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Yet another SWBO thread

Thread Status: Hello , There was no answer in this thread for more than 60 days.
It can take a long time to get an up-to-date response or contact with relevant users.


New Member
Feb 1, 2005
Okay, sorry to do this, but I've gone through all the blackout threads I could find and haven't seen the answers I'm looking for.

Essentially, I'm trying to understand where the risk really begins. I think I'm familiar with the various contributing factors (hyperventilation, depth, duration, exertion at depth, etc.) but I guess what I'm really trying to find out is what kind of dive profiles and pre-dive preparation result in "very low risk" dives vs. "higher risk" dives. For instance, one can assume that a 15 second dive to 10 feet with no hyperventilation carries with it a near zero possiblity of SWBO, while hyperventilating for 5 minutes and then pushing down 30 feet lower than you've ever been to free a stuck anchor carries with it an exceptionally high risk.

So I'd like to hear opinions on the kind of dive profiles and pre-dive prep that would seem to be relatively "safe", and I'd be interested in hearing personal anecdotes about any SWBO that occured during what would seem to be very mild profiles. (I went through the "Have you experienced SWBO" poll thread with great interest, but it seemed as though most -- if not all -- of the incidents involved exceptional exposures.)

FWIW, I gave up diving about 10 years ago and am now thinking about starting again. While I was aware of SWBO back then, it seemed like somebody else's problem. My dives were limited to 1:30 and about 60 feet; it never occured to me that I might be taking any sort of risk, at least as far as SWBO went.

I've never experienced any sort of loss of conciousness during diving or training (not counting the 4:45 static dry that ended when the doorbell rang and I jumped out of bed to answer it) but reading all that's now available on the internet makes it seem as though blackout is almost universal among freedivers. I'm awfully pleased with being alive these days, and don't intend to take any serious risks for what is, to me, a recreational activity. All this talk of SWBO is the one thing that's really keeping me out of the water right now, and I really need to asses the risk to the "recreational" free diver.

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Hi Noel, welcome to DB.

You will find answers to a lot of things here, but this is a hard one. We really don't have a good understanding of what exactly what kicks off a given BO. It seems to be extremely individual and circumstance dependent. I posted the same question a while back and was a little frustrated not to find a simple answer. The best advice is dive with a well trained buddy. BO is a strange thing, with a good buddy, its no problem (almost); otherwise its real easy to end up dead.

Here is my experiance and 2 cents worth. There will be lots of disagreement.

As a young diver, I samba'ed several times until I figured out that hyperventaltion was a bad idea. After that I spent 30+ years banging around spearing in less than 50 ft with little thought of safety and no problems, only saw one BO and he was grossly exceeding his limits. In that period, I stayed down way to long way too many times. Since discovering DB two years ago, I'm diving more than twice as deep and my average dive has almost doubled, but I don't think my "max" dive has increased very much. In my opinion, what I used to do wasn't very likely to result in a BO. That isn't true today and I have gotten pretty serious about having a trained buddy in my face at the end of every dive.
One of my buddies BOed last year after surfacing from a 120 ft dive. He is a 2 minute diver and used to deep stuff, but had never dove in coral and got too interested in what was going on around him. I was in his face and it was spooky but worked out just fine. There is a good thread on this in freediving stories. Contributing factors: 1, total dive time too long, 2, repetitive dives with too short surface interval, and 3, (I think), he didn't exhale in the last 10 ft. Other things that seem to contribute to BO's in general are dehydration, being tired, sambas or BO's earlier in the day, and almost anything else that puts you off your peak.

Sorry I can't be more specific, but thats just how it is.

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I appreciate the reply, Connor, and thanks for the welcome.

One of the reasons I dropped out of diving is that I couldn't find anyone of similar skills and motivations to dive with. I never was very interested in spearfishing and -- at the time, anyway -- the only people I could find in Southern California who were freediving were doing it solely to catch fish. Trying to talk one of them into watching me float up and down in the water column all day was less than rewarding. I don't know if that situation is much different these days, but I assume I will need to do at least some of my diving alone.

Now, back in the day I was cutting those 90 second, 40-60 foot dives without concern. When I wanted to push, or when I did pool training, I would make sure I had a competent buddy, but as I said, at the time it seemed to me that SWBO was somebody else's problem.

I suppose that if nothing else I would like to able to some kind of ocean diving alone, even if that means 60 seconds with a 30' max depth -- or even less -- but now I'm wondering if even that profile leaves a diver susceptible to SWBO.

Again, thanks for any replies.

"I started serious freediving about five years ago and noticed that we were losing divers. It must have been a dream world that I dove in for the first fifty years 'cause we only lost a few."

