K-CCR Bailout Procedures

 

           

 

            So, you’re diving along, happy as a clam, or maybe a seal, and something doesn’t feel quite right, what do you do?

 

            There are many different failure points on any rebreather, as the owner-diver of an RB you should be very familiar with your specific unit.  This is the kind of stuff that you should have learned from your original RB instructor during your first hours with your unit.  Maybe your instructor was having a bad day, maybe s/he wasn’t up to the task, maybe you forgot the things you were taught, after all that was a lot of info in a short period of time and its difficult to absorb all of it.  I find that I learn more about a subject if I return to the textbook/manuals etc after using something for a while and pick up on the details that I may have missed the first time through.  This article is to help address bailout procedures specific to the KISS conversions of the Drager Dolphin and other K-CCRs, you may learn something whatever you dive.  Directive number one is to properly prepare your unit, don’t let anyone (even yourself) rush you through your pre-dive checks.  You may think that you will be missing the most awesome dive of your life if you don’t get in the water fast.  STOP, do your checks, better to be late for the best dive of your life than early for the LAST dive of your life. 

 

FAILURE MODES

 

1)     LOOP VOLUME DEPLETED.   Upon descent you find that you cannot take a full breath.  If your RB has an ADV (automatic diluent valve) you should check whether the diluent tank has been turned fully on, if it has and you still don’t have enough gas in your counter lung, abort the dive.  At this point you may discover that not having gas for your counter lung also means no gas for your BC or dry suit and you are sinking fast.  You can still regain breathing gas and buoyancy by quickly filling your loop with Oxygen from your KISS valve, this will inflate your loop, giving you gas to breathe and making you closer to positively buoyant, don’t mess around, get your self to the surface and fix your unit.  This is not a safe solution if you are very deep, but works if you are making your initial descent.  The best fix for this problem is to make sure your ADV works and all valves are turned on BEFORE you enter the water.

2)     WATER IN THE LOOP.  First, is the water up stream or down stream of the DSV?  If it is down stream and just a slight gurgle on exhalation, its an easy fix to drop your right shoulder into a roll while exhaling, dumping the unwanted moisture into the exhale CL/water trap, be careful of loose lips on the mouthpiece.  If the gurgle is up stream of the DSV, you may be heading for the caustic cocktail, inhale carefully while facing down, if you smell or taste metallic or Listerene you have gotten moisture into your scrubber.  First try dipping your right shoulder and cautiously taking a few breaths, you may be able to get the bad stuff to slide past the DSV into the exhale side and eventually dump it into the water trap.  DON’T DO  A FULL ROLL YET, wait until you are sure all the caustic solution is on the exhale side and no more is coming.  If this fixes the problem and doesn’t taste or smell bad anymore, continue the dive.  If you continuously have moisture coming down from the inhale side, its time to end the dive, Close your DSV and switch to  OC  and complete any deco time you may have acquired.

3)     CATASTROPHIC LOOP FAILURE.  You take a breath and nothing but water, first CLOSE YOUR DSV!!! You will lose more buoyancy quickly by leaving it open when you bailout to OC, as this is the only alternative with a full loop failure.  Prevent this by doing your pre dive checks carefully, positive and negative pressure checks and making sure your loop hoses are attached properly.

4)     PP02 TOO LOW.  Add 02 with your KISS valve.  No 02 coming in?  Do a quick purge with diluent, exhale through your nose and inhale from your mouth 3 times to exchange the loop gas with fresh diluent, this will give you a few moments to figure out what’s wrong with your 02 add system.  Check the tank valve, fully open?  Do you have another valve in the line?  Did it get turned off accidentally?  Check your contents gauge, are you out of 02?  If your 02 add system has truly packed up (and gone home) then its time to abort the dive and bailout to SCR, see section below.

5)     PP02 TOO HIGH.  This can be caused by too high of intermediate pressure in your 02 add reg, best to turn it down so it bleeds the amount of 02 you need at rest, you can always add more via the KISS valve.  This can also be caused by a stuck 02 add valve, if this happens, turn off your 02 at the tank or auxiliary shutoff, you can manually control the 02 by actuating these valves but the task loading will be excessive, best to end the dive under manual control or by bailout to SCR, see section below.  If you are at depth and the PP02 is excessive, you may lower it by purging the loop with diluent.

6)     SYMPTOMS OF HYPERCAPNIA (CO2 HIT).  This can be caused by scrubber breakthrough due to trying to stretch your scrubber too long, by channeling, the C02 rich gas sneaking around the scrubber material that may be too loosely packed or omitting the rubber dam (drager dolphin), over breathing the scrubber (too much exertion) or by not filling the scrubber at all (don’t laugh, its been done).  The symptoms of this are feelings of anxiety, breathlessness, rapid breathing, headache, confusion, weakness, nausea and if unchecked, unconsciousness and death.      THE PRICE OF A REFILL OF SCRUBBER IS NOT WORTH YOUR LIFE!!!!   If you are getting any of these symptoms, stop your exertion, purge your loop with fresh diluent and if the symptoms don’t resolve, close your DSV, Bailout to OC, and end your dive.  Ascending to a shallower depth may also lessen the effects of C02 by lowering the partial pressure.

7)     PP02 DISPLAY FAILURE.  You should have at least two of these, one may be tied to your deco computer and another separate unit just reads PP02.  If the secondary display fails, end the dive on the unit tied to your deco computer.  If the sensor fails that is tied to your computer, end the dive monitoring the secondary display, set the computer for a fixed PP02 so it will continue to calculate your deco, you must  keep your breathing loop PP02 as close to that value as possible.  The odds of both 02 monitoring systems packing up at the same time are pretty low, however if this happens, you can still bailout to SCR mode using backup bottom timer or depth gauge.  See SCR Bailout below.

