What is nitrox, and does it let you dive deeper?

At 18 metres, the PADI Recreational Dive Planner gives a diver on air 56 minutes before a decompression stop becomes mandatory. Switch to EAN32 and the same planner allows 95. Each breath of nitrox carries less nitrogen, so your tissues load more slowly and the no-stop clock runs longer. That buys time. Not depth. The extra oxygen puts a hard floor under the dive, close to 34 metres for EAN32, which is shallower than the 40-metre limit a recreational air diver works to.

Blame the word "enriched", which sounds like an upgrade in every direction. The US Navy and commercial divers used nitrox in the 1950s. NOAA brought it to scientific diving in the late 1970s, when J. Morgan Wells proposed a 32% oxygen blend. Recreational training followed in 1985, and PADI now lists Enriched Air Diver as its most popular specialty. The name sells the oxygen. The benefit comes from the nitrogen that's been taken out, and the cost comes from the oxygen that's been added.

What is nitrox, and what does EAN32 mean?

Recreational nitrox is enriched air with between 22% and 40% oxygen, according to PADI. Normal air is about 21% oxygen, with nitrogen making up nearly all the rest. The label gives the oxygen share, so EAN32 is 32% oxygen and 68% nitrogen, while EAN36 carries 36% oxygen and 64% nitrogen. Those two are the common recreational fills. The oxygen figure sets your depth limit, which is why it's the number you confirm on an analyser before the cylinder goes on your back.

How does nitrox give you more bottom time?

Nitrogen, not oxygen, sets your no-stop limit. At depth, your tissues take on nitrogen in proportion to its partial pressure. The limit arrives when the modelled tissues near the most nitrogen they can carry on a direct ascent. Drop the nitrogen from 79% to 68% and the loading slows, so the limit arrives later. Divers express this as equivalent air depth: EAN32 at 30 metres loads nitrogen much like air at about 24 metres. DAN makes the same point in feet, putting 32% nitrox at 110 feet level with air at 90 feet.

Nitrox earns its keep on the dives where air limits bite. Shallower than about 15 metres, your gas supply tends to end the dive before an air no-stop limit does, so extra minutes on paper change little. The second dive of the day benefits too, because you surface from the first with less leftover nitrogen. What that leftover nitrogen does if it comes out of solution too fast is covered in our guide to how nitrogen supersaturation causes the bends.

Why does nitrox reduce your maximum depth?

Oxygen turns toxic under pressure, and pressure is what depth adds. The partial pressure of oxygen, written PO2, is the oxygen fraction multiplied by the absolute pressure. Sea water adds roughly one bar every 10 metres, so EAN32 at 34 metres gives 0.32 × 4.4 bar, or about 1.4 bar. PADI sets a limit of 1.4 bar for open-circuit nitrox, and DAN treats 1.4 to 1.6 bar as a caution zone. The depth where your mix hits that ceiling is its maximum operating depth, or MOD.

Working out a MOD takes one line: MOD in metres = (maximum PO2 ÷ oxygen fraction − 1) × 10. More oxygen in the cylinder means you reach the ceiling sooner. Air doesn't touch 1.4 bar until almost 57 metres, well past recreational limits, which is why air divers seldom hear about oxygen toxicity. On nitrox, the ceiling sits inside ordinary dive depths.

Mix	Oxygen	MOD at 1.4 bar	MOD at 1.6 bar
Air	21%	56.7 m	66.2 m
EAN32	32%	33.8 m	40.0 m
EAN36	36%	28.9 m	34.4 m
EAN40	40%	25.0 m	30.0 m

Read the 1.6 column as margin, not as a second plan. A diver who plans to 1.6 bar to squeeze out a few extra metres has used up the margin before leaving the boat. DAN names an unplanned depth excursion as one of the things that raises the risk between 1.4 and 1.6 bar. A missed depth check or a buddy drifting down can add two metres without anyone deciding to go there. Two metres. That's what the 1.4 plan was protecting.

What happens if you go below your MOD?

Go past your MOD and you risk central nervous system oxygen toxicity, whose worst symptom is a convulsion. DAN lists warning signs that include flashing lights, tunnel vision, ringing in the ears, nausea, confusion and twitching, especially around the lips. DAN's advice for any of them is to alert your buddy and make a controlled ascent. It also tells dive teams to prepare for a convulsion even at 1.5 to 1.6 bar. A seizure underwater can cost a diver the regulator, and that's how oxygen toxicity turns into a drowning. Carbon dioxide adds to it, since divers who retain CO2 during exercise may be at higher risk, so finning hard near your MOD stacks two problems on one dive.

