I wonder if anyone can help.

I am involved with an old Government Building, ( an 3 story old old tax office). The ceilings are the old original fibre board fixed I think to wooden groundings below the Concrete floor slabs. The building has had a Fire Risk Assessment by a Fire Consultancy, ( apparently ex Fire services). They have certified the building, but I have reservations due to the ceilings being the old fibre board type. I am trying to find fire rating information both Resistance and fire spread, but being an old material I am struggling to find any. I wonder if anyone has any thoughts and knows where I can find this kind of information.

Usually I advise clients to upgrade these ceilings to plasterboard to gain 30 min protection.