As far as mCCR vs eCCR, it would seem, if the stats reveal a true tendency, that mCCR's are safer. If there is a linear relationship in the stats, in other words if the difference in fatalities does reflect an inherent difference rather than simply reflecting that eCCR divers tend to be folks who push the envelope more, then perhaps it lies in the fact that an mCCR diver not only watches their PO2 frequently but actually has to be intimately engaged in the O2 controlling system, not just looking and monitoring but actually thinking and adjusting it acordingly. It has been argued that this level of engagment requires that the mCCR diver be on top of things constantly, never relying entirely on their system to keep them alive. While many would argue that this is still inconclusive, the numbers are compelling... 0% fatality rate on the KISS.