That's an interesting sentence to me. What was the difference between the first fifty(!) years and the last five? I assume "serious" freediving means exceptional exposures...


< edit > No, I haven't lost my mind. :wave Somebody is playing "Incredible dissappearing post".
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I think part of this is the fact that we are more aware of the BO and deaths now due to the communication amongst freedivers on internet forums like this.

I think I can come up with some guidelines.

First of all, among my friends and I, we find that our recreational limit is half or less of our maximum depth. For example, take a diver who has reached 150 feet on a line, with a buddy, and felt he was near his limit. As a basic rule, that same diver will have a ULTIMATE safe limit of 75 feet on a 'fun' dive. That would only be in EXTREMELY IDEAL conditions and usually his safe limit would be much less than that. My point is that if you are ever diving to more than half of your max, without a descent line & buddy, then you are risking death.

However, in my own case, the one time I ever suffered a samba on a 'fun' dive was a dive to 23m for 1'30", when I had previously done 5'02" at 20m and 3'16" at 88m in supervised conditions. My point is that on the 23m/1'30", I was at about 1/4 of my max depth, at less than 1/3rd of my max dive time. The problem was I took too short of a recovery since my previous dive, and I couldn't feel satisfied. I also had a thick suit and heavy weight belt.

From that experience, I have found a simple, but labour intensive, method of checking your risk factor. That method is to do moderate static breath-holds on the surface. If I would need to do a dive closer to my safe limit, and I was wondering if I was drained etc., I would take one breath through my snorkel and hold until I felt the first stimulus to breathe (mouth still on the snorkel!). Then, I would wait a little longer (20 seconds or so), exhale, take two or three breaths, and then hold gain until the first stimulus to breathe. For me, I know when that stimulus should come, if I am rested, recovered and in the zone. If the stimulus comes extra early (or extra late), then it is not safe to do a dive. The test must be done several times to wipe out the effect of any excessive breathing you have done after recovering from your dive.

Further, diving with a heavy weight belt, in a configuration where you sink most of the descent and do all the work on the way up, vastly increases your risk--it was another contributing factor in my 23m/1'30" samba.

With experience, you get to know your own body to the extent that you can reduce your own risk factors, along with common sense like the above suggestions. It is my personal belief that with slow, gradual experimentation, along with occasional 'max effort' dives with supervision, one can learn one's own body to the point where moderate recreational dives are far safer than sports such as skiing.

Many people criticize those who push their limits in controlled, safe conditions. But, it is my belief that the only way to learn your own signals & feelings is by pushing it under safe conditions. The highest risk dives I ever did were BEFORE I had ever done any 'max' effort dives under supervision, and they were before I had ever had a blackout. Once I had done max effort dives under safe conditions, I slowly learned to know my body far better than I did before.

However, NO internal signals or feelings can ever act as a foolproof guide DURING THE DIVE.

For example, in my case, I always pack before starting my dive. This increases the safety for me in a strange way. If I am dehydrated, or I have low blood pressure, or if I am very hot, or if I breathed too much before hand, then I will get light headed during the packing -- A SIGN THAT I SHOULDN'T MAKE THE DIVE.

For example, my first ever blackout was the worst of my diving career. I was diving with a buddy, and I was incredibly hot and dehydrated. I tried to pack my lungs, and I did, getting very light headed. I started the dive and actually blacked out a couple of seconds into the tuck dive, from the packing effect. I woke up underwater at 8 feet of depth uncertain of where I was--it was murky, so I assumed I just lost the line. I went back up, told my buddy I lost the line, and then breathed AGAIN for 3 minutes (even though I hadn't accumulated any CO2 from the 10 second dive). Then I tried packing and felt the light headedness coming, so I stopped packing and dove without any packing. I went 8m farther than my pb and blacked out badly at around 2m on the ascent. At the time I had no clue about the 'signal' of getting light headed during the packing, etc.... So, if you look at that dive, here was what went wrong:
- Extremely dehydrated
- Way too hot
- Ignored signal of light-headedness during packing
- Dove WITHOUT ANY PACKING, meaning 3L of less air in my case
- Tried to break my pb by 8m (way too much), a pb which was set WITH PACKING
- Used 3-4lbs MORE weight on my belt than I had used on the pb dive
- Ended up breathing far too much, due to the initial blackout from packing, then breathing up from the beginning again
Don't despair on not finding any buddies ever. Fill your location in your profile and post on the 'find a buddy' forum. Try also using the 'search' option on your location and/or posting a thread that might capture some lurker's eye.

Regarding keeping your limits while diving alone... I can only say that I'm guessing when I (very rarely nowdays) do so. That's why I don't like it.
I try to have long enough intervals YET try to take more CO2 down with me as a limiting factor (no purge breathing of anykind!). I don't pack for diving in anycase.

