BO correlations

[Triton1715]

I've been pondering the issues around blackouts and their seemingly unpredictable nature. Does any know if there is either a database (perhaps from competitions and such) that records the parameters of the divers that have had a BO.

If not, I think that there's a strong case to be made for gathering as much information as possible each time there is one. For example, if the diver was attempting a max of some sort, a BO isn't really unexpected at all. We know they were pushing themselves to edge. It would be more telling to know the details around the truly unpredictable ones.

My current guess is that out of all the BOs that have occurred, if you tossed ones due to max attempts, ones where the diver had packed, any brought on by HV, and any that happened after a day of serial dives, I suspect that there would be a dramatic drop off in the amount of BOs. This may sound like Captain Obvious talking since we all seem to know there's a correlation between these factors and a BO, but it's the ones that remain after these have been weeded out that I would like to know more about. For the past 16 years I've heard how unpredictable BOs seem to be, but with nearly every story, there's usually some clue in it as to what went wrong and it almost always involved one of the aforementioned issues. Still, BOs nonetheless occur even with these taken into account and I would love to know more about the specifics around those events. As near as I can tell, no one has been actively compiling the evidence around these events to string together a coherent pattern beyond the usual caveats of: don't push your limits, don't hyperventilate. Obviously, many of these happen away from events and good means of measuring or collating the data, but it just seems like we out to have a thread where anyone that experiences a blackout (or witnesses one) can post on to gather as much information on it as possible. It isn't magic and while there might be many variables to account for it, I believe that given enough information, it's possible to get to the root of it all.

Of course, I'm writing this during my lunch break and my head often wanders so maybe this has been discussed before and everyone has collectively said, "there's just too many variables. Dive with a competent buddy, stay within your limits, and don't worry about it."

 

[cdavis]

A subject dear to my heart. Like you, I figured it had to be possible to analyse BO factors and come up with a reliable profile. After lots and lots of thought and some modest experience, I don't think so anymore. The old rule of "only those who have gotten good at freediving are in danger of a BO" doesn't apply anymore. There is just too much knowledge easily available.

I've witnessed a fair number of BOs and similar events in open water diving, spearfishing or similar (not line diving and not competition) plus one in the pool. The only common factors I can come up with are C02 tolerance and maybe max depth of the dive. Those with very good tolerance seem to be more at risk of a BO or similar. Otherwise, some BOs came when the diver was screwing up and knew it, others were well within the divers capacity, no warning at all. I my personal case and before I had found DB, I had done a huge amount of very stupid stuff and never had a BO, only had tunnel vision and seen stars twice and that a long time ago. What I was doing at at the time was triple stupid. My co2 tolerance is lousy.

 

[Triton1715]

Well, I didn't necessarily mean a reliable profile, but more of a graph that would indicate potential chances for BO. To be extremely simplistic about it (and I'm spit-balling here for the sake of conversation so don't look into these numbers at all. . .they're just placeholders), a 15s breathhold may have a .01% chance of a BO whereas a max attempt may have something more like a 75% chance of BO or samba with a variable like +5% if you're dehydrated, etc. We know for sure that various things increase your chances of having a BO. . . HV, being dehydrated, being tired, having vigorously exercised prior, high CO2 tolerance, repeated deeper dives, max attempts, etc. and the "compounding interest" of having a combination of those at play simultaneously. Each one contributed to the odds, some more than others and it obviously depends where on the scale you are to start as to how much more prone you may be. For instance, being dehydrated after a day of serial deep dives and then doing a near max attempt is going to be much more dangerous than being well rested, well-hydrated, and just playing around in short dives in the shallows. I guess what I'm trying to get at is that while we can't predict with absolute certainty if you'll have a BO, we do know what contributes to those odds and to a certain extent, the role that they play. I think if we were able to plot with actual evidence all the info from BO, we could at least get a vague percentage figured out as to when you're really rolling the dice vs. merely playing with fire ;-) Again, it wouldn't be a reliable predictor, but it certainly would be better than looking into my crystal ball and hoping I don't BO today.