8)     DIVE COMPUTER FAILURE.  If you are doing recreational dives, no problem, monitor your secondary PP02 display and backup bottom timer/computer and end the dive.  If you are doing technical, trimix, or deep dives requiring decompression, you should have a backup deco table with you for just this occasion, refer to your backup bottom timer/computer and your bailout tables, complete your deco obligation and surface.

9)     MASSIVE AMOUNTS OF BUBBLES ESCAPING.  Is one of your OC buddies playing a trick on you?  No time to think this one through, quick, turn off your supply tanks and check your contents gauge for which tank has lost volume, if you cant tell, crack each on slowly and listen for leaks.  So you discover its your 02 supply, keep the tank off and bail to SCR, see procedure below.  If you discover that the leak is in your diluent side, then begin your ascent, as long as you don’t descend, you wont need any more diluent.  When you reach the surface you can inflate your BC orally, remember scuba 101.

 

 

 

BAILOUT TO SCR PROCEDURE.   If you are diving a converted drager dolphin or other SCR converted to CCR via the KISS valve then you should remember the SCR’s mode of operation.  Fresh diluent plumbed in constantly.  You can easily do this on you CCR by exhaling from your nose every 5th breath.  You will be using up the oxygen in the loop but replacing it with fresh diluent continually, just like diving a SCR.  You would use this mode if you had an 02 add failure, or had no way of knowing what the PP02 is in the loop.  If you still have 02 add capability, when you reach 20 feet of depth, you may purge your loop with 100% 02 and do your safety stop.  If you had an 02 add failure, don’t hang around in shallow water, (remember your diluent probably only has 21% or less 02 in it and is not a good gas for SCR’s in the shallow water)  get to the surface, close your DSV and breathe fresh air.  If you have deco time or want a safety stop, switch to OC when you get to the shallow water. 

 

 

Your rebreather has many different failure modes, but just as many recovery modes.  Many times you may think that your only option is bailout to OC, and that is OK, but depending on how much gas you are carrying, this may not be the wisest choice. Consider the SCR bailout and extend your range, giving you more time to get to the surface and/or sort out your problem.  The SCR bailout is the quickest way to get breathable gas into your lungs.  So imagine a diver, checking PPO2 at depth and reading .12  MERDE!!!!  Heart rate doubles, respiration increases, adrenaline dumps into the bloodstream and that tiny bit of O2 left in the loop is gone in moments, our diver doesn’t have the energy to move the lever on the DSV and passes out fumbling for his bailout regulator.  Ok, now our SCR bailout trained, diver notices his PPO2 and immediately purges the loop, venting gas from his nose and inhaling from his mouth which fills the loop with fresh oxygen rich gas using no more energy than he was before, the PPO2 comes up, INSTANTLY , right now he is breathing a gas that will support life, probably the same gas he would have gotten to via the OC reg, only now he has time to sort out the problem, O2 turned off? Out of gas? Whatever. If you in fact have to bailout to OC, remember to close off your DSV, if it floods you lose your buoyancy quickly, and if you are bailing out, you don’t need any more problems to deal with, the habit of shutting off the DSV should be ingrained as well as taking off your shoes when entering Grandma’s house.

 

Necessary equipment for CCR Diving.  At least 2 ways to monitor your PP02, if they don’t agree, purge your loop with diluent and do the math to see which one is correct, end the dive using that display.  Check PPO2.com for some neat and inexpensive ways to monitor a RB’s PPO2. Backup device to monitor your depth and BT.  Bailout OC regulator, can be fed from your diluent cylinder or an off board sling.  CCR Capable dive computer, currently there are 2 models available, the HS Explorer  and the Delta P VR3, both are capable units, I have chosen the HS Explorer.  Both units are available with external connections to Oxygen sensors to monitor your PP02 in real-time.  The Uwatec AirZ 02 and Oxy2 are fine units for use with a SCR, they are not recommended for use with a unit converted to CCR.  The correct amount of OC Bailout gas is imperative to surviving a lifetime of RB diving.  In the event of a total loop flood, you will need to make it to the surface on OC.  Most rigs allow breathing of your diluent gas via an OC reg, this can sometimes get you all the way to the surface.  Try this on your next dive, at the point of your normal ascent from depth, switch to your OC bailout reg and begin your ascent, you can still go back to your loop if you don’t have enough OC gas.  BEWARE, if your loop doesn’t have a overpressure relief valve installed you have to vent your loop manually during ascent while on OC.  Also, if you go back to the loop, the PPO2 will be low, you will need to add some O2 quickly.  Did you have enough gas to make it to the surface?  Yes, great.  No, time to rethink how much diluent you carry or maybe think about an off board supply or sling bottle.

 

OC bailout from technical dives.  This is a complete other can of worms.  If you are doing technical, deep, trimix or other dives requiring significant deco times, you need to have additional quantities of bailout gas that will suffice for a bailout from your deepest, farthest point of the dive, in the event of a total loop failure/flood.  If you are qualified to be doing these types of dives, part of your planning will include calculations of your RMV and quantities of bailout gas including bottom mix, travel gas and deco gas.  You should also have run deco tables based on OC, your rebreather constant PPO2 planning will not do for bailout.  The HS Explorer simulator has the capability of cutting tables for OC bailout, you can set it up to run your dive on constant PPO2 until bailout and then switching to OC for the remainder of the dive, you can then use that data, along with your personal RMV to calculate your gas needs, I have printed out these tables, laminated them and taken them with me on dives.  Download the HS Explorer simulator from http://www.hs-eng.com.

 

If you have any questions about any of this material, feel free to contact me at ron (at) tmishop (dot) com.   My thanks to Peder Seippel and Jean Michel for thier suggestions on improving this page.