F Rating: An F rating is the time period for which the perimeter
fire containment system prohibits the passage of flames sufficient
to ignite cotton waste through or around the boundaries of the
materials installed within the void.
T Rating: A T rating is the time period for which the perimeter fire
containment system: a. Prohibits the passage of flames sufficient
to ignite cotton waste through or around the boundaries of the
materials installed within the void; b. Limits the temperature rise on
the unexposed (top) side of the materials installed within the void to
a maximum at any individual point of 325oF (180oC) above its initial
temperature; and, for joints with a maximum width greater than 4
inches, c. Limits the temperature rise on the unexposed (top) side
of the materials installed within the void to an average of 250oF
(140oC) above its initial temperature.
Note the temperature rise limitations for a T rating match the
maximum individual point and average temperature rise from
the ASTM E 119 and UL 263 test used for determining the fire-
resistance rating of the floor assembly. By the T-rating test imposing
the same temperature rise limitations, it has essentially extended
the fire-resistance rating of the floor assembly to the interior face of
the curtain wall. Obtaining a T rating is more difficult than obtaining
an F rating. This is because the T rating indicates the perimeter fire
containment system is not only capable of stopping the flames from
passing through the void as an F rating does, but it must also limit
the heat transfer to the unexposed side of the materials used to
protect the void.
The code, in Section 715.4, requires perimeter fire containment
systems to have an F rating, which is equal to or greater than the
fire-resistance rating of the floor. This expected level of performance
was addressed previously.