A diver should never _______ during ascent to avoid air embolism.

The most important guideline during ascent is to ensure that a diver does not hold their breath. This is crucial because as a diver ascends, the pressure around them decreases. If a diver holds their breath while ascending, the air in their lungs expands due to the lower pressure. If this expansion occurs without allowing the air to be exhaled, it can lead to serious lung over-expansion injuries, such as air embolism. An air embolism happens when air bubbles enter the bloodstream and can cause blockages in blood vessels, which is a life-threatening condition.

Other factors, like breathing rapidly, ascending too quickly, or diving deeper, while they can contribute to diving risks and require caution, are not directly as critical as holding one’s breath during ascent. Rapid breathing could lead to other issues, and ascending too quickly also poses risks, but the specific danger of air embolism is most pronounced when a diver does not exhale during ascent.