metal door frame
Fire doors frames are not affected by the exposure ratings and opening classifications that apply to doors. There are no hourly ratings for a basic fire door frame unless the labeling on the frame specifically states that the frame is rated for something less than 3 hours. If a frame bears a recognized label qualifying it as a fire door frame, it may support a 3-hour, a 1-1/2-hour, a 3/4-hour, or a 1/3-hour door. Frames used in masonry walls may be used with a maximum 3-hour fire door, while frames used in drywall walls are intended to be used with a maximum 1-1/2-hour fire door.