Packing might be a problem I think. It widens the range of one's blood pressure and lung volume change, so I think it's more plausible that something unexpected might happen. On the other hand, if you're used to dive with packing you will have different feelings without and might misread them.
No easy solution to diving without a buddy, I think it's gumbling. All the rest is just reducing the chances of something bad happening.
Interestingly enough, this thread and its ideas are very useful. By that I mean that many divers who have a buddy have no clue about their own bodies and signals, just relying upon the buddy to 'bail them out,' when in fact, during a 'fun' diving situation, even if a problem happens there's a good chance you're buddy may not see you/find you/ etc...

So, here in Vancouver we take a different approach---every FUN dive is approached as if it were a dive alone--even if there is a buddy. Don't expect your buddy to bail you out (unless you are diving on a line in controlled conditions etc..)
Erics post on recreational limits is very interesting and, I think, has some general applicability. Without planning it as such, I have settled into a very similar pattern for line diving vs diving without a line.

Thanks for the tip on short statics as a test, I'll try that.

To give some details on my (limited) experiance, we dive in very clear warm water. My line diving pb is 120 ft and I don't expect any problem with 140 this summer. We dive ledges in 75-90 (sight seeing) without a line, but seldom go all the way to the bottom. When diving like that, you can see your buddy at all times and we generally meet each other at 20 or 30 feet, much like a line dive. It works out slightly more agressive than Erics guidelines, but pretty close. When spearing in 30-50 ft, we stay in visual contact nearly all the time, don't meet each other under the surface, but are close and watchful at the surface until the diver has taken several breaths. Within that depth range, the deeper, the more careful we are. I don't think about time on a dive, my CO2 tolerance is lousy and I'd just as soon keep it that way; desire to breath has always been a good signal for me. When line diving deep (for me) it kicks in real early, partial preasure effects I think.

Don't despair on a buddy, pure freediving is getting more and more popular.

"By that I mean that many divers who have a buddy have no clue about their own bodies and signals, just relying upon the buddy to 'bail them out,' when in fact, during a 'fun' diving situation, even if a problem happens there's a good chance you're buddy may not see you/find you/ etc..."

You know, I did most of my SCUBA diving alone as well, primarily because the "buddy system" ended up being such a joke. It seemed as though buddies all fell into one of two groups: the experienced old mossback who is just paying lip service to the buddy system (the "same ocean same day" dive), or the diver who really isn't competent and is depending upon somebody else for his safety.

I never minded diving with the first type but didn't kid myself that this was "buddy" diving. Never saw the point in diving with the second guy; I'm not a SCUBA instructor. The point with all this is that it seemed to me a lot of my freediving "buddies" fell into one of those categories too. I'd either be in the water with an old spearo who really didn't want company, or a neophyte who was probably more likely to need help than give it.

I'd love to find a buddy of similar skills and goals, serious about diving safely, who lives somewhere nearby and has a similar schedule. I'll take the advice of Michael and Connor about filling in my profile (once I figure out how) and taking another look through the "find a buddy" thread, but I still have to admit to a certain amount of pessimism. It's hard to imagine finding the "perfect" diving partner.
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I guess that brings up another question or two:how often do you (anyone) typically dive, and how does the availability (or lack) of a buddy affect that? Do many of you still go for "fun" dives by yourself?

And how do you manage pool training? Do you all have a competent diving buddy alongside? Enlist the aid of wife/girlfriend/family member? (There's no way in hell I could get my fiance to supervise me. Explaining blackout, samba, and other risks to her would absolutely ensure that I would never be allowed near open water again!) Or do you simply ask the lifeguard to keep an eye on you and hope for the best?
Craig Molle was a Canadian freediver who had spoken with the lifeguard at his pool, and told the lifeguard what he was doing and told the lifeguard to keep an eye on him. Sadly, he eventually blacked out, sank to the bottom and died in the pool. So I'd say trying to 'work with the lifeguard' is a no-win situation. For pool training a buddy is a must. For the ocean, I will go on occasional 'fun' dives if I really 'need' the dive and there isn't anyone available. As a result, pool training is actually less accessible for me, since I can't always find someone to go with.
I think that the same priniciple of limiting "fun" dives in the open water to 50% of one's PB should also obtain in pool training, so that doing a dynamic that is 50% of one's PB should be safe (considering proper rest, hydration, breath-up) even without a safety. However, I tend to push a bit further than 50% of PB in the pool, on the theory that the pool is a more a controlled environment than the ocean, less chance for something going wrong. I admit this may be a misjudgement though, so I will pose the question: has anyone samba'd or BOd (or known anyone who has) on a dynamic effort of 60-70% of max?
diving with a heavy weight belt, in a configuration where you sink most of the descent and do all the work on the way up, vastly increases your risk

Why is this, Eric? Does it relate directly to the efficiency of the dive, or is it simply because diving like this makes it too easy to stay on the bottom for too long, in the case of spearos and rec. freedivers?

