T Rating : A rating usually expressed in hours indicating the length of time that the temperature on the non-fire side of a fire-rated assembly does not exceed 325F above ambient temperature
William J. McHugh, Jr., Glossary of Firestop Terms (Article, Life Safety Digest magazine), Firestop Contractors International Association FCIA, Hillside, IL, USA 2010. http://www.fcia.org/articles/glossary.htm , (Firestop - Amer) {511}