Nitrox, Part 2: From “Why” to “How” – Analyser, MOD, and Real-World Use

Building on Part 1, this follow-up turns the core ideas into a practical, step-by-step workflow you can use at the fill station, on the boat, and in your dive log.

Big picture refresher: Nitrox (oxygen-enriched air) reduces the fraction of nitrogen you absorb, which can extend no-decompression limits – but it introduces oxygen exposure limits you must manage with MODs and good habits.Calibrate your O2 analyser (usually to 20.9% in air), sample from the tank with a flow limiter, and let the reading stabilise. Record the exact FO2 you’ll dive. Label the cylinder with FO2 and MOD so you and your buddy can verify it at a glance.Use a conservative working limit of 1.4 bar pO2 (with 1.6 bar reserved for emergency/stop contingencies). Then set a personal buffer.Enter your analysed FO2 and enable any pO2/MOD alerts. If computers are mixed in the team, plan for the most conservative settings.Check NDLs/EADs for your target depth so you know whether gas supply or NDL is the real limiter for the dive.Swap cylinders to verify that each other’s labels and computer settings match the actual FO2.Log FO2, MOD, pO2 settings, max depth, and any CNS% the computer reports. It makes repetitive dive planning faster and safer next time.

• MOD at 1.4 pO2
  • EAN32 -> ~34 m / 111 ft
  • EAN36 -> ~29 m / 95 ft

These are standard recreational figures you’ll also find on PADI and other tables and charts.

• EAD at 21 m (70 ft )
  • EAN32 has an EAD ~17m (56 ft) -> table NDL ~55 min (vs. air).

• Working limit: plan for 1.4 pO2;
• Contingency: 1.6 pO2 for brief stops/emergencies;
• CNS%/OTUs: let your computer track these and keep them modest on multi-dive days. The key is to never exceed MOD and to keep total exposure conservative.

• Not analysing the tank yourself -> Always analyse, label FO2 + MOD, and sign the fill log if required.
• Forgetting to set the computer -> Make “FO2 set?” part of your pre-dive check – every dive.
• Chasing depth on rich mixes -> Higher O2 = shallower MOD. Respect it absolutely.
• Assuming Nitrox = safer in all ways -> It reduces nitrogen loading but adds oxygen-toxicity risk and fire hazards during blending/handling. Training + procedures keep you safe.

• Shines: repetitive diving days in the 15–30 m / 50–100 ft band where NDLs can be the limiter. Pair with solid gas planning.
• Less impact: very shallow, single-tank fun dives where gas (not NDL) ends the dive first.

• Analyse gas -> write FO2 + MOD on tape/tag
• Set computer FO2 + pO2 alarm
• Plan to 1.4 pO2 (keep buffer)
• Confirm EAD/NDL fits gas plan
• Buddy cross-check labels & settings
• Log FO2, MOD, max depth, CNS%