Hydraulic ventilation is another method of ventilation that is very useful if vertical ventilation or positive pressure ventilation is either unsafe or not a feasible strategy. Hydraulic ventilation is done by setting up a hose line on a fog stream and directing it out a window.
The passage describes hydraulic ventilation as a viable option for situations where traditional methods like vertical ventilation or positive pressure ventilation are unsuitable. It involves using a hose connected to a fog stream and directing it out of a window.