What are the two factors that determine total oxygen "dose" in diving?

The total oxygen "dose" in diving is primarily determined by the partial pressure of oxygen (ppO2) at a given depth and the duration of the exposure to that pressure. Partial pressure refers to the amount of oxygen in a gas mixture and is influenced by both the depth of the dive and the percentage of oxygen in the breathing gas. As a diver goes deeper underwater, the pressure increases, which raises the ppO2 and consequently increases the risk of oxygen toxicity.

The duration of exposure is equally significant because prolonged exposure to elevated ppO2 can lead to accumulating effects on the body. Each diver has a different exposure limit based on the ppO2 and exposure time, making this consideration critical for safe diving practices, especially when using enriched air nitrox, which contains a higher percentage of oxygen compared to standard air.

In contrast, the other factors mentioned, such as a diver's weight and experience level or environmental conditions like water temperature and visibility, do not directly affect the calculation of total oxygen dose, making them less relevant in the context of oxygen toxicity risk assessment. Likewise, while the equipment and depth of the dive can influence safety and dive planning, they do not fundamentally define the total oxygen dose.