Breathing 100% O2 at depth...

[kinetic]

Dear All,

I posted up and asked a question about breathing inert gas in a dire situation, just so you could breathe something so as to make your way up on a rapid ascent, for example.

My next question is what could/would happen if say, you had to take one or two breaths from a 100% stage bottle at depths below the recommended for 100%.

Scenario, all back gas (air) is gone and your only option is to fly from 120 feet, or deeper within air limits, upto 20 feet (6m) breathing once or twice from pure O2 and then deco as best as you can with what's left at safe depth.

What would happen or is that an impossible question?

I understand the limits but I am just asking about those "no choice" situations, like the inert gas question I posted previously, same scenario.


Thanks in adavnce.

kinetic

[john]

your dead.

http://www.sptimes.com/News/82399/Hernando/State_agency_bars_acc.shtml

More recently, in April, Guido Gaudenzi of Italy died in a sinkhole under the Sand Hill Scout Reservation on a dive led by Derksen; he accidentally sucked air from a tank full of pure oxygen at 120 feet, a depth at which it is toxic.

--------------------------------------------------------------------------------

Mistake costs diver his life:[STATE Edition]
GRAHAM BRINK. St. Petersburg Times. St. Petersburg: Apr 28, 1999. pg. 1
Full Text (1380 words)
Copyright Times Publishing Co. Apr 28, 1999



(ran ET edition of TAMPA & STATE)

An Italian tourist apparently inhaled from the wrong tank during a dive in the Diepolder cave system Monday.

Guido Gaudenzi recently traveled from his hometown in Italy to Florida, lured by one of the world's largest and most spectacular networks of underwater caves.

The experienced diver came with plans to write a magazine article and take photos of the gin-clear waters and strange marine life that lurks in the porous limestone.

Instead, a spring-fed cave at the Sand Hill Scout Reservation off State Road 50 claimed Gaudenzi on Monday night as its second drowning victim this decade. Gaudenzi, 29, apparently breathed from the wrong tank, sucking in toxic pure oxygen, on the way up from what one of his partners described as an uneventful dive.

The fatality illustrates the perils of cave diving, an increasingly popular activity with many more risks than traditional open-water diving.

"It's unforgiving," said Chris Grant, director of the O2 Wound Care & Hyperbaric Center in Inverness and former editor of Scuba Times. "Making a mistake in a cave is often the last mistake you make."

Gaudenzi, his Italian friend Simone Roncoli, and their guide, Spring Hill resident Sandra Derksen, arrived at the sinkhole that leads into the underground caves about 5 p.m., according to a Hernando County sheriff's report. They signed the release - a requirement for diving at the Diepolder cave system, named for the man who owned the land - donned their cumbersome gear and plunged into the murky entrance.

They descended about 190 feet through a chute before entering a cave the size of a basketball stadium full of crystal-clear water. Once there, they swam to the top of the cave and made their way around most of the circumference before exiting and ascending through the same chute.

Divers who go deeper than 200 feet often use different gas mixes in their tanks than the compressed air used for more shallow dives. The mixes, a combination of oxygen, nitrogen and helium, allow them to stay longer at deeper depths, among other things. Some deep divers carry four separate tanks filled with different mixes.

Even with the complex gas mixes, deep divers must make decompression stops several times at different depths on their ascent to help dispel nitrogen and other gases from their bodies. If they don't stop and instead go straight to the surface, they likely will die.

Deep divers often take a bottle of pure oxygen with them, which helps them decompress in less time. The oxygen, however, should only be used at the last decompression stop, usually at 10 to 20 feet below the surface. Below 66 feet, oxygen becomes toxic to humans, so many divers secure the tank at the 20-foot level on the descent to avoid mistakes.

Gaudenzi took his with him. He was at the prearranged 120-foot decompression stop when the problems arose, the report said. He apparently switched mouth pieces and took a breath from the wrong tank, the report said. He immediately began convulsing. The regulator fell out of his mouth. His teeth clenched. Derksen and Roncoli swam to help their shaking partner, but it was too late.