I ask because I gathered from another of your posts (can't remember where or when) that you believed diving with this configuration was more efficient, for reasons I found compelling - because it makes better use of anaerobic metabolism as the blood flow to one's legs is greatly reduced by the second stage of the dive where the ascent is made, as opposed to a diver working hard aerobically from the start prior to vascoconstriction(sp?) and burning oxygen needed by the core. Perhaps this is only the case for deeper dives, where the dive reflex is a lot more marked, rather than for common recreational depths?

It tends to be how I dive, particularly for supervised CW, and I'd be more than a little concerned if this was putting me at risk of a blackout...
Some comments:
- Doing pool 'training' at 50% of max isn't going to have any effect, unless your just training technique work. To actually get physiological adaptations you'll need to be up around 75-80% of max at least.

- Concerning diving heavy, I still think it is an efficient way of diving, but it presents risks in uncontrolled environments. The reason is that if you have a bad 'breath' to start the dive, and you are buoyant, you'll feel the burn before you even get down to the bottom. If you have a bad 'breath' and are diving heavy, you'll sink to the bottom and be able to remain there (quite still) for a long time before you realize you had a bad breath. Now, when the urge to breathe hits you, you have a huge task ahead of you to get back up.

To think of it in even simpler terms, it is highly unlikely that you will black out without ever feeling ANY urge to breathe. Once the urge to breathe hits you, you may not have long before the blackout hits you. So, in the worst case, when that urge to breathe hits you, you should be able to get back up as fast and as efficiently as possible -- not the case when diving heavy.

Here's another way to think of it. When diving very heavy (on a line), many divers (including myself), will turn around at the target depth without feeling any urge to breathe. People ask, 'how did you know when to turn?' The answer is that I've done such dives many times by trial and error, and figured out when to turn by logical calculations.

When fun diving, there is no such formula. If you dive heavy (for fun), on a deep dive you may have to start for the surface before you even feel anything in your lungs -- so how do you know when to go up?

I have done some dives in the 40-43m range where I was taking pictures of gorgonian corals. In each case, struggling with the camera on the bottom, I had to start for the surface before any urge to breathe hit me, because I had a 40-43m ascent with a 14lb weight belt.

As the ultimate example of diving heavy, I'll tell the story of the deepest fun dive I ever did. I was diving on the wall at Ansell point, a wall which I know very well. I had hit the bottom of the wall many times--it flattens out onto sand at around 39-43m. The alarm on my D3 was set for 40m.

As I descended the wall I felt great. Of course I can't read the D3 beyond 25m because it is too dark and my D3 has no light. I kept going down the wall, waiting for the sand, which should have been at 40m. Finally I heard the alarm at 40m, but the no sand! I sank for a second or two, then, still without feeling any urge to breathe, I turned around, and I got super dizzy on the turn around--the narcosis felt much worse than on a routine 40m dive. That was when I realized I was screwed---looking up to the surface it was totally black, meaning I was way past 40m. It turns out I was at 53.5m! I started my way up and was a bit nervous---it took forever to get up. As it got lighter, I knew I would make it, but it would be pushing it far beyond my safe limit for fun diving. I got to the surface after 2'24" and gasped for a few breaths -- a clean recovery, and my buddy was watching about 30m away, but had I never surfaced he would never have been able to find me. I was wearing a 5mm elios with a 13-14lb belt.
Noel said:
I guess that brings up another question or two:how often do you (anyone) typically dive, and how does the availability (or lack) of a buddy affect that? Do many of you still go for "fun" dives by yourself?

And how do you manage pool training? Do you all have a competent diving buddy alongside? Enlist the aid of wife/girlfriend/family member? (There's no way in hell I could get my fiance to supervise me. Explaining blackout, samba, and other risks to her would absolutely ensure that I would never be allowed near open water again!) Or do you simply ask the lifeguard to keep an eye on you and hope for the best?

My wife and I have taken the freediving course together. So I always have a partner when we train in the pool doing wet statics, or dynamic training. She also freedives with me when we visit tropical waters. However she refuses to dive in the "cold" Pacific waters, so when it comes to beach diving here in So.Cal. I am on my own (so far I have gone a few times to Crystal Cove in OC).

I mitigate the risks (I think) by not diving deeper then 40' feet and never pushing my limits timewise. I don't spearfish at this point, and freedive just for the enjoyment of it.
Crystal Cove is in my back yard. If I do decide to get back into it, you'll have a diving partner, if you want one.

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