Testing a Spare Air

[caruso]

Let's look at the example of a typical diver who runs out of air at 90' on a dive that is going badly. With a direct ascent to the surface and a SAC rate of 0.8 under the circumstances

Who CARES what the SAC rate is when it's an emergency ascent? SAC rates are measured under typical dive conditions when the diver is not stressed and is not looking to stretch every lungful of air to it's limits. My SAC rate is a bit on the high side at about .6 but like I said I can still swim 2 lengths of a 40' pool on one breath and if my life depended on it I could probably go yet another length. The conditions under which a diver must stretch every last bit of gas to save is or her life are completely unrelated to conditions when SAC rate is measured or when SAC rate even matters.

 

[markmud]

Who CARES what the SAC rate is when it's an emergency ascent? SAC rates are measured under typical dive conditions when the diver is not stressed and is not looking to stretch every lungful of air to it's limits. My SAC rate is a bit on the high side at about .6 but like I said I can still swim 2 lengths of a 40' pool on one breath and if my life depended on it I could probably go yet another length. The conditions under which a diver must stretch every last bit of gas to save is or her life are completely unrelated to conditions when SAC rate is measured or when SAC rate even matters.

Hi Caruso,

I think you are writing that your breathing will become measured, careful, and prudent while performing a real emergency ascent on a pony bottle. Is that correct?

markm

 

[caruso]

I think you are writing that your breathing will become measured, careful, and prudent while performing a real emergency ascent on a pony bottle. Is that correct?

I'm thinking that if I need to do an ascent using my 19 cf pony bottle there's no reason to rush things.

I'm also thinking if I'm out of air at 100' and I've got the contents of my lungs plus a SpareAir then I'm going to get a lot of mileage out of those half a dozen or so breaths available to me out of that tiny cylinder and my SAC rate has nothing whatsoever to do with the outcome.

Say you take 10 people and play that "who can hold their breath the longest" game in the shallow part of the pool. Everyone takes a breath and drops to the bottom for as long as they can. One by one they pop up to the surface. What sort of correlation do you think there is between their SAC rate and how soon they surface? I say "little to none". Now expand that to a situation where a person is at 100' and has a limited amount of air available. The results will vary but again, not because of sac rate, but due to how well that limited air can be conserved and how long a diver can "hold his breath" although in such a scenario the diver would of course be venting gas as they ascend. Nothing to do with SAC rate.

 

[markmud]

I'm thinking that if I need to do an ascent using my 19 cf pony bottle there's no reason to rush things.

I'm also thinking if I'm out of air at 100' and I've got the contents of my lungs plus a SpareAir then I'm going to get a lot of mileage out of those half a dozen or so breaths available to me out of that tiny cylinder and my SAC rate has nothing whatsoever to do with the outcome.

Say you take 10 people and play that "who can hold their breath the longest" game in the shallow part of the pool. Everyone takes a breath and drops to the bottom for as long as they can. One by one they pop up to the surface. What sort of correlation do you think there is between their SAC rate and how soon they surface? I say "little to none". Now expand that to a situation where a person is at 100' and has a limited amount of air available. The results will vary but again, not because of sac rate, but due to how well that limited air can be conserved and how long a diver can "hold his breath" although in such a scenario the diver would of course be venting gas as they ascend. Nothing to do with SAC rate.

Caruso,

I agree with your greater premise for sure.

Even when I am doing a practice pony bottle ascent, I am very measured. I am breathing to avoid AGE, I am breathing to exhaust nitrogen and CO2. I am not sucking in huge "lung full" breaths and then immediately exhaling that entire load of gas. I am not blowing my nose and removing my mask to clean it...

My sac rate that is derived by swimming at a moderate clip while at a constant depth has no correlation to an emergency pony bottle ascent.

For those that would freak-out and suck their gas down in a minute, you don't belong in my world of diving. I don't appreciate people who can't master their fears. It is a weakness; and I won't allow your weakness to kill me.

cheers,
markm

 

[Coztick]

ARule 1:[/QUOTE]

Rule 1: Getting to the surface even bent or embolized is treatable. Body found on ocean floor with weights secure, not so much. How often do you practice grabbing weights?

Panic kills!
I can't imagine forgetting to drop lead in an emergency...
I handle both 2 lb weights once during every single tank w/pony dive I do because I sm the single and move weight twice to compensate for gas weight.
Both are clipped to my butt D ring with a tether and rest on either hip.
More effective for me in the case of a loss in bouyancy would be my dsmb as I only have 4lbs to drop.
While I connect and test my power inflation predive, I try not to use it. I actually found it relaxing to draw a big breath at 40 or 50 fsw and transfer it to my wing and, to a lesser extent, again to become neutral at depth. No need for many adjustments beyond that.

How often does anyone practice manual control of their bouyancy?

Cheers

 

[DandyDon]

Most bodies are found with weights attached.

 

[Coztick]

Scuba is fun, easy and safe until it's not.
Be prepared to handle yourself when...

 

[markmud]

Most bodies are found with weights attached.

Hey Dandy,

How many BCDs with no bodies attached are found on the bottom? If you can't find your lead to release it, release your BC. If you are wearing neoprene, you are going straight for the surface.

Davey Jones and his locker can have my stink'n BC.

Panic kills is right.

markm

 

[Bert van den Berg]

My simple take on this is that some extra air is better than none. more extra air is better.
I started with a 6 cu ft pony, then progressed to a 13 cu ft. Pony and am now using a 19 cubft. Pony.

Was told by more experienced divers that a small amount of extra air could lead one to believe that they would be ok when in truth they might not be.

On a a slightly different topic, if you do have an air failure at depth and manage to control your panic I assume that one should ascend as much as possible without using the spare air in order to make what you have last a bit longer. Not sure about this but someone may have the correct answer.

 

[Bob DBF]

Most bodies are found with weights attached.

Divers suffering an acute medical event, or say CO poisoning are in no condition to drop a belt. So it would decrease the number of divers that are able and don't drop their belt by an undertemined amount. Not to say it dosent happen, but it is nowhere near the number on the bottom.

Not to say it isn't a good reminder.

I practice dropping and have actually dropped my belt twice, I know it saved my life once.


Bob