Alonso, this is all about access rooms and inner rooms. In this case, the staff room is the access room and the kitchen is the inner room. If the only escape route from an inner room is via the access room, then early warning of fire must be provided to people in the inner room. The three generally accepted methods of doing this are: leaving a 500mm gap between the had of the dividing wall and the soffit, providing a vision panel so that the access room remains in view of occupants of the inner room, or providing smoke detection (heat detectors respond too slowly to provide suitable early warning) in the access room and ensuring that the FA sounders are audible in the inner room.
I have known people to remove doors between access rooms and inner rooms, thereby effectively making the two rooms a single room, and similarly, if it can be guaranteed that the door would remain open at all times that the inner room is occupied, it could be argued that the risk was suitabley controlled, although I think that it would be a tough one to manage. I wouldn't hang my reputation on such an arrangement.