Re-using air from BCD in dire emergency?

[pittyyofool]

DCBC, If YOU set your IP to 140psi, that implies that you service your own regs. If you do service your own regs this concerns me, because you have exhibited that you don't know how a 1st stage works. how are you to fix something, if you don't know how it works? Please tell me that you ONLY do your own regs and don't touch anyone else's. Before you touch any regs but your own please take a repair class from a good and competent instructor that will teach more than just doing but how and why. Or at least read a good book.

 

[Cave Diver]

I just tested it and actually just sucked one on my tanks in to a slight vacuum.

And all this time whenever I heard someone really sucked, I thought it was a figure of speech!

 

[pittyyofool]

And all this time whenever I heard someone really sucked, I thought it was a figure of speech!

HAHAHAHAHAHAHA, well people currently call me a wind bag, what is the opposite of that? I feel a new nickname coming...

 

[DareDevil]

I never said that.

So if you NEVER said that:

"a CESA at 60 fpm is safer than ascend at 30 fpm getting one-two breaths from regs/BCD/whatever"

then you agree that:

"ascending at 30 fpm getting one-two breaths from the regs/BCD whatever is safer than ascend at 60 fpm".

Which is what I am telling since the beginning...

DareDevil

 

[Rick Murchison]

So if you NEVER said that:

"a CESA at 60 fpm is safer than ascend at 30 fpm getting one-two breaths from regs/BCD/whatever"

then you agree that:

"ascending at 30 fpm getting one-two breaths from the regs/BCD whatever is safer than ascend at 60 fpm".

Which is what I am telling since the beginning...

DareDevil

Hmmm... hmmm.... in the long run, that'd depend on what's growing in the BC bladder, and whether you breathed in a spore that took root or not, wouldn't it?
If I'm within the NDL and have the choice between 30fpm breathing from a BC and a 60 fpm CESA, I'll take the CESA.
But then, I have the benefit of a quarter century using the 60/60/60 tables successfully...
That said, I wouldn't hesitate to use the BC if the choice were that or not getting to the surface at all.

Rick

 

[Ayisha]

So if you NEVER said that:

Boulderjohn really never said that. What he has been trying to explain to you so patiently and repeatedly was explained by him quite nicely way back in post # 91:

DAN's study of ascent rates found taht a 30 fpm ascent rate was marginally better than a 60 fpm ascent rate, but that safety stops were more important than either.

Diving practices have changed dramatically over the last 40 years. The practices many of us consider too risky or unsafe now were common practice back then. Much of the gear we take for granted now and that makes our diving easier/safer was not even thought of back then. Back then, you just tried not to ascend faster than your bubbles, I believe. Once you drew your last breath, you used your reserve just to get to the surface, no matter what depth you were at. Most of those divers did just fine for many years.

Unless you are a very new diver, most divers were probably trained to ascend at 60 feet per minute. Even now, many computers have a built-in expected ascent rate of 60 feet per minute until you get to 30 fsw, where it becomes 30 feet per minute. Throw in different versions of deep stops over dive history, graduated ascents, safety stops being 15 or 20 feet deep depending on training/computer, and extended safety stops, and you have a whole lot of change in recreational diving. None of it was wrong before. The sport has simply evolved to minimize the inherent risk.

The bottom line is that if you were negligent enough:
* in your gas management
* or your buddy awareness that you lost your buddy and extra gas
* or you were ill-equipped/trained/experienced to dive solo
* and you have no gas available to you at the depth you're at,
you do whatever you can as slowly as you can to get to the surface alive.

If you can't manage to ascend any slower than 60 feet per minute, history shows that your chance of surviving is just fine.

If you run out of gas at 20 feet, you will react differently than if you "run out" of gas at 130 feet (or deeper or in an overhead envt). How you respond is your own decision that you will have to live with - or not.

 

[boulderjohn]

So if you NEVER said that:

"a CESA at 60 fpm is safer than ascend at 30 fpm getting one-two breaths from regs/BCD/whatever"

then you agree that:

"ascending at 30 fpm getting one-two breaths from the regs/BCD whatever is safer than ascend at 60 fpm".

Which is what I am telling since the beginning...

DareDevil

This is my last attempt.

The scenario we are discussing is using your BCD as a rebreather during ascent. The fact that you can use the remaining air in your tank through your regulator was my suggestion as a reason you did not have to breathe from your BCD, so I am going to confine my response to rebreathing air from your BCD. If you are rebreathing from your BCD, you are not breathing from your regulator, so you can't combine them into one scenario. It is either one or the other.

You seem to think that there is only one risk in all of scuba--DCS. In fact there are multiple risks.

