New CNS oxygen exposure limit for 1.3 atm
- Thread starter Dr Simon Mitchell
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"Resting" was defined as an RMV under 22.5 L/min (0.8 cuft/min). That's effectively my whole dive, even when kicking into the flow into Ginnie.
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Tassi Devil Diver
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Interesting to note that from the paper (Figure 1) according to US Navy testing a PO2 of 1.3 has a 0% chance of CNS toxicity, with the Navy establishing an arbitrary limit of 240 minutes at 1.3 because of potential onset of pulmonary toxicity.
pisauron
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pisauron
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OP
Well guess we just keep doing our usual stuff then.
You are welcome to keep doing your "usual stuff". However, if you want guidance that is actually evidence based and that allows you to perform prolonged technical dives that were previously in breach of the prescribed limits, then you might want to consider staying at 1.3 and following the new guideline. You will probably be safer too. I am sure that technical diving instructors will welcome the opportunity to teach dives that don't violate recommended limits.
Further to rjack's comment, virtually all the questions you have asked on this thread are answered in the paper.
selfdiver:
Just to be clear, the new 1.3 limit is not 240 minutes, it is 480 minutes but with no more than 240 minutes of working dive. In fact, in most deep technical dives the vast majority of the dive is spent on resting decompression.
All of the inspired PO2 levels you cite other than 1.3 probably need adjustments in the limits, but we lack the evidence to do this objectively. We felt we had enough to do it for 1.3 but nothing else. As we say in the paper you could apply the new 1.3 limit to any PO2 lower than 1.3 with confidence that it would be even safer. Above 1.3 we just don't know, and again, as we say in the paper, we were not in the business of replacing guesswork with more guesswork.
On the subject of pulmonary oxygen toxicity (a similar issue to that raised by Mobulai), what we are saying is that if you take advantage of the new 1.3 limit to perform longer dives, there is an increased chance that you will encounter symptoms of pulmonary oxygen toxicity. Yes, in those long 1.3 exposures we would expect pulmonary symptoms to be more prevalent than convulsions. However, to our knowledge, there has never been a diver who suffered permanent lung injury from pulmonary oxygen toxicity, and so long as you allow any symptoms that appear to resolve between dives it should present no long lasting hazard.
Simon M
pisauron
Contributor
No doubt about it! It's just easier to ask directly the info I (and maybe others) want. Thanks.
Current critical care guideline on mechanical ventilation suggests maximum 12 hours on 100% FiO2, is it possible to extrapolate that as PO2 1.0 is safe for 720 minutes? Seems reasonable compares to the 1.3 for 480 minutes in this study.
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