Petrel GF for deep stops

[Qasar]

Good afternoon all
I just bought a Petrel 2 and wonder how to use the GF or GF 99 to decide and monitor deep safety stops.
Well some points before:
1. I'm a Dive leader (BSAC), I know the gradient theory and M factor (at least I read the articles on that)
2. I don't intend to use that for real deco deep stops, it's just safety deep stops, if I want to do some of them in a deep recreational dive
3. Telling me to follow the computer and have 5 mn safety at 6m won't help a lot
My interest here is just to know what I have to look for to better understand what is going on during the ascent and if the deep safety stops are improving or worsening the offgasing.

Thank you for your help

 

[rhwestfall]

perhaps monitor/utilize the @+5 calculation & TTS???

 

[victorzamora]

@+5 and TTS are only for deco, and I believe the OP was asking specifically about Recreational diving.

Watch this video to get the best idea of what's going on:
https://www.youtube.com/watch?v=O81vX79X_mA

 

[dreamdive]

GF settings matter for decompression. So if you don't go into deco, you will not utilize the GF settings. However, if you decided to alter your ascent and build in "deep stops", the Petrel will track that. However, don't be surprised if your NDL time decreases. As you are performing "deep stops" you also will be on-gassing and that might affect your NDL time.

 

[mac.calder]

You could use the Tissue Loading graph as a quick way of telling whether you are on or off gassing. Watch their video on it here. If you are ongassing on your deep stops then they really aren't doing anything for you. To off gas you want your tissue loadings to be above the ambient pressure line.

 

[Dr. Lecter]

GF99 is probably going to be most useful for your purpose. Dreamdive is partly correct that "deep stops" may cause ongassing across the board - depending on the depth you choose and your degree of loading. Then again, you may be at a point where fast tissues are offgassing while slow tissues are still loading.

What you want to do is figure out where in the ascent you're no longer ongassing and have switched to some level of offgassing tissue tension in the leading compartment(s) -- which the GF99 value will show (theoretically, of course). If your "deep stop" depth is so deep that you're still seeing "Ongas" where a GF99 value would normally be...well, do with that info what you like. Assuming your deep stop depth is above the ongassing depth, then the question becomes what GF99 tension do you want to tolerate vs. where do you think a deep stop would help you. If you want to do 2 minutes at 60' after a 120' dive, and you see the GF99 value at 60' is only going to be 1%...maybe not a very useful deep stop. If you've been deep so long that going straight to 60' gives a GF99 of 40% (that'd probably be in deco, but you get the idea), maybe deeper would be more prudent by your standard.

 

[manni-yunk]

@+5 and TTS are only for deco, and I believe the OP was asking specifically about Recreational diving.

Watch this video to get the best idea of what's going on:
https://www.youtube.com/watch?v=O81vX79X_mA

Im not sure thats entirely true......deco or no deco I believe he could utilize both as well as the tissue loading graph to get the info he is looking for.

 

[guyharrisonphoto]

You also might want to look at the recent DAN information that suggests deep stops on recreational dives are not beneficial and might actually be potentially risky for repetitive dives due to some tissues still ongassing at the deep stop. Not saying not to do deep stops as that is your call, but it is worth taking into consideration and an alternate strategy might be to concentrate on a properly slow ascent of 10m/min.

 

[Qasar]

You also might want to look at the recent DAN information that suggests deep stops on recreational dives are not beneficial and might actually be potentially risky for repetitive dives due to some tissues still ongassing at the deep stop. Not saying not to do deep stops as that is your call, but it is worth taking into consideration and an alternate strategy might be to concentrate on a properly slow ascent of 10m/min.

Hi all
thank you for your inputs. May be a little more help on how to use gf99 in coordination with the tissue graph?
IN addition guyharrisonphoto coul you post a link to the DAN info?
Thank you

 

[guyharrisonphoto]

Here is the link to the recent DAN article. there is a lot of "follow your computer and do deep stops if it tells you to" but the article also references to a navy study showing that deep stops may actually increase risk.

Alert Diver | Deep Stops