DEEPLOU:
Actually rebreathers are more dangerous in shallow water. Like flying low in a helicopter.
SCUBA accident in Pool - Scuba Instructor Drowns While Testing Equipment
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Actually rebreathers are more dangerous in shallow water. Like flying low in a helicopter.
DiveGolfSki:
Normally no - Your primary respiratory response is trigged by the CO2-levels in your bloodstream. When you feel out of breath its the CO2-levels your body registers.
Too high CO2-levels will make you feel out of breath.
The O2-levels are also used for respiratory control, by your body, but are easyli suppressed by the brain.
The inherent danger in a rebreather is, that if it scrubs out the CO2, but does not feed enough O2 - or feeds TOO much O2. High ppO2 levels (app. above 1.4bar) can cause sudden loss of consience, and low levels of O2, can be suppressed, also with loss of consience.
A RB should do redundant monitoring of ppO2 (i.e. at least 3 independant monitors) that can decide one is malfunctioning, and disable this one (while the diver immedialtely surfaces, or switches to bailout-gas) - but the unit essintially still works.
Disclaimer: I've no pratical experience with RB's - so perhaps I've missed a few points.
Folks,
I dive a couple of different rebreathers, and teach on both. At least a couple of our members have posted very important information about how rebreathers work, and what failure modes can do to you. I see no need to repeat that information.
I will point out one thing, however, and that is that a rebreather can kill you very gently. Unless you monitor the system and ALWAYS KNOW YOUR PPPO2, it will find a way to kill you...softly!
Testing new, or newly repaired equipment, without someone to monitor you and be a Safety Officer is ALWAYS a bad idea. It is a trap, and a deadly one.
My prayers were raised for the soul of someone who, by all report, was a good and decent person. Again they go out for his family. My heartfelt condolences.
I dive a couple of different rebreathers, and teach on both. At least a couple of our members have posted very important information about how rebreathers work, and what failure modes can do to you. I see no need to repeat that information.
I will point out one thing, however, and that is that a rebreather can kill you very gently. Unless you monitor the system and ALWAYS KNOW YOUR PPPO2, it will find a way to kill you...softly!
Testing new, or newly repaired equipment, without someone to monitor you and be a Safety Officer is ALWAYS a bad idea. It is a trap, and a deadly one.
My prayers were raised for the soul of someone who, by all report, was a good and decent person. Again they go out for his family. My heartfelt condolences.
I don't believe that we've ever had the final results of the investigation published here have we as this thread is a few months old.
caveseeker7
Contributor
Well, not quite.
The inherent danger in a rebreather is that the gas in the loop is not the same as in the tank(s).
You can still breath from the loop, but you don't know if the gas supports life.
You have to differ between semi-closed units and closed ciruit rebreathers.
Current production civilian SCR use pre-mixed gas, for most part nitrox.
Those are the Drägers, Submatix and Azimuth. Gas is added via constant flow, which is usually higher than the diver's breathing rate. The excess gets vented, hence semi-closed. There are bubbles, but less and smaller than OC. Say you use Nitrox32. In the loop you will usually have a few % less O2 than in the tanks since you use some breathing from it. As an example let's say 30%. But the fraction of O2 is less important than it's partial pressure.
At 30 msw the pO2 for the mix would be 1.28 ata, for the loop 1.2 ata. All is fine, it's below the normal rec limit of 1.45 ata.
If you are at 10 msw, the pO2 at 2 ata would be 0.64 for Nitrox32, but only 0.6 in the loop.
When the diver does a lot of work, he breathes harder and uses more O2. The O2 percentage goes down. So if you're out of shape, swimming against a nasty current, anything like that and the pO2 will drop. Say to 0.25 at the surface.
At 30 msw it will now be 1.0 ata, still good to go. At 10 msw it'll only be 0.5 ata and that's as low as you want to get. Now ascent and you may have problems. If for some reason it falls below 0.16 ata you'll likely loose conciousness.
Usual protocol for SCR is to flush the loop (exhale it into the water and get a fresh refill from the tank). A pO2 monitor obviously can help here, and a single cell monitor or deco computer with an integrated cell is enough.
