Rebreather Discussion from Brockville Incident

[flots am]

So do car wrecks, cancer and tack hammers wielded by angry ex girlfriends.

I wonder if we can find a tack hammer that meets Gian's lofty, and arbitrary, safety standards?

I know I mentioned this before, but there is a significant difference.

Out of all the comparison items and events mentioned by you and others, none puts you to sleep before killing you. Only a rebreather does that.

flots

 

[mathauck0814]

I know I mentioned this before, but there is a significant difference.

Out of all the comparison items and events mentioned by you and others, none puts you to sleep before killing you. Only a rebreather does that.

flots

You seem to be really hung up on this. And while it's possible, it's just not likely. You really do have to screw up (badly and consistently) for a rebreather to just put you down as you suggest. I feel like we're going around in circles on this.

I know that my gas tank could potentially rust and that fuel could potentially drip out and a spark could ignite it and the car could explode and that all of that could happen without my knowledge. Of course, I could do routine maintenance and ensure that there is not rust on critical components of my car as well ;-)

Accidents have chains of events leading up to them. Rebreathers are simply no different. I flatly reject that you can do absolutely everything right and still die. You just can't. You have to screw something, forget to do something up, cut corners or act negligent up to end up dead.

 

[flots am]

I flatly reject that you can do absolutely everything right and still die. You just can't. You have to screw something, forget to do something up, cut corners or act negligent up to end up dead.

Being human means that you're going to screw up eventually.

Airline pilots screw up. Even astronauts screw up. Divers do to.

flots.

 

[Dsix36]

Being human means that you're going to screw up eventually.

Airline pilots screw up. Even astronauts screw up. Divers do to.

flots.

And so do OC divers.

 

[mathauck0814]

Being human means that you're going to screw up eventually.

Airline pilots screw up. Even astronauts screw up. Divers do to.

flots.

Sure - and just like everything else we do, screwing up MAY kill you. But it certainly won't guarantee that it'll kill you. For example. It's entirely possible to do a prebreathe with your O2 shut down and keep a reasonably high PO2. You can jump off the boat with your O2 turned off and you can start your descent. However your loop volume will compress and begin to fill with diluent. You could ignore the dropping PPO2 on your HUD and/or handset and continue to descend but when you stop to do a cell linearity test at 30fsw you'll find that your O2 is off. You could skip the linearity test and continue to the bottom where you'd have to continue to ignore a low PPO2 before you became hypoxic and eventually passed out... but in order for all this to happen you have to:

1. Not turn on your oxygen on the boat.
2. Not realize the PPO2 dropped more than it should on the prebreathe
3. Not realize that the ADV was filling your loop with diluent to compensate for depth
4. Not realize the resulting drop of PPO2 from the diluent flood
5. Not pause for a cell linearity test at 30fsw
6. Not notice, ever, that your HUD and Handset were freaking out about your PPO2

That's a pretty obtuse set of mistakes to make. You can make any one of those mistakes - hell, you can make several of them - and recover quite nicely. It's not as though any one of those would render you unconscious and therefore dead.

 

[tracydr]

I'm very interested in rebreathers for several reasons but I've always been Leary of them, mainly because of my own issues with inability to maintain attention to detail.
I would really like somebody to explain how a rebreather diver dies
1: in 4 feet of water in Lake Pleasant
2: a rebreather instructor dies in his own pool
Not trying to start any arguments. I just truly want to know. Because if rebreathers are as safe as some people seem to make them sound like they are, I'd start getting a lot more interested in them. There are so many benefits to rebreather diving- warmer,shorter deco,lighter.

 

[mathauck0814]

I'm very interested in rebreathers for several reasons but I've always been Leary of them, mainly because of my own issues with inability to maintain attention to detail.
I would really like somebody to explain how a rebreather diver dies
1: in 4 feet of water in Lake Pleasant
2: a rebreather instructor dies in his own pool

I'll simplify for brevity as you can read more indepth explanations of this type of event elsewhere:

Depth is only relevant in certain rebreather accidents. You can drown in a few inches of water. But some possibilities include:
- Diver went hypoxic (not enough oxygen to sustain life) this can happen for a number of reasons, all of which are user error and not generally the result of a single mistake.
- Diver had a hypercapnia event (too much CO2) this can also happen for a number of reasons, all of which are user error and/or not generally the result of a single mistake.
- Diver had a completely unrelated cardiac event and happened to be wearing a rebreather

There are so many benefits to rebreather diving- warmer

People say this, but I would argue its merits. You exhale gas into a bag which is (in most cases) in direct contact with cold sea water. I can't believe that gas returning to your lungs from the counterlungs isn't at least ambient temperature. I have no data to this effect, but I certainly haven't noticed any measurable difference in warmth (could be that I'm just not usually cold as well)

shorter deco

This is true on shallow dives. As you progress deeper you'll find that your dives mimick or have more deco than your open circuit counter parts. This has to do with PPO2 and CNS clock. Open circuit divers only experience high PPO2 exposure on the bottom phase (relatively small portion of a big dive) and at gas switches where a rebreather diver is exposed to a constant PPO2 throughout the dive. As your dives get longer the constant PPO2 you expose yourself to necessarily goes down to keep you within a workable range on the CNS dimension. As the PPO2 goes down your efficiency goes down and you incur greater deco obligations.

lighter.

Than doubles, yes. Than a single tank - sometimes.

They're a great tool. Read as much as you can, ask a lot of questions and be honest with yourself. Go in with your eyes open and if you decide it's right for you, it'll open up a world of opportunity for you.

 

[Garth]

There are more benefits than those listed however if attention to detail is one of your weaknesses then a rebreather wouldn't be a great option for you.

---------- Post added July 24th, 2013 at 07:03 PM ----------

To comment further about the diver who died in 4 feet of water.. I suppose you could die on a rebreather while not even in water. If the mouthpiece is in your mouth and you forget to install your scrubber.. Well you never know how you react until it happens to you. Those that recommend trying it on your couch also recommend that you have somebody nearby assist.

 

[HIGHwing]

I'm very interested in rebreathers for several reasons but I've always been Leary of them, mainly because of my own issues with inability to maintain attention to detail.
I would really like somebody to explain how a rebreather diver dies
1: in 4 feet of water in Lake Pleasant
2: a rebreather instructor dies in his own pool
Not trying to start any arguments. I just truly want to know. Because if rebreathers are as safe as some people seem to make them sound like they are, I'd start getting a lot more interested in them. There are so many benefits to rebreather diving- warmer,shorter deco,lighter.

It's feels counterintuitive doesn't it? Imagine a rebreather is nothing more than a ziplock bag. At the surface the bag holds 10 molecules of air which means about 2 molecules are oxygen. If your body burns one molecule per minute and no molecules are replaced you can easily see that in two minutes you're in real trouble. Now imagine we're descending while breathing in and out of zip lock bag, obviously the bag will crush from pressure exerted by the water. We will need to add gas to the bag to be able to breathe from it. At 100ft the bag now has 40 molecules of air, meaning 8 molecules of oxygen are present. We know that our body burns 1 molecule of gas per minute in this example. At 100ft we will live for eight minutes, shallow we live for two minutes.

Remember we only consume the amount of oxygen we actually burn at literally the molecular level (with a few exceptions), so if there are more molecules in the ziplock bag because the gas is denser we live longer.

The shorter answer is the reduced gas density in shallow water make the available breathing gas much less "stable" i.e. more affected by simply breathing in shallow water. Some have even advocated using only pure oxygen in pool environments so you never make the mistake of introducing a lean oxygen gas into the loop.

 

[nadwidny]

Rebreathers kill divers.

Being under water kills divers.