Bobby
Contributor
I am a CCR diver. A few of my thoughts.
I disagree with the statement "most of the incidents are user error". It is not fair or correct to blame user error when the user has not been taught properly. O2 cell linear deviation and cell limiting are, IMHO, the most important topics a CCR diver needs to understand completely. 99% of the classes barely give the subject lip service much less teach it to a level of understanding. There are instructors and IT's that will tell students that linear deviation and limiting are hog wash, which only makes things worse. I have heard such nonsense as "don't do an O2 flush at 20', you will bombard your cells with O2". I've also heard that "no cell will actually be linear". I've been doing the math for decades on every CCR dive I do. Along with 20' checks, both at the start and end of the dive, I've caught many cells that seemed OK however were not do to either linear deviation or limiting.
I disagree with the statement "if a cell goes bad that is what voting logic is for". I've had personal friends die because two of their cells were limited and the third good cell was voted out. Doing the math to check linear deviation and a 20' foot check would have kept them alive.
I disagree with "calibrate before every dive or every day of diving". Calibrating is the number one easiest way to screw up the information you are getting from the unit. The only time I calibrate is when there has been enough linear deviation to skew my handset readings. I have gone as long as 8 months without calibrating, granted that is a rarity however the point is that there is no reason to calibrate if the readout is correct. What is important is knowing if the cells have too much linear drift or are limited regardless of what the handset readout is. The only way to know is by doing the math along with a 20' check. If you, as a CCR diver, don't understand why calibration is the number one easiest way to screw things up then you need to seek more knowledge.
I disagree with "just replace a cell every 3 months and you will be OK". I've had many cells fail out of the bag and even more of them fail within the first few dives. If I calibrated every dive or day I likely would not have even noticed there was a problem.
I disagree with "a CCR is just as safe as OC". Reality is that a CCR has more failure modes during the dive than OC and it requires a deeper understanding in order to recognize the potential failure modes and they are more subtle. A CCR is a tool and for more complex dives it can be a safer tool than OC. For most dives OC is the safer tool, until you have enough depth and/or over head penetration distance that the gas logistics make the CCR a better choice. The reality is that time and experience is needed on a CCR to be proficient so the easier dives are needed to have the skills and experienced for the bigger dives. It is a choice that most don't understand when going into CCR. They are sold on marketing hype and given easy "just do this" instruction that sends them down the road without the basic knowledge they need.
The math is not difficult, it is simple division and multiplication. I've taught people that have a lot of difficulty with math to a point of complete understanding. It does take some people more time however that is what teaching is about, spending the time to teach something to the level of understanding. The focus though is on cheaper, easier, and faster courses so the subjects that have a learning curve are the first to be cut out or severely shorted.
I've covered this in blogs, papers, and with many people after they have been certified on CCR. I've talked with instructors, IT's, agencies, and manufacturers in an attempt to make this required to teach to a complete level of understanding. They simply refuse to change anything that adds more time or complexity to teaching. If you have a cell that puts out 10.3 mv in air we need to do the math to know what perfectly linear would be. We are only concerned with the oxygen as that is all that an O2 cell reads. In air (at one atm) the O2 content is 0.21 or 21%. We want to know what the mv reading will be with 100% O2 if it were perfectly linear. To get that number we divide the mv reading in air by its percentage of O2. 10.3/0.21=49mv. Now we flush our unit to bring the O2 content up to 100% O2. What we actually see is 46.6mv, my question to all the CCR divers before we move on is, would you be comfortable with this cell? Many would answer no because they have been told that they should bin a cell if it drops below 48mv, which is horse hockey, IMHO. Let's do the math, to find the deviation we need to divide the smaller number by the larger number between the mv in O2 and the perfectly linear number. 46.6/49=0.95 which tells us that our cell is 95% linear or it has 5% linear deviation. My experience is that most cells for most dives are good to go with as much as 10% linear deviation. Depth, time of dive, and other considerations will affect my decision to change a cell or not.
This is not about saving money, keep in mind that cells fresh out of the bag and ones with only a few dives on them can easily die, have a lot of deviation, or be limited. This is about knowing the actual health of all of your cells and making a decision about using a particular cell based on simple straight forward math. It is about having confidence, in the water during the dive, that you know that the output of your cells is accurate.
So to answer the OP's question "how great is the risk"? It really depends on the level of understanding. IMHO without complete understanding of linear deviation and limiting the risk is extreme. Even with solid understanding the "risk" ,IMHO, is higher compared to OC until depth and time make the logistics of gas management tip the scales in favor of CCR. Many get away with it because classes have found quick work around's that get you buy most of the time. The problem is that when that work around doesn't get you by, the result is a statistically much higher incident rate of death. Personally I don't want to be a statistic in that category, so I will continue to question everything I have learned and what others tell me. I will continue to seek out new knowledge and understanding then continue to question that as well.
