Rebreather problem in documentary

[KHedahl]

I have absolutely no experience with rebreathers, but was watching a documentary on a cave dive and had a question. At 22:30 into the video the diver is testing his rebreather and realizes that there is a problem with the O2 mix. How did the diver know this? The video shows him breathing on the mouthpiece, was there a difference in flow or is there some other way of knowing?

Into the Darkness - YouTube

 

[TSandM]

Many if not most rebreather systems have a method of monitoring the oxygen concentration in the loop. One of the tests you do before diving is to prebreathe the loop for a period of time. If you see the oxygen level dropping below target levels while you do this, you know the device is not adding oxygen when it should. In addition, in some rebreathers, you can hear the solenoid open and close as it activates the oxygen addition.

In short, the pre-dive procedure for rebreathers involves tests that make sure the oxygen addition is working, the dil addition is working, and that everything is sealing as it should.

 

[KHedahl]

Awesome. Thanks for satisfying my lust of knowledge.

 

[ajduplessis]

All RB's measure O2 and display the information on the integrated dive computers or HUD. Some do this automatically or manual, either way you have to keep track of the PPO2 levels. To low and you will pass out, too high and the oxygen become toxic and potentially dangerous. I did not watch the video but would guess his computers would have warned him there is a problem.

 

[skankpile]

Saw some inspirations, but his looked like an scr rb80? Looked to me like his orifice was dirty and he was cleaning it, or he had an issue with the block on an mccr.

He is holding a a green Cochran EMC-20H when the video shows him tinkering with the breather on the rocks.

 

[Garth]

All RB's measure O2 and display the information on the integrated dive computers or HUD. Some do this automatically or manual, either way you have to keep track of the PPO2 levels. To low and you will pass out, too high and the oxygen become toxic and potentially dangerous. I did not watch the video but would guess his computers would have warned him there is a problem.

This brings up a good point about that rebreather. I wouldn't know but have heard that some say they don't need to monitor pO2 in the RB80. WKPP incident where the diver ran with his 70ft bottle instead of dropping it and dropped his 212 bottle. Were they ever monitoring PO2?

 

[rigdiver]

One MUST analyze each cylinder before ever hooking them up to the ccr or scr. You can verify the electronics are working by a couple of ways. Flush the loop on the way down at 20' with pure O2 and see if you get a 1.6ppO2 reading or knowing your dil and flushing at known depths to get a specific ppO2. Like 0.21 O2 in the diluent should read 0.42 @ 33fsw. Many diver's write what a dil flush would be at incremental depths.

 

[Mr.X]

I have absolutely no experience with rebreathers, but was watching a documentary on a cave dive and had a question. At 22:30 into the video the diver is testing his rebreather and realizes that there is a problem with the O2 mix. How did the diver know this? The video shows him breathing on the mouthpiece, was there a difference in flow or is there some other way of knowing?

Into the Darkness - YouTube

The guy is cleaning out the O2 injection in his Classic Kiss RB. The Classic at that time had a triple display O2 meter which lets him know if the unit is trickling in enough O2. Cleaning it out is not a biggie and hitting the inject on this manually operated RB is not a biggie. Before the guy is working on the Classic Kiss he is working on a Italian O2 rebreather much like a LAR V where it looks like he is doing a pre-breathe check. I do notice the guys are using the Classic Inspiration...just wondering why they are not diving compatible gear if the Classic gets used?

Note: I did not watch all of the video. Years ago I found this stuff fascinating but no longer so. Too many crappy experiences and close calls.

 

[Plumb bob]

Years ago I found this stuff fascinating but no longer so. Too many crappy experiences and close calls.

Well it's a pity you seem to have a negative inclination toward RBs now. It was the case early on that the pool of knowledge regarding the safe operation of RBs was limited. There was a spate of accidents due to what were at the time "received wisdoms" of how things were done.

Now that it has matured somewhat and many of the fault modalities have been identified and corrected/mitigated it is less of a "crap shoot".

It is still inherently riskier than OC but IMO some rewards are worth increased risk.

Better PO2 monitoring in the form of more reliable O2 sensors will be a welcome thing!

Oh and as to your query over why they don't have the same RBs in the video. My take is that it's not necessary, they were diving autonomously so little is to be gained by having the same gear. Sure you can share spare parts if you have a gear failure whilst topside but if you didn't buy gear with a particular buddy in mind then it's awfully expensive re-buying simply to take advantage of that.

 

[rigdiver]

Yes, the benefits are real.