Incidentally, regarding HV and BO potential--I first took a freediving class back in 2000. The breath-up techniques we were taught turns out to have been classic HV, but without all the rapid breathing. At the time, this wasn't thought to be so though. In fact, we were taught that the "cues" that signaled you were ready to dive were all the signs of HV (light-headedness, tingling in fingers, metallic taste in mouth!). During that year, I came up from about 6 dives being very light-headed, blue-lipped, and twice I saw stars. Fast forward about 8 years and while training on my own at the pool, I came up from what should've been an easy dynamic (50m) and noticed on my way that I had a vague sense of light-headedness. Now, at this time I had been used to surfacing and being light-headed. It was all I had known and wasn't overly concerned about it except this time felt different. I can't really describe why, but it was. By dumb luck, I had chosen a lane near the swim ladder. When I surfaced near it, I shot my arm through and hooked my arm in it. Just as I was doing that, I got tunnel vision, everything went black, and I lost control of my muscles and swung, pivoted on my hooked arm, backward into the pool (a 180 from my position) and banged the backside of my head on the pool edge. Had my arm not been hooked in there, I would've gone under (and yes, like a moron, I was alone). That put me off freediving for a number of years, but when I got back into it, I was determined to make sure to go about it the safest way I can. . . .absent a reliable partner. Over the past 3-4 years, I've scoured the DB forums and stories and with only perhaps 3 exceptions, there always seems to be a likely culprit in all the BO stories I've heard. Though I don't call my experience a BO as I'm not totally sure I lost consciousness and if I did, it would've only been for about 5 seconds, I know it was because I had hyperventilated (though at the time I thought I wasn't). Since changing my dive-style, I've never once even had the slightest bit of light-headedness or any other potential issues meaning that I obviously did something to reduce the risk factor.

Anyhow, knowing that we can reduce some factors and increase others, I thought it may make for an interesting chart to see exactly where and why *most* BO seem to happen and what the odds are against time of experiencing one (i.e. there will be more BOs after a 6 min static, than a 4). It still wouldn't be any sort of guarantee, but it would at least give us a window to look further into. Looking back, usually someone has the answer each time with only a few exceptions. . . there's always a reason. . . we just need more information.

 

[Fondueset]

Well, I didn't necessarily mean a reliable profile, but more of a graph that would indicate potential chances for BO. To be extremely simplistic about it (and I'm spit-balling here for the sake of conversation so don't look into these numbers at all. . .they're just placeholders), a 15s breathhold may have a .01% chance of a BO whereas a max attempt may have something more like a 75% chance of BO or samba with a variable like +5% if you're dehydrated, etc. We know for sure that various things increase your chances of having a BO. . . HV, being dehydrated, being tired, having vigorously exercised prior, high CO2 tolerance, repeated deeper dives, max attempts, etc. and the "compounding interest" of having a combination of those at play simultaneously. Each one contributed to the odds, some more than others and it obviously depends where on the scale you are to start as to how much more prone you may be. For instance, being dehydrated after a day of serial deep dives and then doing a near max attempt is going to be much more dangerous than being well rested, well-hydrated, and just playing around in short dives in the shallows. I guess what I'm trying to get at is that while we can't predict with absolute certainty if you'll have a BO, we do know what contributes to those odds and to a certain extent, the role that they play. I think if we were able to plot with actual evidence all the info from BO, we could at least get a vague percentage figured out as to when you're really rolling the dice vs. merely playing with fire ;-) Again, it wouldn't be a reliable predictor, but it certainly would be better than looking into my crystal ball and hoping I don't BO today.

Incidentally, regarding HV and BO potential--I first took a freediving class back in 2000. The breath-up techniques we were taught turns out to have been classic HV, but without all the rapid breathing. At the time, this wasn't thought to be so though. In fact, we were taught that the "cues" that signaled you were ready to dive were all the signs of HV (light-headedness, tingling in fingers, metallic taste in mouth!). During that year, I came up from about 6 dives being very light-headed, blue-lipped, and twice I saw stars. Fast forward about 8 years and while training on my own at the pool, I came up from what should've been an easy dynamic (50m) and noticed on my way that I had a vague sense of light-headedness. Now, at this time I had been used to surfacing and being light-headed. It was all I had known and wasn't overly concerned about it except this time felt different. I can't really describe why, but it was. By dumb luck, I had chosen a lane near the swim ladder. When I surfaced near it, I shot my arm through and hooked my arm in it. Just as I was doing that, I got tunnel vision, everything went black, and I lost control of my muscles and swung, pivoted on my hooked arm, backward into the pool (a 180 from my position) and banged the backside of my head on the pool edge. Had my arm not been hooked in there, I would've gone under (and yes, like a moron, I was alone). That put me off freediving for a number of years, but when I got back into it, I was determined to make sure to go about it the safest way I can. . . .absent a reliable partner. Over the past 3-4 years, I've scoured the DB forums and stories and with only perhaps 3 exceptions, there always seems to be a likely culprit in all the BO stories I've heard. Though I don't call my experience a BO as I'm not totally sure I lost consciousness and if I did, it would've only been for about 5 seconds, I know it was because I had hyperventilated (though at the time I thought I wasn't). Since changing my dive-style, I've never once even had the slightest bit of light-headedness or any other potential issues meaning that I obviously did something to reduce the risk factor.

