Adding to a safety stop

[Lorenzoid]

This has been educational. If I may interject a simple question, assuming a diver is ascending from a typical recreational dive well within the no-deco table limits (taking into account any previous dives), would it be correct to say there is no compartment that could still be ongassing during a 10-20 foot safety stop?

 

[igor p]

This has been educational. If I may interject a simple question, assuming a diver is ascending from a typical recreational dive well within the no-deco table limits (taking into account any previous dives), would it be correct to say there is no compartment that could still be ongassing during a 10-20 foot safety stop?

What is that typical recreational dive? Some more data is needed to answer correctely.

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[Lorenzoid]

What is that typical recreational dive? Some more data is needed to answer correctely.

Oh, c'mon. I started writing more detail but then simplified my wording, figuring most people would know what I mean. Take the Recreational Dive Planner and find a point in the middle of the table. If you're going to force me to be specific, think diving on vacation, a coral reef ... okay okay, how about 60 feet for 30 minutes if you must have actual numbers. But really, it could be somewhat deeper for somewhat less time, or somewhat shallower for somewhat more time--again, well within the interior of the table. Is that enough?

 

[igor p]

Oh, c'mon. I started writing more detail but then simplified my wording, figuring most people would know what I mean. Take the Recreational Dive Planner and find a point in the middle of the table. If you're going to force me to be specific, think diving on vacation, a coral reef ... okay okay, how about 60 feet for 30 minutes if you must have actual numbers. But really, it could be somewhat deeper for somewhat less time, or somewhat shallower for somewhat more time--again, well within the interior of the table. Is that enough?

Yes enought for aproximitation.

There are based on ZH-L16 algorithm last two tissue at the end of the dive with very low partial pressure of inerts so I think those are still ongassing. I am judging visualy this based on Pastodeco graph of tissue status. I entered 60ft depth, 30 min bottom time and 33ft/min ascent , descent 66ft/min. GF set quite agressive 85/85.

If I would be at home I could run a simulation in my software and answer better (am at work now).

Igor P

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[TSandM]

There are theoretical considerations, and there are real considerations. I remember reading a while back that the most common day to get bent on a multi-day trip is the first one. I recently read a research article by Neil Pollock of DAN, looking at bubble grades in divers diving multiple days, and although it was one dive a day, and not the typical pattern of a liveaboard trip, the bubble grades were highest on the first day, and fell thereafter.

It is quite possible that the theoretical very slow compartments might be ongassing during a long safety stop. What's unknown is what clinical relevance that has, if any.

 

[tomfcrist]

I believe the general consensus across the board in recreational NDL diving is that Pyle stops aren't going to hurt at all( we are talking about 1/2 depth 1-2 minute stops here). Regardless of if you are on gassing slow tissues during the stop you don't have any deco obligation anyway, so in reality you are protecting the fast tissues while minimally loading the slow ones...I have yet to hear anyone say that that is a bad thing...NEDU doesn't even remotely address it. If anything else, consider it a multi level no deco dive profile.

 

[igor p]

There are theoretical considerations, and there are real considerations. I remember reading a while back that the most common day to get bent on a multi-day trip is the first one. I recently read a research article by Neil Pollock of DAN, looking at grades in divers diving multiple days, and although it was one dive a day, and not the typical pattern of a liveaboard trip, the bubble grades were highest on the first day, and fell thereafter.

It is quite possible that the theoretical very slow compartments might be ongassing during a long safety stop. What's unknown is what clinical relevance that has, if any.

Hi TSandM, agree with you. Lot of still unknown. But anyway, my opignion is in this last case you mention ongassing on last stop has no clinical relevance.
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[doctormike]

so in reality you are protecting the fast tissues while minimally loading the slow ones...I have yet to hear anyone say that that is a bad thing...

It's not a question of it being a bad thing, it's a question of taking a conceptual model (tissue compartments) and making the leap that you can precisely predict real human pathophysiology based on calculations that are based on assumptions.

So yes, if this was an experimental apparatus with 16 different test tubes containing material with 16 different inert gas diffusion constants, you could do things like precisely figure out the tradeoff in bubble formation for x minutes at y depth after a given profile in each material. But it's not, so all of these mathematical models that predict whether or not an average human being will get bent are based on empirical observation and educated assumptions.

That's not a bad thing at all, it's the best that we have. Tables and computers have made DCS a relatively rare condition in divers who follow these algorithms. I just think that it's important that we keep in mind what all of this is based on when we try to extrapolate.

 

[Lorenzoid]

Thanks for the replies to my question. That makes sense.

 

[clownfishsydney]

The rule in our dive club when out on members' boats is that a minimum of 5 minutes safety stop is required. Anyone who does not follow this rule, no longer gets invited out on a boat. Obviously if there was a very, very good reason for doing less, then a shorter time would be accepted. However, lack of air would not be one (since running low/out of air would be considered a failure to dive correctly), but threatening action by a shark or sea conditions that had deteriorated to an extent that safety was compromised would be okay.

When we go on overseas trips with multiple days of diving, we do a minimum of 10 minutes and up to 20 minutes safety stop.

It certainly cannot be a bad thing to do more.