Oxygen saturation point question

[Soarhuff]

My dive computer i300 Aqua lung for nitrox diving shows in the log oxygen saturation % - and on a deep
dive to 115 ft the dive recorded my saturation number as 17? what does this 17% I assume mean and is
it calculated automatically and alarm I dont set will go off at 100% saturation?

 

[iamrushman]

that's your Oxygen saturation,,,you have 17 "O2 units" and you get 100....so dive on my friend.

 

[rsingler]

Oxygen "rusts" stuff, including your lungs. The "partial pressure" of oxygen at sea level is 0.21 atmospheres. At 99 feet, it is .21 x 4 atm = .84
As discovered in Intensive Care Unit patients, being on over 50% oxygen (ppO2 0.5) for days at a time is irritating/toxic to the lungs. A scale was developed to limit oxygen exposure with this in mind. Divers who regularly dive deep try to keep their oxygen exposure below 80. If on a dive trip where repeated exposure to higher ppO2 keeps the oxygen number high'ish, then it's common to take a dive break every five days.
When you learn to dive with Nitrox, you'll discover that you trade decreased nitrogen for increased oxygen. You cannot dive as deeply on nitrox as on air, because in addition to the oxygen exposure limits you discovered on your computer, oxygen is also acutely toxic above a partial pressure of 1.4-1.6 atmospheres (not a DEPTH of 1.4-1.6 atmospheres, unless you're diving with 100% O2). So diving with Nitrox 36 (EAN36 = 36% oxygen) limits your dive to 95 feet.

Great question!
Yeah, with 17, you're just fine. It'll drop quickly in 4 hours.

Diving Doc

 

[Akimbo]

@rsingler

Nicely stated. To expand a bit for other divers: Oxygen "saturation" is a confusing choice of words since gas saturation in the diving context is normally associated with tissue saturation. Something like Oxygen Clock or Limit would be a better choice to label that parameter. For all practical purposes, tissue doesn't "saturate" on oxygen like it does with Nitrogen because the cells metabolize it too fast.

 

[PfcAJ]

Oxygen "rusts" stuff, including your lungs. The "partial pressure" of oxygen at sea level is 0.21 atmospheres. At 99 feet, it is .21 x 4 atm = .84
As discovered in Intensive Care Unit patients, being on over 50% oxygen (ppO2 0.5) for days at a time is irritating/toxic to the lungs. A scale was developed to limit oxygen exposure with this in mind. Divers who regularly dive deep try to keep their oxygen exposure below 80. If on a dive trip where repeated exposure to higher ppO2 keeps the oxygen number high'ish, then it's common to take a dive break every five days.
When you learn to dive with Nitrox, you'll discover that you trade decreased nitrogen for increased oxygen. You cannot dive as deeply on nitrox as on air, because in addition to the oxygen exposure limits you discovered on your computer, oxygen is also acutely toxic above a partial pressure of 1.4-1.6 atmospheres (not a DEPTH of 1.4-1.6 atmospheres, unless you're diving with 100% O2). So diving with Nitrox 36 (EAN36 = 36% oxygen) limits your dive to 95 feet.

Great question!
Yeah, with 17, you're just fine. It'll drop quickly in 4 hours.

Diving Doc

The oxygen “clock” (0-100%) is not the same thing as Oxygen Toxicity Units.

OTUs attempt to measure the effect of increased po2 on the lungs. The “clock” (which is what’s being discussed here) attempts to measure CNS toxicity.

 

[rsingler]

The oxygen “clock” (0-100%) is not the same thing as Oxygen Toxicity Units.

OTUs attempt to measure the effect of increased po2 on the lungs. The “clock” (which is what’s being discussed here) attempts to measure CNS toxicity.

Absolutely true, but beyond the scope of Basic Scuba Discussions. Suffice it to say that there is a time-weighted toxicity of oxygen that has both CNS and pulmonary components. At one end you have acute seizure activity as you exceed some PPO2 over 1.4 depending upon multiple factors. At the other, you have chronic pulmonary effects from oxidative change.
And then you have the NOAA oxygen clock, which was designed to cumulate possible CNS effects. Those effects are less precise than the one-stop limit of 1.6 atm. However, at the same time, we also have the onset of pulmonary changes which, I agree, were not designed into the CNS clock. Nonetheless, they exist, and begin early.
As an overly simple answer to a complex question, I chose to conflate the two.

For a far better discussion, and one which does not spend time on the pulmonary side, but which restricts itself to the CNS clock and CNS symptoms, see this excellent DAN summary:
OXTOX: If You Dive Nitrox You Should Know About OXTOX — DAN | Divers Alert Network — Medical Dive Article

 

[Compressor]

Others have given great explanations. RSIngler on the spot and so is Akimbo.
Wish they would use a different term. Oxygen saturation is a medical term used to describe the saturation of the hemoglobin molecule (blood). Normal is 96-100%.
They should have picked another term for goodness sakes.

Link to O2 Saturation on Wikipedia.

 

[Akimbo]

Is Nitrogen or diluent gas saturation of tissues an advanced subject or is it discussed in OW training? Is Nitrox training considered a basic or advanced topic? (true question, not facetious at all)

@compressor
Good point about the use of Oxygen saturation in the medical setting. I always thought of saturation in terms of commercial diving before joining ScubaBoard. It is interesting how the language evolves.

 

[runsongas]

depends on the instructor and the length of the ow class i imagine. when i did ow, tables were covered which included nitrogen tissue saturation determining NDL limits and offgassing/ongassing for surface intervals/repetitive dives. nitrox was not covered so OTUs and CNS clock were not covered as part of OW. got covered separately in the nitrox class.

 

[hhmoore]

Others have given great explanations. RSIngler on the spot and so is Akimbo.
Wish they would use a different term. Oxygen saturation is a medical term used to describe the saturation of the hemoglobin molecule (blood). Normal is 96-100%.
They should have picked another term for goodness sakes.

Working in my field, I deal with O2 saturation daily; so I was preparing to comment when I saw your post. Yes, O2 sat is a very real thing, and somewhat different from the context used here... but so is pO2. I struggled with the terminology when I took my nitrox course, because the information didn't make sense. (It was in conflict with things I've known and practiced for 30 yrs)