Nitrogen-oxygen (NITROX) diving is a unique type of diving using nitrogen oxygen breathing gas mixtures ranging from 75 percent nitrogen/25 percent oxygen to 60 percent nitrogen/40 percent oxygen. Using NITROX significantly increases the amount of time a diver can spend at depth without decompressing. It also decreases the required decompression time compared to a similar dive made to the same depth using air. NITROX may be used in all diving operations suitable for air, but its use is limited to a normal depth of 140 fsw.

NITROX breathing gas mixtures are normally used for shallow dives. The most benefit is gained when NITROX is used shallower than 50 fsw, but it can be advantageous when used to a depth of 140 fsw.

Advantages and Disadvantages of NITROX Diving.

The disadvantages of using NITROX include:
! Increased risk of CNS oxygen toxicity.
! Producing NITROX mixtures requires special equipment.
! NITROX equipment requires special cleaning techniques.
! Long-duration NITROX dives can result in pulmonary oxygen toxicity.
! Working with NITROX systems requires special training.
! NITROX is expensive to purchase.

EQUIVALENT AIR DEPTH
The partial pressure of nitrogen in a NITROX mixture is the key factor determining the diver’s decompression obligation. Oxygen plays no role. The decompression obligation for a NITROX dive therefore can be determined using the Standard Air Tables simply by selecting the depth on air that has the same partial pressure of nitrogen as the NITROX mixture. This depth is called the Equivalent Air Depth (EAD). For example, the nitrogen partial pressure in a 68% nitrogen 32% oxygen mixture at 63 fsw is 2.0 ata. This is the same partial pressure of nitrogen found in air at 50 fsw. 50 fsw is the Equivalent Air Depth.