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Nitrox Diving 101: Everything You Need to Know

Have you ever wanted to extend your bottom time or go just a little bit deeper on a dive? If so, nitrox could allow you to dive longer, safer, and with less fatigue.

As a diving novice, you’ve likely been taught that air is what you breathe underwater. But air is only 21% oxygen, with the rest being mostly nitrogen. By increasing the oxygen percentage in your tank, nitrox gives you more bottom time, decreases decompression sickness risk, and reduces post-dive tiredness.

However, with the benefits come potential dangers. Use nitrox incorrectly, and you risk serious health consequences from oxygen toxicity. This is an extensive guide forged by me to get you through the basics of nitrox in case you wish to replace your boring regular compressed gas mixture with it.

What Are the Prerequisites To Get Nitrox Certified?

Nitrox isn’t for all divers. Before considering it, you should:

  • Have an Open Water certification: Preferably AOW certification from PADI or AOC level 3 from SSI and 50+ logged dives with regular air as stepping stones.
  • Have excellent buoyancy control and trim: Nitrox diving demands less exertion from you so that you do not end up drawing excessive oxygen-rich air underwater and suffer from OT. So you need to be proficient in all the skills that are aimed at reducing underwater exertion and that includes your ability to be neutrally buoyant and to properly trim.
  • Understand dive planning: You need to be well-versed in reading dive computers as well as dive tables (for redundancy). Knowledge of universal gas laws, partial pressures of Oxygen and Nitrogen, formulas for calculating SAC rate, air duration, etc. should be at the edge of your mouth.

Common Nitrox Blends

For recreational diving, there are 2 commonly used nitrox blends available:

  • Nitrox 32 – 32% oxygen, 68% nitrogen. A good entry-level nitrox blend offering slightly extended bottom times.
  • Nitrox 36 – 36% oxygen, 64% nitrogen. Allows bottom times up to a third longer compared to air. A popular recreational nitrox blend.

Apart from the 2 mentioned above, there are more concentrated nitrox blends available but they generally offer very little in terms of practical use because of their MOD limitations.

Benefits of Nitrox Diving

Nitrox contains a higher percentage of oxygen than standard compressed air. While regular air is only 21% oxygen, nitrox mixes contain anywhere from 22% to 40% oxygen. The remaining gas is primarily nitrogen.

The key benefit of nitrox comes from this oxygen increase. Underwater, the nitrogen component of air causes narcotic effects and requires mandatory decompression stops. More oxygen means less nitrogen, so using nitrox:

1. No More Worries About no-decompression Limits

Less nitrogen in your tank means less nitrogen absorbed into your body tissues during a dive. This reduces decompression stress and fatigue.  Specifically, nitrox can reduce decompression obligation by up to 50% compared to air at the same depth.

Since there are almost negligible chances of decompression sickness your no decompression limits (NDL) are practically non-existent at recreational depths (<25m).

With fewer decompression ascents and descents, you’re subject to fewer depth and pressure changes, hence, you can cut down on your need for constant ear equalization. Equalizing ears frequently is the bane of a lot of recreational divers and they often end up with blocked ears. For them, a nitrox mixture might be the perfect solution.

2. More Bottom Time

With the EANx mixture, you can stay down longer and tone down your frequency of decompression stops since you absorb less nitrogen per minute. At 30-34 meters, a 32% nitrox blend lets you stay 55 minutes vs only 35 minutes on regular air.

3. Reduced Risk Of Nitrogen Narcosis

Nitrogen narcosis refers to the intoxicating effects that build up when divers breathe compressed air at depths beyond 30 meters, caused by nitrogen being absorbed into the body under high pressure and affecting the brain similarly to alcohol intoxication, impairing judgment and coordination.

Higher oxygen levels help clear nitrogen from your system, reducing intoxication risk on deep dives. Nitrox provides a safer cushion before the onset of impairment.

4. Less After-Dive Exhaustion

You can bid farewell to post-dive exhaustion. Inhaling all that extra oxygen content in your gas mixture supplies more energy to your muscles and brain and keeps them more fired up than usual. This is especially noticeable when you’re diving in warm tropical waters.

Disadvantages of Diving with Nitrox Mixture

Despite its benefits, EANx has its fair share of shortcomings too.

1. Increased Risk Of Oxygen Toxicity

Breathing higher concentrations of oxygen at depth increases the risk of central nervous system oxygen toxicity, which can cause seizures and drowning. This alone can drastically reduce your permissible diving depths depending on the oxygen content in your EANx mixture.

2. Maximum Operating Depth Is Limited

The maximum operating depth (MOD) for Nitrox blends is inversely related to the amount of oxygen content in the blend due to the risk of oxygen toxicity to the diver at increased depths.

Generally, with a 32% EANx blend you can expect to dive at a MOD of 110 feet which decreases as the oxygen content in your mixture increases.

3. Nitrox Is More expensive

Typically, filling your tanks with nitrox mixture will cost a few bucks more than normal breathing gas mixtures. While this may seem negligible, the costs compound pretty quickly if you’re a frequent diver.

4. Equipment Compatibility

Not all diving cylinders and other equipment like regulators can handle elevated oxygen levels. The equipment must be “oxygen clean” and nitrox compatible.

5. Requires Thorough Dive Planning

To make up for the risks of oxygen toxicity and MOD issues divers are required to pre-plan their dives with extra caution. You have to calculate your MOD based on the oxygen content in your EANx mixture before each dive. For recreational divers, this can be quite cumbersome.

So, be advised. Nitrox isn’t your premium ticket to reckless diving.

How To Minimize the Risk of Oxygen Toxicity While Using Nitrox?

