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Hi all,

I've noticed something odd, first in OSTC-planner, and now I think I've seen it on a dive and I'm wondering if it's something to be worried about or not.

I dive gradient factors at the default settings (30/85?) and it seems like it's possible for the decompression ceiling to rise whilst the diver is on-gassing. That doesn't seem right to me, and I'm wondering if it's a symptom of a bug.

It's easiest to show in ostc-planner. Plan a deep dive at a constant depth for a reasonable time and plot the deco ceiling. In some cases, whilst still on the bottom the deco, ceiling will go shallower, and then go back deeper again.

I thought maybe this was a quirk of ostc-planner, but I think I've now seen it on a dive. Has anyone else seen this? Is it a side effect of gradient factors?

(I'm at work at the moment so I don't have planner here, otherwise I'd post a proper example)

Hi,

dou you see this behaviour when ascending and staying a very long period of time on a deeper stop?
Then it makes sense from my point of view.
Due to different tissues with different speed of saturation / desaturation it might happen that a faster tissue is first desaturating on that particular stop but a slower tissue will saturate over long period of time.
As the ceiling is controlled by the tissue with the highest gas-load this behaviour might happen on a deeper stop.

Or do you see this beaviour when still staying on the bottom?
Then it doesn't make sense for me neither.

Reiner

Nope, no deeper stop. I see it whilst still deep.

When I get home I'll try to show an example on the planner.

Here's an example on OSTC-Planner, a 42m dive for 40 minutes on air

[IMG]http://i.imgur.com/9W7y2.jpg[/IMG]

You can see the ceiling getting shallower about the 16 minute mark and the 25 minute mark.

Here's a snippet of the verbose simulation:
[pre]
16:12 42.0m Deco:
15 m : 1 ' 20 '
12 m : 2 ' 22 '
9 m : 1 ' 23 '
6 m : 14 ' 38 '
0 m : --- ' 39 '
TTS = 23 '
CNS = 8%
16:20 42.0m Deco:
15 m : 2 ' 21 '
12 m : 1 ' 22 '
9 m : 2 ' 25 '
6 m : 14 ' 39 '
0 m : --- ' 40 '
TTS = 24 '
CNS = 9%
16:28 42.0m Deco:
12 m : 2 ' 21 '
9 m : 2 ' 24 '
6 m : 14 ' 38 '
0 m : --- ' 39 '
TTS = 23 '
CNS = 8%
16:36 42.0m Deco:
12 m : 2 ' 22 '
9 m : 2 ' 24 '
6 m : 14 ' 38 '
0 m : --- ' 39 '
TTS = 23 '
CNS = 8%
[/pre]

We went from having to do 2 minutes at 15 metres and 1 minute at 12 to 2 minutes at 12 metres. It's similar around 18 metres:

[pre]
24:40 42.0m Deco:
18 m : 2 ' 29 '
15 m : 1 ' 30 '
12 m : 4 ' 35 '
9 m : 5 ' 40 '
6 m : 46 ' 86 '
0 m : --- ' 87 '
TTS = 63 '
CNS = 12%
24:52 42.0m Deco:
18 m : 2 ' 29 '
15 m : 1 ' 31 '
12 m : 4 ' 35 '
9 m : 5 ' 40 '
6 m : 48 ' 88 '
0 m : --- ' 90 '
TTS = 65 '
CNS = 12%
25:04 42.0m Deco:
15 m : 2 ' 30 '
12 m : 3 ' 33 '
9 m : 5 ' 38 '
6 m : 47 ' 86 '
0 m : --- ' 87 '
TTS = 62 '
CNS = 12%
25:16 42.0m Deco:
15 m : 2 ' 30 '
12 m : 3 ' 33 '
9 m : 5 ' 39 '
6 m : 48 ' 87 '
0 m : --- ' 88 '
TTS = 63 '
CNS = 12%
[/pre]

That doesn't seem right to me.

I'm a little confused about the ascent too.

[IMG]http://i.imgur.com/o5st5.jpg[/IMG]

It looks like the first stop is spiking the GF at ~50% (GF Low is 30%) and whilst the GF drops off steadily most of the time it has big vertical drops in the middle of the last 3 stops.

Paul

[hr]

Edit: Images didn't work so turned them into links.