I.out [美 aʊt, 英 aʊt]副out often appears as the second element of certain verb structures in English (come out, keep out, knock out, etc). For translations, see the relevant verb entry (come, keep, knock, etc).
She always wears headphones which blares music into her ears to black out the sounds of the surrounding world thereby giving her a safe refuge in her own world.
Rapid depressurisation certainly answers the question as to why victims black out so close to the surface and without distress but it is still unclear why it happens at all.