Flood recoverability

[JonG1]

Picking up on some of the recent threads on features to look for, important criteria to consider, one of the discussion points related to flood tolerance or recoverability, so not how resistant the unit is to a flood but if it floods can you de-water it and continue.

This got me thinking and wanting to understand the concept further.

First of all definition of flood is tricky, most units have traps or points that will allow a certain amount of ingress without functional impact.

It seems as if there are some floods that could not be recovered, e.g. traumatic damage to a hose, component fracture, etc. There could be slow insidious barely detectable leaks that allow water ingress, or user errors such as overly loose lips or DSV/BOV drops.

Obviously traumatic damage can't be fixed, so you are off the loop.

Small leaks could be periodically de-watered, user errors could be de-watered.

However depending on the unit is it possible that an incomplete dewatering could leave the potential for a caustic cocktail depending on unit design, trim, exit or ascent orientation etc, is it worth the risk?

What is the impact on scrubber duration post flood, does it change and if so how much if it's one short total drenching or a small but frequent leak? If you don't know would you chance it?

Does it affect WOB, I understand that even a change in WOB barely perceptible at the user level may result in a later hypercapnic event, does the risk of late onset breakthrough which apparently occurs quickly became more of a reality?

If so are these gambles that aren't worth taking?

Does sea water have a different effect on sorb than freshwater?

Is there a risk that having the capability doesn't necessarily improve the safety, given that it may encourage staying on the loop when a bailout would be safer all round?

Is the range of potential scenarios that de watering can resolve small enough that the extra failure point that the de watering device creates wouldn't stand up to a cost benefit analysis?

It seems from the recent threads that de watering at the major flood level is more useful to the longer range diver at the limits of penetration or depth/profile, is there an argument that it should be an add on or upgrade to avoid another potential failure point which has little relevance to the average diver carrying adequate bailout?

Just thought it may be worthy of discussion.

 

[Whitrzac]

At this level of diving, there is no right/wrong way. Everything is someone's opinion.
Nothing will come out of this thread that hasnt been hashed out before. We're no longer beating a dead horse, but where the dead horse use to be, lol.

 

[JonG1]

I did have search albeit brief of previous threads but don't recall any discussion on the potential impact on sorb, or the cost benefit analysis of the de watering device plus stuff gets re-hashed a lot on forums generally, and sometimes learning or experiential feedback changes with time, or is forgotten and can be a useful reminder to anyone engaged in the thread.

My unit is virtually impossible to de water, I've taken the view that given my diving doesn't demand it it's not an issue but if I were to change it or add a 2nd to the stable, it may be a feature I'd consider if there was merit, hence the thread really.

 

[Wibble]

Would love to have a little button "pump" on the DSV just the other side of the exhaust mushroom valve. Once it starts gurgling, a couple of presses on the "pump" and the water's thrown overboard.

 

[broncobowsher]

You mean the road kill that has been ran over so many times it is hardly a stain on the road anymore?

You left out what kind of diving you are doing. Being 2 miles back in a cave is very different than nice warm water circling wrecks in Truk.

 

[Brad_Horn]

Jon,
As soon as you start talking about water getting to the sorb from a flood, there have only been two designs engineered to not be impacted by it, the Cis-Lunar Mk5p with its waterproof scrubber and the Open Safety series of rebreathers using MicroPore EACs. The Apocalypse Type IV CCR being the only recreational unit on the market available to conduct a full underwater flood recovery on as a routine activity. With the back shell off, an instructor or buddy is able to visually verify through the scrubber viewing port, that the water has been drained out of at least the top half of the scrubber media.

With an EAC the water just drains out and there is no impact on WOB once the unit is recovered from the flood. Likewise scrubber duration. Both have been tested.
As as oxygen cells are located at the very top of the mCCR Apoc (and eCCR Incursion for that matter), as long as you don't invert with a flooded loop - a process not recommended unless you have bailed out - then your cells are still dry even after you conduct a 99% full flood recovery. You can invert with roughly 1L of water in the scrubber/BMCLs and not breathe the water in due to the in-CL snorkals.

With granular sorb as soon as it floods, or even just gets wetter, the WOB goes through the roof https://www.opensafetyglobal.com/Safety_files/Effect_of_flooding_with_granules_061027.pdf and as it isn't recoverable, you no longer have any duration out of that sorb, so that isn't a factor. Just a significant caustic cocktail risk!

While there isn't a lot of published testing of either the WOB or scrubber duration for most granular rebreathers on the market, the variation of the WOB throughout longer dives as the granular sorb get progressively wetter, would certainly be interesting to see studied.
WOB testing for CE et al is done at the start of a dive with fresh sorb....
For very obvious marketing reasons no one publishes any testing of WOB at the end of a granular scrubber duration run; when the scrubber media is exhausted and moisture has naturally built up in the loop.

Wibble,
If your unit has right to left professional gas flow direction, then the ALVBOV includes a water purge button below the faceplate, that enables you to drain that last little bit of water out of the loop in CC mode. It will also lower your units overall WOB.

 

[rjack321]

Some "leaks" never make it to the scrubber.
Megalodon Destruction Challenge (Original) on Vimeo

In other units (kiss classic, sidewinders come to mind) almost any perceptible leak is an immediate bail situation.
There a lot of units or configurations in between these extremes.

As a general rule, I think people judge CCR issues to be smaller than they actually are and stay on the loop longer than they should. Overconfidence in our ability to diagnose and troubleshoot a problem while slightly narced and often can't even *see* the issue is a big problem with CCRs.

 

[Wibble]

If your unit has right to left professional gas flow direction, then the ALVBOV includes a water purge button below the faceplate, that enables you to drain that last little bit of water out of the loop in CC mode. It will also lower your units overall WOB.

Thank for that info.