At 120 feet under water, one deep breath of pure oxygen would shut a person's central nervous system off like a light switch, said Bruce Ryan, a cave diving specialist with the National Speleological Society.

"It would have been over in seconds," Ryan said. "There's nothing anyone can do, including an experienced guide, when someone does that."

Derksen and Roncoli realized they could do little for Gaudenzi, whose body began to float toward the surface, the report said. They made their decompression stops every 10 feet and exited the water about an hour after Gaudenzi drowned. The ranger who lives on the reservation called the Sheriff's Office. A dive team retrieved the body late Monday night. An autopsy was performed Tuesday.

Gaudenzi's family in Brescia, Italy, could not be reached for comment. Derksen did not return phone messages left by the St. Petersburg Times.

"It looks like a tragic accident, nothing suspicious," sheriff's spokeswoman Deanna Dammer said.

The surreal rock formations and wildlife, including albino crayfish, entice divers into the caves. Many call the experience spiritual and calming. Like a trip to space, say others.

For those reasons, the number of people cave diving in Florida is increasing, Ryan said. Hernando has at least a half-dozen dive shops and guides, and several more are in Citrus and Pasco counties. The diving in Spring Hill and Weeki Wachee was mentioned in an 18-page article about exploring Florida's caves that appeared in the March issue of National Geographic.

Cave-diving enthusiasts usually enter the water with no less than $6,000 in equipment strapped to their bodies. There are tanks, safety lines, lights, computers, bottom timers - backup systems for backup systems. The mix of danger, exploration and scenery is too much for some to resist

"It's an incredible experience. Once you do it, you're addicted," said Ryan, who has logged more than 500 cave dives, including the one where Gaudenzi died. "I'm sure that addiction is what brought him to this area."

Florida's caves are also some of the most difficult to negotiate in the world. They are tighter, siltier, deeper and more extensive, all of which can disorient divers and lead to panic and accidents.

"If you can cave dive in Florida, you can do it anywhere," said Grant, a 17-year diving veteran who has lost five friends to cave- diving accidents.

Hernando County and in particular the Diepolder system, which contains two main sites, have not been immune to accidents.

Lloyd Morrison, 25, of Hudson drowned in May 1990 after he drifted away from a group exploring the same sinkhole where Gaudenzi died. Morrison was a licensed cave diver but had little experience diving in the sinkhole where he drowned.

Three months later, 29-year-old Tallahassee resident Brent Potts was killed and another man was injured in a scuba diving accident at the Eagle's Nest sinkhole off Ostrom Way north of Weeki Wachee. Potts died while diving about 200 feet below the surface of the 320-foot- deep sinkhole.

In 1987, Springstead High School student Jason Tuskes, 17, drowned in a silty network of caves in a spring near Jenkins Creek. Tuskes, apparently aware of his fate, removed the harness from his body and used a knife to scratch a message to his parents and brother on the tank: "I love you Mom, Dad and Christian." He had little training in cave diving.

Experts estimate that about 400 people have died cave diving in the past three decades. Fatalities peaked in the mid-1970s, but the numbers have dropped since cave training has become widely available and the equipment has improved.

Still, about half of the deaths can be attributed to young divers venturing into underwater caves without proper training or equipment. Fully certified cave divers undergo specific cave training that includes at least 16 instructor-led dives and several hours of classroom training.

But it's not just the inexperienced who perish. The ones driven to explore new areas - called by industry insiders the "Star Trek syndrome," a desire to boldly go where no one has gone before - or try to set depth records are also vulnerable. Sheck Exley, considered by many people in diving circles to be the world's premier deep-cave diver, died in 1994 while trying to break his own depth record of 881 feet in a cave on Mexico's Yucatan Peninsula.

Gaudenzi had four years of cave diving under his belt, Dammer said. The scout reservation requires divers to dive at least twice at the easier of the two sites before trying the cave where Gaudenzi died, said Tony Davidson, who runs Down Under Dive in Spring Hill.

