Fatalities statistics: what kills people the most in scuba diving?

[mdb]

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

In my 1972 NASDS course we practiced "blow and go" on every training dive. The first 150-200+ dives I made we did the same.

It came in handy a time or two.

 

[chillyinCanada]

As I understand it, CESA is still taught and during lessons practiced at least once, however, it is done across the water column rather than from depth to surface. As it was explained to me by instructors from one agency, this due to the belief that for new divers/not yet certified, it is too dangerous to drill in the course. This of course leaves the newly certified at a minimum, filled only with book learning and no real experience should it become necessary to do a CESA.

 

[freewillie]

I came across this thread last night so I'm a little late to the dance.

I find the banter regarding statistics very interesting. It is almost like arguing opposite sides of the same coin. You can utilize statistics to show that a particular incident happens at a certain rate, such as the number/percentage of dive related deaths and divers being out of air. You can't then make the leap that being out of air will lead to a diving death. In other words, if you take the total number of divers who died, tallied up what contributing factors played a role then the stats say 41% of divers were out of air and 50% of divers who died had less than 20 dives. You can't make any more assumptions about how many times an out of air situation actually resulted in death, or that if you have less than 20 dives you have a 50% chance of dying while scuba diving.

Statistically the prevalence is the number of events for a specified time. Take for example lung cancer. The total number of patients who carry a diagnosis of lung cancer for, say, the year 2012 includes not only patients who were newly diagnosed but also includes the patients that have already been diagnosed regardless of time. So, if you were just diagnosed for that time period, or had it for a year, or had it for 10 years you are all included in the prevalence.

The incidence is the number of new cases for the specified time. If the number of divers who died were determined to be LOA or OOA was 41, and the total number of deaths was 100 the incidence of being OOA and deaths is 41%. The actual prevalence can be higher and by statistical variable just about impossible to measure unless we measure every diver who has an OOA situation and even then would be under reported since not every event will be recorded.

From statistical analysis you cannot make assumptions (Ken would call this speculation) between cause and effect. Just because there is a statistical correlation does not conclude cause and effect. Things can happen at the same time but do not necessarily have to be linked to each other. My favorite example is that there is a measurable increase in the month of June and the number of pot holes in the road that are fixed. In the month of June there is also a statistical increase in the number of live births. So, if you fix more pot holes you will cause more babies to be born since both happen at the same time for the same month. One has no relationship to the other except both happen at the same time.

Any further discussions based on personal experience become anecdotal evidence, ie. not based on statistical analysis but based on personal experience of observation. Some may correlate to published statistics, some may conflict with published statistics. But, be very careful about trying to make sense of what you think should be true.

Take for example hormone replacement therapy in women. For years it was argued that taking hormone replacent therapy was beneficial for women but that was based on correlation not studies. Women had lower rates of heart disease than men, women have more estrogen than men, estrogen should lower heart disease since women taking hormones have higher good cholesterol and less bad cholesterol so that must be the reason why estrogen is good for preventing heart disease. But, in a large randomized placebo controlled study there was a statistically significant increase in the rate of heart disease. Oops, not what the researchers expected.

From the published reports, if you run out of air or get low on air underwater 41% it lead to a fatalitiy. It does not imply or infer what lead up to this running out of air, it does not indicate how the diver responded to the situation, it simply measures that for the total number of divers who died 41% of the time they ran out of air. If nothing else it means that running out of air is bad.

From the data reported, it also means that of all the diver deaths, almost half had very few dives, less than 20. That means that like any other activity your greatest risk for adverse event or outcome is when you are still a beginner. Driving is another activity that comes to mind based on the number of new drivers who are involved in accidents. It becomes a contributing factor but to what extend is, well, speculation.

The purpose of discussion is just that - to discuss what triggers are involved in accidents, and to what extent can those risks be modified and decreased. Don't run out of air, and if you are a novice diver dive with more experienced divers. A recent post and article in DAN recounts the unfortunate death of a 26 yo diver on her first boat dive, first dive ever after certification, being paired with a novice diver as well and the result was tragic.

 

[Ken Kurtis]

From statistical analysis you cannot make assumptions (Ken would call this speculation) between cause and effect.

You're speculating that I'd call it speculation . . .

