The overlap between the leaf and the door frame of the steel fire door shall not be less than 10mm, and the gap on both sides between the leaf and the door frame shall not be greater than 4mm. After the fire door is installed and closed, the gap should not be too large, otherwise the airtight performance of the fire door will be difficult to guarantee, and it will be difficult to reflect its function of suppressing the spread of fire and smoke under fire conditions.