Altitude at which the water boiling point equals human body temperature is 18,000m, and it's called Armstrong's line. The blood in the blood vessels wouldn't boil because it's still under pressure, but exposed liquids (eyes, mouth, nose, lungs) would. A person would lose conciseness 10s after decompression, and would die a minute or two after. A standard oxygen mask would not prevent this, only a pressure suit would.
I don't think this is modeled in DCS.