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Diving Medicine Rebreathers

Rebreather Fatalities

Statistics show that almost always the cause is diver error
By Dr. David Sawatzky

Photo: Jill Heinerth
Photo: Jill Heinerth

In the last column I outlined how rebreathers work. There are many brands available and more coming on the market though the basic concepts for all of them are the same.  Rebreathers are complicated. There are many correct responses for the problems that can develop and it’s also true that many of the reflexes we have developed diving open circuit are inappropriate and can kill us when we are diving a rebreather.

When diving open circuit you are virtually always okay if you have gas to breathe.  This stops being true when you move into technical diving where breathing your decompression gas too deep can kill you from an oxygen (O2) seizure and breathing your bottom gas for a deep trimix dive too shallow can kill you from hypoxia.  When diving a rebreather the gas you are breathing can kill you if the partial pressure of oxygen in the gas is too high or too low, or if the partial pressure of carbon dioxide is too high.  Experienced open circuit divers intuitively believe that as long as they have gas to breathe they are okay and as a result often forget to monitor the partial pressure of oxygen (pO2) in the breathing loop on a rebreather.  This is frequently a factor in rebreather accidents.

In addition, when diving open circuit (no decompression), the ultimate response to virtually any problem is to exhale and ascend to the surface.  This is not an option when you are inside a wreck or cave.  As well, if you have a significant decompression obligation, ascending directly to the surface can kill you from decompression sickness (DCS).  These two situations are often factors in rebreather fatalities.

As a result of the above, rebreather training is quite long and complicated.  In addition, every rebreather is different and requires specific training.  I am an Instructor Trainer for the Inspiration (not currently active) and a certified diver on the Megalodon and the Optima.  Training is organized roughly as follows by most agencies:

  • Recreational CCR – maximum pO2 1.2 ata, max depth 70 fsw (21 msw), no decompression
  • CCR Diver – maximum depth 140 fsw (42 msw), max decompression 15 minutes
  •  CCR Normoxic Trimix – maximum depth 200 fsw (60 msw)
  •  CCR Trimix – maximum depth 300 fsw (90 msw)
  •  CCR Expedition Trimix – maximum depth 400 fsw (120 msw)
  •  CCR Cave, Wreck, etc.

The first rebreather course usually requires a minimum of eight hours in water dive time to allow the student the opportunity to unlearn some of their open circuit habits and to learn a completely new, complex set of rebreather practices.  In addition, a significant amount of diving should be done between every course.  Rushing into advanced diving using a rebreather is also frequently a factor in rebreather fatalities.

Open circuit diving fatalities are usually caused by heart attack, arterial gas embolism, running out of gas or environmental factors (lost, trapped, etc.).  In technical diving you also see oxygen seizures, hypoxia and decompression sickness (DCS).  When diving a rebreather you see all of the above plus too much carbon dioxide and failure of the rebreather.  Let’s look at some rebreather accidents/fatalities.

Photo: Jill Heinerth
Photo: Jill Heinerth

What Happened
An experienced closed circuit rebreather (CCR) diver made a 300 fsw (90 msw) dive with a 20-minute bottom time.  Decompression proceeded normally until the diver experienced a problem during the 60 fsw (18 msw) stop.  The diver ascended directly to the surface.  This diver’s partner still required approximately an hour of decompression and, wisely, he stayed at depth and finished his decompression.  Had he ascended, likely he would have developed serious decompression sickness from which he could have died.

The diver who did ascend directly to the surface was recovered almost immediately (unconscious) and was promptly taken to a nearby hospital equipped with a hyperbaric chamber.  Unfortunately this diver (age approximately 60, grossly obese, poor physical condition) had suffered a heart attack and was never stable enough to be placed in the recompression chamber for treatment of his serious DCS.  He died five hours after arriving at the hospital.  

During an expeditionary caving trip, a diver died while making a solo dive deep inside the cave.  No defects were found with the CCR.  He was a newly diagnosed diabetic in denial and in poor control.  He almost certainly lost consciousness on the dive as a result of his diabetes, and drowned.  A second diabetic on the trip who was in excellent control and who had never had a problem was found unconscious at an underground camp and was revived.  When the stresses of daily living are changed, diabetics can very easily lose control of their blood sugars.

