What does the ‘T’ rating indicate in firestop assemblies?

The 'T' rating in firestop assemblies specifically indicates the time in hours before the surface on the unexposed side of the assembly exceeds 325°F. This measurement is critical in assessing the fire resistance properties of a building's materials during a fire, as it determines how long the unexposed side of the firestop assembly can remain at a safe temperature before potentially producing a hazard.

Maintaining a temperature below 325°F is essential since this threshold is aligned with the potential for heat to compromise other materials or cause ignition of combustible materials on the unexposed side. A proper understanding of the ‘T’ rating helps in evaluating and ensuring safety during scenarios that involve fire, thus playing a crucial role in building design and fire protection strategy.

The other options, while they may relate to different aspects of firestop testing or safety, do not directly correlate with the definition of the 'T' rating.