Scubagolf
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Fatalities statistics: what kills people the most in scuba diving?
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Hatul
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Swimming horizontally under water is not the same as a vertical ascent, especially with a good tissue load of nitrogen as would likely be the case when running out of air in a deep dive. I think there is a high risk of injury running out of air on a deep dive.Now, I also agree that we should avoid OOA situations. But my feeling is that with sufficient watersmanship (or waterswomanship) OOA by itself should not induce panic. It can easily be coped with in normal sport diving environments (defined is less that 120 feet depth, with no "overhead" environments, including no decompression obligations).
SeaRat
---------- Post added February 17th, 2013 at 07:20 PM ----------
I am curious as to why this thread was moved from the Accidents and Incidents forum to the Basic Scuba forum?
John
I was very careful to define this as "sport diving" which by definition does not have high tissue loads of nitrogen. Sport diving to me is no-decompression diving, and no "overhead environment" (ice, cave, wreck) diving. I actually said that in the quote, but I will repeat it here too. So you are right in that respect, this does not apply to deep diving.
I'll explain later the reasons behind the way I was able to swim 75 feet after not having air today.
SeaRat
---------- Post added February 17th, 2013 at 11:58 PM ----------
Rich, I have worked in professional safety for over 35 years now, and the DAN accident sequence is unique to DAN. That is the trigger (Initiating root cause), harmful action (root cause as an effect of the trigger), disabling injury (causes death or makes drowning likely), and cause of death (COD) specified by the coroner. This is probable unique because DAN was limited by the types of information available to them about the scuba fatalities.
There are other models that I have used over the years. Dan Peterson talks about overloads, mismatches and traps which cause errors. I have used fault tree analysis to isolate the factors which come together in an accident. And I have used David DeJoy's Human Factors Model of Accident Causation. That model looks like this:
Note that all these factors cause a human error which leads to the accident, injury/fatality.
For diving, I would like to concentrate on the decision-making box. I am trying to promote decision-making that gives the diver options. Many times, factors come together that overwhelm the person trying to make the decision. By having more options, there are better choice selections available to the diver. What I'm trying to get away from is what I feel is a pre-disposing factor--saying that if you run out of air, you will die. As I have shown, that doesn't have to be the case. If we pre-dispose divers to think that there is no alternative but the buddy, an alternative air source, and they do not have those available, panic like you described is more likely.I'll write about that later.
SeaRat
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Rich Keller
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The reason I asked about the type of dives involved and I should have added to that the level of training of the victim in these accidents was to determine if the decision to get in the water at all was the first and perhaps biggest mistake.
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nothing pointed towards bad instruction?
dumpsterDiver
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I was very careful to define this as "sport diving" which by definition does not have high tissue loads of nitrogen. Sport diving to me is no-decompression diving, and no "overhead environment" (ice, cave, wreck) diving. I actually said that in the quote, but I will repeat it here too. So you are right in that respect, this does not apply to deep diving.
I'll explain later the reasons behind the way I was able to swim 75 feet after not having air today.
SeaRat
---------- Post added February 17th, 2013 at 11:58 PM ----------
Rich, I have worked in professional safety for over 35 years now, and the DAN accident sequence is unique to DAN. That is the trigger (Initiating root cause), harmful action (root cause as an effect of the trigger), disabling injury (causes death or makes drowning likely), and cause of death (COD) specified by the coroner. This is probable unique because DAN was limited by the types of information available to them about the scuba fatalities.
There are other models that I have used over the years. Dan Peterson talks about overloads, mismatches and traps which cause errors. I have used fault tree analysis to isolate the factors which come together in an accident. And I have used David DeJoy's Human Factors Model of Accident Causation. That model looks like this:
Note that all these factors cause a human error which leads to the accident, injury/fatality.