Time counts alongside depth, because the risk builds with exposure. That's why NOAA sets a time limit for each oxygen partial pressure instead of a single depth. Why recreational divers don't breathe pure oxygen at depth is covered in our guide to what's in a scuba cylinder and why it isn't oxygen.

Does nitrox make you less tired or safer?

Controlled trials haven't found the post-dive energy many nitrox divers describe. In a double-blind chamber study published in 2003, Harris and colleagues took 11 divers to 18 metres for 40 minutes on air or EAN36. They found no measurable difference in fatigue, attention or concentration afterwards. DAN Southern Africa's review of the evidence lands in the same place. The experts it consulted point to poor sleep on holiday, alcohol, jet lag and cold as likely culprits.

Bubble counts show a clearer benefit. In a 2016 double-blind trial in PLOS ONE, 12 bubble-prone volunteers did the same 55-minute chamber dive to 28 metres twice, once on air and once on EAN36. Nitrox cut the median cumulative bubble score from 8 to 1. All three mild decompression incidents, each a case of skin itching, happened on air. Because the profile stayed identical, the result points to a second way to use the gas: dive your air limits on nitrox and keep the difference as safety margin.

What does nitrox training cover?

Scuba Evolution runs the PADI Enriched Air Diver course as the Nitrox Course. It covers planning a nitrox dive, analysing a cylinder's oxygen content yourself and setting a dive computer for the mix. There are no open water training dives. The analyser step is the one that protects you on the day. A fill tag records what someone meant to put in the cylinder, while your own reading in the fill log records what's in it.

Same with the computer. A unit left on its air setting while you breathe EAN32 still gives conservative nitrogen limits. It also tracks your oxygen exposure as if you were on 21% and won't warn you at the real MOD, which removes the main protection nitrox training exists to add. How different computers handle the same profile is covered in our guide to what a dive computer's algorithm changes.

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Frequently Asked Questions

Does nitrox reduce nitrogen narcosis?
Don't count on it. PADI, along with CMAS, GUE and PSAI, teaches that oxygen is narcotic at the pressures divers breathe it, so swapping nitrogen for oxygen doesn't clear your head. Plan a nitrox dive as if narcosis arrives at the same depth it would on air.

What's the best nitrox mix for a 30 metre dive?
Divide the maximum PO2 by the absolute pressure at depth: 1.4 ÷ 4 bar gives 35% oxygen. That mix sits exactly at the limit on the deepest point of the plan. EAN32 is the more forgiving choice, reaching 1.4 bar at 33.8 metres and leaving a few metres of margin.

How old do you have to be to learn nitrox?
PADI accepts divers from age 12 who already have an Open Water Diver qualification. PADI says the course can be completed in a few hours. It adds planning and gas checks rather than new in-water skills, which is why it sits comfortably straight after Open Water.

Is 1.6 bar a safe PO2 to plan a dive around?
DAN treats 1.5 to 1.6 bar as suitable only when a diver is at rest, such as on a decompression stop, and says recreational divers shouldn't exceed 1.6. NOAA's limit at 1.6 bar is 45 minutes for normal diving. Planning to it leaves nothing in reserve if the dive runs deeper or longer than intended.

Can you still get the bends on nitrox?
Yes. Less nitrogen reduces the load but doesn't remove it, and exceeding the nitrox no-stop limit or ascending too fast still causes decompression sickness. Even in the 2016 bubble trial, nitrox lowered bubble scores without eliminating them.

Does nitrox make your cylinder run out faster?
No. How long a cylinder lasts depends on its size, your breathing rate and the depth, and the oxygen share doesn't change any of those. What changes is which limit ends the dive, since the no-stop clock tends to outlast the gas at moderate depths on nitrox.

This is general information, not a substitute for dive training, a dive medical or advice from a doctor trained in dive medicine. In an emergency, contact DAN Southern Africa on +27 82 810 6010.

Reviewed September 2026. Devon Ford runs Scuba Evolution, a PADI 5 Star Dive Centre in Glenvista, Johannesburg.