Oxygen Toxicity Discussion

[raftingtigger]

I think you are confused about the purpose of this forum. The sort of useful discussion we are having is the only valid reason to dissect an incident like this.

Oh I understand, and wholeheartedly agree with, the purpose of this forum. I was trying to get this particular thread to go back to information - if there is any more - on the specific accident and what we can learn from it.

The initial discussion on oxtox, pulmonary ox toxicity, and other problems with deep air were right in line with the initial speculation on the accident. The thread has evolved into really a discussion on deep air and oxygen toxicity and really should get split off into its own thread. There is a lot of good information being passed back and forth.

The comment on 'fantasy' may have been unwarranted, but several posts in the last few pages are so far from anything reasonably likely that the word 'fantasy' just slipped out. Every time I make a post part of me wonders if I have stuck my foot in my mouth. I may have with 'fantasy'. OTHO, there are several posts within this thread that demonstrate either a momentary brain lapse, or a disturbing lack of understanding of nitrox, narcosis, nitrogen loading, and what oxtox is that begged correction or at least looking at some numbers.

 

[peterbj7]

I do feel there is quite a lot of alarmist talk here. For normal warm water recreational O/C scuba I generally observe the 1.6/1.4 limits, though I have in the past taken my pO2 up to maybe 2.5 for short spells. I have never had any ill effects, though obviously I don't recommend this to others. I don't drink alcohol or smoke and I ensure I am well hydrated before I dive. A friend routinely dives to 109mtr in a very cold flooded quarry on air (max pO2 over 2.3) and has had no problems. He is however in his 20's and very fit, and he also hydrates well before diving and also doesn't smoke.

I have experienced chest irritation on long CCR dives and for any dive that is likely to exceed say 150 mins I dial back my pO2 to 1.3 or for multiple dives 1.2. I can still feel the irritation, but it's manageable at those levels.

 

[Kevrumbo]

Re-posting & quoting Joel Silverstein's anecdote post on extreme PO2 Exposure:

. . .We removed the Exceptional Exposure Oxygen tables from the NOAA diving manual 4th editon because there was fear that if the general public saw them printed that they might take it as an endorsement to use them.

The NOAA exceptional exposure limits are set for extreme emergencies only and are not for routine use. IE: should be used for life saving only.

These are for a working dive meaning with lite exertion. Remember that there are a variety of factors that come into oxygen toxicity, and crossing the 1.6 atm 45min line does not guarantee convulsion, it also does not guarantee it won't.

NOAA OXYGEN
EXCEPTIONAL EXPOSURE LIMITS
PO2 Minutes

2.8 5
2.4 10
2.0 30
1.9 45
1.8 60
1.7 75
1.6 120
1.5 150
1.4 160
1.3 240


As you can see the exceptional times allow you a fairly large margin to use this method for an "escape." The table is NOT linear. Note that exceptional exposures are DANGEROUS and can only be done once in a day. . .

My personal physiological deep air depth limit was a solo dive descent approaching 60m in the Nagano Maru's cargo hold, Truk Lagoon 2007: Started seeing the "starfield simulation Windows screen saver" all around me, which at the time I thought was due to the severe nitrogen narcosis at 7 ATA ambient pressure (immediately ascended out of the cargo hold and stayed on the deck around 45 to 51m for the duration of the dive). In retrospect, the effect could also have been the beginning symptoms of an Ox-tox event just as well (PO2 at 1.5 ATA). . .

 

[Rich Keller]

Chances are if the morons have grey hair they learned about O2 tox in basic scuba 40+ years ago when they taught theroy and physics before we got in the water.

That is when I learned about it. When I went into commercial diving ten years later we also took an O2 tolerance test. Some people are more susceptible to oxygen toxicity just like there are people who are more susceptible to nitrogen narcosis. This test was used to weed out those who were naturally at greater risk.

---------- Post added June 2nd, 2013 at 06:23 AM ----------

If that were true, Nitrox would hardly be worth the bother...

I do not think Nitrox is worth the bother. It was originally intended by NOAA to be used on decompression stops. It was never intended to be used at greater depths. According to the people I talked to at the NEDU the increased risks of using Nitrox far out weigh the benefits.

---------- Post added June 2nd, 2013 at 06:40 AM ----------

One of such medications that make you more susceptible Ive been told is a very popular one called Sudafed - dont know if that holds true though..

I have never heard that before but I do not use Sudafed for another reason, it can be addictive if used improperly. Actifed is a much better choice.

---------- Post added June 2nd, 2013 at 07:23 AM ----------

A lot of the posts here start with detailed talk about 1.2 vs 1.4 vs 1.6 but usually end with words like probably, should be, maybe, I think it is ok. Seems to be a lot of gray area there and no discussion about the tables themselves. Most of these tables, like the Navy tables were designed for men in their 20s and in good physical condition. Last time I was on a dive charter I did not see too many people that fit into that category. While your calculations maybe 100% correct on paper, in the water it is a different matter if you are not in the group these tables were designed for. My feeling about Nitrox is that it is being used to narrow the safety margins in order to increase bottom time. In my opinion that is an increased risk that I see no reason to take.

