The fire resistance of steel fire doors is different. The fire resistance can be divided into three grades: A, B and C. Steel fire doors of different grades can be used in various places. The fire resistance time of Class A steel fire door shall not be less than 1.5 hours, that of Class B steel fire door shall not be less than 1.0 hours, and that of Class C steel fire door shall not be less than 0.5 hours.

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