Sixteen minutes. That’s roughly what the no-stop clock gives you on El Aguila wreck dive site breathing air. On a 32 percent mix it’s closer to thirty three.

Same wreck. Same depth. Twice the time in it.

That’s the whole pitch for Enriched Air, and it’s why the green and yellow tanks on our dock in West End get picked over first.

What Enriched Air actually is

The air you’re breathing right now is about 21 percent oxygen and 79 percent nitrogen. Enriched Air Nitrox is any mix carrying more oxygen than that, which by definition means less nitrogen. Recreational diving caps it at 40 percent oxygen. Most of what comes out of our fill station is 30 or 32.

Nitrogen is the problem gas. Your body doesn’t use it. It dissolves into your tissues under pressure and comes back out slowly, and that slow release is what the no-stop limit on your computer is counting. Take some nitrogen out of the tank and there’s less going in.

Doing the math

Drop to 30 meters and you’re sitting at 4 bar of pressure. Four times what you feel on the beach.

That gap is your extra bottom time. Nothing mystical about it. Your computer reads a smaller nitrogen load and gives you longer before the no-stop limit runs out.

Four things it changes

Longer no-decompression limits. The headline benefit, and the one you’ll feel on the first dive of the day.

Shorter surface intervals. Less nitrogen in means less to offgas between dives. On a two-tank morning trip that’s the difference between a comfortable break and watching a clock.

More bottom time on the repetitive dive. Dive two is where the mix pays for itself. Your first dive on air sets the ceiling for your second one. Nitrox raises both.

Less fatigue. Plenty of divers say they finish a three-tank day feeling better on Nitrox. Worth being straight about this one: it hasn’t been demonstrated in controlled research. It’s an anecdote repeated by a lot of experienced people. Take it as that.

It’s older than you’d think

Henry Fleuss built the first workable rebreather in 1879, at Siebe Gorman in London, running oxygen instead of air. Navies picked the idea up from there. By the Second World War, closed-circuit oxygen rebreathers were standard kit for combat swimmers, chosen because they leave no trail of bubbles on the surface.

Recreational diving took decades longer to come around, and the certification agencies longer still. The gas isn’t new. The card is.

What Nitrox doesn’t do

It doesn’t let you go deeper. It’s the opposite. More oxygen means a shallower maximum operating depth, because oxygen turns toxic under pressure. EAN32 has a hard ceiling around 33 metres. Below that you’ve swapped a short no-stop limit for an oxygen toxicity risk, which is a far worse trade. This is why our Deep Diver course runs its deepest dive on air.

It doesn’t fix narcosis. Oxygen is narcotic too. Don’t plan a dive around the idea that a green tank keeps your head clear at 35 metres.

It doesn’t make you a better diver. Air consumption is a weighting and trim problem before it’s a gas problem. If you’re emptying a tank in thirty minutes, the Peak Performance Buoyancy course will do more for you than a different mix will.

How the PADI Enriched Air course runs at our dive shop

Two parts, and neither one eats your week. You’ll complete the theory portion via PADI eLearning before you fly. It covers:

• what enriched air is, and how cylinders get labelled and logged
• equivalent air depth, and how your computer handles a mix
• oxygen exposure limits and why they exist
• maximum operating depth, and calculating it for the mix in your hand
• analysing your own tank and signing the fill log yourself
• setting a dive computer for enriched air before you get in

Then you analyze a tank, log it, and dive it. PADI allows the certification without any dives at all. We’d sooner you got in the water with it, and most people here do.

Where it pays in Roatan

• El Aguila. Near 33 metres on the sand. Around sixteen minutes on air, roughly thirty three on EAN32. If you’re doing the Wreck Diver course, this is the single best argument for having the Nitrox card first.
• The Odyssey. The bigger of the two wrecks, similar depth. About thirty five minutes with a mix.
• Texas. Eighteen to twenty one metres, which is the sweet spot. You’ll run out of gas long before your computer runs out of no-stop time, and that’s exactly where a diver stops counting minutes and starts looking at the reef.

Our morning two-tank trip runs the deeper sites and it’s the trip where Nitrox earns its surcharge. Afternoon dives are single tank and shallower, where you’ll notice it less. We fill on site, so there’s no hunting around West End for a shop with a blender.

Getting the PADI Enriched Air Card

Enriched Air sits on our PADI specialty course list and it’s the one we’d put first for almost any certified diver. It counts toward Master Scuba Diver, it takes a day or less, and unlike most specialties it changes every single dive you do afterwards instead of one specific type of dive.

We’ve been filling tanks from the same dock in West End since 2002. Ask us about a Nitrox course, or come and join a certified dive trip and watch someone else stay down longer than you. That tends to settle it.