Thermally broken hollow metal frames are commonly used for exterior openings because they improve thermal efficiency. These frames are not fire rate-able. The reason for this comes down to the thermal break itself.
These frames include a plastic material between the door side and the non-door side to reduce cold transfer from the outside. In a fire, this material cannot withstand extreme temperatures and can melt, causing the frame to lose its structural integrity and possibly separation or distortion.
Fire rated assemblies require one piece steel construction so the frame and door can remain intact and operational during a fire.
Understanding this limitation helps ensure code compliance and proper life safety planning in building design.
