The infamous 0.40 bac

How many times have you heard that a 0.40 bac is lethal, “your dead” if you drink to a 0.40… im just curious because I didn’t have a tolerance (I don’t know how much this effects overall bac)…that being said drank about 20 shots in a hour last fall… puked then passed out 40 min later… woke up the next day covered in puke still piss drunk 12 hours later. Yes I know I’m lucky to be alive but im interested in the science of it; I’ve heard stories of people surving 0.5 & 0.6 bac even. So if anyone here knows the science behind surviving such an amount of booze, lmk your take? Is it just respiratory failure & what not? I’m just guessing it was a 0.40 because I’ve had blood draws before where it turned out to 0.30 & didn’t feel anywhere close to that night I drank 20 shots…