When is a Fire Door Required?
This is to some degree, bespoke to your building, generally to be tackled in conjunction with an overall Fire Strategy with an accompanying Fire Risk Assessment. Every building varies in many ways (size, floors, usage, occupancy, etc) as such different buildings will have very different needs for when a Fire Door is required.
A general rule, however, is that a Fire Door is required within a fire compartment line/wall to provide access to an area whilst retaining the fire compartment. In some buildings, not every door needs to be a Fire Door. Generally, the Fire Doors will be contributing to the fire line, with some additional Fire Doors (and compartments) required to rooms such as Kitchens, Plant Rooms, or other high-risk areas, and these may be standalone compartments.
Fire Doors will also be included to ensure escape routes remain protected wherever possible aiding a safe means of escape in the event of a fire.