Anyhow, knowing that we can reduce some factors and increase others, I thought it may make for an interesting chart to see exactly where and why *most* BO seem to happen and what the odds are against time of experiencing one (i.e. there will be more BOs after a 6 min static, than a 4). It still wouldn't be any sort of guarantee, but it would at least give us a window to look further into. Looking back, usually someone has the answer each time with only a few exceptions. . . there's always a reason. . . we just need more information.

Quite a few BOs occur after unexpected exertion - or a distraction that causes the dive to be prolonged - hence spearos. I've experimented sprinting in the pool and, as others have observed, exertion very easily distracts from the urge to breathe (CO2) - simultaneously burning O2. I've seen one very near and one pretty Bad BO. The near one was during a relatively shallow PB attempt and was definitely the result of the diver being too wound up (not relaxed) and not enough surface time. The other one was a deeper PB by an inexperienced diver and was quite severe. I've never had even a near BO. I come up from every pool training lap capable of immediate conversation. But I've also never hyperventilated to the point of tingling or light-headedness.

The reasons can range of hydration to fatigue to low-sugar, technique, exertion/distraction, barometric pressure, water temp, accidentally breathing boat exhaust (HUGE), nerves, personal problems, low bp (another sub-list of causes) etc. etc. And thats just a start at stuff thats not pathological. I think it's good to quantify everything we can but the bottom line is that you've got to take each dive one at a time and make no assumptions - as well as developing a good ability to feel yourself. Except for competition and training (with a partner) I am not a big fan of establishing expectations for your dives. To my mind coming up light-headed in any unsupervised dive means you've already pushed it too far.

 

[Triton1715]

Quite a few BOs occur after unexpected exertion - or a distraction that causes the dive to be prolonged - hence spearos. I've experimented sprinting in the pool and, as others have observed, exertion very easily distracts from the urge to breathe (CO2) - simultaneously burning O2. I've seen one very near and one pretty Bad BO. The near one was during a relatively shallow PB attempt and was definitely the result of the diver being too wound up (not relaxed) and not enough surface time. The other one was a deeper PB by an inexperienced diver and was quite severe. I've never had even a near BO. I come up from every pool training lap capable of immediate conversation. But I've also never hyperventilated to the point of tingling or light-headedness.

The reasons can range of hydration to fatigue to low-sugar, technique, exertion/distraction, barometric pressure, water temp, accidentally breathing boat exhaust (HUGE), nerves, personal problems, low bp (another sub-list of causes) etc. etc. And thats just a start at stuff thats not pathological. I think it's good to quantify everything we can but the bottom line is that you've got to take each dive one at a time and make no assumptions - as well as developing a good ability to feel yourself. Except for competition and training (with a partner) I am not a big fan of establishing expectations for your dives. To my mind coming up light-headed in any unsupervised dive means you've already pushed it too far.

Thanks for the input Fondueset. I agree 100%. Every dive needs to be taken on its own and I'm certainly not advocating some sort of chart that one can reference to see how long they can safely dive (not that you implied this, but just to be clear). Rather, I think it would be interesting to see the increase in percent of chances of a BO as various factors combine based upon actual BOs. Kind of a pseudo-risk assessment chart. While there are so many variables it can be likened to chaos theory, some obviously bear more weight than others and can generally be the dominant factor in why it occurred rather than a contributing factor. For example, attempting a PB is more likely to result in a BO than the barometric pressure on a given day. Conversely, while barometric pressure may have contributed to a PB blackout, it would be highly unlikely that barometric pressure would, on its own, be responsible for a BO when a diver is otherwise well within their limits. Putting all these factors together and determining their level of import would be a really helpful thing from a generic safety stand-point. . . .kind of a "freediving checklist" that lets you gauge the general level danger, while recognizing that you are always in danger while doing U/W apnea. As a case in point, I had hoped to try out a pool I found today a little ways away, but was out late last night. I know that my level of exhaustion right now puts me at a much greater risk of a BO than if I was well-rested and I'm simply not going today. Being consciously aware of these things (I know being tired is an obvious one, but am thinking more about that more easily forgetable ones like; did I drink enough water today? Have I had a lot of caffeine? Should I dive with a headache or after having taken an ibuprofen for one?, etc.) may help more people consciously stay within their limits on days they're still bound and determined to go out as well as bring those ideas to forefront of their mind when they're contemplating just a few more moments to line up that shot on the fish.

