k dives. His wife in the other end is level 1 CMAS with around 30 dives I guess.

Today during the second dive her computer (SUNTO) give her a stop of 12 minutes at 5m. It was unclear if she exceed her NDL, but there is a probability. Back to the dive center, the manager ask to see her dive computer and claim that if she exceed the NDL she wouldn’t be able to dive for 48h.

His husband claim that it was a non-sense, the dive together and blame the conservative algorithm of the SUNTO. He also claim that the 48hours out of the water is irrelevant. He also explain that normally you can exceed the NDL by a few minutes, because we will slowly ascent and spend some time at 10m, so computer will clear the deco stop.

I’m a bit confuse, I do not plan to go behind my NDL, but interested to know what happen if you exceed by a few minutes. Does this 48hours no dive time make sense if you follow your computer deco stop? Is it the dive center who is to precautious?

The 48 hour thing is either shop policy (to ensure a diver has totally cleared nitrogen from their system, as they obviously aren't tech diving) or what is needed to clear out a locked suunto (I don't recall, but know it takes a while). Tech divers will frequently make deco dives the next day or same day (depending on dive times). A 13 minute stop seems realllllllly punitive so either suunto's are worse than I remember or that diver was more than just "a few" minutes past their NDL.

 

[Gareth J]

I just have a question about this because I was in the middle of a argument between two instructors today and wonder what’s the right behavior.

Context, I’m in a dive center, doing two tanks dive per day with surface interval between 45-60min in warm water. Unfortunately no Nitrox available and the dives are mostly around 20 to 25 m, for 45 min total (incl. safety stop). As a results we are often close to NDL limit (specially on second dive). I always try to ascend when I reach 5min before NDL and was once at 1min, never exceed.

Diving with us is a couple, he is dive instructor (CMAS) he also have PADI dive master, teaching TEC, more than 5k dives. His wife in the other end is level 1 CMAS with around 30 dives I guess.

Today during the second dive her computer (SUNTO) give her a stop of 12 minutes at 5m. It was unclear if she exceed her NDL, but there is a probability. Back to the dive center, the manager ask to see her dive computer and claim that if she exceed the NDL she wouldn’t be able to dive for 48h.

His husband claim that it was a non-sense, the dive together and blame the conservative algorithm of the SUNTO. He also claim that the 48hours out of the water is irrelevant. He also explain that normally you can exceed the NDL by a few minutes, because we will slowly ascent and spend some time at 10m, so computer will clear the deco stop.

I’m a bit confuse, I do not plan to go behind my NDL, but interested to know what happen if you exceed by a few minutes. Does this 48hours no dive time make sense if you follow your computer deco stop? Is it the dive center who is to precautious?

If the diver with the compulsory decompression stop completed the stop as required by the computer. Then there is no issue for that diver if they continue diving. They effectively leave the water with the same nitrogen loading as they would have if they had run the NDL right to the limit.

The normal punitive off-gas figure is 24hours (clearing all excess Nitrogen). This is the limit recommended if you intend to fly. Most tables, have a much lower off-gasing period (BSAC88 give 16 hours to completely de-saturate {off-gas} even if you have been doing aggressive decompression diving).
The 48 hours sounds like the dive centre has chosen to be vindictive.

The issue is does the dive centre want to punish divers that incur compulsory decompression stops.

A policy of punishing divers who over stayed the NDL is foolish. It results in fast ascents, missed stops and accidents. Any reputable facility doing that is doing a disservice to their customers. If divers can't stay within the planned dive times and depths, then they dive with a DM to manage the dive.

If the "group" are all within the NDL limit and have stayed within the depth limits, and one particular computer requires a stop. Then it shows this computer is either more conservative, or has the conservative settings turned up. Punishing a diver for this is foolish and shows a lack of understanding of decompression theory, NDL and dive computers. The same dive has been done by all the divers!