"The industry is well-regulated and for the most part safe as long as people do not exceed their training or experience," he said. "Everyone has close calls, and it's the ones who have the training who survive. There's not much margin for error."

- Information from Times files was used in this report.

[Illustration]
Caption: (1991) A diver explores one of Florida's caves, which are deeper and siltier than others, and can disorient divers and lead to panic. (ran HT); Photo: COLOR PHOTO, MIKE PEASE




Reproduced with permission of the copyright owner. Further reproduction or distribution is prohibited without permission.
Dateline: SPRING HILL
Section: HERNANDO TIMES; CITY & STATE; METRO & STATE; TAMPA & STATE
Text Word Count 1380

[andrebasso]

Technically, in a state of perfect calm, your body can tolerate high levels of oxygen far above the PP02 diving limit of 1.4. In a typical table 6 chamber ride for example, the pure O2 in the chamber can reach PPO2 levels as high as 3.00. Anyone who has ever taken a chamber ride can attest that you feel perfectly fine at this level. Actually, in a chamber you might not start convulsing until you hit PPO2 of around 4.00 or maybe even slightly greater. The body's response to oxygen is very strange though and is unpredictable, especially when under stress or heavy breathing - hence the tighter margins of safety when diving.

Is it possible to breathe high PPO2's when diving? Well, it has been done in the past. The macho fad of "going deep" using AIR in the 70 and 80's proved that many people can actually get close to PPO2 of 2.5 while diving, without convulsing. Guess what, many people also died while attempting this. If you consider that people have died while getting close to PPO2 of 2.5 you would be TOTALLY INSANE to use pure oxgen at 120' -- the PPO2 level would be exactly 4.636. One breath - you're dead!!

As for ascending in open water if you run out of air...
There's a reason why they teach CESA in open water scuba class. It works. Try doing a controlled swimming ascent from 70' or 80', you'll be surprised how far you can go without feeling the urge to breathe. If you do feel desparate to breathe - take a swig from your reg - you'll be surprised to find that the expanding air in the reg, hoses and tanks will provide one good and final inhalation.

Bottom line, pure O2 below 20' - BAAAAAD!

[Gibby]

Based on your questions I’m going to interject on andrebasso and recommend that you DON'T try a swimming ascent from 70 or 80 feet.

I can see that going south real fast.

[andrebasso]

Based on your questions I’m going to interject on andrebasso and recommend that you DON'T try a swimming ascent from 70 or 80 feet.

I can see that going south real fast.

IMHO, practicing a swimming ascent from within recreational limits is perfectly vaild and helps to build the OW diver's confidence. In fact, knowing that you can do it in an emergency is the best way to put an end to nonsense about breathing Argon or Oxygen...

[divindoubles]

I tried one from forty feet once, it was not all that hard. I must confess though that I took one hell of a breath before I shot maniacally toward the surface. I would hate to have started after an exhale.

[Tegg]

You may just want to focus on not running out of gas at depth.

Things like diving 1/3rds, carry AL when solo with backmount, gas management, etc...

If you run out of backgas at depth, you did more then one thing wrong already.

[bigbaldberg]

hey knitec,
while there is an abundance of reasearch in chambers, in water research is somewhat limited. the principles i argree with most are that breathing 100% deeper that 20ft is more dangerous than say breathing air at 250. the reason being is that some speculate, myself included, that narcosois actually helps defend against ox tox. high po2's are dangerous, howver canbe mitigated. some research idicates that anti anxiety prescriptions actually help prevent ox tox. the mis-firings in the brain are basically because of the added oxygen increaseing the amount of "activity" in the brain, and perhaps narcosis and anti-anxiety drugs slow down this process. i am a strict believer in 1.4 working, and 1.6 deco limits. i have however "had" to breathe gasses at higher po2's. more tothe point of your question though, my brother and i worked on a "different" configuration last year. typicaly in Guam, we can do300ft shore dives. on the mid-range stuff 130-200 we were playing with a single back cylinder and a 40ft deco/bailout bottle. the thought being if a catistrophic failure occured, we could do a CESA to the mod of the bailout, usually 40%. i tried this several times and from 200-100 with nothing to kickoff from is somewhat difficult, but do-able under most circumstances. obviously we'd prefer to share gasses and ascend slowly, but alot of our diving was solo. (i'm not interested in flames to this approach). one of my mentors lost his mid-mix gas on a "bigboy" dive and actually blended his back (15-50) with his deco (100) in his lungs in an emergency. this is not ideal, but certainly beat a cns hit. dive enough and #### will go wrong, but think through the problems and you'll survive, probably.

