Deco + safety stops?

[Nick_Radov]

Don't presume to justify any of those decisions as "scientific". Do it whichever way makes you happy but there has never been an apples-to-apples comparison in a high-quality RCT to definitively establish one approach as being safer than another. And in real world diving there are more factors to consider than just minimizing DCS risk.

 

[grassybreakfast]

Don't presume to justify any of those decisions as "scientific". Do it whichever way makes you happy but there has never been an apples-to-apples comparison in a high-quality RCT to definitively establish one approach as being safer than another. And in real world diving there are more factors to consider than just minimizing DCS risk.

"Whichever way makes [me] happy" is the way that is best supported by the current body of scientific evidence. And this post is about trying to determine what that is.

Obviously as deco theory continues to evolve, our methods will have to evolve with it, as they have been for the past decades. Yes, obviously also other factors to take into account on a real dive.

 

[tursiops]

so 6 minutes on the final 6 meter ascent, where the pressure differential is greatest.

I hope you just said this without thinking about it, because it is not true, no matter how many times people say it. 6m of water provides the same pressure differential at any depth. What is different about being shallow is the pressure ratio, not differential.
That is, if P6 is the pressure at 6m, and P0 is the pressure at the surface, then P6-P0 is the pressure differential (i.e., 6m of water, or 0.6 ATM); that is the same as, say, P66-P60. But P0/P6 is the pressure ratio you undergo for those last 6m, which is a much greater drop than, say, P60/P66, which is nearly unity (0.92), whereas P0/P6 is 1/1.6=0.625 ATM.

 

[Nick_Radov]

"Whichever way makes [me] happy" is the way that is best supported by the current body of scientific evidence.

You are imagining a body of scientific evidence which doesn't exist. But feel free to extend your shallow deco stops beyond what the models require if that doesn't piss off your dive buddies and boat crew. If you're lucky there might be some jellyfish or something to look at.

 

[steinbil]

I hope you just said this without thinking about it, because it is not true, no matter how many times people say it. 6m of water provides the same pressure differential at any depth. What is different about being shallow is the pressure ratio, not differential.
That is, if P6 is the pressure at 6m, and P0 is the pressure at the surface, then P6-P0 is the pressure differential (i.e., 6m of water, or 0.6 ATM); that is the same as, say, P66-P60. But P0/P6 is the pressure ratio you undergo for those last 6m, which is much greater drop than, say, P60/P66, which is nearly unity (0.92), whereas P0/P6 is 1/1.6=0.625 ATM.

Thanks for the correction. The problem was not lack of thinking, but lack of familiarity with the terminology. I got the terms mixed up, maybe because, as you said, it's a common mixup.

 

[Alex Ouroboros]

Whether or not this is a good idea is a matter of debate. There is a big difference between dives with required decompression and NDL dives, and this issue is at the heart of that difference.

On an NDL dive, if you begin the ascent within NDLs, it does not seem to matter how long you take on that ascent, as long as you do not exceed NDLs along the way. If you leave 100 feet within NDLs, you should be able to go directly to the surface (at a safe rate of speed), do a 3 minute safety stop, do a 5 minute safety stop, check out a shallower portion of the reef for 15 minutes--whatever. Extending time at safety stop depth is beneficial, whether needed or not.

If you have required decompression, it is quite the opposite. If you extend deeper decompression stops, you have to extend the shallowest stops to compensate. While you are extending those deeper stops, your slower tissues are on-gassing, and you will need to give them time to off-gas during the shallow stops.

It is very much like the change in thinking on deep stops. Twenty years ago, people thought doing stops much deeper than were traditionally done was good practice, but that thinking has largely gone away as research shows that the added nitrogen loading at depth was not a benefit.

I don’t extend the deep ones, before I leave each one I do check how I feel as I believe you should, the only one I usually extend if safe to do so is the last stop,,, possibly the 9m one as well but only if it’s been a pretty deep dive for considerable time (ie 3-4hr deco) ironically I’m not sure I feel any better for not doing the old deep stops that we used to,
Yeah of course we go with science but I always listen to my body and usually know how I’m going to feel for the next day or two before I’ve even left the last deco stop, padding that one out in my experience makes a huge amount of difference,,,
I’ve seen many people watching their computers like a sort of stopwatch at 6m and exiting asap after it clears while there is no rush to leave and then I see very washed out faces that look tired on the boat which are obviously suffering the residual bubbles within a hairs breadth of a full on bend when they could of had another 15min at 6m while waiting for other divers…