ADDENDUM
A facility with that lack of understanding, or with such a vindictive attitude would go on the avoid at all costs list.

 

[azstinger11]

If the diver with the compulsory decompression stop completed the stop as required by the computer. Then there is no issue for that diver if they continue diving. They effectively leave the water with the same nitrogen loading as they would have if they had run the NDL right to the limit.

The normal punitive off-gas figure is 24hours (clearing all excess Nitrogen). This is the limit recommended if you intend to fly. Most tables, have a much lower off-gasing period (BSAC88 give 16 hours to completely de-saturate {off-gas} even if you have been doing aggressive decompression diving).
The 48 hours sounds like the dive centre has chosen to be vindictive.

The issue is does the dive centre want to punish divers that incur compulsory decompression stops.

A policy of punishing divers who over stayed the NDL is foolish. It results in fast ascents, missed stops and accidents. Any reputable facility doing that is doing a disservice to their customers. If divers can't stay within the planned dive times and depths, then they dive with a DM to manage the dive.

If the "group" are all within the NDL limit and have stayed within the depth limits, and one particular computer requires a stop. Then it shows this computer is either more conservative, or has the conservative settings turned up. Punishing a diver for this is foolish and shows a lack of understanding of decompression theory, NDL and dive computers. The same dive has been done by all the divers!

ADDENDUM
A facility with that lack of understanding, or with such a vindictive attitude would go on the avoid at all costs list.

Excellent, excellent post!

I did do a little digging, it does appear that Suunto locks out computers for 48 hours though. Suunto D5 user guide :

"Suunto Fused™ RGBM 2 algorithm is locked for 48 hours if you omit to take decompression stops for longer than three (3) minutes. When the algorithm is locked, no algorithm information is available and Locked is shown instead. Locking the algorithm is a safety feature, highlighting that the algorithm information is no longer valid."

So perhaps it was a miscommunication, that while the diver could go diving (after probably a 24 hour total off gas and switch to new computer), the suunto computer in question could not.

 

[Gareth J]

Excellent, excellent post! I did do a little digging, it does appear that Suunto locks out computers for 48 hours though. Suunto D5 user guide :

"Suunto Fused™ RGBM 2 algorithm is locked for 48 hours if you omit to take decompression stops for longer than three (3) minutes. When the algorithm is locked, no algorithm information is available and Locked is shown instead. Locking the algorithm is a safety feature, highlighting that the algorithm information is no longer valid."

I am not clear from the OP if the diver skipped the stop, or completed the stop and the dive centre are sulking. If the diver skipped the stop because the guide insisted, that is on the guides head and the centres.
If someone told me to skip a stop I would tell them to take a running jump (but not so politely).

On one of my early Trimix trips after qualifying, we where diving in buddy pairs, it was a requirement of the organiser, I was diving with someone who was supposed to keep an eye on me, he was very experienced and known to the organiser, I wasn't. At the end of the dive my buddy wanted to extend the bottom time beyond my drop dead figure - extended plan - (We always carried multiple plans short dive, standard dive, extend because its excellent [plus loss of gas, etc]). I left them and started my ascent as per the extended plan waiting at the 6m on the trapeze for my buddy so we exited together. It was noted I solo'd the ascent - difficult to miss when we all had to ascend to the trapeze, it was also noted we surfaced together. Guess who got the bollocking!

 

[L13]

If the diver with the compulsory decompression stop completed the stop as required by the computer. Then there is no issue for that diver if they continue diving. They effectively leave the water with the same nitrogen loading as they would have if they had run the NDL right to the limit.

Preach!
It shows a fundamental lack of understanding of dive science to treat a completed Deco any different than a dive right at NDL for the same conservativeness settings. If you are using gradient factors, and surface right on the limit with the same GF for both an NDL and a Deco dive, you will have the same excess nitrogen in your system for both dives.