• DCS--As I have said over and over and over again, the risk of DCS is miniscule to begin with, and the difference in safety between a 60 foot ascent rate and a 30 foot ascent rate is so marginal it is not worthy of concern.
• Uncontrolled ascent leading to lung overexpansion--This is a very serious concern, and a check of DAN fatality statistics will show that lung over expansion injuries while on a fast ascent due to a low on air emergency causes a number of deaths each year. If you are rebreathing a BCD, then you are adding air to it (inflating it) while you are ascending, something you are taught never to do. You are doing so in a way you have not experienced, and you are very likely to find yourself in such an uncontrolled ascent as you fumble with an unfamiliar process during an emergency.
• Drowning--You are OOA and trying to do something unfamiliar to you. You are breathing from a device that is not designed for that process. It will be very easy to aspirate water, begin choking, and thus turn a very simple ascent to the surface into a chocking, spasming fight for your life.
• Hypoxia--If you linger while breathing air with less and less O2 in it, you run the risk of blacking out and drowning because of hypoxia.
• Disease from contaminated air--what kind of unwholesome things live in your BCD?
  

Summary: In order to provide a teensy extra margin of safety for a risk factor that is nearly nonexistent to begin with, you are willing to increase the risk level of 4 other much more real and dangerous scenarios. You are taking a safe end effective practice and adding a very high level of risk for nearly no gain whatsoever.

 

[Cave Diver]

This is my last attempt.

The scenario we are discussing is using your BCD as a rebreather during ascent. The fact that you can use the remaining air in your tank through your regulator was my suggestion as a reason you did not have to breathe from your BCD, so I am going to confine my response to rebreathing air from your BCD. If you are rebreathing from your BCD, you are not breathing from your regulator, so you can't combine them into one scenario. It is either one or the other.

You seem to think that there is only one risk in all of scuba--DCS. In fact there are multiple risks.

• DCS--As I have said over and over and over again, the risk of DCS is miniscule to begin with, and the difference in safety between a 60 foot ascent rate and a 30 foot ascent rate is so marginal it is not worthy of concern.
• Uncontrolled ascent leading to lung overexpansion--This is a very serious concern, and a check of DAN fatality statistics will show that lung over expansion injuries while on a fast ascent due to a low on air emergency causes a number of deaths each year. If you are rebreathing a BCD, then you are adding air to it (inflating it) while you are ascending, something you are taught never to do. You are doing so in a way you have not experienced, and you are very likely to find yourself in such an uncontrolled ascent as you fumble with an unfamiliar process during an emergency.
• Drowning--You are OOA and trying to do something unfamiliar to you. You are breathing from a device that is not designed for that process. It will be very easy to aspirate water, begin choking, and thus turn a very simple ascent to the surface into a chocking, spasming fight for your life.
• Hypoxia--If you linger while breathing air with less and less O2 in it, you run the risk of blacking out and drowning because of hypoxia.
• Disease from contaminated air--what kind of unwholesome things live in your BCD?
  

Summary: In order to provide a teensy extra margin of safety for a risk factor that is nearly nonexistent to begin with, you are willing to increase the risk level of 4 other much more real and dangerous scenarios. You are taking a safe end effective practice and adding a very high level of risk for nearly no gain whatsoever.

Nice list, I'll add another to it:

• Hypercapnia--elevated amounts of CO2. Symptoms and signs of early hypercapnia include flushed skin, full pulse, muscle twitches, headache, confusion and lethargy. Hypercapnia can induce increased cardiac output, an elevation in arterial blood pressure, and a propensity toward arrhythmia. In severe cases, hypercapnia can lead to disorientation, panic, hyperventilation, convulsions, unconsciousness, and death.

Even if Hypercapnia doesnt kill you, going unconscious underwater probably will.

 

[ScoobaDooba]

god for bid if you ever pick up a cool looking rock or grab a few lobsters or scallops if you get hungry. That will throw your "buoyancy rated pressure gauge" way off, and you might just find your self in an OOA situation while 10 lbs. negative.




the air doesn't really expand because it is stored in a rigid container. But the apparent pressure in your tank will increase by 14.7 psi per ATM (30ft) as you ascend. this will provide you with about 1/2 of a small breath every ATM.
Trust me, been there and done that, tested it. I was EXPECTING to empty my tank, so don't bust my chops for a OOA


and to the OP's ?
do you wand to know how long the air in your bc will last you.
TEST IT!
Sit in your living room, put an average amount of air in your bc. breath out of it, and have a friend time you until you pass out. Then you know. If you really want some kicks; video tape it and have your buddy call in your unsuspecting wife right before you drop to the floor. Ps. put it on youtube and post it here so we and laugh to.

hahahahaha

 

[AfterDark]

the air doesn't really expand because it is stored in a rigid container. But the apparent pressure in your tank will increase by 14.7 psi per ATM (30ft) as you ascend. this will provide you with about 1/2 of a small breath every ATM.
Trust me, been there and done that, tested it. I was EXPECTING to empty my tank, so don't bust my chops for a OOA

What are you talking about rigid container?

Robert Boyle employed a J-shaped piece of glass tubing that was sealed on one end. A gas (air) was trapped in the sealed end of the tube and varying amounts of mercury were added to the J-shaped tube to vary the pressure of the system. Boyle systematically varied the pressure and measured the volume of the gas. These measurements were performed using a fixed amount of gas and a constant temperature. In this way Boyle was able to examine the pressure-volume relationship without complications from other factors such as changes in temperature or amount of gas.

Boyle's original experments were with gas in a rigid container, a glass tube. What difference would a rigid container make anyway?