Rebreather question

[Freedive WI]

As you may have heard, Tanya Streeter just broke another freedivng record- this time she has even beaten the men's record as well as the woman's. Many of her safety divers wear Inspirations, and some of them even wear Twinspirations. She talks about a problem on one training dive and mentions:

Andre had a rebreather malfunction that meant he was getting pure oxygen before it could be remedied. This was a situation that was unnerving at 50m but would have been much worse at 100m which is where he was going to be for me. Their emergency procedures were excellent and everybody was completely safe, but it did make us wonder if we were being controlled by fate today.


My question, for those in the know , is what went wrong and what do you do to fix it?

I assume his handset was working correctly so that he see he was getting to much 02 and he then went to manual mode. Is that a close guess? How would you bailout from a dive like that? What would happen if the handset wasn't working, just count on the back-up handset?

Jon

[Chuck_Northrup]

Andre had a rebreather malfunction that meant he was getting pure oxygen before it could be remedied.

The Inspiration always adds pure oxygen, except when diluent is used (typically only upon descent) so the addition of pure o2 is not a “malfunction”.

This was a situation that was unnerving at 50m but would have been much worse at 100m which is where he was going to be for me.

There are several “situations” which could lead to rapid o2 addition. The two most likely would be a stuck manual inflator and/or a stuck solenoid. More on this later.

Their emergency procedures were excellent and everybody was completely safe

I agree completely. Obviously these were well trained divers and were diving within their limitations.

but it did make us wonder if we were being controlled by fate today.

Tanya is constantly pushing the envelope and trusts quite a bit more to “fate” than a rebreather diver doing similar depths. The rebreather diver knows s/he has enough gas, Tanya may not.

I assume his handset was working correctly so that he see he was getting to much 02 and he then went to manual mode.

All he would have to do is shut of o2 and possibly (but not necessarily) a dil flush. He would only need to go manual if the solenoid was failed open. He may have had a high po2 alarm and noticed the high po2 displayed on the handset, or he may have just heard the stuck solenoid, or noticed a rise in buoyancy.

How would you bailout from a dive like that?

If you have off board 80% or better and feel comfortable flying manually you may not need to bailout. If you need to bailout just ascend (the easiest way to drop po2) and/or do a diluent flush.

What would happen if the handset wasn't working, just count on the back-up handset?

The hand sets are just glorified oxygen analyzers. The importance of voting logic and independent readings means for ccr diving you need at least 3 o2 cells. The Inspiration has two independent readings of 3 cells one Master one Slave. If the slave revolts and kills the master the slave becomes the master. Most people would abort the dive upon the failure of one handset, but if it occurred during a dive/deco it would not be a catastrophic event.

Safe Diving,

Chuck Northrup
Going Under Dive Center

[Inspirationdiver]

There are also several other techniques that are taught in the training class that don't involve bailing out to OC that could have been justifiable in this situation. I won't go into great detail, that's what the class is for, but I'll give you an idea of the many possible options this diver had. Assuming that the oxygen solenoid was stuck open, the diver could have shut the valve off to stop the rapid addition of oxygen. Then by monitoring the handsets, you can manually open the valve in small spurts to add the necessary oxygen. The ascent could then be completed on the loop with no problems.
If it was the manual inflator button that was stuck open, the diver could have simply disconnected the hose feeding the inflator button, the same as disconnecting a stuck drysuit inflator. The oxygen controller and solenoid would still function normally and the ascent could be completed easily.
If it was the handsets and/or the oxygen sensors that were giving inaccurate reading and causing the unit to add unnessary oxygen, the handsets can be shut off and the unit can be run in semi-closed circuit mode. Simply vent all the gas out of the loop and inject new fresh gas every 3-5 breaths. You can still achieve much greater gas efficiency and stay on the loop.
These are just some of the many options a CCR diver has when not everything is working perfectly. In my opinion, one of the greatest advantages of diving CCR is the many options a diver has in the event of failure.