I disagree with the statement "most of the incidents are user error". It is not fair or correct to blame user error when the user has not been taught properly. O2 cell linear deviation and cell limiting are, IMHO, the most important topics a CCR diver needs to understand completely. 99% of the classes barely give the subject lip service much less teach it to a level of understanding. There are instructors and IT's that will tell students that linear deviation and limiting are hog wash, which only makes things worse. I have heard such nonsense as "don't do an O2 flush at 20', you will bombard your cells with O2". I've also heard that "no cell will actually be linear". I've been doing the math for decades on every CCR dive I do. Along with 20' checks, both at the start and end of the dive, I've caught many cells that seemed OK however were not do to either linear deviation or limiting.
I disagree with the statement "if a cell goes bad that is what voting logic is for". I've had personal friends die because two of their cells were limited and the third good cell was voted out. Doing the math to check linear deviation and a 20' foot check would have kept them alive.
I disagree with "calibrate before every dive or every day of diving". Calibrating is the number one easiest way to screw up the information you are getting from the unit. The only time I calibrate is when there has been enough linear deviation to skew my handset readings. I have gone as long as 8 months without calibrating, granted that is a rarity however the point is that there is no reason to calibrate if the readout is correct. What is important is knowing if the cells have too much linear drift or are limited regardless of what the handset readout is. The only way to know is by doing the math along with a 20' check. If you, as a CCR diver, don't understand why calibration is the number one easiest way to screw things up then you need to seek more knowledge.
I disagree with "just replace a cell every 3 months and you will be OK". I've had many cells fail out of the bag and even more of them fail within the first few dives. If I calibrated every dive or day I likely would not have even noticed there was a problem.
I disagree with "a CCR is just as safe as OC". Reality is that a CCR has more failure modes during the dive than OC and it requires a deeper understanding in order to recognize the potential failure modes and they are more subtle. A CCR is a tool and for more complex dives it can be a safer tool than OC. For most dives OC is the safer tool, until you have enough depth and/or over head penetration distance that the gas logistics make the CCR a better choice. The reality is that time and experience is needed on a CCR to be proficient so the easier dives are needed to have the skills and experienced for the bigger dives. It is a choice that most don't understand when going into CCR. They are sold on marketing hype and given easy "just do this" instruction that sends them down the road without the basic knowledge they need.
The math is not difficult, it is simple division and multiplication. I've taught people that have a lot of difficulty with math to a point of complete understanding. It does take some people more time however that is what teaching is about, spending the time to teach something to the level of understanding. The focus though is on cheaper, easier, and faster courses so the subjects that have a learning curve are the first to be cut out or severely shorted.
I've covered this in blogs, papers, and with many people after they have been certified on CCR. I've talked with instructors, IT's, agencies, and manufacturers in an attempt to make this required to teach to a complete level of understanding. They simply refuse to change anything that adds more time or complexity to teaching. If you have a cell that puts out 10.3 mv in air we need to do the math to know what perfectly linear would be. We are only concerned with the oxygen as that is all that an O2 cell reads. In air (at one atm) the O2 content is 0.21 or 21%. We want to know what the mv reading will be with 100% O2 if it were perfectly linear. To get that number we divide the mv reading in air by its percentage of O2. 10.3/0.21=49mv. Now we flush our unit to bring the O2 content up to 100% O2. What we actually see is 46.6mv, my question to all the CCR divers before we move on is, would you be comfortable with this cell? Many would answer no because they have been told that they should bin a cell if it drops below 48mv, which is horse hockey, IMHO. Let's do the math, to find the deviation we need to divide the smaller number by the larger number between the mv in O2 and the perfectly linear number. 46.6/49=0.95 which tells us that our cell is 95% linear or it has 5% linear deviation. My experience is that most cells for most dives are good to go with as much as 10% linear deviation. Depth, time of dive, and other considerations will affect my decision to change a cell or not.
This is not about saving money, keep in mind that cells fresh out of the bag and ones with only a few dives on them can easily die, have a lot of deviation, or be limited. This is about knowing the actual health of all of your cells and making a decision about using a particular cell based on simple straight forward math. It is about having confidence, in the water during the dive, that you know that the output of your cells is accurate.
So to answer the OP's question "how great is the risk"? It really depends on the level of understanding. IMHO without complete understanding of linear deviation and limiting the risk is extreme. Even with solid understanding the "risk" ,IMHO, is higher compared to OC until depth and time make the logistics of gas management tip the scales in favor of CCR. Many get away with it because classes have found quick work around's that get you buy most of the time. The problem is that when that work around doesn't get you by, the result is a statistically much higher incident rate of death. Personally I don't want to be a statistic in that category, so I will continue to question everything I have learned and what others tell me. I will continue to seek out new knowledge and understanding then continue to question that as well.