A diver smoking dope set up his unit incorrectly…then dived. I would call this fatality ‘natural selection’

Another diver was doing his second day of diving on a deep wreck.  He jumped off the stern of the boat and was swimming alongside the vessel towards his partner at the down line when he sank directly to the bottom in 240 feet (73m) of water.  When the body was recovered several hours later, his computer showed a direct descent to the bottom and no change in depth after that.  Examination of the rebreather revealed some minor problems that should not have been a factor.  Autopsy revealed a serious infection of the heart.  This diver almost certainly suffered a cardiac arrhythmia, lost consciousness, sank and died.  He was obese, in very poor physical condition and had mentioned feeling a bit unwell the previous day.  As with open circuit diving, rebreather divers sometimes die as a result of medical problems.

On a dive trip to the Galapagos Islands a CCR diver entered the water, was swimming at about 30 fsw (9 msw) depth when he lost consciousness and began sinking, but was rescued by his very alert partner.  He was revived, suffered some lung damage from near drowning but survived. He had not properly prepared his rebreather for diving, and he lost consciousness from hypoxia.  He had also, obviously, not checked the composition of the gas he was breathing or he would have noticed his pO2 was too low.  This diver had thousands of open circuit dives logged and was a photographer, a combination that is often deadly when diving CCR.  I firmly believe every CCR photographer should have a partner whose only job is to keep them alive!

Photo: Jill Heinerth
Photo: Jill Heinerth

An instructor was diving CCR while teaching open circuit students in a quarry.  They entered the water, descended to about 20 fsw (6 msw), did a few drills then descended to 40 fsw (12 msw).  After a few minutes the instructor swam off into the murk.  The instructor’s body was later found on the bottom nearby. The O2 tank on his rebreather was turned off.  Calculation of his probable O2 consumption, dive profile and rebreather loop volumes revealed that if the O2 tank had been turned off from the beginning of the dive, the pO2 in the loop at that depth would have dropped to a level causing the instructor to lose consciousness about the time he disappeared.  He had also, obviously, not checked the pO2 of the gas in the rebreather during the dive.  A rebreather diver is trained to check the pO2 in the gas they are breathing every few minutes.

A photographer left his dive companions on the bottom at 45 fsw (14 msw) to surface and get more film.  His body was found about 45 minutes later on the bottom.  Autopsy revealed high levels of stimulants and narcotics.  He had a habit of elevating the pO2 during decompression to reduce the risk of DCS.  He almost certainly suffered an O2 convulsion as a result of the chemicals in his body and elevated pO2 during his short decompression stop.

Increasing the pO2 during decompression at the end of a rebreather dive is a VERY bad thing to do.  The body has been exposed to high levels of O2 for the entire dive and is already at risk of an O2 seizure.  In addition, increasing the pO2 during decompression has a very small effect on the risk of DCS.

Another diver was doing a 130 fsw (40 msw) dive with a long bottom time.  While still on the bottom he appeared to become disoriented, made a rapid ascent and sank 12 minutes after surfacing.  Although we will never know for sure what happened, the sodasorb in his rebreather was completely expended and it is most likely that he suffered a problem from elevated carbon dioxide in his breathing loop while on the bottom.  These accidents all qualify as ‘diver error’, common in rebreather fatalities.

A CCR diver made a 160 fsw (48 msw) wreck dive, lost consciousness and drowned.  He started the dive with two of the three O2 cells in his rebreather not working.  Another diver started the dive with no way to monitor the pO2 in the breathing loop, convulsed during decompression and died.  A third made a solo CCR dive with no open circuit options.  His rebreather developed a leak in the breathing loop and he died in 16 fsw (5 msw) of water.  A rebreather should never be dived without some way to breathe if the rebreather fails (carry a bailout bottle).  In these three fatalities there were equipment problems but a properly trained rebreather diver should be able to survive any equipment problem.

Another diver did a basic CCR course, a couple of dives then did a deep, solo, CCR trimix dive and never surfaced.  A second diver was smoking dope, set up his unit incorrectly and went diving.  I would call these fatalities ‘natural selection’.

Rebreathers are relatively complicated and the correct response to a problem is less obvious than when diving open circuit.  Rebreathers require extensive training and constant vigilance to dive safely.  To call them ‘hideous insidious killing machines’ is not completely inaccurate.  At the same time, they are awesomely efficient and allow us to make dives that are simply impossible on open circuit.  Rebreather fatalities (other than medical problems) are almost always due to ‘diver error’. 

