I found a couple of interesting posts on a different thread from 2006:
Dr. Lecter, forgive me, but I was unfamiliar with the Hannibal Lecter series of novels. You might note that it is easy for someone unfamiliar with that series to mistake your moniker for something entirely different.
SeaRat
http://www.scubaboard.com/forums/accidents-incidents/123276-rebreather-diver-dies-pool-oregon-5.html[/QUOTE]This is the second try, I answered this earlier and got some absurd message ... :bluthinki
webmonkey:I'd be interested to hear why rebreathers are still being sold that allow a user to continue breathing a mix that will not support life.
That is, as they say, the nature of a rebreather. And it's biggest danger. You can breath as long as there is enough gas volume to match your lungs. It doesn't mean the gas you're breathing supports life.
Every rebreather diver knows this!
And every rebreather diver accepts this, just as every diver accepts nitrogen narcosis or possibility of DCS.
The dangers generally involved here are hyperoxia (O2 poisening), hypoxia (O2 starvation) and hypercapnia (CO2 poisening). Hyperoxia, while possible on an SCR, is limited to diving past the MOD for the supply gas as it is for nitrox in general. Hypoxia, expected to be the cause here, can happen when fresh gas (SCR) or O2 (CCR) isn't added to the loop to replenish the O2 metabolized by the diver. Hypercapnia can occur when the scrubber is exhausted, CO2 is channeling through the scrubber bed or when the scrubber is just fine but the diver doesn't fully exhale the CO2 he generates. Holding one's breath, skipbreathing, shallow breathing will all do it. On OC too, by the way, even free diving (shallow water blackout has caused many free diving fatalities).
No SCR currently in production has a pO2 monitor in it's stock configuration.
All but one offer it as a factory option and are prepared to have it installed.
In can be done on that remaining one without any problems with monitors from several manufacturers.
Reasoning here is that cmf units continiously add gas at a higher rate than should be consumed by the diver plus have a separate addition valve to increase that flow when necessary, and that rmv-keyed units add gas per breath and hence accomodate high work rates. The latter also dump a measured amount per breath, so if gas addition ceases WOB will go up as only a few breaths are left.
CCRs operate with a fixed pO2 (setpoint) and hence have three O2 sensors that allow the diver and/or the setpoint controller to monitor and maintain the setpoint. When diving with a setpoint the fO2 in the loop changes and hence monitoring is required. Most CCRs have audible, visiual and/or vibrating alarms to notify the diver if the setpoint drifts or a cell is bad. The exception are the KISS rebreathers that are manually controlled by the diver who is trained to pay attention to the pO2 displays in the first place and fly manually.
There is currently no CO2 monitoring system available in rebreathers outside the military.
Over the years several individuals and companies have tried to make CO2 monitoring work, but there are problems have yet to be mastered, not the least of which are reliability and cost.
Ambient Pressure has implemented a scrubber monitor. While not warning of CO2 in the loop, it will warn if the absorbant fails. Not perfect, but a step in the right direction.
That being said, Rule Number 1 is: Always know your pO2!
I also singled out the quote that bradshi did above.
If the victim just wanted to fill his tank, and made an impromptu decision to jump in the pool to use up the remaining gas left in his cylinder, there is a fair chance that he didn't do a full pre-dive check that would have included checking the gas flow in his unit and the contents of the tank. I find that much more likely than anything else, as sitting on the floor of the pool doesn't lend itself to physical excertion.
Low pO2 in a cmf SCR can be brought about by mismatching gas and orifices, overbreathing the gas addition capabilities (not all that easy, I tried that on a Dräger in the pool once with a pO2 monitor installed and got worn out before the unit did) or no gas coming from the tank, either due to an out of gas situation or 1st stage/valve failure.
So more likely than not this accident was indeed human failure, and the past accounts of the victims abilities don't exactly make that any less likely.
Either way, the unit was recovered, so it should be easy enough to check the gas in the tank (both volume and composition) as well as the gas addition system (though the tank may be empty by the time he was found as gas flows continiously through the orfice).
So apparently there are some solutions out there.One system at least has been developed for military that includes CO2 sensing, auto flushes the loop with diluent when sensing CO2 or high pO2, even returns an unconcious diver to the surface. But aside from containing technology not yet cleared for civilian consumption the electronics cost more than most current CCRs. At their low production numbers the price would much more than double, so it's just not feasible yet.webmonkey:It's a final effort by the equipment to try to prevent your death.
There have been plenty of accidents and fatalities on open circuit due to divers accidentally picking the wrong gas for a given depth. Try swimming on Tx10/50 on the surface or take a few breaths of O2 at 200 feet and see how far you get. To err is human.It's not like any sane person would choose to dive with a mix that can be predicted to cause death.
webmonkey:
In my previous post I mentioned the manually controoled KISS CCR.
A couple of guys thought the same way you did and designed an aftermarket control system. Adds a HUD display in the line of sight and solenoid and setpoint controller to the KISS (as well as a different display and the option to plug a dive coomputer with yet another pO2 display in). The setpoint controller/solenoid act as a safety parachute, injecting gas only when the setpoint falls below 0.4 ata.
The system costs $1,800.
http://www.scubaboard.com/forums/accidents-incidents/123276-rebreather-diver-dies-pool-oregon-5.html
Dr. Lecter, forgive me, but I was unfamiliar with the Hannibal Lecter series of novels. You might note that it is easy for someone unfamiliar with that series to mistake your moniker for something entirely different.
SeaRat
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