Is DCS possible under 20fsw, or 100% impossible?

[tursiops]

The phrase "filling the bucket" implies a bucket of a specific size, and as it was used in the thread I described, once the diver was underwater, the bucket will start filling, and will keep filling until it is fill. If the diver goes to 99 feet, the bucket will fill twice as fast as it would at 33 feet, but it will fill either way.

That is, of course, not remotely true, but I think most divers believe that.

The bucket is an OK analogy for a fixed depth. The problem is the bucket gets bigger with depth, and we don't have a simple analogy for that.

 

[MaxTorque]

Given that the common dive tables and algorythms used by the massive number of divers year round mostly stop people getting, on average, bent, then we can look at those numbers to see at what depth we get to a limiting tissue tension assuming saturation and instantaneous surfacing.

 

[boulderjohn]

Given that the common dive tables and algorythms used by the massive number of divers year round mostly stop people getting, on average, bent, then we can look at those numbers to see at what depth we get to a limiting tissue tension assuming saturation and instantaneous surfacing.

Perhaps I am misunderstanding what you are suggesting, but it seems to me you are saying we should look at the numbers of people who get bent after spending many, many hours on a dive shallower than 25 feet to see if we can spot a trend. The trend I would expect would be that not many people are spending many, many hours on a dive shallower than 25 feet, and few, if any, of them get bent.

 

[dmaziuk]

None of this matters for the question as posed: since we don't 100% know what causes DCS, we can't with 100% certainty say it won't happen on any given dive, and dives shallower than 20fsw are a subset of any. It's simple logic, the only deco theory required is the part in bold.

 

[MaxTorque]

Perhaps I am misunderstanding what you are suggesting, but it seems to me you are saying we should look at the numbers of people who get bent after spending many, many hours on a dive shallower than 25 feet to see if we can spot a trend. The trend I would expect would be that not many people are spending many, many hours on a dive shallower than 25 feet, and few, if any, of them get bent.

Sorry, no, i should have been clearer!

Over the last 100 odd years the deco tables have been calculated, estimated and currated. On average, those tables are conservative enough to mostly stop us divers getting bent. So we can look at the values in those tables and use that to estimate the limit case for shallow depths.

For example, if the maximum tissue tension for a given compartment in the Bul16 model is say 1 bar, then we hit that tissue tension by staturating that compartment at a depth of 10 meters (33 feet). Above that depth (shallower) no matter how long we stay at that depth we cannot ever get to the maximum allowable (with 100% GF) tension, ie we can never end up needing to do deco for that compartment.

Generally speaking the slower compartment have lower max tensions, but at some point, those comparments gets so far from anything that is being perfused that it's probably almost irrelevant as if gas comes out of solution in that compartment it may not actually cause an issue. We know the worst case is probably the middling comparments, which are slow enough to take time to off gass, but can dump there inert gas loadings into the blood stream and cause problems else where.

 

[tursiops]

None of this matters for the question as posed: since we don't 100% know what causes DCS, we can't with 100% certainty say it won't happen on any given dive, and dives shallower than 20fsw are a subset of any. It's simple logic, the only deco theory required is the part in bold.

This is silly. Asserting we do not have 100% certainty is irrelevant. Worse, Implying that without 100% certainty we therefore know nothing and cannot make reasonable statements is worse than silly.

 

[kelemvor]

In the end, I choose to dive with a non-zero risk of the bends, and try to dive in such a way to keep that risk small, using the imperfect information available. I also choose every day to drive my car, and cross the street, and drink beer, and tie my shoes. Even though I cannot say for certain that these are risk-free activities, the reward outweighs the risk, so I do them.

Driving a car (with manual controls) is by far the most dangerous of those activities. I urge you to reconsider.

 

[boulderjohn]

For example, if the maximum tissue tension for a given compartment in the Bul16 model is say 1 bar, then we hit that tissue tension by staturating that compartment at a depth of 10 meters (33 feet). Above that depth (shallower) no matter how long we stay at that depth we cannot ever get to the maximum allowable (with 100% GF) tension, ie we can never end up needing to do deco for that compartment.

Sorry, but I am still not understanding. Yes, it is true that at a specific depth, no tissue can ever have a tissue pressure greater than the pressure at that depth. Yes, it is true that if a diver never goes deeper than that depth, the diver can ascend to the surface. That is, in fact, what this thread is all about. Current thinking, based on research, is that depth is somewhere around 20 feet/6 meters.

 

[Duke Dive Medicine]

Sorry, but I am still not understanding. Yes, it is true that at a specific depth, no tissue can ever have a tissue pressure greater than the pressure at that depth. Yes, it is true that if a diver never goes deeper than that depth, the diver can ascend to the surface. That is, in fact, what this thread is all about. Current thinking, based on research, is that depth is somewhere around 20 feet/6 meters.

John, I think what he's saying is that if a given tissue will tolerate 1 bar of supersaturation, saturation at any depth less than that will not result in the tissue reaching its M value on ascent.

Best regards,
DDM

 

[MaxTorque]

^^^ that is exactly what i was trying to say, thanks DDM !!!