For diving, I would like to concentrate on the decision-making box. I am trying to promote decision-making that gives the diver options. Many times, factors come together that overwhelm the person trying to make the decision. By having more options, there are better choice selections available to the diver. What I'm trying to get away from is what I feel is a pre-disposing factor--saying that if you run out of air, you will die. As I have shown, that doesn't have to be the case. If we pre-dispose divers to think that there is no alternative but the buddy, an alternative air source, and they do not have those available, panic like you described is more likely.I'll write about that later.
SeaRat
I have been thinking about your position for a while. Although I agree with the concept that if people are competant and fit, that they should be able to swim up in a "low on air" emergency. However,,, a big HOWEVER dive training now is so short, that it is entirely impractical to try to develop the skills and instil the level of confidence that you (and I) think is essential for safe diving. In the current dive training environment... teaching people to NOT run out of air is probably a much better use of time, then spending a few moments telling them they CAN swim to the surface.
If dive training prgrams really wanted to instill this level of confidence and proficiency, they would require some freediving ability.. even to a depth of 25 or 30 feet... but that is past the capabilities of probably many scuba instructors....
I know when I taught my young sons to scuba dive, they were required to be able to freedive. But it just ain't gonna happen in today's training environment.
[video=youtube;IyLYmEMoKE4]http://www.youtube.com/watch?v=IyLYmEMoKE4&feature=share&list=UU1utDku8vJ RJYgBZImLyLJQ[/video]
Ken Kurtis
Contributor
Although some of it may have been indicated in the narrative of the case, in general terms, no, there's no breakdown. Also realize that it's such a statistically small sample size (one of the problems with trying to over-analyze any of this type of data) that as you break it down into smaller and smaller bites, your margin of error increases appreciably to the point of making the conclusion you draw potentially useless (and wrong).
The example I like to use is our L.A. County stats. In 1998 we had 4 fatalities. In 1999, we had 1. In 2000, we had 4. Was diving in LA County four times LESS dangerous in 1999 than it was in 1998 and then four times MORE dangerous in 2000 than it wass in 1999? No. It's simply a skew in the numbers which are so small to begin with that a few extra here or a few fewer there skews the numbers tremendously and it's easy to draw a false conclusion when you just look at those numbers and don't take a few steps back to look at the bigger picture.
---------- Post added February 18th, 2013 at 11:24 AM ----------
Not to split hairs here John, but I don't think "high" needs to mean "deco." You can be at 99% of the predicted nitrogen load and still be within sport diving (no-deco) limits. And there are plenty of instances of divers who either do a rapid ascent to change the equation and make a no-deco dive into a missed-deco dive, or instances where - due to body physiology - the tables or computers (theoretical mathematical models) don't apply to that particular person. So while that table/computer may be saying "not bent," the body is saying "Get me to a chamber!!!"
sorry for the late response, I was out diving all weekend
My point earlier regarding "if you are out of air, you can't breathe and you die" was meant to be literal and was not intended to mean "if you empty your tank, you can't breathe and you die"
If you are under a gill net and your instructor turns off your air, but you are able to buddy breathe with someone else, you are not out of air. Similarly, if you are on a reef and you empty your tank, but you can get to your buddy's octopus, then again, you are not really out of air, or if you can get to the surface by way of a CESA, then again you are not out of air.
Dumpsterdiver,
Concerning the instructors, I hope it is not outside their capability to free dive to 35 feet; that would be a rather harsh indictment of today's instructors. So I hope you are wrong on this count. My sons learned snorkeling from me, and were swim team members (as was I way, way back). They did some scuba diving with me, but have no formal coursework in scuba and neither elected to pursue it in adulthood. But, they were competent in the water, and that is the main thing. My older son went through team and high school swimming and did well, but did not break any records. My younger son was a Junior Nationals Swimmer, and could have competed on a national level if he had better coaching (we were in a rural community, with limited resources). We discouraged both from pursuing sports as a vocation; my older son has a Masters degree is Mechanical Engineering, while my younger has his PhD in Robotics. So both have done well, even if they did not pursue my favorite hobby--scuba diving.