[Cave Ranger]

I concur with Tegg. Having to do a free assent from any significant depth is a very BAD option. Even as a new "Openwater" diver I had read enough on the subject and hung out with enough Tech guys to know that doing an emergency free assent while humming Ahhhhhhh through your Regulator was not the best self rescue plan. I bought and used a 30 cu ft Pony on every dive.
While on a Cattle Boat down in Pompano Beach this big smarmy guy thought it was funny that I felt the need to carry such a large Pony Bottle. I was the only one with one on the Boat.
Besides looking like 350 lbs of lumpy Oatmeal stuffed in a Neoprene wetsuit he had one of those 1.5 cu ft "Spare Airs" attached to his B.C. with a coily cord. Since the first dive was on the "Rodeo 25" wreck which is at around 130 fsw, I pointed out to him that if something went wrong at that depth that the only way that "Spare Air" was going to save him is if he stuck it where the Sun never shines, breaks the valve off and maybe if he was lucky it would blast him up to the surface. It was funny at the time but after the Boat was back at the dock he told me that after thinking about it he was going to upgrade to a Pony.
Carrying a Pony early on also got me used to carrying Deco bottles as I became a more advanced diver.
IMHO: Not just Tech and Cave but EVERY Scuba Diver should dive plan with the mindset of "Problems that occur underwater......get solved underwater" and equip themselves accordingly.

[JDostal]

I pointed out to him that if something went wrong at that depth that the only way that "Spare Air" was going to save him is if he stuck it where the Sun never shines, breaks the valve off and maybe if he was lucky it would blast him up to the surface.

ROTFLMAO!!!

That is the BEST description of a Spare Air I have ever heard!! HAHA!

[BillBowden]

Breathing the wrong gas at depth may be better than breathing no gas- the result will be the same, but you'll likely be unconsious when it happens.

Please continue to ask these questions- we learn when we play the "what if" game. In my early days of cave diving, that was one of the things that kept me alive.

[novadiver]

protocol says to leave the backgas reg in your mouth and wait for the gas left in your tank to expand as you ascend. This shoud give you a few small breaths.

[Jim Wyatt]

You may just want to focus on not running out of gas at depth.

Absolutely.

[kinetic]

Thanks all for the some of the useful comments.

Noting some of the comments regarding focussing on running out of gas, thanks for the pointers by the way, can I refer to the example I gave and this post followed on from my question regarding breathing inert gases in dire circumstances, that is to say a violent and sudden loss of back gas leaving gas that, under normal circumstances you would never ever dream of using in the emergency situation that I posed and some of you picked up on.

I am well aware that breathing inert gases is never ever advisable nor 100% O2 below 6m.

The thrust of the two posts was, in a really nasty situation you could be forced to take a decision to breathe inappropriate gases and I was trying to establish, whether ONE OR TWO BREATHS would be crtically bad or get you out of the situation....or as I asked.....is this an impossible question?

Thanks again.

kinetic

[Jim Wyatt]

Thanks all for the some of the useful comments.

Noting some of the comments regarding focussing on running out of gas, thanks for the pointers by the way, can I refer to the example I gave and this post followed on from my question regarding breathing inert gases in dire circumstances, that is to say a violent and sudden loss of back gas leaving gas that, under normal circumstances you would never ever dream of using in the emergency situation that I posed and some of you picked up on.

