Check the original as built fire strategy as office doors do not usually need to be fire rated (except dead ends, high risk areas etc). It may be that at some point in time someone has put fire signage on the doors
Protected corridors
2.24 A corridor serving as part of the means of escape in any of the following circumstances should be a protected corridor.
a. Every corridor that serves bedrooms
b. Every dead-end corridor (excluding recesses and extensions a maximum of 2m deep, as shown in Diagrams 2.7 and 2.8).
c. Any corridor shared by two or more occupancies (paragraph 2.17).
Enclosure of corridors that are not protected corridors
2.25 If a corridor is used for a means of escape but is not a protected corridor, even though the enclosing partitions may have no fire resistance, both of the following should be met to inhibit the spread of smoke.
a. Partitions should continue to the soffit of the structural floor above, or to a suspended ceiling.
b. Openings into rooms from the corridor should be fitted with doors, which do not need to be fire doorsets.
Open planning will not inhibit the spread of smoke, but occupants can become aware of a fire quickly.