When I first watched the videos, I braced myself for seeing people screaming as their skin froze, Ice-9-style. While
thatskin damage could be a danger to adding liquid nitrogen to a pool, Bracher doesn't think that happened because, well, the swimmers didn't scream or jump out of the pool or anything. Instead, he told me in an email, it seems staffers added the liquid nitrogen slowly enough that it boiled away before it touched anyone's skin. Liquid nitrogen has an extraordinarily low boiling point of -196 degrees Celsius, or -321 degrees Fahrenheit, and quickly boils at room temperature. It was that boiling action that displaced oxygen for the swimmers.