Two divers critical - Hawaii

[doctormike]

Curious - not a CCR diver yet, but I guess my question boils down to this:

Why would a CCR not be monitoring O2 in the breathing loop once it detects it's in the water?

A CCR knows when it's in the water. If it measures any kind of depth, then it knows it's definitely in the water. So if it knows it's in the water, why wouldn't it automatically monitor O2 levels and override "surface mode?" I understand passing out if you're on land at the picnic table, but when it's wet why is this allowed to happen?

If the unit's wet and at any kind of depth, shouldn't it automatically be monitoring O2 content in the loop by default and alarm immediately when there is a drop?

I'm not a Liberty diver, but from what I can gather from that published analysis and the comments of a Liberty instructor here:

- It monitors the PO2 whenever it's powered up, through the visual display, in surface or CCR mode.

- When it's in CCR mode, in addition to visual alarms, there are tactile alarms when the PO2 drops below a certain threshold

- It automatically switches from surface to CCR mode at 1.5 meters.

- No matter what mode it's in, if you aren't paying attention and the O2 is off, no rebreather can keep the loop PO2 at a level that will support life.

 

[fuzzybabybunny]

I'm not a Liberty diver, but from what I can gather from that published analysis and the comments of a Liberty instructor here:

- It monitors the PO2 whenever it's powered up, through the visual display, in surface or CCR mode.

- When it's in CCR mode, in addition to visual alarms, there are tactile alarms when the PO2 drops below a certain threshold

- It automatically switches from surface to CCR mode at 1.5 meters.

- No matter what mode it's in, if you aren't paying attention and the O2 is off, no rebreather can keep the loop PO2 at a level that will support life.

Right, I understand that it monitors PO2 all the time, but does it sound a low PO2 alarm when the unit is wet?

A typical car has no way to disengage the handbrake if you've already yanked up on it, but at least it can bleep and yell at you the moment you put the shifter into drive. Shouldn't CCRs bleep and yell at you the moment it gets wet if it doesn't detect flow from the O2 tank and/or sees any kind of a drop in PO2 from normal?

How long can a person survive breathing just his exhaled air in his counterlungs?

 

[Superlyte27]

Right, I understand that it monitors PO2 all the time, but does it sound a low PO2 alarm when the unit is wet?

A typical car has no way to disengage the handbrake if you've already yanked up on it, but at least it can bleep and yell at you the moment you put the shifter into drive. Shouldn't CCRs bleep and yell at you the moment it gets wet if it doesn't detect flow from the O2 tank and/or sees any kind of a drop in PO2 from normal?

How long can a person survive breathing just his exhaled air in his counterlungs?

Yes, his Liberty was sounding an alarm once it became wet. Too bad he was already unconscious.

Edit*
That’s brief and blunt, but this has been spelled out in the previous pages.
The Liberty in surface mode has 4 visual indicators saying that the loop can or cannot support life. Three for the diver, 1 for bystanders.

In dive mode, add two vibrating handsets that can’t be ignored and can be heard while underwater.

The diver never switched to dive mode and never bothered to noticed that his loop wouldn’t sustain life. The bystanders didn’t notice either.

What likely happened is he passed out from breathing on a loop that wouldn’t sustain life. Once passed out, he sank in the water. The Liberty noticed the depth, switched to Dive Mode and started adding Oxygen. However, his valve on his oxygen bottle was off, and no rebreather can overcome that.

 

[doctormike]

Right, I understand that it monitors PO2 all the time, but does it sound a low PO2 alarm when the unit is wet?

Different units have different alarm settings. Superlyte27 (a Liberty instructor) went over this upthread. The Liberty has vibrating handsets that alert you to low PO2 in dive mode, but not in surface mode (see explanation here). Most CCRs don't have this, they have visual alarms. You do need to be paying attention.

How long can a person survive breathing just his exhaled air in his counterlungs?

Six minutes and thirty six seconds, on the surface...

-

 

[Superlyte27]

Way less than 6 minutes if the loop was at .21ppo2 (aka ambient air)

 

[fuzzybabybunny]

Yes, his Liberty was sounding an alarm once it became wet. Too bad he was already unconscious.

Edit*
That’s brief and blunt, but this has been spelled out in the previous pages.
The Liberty in surface mode has 4 visual indicators saying that the loop can or cannot support life. Three for the diver, 1 for bystanders.

In dive mode, add two vibrating handsets that can’t be ignored and can be heard while underwater.

The diver never switched to dive mode and never bothered to noticed that his loop wouldn’t sustain life. The bystanders didn’t notice either.

What likely happened is he passed out from breathing on a loop that wouldn’t sustain life. Once passed out, he sank in the water. The Liberty noticed the depth, switched to Dive Mode and started adding Oxygen. However, his valve on his oxygen bottle was off, and no rebreather can overcome that.

So the diver jumped into the water.

At the surface, with his head still above the water, his unit was already blaring an alarm in addition to giving three visual indications to the diver?

And he ignored all of them while he was bobbing with his head above the water, telling his buddy on the boat to hand him his camera?

And he ignored the audible alarms and visual indicators for 6 minutes until he passed out?

