Buoyant ascents

[uncfnp]

My last trip there were actually 2 SPG malfunctions. A fellow diver's computer on AI fixed at 5000 psi. She immediately ended the dive. Next day my dive buddy came up with 1200 in his tank. Unusual for him. Later I checked the tank and it had less then 250 psi in it. Not good.

 

[dumpsterDiver]

I didn't know there was some guidance about below 18 meters versus above 18 meters. I think the answer is supposed to be:

When you run out of options, then you gotta shoot for the surface.
If you had just run "out" or are very low on air and it is hard to inhale... AND you are neutrally buoyant.. then you can probably kick up gently and sip the air.

For me, if I had some air in the tank, I would pop some air in the BC, begin a buoyant ascent and try very hard NOT to kick and to conserve my energy. I would plan on riding the BC up and vent air and try to come up as slow as I think I can.

What if you are diving without much of a wetsuit, you are weighted to be heavy and to be able to work on the bottom and you slam yourself under a ledge and it rips off the second stage hose from the regulator? Now you have nothing the breathe, nothing to inflate the BC and are negatively buoyant. Unless you are very shallow and/or a very strong diver, you should probably be thinking about ditching lead. In a situation like this, you HOPE you have some ditchable lead, but if you have little or no wetsuit on, you probably have less than 10-12 lbs of ballast to ditch. Dumping 10-12 lbs is NOT going to send you rocketing to the surface.

If you are wearing a 25-lb weightbelt (i.e., a thick suit) then dropping all that lead IS going to give you a faster ascent rate. However, as mentioned by others, if you flare out on your back and remember to dump air as you approach the surface, you should not be going that terribly fast.. If your lungs are healthy and you exhale - it is very unlikely to get an AGE - even with an accelerated ascent rate.

Yesterday, i had a buddy who felt uncomfortable, aborted a dive and then forgot to vent the BC on ascent, allowed it to get completely full when coming up a line.. and then let go of the line and kicked up toward the surface for the last 15-20 feet. The diver did not get bent or hurt and went on to do another dive an hour later.

I think the best answer is.. ditch the lead if you think you must.

 

[oly5050user]

Assuming I'm deep, have no buddy, no alternate air source and am ooa (something I can't fathom but will for the sake of your question). You would have two options. Keep your weights and do a Cesa using your wing or bcd as a rebreather for a few breaths (likely to result in a possibly leathal lung infection), or, ditch weight. A shockingly huge percentage of scuba accidents resulting in death involve people with their weights still on. This would suggest ditch weights.

You are an instructor and advising to breath off a bcd? What agency is this? I suggest that you call your agency and tell them what you advised ..learn how to say" would you like fries with your order " as well. You started out ok saying "do a cesa" but lost me at "use wing / bcd as a rebreather". I hope you do not advise your students to do this.

---------- Post added September 13th, 2015 at 10:36 AM ----------

The best approach is to not run out of air or buddy and certainly not both at the same time!

When I first started diving back in 1969, I did not own an SPG. Instead, I relied on the then, ubiquitous J-valve. My J-valve's detente did not work very well, so I often had to do a CESA. Since I was very neutrally weighted (no BC), I simply did a CESA without ever a thought to dropping weights. But that's the point: I was neutral on the bottom, which made me progressively buoyant as I surfaced. None of how to do a CESA was taught to me when I first learned to Scuba. Kicking like mad to the surface was a pretty natural solution when I was out of air. No, neither my buddy or I had an 'octo' either, so when you were out you simply scrambled to the surface. It's really not that hard.

Then I started using an SPG. Thousands of dives later with an SPG, and I have yet to run out of gas. Moreover, my buddies have yet to run out of gas since I'm responsible for their air too. My preference, and my decision is to simply never to run out of gas or buddy. It's worked well so far!

Learned and dived same way here.

 

[Bob DBF]

The thread about amount of air you should come up with had got me thinking about the padi guidance that if you are ooa at a depth greater than 18m you should ditch weight and do a buoyant ascent.

One reason this may come up, is with wetsuit crush and your BC holding no air you are negatively buoyant.
If you are diving normally swimming up will make you more buoyant until the BC is full or you let some air out of it to slow your ascent.

My question is, should you actually do that or should you do a cesa, not releasing weight until you get to the surface?