I am well aware that breathing inert gases is never ever advisable nor 100% O2 below 6m.

The thrust of the two posts was, in a really nasty situation you could be forced to take a decision to breathe inappropriate gases and I was trying to establish, whether ONE OR TWO BREATHS would be crtically bad or get you out of the situation....or as I asked.....is this an impossible question?

Thanks again.

kinetic

If I were at 100 feet with no gas except O2 & knew I could not make it to the surface without breathing something I would take a breath of it and go, quickly. If I needed 3 or 4 more I'd take them.

If its between breathing the O2 or just drown at depth, I'd breathe the O2.

[JE]

Doesn't one of our basic scuba classes teach us certain physics & laws {Boyles} that relate to our decreases of gas while descending & the increase of gas volumn during ascents-? It seems to me, that if you are at 100' & you drain your tanks dry, would you not have an additional cf of gas by swimming up an atmosphere of 7'-? I have actually proved this very point from depth {60'} by breathing my tanks dry & then ascending to 50', thereby increasing a cf of gas {air} I didn't have at 60'-! While we are restricted in a cave at depth, the concern we should have is what we are all taught in the first place: 'One third in......two thirds out-! If you are 1500' back into Little River or some place similar, & you have breathed your tanks bare, unless you have a buddy bottle w\you, your 0-2 bottle isn't going to help-!
If you are in Eagles Nest with a straight ascent up, then just maybe you'll have some gas left in your tanks.

Just a opinion

J.E. 8)

[mfascuba]

Just to add what I'll admit is a hare-brained suggestion, if a person wanted to add a LP inflator hose to the pony bottle, it could be injected into the wing and rebreathed until the CO2 blackout took over.

As was suggested, it's best to plan on not running out by planning the dive, and planning for failures, contingencies, etc.

Mark

[Cindy]

Human nature is to seek resolution to not having air by breathing. Having sucked the last out of a tank myself there are two things I can tell you. First you will breathe the first gas you can get no matter what it is and the second is that you may not even remember you have a tank of oxygen hanging on you. Hypoxia does weird stuff to your brain. Not that many dive with O2 hanging on them like your hypothetical problem but lets pretend...
You would then have a seizure and if no one is around you will drown. Will you have improved the situation? Not really. Will you be awake when you drown, most likely not. The people I have spoken to that have seizures tell me it's not all that bad until you come out of it. There is a reason the tender is in the chamber with you when you get bent. It's because if you have a seizure while on high oxygen you won't die and your family won't sue. Your tender is not on oxygen like you are.
Once you witness a few seizures you won't be quite so calm about causing one. I do have a video of a diver who did have a seizure in open water while on deco. He dropped another tank and went after it on high oxygen. He was lucky that there were well qualified people there to save his butt. It's not a pretty piece of video footage.
I'm not sure if there is a reason for these kind of 'what ifs'. I was taught that 'what if's' were a good exersize for training because they make you think. Ours were about what to do if we couldn't find the line, all our lights went out, we lost our buddy, we encountered a line arrow pointing the wrong direction, or got line trapped on the way out in zero viz. Basicly things that thinking can resolve and it gives you an idea how to configure gear, plan gas and pick buddies. This stuff of taking about how to die in a cave is just spooky to me and doesn't really have a meaningful purpose.
I am not tossing salt over my shoulder, but this whole deal gives me the shivers. Cindy :(

[Gary]

increase of gas volumn during ascents-? It seems to me, that if you are at 100' & you drain your tanks dry, would you not have an additional cf of gas by swimming up an atmosphere of 7'-?
As 33' = 14.7 psi - 100' to 0' would provide less then 50 psi of availiable pressure in your tanks. Possiably less then the volume of a spare air canister.

One record deep diver diving to 1000' and carrying many huge tanks joined together did say his gas use durring ascent from 600'(?) up to his first real stops was met by the decrease in ambient pressure. So the idea is valid even if it takes an extreme situation to derive significant benefit.

