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Old 26th March 2006, 08:50   #1
BubbleTrouble
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CCR emergency procedures

Folks, in my quest to learn about rebreathers and ultimately decide if going for one is worth the trouble, I'd like to ask any and all of you experienced pilots, some specific questions.
I understand with rebreathers, divers train to essentially be self-reliant in an emergency, but you always have a buddy too. In an OC world, it's relatively simple, run out of air go to your buddy,etc etc.

But obviously in a rebreather situation this may be different, so...
- what kind of emergencies are likely to occur?
- how do you resolve each type of emergency?
- are some rebreathers better than others in terms of handling emergency and why?

I also realise, procedures will be different between various types/makes of rebreathers. Any info would be appreciated.

cheers
Mike
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Old 26th March 2006, 09:13   #2
DaveB
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Re: CCR emergency procedures

This is a big subject, with some different opinions; mine are still open to review! (I dive an Evolution, a fully closed circuit rebreather)

What can go wrong compared to OC:
  • Too much or too little O2 - happens fairly slowly and should be picked up by standard monitoring (either wrist/dangling displays or Head up lights. Unless you have actually run your O2 cylinder dry this requires you to run the unit manually in one form or other and should be practiced regularly.
  • Too much CO2 - happens when there is something wrong with the scrubber - channelling - badly packed scrubber or O ring problems, or something wrong with the material - normally overuse but some have reported 'bad lime' though no one I know personally.
  • Complete electronics failure - very unlikely as most units have a least one form of electronic redundancy, but if it does you can use the unit in semi closed mode.
  • Water in the breathing loop - happens when the loop is not sealed to start with, or you tear something underwater. Has also happened when the mouthpiece is not operated correctly underwater. Most units (inc Inspirations and Evolutions) are very tolerant of water in the loop, trapping it in he exhale counterlung. I know of a specific case where poor mouthpiece drills (during a Mod1 course) allowed 2 or 3 inches of water into the scrubber after filling the counterlung - the unit continued to operate throughout a normal ascent.
Others following may disagree with some of the above - but I hope that bit is fairly uncontroversial. However, now comes the philosophical divide. At the extremes are those who feel that you must allow for the unit to comprehensively fail and carry enough OC bailout to get back to the surface safely. The other end of the extreme are those who feel that if you pay proper attention to the unit set up, and dive appropriately, you can cope with any equipment failure with a combination of manual drills and SCR fallbacks, remaining on the loop throughout and not carrying any bailout. (Alpinist view). Middle ground is to carry some bailout to get you back to surface supplied or team resources.

I started out on the total OC bailout approach, but have become more confident of the unit the more I dive it. Not totally Alpinist yet, but moving in that direction.
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Old 26th March 2006, 17:10   #3
caveseeker7
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Re: CCR emergency procedures

Dave summed it up pretty nicely. And very general, as that is really the only simple way answer. The units are so different that detail description of possible problems and all their possible solutions vary for each model.

But just a few more thoughts:

While O-O-G is the most likely problem OC divers face, hypercapnia (CO2 poisoning) as well as hyper- and hypoxia (wrong mix for depth) have occured on OC, too. They are just considerably rarer events.

As mentioned, many problems that occur on rebreather take their time, and a vigilant diver has a good chance to solve them.

Usually rebreathers have plenty of redundancy build into them, such as the normally used automatic gas addition systems backed up with manual systems. Separate power supplies. Tripple redundant sensors for measuring pO2. Redundant displays to convey the info to the diver. But even redundancy varies, there are redundant setpoint controllers and even tripple redundant controllers. In addition there are alternate operating modes, for example using a CCR in SCR mode. And last but not least, OC bailout.

Of course, the redundancy and the more sub systems are added, the more failure points are introduced and the more complex a rebreather gets. Which in and by itself is seen by many as a disadvantage and has led to the development of 'simple' systems.

But there are differences when it comes to flood tolerance loop recoverability.
Differences in gas management, differences in manufacturer provided bailout.
Hence each unit has its own training course.

I suggest reading "Mastering Rebreathers" by Jeff Bozanic as it lists the most common emergency situations as well as their solutions.

Last edited by caveseeker7; 26th March 2006 at 17:41..
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Old 27th March 2006, 06:35   #4
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Re: CCR emergency procedures

Quote: (Originally Posted by BubbleTrouble)
I also realise, procedures will be different between various types/makes of rebreathers
I can only speak for eCCRs but I've always thought that faults fall in three types:
1) Loop gas is wrong.
2) Don't know what the loop gas is.
3) Loop has gone away.

1) You have cell readings you trust but the injection system is dud. This is time for the manual modes you learn in CCR 101. I might just continue the dive unless I think it is the batteries.
2) The dead handsets problem or the cells are all reading differently. With a flush you may be able to decide which cell(s) to trust but otherwise you are into semi-closed or 'top-up' mode drills. This is the hardest one. If you're unsure goto (3). Definitely the end of the dive.
3) Flooded or CO2 break through. The easy decision. Bail out and get out. No-stop diving I'm onto the DIL and then the O2 once I reach 6m. Deco diving I carry my two 7s of bottom mix and 50%.
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Old 29th March 2006, 03:04   #5
BubbleTrouble
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Re: CCR emergency procedures

Cool. Thanks guys. I found this very interesting. I have also located a full description of the KISS CCR course and that has some really really useful info.

Here it is.
KISS Course.pdf

cheers
Mike
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