In the beginning of the film when Frank and Freddie accidently release the trioxin gas. The next shots follow the gas through the warehouse's main duct work. The gas then finds its way to the room where the Cadaver is hanging. This room was previously explained during the "warehouse tour" as being a freezer which would have had a sealed door and would have had its own separate refrigeration unit and a duct system separate from the warehouse's main HVAC system. This Zombie should not have reanimated.