What limits the time you can stay at depth while diving?

The correct answer is based on the effects of nitrogen on the body during a dive. As divers descend into deeper waters, the pressure increases, which causes nitrogen from the breathing gas to be absorbed into the body tissues and bloodstream. This phenomenon is particularly significant because the increased concentration of nitrogen can lead to a condition known as nitrogen narcosis, which impacts cognitive function and can be dangerous.

Furthermore, when a diver ascends, the nitrogen must be released from the body slowly, or it can form bubbles, resulting in decompression sickness, or "the bends." Therefore, the limits on how long one can stay at depth is primarily dictated by nitrogen absorption and the need to avoid the risks associated with too much nitrogen in the tissues.

Oxygen, while playing a crucial role in diving, is not the primary limiting factor at typical recreational depths. At depths greater than 30 meters (about 100 feet), oxygen toxicity can occur, but for most recreational diving, limits are more often set by nitrogen considerations.

Carbon dioxide accumulation is a concern related to breathing efficiency and can lead to hypercapnia, but it is more about the management of dive profiles and gas mixes rather than a direct limit on bottom time. Helium may be relevant in specific circumstances