You can't hold your breath in a low pressure environment. Also the low partial pressure of oxygen causes it to diffuse out of your blood instead of in. Even peo

You can't hold your breath in a low pressure environment. Also the low partial pressure of oxygen causes it to diffuse out of your blood instead of in. Even people who can hold their breath for a couple minutes under normal circumstances will have severe hypoxia impairment in less than a minute above 30K feet. https://en.wikipedia.org/wiki/Time_of_useful_consciousness https://en.wikipedia.org/wiki/Time_of_useful_consciousness