How does the total oxygen "dose" change if a diver takes a longer bottom time at the same depth?

When a diver spends more time at the same depth while breathing enriched air nitrox, the total oxygen dose increases. This is because the total oxygen exposure or dose is calculated based on both the partial pressure of oxygen at the given depth and the duration of exposure.

As the diver remains at a constant depth, the partial pressure of oxygen remains the same. However, an extended bottom time means that the diver is inhaling oxygen for a longer duration, directly increasing the total amount of oxygen absorbed by their body. This accumulation can have implications for oxygen toxicity, necessitating careful planning and monitoring of dive times when using nitrox mixtures.

The other options do not accurately reflect how total oxygen exposure relates to time and depth. A decrease or constant measure of oxygen dose would not be possible if the bottom time is extended. Additionally, the idea that the oxygen dose becomes irrelevant ignores the critical importance of monitoring and managing oxygen exposure in diving safety.