In the TV series "The Protectors", a villain plans his escape through the ventilation ducts, which have circulation fans on timers. If he times it right, the fans will switch on, blocking any pursuit..
In "The Middleman", the headquarters are invaded, so the Middleman activates the Nakatomi Protocol. This enlarges every ventilation duct in the building, so the Heroes can move around undetected.
And of course, "Voyage to the Bottom of the Sea", where it seems that EVERY room and compartment on the Seaview is accessible via large ventilation ducts.
David.