10 Comments Leave A Reply

10 Responses to “Rebreather Fatalities”

  1. Frank

    Dr. Swatzky,

    Thanks for the informative article. Did you hear about a rebreather fatality in Galapagos in 2012?

    You stated that, “A second diver was smoking dope, set up his unit incorrectly…” Do you know what he was smoking?

    I used to receive their official skydiving magazine when I was an active member of the United States Parachute Association. Every time I received the latest issue in the mail and opened it for the very first time, I would immediately turn to the page (or pages) about recent known skydiving incidents, so that I could learn from them right away.

    I know that there are tons of SCUBA magazines in print, but is there an equivalent magazine or “page” for details of SCUBA incidents (OC and CC)? (I have a US mailing address, so an American magazine would probably be best for postage costs.)

    And Happy New Year’s Eve Eve Eve!


  2. Mariano Sciacca

    Dear Sirs,
    Please Note; CCR Rebreathers until today 2016 Year, are NOT, the correct DeepDiving Choice!
    The safe Correct DeepDiving Choice remain the “narghilè” Professional Gears.
    The Rebreathers are always a “diving Russian Roulette”.
    Sincerely Yours,
    mariano sciacca
    Pantelleria Island

    • The "narghilè” is a hookah system, are you stupid?

      What is that supposed to mean? You think that deep diving is safer with a hooka system, why spread stupidity like that?

  3. John Harris

    After years of thinking about it and trying to figure out how to shoehorn it into the budget (without my wife noticing it), I have decided not to bother with a rebreather. I have survived cancer. I don’t think I need to purposely need to put my life at that much risk in the name of recreation. I’ll carry a bigger tank, or possibly two. I just won’t suck the fun out of my dives by piling on the risk and having to pay such attention to detail, where I will be so busy that I won’t have time to enjoy it.

  4. Michelle Cunney

    Thank you for sharing this article. My aunt and uncle both died on June 28th, 2019 during a dive to explore the wreck of the SS L.R. Dotty in Lake Michigan at 300 feet deep. They were highly trained, experienced, certified technical divers. They chose to use a rebreather so they could explore the wreck for a longer period of time. I know they were extremely educated and had hundreds of practice hours logged using the rebreathers. They have been featured on the cover as well as being the top story in quite a few scuba diving magazines multiple times. They were asked and paid to perform dives with professional scuba diving photographers for these magazine photos. They have literally been all over the world for their scuba diving adventures and they loved every second of it. About 45 minutes after they started this dive my aunt was spotted floating face down by the boats captain who took them the 12 miles off shore where the wreck was located. He immediately took action with the crew to get to her and try to revive her as well as one member of the crew who went below deck and knocked a specific number of times on a glass window that apparently all the divers are able to hear and know that it means start to surface immediately. They got my aunt from the water onto the boat after removing all her gear and performed CPR until the coast guard rescue boat arrived with a helipad for the helicopter that had been hovering over the boat waiting they were on until they were able to land on the other boat, which immediately got right up against the boat that had taken the divers to the wreck, the team of people who’s job is specifically to do any and all means necessary to revive a scuba diving victim immediately jumped onto the boat and took over compressions and breaths while another man connected my aunt to a CPR machine so they could get her in the helicopter and to the nearest hospital(from what I know they never had a chance of being able to save her life) By this time the other 3 diving buddies had surfaced when one crew member realized my uncle hadn’t. They immediately called for a search but they only way they were able to search was to look for him elsewhere above the water because certified technical scuba divers aren’t easy to come by no one from the sheriffs office or the coast guard could actually search for him near the wreck. After 8 hours the search was called of and began a day and a half later. The team included the Milwaukee sheriff’s department, coast guard and the most amazing non profit organization dedicated to recovering the bodies of drowning victims, called Bruce’s Legacy. They brought a submarine that was built specifically for this purpose… it had robotic arms and was able to pick up something as small as a shoe but was used to bring the drowning victim to the surface. They did recover my uncles body(thank God)… my aunts autopsy showed that her ultimate cause of death was drowning due to water found in her lungs and some sort of mark or popped blood vessel on her face or neck somewhere that appears when people drown. They were unable to find any possible cause of death for my uncle. An investigation was started almost immediately after they had recovered all the equipment that they had lost of my aunts because to get her out of the water they had to remove all of it and it of course sank, they found all my uncles equipment that had been lost sometime while he was in the water. They told us they estimated the investigation would take 2-3 weeks. They had to review all the computer info etc and they sent the tell rebreathers to the manufacturer to be checked for any malfunction etc, well the investigation was finally closed a week ago, the meeting set up with my family to explain what they discover and what their theory regarding what actually happened is. It apparent took so long because my uncles computer was never turned off and I don’t know how long it lasted until the battery died but there was so much information to go through it apparently made an investigation that would have taken a few weeks turn into one that took nearly 5 months. My dad had been in touch with the people in charge of the investigation the whole time and he just told me today that he had been told a few things that he hadn’t shared with anyone other than my mom. They think my uncle passed out… they know that part of one of the scooters fell off(so they think the both tried to find it) which could be a possible explanation for maybe my uncle forgetting to check the gas levels and all that causing him to pass out with no warning signs and no ability to switch from the rebreather to his back up breathing gear(I don’t remember what it’s called). They think my aunt tried to revive him somehow for 20 minutes ( (apparently it can be done, I just can’t understand how you could revive someone underwater, wearing extremely heavy equipment, breathing through a machine and all that but they have audio that makes them think that she was trying to get him back. They said we can listen to but warned us that they didn’t think we should because whatever they heard in the 20 minutes of the recording would be extremely devastating and traumatic and they thought our family had already been traumatized far too much) I guess they think my aunt started to surface and somehow drowned. She didn’t forget to stop every however many feet for the right amount of time while she was attempting to surface and they know this because she didn’t die from decompression sickness etc… my only guess even though I’m not educated at all about any of this stuff to really even have a guess is that she was so traumatized by my uncles death and having to leave him at the bottom of the lake that she was crying so hard and probably having a panic attack leading to her starting to hyperventilate or something and ultimately somehow it allowed water to get in and she could not regain control of her breathing because it’s not easy under normal circumstances once you’ve started to hyperventilate so I can’t imagine being able to stop it after going through what she just had as well as being so deep underwater and all of that so she started basically inhaling water into her lungs.

