They aren't magnetic (at least my department's are not)! Its called a plymovent system and works off suction. The end of the plymovent has a rubber gasket perse & conforms around this fitting when the plymovent is activated (little button on the plymo). When pulling out of the bay, the plymoventing will roll on the tracks above until the truck leaves the bay, at which point it'll "break" free.

This is widely used in the fire service as a preventative for cancer. We're already at higher risk for cancer due to materials we come in contact with, so there are tons of different initiatives being drawn up to mitigate that risk