F Rating: The time period for which the penetration firestop system
limits the spread of flames through the penetration when tested in
accordance with ASTM E 814 or UL 1479. In order to achieve an F
rating, the firestop system must also maintain its structural integrity,
as evaluated through a hose stream test. See Figure 2.8 for an
illustration of the difference between an F rating and a T rating. F
rating is measured in minutes or hours.
T Rating: The time period during which the penetration firestop
system limits the spread of flames through the penetration and limits
temperature rise on the unexposed (non-fire) side of the assembly,
including that on the penetrating item, to a maximum of 325°F
above its initial temperature when tested in accordance with ASTM
E 814 or UL 1479. In order to achieve a T rating, the firestop system
must also maintain its structural integrity, as evaluated through a
hose stream test. See Figure 2.8 for an illustration of the difference
between an F rating and a T rating. T rating is measured in minutes
or hours.
The temperature-rise limitations match the maximum individual
point temperature rise from the ASTM E 119 and UL 263 tests,
which are used for determining the fire-resistance rating of the wall
or the horizontal floor or roof assembly. By the T rating test imposing
the same maximum temperature rise limitations, it has essentially
restored the fire-resistance-rated wall or horizontal assembly back
to its original condition and shown that the penetration does not
reduce the original assembly’s ability to stop a fire from spreading.
Obtaining a T rating is more difficult than obtaining an F rating. This
is because the T rating indicates that the firestop system is not only
capable of stopping the flames from passing through the assembly
at the penetration, as an F rating, but it also limits the heat transfer
to the unexposed side of the assembly.