[WJH]

your dead.

http://www.sptimes.com/News/82399/Hernando/State_agency_bars_acc.shtml. . . "They signed the release - a requirement for diving at the Diepolder cave system, named for the man who owned the land - donned their cumbersome gear and plunged into the murky entrance." . . .

Why were they wearing cumbersome gear instead of the usual fashionable cave diving attire?

Reporters are so dramatic.

WJH

[Genesis]

If I had no option other than a deco bottle full of 100%, I'd take a hit (or more) off it. However, I'd expect to die anyway, and for it to be less painful in my last seconds/minutes due to the seizure which would "mask" my consciousness of the final event.

Problem is, you won't have it with you in a cave. Protocol is to drop deco gas just below its safe breathing limit, so it does not encumber you with a gas you can't safely breathe anyway.

In the ocean this situation can arise however, since in the ocean protocol is NOT to drop deco gas, since you may get blown off the wreck, away from the ascent line, etc - and if you don't have it and need it, you're screwed.

With a cave TYPICALLY you come out the way you went in (intentional traverses excepted), so most times you would not carry it with you.

[Limestone Cowboy]

I hesitate to wade into this conversation, but since I saw a particular point repeated that is in extreme error I have to....

The air in your tank does NOT "expand" as you ascend. It does not change pressure by itself either. It is a FIXED volume.

What -does- happen is the pressure differential as you ascend between whats on one side of the regulator (inside the tank), and what's the ambient pressure on the other side of the piston or diapraghm, allows the regulator to release a little more of what's left in the tank. It's why you leave the regulator in your mouth on an emergency ascent, among a few other reasons.

This is real basic OW-I stuff I thought. If you don't grasp this, you sure shouldn't be dishing out potentially life-ending advice on the internet.

Be safe, Drew

[jess]

IMHO:
You're in deep open water, catastrophic gas loss, all you have is an O2 bottle:

I'm thinking you need to get to the surface (or 20ft deco depth) quick!

Why aren't you swimming like heck for the surface- instead of locating and deploying the reg, turning on the bottle, switching regulators, etc.

You are wasting precious time! SWIM YOU FOOL!!!!!! ;-)

Given the choice of breathing O2 at depth, I'd take my chances on the back gas remaining in my wing, if I absolutely HAD to breathe.

(Obviously, if you're in an overhead environment, you're toast.)

[Limestone Cowboy]

As 33' = 14.7 psi - 100' to 0' would provide less then 50 psi of availiable pressure in your tanks. Possiably less then the volume of a spare air canister.



assuming a fixed tank pressure vs ambient point where your regs will deliver...

44.1/2640 = x/208 (double 104s)

cross multiply

44.1 * 208 = x * 2640

x= 9172.8/2640

x equals roughly 3.5 cubic feet...not a huge amount but several breaths at least

Drew

[Genesis]

Depends at "what depth". If you're seriously deep then you're almost certainly ###### - if you explosively decompress you're dead (and that's gonna HURT) if you don't hit the O2 you're dead (and you ain't gonna like it) you may as well hit the O2 and go without knowing what happened.....

May be morbid to see it this way, but what are your alternatives? Go for it? Depends. If you have the O2 its probably because you also have a nice obligation at that point in time (since you just ran out of gas, right?) which means explosive "blow and go" is not gonna be a fun way to buy it....

BTW if you're tempted to practice an emergency ascent please do it with NO inert gas load. Instructors have been known to get bent this way doing them with OW students from 20'! This is definitely a "last ditch" thing.

This is one - of many - problems I have with the "party line" when it comes to diving...... IMHO if you're going to dive in open water more than 60' deep you should have a real pony (at least a 13 and a 19 is better) - and in any overhead (real or deco-induced virtual) you need DOUBLES (or independants)

[Anonymous]

This is one - of many - problems I have with the "party line" when it comes to diving...... IMHO if you're going to dive in open water more than 60' deep you should have a real pony (at least a 13 and a 19 is better) - and in any overhead (real or deco-induced virtual) you need DOUBLES (or independants)

Ding! Ding! Ding! We have a winner.

