It's the only move on the part of a villain that's stupider than Locking MacGyver in the Store Cupboard (or any room with a bed). When heroes find themselves trapped in a room with all doors and windows locked, the quickest exit is always through the ventilation duct. Air vents also work excellently in reverse for breaking in and infiltrating a facility, as well. Covers require little or no effort to remove, openings are always within reach, they're always able to support the weight of a person even though they were only designed to carry air, they are wide enough in diameter to allow an adult to pass through, there are no internal obstacles like bracing or blowers (except for the occasional menacing giant fan blocking the branching corridors), they are free of normal sheet metal's dangero