CNS Oxygen Exposure Tables

[loosenit2]

Have been doing research on CNS Oxygen Exposure over the last two days. I understand that most computers do CNS Oxygen Exposure calculations *live* for you while diving, but I wanted to understand the underlying math and algorithms that they use.

Of particular interest to me was the difference between the PADI Oxygen exposure table and the more detailed multi-level calculations that my computer appears to be doing. The PADI table just lists a highest PP02 and the max dive time allowed. This would force one to use a square profile for the dive. The computer appears to do a multi-level dive calculation giving credit for shallower depths.

The best reference that I have found is the NOAA Divers Manual, Chapter 3 which gives % saturation calculations for various PP02s in 5 minute intervals. This would allow one to calculate Oxygen saturation in multi-level and repetitive dives manually

As I researched the Shearwater algorithms it appears they have extrapolated the data in the NOAA 5 minute interval tables to do live calculations.

Two questions:

1. Do other computer manufacturers do the same thing?
2. Is there a published table somewhere that shows the data with a data interval of less than 5 minutes?

 

[ChuckP]

Take a program like MultiDeco, a planning software, play around with run times and deco gases and you can almost see the math is way out to lunch at high levels - the math they use that is - other planning software doesn’t match up either.

In rec diving, it’s hard to worry about it. The deco diving is different though.

 

[EFX]

Check this paper out by Erik Baker, P.E.
Oxygen Toxicity Calculations:

 

[rjack321]

Check this paper out by Erik Baker, P.E.
Oxygen Toxicity Calculations:

The formulae are perfect.
The output is almost useless sadly.

 

[Graeme Fraser]

Have been doing research on CNS Oxygen Exposure over the last two days. I understand that most computers do CNS Oxygen Exposure calculations *live* for you while diving, but I wanted to understand the underlying math and algorithms that they use.

Of particular interest to me was the difference between the PADI Oxygen exposure table and the more detailed multi-level calculations that my computer appears to be doing. The PADI table just lists a highest PP02 and the max dive time allowed. This would force one to use a square profile for the dive. The computer appears to do a multi-level dive calculation giving credit for shallower depths.

The best reference that I have found is the NOAA Divers Manual, Chapter 3 which gives % saturation calculations for various PP02s in 5 minute intervals. This would allow one to calculate Oxygen saturation in multi-level and repetitive dives manually

As I researched the Shearwater algorithms it appears they have extrapolated the data in the NOAA 5 minute interval tables to do live calculations.

Two questions:

1. Do other computer manufacturers do the same thing?
2. Is there a published table somewhere that shows the data with a data interval of less than 5 minutes?

The PADI Tec40-45-50 manual does include CNS % and OTU unit per minute tables. Students are expected to use these to accurately complete a dive plan with various depths including average ascent, deco and gas switch.

 

[loosenit2]

Check this paper out by Erik Baker, P.E.
Oxygen Toxicity Calculations:

thank-you. This article would seem to confirm that all the computer is doing is using the NOAA table data and extrapolating for points that are not explicitly stated using a linear function and straight line connections between the known data points. It does give a methodology to do this manually if I wanted which is what I was looking for.