Exceeded NDL by a bit, but computer cleared me. What should I do?

[inquis]

it is possible that following the computer's recommended ascent rate will clear that decompression obligation along the way.

This will depend on the computer. Shearwater, for instance, computes the ceiling expecting that you will ascend at 10 m/min. As such, you would always have that stop if that recommended ascent rate is followed. Other computers may vary in their ceiling calculation.

Now, going slower than recommended (what I suspect the OP did) is complicated. The stop time may reduce or even clear (e.g., a fast tissue dominated and the ascent speed was still fast enough to avoid excessive loading of the next tissue). In some other cases, the stop time will definitely increase. All in all, I think it's best to follow the computer as soon as the inadvertent deco is discovered.

 

[arew+4]

I still don't understand.

If a diver stays too long at 80 feet and goes into decompression, then that diver has a decompression obligation. It is the same as if the diver went to 150 feet and went into deco. Either way, that decompression obligation must be met through a combination of ascent rate and stops. Either way, a diver using a computer should follow the advice of the computer, advice based on a tested algorithm.

Just pulling numbers out of my a** for this, but...

Say the plan was go down the slope to 70' for fifteen, then up to 50 for 10-15 depending on gas and NDL, then up to 35 and turn back. At 70 feet I see something really cool at 85 and I drop down for few to check it out. Continue the dive at 70 go to head up to 50 and see I've got a short obligation at 15' and a half a tank of gas. I could go to 15' do my deco and exit bumping on the red for N2 loading, or I could go 35 turn and head back knowing that the deco will clear on it's own at 35' and that my buddy and I have plenty of gas should one of us have an equipment failure. Still do a safety stop at 15, and exit the water in the green for N2 loading.

 

[scubadada]

Just pulling numbers out of my a** for this, but...

Say the plan was go down the slope to 70' for fifteen, then up to 50 for 10-15 depending on gas and NDL, then up to 35 and turn back. At 70 feet I see something really cool at 85 and I drop down for few to check it out. Continue the dive at 70 go to head up to 50 and see I've got a short obligation at 15' and a half a tank of gas. I could go to 15' do my deco and exit bumping on the red for N2 loading, or I could go 35 turn and head back knowing that the deco will clear on it's own at 35' and that my buddy and I have plenty of gas should one of us have an equipment failure. Still do a safety stop at 15, and exit the water in the green for N2 loading.

What's the point, you were in deco and cleared it at a shallower depth, allowing a longer dive time? That's one of the advantages of a dive computer, right?

 

[DeepSeaExplorer]

Looking at this from the other side of the NDL…

This is quite common when doing smallish deco dives. I have been on a number of dives where I planned to do deco, took an O2 bottle, only to find the computer cleared before I got to the first stop. It’s really not a big deal, especially true if your computer has gradient factors set conservatively.

 

[johndiver999]

I think the point was that the deco stop cleared during ascent before reaching the stop depth. No deco done, not a deco dive... But of course, if they’d have felt an urgent need to do a CESA at the point they were in deco, then it would indeed have been a deco dive…

That makes zero sense to me. Once a diver has been informed that he is under a deco obligation, then the situation has changed. Their options (or at least the viability of various options) have changed, specifically because they have acquired a decompression obligation

Just because someone comes up slower than the computer allows (thinks is the fastest safe rate) on a decompression dive, does not mean they were not in decompression. To think otherwise in non-sensical.

 

[scubadada]

Looking at this from the other side of the NDL…

This is quite common when doing smallish deco dives. I have been on a number of dives where I planned to do deco, took an O2 bottle, only to find the computer cleared before I got to the first stop. It’s really not a big deal, especially true if your computer has gradient factors set conservatively.

Why would GFs set conservatively clear any faster than more liberal GFs dived to the same point exceeding deco? Makes no sense.

 

[DeepSeaExplorer]

That makes zero sense to me. Once a diver has been informed that he is under a deco obligation, then the situation has changed. Their options (or at least the viability of various options) have changed, specifically because they have acquired a decompression obligation

Just because someone comes up slower than the computer allows (thinks is the fastest safe rate) on a decompression dive, does not mean they were not in decompression. To think otherwise in non-sensical.

Ok, so you plan to do a dive with requiring 20 minutes of deco. Then, the dive ends up being slightly shallow and shorter than planned. Do you still do the 20 minutes of unnecessary deco? Of course not.

 

[DeepSeaExplorer]

Why would GFs set conservatively clear any faster than more liberal GFs dived to the same point exceeding deco? Makes no sense.

When the computer clears there’s an additional margin.

 

[jborg]

That makes zero sense to me. Once a diver has been informed that he is under a deco obligation, then the situation has changed.

Yeah I expressed my post really badly. I started by "explaining" the supposed point (no deco actually done => not a deco dive), but highlighting the fact that had they needed to surface it would have been obvious it was in fact a deco dive. So I agree fully.

 

[johndiver999]

Ok, so you plan to do a dive with requiring 20 minutes of deco. Then, the dive ends up being slightly shallow and shorter than planned. Do you still do the 20 minutes of unnecessary deco? Of course not.

How is that remotely related to the discussion? Telling beginning divers that when their computer tells them they are in deco, it might not be "real DECO" ; is the issue.

Words have meaning and you either have a deco obligation or you don't.