[novadiver]

I hesitate to wade into this conversation, but since I saw a particular point repeated that is in extreme error I have to....

The air in your tank does NOT "expand" as you ascend. It does not change pressure by itself either. It is a FIXED volume.

What -does- happen is the pressure differential as you ascend between whats on one side of the regulator (inside the tank), and what's the ambient pressure on the other side of the piston or diapraghm, allows the regulator to release a little more of what's left in the tank. It's why you leave the regulator in your mouth on an emergency ascent, among a few other reasons.

This is real basic OW-I stuff I thought. If you don't grasp this, you sure shouldn't be dishing out potentially life-ending advice on the internet.

Be safe, Drew

theirs always somebody to split hairs with on the net.

leaving the reg in and waiting for another breath on ascent is the way it's done. No need to bring the science of piston VS. diaphragm regs out, it will just muddy the water

And Like some of the other members of this board have stated. You should train for gas failure (so you know how to survive) and you should use a gas management plan that will insure your (and your buddies ) survival.

Training and proper gear is the key to not getting in this situation .

[Limestone Cowboy]

It's not splitting hairs. The gas in your tank does not expand, period. It has little to do with what type of regulator either.

It really is important to know how this stuff works you know.

The rest I agree with you on.

Drew

[Gary]

It's not splitting hairs. The gas in your tank does not expand, period.
Well in the spirit of splitting hairs: :twisted:

The air in the tank does expand as it leaves the tank thru the regulator. As a closed system the total volume of the gas certainly expands - or if you consider it as an open system the gas that doesn't leave the tank "expands" to fill the void of the gas leaving the tank and the absolute pressure of the remaining gas is lower.

Not only that the `3.5 cu ft you get (from 104s ascending 100') isn't really 3.5 cuft in the tank. The volume of the gas in the tank is relatively fixed and the 3.5 cuft of gas is it's measure at STP. The tank is not at STP as it is likely still compressed to at least the ambient pressure at depth.

When considering the differential pressure reduction gained from ascent and the relative equivalent volume of gas at STP that becomes available when exiting the regulator to the diver also however consider the the gas released will expand to a larger volume at 33' then at say 66' or at 99'.

104s ascending from 100' to the surface providing ~3.5 cuft is plenty of gas to make the ascent. It is quite a few "breaths" when you consider a mean tidal volume of about 0.05 cuft X ATM but in terms of time only about 2.5 min even at 33' (3.5 cuft / 2 ATM / .7 cuft/min SAC). That is neglecting the acent and the fact you don't have the full 3.5 to work with because you haven't fully ascended to the surface yet.

For that matter spare air generally come in 1.7 3.0 and 6.0 cuft canisters (3.0 is standard). So it is still less then one might get from a spare air.

Enough for a controlled ascent but not much more. Still better to avoid running out of air in the first place. ;)

OK - I'm done :) :twisted:

[Genesis]

ONE breath on the way up from 100' to the surface is probably enough IF you don't care about ascent rate.

The problem is that you do..... especially if you just ran out of air, as that is likely accompanied by a fairly significant inert gas load. Very rapid removal of the pressure on your body is going to lead to you having a very bad day.....

Adding to this is the paradox that high-performance regs actually make detecting an imminent OOA situation very hard. They breathe REALLY WELL down to 150psi over ambient pressure - unlike the unbalanced regs that start to get tough to suck on at 500psi or so. You can basically suck a tank to near-vacuum before you get any warning at all with most high-performance regulators.....of course if you run out of gas, who's fault is it that you were not looking at the gauge?

The more serious potential event is one that results in NO air being available. The most obvious example is a blown low pressure hose (or turret on regs that have them), which will immediately drop the IP to zero and render any second stage on that post instantly worthless. Even if you can shut off the tank and preserve some of the contents you can't get to it through that first stage any more.....

