How does increasing the percentage of oxygen in a gas mixture affect the maximum operating depth?

Increasing the percentage of oxygen in a gas mixture decreases the maximum operating depth due to the increased risk of oxygen toxicity. As the proportion of oxygen rises, the partial pressure of oxygen at depth also increases. This elevated partial pressure of oxygen can lead to harmful effects, including CNS (central nervous system) toxicity, which can manifest as seizures and other severe complications if the partial pressure exceeds safe limits.

The maximum operating depth for a nitrox dive is typically calculated using the formula to ensure that the partial pressure of oxygen does not exceed 1.4 ATA (atmospheres absolute) during the dive. As the oxygen content increases, the depth at which this safe partial pressure is reached becomes shallower. For instance, when using air (approximately 21% oxygen), divers can safely reach greater depths than when using a gas mixture with a higher oxygen percentage, like 32% or 36% nitrox, where the maximum operating depth must be adjusted accordingly.

Thus, with higher oxygen concentrations, divers need to be aware of their maximum operating depths to avoid exceeding safe levels, making it crucial for their safety.