There’s a scene in later part of The Expanse that has a moment like this
Can’t remember the exact biology (and there wasn’t consensus)
But most agreed you’d last about a minute
Right, the old Scottish space sailor had to walk the plank.
What literally kills you ("first") is gas bubbles forming in your blood that stop blood flow. This causes you to pass out in 15 seconds and this also causes you to die in about a minute.