1. EANx (Enriched Air Nitrox) mixtures with a higher content of oxygen than in air are called enriched air mixtures, where the letter “ex” at the end of the mixture is followed by the percentage of oxygen, or oxygen fraction F02.
2. The two most common EANx mixtures are EANx32 and EANx36. The maximum diving depth with EANx32 is 40 msw (130 fsw), and EANx36 is 34 msw (110 fsw).
3. In absolute atmospheres, absolute pressure (P) is measured. The unit of measure “ATA” is used for all calculations relating to gases.
P absolute pressure.
PATA absolute pressure in ATA
D msw depth in meters of salt water
4. calculating the depth by absolute pressure:
PATA = (D msw : 10 msw) + 1 ATA
(D msw + 10 msw) : 10 msw
5. Calculation of absolute pressure by depth:
D msw = (PATA – 1 ATA) x 10 msw
(PATA x 10 msw) – 10 msw
6. To find PO2, knowing FO2, you must first
calculate the absolute pressure at a given depth.
PO2 = partial pressure of oxygen P02 = oxygen fraction P# = partial pressure of nitrogen B# = nitrogen fraction
7. Dalton’s law formula for air and NITROX mixtures:
P = P02 + P#
8. Dalton’s crystal is used to make
equations: cover the desired component with the palm of your hand, and get the
You can use Dalton’s crystal to create an equation: Put your palm on the component you are searching for.
The following questions can be answered with Dalton’s Crystal:
Optimal mixture? Maximum depth? Oxygen content?
FO2 = P02 : P P02 : FO2 P02 = FO2 x P
9. The maximum oxygen partial pressure during dives should never exceed 1.6 ATA.
10. Using the maximum partial pressure of oxygen equal to 1.4 ATA for calculations is recommended for diving in cold water or in conditions requiring increased physical exertion.
11. Oxygen limits time are determined by the NOAA charts.
If you have exhausted your single oxygen limit, NOAA recommends that you make a surface interval of at least 2 hours. If the daily oxygen limit dives, an interval of at least 12 hours is necessary.