One dead, one missing (since found), 300 foot dive - Lake Michigan

[rjack321]

Dr. Mike,

Looking at this, it appears that an emergency swimming ascent is not achievable using CCRs. Is it in the training protocol that the diver cannot make such an ascent, as it may be beyond the CCR's ability to add enough oxygen to make the ascent achievable without blackout. I saw on the CCR website that at a depth of some 220 feet, the oxygen level is at about 10% (from memory). This is in safety terms an IDLH environment (Immediately Dangerous to Life and Health) for oxygen levels is anything below 19.5% (NIOSH and OSHA) or 18% (ACGIH) at the surface. How much is taught in rebreather courses about this?
https://www.acgih.org/docs/default-source/presentations/2004/aihce_slides_4.pdf?sfvrsn=f6fadf0d_2

SeaRat

If you do a CESA from 300ft you are going to die. Period. There is no other outcome.

OC gas for that depth is 12/65 or 10/70. You can't breath that on the surface. ppO2 in a CCR will drop and become unbreathable as well. But hypoxia is not really the problem since you by definition have a substantial decompression obligation. Even if you had a chamber on the deck of the boat unless they blow you down to 165ft (Navy Table 4) you are going to die. If they get you back down with a Navy Table 4 immediately - there's a chance you might live - a chance.

Tech divers doing 300ft dives have to solve their problems in the water.

 

[doctormike]

Dr. Mike,

Looking at this, it appears that an emergency swimming ascent is not achievable using CCRs. Is it in the training protocol that the diver cannot make such an ascent, as it may be beyond the CCR's ability to add enough oxygen to make the ascent achievable without blackout. I saw on the CCR website that at a depth of some 220 feet, the oxygen level is at about 10% (from memory). This is in safety terms an IDLH environment (Immediately Dangerous to Life and Health) for oxygen levels is anything below 19.5% (NIOSH and OSHA) or 18% (ACGIH) at the surface. How much is taught in rebreather courses about this?
https://www.acgih.org/docs/default-source/presentations/2004/aihce_slides_4.pdf?sfvrsn=f6fadf0d_2

SeaRat

Rainpilot explained it better, but the bottom line is that CESA from 300 feet is more of a thought experiment in physics than it is a procedure to be relied on in case of an emergency.

CESA has nothing to do with scuba gear or the gas in your tank or loop. CESA implies an ascent with continual venting of gas from the lungs as ambient pressure drops. You don't inhale while doing a CESA, so the CCR's ability to supply gas at any PPO2 is irrelevant.

As you know as an instructor, standard practice for CESA involves keeping the regulator in your mouth, but that is to prevent aspiration of water, especially after surfacing, in case a mistaken attempt is made at inhalation. But it is not to provide gas to the lungs.

As far as what you read on a CCR website, I think that you may be confusing PPO2 and FiO2. At 220 feet (7.6 ATA), to achieve a loop PPO2 of 1.3, you would need an FiO2 of 0.17 (17% O2). For deep dives, hypoxic diluent is used to avoid O2 toxicity. But even if the effective loop FiO2 is 10% (as it might be for even deeper dives), what counts in terms of maintaining consciousness is PPO2, not FiO2. PPO2 = FiO2 x ATA.

If you were to CESA from depth with a low FiO2 in your lungs, it seems to reason that your PO2 would drop on ascent, and that can certainly cause blackout. But again, not really something that is done from those depths, so not sure that it has been studied in actual divers.

 

[doctormike]

RainPilot,

What features of CCR will warn the diver of PPO2 drop, other than a blackout?

Redundant oxygen sensors

..what are the Person (Diver) Machine Communications that would indicate such a failure?

Different rebreathers have different systems. Mine has visual warnings on the controller and on the heads up display (Shearwater NERD). Others have tactile and/or audible alarms.

If a diver is preoccupied by environmental factors, can this communication overcome the distraction?

Unfortunately not always.

 

[RainPilot]

RainPilot,

What features of CCR will warn the diver of PPO2 drop, other than a blackout? PPO2 drop physiologically has no warning. Again, going to the DeJoy diagram, what are the Person (Diver) Machine Communications that would indicate such a failure? If a diver is preoccupied by environmental factors, can this communication overcome the distraction?

SeaRat

Hey John.

Most any CCR will have multiple redundant readouts of the (multiple, redundant) O2 sensors in the loop. These often take the form of Shearwater handsets or similar, and very often there is a HUD and/or other alerting mechanism.

My unit, the Poseidon, has a handset, vibration unit and HUD combination, audio alarm and a big flashing light on the back to tell my buddy if I missed all these other warning signs.

The problem is usually a sensor issue rather than a diver/machine interface problem.

 

[chillyinCanada]

Pure speculation on my part but inasmuch as, the wife came up and the husband didn't, I'm left wondering if he was the one with the problem first (whatever that was) and she tried to rescue him unsuccessfully. In the end, she tried to rescue herself and managed to make it to the surface but the damage (whatever that was) had been done, in her case.

 

[telemonster]

RainPilot,
What features of CCR will warn the diver of PPO2 drop, other than a blackout?
SeaRat

If it's a Shearwater it will indicate on display, with a total lack of offset weight motor (vibrator) or audible alert. No idea why they left those off??
The O2 sensors only see what is in front of them and take a slight bit to respond as well.

 

[Marie13]

Pure speculation on my part but inasmuch as the wife came up and the husband didn't, I'm left wondering if he was the one with the problem first (whatever that was) and she tried to rescue him unsuccessfully. In the end, she tried to rescue herself and mansged to make it to the surface but the damage (whatever that was) had been done, in her case.

Something similar to this has been my best guess.

 

[grantctobin]

Something similar to this has been my best guess.

Based on?

 

[Basking Ridge Diver]

Based on?

Does the name Rouse mean anything to you? May want to look it up - or read Shadow Divers....

 

[rjack321]

Pure speculation on my part but inasmuch as the wife came up and the husband didn't, I'm left wondering if he was the one with the problem first (whatever that was) and she tried to rescue him unsuccessfully. In the end, she tried to rescue herself and mansged to make it to the surface but the damage (whatever that was) had been done, in her case.

Unfortunately its just as plausible that she had the issue and he tried to help but let her or sent her up to the surface. But by that point he was so overwhelmed and/or had violated his ceiling that in-water DCS incapacitated him. He sank when the loop came out and the unit flooded.