For the record, my light-headedness was clearly due to hypoxia during my early years due to HV and should obviously be avoided at all costs. Since learning that what I had been taught was, in fact, very dangerous about 4-5 years ago or so, I have adopted a focus on relaxation and have not, in the past 4-5 years ever experienced any light-headedness and never surfaced with any sense of being "out of breath" or requiring heavy breathing. I've always been able to immediately converse, etc. . .which incidentally I have you to partially thank for that. The information you've given me the past couple years has been very helpful for me trying to find the right path again after years in the wilderness.

Want to hear something truly scary? Here's an excerpt from the freediving manual I was given back in 2000 when I took my class. (Any inexperienced readers should note this is NOT safe nor should it ever be practiced!)

"At any point in the ventilation or super ventilation cycles, your body may generate signals. These signals should override any preconceived number of cycles, time of cycles, number of ventilations, etc. Signals that our body may give us to know that we are at our peak oxygenation point include:
-Dizziness
-Numbness/tingling in extremities (fingers, lips, toes)
-Iron (metallic) taste in mouth

If these signals are felt, do NOT complete additional ventilation cycles, you are ready. Go to your last breath sequence and initiate your free dive."

Knowing what I've learned that past 4 or 5 years, how absolutely terrifying are these instructions?! As much as I don't want to contemplate it, I can't help but wonder if any previous students have been lost over the last 15 years following this freedive training as all they've been taught is how to start a dive under the most dangerous position they can put themselves in. It was following this stuff that lead to my various light-headed, blue-lipped adventures as well as my pool mishap. They always hit in the last 15-20 ft too. . never thought I was pushing myself and then all of a sudden, I was light-headed again. I hate to think how close I can to a BO, alone numerous times.

 

[HydroApprentice]

Yes, that sounds pretty bad... But on the other hand, I'm curious about how we're gonna look back in a couple of years. Surely, some of our current techniques, or even some of our general world-view might look ridiculous in retrospect. Progress is awesome [emoji4]

 

[xristos]

Triton what you suggest creating sounds more than sensible to me. If only I knew earlier that exhaustion could increase BO chances.

 

[noa]

This is a subject that is so under researched, yet should be an absolute priority in any freedive training and practice.
It baffles me how little is known, and how that is passively the accepted norm through the freediving community.
The day this trend changes is the day our passion can start to open up to a larger audience. In awareness and safety...

 

[xristos]

The problem is,
take for example exhaustion. It is a lot different to someone of top fitness and someone that is sedentary.
1) The way I think we could use this experience is translate it into concrete facts through experimenting one variable each time
2) The way we tell don't hyperventilate in a really BOLD manner, we could add, depending on your fitness level too many dives can result in black-out, even in a dive you are used to.

I think there is correlation also with dehydration, mental factors ( eg. competitiveness with buddy ), previous days diving, change in your diving routine.

 

[Slowmo]

Thank you Triton1715 for starting a great thread.
I have often wondered if you can BO without first having contractions (asuming no hyperventilation)?
I too believe that BO risk should be measured so it can be managed.

 

[Simos]

I've been pondering the issues around blackouts and their seemingly unpredictable nature. Does any know if there is either a database (perhaps from competitions and such) that records the parameters of the divers that have had a BO.

If not, I think that there's a strong case to be made for gathering as much information as possible each time there is one. For example, if the diver was attempting a max of some sort, a BO isn't really unexpected at all. We know they were pushing themselves to edge. It would be more telling to know the details around the truly unpredictable ones.

