Missed deco stop, lock out?

[EFX]

The alternative design decision is to keep computing the loadings, with no regard to how far above the M-values they are. I can see how some technical divers in emergency situations may find that useful -- but as a programmer I much prefer code that has well-defined limits and throws EOUTOFRANGE when the luser tries to push it beyond its design specs.

I can't speak for other tech DC's but the perdix does continue to track tissue loadings even after the dive has ended. It does have well-defined limits in that if you blow through a deco stop(s) the stop depth and time will blink red alerting you to descend deeper than your stop and then ascend and follow the deco ascent schedule. In the case of missed stops what's being pushed beyond the design specs is not the DC -- it's the user.

The manual, I think, assumes you're still in the water when it advises you to go deeper and follow the deco ascent schedule. The problem is what do you do if you're on the surface and the DC has ended the dive. I couldn't find it in the manual so I assume the Perdix, when the dive ends, continues to calculate tissue loadings on air. It would be nice if you could select 100% (or another rich mix) O2 in surface mode as one option for safe post decompression (the other option which is not as safe is in-water re-compression and subsequent decompression).

Shearwater, are you listening?

 

[BRT]

I can't speak for other tech DC's but the perdix does continue to track tissue loadings even after the dive has ended. It does have well-defined limits in that if you blow through a deco stop(s) the stop depth and time will blink red alerting you to descend deeper than your stop and then ascend and follow the deco ascent schedule. In the case of missed stops what's being pushed beyond the design specs is not the DC -- it's the user.

The manual, I think, assumes you're still in the water when it advises you to go deeper and follow the deco ascent schedule. The problem is what do you do if you're on the surface and the DC has ended the dive. I couldn't find it in the manual so I assume the Perdix, when the dive ends, continues to calculate tissue loadings on air. It would be nice if you could select 100% (or another rich mix) O2 in surface mode as one option for safe post decompression (the other option which is not as safe is in-water re-compression and subsequent decompression).

Shearwater, are you listening?

So maybe at some point of missed deco the computer could start requesting you do a table 6 recompression? I just think at some point you have exceeded the capability of the computer to predict what might happen.

 

[dmaziuk]

This is how I look at it. I assume the models that keep calculating show you decompressing really fast when you are on the surface when you should be at 30 feet? Does it work that way or do big bubbles leave slower?

That's the problem, isn't it: the plain formula would have you decompressing even better if you go flying or drive up a tall mountain instead of hanging at 30'. I read it somewhere that bigger bubbles are supposed to leave slower, but who knows what actually happens and/or what is programmed in proprietary computers. Plain ZH-L doesn't care.

 

[rongoodman]

So maybe at some point of missed deco the computer could start requesting you do a table 6 recompression? I just think at some point you have exceeded the capability of the computer to predict what might happen.

The computer can't possibly predict what might happen. All it can do is to tell you how much inert gas it thinks you have on board and how long and how deep you will need to pause to let it dissipate, warning you if you ignore its suggestions. I would prefer that it not decide to stop doing that because it thinks the diver needs to have his hand slapped.

 

[BRT]

The computer can't possibly predict what might happen. All it can do is to tell you how much inert gas it thinks you have on board and how long and how deep you will need to pause to let it dissipate, warning you if you ignore its suggestions. I would prefer that it not decide to stop doing that because it thinks the diver needs to have his hand slapped.

All of which sounds good, except at some point the computer output has no basis in reality and that is why they quit calculating.

 

[rongoodman]

It’s not clear what you mean by “reality”. When and why do you think the dissolved gas or bubble size calculations might no longer be valid? How they correlate to possible clinical signs and symptoms of DCS is, of course, a different question.

 

[fsardone]

All of which sounds good, except at some point the computer output has no basis in reality and that is why they quit calculating.

No DC output has any basis in reality ever ...
They just have a mathematical model based on assumption or at best on observation or a relatively modest statistica population and crunch a few numbers based on such models.

Basis in reality need to have a connection to the human body to assess the real load and how critical load is reached in each and every tissue (not ideal compartments) ... I don’t think it will ever be possible that a DC has connection to reality.

 

[dmaziuk]

... a connection to the human body...

Was, last I looked, defined pretty much as goats are easy to work with and have body mass similar to that of a human.

 

[BenjaminF]

Was, last I looked, defined pretty much as goats are easy to work with and have body mass similar to that of a human.

Sometimes they use Navy divers instead. Obviously some things are too dangerous for goats to do, and Navy divers are similar to humans...

 

[fsardone]

Was, last I looked, defined pretty much as goats are easy to work with and have body mass similar to that of a human.

Yes by doing statistics and validating a model but reality? For that dive and that diver?