    Anyways, when I was talking to my dad this morning and he told me the few things he had been told and warned me that if I decided to come to the meeting where they explain everything the know for a fact and whatever they don’t know they will explain their best theory about what happened that the would probably place some of the blame on my uncle not being diligent enough and didn’t do the things he was supposed to do like checking the gas levels every few minutes and he knows me well enough to know that even if I know they aren’t actually blaming him or criticizing him I will automatically go into my defensive mode and start screaming at them for making this tragedy his fault in any why shape or form.. on that note I wanted to say that when you called a few of the deaths “natural selection” I think it is incredibly inappropriate that you actually put it in the article regardless that it’s what you think.

    Thank you for the article over all, I’m just trying to learn all I can about rebreathers right now because I have to find a way to make sense of this in my head in order to even start to heal, because I’m truly broken over this.

    • John

      Thanks for sharing. I hope you found closure from this.

      Also think using ‘natural selection’ is pretty callous. A lot of people who end up on this page will do so in response to deaths or near deaths of people they care about. It’s not the case for me (just researching technical diving), but it’s something to think about.

      Additionally it’s just kind of obnoxious and lacking in awareness. We’re all engaging in one of the more dangerous activities on the planet. Even doing everything right it’s possible to have your body fail, and a mistake in this activity has the potential to be dangerous or fatal on a level that mistakes in most other activities don’t reach. As a result there would be a case to be made that everyone who engages in Scuba, and especially technical diving, cave diving, ship wrecks, etc and dies is an example of natural selection. They all undertook activities that carried dramatically more risk than anything the average person does, and did so purely for their own enjoyment. But I think you probably wouldn’t be happy to hear someone say your brother or friend’s death was natural selection because they participated in a dangerous activity – compounding mistake or not.

      Good information and write-up thanks for helping educate me, this is just a note on the tone.

  5. Not Much

    “Another diver did a basic CCR course, a couple of dives then did a deep, solo, CCR trimix dive and never surfaced. A second diver was smoking dope, set up his unit incorrectly and went diving. I would call these fatalities ‘natural selection’.”

    Extremely callous for no real reason

    I guess they had pretty painless deaths though which is nice

    Hopefully they didn’t leave big messes behind in their social lives

  6. Rick Donnelly

    Thanks for this article. This has been on my mind lately because of a close call a friend had similar to Michelle’s story above. There are some important takeaways for me here. The first is the need to unlearn certain OC habits and reflexes. The same is true for moving from recreational to technical OC diving. You’d be wise in both cases to make a lot of training dives and work on emergency drills before tackling hard stuff, but few people do. That’s not as egregiously stupid as smoking dope before a dive but it’s hard to argue that the latter is reckless while the former is not.

