Very high PPO2

[Dr Deco]

Dear Readers:

Deep Oxygen

folks have breathed oxygen in a chamber at quite high pressures for very short durations. These were studies to determine the limits. They were always too variable for any use with scuba gear.

There was a finding by JBS Haldane (JS Haldane’s son) that he found to be interesting, namely, that oxygen at 5 - 6 atmospheres of pressure tasted like ginger beer! Estimates of “safe” duration for that pressure are about three minutes.:wacko:

Dr Deco :doctor:

Readers, please note the next class in Decompression Physiology :grad:
http://wrigley.usc.edu/hyperbaric/advdeco.htm

 

[Coral_reef]

:doctor:

check:
http://sportsillustrated.cnn.com/si_online/covers/issues/2003/0616.html

 

[DA Aquamaster]

Tom Mount did a lot of early deep air diving and set the air record at 360 ft in 1965.

However, Brett Gilliam was the guy who went to 452 ft in Feb 1990 and wrote no s__t on a slate reminding him to stop. He also answered questions on another slate including what day is it? what time is it? and math problems like 3x10x22. In 1993 he went to 475 ft on air.

Dr. Dan Manion went to 509 ft in 1994 on air but blacked out and remembered nothing until he found himself ascending. He had however been to 490 ft the day before without problems. As far as I know this is still the record depth on air.

Both Gilliam and Manion used a series of adaptive dives to 300 ft plus to work up to their record dives.

 

[Charlie99]

mello-yellow once bubbled...
At 295 feet the pressure is 10 ATA, and PPO2 is 2.1 ATA. What is the maximum exposure time for that? (My Nitrox table goes only as high as 1.6 ATA)

I don't know the source for their choice of numbers, but the Oceanic Data Plus has 11 minutes of allowable time at 106', EAN50 -- ppO2 of 2.1.

 

[Saturation]

You'll find a detailed discussion on pp02 limits and oxtox by doing a search on this eboard.

In general inwater exposures at pp02 > 1.2, the more likely the onset of convulsions become, above 3.0, its too high too be of any practical concern and is to be avoided, period. The onset of convulsions could be in minutes past 3.0, and depends on co-factors, such as stress and c02 buildup.

Deep air has the benefit of sedating the subject to reduce the co-factor components of stress and CNS excitability. Thus, properly conditioned to deal with the narcosis, many divers can routinely dive deep air to about 300' and reach higher pp02 levels on AIR. Doing the same pp02 limits with trimix, with its reduced narcosis, is risking the pp02 exposure.

Most deaths from deep air have been due to the confusion caused by the narcosis.

 

[BigJetDriver]

Saturation once bubbled...
You'll find a detailed discussion on pp02 limits and oxtox by doing a search on this eboard.

In general inwater exposures at pp02 > 1.2, the more likely the onset of convulsions become, above 3.0, its too high too be of any practical concern and is to be avoided, period. The onset of convulsions could be in minutes past 3.0, and depends on co-factors, such as stress and c02 buildup.

Deep air has the benefit of sedating the subject to reduce the co-factor components of stress and CNS excitability. Thus, properly conditioned to deal with the narcosis, many divers can routinely dive deep air to about 300' and reach higher pp02 levels on AIR. Doing the same pp02 limits with trimix, with its reduced narcosis, is risking the pp02 exposure.

Most deaths from deep air have been due to the confusion caused by the narcosis.

Doc,

I may not quite be understanding your comments as stated above!

A generalized and conservative PPO2 setting for the rebreather community is 1.3 PPO2, tending higher on deco (but not above 1.6) and lower with deep missions and long dive times due to both the CNS and OTU clocks.

Divers have been much deeper on air than 300 fsw, but the general consensus is that for many reasons, doing deep air diving is NOT a good idea! "The Last Dive" by Bernie Chowdhury relates a perfect example of why not!

Trimix, blended for your MOD, with the proper amounts of oxygen, helium, and nitrogen will reduce the narcosis effect, lend mental clarity, and REDUCE the chance of oxygen toxicity (due to the lower than normoxic O2 FRACTION).

When you were talking about trimix, were you saying: "...trimix with the same O2 fraction as AIR?" I don't believe you would ever want to do that for the depths you are descibing, would you?

 

[JohnStrr]

******KIDS DO NOT TRY THIS AT HOME********


The article on deep air diving, http://www.saudidiving.com/deep-air.htm , mentions the WAH-WAH effect. I totally don't recommend this but if anyones interested this is something you can experiance without diving, in case you want to be mentally prepared for it or something (it being Sht hits fan), by rebreathing and finally holding a few lungs worth of N2O (nitrous oxide). I'll leave out where to find it for the safety of the young readers. The effect can REALLY screw up any sort of cognition that you had going on, STOP all vision and hearing, and generally screw you up. I've done this, in my past days of stupidity, I can see how it could be lethal at any depth (or on land).

 

[Saturation]

HI BJ:

On reading the quote of what I wrote it makes it appear that I favor deep air, my apologies. I do not favor deep air, but more specifically, long decompression dives on air or nitrox
[long defined as deco time greater than bottom time]. What I was referring to was the value of high ppN2 in protecting against oxygen convulsions, but traded off for narcosis.

Trimix is preferred because of more predictable properties of He. Making fatal errors under narcosis and the risk of suffering dysbaric osteonecrosis, DON, are greater diving decompression with a higher fraction of N2 in the breathing mix [DON risk rises if one does not decompress 'cleanly'.]

Before trimix, there were few reports [if none at all ] of 02 convulsions on deep air between 200-300'. However, its common to hear convulsions on trimix at the 200-300' range if pp02 >= 1.4, reinforcing the idea that ppN2 protects against convulsions.

Unlike trimix, deep air is a 'standard mix' of 21% 02 and ~ 79% N2. No well trained trimix diver would dive 21% 02 in trimix between 200-300', ... this is what I mean by the quote: ... Doing the same pp02 [of air] with trimix's reduced narcosis, is risking [convulsions]with the pp02 exposure.

As you said, older divers have dove deep air beyond 300' [pp02 of 2.1] , where the pp02 are exceeding toxic and in other breathing gases, would almost gaurantee o2 convulsions, yet 02 convulsions on deep air is rare indeed.

In long rebreather dives reported to me, there have been episodes of vision changes persisting for weeks after an exposure to pp02 >= 1.3. Whether this leads to permanent eye changes is unknown. Thus, pp02 of 1.3 maybe just on the threshold of sustained whole body toxicity and it maybe useful to reduce it further to <= 1.2 as recommended by Dr. Vann in the early 1990s. There is a report in Medline of the same phenomenon:
http://www.ncbi.nlm.nih.gov/entrez/...ve&db=PubMed&list_uids=10353183&dopt=Abstract