Why do people add a few minutes to their last deco stop?

[Tracy]

For me it depends. If I am the last to clear, then I start my ascent. I do a five minute ascent from my last stop. If others aren't clear yet, I will hang out until they clear. That would be the only time I add to my stops.

 

[Vicko]

I don't necessarily add to my stops, but I like being in the water so I have no problem with staying there for another few moments.
If that helps with any deco, great. If not, it's still time spent diving, so again, great.

 

[NDonahue]

Hmmm. If you're using 100% oxygen, then the last deco stop is at 20 fsw, correct? In this case, is there a need to add minutes to the last deco stop? And, moreover, you need to be mindful of your oxygen clock as relates to not only the current dive but to the repetitive dives, too.

If your last deco gas is NOT 100% oxygen, then aren't the slowest tissues still on-gassing N2 when you add minutes to the last deco stop(s)?

rx7diver

I think you’ve got that backward. At 10 feet on air or 20 feet on high O2 gas, it is unlikely that any tissues are meaningfully on-gassing after spending a tanks worth of time at depth.

It is ones fast tissue that would be likely to reach equilibrium soonest, but even then, they wouldn’t on-gas, they’d just stabilize at the partial pressure of that stop depth / gas mix.

 

[dmaziuk]

At 20 feet no tissues are meaningfully on-gassing either, the no-limit depth du jour is somewhere around 7.8 msw depending on who you ask.

One theory is bubble size: at 3-5 msw they are smaller than at the surface and therefore are passing through cellular membranes easier. I.e. you are off-gassing faster at the SS depth than topside. (Whether that is true or not is another question.)

 

[arew+4]

Hey buddy, I paid for the gas, I'm gonna breathe it. That ok with you pal.

 

[Manatee Diver]

Hey buddy, I paid for the gas, I'm gonna breathe it. That ok with you pal.

Except for air we pay by the cubic foot down here, so I don't waste gas for filling my suit at the surface.

 

[rjack321]

My instructor says he'll often add a few minutes to his last deco stop, and I've seen a few people on these forums mention that they do a similar thing.

It doesn't make a lot of sense to me, when I hear that in my brain I hear "I don't think my deco plan / GFHi is conservative enough so I'm going to add extra deco on top of it". Why not just decrease the GFHi instead of arbitrarily adding a few minutes on the end (Note: I'm not talking about doing the slow ascent from last stop to surface, I'm talking specifically about adding extra time to the last stop before starting the ascent to surface).

Why do you want to stop diving on the button? Deco plans are "best pseudo-scientific guesses for you" even on perfect days. Sometimes people might have one plan but end up working harder, being colder from sweat or a minor drysuit leak, feeling ache-y on the lower stops, or feeling "dry" on the actual dive. (Looking at the DT guys here) and those are all good reasons to adapt on the fly and add more time. Or maybe just cool fish keep swimming by.

 

[tursiops]

Deco plans are "best pseudo-scientific guesses for you"

Why "pseudo"? Why "guesses"? If you have that little confidence in your deco plan, why do you even use it?

 

[rjack321]

Why "pseudo"? Why "guesses"? If you have that little confidence in your deco plan, why do you even use it?

Because people are unique, every day and dive presents a slightly different physiology, workload, and inert gas exposure than a model might predict, and we're really just terrible experimental units. Plus ethically we can't knowingly make them do profiles which have a high likelihood of harm.

But you know all that, troll on mate.

 

[tursiops]

Because people are unique, every day and dive presents a slightly different physiology, workload, and inert gas exposure than a model might predict, and we're really just terrible experimental units. Plus ethically we can't knowingly make them do profiles which have a high likelihood of harm.

But you know all that, troll on mate.

Yes, I know all of that.
I'm questioning calling this pseudo-scientific, and producing just guesses.
Seems like hyperbole....
I'd of thought you could do better.