All dives are deco dives. As soon as you go below the surface, nitrogen enters tissues. On an NDL dive this nitrogen leaves the tissues (deco) as you surface, especially if you do a safety stop. An NDL dive is merely a deco dive where the standard ascent (without safety stop) is adequate (or more than adequate) deco, and an extra safety stop is added for additional deco/safety margin.

The difference is that <NDL you may be able to go directly to the surface without exceeding your planned limit, and if you ascend at the planed rate you will not exceed your planned limit.

At ~NDL, you won't exceed your planned limit as long as you do not exceed your planned ascent rate, but might exceed it if you ascend faster than your planned ascent rate.

In Deco you will not exceed the same planned limit as long as you don't exceed your planned ascent rate, including stops.

The normal punitive off-gas figure is 24hours (clearing all excess Nitrogen). ...

24 hours does NOT clear all excess Nitrogen, especially on multi dive days. Though in most cases (but not all) it might reduce it to negligible.

ADDENDUM
A facility with that lack of understanding, or with such a vindictive attitude would go on the avoid at all costs list.

Yes!

 

[azstinger11]

I am not clear from the OP if the diver skipped the stop, or completed the stop and the dive centre are sulking. If the diver skipped the stop because the guide insisted, that is on the guides head and the centres.
If someone told me to skip a stop I would tell them to take a running jump (but not so politely).

On one of my early Trimix trips after qualifying, we where diving in buddy pairs, it was a requirement of the organiser, I was diving with someone who was supposed to keep an eye on me, he was very experienced and known to the organiser, I wasn't. At the end of the dive my buddy wanted to extend the bottom time beyond my drop dead figure - extended plan - (We always carried multiple plans short dive, standard dive, extend because its excellent [plus loss of gas, etc]). I left them and started my ascent as per the extended plan waiting at the 6m on the trapeze for my buddy so we exited together. It was noted I solo'd the ascent - difficult to miss when we all had to ascend to the trapeze, it was also noted we surfaced together. Guess who got the bollocking!

I haven't looked at a Suunot computer in a long time, maybe someone who has one can chime in, but if a diver completed their NDL would their, completed, stop time be visible in the on-board log? I didn't think it was? If that's true the dive center asked to see the computer and saw it was locked, and perhaps the 48 hour remark. This dive center does sound scummy and vindictive but we are also getting 2nd hand information so at least trying to see the other side. They very well could have seen the locked dive computer and said it can't go diving for 48 hours (which is true, Suunto locked it out). They could also just be vindictive little goblins 50/50 lol.

And yes if any dive center staff told me to skip a stop they get a very clear hand sign of what they can do lol.

 

[dmaziuk]

I haven't looked at a Suunot computer in a long time, maybe someone who has one can chime in, but if a diver completed their NDL would their, completed, stop time be visible in the on-board log?

Dunno about that, but if the diver did not complete their mandatory deco stop and did get her computer into the 48-hour lockout, that would be clearly visible on the computer's screen: "GAMOVER", "VIOLERR", or however Suunto displays it. If that's what the computer is showing, then the dive center is entirely correct.

 

[azstinger11]

Dunno about that, but if the diver did not complete their mandatory deco stop and did get her computer into the 48-hour lockout, that would be clearly visible on the computer's screen: "GAMOVER", "VIOLERR", or however Suunto displays it. If that's what the computer is showing, then the dive center is entirely correct.

yeah i guess that's all I'm getting at. The dive center may not be over reacting as much it sounds like. 48 hours for the diver is still a bit much, could sit out for 24 hours and rent a new computer and be okay (last time I looked at a dive table, 24 hours would clear anything but could be wrong). They could be just as easily be over reacting though, hard to know with 2nd hand information from only one party.

 

[AJ]

If I'm understanding this rght, the Suunto locked out for 48 hours. So if she had been diving a Shearwater for instance, which does not lock you out ever, there would have been no problem?

If that is true, the dive center seems to have no clue about deco theory and procedures.