When is it okay to exceeding training limits?

[Steve_C]

Different thing to ponder. At 130, you're at approximately 5 atm, right? So, you have roughly 5 times as much O2 contained in your lungs as you would at the surface (assuming you're breathing air and not Nitrox). So, does that mean that if you stayed at that depth and held your breath, you could hold it 5 times as long as you could at the surface?

Problem is that as you go up the PO2 will drop. If you have used up some of that extra oxygen at depth then you are missing some as you get shallower. You may not have enough oxygen at shallower depthss or the surface. This is the problem of "shallow water blackout" that freedivers going for depth have to worry about. They need safety personal at the surface. It also kills a few free divers.

 

[RJP]

One rule of thumb might be, when you get to the point (a depth, a temperature, whatever) that it scares you, you have exceeded your limits.

The problem is that there are a lot of people out there that just aren't smart enough to be scared when they oughta be.

 

[rhwestfall]

so, anything (and I mean a-n-y-t-h-i-n-g) other than the EXACT same conditions you earned your certification in are then off limits without instruction....

 

[Akimbo]

The problem is that there are a lot of people out there that just aren't smart enough to be scared when they oughta be.

Darwin has a solution for that. There was a time that training was long enough for instructors to recognize the great majority of trainees that lack the judgment to be a safe diver and suggest another pastime. Unfortunately, Darwin has to do the work that far too many instructors don’t.

 

[ddmattos]

Well THAT might be a problem! LOL Remember, ignorance is bliss!

This does make me think of a semi-related question:

Imagine that you're a newb (say, like me) and you dive to 130'. Because you're a newb and haven't been educated properly on gas consumption, you stupidly run completely out of air while you're at 130'. And, also because you're an inexperienced newb (possibly diving with a newb buddy), when it happens you don't see your buddy anywhere close by. Though you are a newb, you keep calm and cool and make the decision to make a controlled emergency ascent, swimming/floating up at 60'/min up to the 60' level and then 30'/min to the surface, skipping the safety stop since it's optional anyway and you're out of air.

By my calculations, the ascent would take 3:10. That is longer than most people can hold their breath. But, with the partial pressure of O2 in your lungs at 130, even though you're NOT holding your breath, you should be able to "last" a lot longer on your lungful of air than you could by holding your breath on the surface, right? Plus, as you ascend and the ambient pressure drops, some of the air in your "empty" tank will become available, right? So you might get another half or full breath out of your tank on the way up?

Or, to summarize all these questions: If you dive to the Rec limit and you have an almost-worst case scenario, is it reasonable to think that a calm, cool, and collected diver could still get themselves to the surface without getting hurt or drowning?

The 100' or 130' CESA?...... I would say odds are against you. But then again your life would depend on it. You would also most likely leave your buddy before he realizes you left or else you would be sharing air. But this would easily be avoided by slinging a 30cf or 40cf with separate reg. You are your first backup, your buddy is the second.

When I first started diving I was very lucky to find an awesome instructor (recommended by a friend) that added value to every dive during training. Plus they were/are role models for me to copy while diving. By learning skills correctly from the start and practice, there will be no bad habits to correct later.

I took OW and AOW/Nitrox one month apart. So basically I took the courses not necessarily for the certs, but for the skills.

 

[Akimbo]

… At 130, you're at approximately 5 atm, right? So, you have roughly 5 times as much O2 contained in your lungs as you would at the surface (assuming you're breathing air and not Nitrox). So, does that mean that if you stayed at that depth and held your breath, you could hold it 5 times as long as you could at the surface?

That depends on your skill in suppressing the effects of CO2, which is the stimulus to breathe. A diver can’t sense the lack of Oxygen, aside from losing consciousness. Doing a free ascent, which CESA is a subset, does expel some CO2 so you can easily hold your breath much longer, but not 5x.

I have practiced free ascents between 100 and 150' at least once a year since I started diving. When practicing, I ascend at 60'/minute which was the US Navy standard most of my life. Practice free ascents are ALWAYS at the start of the first dive of the day. It is amazingly easy once you learn how.
The BIG caveat is to make sure you understand air embolism and keep your airway open. Don’t even try this in a swimming pool until you do.

 

[boulderjohn]

By my calculations, the ascent would take 3:10. That is longer than most people can hold their breath. But, with the partial pressure of O2 in your lungs at 130, even though you're NOT holding your breath, you should be able to "last" a lot longer on your lungful of air than you could by holding your breath on the surface, right? Plus, as you ascend and the ambient pressure drops, some of the air in your "empty" tank will become available, right? So you might get another half or full breath out of your tank on the way up?

Years ago there was a prolific poster on ScubaBoard who told of the graduation exercise for an advanced program he had taken--a CESA from 100 feet. I have personally talked to people who have done emergency CESAs from 75 feet and from 100 feet and gotten a full description of the experience from them. Yes, it can be done, and it has been done. Here are some factors to consider.

1. If I were in that situation, I would probably ascend at greater than 60 FPM the whole way. I am not worried about a mild case of DCS. I want to get to the surface. It would take me less than 2 minutes.
2. Once you are ascending and the air in the air in the lungs expands, it starts coming out pretty clearly. It is not like the experience with a horizontal CESA in the pool. The people I talked to said that once it started coming out, it would have been hard to stop.
3. Because of the expanding air, you can exhale all the way to the surface much longer than you can hold your breath.
4. The main reason you can't hold your breath longer is mental. You don't need any more oxygen to hold your breath longer. It's the buildup of CO2 that gives you the panicky urge to breathe. You can get over that. Not only that, the constant exhaling is releasing CO2, so you won't get as much of an urge to breathe as you normally would when holding your breath that long.
5. Yes, as you ascend and the ambient pressure gets lower, you will be able to get air from your tank, and more than you might expect. I tell my students that in a deep OOA situation, your tank is not OOA--it just thinks it is.

If you are in that situation, the worst thing you can do is think you can't make it to the surface with a CESA, because having that bad notion may cause you to hold your breath.

 

[Lorenzoid]

Is the question of whether a CESA from 130 feet is practical really related to the original question of whether it's okay to exceed one's training "limits" under certain conditions? There are reasons why 130 feet was established as a squishy "limit" for recreational diving, but it's my understanding that the practicality of a CESA from that depth was not one of them. Am I wrong?

 

[Akimbo]

Problem is that as you go up the PO2 will drop. If you have used up some of that extra oxygen at depth then you are missing some as you get shallower. You may not have enough oxygen at shallower depthss or the surface. This is the problem of "shallow water blackout" that freedivers going for depth have to worry about...

That only applies to freedivers, not Scuba divers. It would be nearly impossible for a Scuba diver making a free ascent to consume enough Oxygen in their lungs to suffer a shallow water blackout. Also keep in mind that their blood and tissues are also super-oxygenated if their bottom time is more than a few minutes.

Panic that causes them to hold their breath or lack of experience doing CESAs/free ascents that causes them to expel gas in their lungs way too fast is the danger on free ascents.

 

[boulderjohn]

Is the question of whether a CESA from 130 feet is practical really related to the original question of whether it's okay to exceed one's training "limits" under certain conditions? There are reasons why 130 feet was established as a squishy "limit" for recreational diving, but it's my understanding that the practicality of a CESA from that depth was not one of them. Am I wrong?

According to the Encyclopedia of Recreational Diving, the primary (but not only) reason for the 130 foot limit is the belief that everyone will be impaired to some extent through narcosis beyond that depth. That is also the depth were we start getting out of no stop ascents and start having to require decompression stops.