These requirements cover the design and construction of "tin-clad" fire doors which have demonstrated in fire tests, fire performance properties sufficient to warrant their use in closure assemblies having a fire-protection rating of up to and including 3 h, when tested in accordance with CAN/ULC-S104, Standard Method for Fire Tests of Door Assemblies.

A door conforming to these specifications consists essentially of a core made up of layers of boards nailed to each other, encased in terne or zinc plates jointed together at their edges and nailed through the seams to the core.

The sizes and ratings for three-ply and two-ply doors, constructed in accordance with these specifications, are given in Table 1. These ratings are designed to enable regulatory bodies to determine the suitability of the door assemblies described in this Standard for use in locations where a fire resistance of a specified duration is required. Requirements for the details of the installation of "tin-clad" fire doors, including the requirements for vent holes, are included in NFPA 80, Standard for Fire Doors and Other Opening Protectives.

Table 1 pertains only to the maximum size of the opening. Doors limited in size by this table fall into two categories:
A Swinging doors intended to be installed within an opening; and
B All sliding doors and those swinging doors intended for surface mounting outside of the opening.