Boiling was the act of vaporising a liquid.
The boiling point of water was much lower in a vacuum, so one's sweat, saliva and the fluid around their eyes would boil if exposed to outer space. (TV: Oxygen)
By the 26th century, the seas of Earth had been polluted, irradiated, set on fire and boiled off into a thick sludge. (PROSE: Ship of Fools)