The 60s limit theory

[Penyu]

Hi all,

has anyone come across this article: http://divewise.org/limiting-freedives-to-60-seconds-for-safety/

It basically argues that for recreational freediving 60s divetime presents a safe limit since SpO2 remains at almost normal levels for that time. After 60s it drops (sharply for dynamic and slowly for static situations). The author goes further to say that at this relatively short divetime a mild amount of hyperventilation (30s) presents no danger, but makes the dive more pleasant due to lack of urge to breathe.

Wonder what other's think about this.

There is a lot of research and resulting literature on how to handle the risk of avalanches in ski mountaineering. The risk is similarly fuzzy as in freediving, but several approaches have developed whereby one can stay relatively safe when adhering to a few rules. These include things like partners (buddies) but also slope angle and avalanche situation (more akin to depth and divetimes). I wonder if similar risk management approaches can be developed for freediving?

Cheers

 

[Pinniped72]

Many thanks for posting, that is really interesting I agree with the author that losses in recreational and military training are totally unacceptable and would extend that to competition as well were vigorous safety measures should be in place. I am no were near an elite free diver in the furthest stretch of the imagination, so don't really know enough to say whether the science is sound or not but it makes sense once read. Holding your breath under water is risky, anything that reduces the risk and information about reducing the risk is welcome in my book

 

[Penyu]

Thanks for you thoughts Pinniped72, but c'mon, nobody else finds this an interesting approach? I know its useless to set new records or PBs, or more serious spearfishing. But for fun, recreational diving this might be helpful. What do all the knowledgeable people here think about it?

 

[japppo]

I shared this already on a national spearing forum and its very interesting in my opinion. I dive and spearfish mostly alone so I have used 1 min as a limit for years. With a buddy watching, I could try longer dives, but my skills are not for record breaking.

I guess 1 min is relatively safe and achievable by anyone, and especially when considering not so optimal conditions, eg thirst, exhaustion, lack of sleep, food, repeated dives etc. My diving is often out of my comfort zone and the days when everything is or feels perfect are quite rare.

 

[growingupninja]

A 'one size fits all' approach to freediving is kinda worthless but the holy grail for mass market freediving instruction.

From the commentary at the end of the article, this would be the real solution, a pulse oxy meter that works underwater. I personally think more research should be done on counted heartbeats also.... Maybe the Navy would commission something...

"DR. SMITH: A huge factor in the spearfishing community is even take a one or two-knot current in the water when you are used to doing a 40-50 ft [12-15 m] dive looking for grouper when it is at slack tide, just having to swim upstream and then having to go down and you put that extra effort, that is a real problem. I can see one thing in the future would be very interesting. I would think we could create a waterproof oxygen saturation monitor that you could put over the carotid artery that could feed back the vibratory signal that as the vibration became stronger you would realize that my sat has gone from 98 to 88% and now it is down to 80% and I better be getting to the top real soon.

DR. BUTLER: I think that is a very interesting proposal. Other people have proposed variations of that. If the Navy or the military community acknowledged that there was a problem in this area, it would be not technologically hard to do."

 

[cdavis]

The 60 second rule is a reasonable one backed up with decent logic. However, you can always think of exceptions. I got myself in trouble twice(slow learner) when the fish were thick with dives about that length with repeated dives, very short surface intervals and hard hyperventilation, stars, tunnel vision, loss of color vision, yada, yada. In general, normal diving conditions, reasonable surface interval, the 60 second rule is a good one that will keep most divers well away from trouble. The problem is "in general", "most", "normal", and "reasonable". The exceptions can kill somebody.

 

[Bill]

I think that Lance nailed it. Too many variables. Diving to a saturation number might be the answer.

 

[Penyu]

I fully agree with the problem of too many variables to consider. That's why any such general guideline would need to be extra conservative. To draw a comparison from backcountry skiing, a general rule there being that below 30 degrees of slope angle avalanches 'generally' do not occur. So you could just ski at low angle slopes. I do think such conservative 'safe limits' do have their place for the purely recreational pursuit without any kind of competitive or challenging aspect to it. In that mode freediving as well as backcountry skiing is done for the enjoyment of playing in the respective environment rather than a sportive challenge. More research, knowledge and experience about such risk assessment would be very interesting. Has anyone heard of BO incidence in less than a minute dive time?

 

[growingupninja]

Has anyone heard of BO incidence in less than a minute dive time?

I don't know of any BO instances but I have done dry sat O2 testing on a diver, with a pre-existing health condition, who had O2 of below 90% after one minute.

 

[Penyu]

Just found this here:
"Limit freedives to 90 seconds. Longer dives tremendously increase the risk of blackout. Attempting breath-hold dives longer than two minutes requires a buddy/safety diver. You can make dives this long only by depressing your physiologic alarm or willfully ignoring the urge to breathe. At this point, almost everyone has a very low blood-oxygen level." Its in an additional chapter on SWB in the book Bluewater Hunter by Terry Maas.

 

[cdavis]

With all due and vast respect to Terry, the 90 second number depends on the conditions. In the conditions he usually dives in 90 seconds would be about the limit of my capability. Diving full lung would probably mean my blood 02 level was getting pretty low. In the conditions I dive in (exhale, warm clear water) I seldom surface in less than 1:45 and two minute dives are common, with a completely clear head, no sign of 02 issues. That said, I follow his buddy diving advice and wear one of his FRVs when that isn't possible.

Ninja is on the right track, a carotid 02 monitor would be the way to get around all the exceptions.

 

[Maghunter]

[QUOTE="I would think we could create a waterproof oxygen saturation monitor that you could put over the carotid artery that could feed back the vibratory signal that as the vibration became stronger you would realize that my sat has gone from 98 to 88% and now it is down to 80% and I better be getting to the top real soon."[/QUOTE]

The issue with an external oxygen saturation or "pulse ox" is the data is delayed by a few seconds. Once the pulse ox reads 85%, for example, your true blood oxygen saturation is actually much lower than that. So the "alarms" would have to start going off at like 93%.

 

[Penyu]

The issue with an external oxygen saturation or "pulse ox" is the data is delayed by a few seconds. Once the pulse ox reads 85%, for example, your true blood oxygen saturation is actually much lower than that. So the "alarms" would have to start going off at like 93%.

Which brings me back to the comparison to the risk appraisal approach taken in back country skiing. In the absence of reliable data (on blood oxygen saturation or snow pack stability at a given location) one might want to take an approach based on statistical correlation, i.e. at a given avalanche risk stay below slope angle of x, or at a given depth limit your dive time to x. Of course such an approach must include safety buffers by being extra conservative, meaning if you know your local environment, snow pack build-up etc. and ski with buddies and and avalanche air-bag, respectively dive one up one down, etc. you might be able to push beyond this. Considering such a stats based approach I wonder if there are statistics on dive time/depth before black out and if it would be feasible to deduct a guideline from it. Cheers!