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part II
Automatic Injection Rebreathers:
ECCR’s address the need for constant po2 by employing an electronic set point controller, a po2 monitoring system that generally requires three o2 cells. O2 cells are notoriously unstable so 3 cells are typically used in eCCR’s where the computer employs an automatic voting logic; the set point controller automatically goes with the two closest readings. While the user is expected to monitor proper function, staying mentally engaged on an automated process has its challenges. The set point controller uses the readings from the o2 cells to drive a solenoid to inject an exacting amount of o2 to maintain constant po2 throughout the dive. Because eCCR’s are able to monitor and maintain a set point, pressure-compensating first stage regulators are used, I get into the reasoning later but this gives them a deeper depth potential in their stock configuration than most mCCR’s in their typical stock configuration.
The firm believers in eCCR's like the convenience of a set point controller, and often believe that it is a “safety net” in case of getting overly task-loaded or distracted. Some even going so far as to run their eCCR’s manually, relying only on the set point controller minimally…however, the injection rate required to do this is significantly higher than on an mCCR because there is no assist from a constant mass flow valve. ECCR's seem particularly attractive to photographers, deep penetration wreck divers and cave divers, those for whom hands free function is a high priority.
Critics of automatic systems refer to them as something more akin to a “safety blanket” which can all too easily encourage dependence and charge that they encourage complacency, leaving the diver vulnerable to the possibility of being “checked out” in that rare but possible moment that they stop functioning properly. For reasons yet to be determined, there are many fatalities associated with eCCR's and this has lead many people to fear rebreathers of all kinds. The trends in eCCR development have been to overcome the apparent added dangers of complexity and dependence by providing ever more sophisticated warning systems to alert the diver before a problem becomes critical. It appears to me that significant strides in this direction are being made.
The drive for solid research into fatalities is growing. Until recently, the efforts to find answers has been hindered by an apparent resistance within the CCR diving community to take a cold hard look at the numbers and create a standard for gathering objective data. The wishes of the families of deceased CCR divers and the closed-book stance of manufacturers to reveal total units produced and causes of fatalities they research have all contributed to an inadequate database for conclusive and objective study…thankfully this is beginning to change. Now that rebreathers are becoming more popular, DAN, with the help of many generous folks, is starting to work on a database and look more squarely at the cause of CCR fatalities to help make improvements in training and manufacturing standards.
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