While nitrox allows you to absorb less nitrogen, the increased oxygen percentage comes with its risks. As you descend deeper on nitrox, the partial pressure of oxygen rises. At high partial pressures, inhaling oxygen becomes toxic. Symptoms of oxygen toxicity include:

  • Visual disturbances and tunnel vision
  • Nausea, dizziness, and disorientation
  • Muscle twitching or convulsions

Oxygen toxicity can onset rapidly and result in drowning if not treated immediately by ascending to a shallower depth. A proper nitrox training course teaches you how to calculate maximum operating depths for a given mix to avoid exceeding safe oxygen partial pressures.

You have to adhere to certain restrictions to steer clear of Oxygen Toxicity.

  • Stick to depth limits: No matter what, don’t give in to the urge to push and test your depth limit more and more.
  • Use conservative mixes: Begin with 32% or less oxygen content in your EANx mixture for wider safety margins until you become more comfortable.
  • Avoid Heavy Exertion: Strenuous breathing increases oxygen intake, raising toxicity risk. So keep your breathing natural, since it’s nitrox there’s no need for dangerous air conservation practices like holding your breath. Just breathe as you do on land, without drawing in excessive oxygen (even if the urge to breathe deep can be tempting), and gently breathe out.
  • Listen to Your Body: Disorientation, visual disturbances, or nausea is a sign that you’re likely treading on the borders of oxygen toxicity territory. End the dive then and there if these occur.

Nitrox Diving Equipment Requirements

You don’t need much special gear to start nitrox diving. At a minimum:

  1. Nitrox-compatible scuba cylinder & valve: Your tank and valve fittings must be oxygen-clean and rated for high-pressure nitrox mixes. Standard aluminum cylinders are fine, just make sure to keep them separated from your standard air cylinders.
  2. Oxygen-compatible regulator: Using a nitrox-rated first stage and sealed second stage reduces fire/explosion risk.
  3. Nitrox analyzer: This device checks and records fill tank oxygen percentages so you breathe the expected mix.
  4. Oxygen-safe lubricants: Use fluorinated grease on tank threads and connections. Avoid standard hydrocarbon greases.
  5. Nitrox-capable dive computer: Although dive computers aren’t necessary for recreational dives with normal air, it’s a must when you’re breathing nitrox, no matter your depth. Set your computer to the oxygen percentage you’re using to properly track decompression status.
  6. Oxygen service equipment: Filling stations require specialized components like oxygen compressors, reservoirs, and purification systems.

With clean equipment and the right training, you can start nitrox diving without breaking the bank on new gear.

Nitrox Fill Prices, Courses, and Additional Gear Requirements

Nitrox involves some extra costs over regular compressed air:

Certification: A nitrox course runs $150 to $250 for classroom and pool training. You are required to show your Nitrox Speciality Course completion certificate at the dive shop to fill your tanks with Nitrox mixture.

Fill prices: Expect to pay $5 to $10 more per tank over regular air fills. Shops need to cover equipment costs and oxygen waste from blending.

Extra cylinders: Having dedicated nitrox tanks avoids mix-ups with air tanks. Plan for an extra $200 to $500 per cylinder. Rental tanks are an alternative.

Regulator servicing: Expect to pay $20 to $60 extra when servicing a nitrox-compatible reg due to oxygen cleaning.

How Do You Get Nitrox Fills and Handle Mixes Properly?

Since you can’t just fill any tank with nitrox from a compressor, getting fills takes some planning:

  • Check availability: Call ahead to ensure the dive shop or resort can blend nitrox when you’ll be diving. Availability varies by region and season.
    • Analyze before filling: Use an oxygen analyzer to confirm tank oxygen levels start at 20-21% before filling. This prevents dangerous high-oxygen mixes.
    • Fill slowly: Fast fills heat nitrox mixes, altering percentages. The filling rate should not exceed 500 psi/minute to ensure blend accuracy.
    • Verify after filling: I’m not implying the tank-filling guys at dive shops are irresponsible. Just err on the side of caution. Re-test oxygen content after filling to ensure you received the expected nitrox mix. Log the percentage in your dive log.
  • Isolate nitrox tanks: Keep nitrox cylinders in designated areas to prevent accidental air fills or mixes. Attach nitrox tank labels and oxygen percentage tags.
  • Avoid oxygen cleaning: Never put nitrox tanks in ozone sterilizers or bleach baths, as concentrated oxygen can ignite with a devastating tank explosion.

5 Must-Know Nitrox Diving Tips for Beginners

  • Start slow and shallow using low oxygen mixes under 32%
  • Follow planned depth and time limits closely and conservatively
  • Monitor computer warnings for maximum operating depth (MOD) and blood oxygen exposure
  • Off-gas for 60 to 90 minutes between nitrox and air dives
  • Analyse fills before and after filling to verify percentages

If you’re a beginner scuba diver you might want to head over to our 11 beginner’s safety tips for scuba diving for some bonus tips for scuba diving in general.

Just Like Every Aspect of Scuba Diving, Nitrox Has Its Ups and Downs

While not wholly without risk, nitrox diving offers huge advantages for moderate depth diving when done carefully and correctly.

With mentoring from an experienced nitrox instructor, nitrox can open an exciting new chapter in your diving career. So don’t let the skeptics dissuade you. Gear up, gas up, and go revel in those dream dives you’ve previously had to rush through. Nitrox lets you breathe easy and unlock your underwater potential. Dive safe!

William Dupre

William Dupre

Retired Master Diver with 20+ years of experience and 2100+ logged dives. Presently, spending my time blogging about Diving and checking off locations one by one from my bucket list of dive destinations.

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