■Diving time management for a single dive per day

If more than 24 hours have passed since your previous dive, residual oxygen exposure from that dive is no longer a concern.

The allowable exposure time varies depending on the oxygen percentage of the Nitrox blend used.

The maximum time considered safe with respect to oxygen toxicity is called the oxygen exposure limit. This limit can be determined using the oxygen exposure table.

Oxygen exposure table

For example, when diving to a depth of 20 m using EAN32, the oxygen fraction is 0.32. Using the formula for oxygen partial pressure:
Oxygen partial pressure = 0.32 × (20 ÷ 10 + 1) = 0.96

In the left column of the table, locate the value closest to but not less than 0.96.
1.20 is the next higher value.
The oxygen exposure limit shown in the right column is 210 minutes.

Similarly, when diving to a depth of 25 m using EAN36, the oxygen fraction is 0.36. Using the oxygen partial pressure formula:
Oxygen partial pressure = 0.36 × (25 ÷ 10 + 1) = 1.26

In the left column of the table, locate the value closest to but not less than 1.26.
1.30 is the next higher value.
The oxygen exposure limit shown in the right column is 180 minutes.