Your point on the length of a Basic Diving Course is well taken; I have been away for so long that I really don't know about that now. Maybe Ken can add some information here. I do know that at Oregon State University in the 1970s, Midge Cramer's NAUI Basic Scuba Course was a 3 credit hour, one term long (3 month) course. I went along with him to Hawaii for some of his checkout dives when he was able to do that. Given that limitation, I would agree about the teaching method, but then looking at the DeJoy Model above, that becomes a pre-disposing factor toward not being able to cope when stuff goes badly. It also becomes a group norm, and saying that you don't have options is like saying you cannot cope with this situation.
---------- Post added February 18th, 2013 at 01:43 PM ----------
Ken, what I was speaking to was a sport diver as I knew him/her. In the 1970s through 1980s, we used to teach people not to get close to the "knife edge" of the no-decompression tables. Now, apparently people are becoming dependent upon their dive computers to tell them where they are concerning nitrogen loading. So I agree that in this age, it may be easy to get into a decompression situation unknowingly. I also know from reading some of the threads that there is concern about non-consistency in the alarms that these computers put out. I was in the pool a few weeks ago with two other divers, who were testing their gear for a subsequent vacation. There was a LP leak in a BC secondary regulator that they needed to attend to. But the computer, apparently sensing this leak, was beeping about air consumption that was "too fast" according to the divers. The idea with these computers is that they have now become the "go to" device rather than a backup to dive planning. In doing so, we may be sacrificing the ability to surface directly--without decompression.
I have a book in my diving library titled Medical Aspects of Sport Diving, by Christopher W. Dueker (A.S. Barnes and Co., Inc., 1970). In it he has a whole chapter an "Respiration." This is such an important topic that it does not get its due in diving instruction, in my opinion. I would urge any diver interested in increasing his/her knowledge on diving medicine to get a copy--it still has a lot of valuable information, although a few concepts have been disproven over the ensuing time (such as the condition of "lung squeeze" for breath-hold divers). But the illustration I have copied below from page 81 of that book provides the explanation of why I was able to swim from my ditched scuba to the "surface" 75 feet away after having exhaled all my breath (again, it was a push, but I was able to do it). Here is what Dr. Dueker stated in his book about our different static lung volumes:
The important point is that on a normal exhalation for most divers, there is still an expiratory reserve volume in the lungs. That is why my second ditching and "surfacing" when smoothly; I still had expiratory reserve capacity (ERV) in my lungs and that was sufficient to oxygenate my blood for the 75 foot swim. My third attempt was a "push" because I was relying upon my reserve volume (RV) to oxygenate my blood.
Now, according to Dr. Duerker, "Residual volume is about 20 percent of total lung capacity. Most people's vital capacity is 3-5 liters; mine is more--6 liters. Using mine, that means that 80% of my total lung capacity is 6 liters. Doing the calculation,
0.80x = 6 liters,
x = 6/0.80 liters,
x = 7.5 liters total lung capacity
If I'm at my residual volume (RV), that's 7.5 liters - 6 liters = 1.5 liters of air still available in my lungs. That was enough (barely) to swim the 75 feet to my "surface."
But we can play around with this more, and I do mean "play." When I'm in the water, I'm playing.
I was at 18 feet depth. In fresh water, 2 atmospheres absolute pressure is at 34 feet. That means that from 34 feet, a volume of air going to the surface will expand to twice its volume. 18 feet divided by 34 feet equals 0.53. So if I divide my 1.5 liters by 0.53, I get 2.83 liters of air available in my lungs for my surfacing from 18 feet depth. This is why, even with having exhaled to my residual volume at 18 feet, once I started climbing "up" toward the real surface, I was able to exhale.
