Don't Use Air Vents!

Here's an old but funny post from John August: Air vents are for air

Thanks to continuous bombardment in television and movies, the idea of characters shimmying through air ducts has become not just a cliché, but almost a given. The moment a hero finds himself stuck someplace, we expect his eyes to drift north to that spot just below the ceiling, where an oversized grate is beckoning: “Just yank twice! I’m not screwed in or anything!”

Maybe they can support... zombies?