Fire doors must meet the requirement of being airtight.

National standards specify clear requirements for the gap sizes at various junctions of fire-resistant doors: for steel fire-resistant doors, the gap between the door leaf and the door frame must not be less than 10mm, and the gaps on both sides between the door leaf and the door frame must not exceed 4mm. The gaps after the installation of fire-resistant doors cannot be too large, otherwise, the door's airtightness cannot be guaranteed, and its role in suppressing fire and smoke spread under fire conditions will be difficult to demonstrate. Therefore, the gap width during the installation of fire-resistant doors is strictly controlled. Installation according to these standards can ensure the effective function of fire-resistant doors to some extent. Consumers must supervise on-site when hiring construction units to prevent issues such as shoddy workmanship. This is the only way to ensure that fire-resistant doors do not cause casualties during fires.