ianr33

02-17-2008, 13:46

From the thread on the Lake Mead accident:

You can actually dive nitrox a little deeper at altitude than at sea level.

That's not true. Diving nitrox requires you adjust your actual depths to a shallower level. In Lake Mead, a dive to 110', the MOD for 32%, is equivalent to the pressure you'd get at about 115', so you would have to adjust your actual depth down to 100'.

I still contend that you can dive nitrox deeper at altitude than at sea level.

The pressure at 5500 ft is about 1/2 ATM (Atmospheric pressure - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Atmospheric_pressure))

Normal max pO2 allowed for bottom gas is 1.4

At sea level ,using 32% the MOD will be :

0.32X Total Pressure = 1.4 ATM

Total Pressure = 1.4/.32 = 4.375 ATM

Take off 1 ATM for the Atmosphere and you get 3.375 ATM due to water pressure

3.375 X 33 = 111 feet

At 5500 Feet pressure is only 0.5. ATM

Total allowed pressure is still 4.375 ATM

Take off 0.5 for the Atmospheric Pressure leaves 3.875 ATM of water pressure

3.875 X 33 =128 feet

So the MOD of 32% nitrox at an altitude of 5500 ft will be 128 feet.

The NDL's will be reduced as the diver is surfacing to a lower pressure,but the MOD for any particular mix will be increased.

Am I correct here ??

You can actually dive nitrox a little deeper at altitude than at sea level.

That's not true. Diving nitrox requires you adjust your actual depths to a shallower level. In Lake Mead, a dive to 110', the MOD for 32%, is equivalent to the pressure you'd get at about 115', so you would have to adjust your actual depth down to 100'.

I still contend that you can dive nitrox deeper at altitude than at sea level.

The pressure at 5500 ft is about 1/2 ATM (Atmospheric pressure - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Atmospheric_pressure))

Normal max pO2 allowed for bottom gas is 1.4

At sea level ,using 32% the MOD will be :

0.32X Total Pressure = 1.4 ATM

Total Pressure = 1.4/.32 = 4.375 ATM

Take off 1 ATM for the Atmosphere and you get 3.375 ATM due to water pressure

3.375 X 33 = 111 feet

At 5500 Feet pressure is only 0.5. ATM

Total allowed pressure is still 4.375 ATM

Take off 0.5 for the Atmospheric Pressure leaves 3.875 ATM of water pressure

3.875 X 33 =128 feet

So the MOD of 32% nitrox at an altitude of 5500 ft will be 128 feet.

The NDL's will be reduced as the diver is surfacing to a lower pressure,but the MOD for any particular mix will be increased.

Am I correct here ??