I have extremely serious "issues" with the various agencies over many aspects of so-called "dive training", which, due to the rules here, I can't be explicit about. However, this is one of the more obvious - is it REALLY that hard to teach people to rig a pony as a stage and dive it? No. Does it put into what I believe is the proper perspective what is the only TRUE emergency underwater (nothing to breathe!)

YES.

Problem is, putting it into that (proper) perspective detracts from the "diving is as dangerous as bowling" mind-set that many in the industry seem hellbent on promoting......

[skip]

From 99 feet the air in your lungs will expand four times the size. that's equivalent to 4 breaths (albeit reduced O2 each time). having done this, i can say that there is no urge to breath, but a very real urge to exhale. you won't even think of inhaling and do not need to go faster than 60ft/min and do not need the air in your BC (which you dump as fast as you dump your lung air/gas). and if you are diving with a buddy he will be there when you hit 15 feet and will lend you a reg for the safety or decompression stop. if not you can then switch regs and take a breath of the O2 you are carrying and figure out what to do from there.

if i had to breath o2 at depth or drown, i'd go for drowning. same for violating decompression. some have been revived after many minutes beyond the 8 they say is brain damage (with no ill effects), but few have managed to violate required deco without very painful death. I am assuming that deco obligation is signficant of course.

[IowaCaveDiver]

this is why when in open water I like to carry a 50/50 deco mix so that if I had a situation like this, I could do a rapid ascent but only to 70' so I could get on that gas, rather than shoot to 20 to get to my 100% bottle. Unfortunatly my computers don't like the deeper stops as much, but I think the gas exchange is better at that depth and helps me to complete a much safer deco schedule.

-Matt

[Dan Thoms]

100%O2 at depth=death
Run times to 1/3rd of your gas, or less, if some of your deco is on back gas. If you dont have the gas needed, you better have a buddy. Or a "buddy" bottle, so you will never need the O2. Life is to important to play the guessing game. Plan your dive, and dive your plan


My opion

[kinetic]

Thanks all.

The posts were much appreciated. The question was posed as an open water question but as this forum is frequented by many well experienced divers I thought I would drop it in.

Regards.

kinetic

[Drmike]

what could/would happen if say, you had to take one or two breaths from a 100% stage bottle at depths below the recommended for 100%.


If it was just one or two breaths probably nothing, see answer below from Dr Bill Hamilton to a similar question I asked him.

"A 3 second breath of O2 every 7 min or so will not be a toxicity threat. This would be true for up to 11 bar as long as the exposures are short.
Best to avoid this need, however. "

There are obviously very good reasons not to do this and it would have to be a VERY bad day out if you had to BUT when your life can depend on it you should have the best knowledge in order to decide what best to do.

Some amazing #### can happen sometimes that you would never imagine could all happen at once and despite the best of planning it is 'possible' that you may end up in the crazy sitiation that all you have access to breathe is 100% (anything is possible)

Basically 100% at depth does not (necessarily) equal death. Can it? Yes, but its not a certainty.

I breathed 100% whilst ascending at a controlled rate of around 20m/min from 72m up to 32m with no ill effects.

Why? Because I had no other choice!!! :-D

[Genesis]

That's pretty much it.

If you have to, you have to. If you die, well, it was your day...... at least an O2 hit will likely leave you unaware of your demise, as opposed to some of the other alternatives....

[Duncan Price]

I breathed 100% whilst ascending at a controlled rate of around 20m/min from 72m up to 32m with no ill effects.

I have (stupidly) run out of air at 14 m in a cave. Fortunately I had an (almost) direct acesnt to air. As I ascended I got another lungful out of my regulator as the amibient pressure reduced.

I have also (stupidly) breathed O2 in same cave at same depth. Had all the syptoms of an incipient tox - story on here somewhere. Not good. I witnessed another regular poster here get onto O2 too deep with the same symptoms I had. Being on a "hot" mix like having too high a ppN2 is a useful experience but not one I would deliberately seek.

However, when the doo doo is in the AC. Any gas is good to breathe. Call it "Plan Zed".