Which of the following actions can likely cause a pneumothorax?

A pneumothorax occurs when air leaks into the space between the lung and the chest wall, which can cause the lung to collapse. Among the actions listed, ascending while holding one's breath can lead to this condition primarily due to the expansion of air in the lungs as pressure decreases during ascent.

When a diver ascends, the pressure decreases, and if they hold their breath, the air trapped in their lungs can expand. If this expansion exceeds the lung's capacity, it may cause the lung tissue to rupture, leading to a pneumothorax. This is a critical point in diving safety, emphasizing the importance of exhaling during ascent to prevent over-expansion of lung air spaces.

Other actions, like staying down too long and descending too rapidly, can cause other types of diving-related injuries, such as decompression sickness or barotrauma, but they are not directly associated with the specific mechanism that leads to a pneumothorax as holding one’s breath during ascent is. While diving too deep can also pose various risks, the direct link to pneumothorax in this context is mainly tied to the improper ascent techniques outlined.