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keywest928

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It was suggested I post this here:
I am not a diver. I am looking to understand a little about what can/might go wrong. A dear friend left for Thailand yesterday to better coordinate a search for her son, who is missing from a scuba trip there. He was using something called a rebreather (?). He is an experienced diver and a good swimmer but the rebreather is relatively new equipment for him. He was with 8 other divers and a dive master. He got in the water, was instructed by the diver to swim to the front of the boat and wait at the mooring rope. He got in, started for the front of the boat...and hasn't been seen for three or four days.
Obviously, since we aren't there we don't know what happened, but at that phase of the dive, it seems impossible he's gone. Any ideas?
 
Actually, many equipment issues (such as improperly packed scrubber, stuck valves, etc.) will present themselves within the first five minutes of use. Such issues can lead to excessive CO2 buildup and consequently unconsciousness. That is one of the reasons why we always prebreathe our rebreathers on the boat for five minutes before we get in to the water (it also serves to activate the scrubber).

Accordingly, if one of the aforementioned issues existed for the unfortunate diver, it would likely present itself when he first entered the water and began to exert himself (causing him to breathe heavily) by swimming for the anchor chain. At that point, the CO2 buildup could most definitely render him unconscious.

I am not saying that is what happened, but am merely correcting your assumption that the swim to the anchor chain is the safest part of the dive when, in fact, it can be the most dangerous when diving with a rebreather.
 
My condolences to his family and friends key west.

As fletcher mentions, rebreathers while very simple in concept (two bags, a box and a tank of gas with some tubes) they have a level of risk involved that is higher than that of conventional open circuit scuba.

Part of the problem is that when rebreathers go wrong, it may not be immediately apparent to the diver, they can continue breathing a gas that cannot sustain life without knowing it. In this scenario, the diver breaths until they fall asleep. This could have been what happened to your friends son.

Key west, you have posted in the right place, I am sure that as more questions arise, that there are people here on the board that can give you some helpful direction and maybe even answers.
 
cancun mark:
My condolences to his family and friends key west.

As fletcher mentions, rebreathers while very simple in concept (two bags, a box and a tank of gas with some tubes) they have a level of risk involved that is higher than that of conventional open circuit scuba.

Part of the problem is that when rebreathers go wrong, it may not be immediately apparent to the diver, they can continue breathing a gas that cannot sustain life without knowing it. In this scenario, the diver breaths until they fall asleep. This could have been what happened to your friends son.

Key west, you have posted in the right place, I am sure that as more questions arise, that there are people here on the board that can give you some helpful direction and maybe even answers.

Thanks to both of you. I realize we are really speculating, but I feel helpless and collecting information is something I can do. We may never get the answers as to what actually happened, but I am just trying to get a sense of what could have happened. I guess the boat could have hit him in the head, for that matter. I will share what I find out, if anything, if only to help people be safe with these things.
Initially, my sense is that it is important to dive with groups that understand these rebreathers so people can look out for each other.
 
Keywest,
as there is a question mark behind the term rebreather let me briefly describe how they work so the previous two post will make a bit more sense.
Rather than inhaling and exhaling the breathing gas as you do on open circuit scuba, the exhaled gas is routed into a loop of hoses, counterlungs (bags) and the scrubber (box). The latter eliminates the CO2 the body produces when metabolizing the O2. If for some reason it doesn't, the CO2 stays in the loop and will be rebreathed, too, until the diver looses consciousness. As the O2 is metabolized, new gas is added to make up for it.

Another possibility in the accident you described is that no new gas was added, for example if the tank was depleted or the valve closed. The diver would still be able to breathe, just pushing the old gas through the loop. That would lead to hypoxia, not enough O2 in the loop to sustain consciousness and eventually, life.

As with hypercapnia (CO2 poisoning), this would occur within several minutes, and rather quickly during a surface swim. Although easily prevented by both the pre-breathing as well as O2 monitoring, if neither was done the signs would onset very quickly. Too quickly to react in some cases, same as hypercapnia.

When loosing consciousness, the diver likely drops the bite piece and water will flood the loop. That will lead to the loss of buoyancy, much like flooding your BCD would, likely the reason your friend wasn't spotted adrift on the surface.

It's always sad to hear the reports of diving accidents and fatalities.
My thoughts are with you and the family and friends, my condolences.

Stefan
 
You posted before I did ... hope you're not offended by my little RB101 lecture.

keywest928:
I will share what I find out, if anything, if only to help people be safe with these things.
Thank you for that.

Initially, my sense is that it is important to dive with groups that understand these rebreathers so people can look out for each other.
I agree with your assessment, a dive buddy might well have made the difference, especially at the surface. Too many accidents and fatalities, both OC and on RBs, happen while the diver is alone.
 
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