What is Nitrox?

The breathing mixture that enables you to do what other scuba divers can only dream of doing.

06 January 2021

By Danel Wentzel

We need oxygen to survive and so we breathe air into our lungs to get this essential life source into our bloodstream. We as scuba divers breathe compressed air from a cylinder in the same way so that we can explore the underwater world, untethered to the surface.

Nitrox or otherwise referred to as enriched air, enriched air nitrox or EANX, is a variable mixture of breathing gas where there is a higher percentage of oxygen than what is found in normal air.

Simplified - the air we breathe contains roughly 21% oxygen and 79% nitrogen. Oxygen is needed for metabolism to produce energy for our bodies to function, while nitrogen is an inert gas that our body cannot use. It does however play a major role in scuba diving.

Diving tables or decompression models take into account the amount of nitrogen in the air we breathe to calculate for how long we can stay at a given depth. It is the rapid release of nitrogen from your tissues, during an uncontrolled ascent, that results in decompression sickness.

So if nitrogen is the culprit then by breathing a mixture that has less of it in the gas we alter the limits it sets on us. Breathing enriched air at depth enables you to dive longer than normal air as the smaller quantity of nitrogen being absorbed will take longer to saturate your tissues.

This equates to a dive to 30 metres on air is normally limited to 20 minutes but on EANX 32% this is extended to 30 minutes. This benefits Open Water divers as well as a dive to 18 metres has a no-decompression-limit of 56 minutes but on EANX 32% this rises up to 95 minutes.

The most common mixes of enriched air supplied at diving centres is EANX 32% and EANX 36%. But you may be wondering, if nitrogen limits our time at depth, then why don't we just breathe 100% oxygen?

And the answer is because there is a maximum operating depth to oxygen under pressure. This means that when breathing normal compressed air the maximum depth that you can dive safely is 56m without risking oxygen toxicity. Oxygen toxicity can cause convulsions underwater which can be extremely dangerous as you may easily lose your regulator and drown.

The maximum depth decreases as the percentage of oxygen increases. Breathing 32% nitrox limits your depth to 34m, 36% limits you to 29m and 100% allows you to dive to a mere 4 metres. Recreational nitrox divers are limited in their training to 40%.

Breathing enriched air nitrox enables you to prolong your bottom time compared to normal compressed air, which may feel like a superpower within the realm of scuba diving but with it comes responsibility and further training.

Understanding the risks of a higher percentage of oxygen in your breathing mix, the nitrox dedicated dive tables, oxygen toxicity and maximum operating depths as well as how to use an oxygen analyser and nitrox mode on your dive computer - is essential knowledge to know before jumping into the water.