 

[DCBC]

My recollection from Nitrox training and review of DAN research is that there have been isolated cases of convulsions and/ or blackouts at ppO2 as low as 1.4, with higher frequency (though still low probability) of toxic effects at ppO2 of 1.6. My recollection is that the recommended maximum ppO2 level for Nitrox diving is 1.2.

Toxicity of O2 will depend on the pO2 and the time of exposure. It's important to note that we are all biologically different and some individuals will have more defenses against O2 radicals than others. A person's defenses against O2 radicals change from one day to the next. We therefore have marked differences in sensitivity to O2 radical damage in different people and on different days in the same person.

The maximum PPO2 recommended has changed over the years and between different certification Agencies (and between levels of certification). Generally a 1.4 is recommended with 1.6 as a maximum.

... Is Oxygen toxicity risk covered now in the OW or AOW classes?

It is mine.

 

[boulderjohn]

Is Oxygen toxicity risk covered now in the OW or AOW classes?

In PADI OW classes, divers are taught not to use nitrox without further training becaseu of the risks of increased oxygen exposure. They are also taught not to dive below 60 feet without further training. They are also taught that the depth limit for all recreational divers is 130 feet. PADI OW students may elect to use nitrox on their 4th training dive, and if they do, the risks associated with increased oxygen exposure are explained in more detail.

All of that has been true as long as I have been an instructor.

 

[vladimir]

I have never heard that before but I do not use Sudafed for another reason, it can be addictive if used improperly. Actifed is a much better choice.

The Actifed I have in my hand contains triprolidine hydrochloride (2.5 mg) and pseudoephedrine hydrochloride (60 mg). But this is Singapore, and we don't have meth labs. The Actifed you buy in the States probably has chlorpheniramine (4mg) and phenylephrine (10 mg). I use chlorpheniramine to put myself to sleep when I have mild insomnia.

"Actifed" is too inexact a description, and it may cause unwanted drowsiness in a diver (or somebody operating heavy machinery ).

A lot of the posts here start with detailed talk about 1.2 vs 1.4 vs 1.6 but usually end with words like probably, should be, maybe, I think it is ok. Seems to be a lot of gray area there and no discussion about the tables themselves. Most of these tables, like the Navy tables were designed for men in their 20s and in good physical condition. Last time I was on a dive charter I did not see too many people that fit into that category. While your calculations maybe 100% correct on paper, in the water it is a different matter if you are not in the group these tables were designed for. My feeling about Nitrox is that it is being used to narrow the safety margins in order to increase bottom time. In my opinion that is an increased risk that I see no reason to take.

I use nitrox to maintain my safety margin and increase my bottom time.

 

[DandyDon]

I do not think Nitrox is worth the bother. It was originally intended by NOAA to be used on decompression stops. It was never intended to be used at greater depths. According to the people I talked to at the NEDU the increased risks of using Nitrox far out weigh the benefits.

For a recreational diver doing square bottom wreck dives, it gives 50% more bottom time. For multi-level reef dives, questionable. I've heard many dive ops spout questionable claims for inflated priced tanks.

I have never heard that before but I do not use Sudafed for another reason, it can be addictive if used improperly. Actifed is a much better choice.

Huh? Exact same stuff, in speaking of the original OTC meds. The original formula for Actifed & Sudafed contained pseudoephedrine hydrochloride (PSE) 60 mg as the nasal decongestant and triprolidine hydrochloride 2.5 mg as the antihistamine. Other brands available behind the counter that use the old formula include Genac and Aprodine. The American pharmacy chain Walgreens produces a house-brand version of Actifed, Wal-Act, which uses the original pseudoephedrine/triprolidine formula. Around here, I get a better buy on Aprodine than Wal-Act and will keep up to the 300 count max allowed in some states in case Texas or the feds ever makes it more difficult to obtain.

New formulas of Sudafed & Actifed usephenylephrine HCl 10 mg as the nasal decongestant, and are almost worthless in my opinion - but have no place in a OxTox discussion. It's the PSE that is rumored to maybe increase risk.

 

[wedivebc]

One observation I have made WRT O2 toxicity is back in the day lots of people were going deep on air, and sustaining PO2 levels far above what is considered safe and it was very unusual to hear of deep air divers going into convulsions (deep water blackout is another possibly related thing though).
Recently there have been reports of CNS incidents occurring at much lower PO2s including one that may have involved sudafed and a PO2 of 1.4.
There was a school of thought that believed part of the reason many people survived high PO2 when diving deep air was that nitrogen was CNS suppressant. Whereas sudafed is a CNS stimulant and the trend these days is to avoid higher levels of PPN2 perhaps we should consider lowering the safe levels of PO2 for the working part of the dive. I personally will continue to bump PO2 to 1.6 or so when doing deco.

 

[DandyDon]

Again, using the brand name "Sudafed" can lead to confusion since they put that name on their new formula - and anything else they can sell. The questionable drug is pseudoephedrine - from which they took the Sudafed name back then.