How to safely ascend with Spare Air

[jagfish]

Did anyone here actually took physics. ....

Yup, and I think a few probably took English as well...

...This problem actually puzzled me for quite a while. As the steel/aluminum tank is rigid, thus no one would actually believe that the ATM at 33, 66, or 100 ft would not affect the residual air in the tank. But I think it does. So therefore, I truly believe that my calculations above are correct concerning residual air in the tank as you rise.

As rethinking about the resistance to the pressure in the tank at 100 ft is simply 3 atm (assuming 1 atm at the surface and 1 atm for each 33 ft). Of course, that pressure encounter the piston in the first stage which lowers the pressure to the second stage. The second stage faces the resistance on our airway, then our trachea, then our lung.

At 100 ft, that pressure in the lung would be 4 atm. 3 atm at 66. 2 atm at 33. and 0 atm at the surface.

Assuming that the resistance at the piston is constant, and you vary only the resistance at the second stage, you thereotically would have an extra tank of air each time you surface 33 ft.

Therefore, as you surface, you should have an extra tank of air, which is 0.39 cu ft with each 33 ft of ascent.

So, unless I did not learn any physics (I did major in engineering and did get an award in physics in college), an empty tank at 100ft is NOT empty at a shallower dept.

As counterintuitive as it seems, I think you may be correct on this point. There was another thread on this topic over the summer. I think that poster also explained that it had to do not with air expanding in the hoses (though that will also provide air on ascent) but from the pressure differential with tank interior and surrounding water pressure.

I am never ashamed to be wrong, as I see most of the posters here are much more experienced than I am (probably 99% of you are), I just need the science to back your words up, and not number of dives or your certificates.

While I think you may be right that a few of the posters might have been off on the physics about the tank providing some air on ascent, I think that most posters are so taken with other flaws in your approach that this point if inconsequetial...for example...

As for the breath holding, I am not questioning the repetition in dive classes and training tape "never never hold your breath", "always breath".

When you panic and go into the breath holding mode you will blow your lungs.

I can not buy this. As a person who has earned basic life support, advanced cardiac life support, and advanced trauma life support in the medical corp of the army, I would like to question this. I have managed airways in infants and , and have intubated hundreds of airways in my career. I do not believe that a conscious person with a regulator in his mouth can consciously close his airway.

You are wrong, it happens...If you do a search, you will be able to find incidences that were posted in the last year.

The same diver who surface with his lips opened and ready to blow bubbles out as he surface might get paralysis from the bends and microemboli in the brain from nitrogen, but he will not suffer from major air emboli and major stroke from a blown lung.

Interesting...you seem to be privvy to knowledge that I have not heard here before from doctors who are apparently very experienced with dive related injuries

The same diver who surface with a regulator in his mouth CAN NOT purposely hold his breath.

Did you ever chug beer or cola from a bottle? Did you choke on liquid during the whole experience? Probably not, know why? You were holding your breath (and your mouth was open).

So, please focus on the discussion thread subject and help me with my physics problem.

There are other more serious problems with this issue than physics...

 

[fisherdvm]

Thank you for a well thought of answer.

As far as drinking is concerning, the swallowing reflex closes the vocal cords, closes the epiglottis, and deviates the trachea downward - this shuts down your airway. The food and liquid will just glide pass the watertight epiglottis. Yes, your lips are opened.

So I am still not convince that a conscious person with a lip around a regulator can mentally shut down his airway.

But you are the only who focused well on the thread....

Thanks....

 

[japan-diver]

You are correct in one thing as you ascend more air is available from the cylinder, this is due to the fact that we cannot breath the pressure in the cylinder below ambient pressure- so as we ascend we can get a couple more breaths from the cylinder.

You can embolism with a reg in your mouth, numerous documented cases in the DAN reports and elsewhere. So all the options you described would result in embolism or DCS or both.

 

[fisherdvm]

Yes, but are these accurate reports of an air embolism from rapid expansion of the lung forcing air bubbles into the arteries?

Or are these reports of microembolism from expanding nitrogen bubbles which have been dissolved in your from a prolonged deep dive.

I think these reports might note the paralysis, brain damage, and other symptoms of microembolism by nitrogen and misrepresent them as air emboli from a closed lipped person.

I have read that the major symptom of rapid ascent and inadequate decompression is paralysis. Therefore, I would seriously doubt that a diver who is unconscious automatically has an air emboli. It is correct to say that he has emboli - but the cause here is microemboli from nitrogen bubbles - which can be treated with a compression chamber.

Major air emboli from an exploding lung is likely to be more dramatic. I am thinking of like major infaction of the brain and bleeding into the lung type of damage.

I am still not convinced that air embolism resulting from a closed air way can occur in a conscious diver with a regulator in his mouth. Assuming that it is properly functioning and allowing pressurized air to escape.

 

[Snowbear]

I realize you will likely once again say you are right and I am wrong, but...

So I am still not convince that a conscious person with a lip around a regulator can mentally shut down his airway.

I can close my airway sitting right here at the computer. I also use breath control, including closing my airway while conscious, to control my buoyancy. Hmmm.. you used Endotracheal intubation experience as credential for your arguement. OK. I've intubated a couple hundred adult humans, maybe a couple dozen children, a few dogs, a couple cats and a horse.

