The main difference between a tension pneumothorax and an open pneumothorax lies in the difference in pressure. If the pressure inside the pleural cavity is approximately the same as the atmospheric pressure, it is referred to as an open pneumothorax. In this case, typically after an injury, the wound allows air to freely enter and exit during breathing. When inhaling, air can enter the pleural cavity, and the air can be expelled during exhalation. At this time, because the system opens and closes with each inhale and exhale, the pressure is roughly equal to atmospheric pressure. On the other hand, in a tension pneumothorax, under certain conditions, when air enters the pleural cavity and cannot escape during exhalation, such as when a sort of flap forms, for example after a trauma causing a rupture in the bronchus or trachea, this flap prevents the expulsion of air from the pleural cavity. Therefore, the pressure in the pleural cavity continues to increase, significantly higher than atmospheric pressure. This is the difference between a tension pneumothorax and an open pneumothorax.