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Frequently Asked Questions

What is Maximum Operating Depth (MOD)?
Maximum Operating Depth (MOD) is the deepest depth at which a specific breathing gas can be used safely without exceeding the maximum acceptable partial pressure of oxygen (PPO2). Exceeding the MOD puts divers at risk of oxygen toxicity, which can cause convulsions underwater.
What PPO2 limit should I use for recreational diving?
For recreational diving, the standard maximum PPO2 is 1.4 ATA, as recommended by most training agencies including PADI, SSI, and NAUI. A more conservative limit of 1.2 ATA is used by some divers for added safety margin. Technical divers may use up to 1.6 ATA for decompression stops.
What is the MOD for EAN32 (Nitrox 32%)?
With a PPO2 limit of 1.4 ATA, the Maximum Operating Depth for EAN32 (32% oxygen) is approximately 33.8 meters (111 feet). With a more conservative PPO2 of 1.2 ATA, the MOD drops to approximately 27.5 meters (90 feet).
Why is Nitrox popular among recreational divers?
Nitrox (enriched air) is popular because it contains a higher percentage of oxygen than regular air (21%), which reduces the nitrogen absorbed during a dive. This allows for longer no-decompression limits, shorter surface intervals, and reduced risk of decompression sickness. However, it also means a shallower MOD due to oxygen toxicity limits.
What is oxygen toxicity and why does it matter?
Oxygen toxicity occurs when a diver breathes oxygen at high partial pressures for extended periods. Central Nervous System (CNS) oxygen toxicity is the primary concern for divers, as it can cause convulsions, visual disturbances, nausea, and muscle twitching. A convulsion underwater is life-threatening, which is why staying within MOD limits is critical.

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