 

[Superlyte27]

I’m starting to think people just didn’t read every post.

The audible/tactile alarm doesn’t start until the CCR switches to dive mode. That doesn’t happen until the CCR reaches 1.5meters. Before that, there are 4 visual alarms.

We can’t guess at the PPO2 in the loop prior to him getting in the water. It could have been at anything from .21 to 1.0. If it was at 1.0 it would take about 6 minutes for him to pass out. If it were at .21 it would take about 60 seconds for him to pass out. I suspect somewhere in between.

 

[fuzzybabybunny]

I’m starting to think people just didn’t read every post.

The audible/tactile alarm doesn’t start until the CCR switches to dive mode. That doesn’t happen until the CCR reaches 1.5meters. Before that, there are 4 visual alarms.

We can’t guess at the PPO2 in the loop prior to him getting in the water. It could have been at anything from .21 to 1.0. If it was at 1.0 it would take about 6 minutes for him to pass out. If it were at .21 it would take about 60 seconds for him to pass out. I suspect somewhere in between.

That's exactly what I'm asking.

Why don't audible alarms sound when the unit is wet and above 1.5 meters?

Why doesn't it start monitoring the drop in PO2 when the unit is wet and above 1.5 meters?

It's obvious the unit's not at a picnic table anymore if it's wet and submerged in any amount of water. Even on a surface swim the PO2 should be monitored and alarms sounded, no?

If you get into a car and the handbrake is on the car doesn't start yelling at you only after you've reached a speed above 15 mph - it starts yelling at you the moment it gets put into drive, while the car is stationary and before your foot is even on the gas pedal.

 

[Superlyte27]

OMG, we’d go nuts if it did that.

Imagine you’re a cave diver. You’ve just got in the water. You’re standing in 4’ of water waiting for your idiot buddy to fix his leaking SPG. Meanwhile, you’re rebreather is beeping like crazy?

Tech divers hate beeping. It’s the reason Shearwater doesn’t have audible alarms.

Or, imagine this...
You’ve just finished a dive. Your rebreather is in the back seat of your car. It’s still wait because you haven’t invented a rebreather dryer yet. So, the entire 2 hour drive home the rebreather is beeping at you because it is wet, and there’s no oxygen in the loop.

There is no fix for this. Not everyone was meant to be a rebreather diver. We’re trying to engineer a solution to complacency. It’s not possible. But let’s say it is possible. We find a way to overcome that crutch. What happens when that crutch fails? Like when wet contacts develop scale so they aren’t triggered properly. This has been happening on the first handsets to current handsets, spanning 20+ years. Now who’s fault is it? The manufacturer who use a wet contact that will fail from scale buildup, or the diver who WAS COMPLACENT IN HIS MAINTENANCE AND DIDN’T CLEAN THE SCALE BUILDUP. It’s never ending. Just fix the simple stuff. No need to engineer complicated stuff that will still result in complacency, only this time on more complicated stuff.

 

[fuzzybabybunny]

OMG, we’d go nuts if it did that.

Imagine you’re a cave diver. You’ve just got in the water. You’re standing in 4’ of water waiting for your idiot buddy to fix his leaking SPG. Meanwhile, you’re rebreather is beeping like crazy?

Tech divers hate beeping. It’s the reason Shearwater doesn’t have audible alarms.

Or, imagine this...
You’ve just finished a dive. Your rebreather is in the back seat of your car. It’s still wait because you haven’t invented a rebreather dryer yet. So, the entire 2 hour drive home the rebreather is beeping at you because it is wet, and there’s no oxygen in the loop.

There is no fix for this. Not everyone was meant to be a rebreather diver. We’re trying to engineer a solution to complacency. It’s not possible. But let’s say it is possible. We find a way to overcome that crutch. What happens when that crutch fails? Like when wet contacts develop scale so they aren’t triggered properly. This has been happening on the first handsets to current handsets, spanning 20+ years. Now who’s fault is it? The manufacturer who use a wet contact that will fail from scale buildup, or the diver who WAS COMPLACENT IN HIS MAINTENANCE AND DIDN’T CLEAN THE SCALE BUILDUP. It’s never ending. Just fix the simple stuff. No need to engineer complicated stuff that will still result in complacency, only this time on more complicated stuff.

I get that you want to eliminate false alerts. Play this through with me.

- If you're standing in 4 feet of water waiting for a buddy and your PO2 continues to drop, guess what? You still have a problem. Isn't that cause for an alarm? You said yourself the O2 should always be turned on even if you're sitting on the boat, so there is absolutely no reason for your PO2 to drop if the unit's, wet, ever. Even if you're standing in 4 feet of water outside a cave.

- If the unit's wet on your 2 hour drive home then your PO2 shouldn't be dropping. So no alarm should sound. There's no problem here.

What you're basically saying is that it's OK for life support equipment to not care about *changes* in life support conditions while it detects that it's currently in an environment that warrants life support.

This isn't stuff that requires a hardware fix or a hardware addition. This is a programming issue.

if(PO2 continues to drop && (unit is wet || submerged one foot))
sound alarm