What you’re looking at is an existing fire rated frame with a new door that I saw recently during a fire door inspection. Most of the other doors that I inspected that day had steel hinge fillers to fill the existing hinge preps before the continuous hinges were installed. So why were a half-dozen or so filled with expandable foam insulation? Hmm…it’s a mystery.
Mystery solved. At some point in the lifetime of these frames, some of the welds holding the hinge reinforcements to the frames broke, and the reinforcements were secured using screws through the door rabbet above and below the hinge prep. When the installer removed the screws to have a flat surface to attach the continuous hinge to, the hinge reinforcements fell into the frames, leaving nothing to attach hinge fillers to.
NFPA 80 requires holes left by the removal of hardware to be filled with door/frame material or steel fasteners, so I had to include the foam as a deficiency on my inspection report. One of the common causes of hinge reinforcement failure is the lack of a door stop, so don’t forget to specify a stop. Whether it’s a simple wall stop or floor stop, an overhead stop, or even an integral stop in a closer, it will help to protect the opening from damage.