With long enough exposure the steam would denature the proteins in the Z's cells internally an eternally killing it. Once the steam got into the Alveoli in the lungs that would be the end of it. It would no longer be able to breathe. No breath => No aerobic respiration. I reckon it would have an hour at the most if it was able to use up all of its fat reserves. By then its blood would be so acidic it would have pickled its self.
Bookmarks