That is what I have done, however on one occasion I dumped the belt because I did not believe it was going to end well. I have only dumped my belt once on the surface (before the days of the BC). I weight myself a a pound or two heavy @ 15', empty BC, with 500# in the tank, this makes me quite buoyant on the surface with an empty tank even with the weight belt on. Also I use a snorkel, so I don't have to keep my head out of the water, which takes more buoyancy.

Assuming you are neutrally buoyant at 18m or more and wearing some sort of thermal protection, chances are you'll have a bit of air in your bc and as soon as you start kicking up, you'll be positive and become increasingly more positive as you ascend. If you have ditched weight, it will be next to impossible to have any control underwater and, I assume, more difficult to control the speed of your ascent.

More difficult is not impossible. You seem to assume that as the wetsuit buoyancy increases that you should not decrease the BC buoyancy. You try to control the ascent as you would any, only a bit faster.

Is ditching weights really the safest course? I know that bends are usually fixable, while drowning isn't, but an embolism may not be fixable either.

This is where experience and knowing your limits come into play, you have to drop the belt before you panic. Considering the alternatives, it would be better on the surface where people can help you than on the bottom where they have already failed.

By the way, I know that the first answer is "watch your air and don't go ooa". The second answer is, "stick close to your buddy, so if you are ooa, you have a source of air". I do both of those things religiously, but let's assume you have an equipment failure and your instabuddy is an idiot who can't execute an air share (I know 2 people that this happened to, one did a buoyant ascent from 18m, one did a cesa from close to 50m, both were fine, although the former gave up diving).

Since I first purchased an SPG, I have never gone unintentionally OOA.
Sticking to your buddy is a good idea, but if you are OOA there is a good chance your buddy is as well.
A CSEA and Buoyant Ascent are emergency procedures that are proven to work, I will do one anytime I feel it is necessary.

I've seen a lot of people give up diving for the same reason, they have been diving well over their skill level and didn't know it, because of an emergency they finally realize diving skills can kill them.

Please just humour me with your opinion on the best approach

Head for the surface at as controlled a rate as possible. A buoyant ascent can be done safely, if a csea is not working for you.
Dump the belt as soon as you think you need to, on the surface if you are not back in complete control.


Do some pool or shallow water work, and find out how you can control an ascent after dropping a weight belt, it is not the death warrant that some make it out to be. I believe dumpsterDiver has a video of his daughter practicing this under his supervision.

In order to make diving fun and available to the masses in a quick class, a lot of information and procedures are no longer thought important enough to cover and practice to the extent you might need them in an emergency. But then, I have a problem with windmills.



Bob
---------------------------------

That's my point, people, by and large, are not taught that diving can be deadly, they are taught how safe it is, and they are not equipped with the skills, taught and trained to the level required to be useful in an emergency.

A man's got to know his limitations.
Harry Callahan

 

[Doby45]

You are an instructor and advising to breath off a bcd? What agency is this? I suggest that you call your agency and tell them what you advised ..learn how to say" would you like fries with your order " as well. You started out ok saying "do a cesa" but lost me at "use wing / bcd as a rebreather". I hope you do not advise your students to do this.

I took the information he provided as a last ditch save your life type maneuver, not a "HEY THIS IS A COOL REBREATHER!!"

Good Lord, step out of your glasshouse.

 

[uncfnp]

I took the information he provided as a last ditch save your life type maneuver, not a "HEY THIS IS A COOL REBREATHER!!"

Good Lord, step out of your glasshouse.

Agreed and he also provided a warning of the risk. I don't recall anyone every teaching me the option of breathing from a BCD but neither do I remember any warning of infection if I did so. I do recall IRL the suggestion that taking a breath from the wing would aid in emptying it for a negative entry dive. Never thought anything about it until I read the risk on SB. As I understand it, there is one reported case. Have there been others?

An article I found interesting... Emergency Breathing from Your BCD: Undercurrent 06/2011

Would I do it as a "last ditch option"? Absolutely. But then I am fanatical at cleaning my gear, including rinsing the bladders after a dive trip.

 

[NAM001]

There is no pressure expansion in the tank as you get closer to the surface..... at 100 ft when you have with no air to draw on, you have 45 # in the tank. as you get closer to the surface and water psi decreases yo now have a DP for the remaining air in the tank to go to the regulator. I have tried the free ascent before and did the ooooo or ahhhhh into the bcd hose so as not to loose the benefit of exhaled air being of some lift value. on the way up you will get air from the tank. if yo have a 15 liter tank and you go from 100 to 40 ft you will have about 7 ltr's you can draw from before running out again. If yo dont need it you can inflate with it.

