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Frequently Asked Questions

What is Maximum Operating Depth (MOD)?
Maximum Operating Depth (MOD) is the calculated depth where a specific breathing gas reaches a selected partial-pressure-of-oxygen (PPO2) threshold. It does not determine whether the gas or dive is safe overall. Exceeding the calculated MOD also exceeds that selected PPO2 threshold and raises oxygen-toxicity risk.
What PPO2 limit should I use for recreational diving?
A PPO2 of 1.4 ATA is a commonly used recreational working threshold, while some plans use 1.2 ATA for more margin. Values up to 1.6 ATA may be used for limited decompression exposure under applicable technical training. Follow your current training, conditions, and whole-profile oxygen-exposure plan.
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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Understanding MOD: Maximum Operating Depth Explained

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