My current guess is that out of all the BOs that have occurred, if you tossed ones due to max attempts, ones where the diver had packed, any brought on by HV, and any that happened after a day of serial dives, I suspect that there would be a dramatic drop off in the amount of BOs. This may sound like Captain Obvious talking since we all seem to know there's a correlation between these factors and a BO, but it's the ones that remain after these have been weeded out that I would like to know more about. For the past 16 years I've heard how unpredictable BOs seem to be, but with nearly every story, there's usually some clue in it as to what went wrong and it almost always involved one of the aforementioned issues. Still, BOs nonetheless occur even with these taken into account and I would love to know more about the specifics around those events. As near as I can tell, no one has been actively compiling the evidence around these events to string together a coherent pattern beyond the usual caveats of: don't push your limits, don't hyperventilate. Obviously, many of these happen away from events and good means of measuring or collating the data, but it just seems like we out to have a thread where anyone that experiences a blackout (or witnesses one) can post on to gather as much information on it as possible. It isn't magic and while there might be many variables to account for it, I believe that given enough information, it's possible to get to the root of it all.

Of course, I'm writing this during my lunch break and my head often wanders so maybe this has been discussed before and everyone has collectively said, "there's just too many variables. Dive with a competent buddy, stay within your limits, and don't worry about it."

I'll dare say it although I am a beginner: a lot of freediving advice around BOs is meaningless for beginners at least. For example, I never understood what 'diving within your limits' means - I've never BO'd so how do I know my limits (if there was such a thing) and to be honest, if everyone was diving within their limits as they know them they would never improve. Having said this, of course if you are coming up with a samba from a 50m dive and you announce 60m in a comp you are clearly going to BO! Pushing your performances a metre at the time seems to make sense and avoid issues but even that approach will eventually hit a wall!

On the subject you mention, unfortunately there are way too many parameters at least and a lot of them are not even measurable so doubt anything will come out of such an exercise.

My only personal conclusion (which is not rocket science to be honest!) is that the more you train in freediving and the more advanced you are, the more in danger of a BO you are (as your CO2 tolerance increases and you push your limits). If you train long enough and have any interest in improving, I think almost by definition you will BO or come close at least at some point (with or without realising).

It's unfortunate but I think freediving is one of those odd sports where the more advanced you are and the more training you do, the more in risk you are! Similarly you are probably at the safest point when you have just started, have received all the education about diving with a buddy, not hyperventilating etc but haven't built a lot of tolerance yet....

 

[noa]

Good points Simos.

 

[J Campbell]

I agree with Simos to a point - it probably is mostly the experienced divers that get into trouble by continually trying to improve. But there are gung-ho typeA very competitive people that are very good at just about any athletic thing they do. These people are in danger as beginner freedivers because they will by habit be pushing themselves from the very start. You can image a competitive swimmer who feels right at home in the water, has no problem clearing his ears, has dived to 15 feet in the pool many times - maybe been in a few breath hold contests as a child - thinks he's an awesome fish.
So when faced with the new and exciting sport of freediving he will by nature want to prove how awesome he is.
He will feel fine as he descends to 20, 30 40 metrers. - still feeling good as he turns back to the top - then BOOM, blackout.

 

[PJB]

Well, I didn't necessarily mean a reliable profile, but more of a graph that would indicate potential chances for BO. To be extremely simplistic about it (and I'm spit-balling here for the sake of conversation so don't look into these numbers at all. . .they're just placeholders), a 15s breathhold may have a .01% chance of a BO whereas a max attempt may have something more like a 75% chance of BO or samba with a variable like +5% if you're dehydrated, etc. We know for sure that various things increase your chances of having a BO. . . HV, being dehydrated, being tired, having vigorously exercised prior, high CO2 tolerance, repeated deeper dives, max attempts, etc. and the "compounding interest" of having a combination of those at play simultaneously. Each one contributed to the odds, some more than others and it obviously depends where on the scale you are to start as to how much more prone you may be. For instance, being dehydrated after a day of serial deep dives and then doing a near max attempt is going to be much more dangerous than being well rested, well-hydrated, and just playing around in short dives in the shallows. I guess what I'm trying to get at is that while we can't predict with absolute certainty if you'll have a BO, we do know what contributes to those odds and to a certain extent, the role that they play. I think if we were able to plot with actual evidence all the info from BO, we could at least get a vague percentage figured out as to when you're really rolling the dice vs. merely playing with fire ;-) Again, it wouldn't be a reliable predictor, but it certainly would be better than looking into my crystal ball and hoping I don't BO today.

