6m last stop vs 3m last stop

[JonG]

I think I remember reading somewhere that staying at 6m as opposed to reducing the gradient by rising to the 3m ceiling improves ISS on surfacing, but can't recall if it was gas agnostic or applied on CCR or just OC.

Obviously conditions or gas management or CNS clock may influence the decision but just wondered if anyone could back up my memory?

[Wibs]

Less impact of waves at 6m. Also less critical of precise positioning as you nod off on your stop.

[graham_hk]

Love a 3m stop - for me the 1.6 to 1 reduction in pressure is way too much! Talking about real dives not 50m for 30min which anything will work

[shapeshifter]

I once spent ages going through the calculations to compare theoretical differences between doing the last stop at 6m or 3m.

The upshot is that the difference in ISS can go either way depending on the preceeding profile, how fast you ascend from the last stop and how soon after the dive you drive home.

[JonG]

This was more what I was looking for SS, were there any trends in terms of preceeding profile/ascent rate and how did the drive home affect things, was it the exercise impact of unloading gear etc?

[shapeshifter]

This was all ages ago but IIRC the biggest difference was was for the safety stop on no deco dives.

The drive home was relevant in my case because I live at 660m and could get there from sea level in three hours if I left straight after the dive.

You've almost got me curious enough to rerun the simulations - do you have any specific profiles in mind?

This was more what I was looking for SS, were there any trends in terms of preceeding profile/ascent rate and how did the drive home affect things, was it the exercise impact of unloading gear etc?

[cathal]

Love a 3m stop - for me the 1.6 to 1 reduction in pressure is way too much!

Agreed, the pressure differential between 1.6b and 1b compared with 1.3b and 1b is not worth it after a decent decompression dive. For good measure I add a good 5 minutes afterwards going from 3M to the surface.

Cathal

[AxeMan]

Love a 3m stop - for me the 1.6 to 1 reduction in pressure is way too much! Talking about real dives not 50m for 30min which anything will work

But it's the partial pressure of the inert gases that is the most important thing. If you're decoing on oxygen, doing your last stop at 3m or 6m makes very little difference to total deco time on buhlmann. CNS is another matter.

[cathal]

6m last stop vs 3m last stop

But it's the partial pressure of the inert gases that is the most important thing.

Agreed it is the pp of N2 that is of concern. But just because your controller says your tissues are clear that does not mean they are clear. The controllers results are just an indicator of your tissue state, based on an algorithm. Your actual tissue states from inert gas dynamics in your body after the dive are another thing completely.

[JonG]

Agreed it is the pp of N2 that is of concern. But just because your controller says your tissues are clear that does not mean they are clear. The controllers results are just an indicator of your tissue state, based on an algorithm. Your actual tissue states from inert gas dynamics in your body after the dive are another thing completely.

This was what I was interested in, a thread on SB referred to differing iss based on holding stop depths longer than prescribed and compared various gases and GFs.

I am interested in whether it's actually safer to keep the pressure on the inerts at 6m and use the gas or loop to elevate inspired PPO2, or whether a move to 3m is preferable.

SS my typical profiles at moment are 50-60m for circa 30-40 mins.

[cathal]

This was what I was interested in, a thread on SB referred to differing iss based on holding stop depths longer than prescribed and compared various gases and GFs.

I am interested in whether it's actually safer to keep the pressure on the inerts at 6m and use the gas or loop to elevate inspired PPO2, or whether a move to 3m is preferable.

SS my typical profiles at moment are 50-60m for circa 30-40 mins.

Purely from a pressure differential, including a 3M stop 'smooths' out the gradient. Also compare the exact same dive plan side by side, one with a 3M stop and one without. The difference is negligible time wise but, and to return to my original point the pressure differential between 1.6b and 1b compared with 1.3b and 1b is not worth it after a decent decompression dive. Even when its rough I find you'll hang on at 4M no problem. Just switch SP to .7 and manually add the O2.

Rgds

[Paulo]

Purely from a pressure differential, including a 3M stop 'smooths' out the gradient. Also compare the exact same dive plan side by side, one with a 3M stop and one without. The difference is negligible time wise but, and to return to my original point the pressure differential between 1.6b and 1b compared with 1.3b and 1b is not worth it after a decent decompression dive. Even when its rough I find you'll hang on at 4M no problem. Just switch SP to .7 and manually add the O2.

Rgds

Do you pad the 6m stops with shallow stops or do you do the last 5-10mins at 3m?

[JonG]

It's all obviously highly theoretical without any evidence or the ability to model ISS with the different FIO2 and pressures, but maybe a halfway house between taking the pressure off the inerts and incurring a significant change in pressure bewteen last stop and surface is merited.

So incl. for the 3m stop but pull half at 6m and half at 3m, effectively elongating the 6m stop, it's also easier I find to keep loop ppo2 up at this depth.

[JonG]

This is the thread for reference, the ISS references are in the latter pages:

https://www.scubaboard.com/community/threads/re-evaluating-my-gf.574700/

[AxeMan]

This is the thread for reference, the ISS references are in the latter pages:

https://www.scubaboard.com/community...-my-gf.574700/

But no one seems to explain what it actually is or how it's calculated