Oxygen Exposure Limits

I am trying to establish the origins of the current US Navy, NOAA and Royal Navy oxygen exposure limits. I have read 'Oxygen and the Diver', which I thought had answered pretty much all my queries, but then I came across and article by Tom Mount

Here

in which exposure limits of 1.8ata for the US Navy are mentioned. Oxygen and the Diver only mentions the fall from 2.0 to 1.6, plus I know (I think!) the US Navy have since lowered the upper limit to 1.3 ata.

Does anyone know of any publication that will clarify the different limits that any/all of the organisations mentioned above have used and when? Web sites, reports, journals, anything that would provide a history of oxygen exposure limits would be incredibly helpful to an increasingly desperate student!!!

My advice is to repost this in the general discussion area.That's where it's most likely to be seen.There are some US navy divers on the boards and one of them is "Deep Sea".Check his profile out and email him.He may be able to help.Most of my experience with scientific findings is that there are some for and some against.The levels are always changing and very few organisations agree in set levels.
Trained Navy divers dive beyond the limits you and I do so their levels are at a higher tolerance.Which is why I was surprised to read 1.3 atms partial pressure.I can't imagine that as right.Maybe there were some diving injuries in nitrox that the navy had to make them so conservative.That may be a good starting point.Nitrox injuries posted on the internet? It's not much but maybe it will help.
Cheers,
gasman

Which discussion area? I shall look for 'Deep Sea', but I really don't now which board you mean for me to re-post my enquiry.

I know I'm missing something here, but it has been a long week (and its only Tuesday).

Sarah,
Recommend you go to the source:
http://www.nedu.navsea.navy.mil/
Pose your question there.
Good luck.
Rick

Sarah:

Greg possibly means the Dr Deco or Medical FORUM. I do not actually know of any reference to the recent oxygen limits.

Oxygen is always toxic to the body, but this is controlled by the scavengers of “reactive oxygen intermediates” or ROI. These scavengers are enzymes (e.g., catalase, super oxide dismutase) produced by the body and present in limited quantities within the cells. These quantities are sufficient to counter any effects when the oxygen is present at normal atmospheric pressure.

When we dive, the oxygen partial pressure is increased, and these ROI increase in concentration. The protective systems can become overwhelmed, and obvious effects of oxygen toxicity appear. These can be either pulmonary or central nervous system effects.

The central nervous system effects (on the brain) are governed, in addition, by the amount of blood flow that actually reaches the brain tissue. This flow is regulated by carbon dioxide. The more carbon dioxide, the greater the blood flow to the brain. [The reverse is also true. In fact, the reason that one feels lightheaded when they breathe rapidly is that they “blow off” CO2 from the blood and reduce blood flow (and thus oxygen) to the brain. It is paradoxical that breathing rapidly (and oxygenating the blood) should produce an effect of low oxygen - - but it is true.]

Now, when breathing oxygen at increased partial pressure, a strong controlling factor is the level of carbon dioxide in the blood. When moving around, such as swimming, the muscle activity can raise the level of CO2 in the arterial blood and increase the flow of oxygen to the brain. This in turn, leads to increase brain tissue O2 levels and increased change of CNS toxicity. When being treated in a hyperbaric chamber, the individual is resting , and CNS effects are very rare even though the partial pressure of O2 might be 2.8 atmospheres.

It is possible that the allowable limit for oxygen for active underwater swimmers is being revised when problems are found to occur. I do not have any specifics and can offer only this general scientific background.

Dr Deco

Rick and greg,

Re: NEDU and US navy divers ...

"rainreg", one of our "forum regulators" is a US Navy Diver and just happens to be one of those SAT Divers (human guinea pig. I just finished calling and talking to him actually at the NEDU, where he has been for the past 20+ years. If ya ever need to ask him a question he would be happy to help.

=-)

Lots of help!

Thank you very much for replying to my query.

I actually e-mailed the NEDU this morning, but was only able to send it to a general address as I didn't know who to contact. Therefore I have just e-mailed rainreg and sent him a copy of the text that I sent in hope that he can shed some light on my problem.

Thanks again for your messages and any further flashes of inspiration will be greatly received.

Cheers

Sarah

I have been looking through the older posts to get current on all the information that has been posted heretofore.

This thread on oxygen limits is quite interesting.

NAUI refers to the NOAA limits in their teaching standards. At least, the last time I checked, they do.

NAUI's general ppO2 limit is 1.4 and for decompression I believe it is 1.5 . Unless that has changed.

Sarah's historic references are quite interesting as well, although the link did not work anymore. I found it on Google instead.