Altitude Diving And Nitrox

[Blueringocto_73]

My thinking on the subject is that these certifications are not only overlapping in areas, but they should be hand and glove.

Remove some of the risk associated with altitude diving.

 

[boulderjohn]

My thinking on the subject is that these certifications are not only overlapping in areas, but they should be hand and glove.

Remove some of the risk associated with altitude diving.

Whether you are diving at altitude or sea level, diving with nitrox has the same level of risk as diving with air--it all depends upon how close you come to the NDLs for that dive.

Diving at altitude does bring in a dimension many people do not consider. Do you know how altitude affects Nitrox MODs?

 

[Blueringocto_73]

I've finished my altitude cert. and 75% done with the Nitrox cert., so I will look forward to your expertise on the subject.

 

[runsongas]

mod is deeper for altitude diving

http://utahscubadiver.com/nitroxandaltitude/

 

[boulderjohn]

Sea Level

To find the MOD for a nitrox mix, first take the PPO2 maximum you want (usually 1.4) and divide by the percentage of oxygen in your mix. For example, for Nitrox 32, 1.4/.32 = 4.375. That is the ambient pressure (ATA) for your maximum depth.

To convert ambient pressure to depth in feet, first subtract the atmospheric pressure. At sea level, that is 1.0 ATA. That gives you 3.375.

Now multiply it by the depth of water equaling 1.0 ATA. In the ocean, that is 33 feet. Your total is 111 feet, the MOD for Nitrox 32 at sea level.​

Altitude

Now let's do the same calculations for Lake Tahoe, where the atmospheric pressure is about 0.8 ATA.

Dividing 1.4 by .32 yields the same result: 4.375. This time, though, we will subtract only 0.8 for the atmosphere, giving us 3.575.

Fresh water needs 34 feet to equal 1.0 ATA, so we multiply that total by 34, giving us 122 feet for our maximum operating depth.​

 

[Blueringocto_73]

^ Thanks! So if a diver wants a safer dive and runs the computer for air instead of Nitrox. While diving Nitrox at altitude, the result will be a conservative profile for the dive. Giving the added protection that it provides.

 

[KenGordon]

Sea Level

To find the MOD for a nitrox mix, first take the PPO2 maximum you want (usually 1.4) and divide by the percentage of oxygen in your mix. For example, for Nitrox 32, 1.4/.32 = 4.375. That is the ambient pressure (ATA) for your maximum depth.

To convert ambient pressure to depth in feet, first subtract the atmospheric pressure. At sea level, that is 1.0 ATA. That gives you 3.375.

Now multiply it by the depth of water equaling 1.0 ATA. In the ocean, that is 33 feet. Your total is 111 feet, the MOD for Nitrox 32 at sea level.​

Altitude

Now let's do the same calculations for Lake Tahoe, where the atmospheric pressure is about 0.8 ATA.

Dividing 1.4 by .32 yields the same result: 4.375. This time, though, we will subtract only 0.8 for the atmosphere, giving us 3.575.

Fresh water needs 34 feet to equal 1.0 ATA, so we multiply that total by 34, giving us 122 feet for our maximum operating depth.​

So, I have read your 34ft number before and thought “how odd” 10m is 33ft not 34. I work entirely in m so don’t care much, but working this through I get a different answer. 3.575 bar is 35.75m which is 78.2 cubits or 117 ft 4 in.

Is the 1.4 bar or atmospheres?

Maybe SB could do yourselves and many divers in measurement challenged countries of the world a big favour and just unilaterally move to metric. All the courses are available in metric. It is all much easier (“tank factors” - really?). It’s not like telling people the water is 100 ft deep is anything other than a number. They don’t need to calculate how many kitchen counter tops will fit between the surface and the bottom.

 

[Exigent]

In the imperial system salt water goes up 1 atm per 33 feet due to its increased density. Fresh water goes up 1 atm for every 34 feet.

 

[tursiops]

So, I have read your 34ft number before and thought “how odd” 10m is 33ft not 34.

10m is not correct for fresh water. The metric system may be very nice, but it does not account for the different densities of fresh and salt water.

 

[KenGordon]

This isn’t about salt vs fresh.

So which units are the appropriate units for ppo2? Bar or atm? If bar then surely the calculation of mod needs to be in bar. And the pressure of 10m of fresh water is 1 bar.