[Skruff]

Question from the ignorant- How quickly does the PO2 level climb when the Solenoid is stuck open? Just curious how much time you would have to react to this type of problem...

By the way thanks for the clarification in the first two posts.

[Inspirationdiver]

The PO2 can climb quickly with the rapid addition of oxygen. This is not the problem that you have to deal with immediately. With the rapid addition of any gas to the loop, you will become positively bouyant very quickly and you must react to control your bouyancy. By reacting quickly to the bouyancy change, you can knock down the climbing PO2 with diluent and prevent exposure to high PO2. A very short time on a high PO2, even as high as 2.0-2.5, will most likely not cause oxygen toxicity issues.

[Skruff]

Good point about the bouyancy- Being an OC person I would never have thought of that as another sign that something is wrong.

[ghosch]

It would be interesting to get more details on the actual event. That being said, the whole "controlled by fate" comment makes it seem to me like they were just trying to add drama to the event (not that a whole lot of drama needs to be added to a 400 descent with one breath of air).

Two weeks ago, while in Whitefish bay, several of the OC divers had freeflows, and one of our divers forgot to zip up his drysuit before jumping in. Stuff happens and you deal with it, but I'm sure we could have made it sound dramatic..."It was like the poor souls of the long dead sailors wanted us to share in their watery fate..."

On a serious note, looking for opinions. I realize that SC mode is not a "by the book" recommended method of bailout. It is however a great way to extend your gas supplies if necessary. If you are breathing the unit in SC mode and making an ascent (assuming the computers are dead and you have no reading of PO2 and assuming your on- board was a low FO2 mix) would you not run the risk of going hypoxic at shallow depths? In this situation would you switch to an off-board diluent during your SC ascent (and would this even help if your off board was bottom mix for a 100m dive)? Also how would you calculate your deco requirements since you are guessing at your FiO2 in SC operation?

[Inspirationdiver]

If you are going to be making your ascent using the rebreather in SCR mode, you would plan the ascent as though you had bailed out to OC. Because you will be replacing the contents of the loop with fresh gas every 3-5 breaths, the effective FO2 will be the same as on OC. In a standard trimix dive I would have my onboard diluent be a 1.0 PO2 at depth, my offboard diluent be 1.6 at depth, and I would carry an offboard deco gas. You can start on the onboard gas, switch to the offboard diluent as you ascend, and complete your deco on the offboard deco gas. You also have the option to use the onboard oxygen in SCR mode once you get shallow enough. Any gas you carry can easily be plugged into the loop and run in SCR mode. Going to SCR mode doesn't gain you any offgassing advantage over bailing out to OC but it will save gas volume 3-5 fold depending on how often you drain and refill the loop.

[ghosch]

I suppose that's true, the difference in inspired oxygen between OC and SCR is probably not substantial, especially at depth where you are metabolizing so little of the O2 with each breath.

Obviously the ideal would be to have an interface to calculate the true profile as there would be some difference. Then again if we think the algorithims are that precise, we are probably fooling ourselves anyway!

[Freedive WI]

COntrolled by fate

Maybe I should have copied more of the story, but it was really long!

There were a series of problems that happened on the water that day and the rebreather problem was only one part of it.

She was having some severe ear/sinus clearing problems that day and they also hade some rough weather. To top things off the sled became unhooked, acutally the clasp that holds it up broke, and it went down early- before anyone was on it. If she had been on it there is a manual break that she could have stopped it with. Since it went down early, the support divers only got to make it to 50 meters instead of the 100 meters where they were to be stationed on that day.

I didn't mean for it to sound more dramatic then it was, I just wanted to find out what went wrong and hoe you can bail out from that kind of a problem. She stills has a much better saftey system than Pipin had in place when Audrey died last year- one diver on air at 300' and another on opencircut trimix at 560'.

Thanks for all of the answers.

Jon