Hand on the weight belt buckle on the way up definitely seems like the best thing to do, but for the sake of this conversation, if you've just perfmormed a CESA and orally inflated your BCD what benefit is there to ditching weights once you're at the surface? Also, once on the surface I would assume due to the expansion of gas in your tank you would probably be able to power inflate your BCD, right?

I know weights aren't worth your life, but I would think the first thing to do once you're on the surface is inflate your BCD. If for whatever reason you had a snag removing your weights or it got caught on something, even for just a second, that could change the outcome of the event. Whereas as soon as you take that first big breath on the surface you dump it into the BCD then at least you've removed the possibility of re-submerging and potentially aspirating water.

Thoughts?

---------- Post added September 13th, 2015 at 12:18 PM ----------

From the first time i did some thinking about free ascent (Post nitrox) I remembered that frrom the OW class of the 60's the instructor said that most divers die in the top 20 ft of water cause PPO2 drops so low that you pass out and drown. Good reason to keep the reg in your mouth. The nitrox course made me think about this. when you breath air you use perhaps 2-3% of the o2 content and the rest of the air is expelled into the water. Percentage of O2 ias not as pmportant as the PPO2 is . As you get closer to the surface the air in the lungs is getting cycled to the body and continues to lower the O2 content in the lungs from 21 to 19 to 17 and pas out.. I always felt that nitrox was a good insurance policy in that you will be depleting O2 from a 32% starting point rather than a 21% point. Yes its co2 that makes you breath but with 32% you will not pass out on the way up. And what little gas you can get from that breath or 2 you can get on the way up you get a richer O2 shot to the lungs.

 

[oly5050user]

I took the information he provided as a last ditch save your life type maneuver, not a "HEY THIS IS A COOL REBREATHER!!"

Good Lord, step out of your glasshouse.

I do not live in a glass house. I only have over 40 years of instructing in the northeast with over 5,000 dives.
As an instructor he is to stick to agency standards and teach as any other prudent instructor would. If a former student tried this trick that this instructor recommended and gets hurt, it would be instructors fault and no insurance or certification agency will assist him in a law suit.
Dodgy with your very limited next to no experience with less than 25 dives , what expertise can you bring to the table to back up why you think this is a cool thing?

 

[CuracaoJ]

You are an instructor and advising to breath off a bcd? What agency is this? I suggest that you call your agency and tell them what you advised ..learn how to say" would you like fries with your order " as well. You started out ok saying "do a cesa" but lost me at "use wing / bcd as a rebreather". I hope you do not advise your students to do this.

---------- Post added September 13th, 2015 at 10:36 AM ----------


Learned and dived same way here.

Not advising it at all nor would I teach it. What I'm saying is if you're at 30 meters doing a Cesa and gonna drown... I'll take a breath from a bc vs. a breath of ocean any day. If you prefer sea water to nasty bacteria filled air that's certainly your choice. Its a hyperbolic answer to a hyperbolic question. But then the question is really moot as that should never, ever, happen. Like you and net doc I learned to dive on Js with no Spg. With current gear this scenario should be impossible.

What I do teach my students is the skills to make sure they aren't ooa beyond 18 meters with no buddy or alternate source. But that wasn't the question and the OP isn't my student.

 

[CuzzA]

Ok, so this statement from the above linked Undercurrent article is wrong then? Or am I interpreting it wrong?

Even if you suck your tank dry, you can get some air through your regulator as you ascend, and the pressure in your tank becomes greater than the ambient pressure.

It's not worded very well, but my thoughts were as you accend and the ambient pressure decreases this puts less resistance on the last little bit of air that "may" be remaining in the tank, yet at depth you weren't able to suck that air out of your second stage due to the pressure at depth. So, once you hit the surface you may have just enough air and pressure to power inflate your BCD. This is all in theory though and I'm not going to experiment to find out.

I should note I'm not making any excuses for not ditching weights. More so just prioritizing your next action once you breach the surface. Take a deep breath, ditch weights then oral inflate BCD vs. Take a deep breath, exhale into BCD. You would already be holding your inflator as you accend so I would think exhaling into the BCD wouldn't be very difficult. Now, that said, if you're feeling like you're out of oxygen and still have a ways to go to get to the surface as you perform the CESA then perhaps ditching the weights first would make more sense since you risk blacking out and at least if you blacked out without your weights you have a chance of surviving. Of course that assumes you don't black out face down once you breach the surface.