    It’s impossible to say from published data how much more dangerous rebreather diving is than recreational OC diving. We need to partition risk into a 2×2 matrix. The rows could be “all diving” and “rebreathers only” and the columns “fit divers” and “unfit divers”. Deaths from “all diving” would be those that would have killed the diver whether diving open or closed circuit. Heart attacks underwater are by no means restricted to technical or rebreather divers. You might argue that diving below recreational limits places greater stress on your heart. Seems intuitive but I’m not aware of any study that has suggested correlation between depth and heart attack incidence (although prompts me to dig deeper into that).

    I count a dozen deaths in your article. One (diver 11) had unknown cause of death. Four died of or had heavily contributing “all diving” causes: diver 1 (heart attack), diver 2 (uncontrolled diabetes), diver 3 (myocarditis), diver 6 (high levels of stimulants and narcotics).

    Seven divers died of “rebreather only” causes that could not have affected an OC diver. All seven made serious mistakes before they got into the water. Two improperly set up their rigs (divers 4 and 12) and one failed to turn on his oxygen (diver 5), which also qualifies as improper setup. The remainder dove despite knowing they had defective hardware or never checked: depleted absorbent (diver 7), inoperable O2 cells (diver 8), no oxygen sensor (diver 9), and no bailout system (diver 10). In only one instance (diver 10) did a presumably properly configured CCR system fail during the dive — and likely survivable with a bailout system that all CCR divers I know *never* dive without.

    What we don’t know about these incidents is also troubling. In a few cases we can spot “unfit divers” in poor health and physical condition. We know little or nothing about the health or diving histories of the others. How many of these divers were “fit divers” versus “unfit divers”? If most were the latter that might certainly change the interpretation. How many were hypothermic? How many were distracted or stressed by low visibility or strong currents? We don’t know. But we do know that they are also big risk factions for diving incidents.

    Confounding all this is that rebreathers themselves are a moving target. The increases in safety, reliability, and redundancy between rebreathers sold 10-20 years ago — to say nothing of the DIY models — and the Divesoft Liberty exceeds the improvements we’ve seen in OC diving methods and hardware over the same period. Granted, the Liberty is out of reach of all but professional or very wealthy divers, but it will hopefully continue to raise the bar in CCR hardware.

    The bottom line for me, which your article helpfully underscores, is that divers need to be in great physical shape regardless of mode of diving. If you’re in the “unfit diver” category you must address that first and foremost, especially if you’re an aged diver like me. Once you move out of those boxes and if you’re super vigilant about your ppO2 at all points in your dive *and* you are obsessive about checklist beforehand the risk of rebreathers seems a lot less than street wisdom suggests. If I had any doubts about those truths your 12 cases would convince me otherwise.

  7. Terrance Deemer

    Old RVN US Army combat vet here…will try to keep it short. While on R&R in Sydney I happened to run into two Air Force PJs (para-rescue) guys. We hit it off immediately and burned the candle at both ends before returning to play war. Our plane landed at Da Nang, where they were stationed. I was a Huey recovery crewchief in Chu Lai, about a hundred miles down the coast (and in no hurry to get back to work) so was invited to spend a few days with the 37TH Aerospace Rescue & Recovery Squadron. While there we figured, since all three of us were leaving the service at the end of 1969, to meet up in Hermosa Beach, CA. Much surfing and diving adventure ensued. About mid-1970 one of the ex-PJs got a bug to sign on to a treasure diving crew in the Caribbean around the island of Roatan. He did a few weeks down there before coming back deciding a mixed-gas outfit would give him extra bottom time. So he bought a Beckman ElectroLung, went to Cozumel for training (on one of the dives a member of the party became disoriented at 300′ and was last seen swimming towards the bottom) and headed back to Roatan. He wasn’t down there for more than a week before the rig malfunctioned and blew his lungs in 25′ of water.

    Don’t know how active this comment section is, but since we never knew whether the story we got was on the level or involved foul play, it would be great to hear info from someone with expertise with similar devices…will be checking back periodically.

    PS: The other PJ died in a suspicious industrial accident around that same time. Miss them both.


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