What is the maximum glazed area in a fire door?

What is the maximum glazed area in a fire door?

This will depend on the certification and fire test evidence for the door. Fire doors are subject to a fire test and will have been tested with a glazed aperture. From the fire test a report is produced giving details of limitations to the size and location of glazed apertures in the fire door. The door manufacturer’s instructions and test evidence must be consulted with regard to the installation of glazed apertures and on-site cutting and glazing is not allowed on CERTIFIRE certificated fire doors because it will invalidate the certification.