A conscious paniced person who thinks they have no air underwater will often instinctively hold their breath (with or without a regulator clamped between their teeth) as they frantically kick for the surface. That's how they die of barotraumatized lungs before they even hit the surface.

No matter how strongly you argue against it, you will not convince many folks here this is not possible.

I will concede one point - You said somewhere below that a conscious breathing person is not holding their breath. That's true, if the person is breathing, the airway is open

I think it's ironic there was recently another argument on the board where a poster emphatically stated it is impossible for an unconsious person (not in seizure) to have a closed airway. Guess that person hasn't heard of laryngospasm?

As for the original question - Another poster was correct in pointing out the seriousness of some of what you suggested drowned out the nitpicking of the possibility of safely ascending with a spare air vs sucking the last .2cf (or whatever it was) from an empty tank. I still maintain there are much safer alteratives than either of those you suggest. Oh... but wait... you don't wanna hear about those.

 

[fisherdvm]

If you are both a vet and a human doc... Nice to meet you. I've met about 4 so far.

I don't think the number of intubation one has done matters in this discussion, it would be a ing contest if an anesthetist would enter the discussion.

Laryngospasm does happen, but it is in response to irritation. I would need to read more about the breath holding reflex to see if you can shut down your larynx in an out of breath situation.

I think it is good to think of the physics of diffusion if all you have left is 0.3 to 1 cu ft of air in an empty tank or if all you have is the 1 to 2 cu ft (usable of the 3 L spare air can).

As air diffuses from partial pressure to partial pressure across the alveoli, the diffusion would be greatest if the difference is greatest.

The goal in preventing decompression sickness is to have the nitrogen diffuses across slowly - that is why we have the "no faster than 30 ft per minute" rule.

The question I pose here, ignoring the air embolism and breath holding discussion, is the spare air or left over air in the tank best used continously as you ascend, or closer to the surface.

I am guessing that a person rising from the bottom at 100 ft after a 40 minute dive would have alot of nitrogen in his . Without any breathing, and he ascend to the surface rapidly, he will have dcs. If he ascend with the 30 ft per minute rule, that would take him 3 minutes.

If one were to save the tank until 15 ft, the partial pressure of nitrogen in the stream will be much greater than the partial pressure of nitrogen in the alveoli, thus would maximize diffusion of air than if you were at 50 or 100 ft.

My argument here is that it would be best to save the spare air or the empty tank breathing until you reach a shallower depth - to maximize the partial pressure difference.

But the bubbles forming in this ascend makes me worry about dcs - so should you start the spare air or breathing earlier?

I only stated my medical background to create a more focused discussion on the safety of ascend. No one can argue that a 6, 20, or 30 cu ft tank is safer. But if we can logically find a way to save people from permanent paralysis by analyzing how one can improve the emergency ascend, it would be worth a focused discussion.

You all have proven without a doubt that pony and deco bottles are the way to go, lets not do it again. Where is my buddy? Why did you let the pressure go too low. As I have read in the other threads, failure of rental equipment occurs, cruds do block valves (as we all have rented tanks), and seals do go bad. So lets not discuss that.

 

[fisherdvm]

Now let us focus on the breath holding discussion.

If your first stage fail, and dump 3000 psi into the second stage, you would lose all your air in a few seconds.

Now your second stage is filled with water, why keep it in your mouth.

As I understand, please teach me again, my scuba instructors, I should try to ascend with by lips pursed open and allowing bubbles to blow out.

I do not see a difference between this act and one which a person has a dry regulator in his mouth, and is not purposely holding his breath aside from not inhaling. The only resistance to letting the air escape at this point is the resistance from the exhaust valves of the second stage.

So is it the wording that I am using that is getting people all upset? Or by not inhaling, I am shutting my airway down?

 

[fisherdvm]

Hey, cool, cybersitter worked pretty well. I forgot to turn it off and it wipes out offensive words like "bl--d stream" or "pi--sing contest". Maybe we should install it on this forum so that we all learn to be more kinder to one another??

 

[japan-diver]

Yes, but are these accurate reports of an air embolism from rapid expansion of the lung forcing air bubbles into the arteries?

Or are these reports of microembolism from expanding nitrogen bubbles which have been dissolved in your from a prolonged deep dive.

I.

Numerous reports include autopsy results showing severve damage/rupture to the aveoli. Therefore I would say massive embolism not diffusion.

 

[fisherdvm]

Thank you very much Snowbear, you have challenged me to something that is so instinctive.

You are vey correct..... I opened my mouth, kept my throat cleared, and was able to completely shut down my larynx. So thank you very much for possibly saving my life in the future.

It is amazing what a little experiment will do. Yes folks, I am an idiot, you can instinctively shut down your larynx to the point of not letting air out of your lung just by thinking about breath holding.

So despite my medical degrees, I will bow and say - a conscious diver who has a regulator in his mouth should continue to breath even if he doesn't get air - as this would guarantee that his larynx will remain open.

By the way, Snowbear, what would a firefighter be doing intubating a horse? Were you trying to tube its stomach and got it in the wrong pipe?? Intubating a live horse is an extremely difficult task, and I have done it only about 3 times in vet school. As for the dogs, cats, and other animals - I think you must be a very wonderful firefighter to help them creatures......

Just kidding, I very much appreciate Snowbear for making me think ..... and possibly might save my life in the future.....