There are other SCR systems, such as the Halcyon, that are keyed to the RMV of the diver. They expel a percentage of the gas on every breath you take and replace it with fresh gas. The pO2 is thus more stable and gas usage more efficient, but they generally also a bit more complicated and expensive.
For CCR, where two different gases are used and the loop content is mixed on the fly to maintain a chosen setpoint three O2 sensors are normal.
In addition there can be problems with gas supply, valves, leaks etc, all influencing or preventing gas addition. While shallow depth may have played a role in this accident, high excertion is unlikely. But trouble with the gas addition would explain the diver passing out and drowning. Even more so if maintainance or modifications were done improperly.
I doubt CO2 was the problem unless there was either no or spent sorb in the cannister.
The Azi's radial scrubber is one of the best designs currently available.
The inherent danger in a rebreather is that the gas in the loop is not the same as in the tank(s).
You can still breath from the loop, but you don't know if the gas supports life.
You have to differ between semi-closed units and closed ciruit rebreathers.
Current production civilian SCR use pre-mixed gas, for most part nitrox.
Those are the Drägers, Submatix and Azimuth. Gas is added via constant flow, which is usually higher than the diver's breathing rate. The excess gets vented, hence semi-closed. There are bubbles, but less and smaller than OC. Say you use Nitrox32. In the loop you will usually have a few % less O2 than in the tanks since you use some breathing from it. As an example let's say 30%. But the fraction of O2 is less important than it's partial pressure.
At 30 msw the pO2 for the mix would be 1.28 ata, for the loop 1.2 ata. All is fine, it's below the normal rec limit of 1.45 ata.
If you are at 10 msw, the pO2 at 2 ata would be 0.64 for Nitrox32, but only 0.6 in the loop.
When the diver does a lot of work, he breathes harder and uses more O2. The O2 percentage goes down. So if you're out of shape, swimming against a nasty current, anything like that and the pO2 will drop. Say to 0.25 at the surface.
At 30 msw it will now be 1.0 ata, still good to go. At 10 msw it'll only be 0.5 ata and that's as low as you want to get. Now ascent and you may have problems. If for some reason it falls below 0.16 ata you'll likely loose conciousness.
Usual protocol for SCR is to flush the loop (exhale it into the water and get a fresh refill from the tank). A pO2 monitor obviously can help here, and a single cell monitor or deco computer with an integrated cell is enough.
There are other SCR systems, such as the Halcyon, that are keyed to the RMV of the diver. They expel a percentage of the gas on every breath you take and replace it with fresh gas. The pO2 is thus more stable and gas usage more efficient, but they generally also a bit more complicated and expensive.
For CCR, where two different gases are used and the loop content is mixed on the fly to maintain a chosen setpoint three O2 sensors are normal.
In addition there can be problems with gas supply, valves, leaks etc, all influencing or preventing gas addition. While shallow depth may have played a role in this accident, high excertion is unlikely. But trouble with the gas addition would explain the diver passing out and drowning. Even more so if maintainance or modifications were done improperly.
I doubt CO2 was the problem unless there was either no or spent sorb in the cannister.
The Azi's radial scrubber is one of the best designs currently available.
was he P.A.D.I.?????
]hammerhead45:
Not the agency - the mindset. X
alscubagal
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I have a few questions for this thread......as you can see im new to this whole thing....Blueboy, who are you???...
although i have been following up with this thread...and im curious about the rebreathers....im not a scubadiver...just someone with questions...if David would to have been knocked unconscience due to the rebreathers the only way he could of die was if his lungs filled with water and drowned.... if his lungs didn't fill... what other possible explaination could their be for the cause of his death that includes the malfunctioning of a rebreather????
God bless him!
-snr
although i have been following up with this thread...and im curious about the rebreathers....im not a scubadiver...just someone with questions...if David would to have been knocked unconscience due to the rebreathers the only way he could of die was if his lungs filled with water and drowned.... if his lungs didn't fill... what other possible explaination could their be for the cause of his death that includes the malfunctioning of a rebreather????
God bless him!
-snr
Diver Dennis
Contributor
This thread is over a year old, a lot of the original posters may not be here.
I missed this thread when it was originally posted. Reading it now, does anyone find the two postings by Rob (BigJetDriver) to be downright erie knowing what happend to him almost exactly a year later?
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