National standards on the fire door joints of the gap size has clear requirements: for steel fire doors, the requirements of the door and frame lap not less than 10mm, the gap between the two sides of the door and frame not greater than 4mm.The gap after the fire door is installed and closed cannot be too large, otherwise the sealing performance of the fire door is difficult to guarantee, and it is difficult to reflect its role in suppressing fire and smoke spread under fire conditions.
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