Now, lets take this one step further. I was simulating an ascent from 75 feet depth, as I swam 75 feet horizontally to my "surface" in the pool. But what if it had been a real 75 feet depth in sea water. That's 33 feet per atmosphere. 75 feet divided by 33 per atmosphere equals 2.27 atmospheres. But we start with one atmosphere at the surface, so we must add "1" to that figure, or 3.27 atmospheres. So the residual volume of air in my lungs will expand 3.27x their starting volume as I ascend from a depth of 75 feet.
Now, lets do some calculations again. If I start out with only my residual volume of 1.5 liters, and multiply that by 3.27, I get 4.91 liters of air, which is not yet at my total lung volume of 7.5 liters. But because there is expansion, I would still exhale during ascent. If I started with my expiratory reserve volume of approximately the same amount as my residual volume (ERV + RV = 1.5 liters + 1.5 liters = 3 liters), and multiplied that times 3.27, I get 9.81 liters of air, which is well over my total lung capacity (TLC).
This emphasizes the need for exhaling on an emergency swimming ascent. But it also shows that the emergency swimming ascent is a means of escaping an Out-of-Air situation from depth. It is de-emphasized today in instruction because of the lack of skill of today's divers, and apparently the lack of time today's instructors have to actively teach students.
SeaRat
John C. Ratliff, CSP, CIH, MSPH
The important point is that on a normal exhalation for most divers, there is still an expiratory reserve volume in the lungs. That is why my second ditching and "surfacing" when smoothly; I still had expiratory reserve capacity (ERV) in my lungs and that was sufficient to oxygenate my blood for the 75 foot swim. My third attempt was a "push" because I was relying upon my reserve volume (RV) to oxygenate my blood.
Now, according to Dr. Duerker, "Residual volume is about 20 percent of total lung capacity. Most people's vital capacity is 3-5 liters; mine is more--6 liters. Using mine, that means that 80% of my total lung capacity is 6 liters. Doing the calculation,
0.80x = 6 liters,
x = 6/0.80 liters,
x = 7.5 liters total lung capacity
If I'm at my residual volume (RV), that's 7.5 liters - 6 liters = 1.5 liters of air still available in my lungs. That was enough (barely) to swim the 75 feet to my "surface."
But we can play around with this more, and I do mean "play." When I'm in the water, I'm playing.
I was at 18 feet depth. In fresh water, 2 atmospheres absolute pressure is at 34 feet. That means that from 34 feet, a volume of air going to the surface will expand to twice its volume. 18 feet divided by 34 feet equals 0.53. So if I divide my 1.5 liters by 0.53, I get 2.83 liters of air available in my lungs for my surfacing from 18 feet depth. This is why, even with having exhaled to my residual volume at 18 feet, once I started climbing "up" toward the real surface, I was able to exhale.Now, lets take this one step further. I was simulating an ascent from 75 feet depth, as I swam 75 feet horizontally to my "surface" in the pool. But what if it had been a real 75 feet depth in sea water. That's 33 feet per atmosphere. 75 feet divided by 33 per atmosphere equals 2.27 atmospheres. But we start with one atmosphere at the surface, so we must add "1" to that figure, or 3.27 atmospheres. So the residual volume of air in my lungs will expand 3.27x their starting volume as I ascend from a depth of 75 feet.
Now, lets do some calculations again. If I start out with only my residual volume of 1.5 liters, and multiply that by 3.27, I get 4.91 liters of air, which is not yet at my total lung volume of 7.5 liters. But because there is expansion, I would still exhale during ascent. If I started with my expiratory reserve volume of approximately the same amount as my residual volume (ERV + RV = 1.5 liters + 1.5 liters = 3 liters), and multiplied that times 3.27, I get 9.81 liters of air, which is well over my total lung capacity (TLC).
This emphasizes the need for exhaling on an emergency swimming ascent. But it also shows that the emergency swimming ascent is a means of escaping an Out-of-Air situation from depth. It is de-emphasized today in instruction because of the lack of skill of today's divers, and apparently the lack of time today's instructors have to actively teach students.
SeaRat
John C. Ratliff, CSP, CIH, MSPH
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