Gill Envy
Contributor
I think what Tienuts (gatta love that handle) is saying is that most, as in the vast majority of the deaths that are associated with rebreathers have occurred on fully automated (eCCR systems) rebreathers.
From what I can tell there have been close to 200 deaths on eCCR's to date and depending on who you talk to about it, that's a staggering 1-2 out of every 100 users! To date there have been a total of about 3 fatalities on manual injection (m-CCR) systems. There are no solid conclusions to be made from the stats since we really don't have objective 3rd party research to work with but many of us feel that we will grow gray and fall in the grave before ultimate conclusions can be drawn... until then we are doing our best to deal with the spotty information we have access to. The numbers have been suggestive enough for me to be compelled to do some research on my own and get personal experience on both styles.
I contacted all the manufacturers of mCCR's last year and totalled up the number of units out there (strangely the eCCR numbers were not given freely from manufacturers of those units). From what I can tell, the fatality rate is about 3 in a thousand mCCR users, though it was zero until relatively recently. The recent uptick in fatalities has a lot of us watching the trend closely, fearing that the popularity of mCCR's may have inadvertently created unrealistic expectations in users with respect to safety... the irony is that as soon as you think your system is safer, your propensity toward fatal mistakes appears to sky rocket. Also there are limits to comparing numbers of eCCR vs mCCR units, while there are impressive dives being done on both, it's hard to tell if it's an apples to apples comparison in total number of diver hours or challenge of dives or even whether mCCR's are self selected by a user group that is inherently more anal. One thing is for sure, more time will tell us more. Still, given the challenge of little solid information, each of us has to make a determination based on the information now available and for me for now, I'm convinced that manual injection is my best bet for reducing overall risk, assuming I continue on with a healthy level of mistrust.
To me the most compelling evidence that the design/human nature match of mCCR's is better in terms of fatalities showed up in personal experience, having put considerable hours on both styles, but I realize that that is anecdotal.
My wife and I started out diving a fully automated type of rebreather and watched our life flash before our eyes with a variety of malfunctions with the computer set point controller, which is designed to keep a steady partial pressure of oxygen in the loop. We had unusually bad luck as these malfunctions came on pretty early in our closed circuit experience. To make matters worse, between the expense of the units, the impressive sophistication of them and the tendency to eventually trust the eCCR system too much, complacency had begun to creep in, leaving us at maximum vulnerability when the malfunctions struck. When we made the switch to mCCR, I noticed a categorical difference in my habits, which I think explains a lot: my level of alertness, my monitoring rate (how often I looked at the screen) and my understanding of how the unit functions expanded exponentially. There was no illusion that a computer would ultimately be more reliable than my own vigilance. The consequences of not paying attention are immediately apparent on an mCCR, your po2 starts to drop! Where as not paying attention on an eCCR has few immediate consequences unless it malfunctions at the same time ... paying attention to a number that rarely changes or requires much action leaves one tempted to "kick back with your feet on the dash board" as TieNuts so apply put. It appears that many people find ways to dive eCCR's safely, but it's sobering that the ones who often die using them are very experienced divers doing relatively mundane dives. Even smart people make stupid mistakes.
that said, I am completely aware that there is risk in diving any kind of rebreather and to speak more directly to the subject of this thread, Semi closed systems have little appeal and are being eclipsed by fully closed units, which indeed are coming down in price, particularly in the used market. I do believe there is a huge potential for a burgeoning market for rebreathers if the price comes down and more conclusive research is done to improve safety. As for predicting the coming of the Apocalypse, many people have tried, and so far, no one has been successful.
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