Incidentally, regarding HV and BO potential--I first took a freediving class back in 2000. The breath-up techniques we were taught turns out to have been classic HV, but without all the rapid breathing. At the time, this wasn't thought to be so though. In fact, we were taught that the "cues" that signaled you were ready to dive were all the signs of HV (light-headedness, tingling in fingers, metallic taste in mouth!). During that year, I came up from about 6 dives being very light-headed, blue-lipped, and twice I saw stars. Fast forward about 8 years and while training on my own at the pool, I came up from what should've been an easy dynamic (50m) and noticed on my way that I had a vague sense of light-headedness. Now, at this time I had been used to surfacing and being light-headed. It was all I had known and wasn't overly concerned about it except this time felt different. I can't really describe why, but it was. By dumb luck, I had chosen a lane near the swim ladder. When I surfaced near it, I shot my arm through and hooked my arm in it. Just as I was doing that, I got tunnel vision, everything went black, and I lost control of my muscles and swung, pivoted on my hooked arm, backward into the pool (a 180 from my position) and banged the backside of my head on the pool edge. Had my arm not been hooked in there, I would've gone under (and yes, like a moron, I was alone). That put me off freediving for a number of years, but when I got back into it, I was determined to make sure to go about it the safest way I can. . . .absent a reliable partner. Over the past 3-4 years, I've scoured the DB forums and stories and with only perhaps 3 exceptions, there always seems to be a likely culprit in all the BO stories I've heard. Though I don't call my experience a BO as I'm not totally sure I lost consciousness and if I did, it would've only been for about 5 seconds, I know it was because I had hyperventilated (though at the time I thought I wasn't). Since changing my dive-style, I've never once even had the slightest bit of light-headedness or any other potential issues meaning that I obviously did something to reduce the risk factor.

Anyhow, knowing that we can reduce some factors and increase others, I thought it may make for an interesting chart to see exactly where and why *most* BO seem to happen and what the odds are against time of experiencing one (i.e. there will be more BOs after a 6 min static, than a 4). It still wouldn't be any sort of guarantee, but it would at least give us a window to look further into. Looking back, usually someone has the answer each time with only a few exceptions. . . there's always a reason. . . we just need more information.

Hi Triton,

An interesting subject to pursue. In my own opinion there is unlikely to be any clear or reliable 'marker' to guide us away from BO. Both the history and the underlying science suggest that we still know too little. The links between training, body types, diet, hydration, temperature and mental state appear to be non-linear, which adds to both the mystique and the risk of the sport. It is intensely individual, but also cyclical. One suggestion is to work towards a deeper level of self knowledge under controlled, safe conditions and then 'feel' your way around until you have a better understanding of at which point your body is getting ready to shut down. Dry apnea walking that simulates and actual dive can assist with this over time. But at the end of the day there's no substitute for self analysis and honesty 'on the day' - because it's never the same day twice. Cheers

 

[BatRay]

I think it's an excellent idea. While such a database might not prove that any particular action causes BO, I'm sure it would point out some strong correlations. A sufficiently sophisticated search function could point out all sorts of information that cannot be pinpointed through anecdote.

 

[Triton1715]

I've been away for a while, but am glad to see that the thread at least had some general interest. While it would be a huge pain to undertake tracking down and compiling all the BO data, I'm convinced that nothing will improve in any meaningful way until such action is taken. Everything in the meantime is left to "meh, there's too many variables, so there's no point in trying". . . which I reject. Yes, there are a LOT of variables, but getting them sorted out would at least help paint a picture of which aspects are the biggest culprits of BOs (statically and not anecdotally). Once those are eliminated or at least better understood, focus can then be on the secondary ones and so on. I'm a belt and suspenders guy when it comes to safety and the more information we have, the better decisions we can make.

Thanks all for the input! Safe diving everyone!

 

[HLanger1955]

Good luck for your compilation, Triton. I appreciate the idea, but one question remains : Any good statistics means a good number of "experiments", sambas, BOs, close to BOs, divers of any level pushing to the edge...Tough job, looks like a big research project...From a statistical view point the combination many parameters/few data brings you off the road

 

[Sorandril]

I would like to line up all these variables myself and study them because a lack of oxygen isn’t random.