Class A fire door: the fire resistance limit is not less than 1.5 hours, which is used in other fire partitions (firewalls, fire compartments, atrium, etc.), densely populated places (cinemas, auditoria, etc.), important warehouse doors (confidential rooms, archives, etc.), etc. Class B fire door: the fire resistance limit is not less than 1 hour, used for opening the door on the safety exit (closed stairwell, smoke prevention stairwell and front room, etc.), entertainment building doors (KTV, entertainment halls, etc.), places with high risk of fire homes (kitchens in public buildings, attached warehouses in civil buildings, etc.), room doors used by vulnerable groups (operating rooms, delivery rooms), etc. Class C fire door: the fire resistance limit is not less than 0.5 hours, which is used for shaft protection (pipe well door, etc.), internal communication door and the door of some equipment rooms open to the outside (transformer and distribution room, etc.). For safety reasons, it is recommended to buy fire door brand products.