Between floors any chase (open space) must be sealed with an approved fire blocking material. This is to prevent heated air by a fire rushing through this space rapidly spreading a fire. So if you have a soffit (ceiling) it needs to be fire blocked at the lower intersection with a wall. Each exterior wall along your perimeter between floors needs to be fire blocked. This is typically done with a 2X4 block. Even any penetration along the wall plates between floors needs to be fire blocked. These holes are caulked with a fire retardant caulking. For retro-fit you can just stuff mineral wool insulation into the larger spaces and fire retarding caulking in areas where pluming or electrical lines go through the floor/wall junction.