Labels on fire doors, fire door frames, or other components of a fire door assembly, are the identifying mark that the door or component has been tested to the required first test standards and has passed the criteria required by those test standards. Labels prove to inspectors, AHJs, building owners, or anyone else observing the fire door assembly that it (as tested) will protect the opening as it did when tested.
[NFPA 80 | http://www.nfpa.org/80], 2013 edition, contains the following language regarding labeled products:
4.2.1* Listed items shall be identified by a label.
4.2.2 Labels shall be applied in locations that are readily visible and convenient for identification by the AHJ after installation of the assembly.
Associated annex language to Section 4.2.1 sheds some light on the intent of the labeling provisions in NFPA 80:
A.4.2.1 Labels can be permitted to be of metal, paper, or plastics or can be permitted to be stamped or diecast into the item. Labels should not be removed, defaced, or made illegible while the door is in service. If the label on an existing fire door has been removed or is no longer legible, it is acceptable to verify the rating of the fire door through other means acceptable to the AHJ such as an inspection or certification service that provides acceptable documentation.
One of the most frequently asked questions that I received regarding labels is whether or not they can be painted. Paint most often will render the label illegible, thus it is not recommended that labels be painted. Proper training and education should be provided to those in buildings who may be doing repair or maintenance work to doors to ensure they are aware of the risks associated with painting fire door labels.
Labels are required in a number of applications on all types fire door assemblies. Where NFPA 80 mandates a label be present, it should meet the requirements of Chapter 4 as noted above.