 

[boulderjohn]

As I understand it, CESA is still taught and during lessons practiced at least once, however, it is done across the water column rather than from depth to surface. As it was explained to me by instructors from one agency, this due to the belief that for new divers/not yet certified, it is too dangerous to drill in the course. This of course leaves the newly certified at a minimum, filled only with book learning and no real experience should it become necessary to do a CESA.

Several agencies do not teach CESA at all, arguing that a diver who is not near enough to a buddy's air source should have already begun the lost buddy procedure and headed for the surface

.Only one agency that I know of only teaches it horizontally in the pool. As I understand it, they are afraid that if students see an instructor doing multiple ascents with students, they will think going up and down like that is the proper way to dive.

The agencies that certify probably 90% of divers still do it both horizontally in the pool and vertically in the open water. The reason they do it horizontally in the pool is because most pools are too shallow to do it any other way.

 

[Hatul]

...

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

That's a good model for escaping from a submarine, and if done properly may save you from drowning and lung barotrauma, but I still think the guy who swims around at 75-120 ft and runs out of air likely has nitrogen loading close to deco, and a rapid ascent will probably result in DCS.

 

[John C. Ratliff]

That's a good model for escaping from a submarine, and if done properly may save you from drowning and lung barotrauma, but I still think the guy who swims around at 75-120 ft and runs out of air likely has nitrogen loading close to deco, and a rapid ascent will probably result in DCS.

Actually, the model for escaping from a submarine is a Buoyant Ascent, not a Controlled Emergency Swimming Ascent (CESA). We did that in the U.S. Navy School for Underwater Swimmers. We were taken down to a set depth (around 30 feet as I remember) in a bubble, made to duck out and hold onto the edge while an instructor is scuba inflated our vest, blow out all our air, and only then let go of the edge for a quick buoyant ascent to the surface. That is where the "blow and go" statement should have been applied.

Looking at the new U.S. Navy No-Decompression Limits and Repetitive Group Designators for No-Decompression Air Dives, Table 9-7 (page 9-62), the "No-Stop Limit" for 70 feet is 48 minutes. For 120 feet the "No-Stop Limit" is 15 minutes (time leaving the surface to time leaving the bottom). If the dives are planned correctly for no-decompression diving, I see no reason that these need be exceeded on a sport dive.

Now, if the guy did have a loading which led to decompression sickness, would it be preferable for that person to stay at depth and die rather than surface and seek treatment? That's the kind of decision I was thinking about. One is what we call a rather "immediate emergency" while the other is a "delayed emergence." Both are emergencies, but the consequences of staying (dying) verses not staying (living with possible decompression sickness and seeking medical attention) are somewhat different.

Again, this assumes many poor decisions which would put the individual at risk, but it has happened.

SeaRat

 

[freewillie]

You're speculating that I'd call it speculation . . .

I would speculate an educated guess.

 

[FlyingSquid]

You can't then make the leap that being out of air will lead to a diving death. In other words, if you take the total number of divers who died, tallied up what contributing factors played a role then the stats say 41% of divers were out of air and 50% of divers who died had less than 20 dives. You can't make any more assumptions about how many times an out of air situation actually resulted in death, or that if you have less than 20 dives you have a 50% chance of dying while scuba diving.

Exactly. That's a common mistake, and I commented extensively about that in previous posts in this thread.

More: if the numbers we have are right, I was forced to conclude that either OOA cases are very rare but fatal when they happen or very common but most people solve it. (Or something in between) The fact is, 144 OOA deaths in 200 million dives is a less than 1 in a million chance of OOA-death in a dive.

No matter how strongly you may feel about OOA, if the numbers we have are right, then equipment and people are doing their job pretty well in staying alive.

 

[freewillie]

Well, diving deaths in general are uncommon. Not going back over in detail but I seem to recall tha the number is 4.5 deaths per million. Not exactly but something like that. So overall divers and equipment makes the fatalities uncommon in general.

The prevalence of OOA situation is unknown, we don't know since we aren't really keeping track of the exact number of times it is happening. We can't necessarily say that it happens but most people solve the problem. What we can say is of all the total diving deaths 41% ran out of air. Bad thing happen if you do so one of the best ways not to be a statistic is to monitor air carefully and don't get into an OOA situation.