How to safely ascend with Spare Air

Please register or login

Welcome to ScubaBoard, the world's largest scuba diving community. Registration is not required to read the forums, but we encourage you to join. Joining has its benefits and enables you to participate in the discussions.

Benefits of registering include

  • Ability to post and comment on topics and discussions.
  • A Free photo gallery to share your dive photos with the world.
  • You can make this box go away

Joining is quick and easy. Log in or Register now!

Status
Not open for further replies.

fisherdvm

Contributor
Messages
3,577
Reaction score
52
# of dives
200 - 499
I would like anyone who post here strictly abide by the subject. There has been enough debate about the worthlessness of spare air, and about the value of pony tanks. Please keep comments and reply directed toward the safe use of spare air in the emergency situation.

My feelings about spare air is that it should not be used until one is above 50 ft. My logics is as followed:

An 80 cu ft scuba tank at 3200 psi holds 80 cu ft of air. At the surface, when emptied, it will hold 0.39 cu ft of air (80 cf / 204 ATM(3200 psi)). At 33 ft, it will hold 0.78 cf (you are now at 2atm). At 66 ft, it will hold 1.18 cf (3atm). At 100 ft, it will hold 1.569 cf (4 atm).

A 3 cf spare air is supposed to give about 40 breaths at surface. This would be 20 at 33, 13 at 66, and only 10 at 100 ft.

If one were to have an incident at 33 ft. My simple minded understanding would be simply to keep my airway open, suck on the regulator, and kick my way slowly up to the top without the spare air. Of course, if I have been at deeper depths at prolonged time, I should stop at 15 ft and suck the spare air dry. But I likely would be safe (maybe achy from the bends, but no spinal paralysis or brain emboli) even without the 15 ft safety stop. If my calculations were correct, at 15 ft, I would have 0.585 cf of air if the tank was emptied. But I rose up from 33 ft, so my "emtied tank" should give me 0.195 cf of air, and my spare air should give me only 2 cf (3 cf divided by 1.5 ATM).

If one were to have an incident at 66 ft, I would hold my breath, but keep my airway open. If I kicked up to 33 ft, I would have an extra 0.4 cf from the empty tank. If I kicked up to 15 ft, I would have 0.595 extra cf from the empty tank, plus 2 cf from the spare air.

If one were to have no air at 100 ft, I would hold my breath, and kick up to 33 ft, and start breathing from my regulator at 33 ft. At this stage, I should have 0.789 cf from the tank. But if I wait till 15 ft, I should have almost 1 full cf of extra air from my empty tank and regulator, plus 2 cf from a full spare air.

My question is, to the experienced divers and researchers in air embolism and the bends:

1. What is the best way to ascend without having air embolism: a. hold your breath completly while you still have the regulator in your mouth (which I assume would mean that your airway is still open as your lips are not clamped shut). b. take only tiny breaths until you reach 33 or 15 ft. c. suck every last bit of air from the tank as you ascend. d. breath from your spare air from the bottom till the top.

2. When and where is the best place to start using your spare air: a. Starting at the bottom. b. Only after your emptied tank is really emptied (it technically will really be not emptied until you reached the surface). c. at 33 ft, after you have used up your main tank. d. at 15 ft, after you have used up your main tank.

3. Where is the best place to do a decompression stop with the limitation of your spare air (2 cf at 15 ft, 1.5 cf at 33 ft, 1 cf at 66 ft): a. at 15 ft or b. at 1/2 of your maximum depth.

Based on my calculations above, and based on my understanding of air ways, you are safe to hold your breath as long as your lips are pursed around a regulator and thus air embolism should not occur. As your lung expands, the air should escape from the regulator. Based on the above understanding, I would hold my breath until 15 ft. I would ascend at a rate which I would feel comfortable without overshooting the 15 ft mark. Then I would breath from the tank, then I would switch to spare air, then I would surface.

Would the physics of diffusion favor decompression at 1/2 of the maximum depth, or the traditional 15 ft (1.5 atm) spot?? Especially when your time is limitted by the tiny amount of air you have here?
 
Where's your buddy during this time?
 
Please focus on the topic and keep opinions to the threads that asks for them. This is strictly on the physics of safe ascend with an empty tank or with an empty tank and spare air.

