To prevent air embolism, a diver should always:

Breathe normally at all times during ascent is the correct approach to prevent air embolism because it allows for the proper exchange of gases in the lungs. When a diver holds their breath during ascent, they risk trapping expanding gas in their lungs, leading to overexpansion and potential rupture of lung tissue, which can cause an air embolism.

Normal breathing helps maintain equal pressure between the gases in the lungs and the ambient water pressure. This reduces the risk of nitrogen bubbles forming in the bloodstream upon ascent. The practice of exhaling during ascent is essential to ensure that any expanding gas can escape without causing harm to the diver's body.

Ensuring the ascent is made slowly also contributes to safety but is fundamentally enhanced by maintaining normal breathing, making the act of exhaling equally important in the context of safe diving practices.