Hope your buddy will always follow and watch over you.
 
hold your breath are you serious? Just cuz your mouth is open or you have a reg in your mouth does not keep you from getting an embolism.
 
fisherdvm:
Please focus on the topic and keep opinions to the threads that asks for them. This is strictly on the physics of safe ascend with an empty tank or with an empty tank and spare air.

Hope your buddy will always follow and watch over you.

This is at the heart of the topic. Look a little deeper friend and ask why you would ever need to ascend with that POS if your buddy was there. Why worry about the physics of something which is going to only come about as the result of going against everything you've already been taught.

OW 101...first day, first class. Problems underwater should be solved underwater. If you are starting to get into the physics of "HOLDING YOUR BREATH!!!" underwater, you definitely missed more of the first class.

Sorry, I won't get into the physics of this because your post indicated that you are looking at the complete wrong end of the equation.
 
Unfortunately I'm not going to be able to abide by your wishes, normally I would just not post, however, your information is incorrect and flawed and therefore dangerous.

An "empty" (at atm pressure) tank is empty, at any depth. The idea to keep the reg in your mouth as you ascend is because the gas in your hoses will expand, therefore giving you access to a bit more air.

The reason "the number one rule in scuba diving is never hold your breath" is to allow gases that would normally expand to escape, if you hold your breath, airway open or not, you will embolize.

The fact of the matter is spare-air will not get you out of the water safely, except maybe 20 ft., the best chances you have of surviving an OOG situation is by diving with a good buddy, the next best solution is a pony bottle, with a minimum of 19 cu. ft. of your choosen bottom mix and for recreational dives only. Any of the options you discussed will leave you bent, embolized or dead, very possibly all three.
 
fisherdvm:
I would like anyone who post here strictly abide by the subject.
Wouldn't we all :wink:
fisherdvm:
Please keep comments and reply directed toward the safe use of spare air in the emergency situation.
OK... The safest use of a spare air in the emergency situation would be to leave it at the dive shop and plan your dives so as not to run out of back gas in the first place... If you should happen to misplan your dive, the next safest
fisherdvm:
1. What is the best way to ascend without having air embolism:
Ascend slowly, breath normally. You mentioned holding your breath several times. This will hurt or kill you. Just 'cause your lips are open does not mean your airway is open.
 
Did anyone here actually took physics. If they did, please help me think this problem out.

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 depth.

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.

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.

I think the worries of holding ones breath and blowing alveoli and sending streams of large bubbles through the arteries mainly applied to the diver who throws his regulator out of his mouth, clamp his lip shut, and purposely hold his breath as he surfaced. His lung would expand 3 times its volume and he will be blowing pink and red bubbles at the surface.

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.

The same diver who surface with a regulator in his mouth CAN NOT purposely hold his breath. What I meant by breath holding is simply - EXHALING - but not inhaling until one is at a shallower depth.

So, please focus on the discussion thread subject and help me with my physics problem. It would be really cool if an engineer from one of the regulator company would get on line and help me with the math problems. If I assume that the coefficient of resistance of the whole system is due to metal spring, the only variable here is the ATM on the skin transmitted through flesh, and finally to the alveoli in the lung and the air in the trachea.

Thanks for thinking for me....
 
To be very honest, I have dived only 13 times, and that was 10 years ago. It is very refreshing to read about these topics here and get input from the veterans. I am planning to get a refresher course and restart diving. It is amazing what a medical residency and having a family can do to your diving hobby.

I am obsessive about science, so I would like more input from other medical folks or engineering types. As for my name, the dvm does imply a veterinarian. I do hold both a DVM and an MD. But it is worth S...T when one is diving. I have intubated hundreds of dogs and cats, about 10 or so infants, and 1 cardiac arrest human . So I believe that I understand the anatomy of an airway from the vocal cord up very well.

I still strongly believe that a conscious person with a regulator in his mouth can not have a closed upper airway.

The use of a rigid airway is to keep an unconscious person who is still breathing from shutting down his upper airway with his tongue. A rigid airway is not needed in ACLS or ATLS if the patient is conscious and breathing.

Please correct me if I am wrong, I will always be the first to admit it.
 
Status
Not open for further replies.
https://www.shearwater.com/products/swift/

Back
Top Bottom