When you look at a UL listed detail that has a 1-hour F rating, what does that tell you? At a very basic level you can expect the assembly was tested and didn’t let fire through for one hour. There is so much more to it than that and once you understand, it might change how you inspect firestop. Keep reading and let me know if it does.
F RATING- as defined on UL website
The F-rating criteria prohibits flame passage through the system and requires acceptable hose-stream test performance. Lets break this into two parts. First it is saying that fire doesn’t breach the assembly during the test period. Obviously, with firestop, we are trying to contain a fire; so we want to know that the rated assemblies will keep a fire at bay for the designated time period which is known as the F rating. A 1-hour rated wall is expected to contain a fire for 1 hour. F ratings for firestop are 1, 2, 3, and 4 hours. The temperature inside the furnace during the test will increase as the duration of the fire increases. For example in a 1 hour test the temperature will be at least 1700F (538C) at the 1-hour mark and 2000F at the 4-hour mark (1093C). Surviving these temperatures is still not enough to obtain an F rating for a rated assembly. There is one more critical element involved in the test procedure called the hose stream test.
HOSE STREAM TEST- what it is and isn’t
I have sat through too many classes on firestop, codes and what not, only to cringe when I hear the instructor tell the class that the hose stream test replicates impact of the fire fighting methods on the fire rated assembly. It is like nails on a chalkboard to me and I can feel it running down my spine. (Yes I am that much of a geek, that it bugs me to the core) By the time the fire fighters are on the scene with their hoses, any loss of life in that area has likely occurred. Property damage is done. Firestop serves no purpose at this point, because the integrity of the assembly has failed and fire has breached the wall or floor. Fire fighting methods are not part of the firestop test. I believe that understanding this critical element of the firestop testing process is integral to the proper inspection of firestop. We will get into this more shortly. In fact, a lot more, because this is a 5-part discussion about why the hose stream test needs to be better understood in order to improve firestop inspections. For now however, I would like to share this article by Chad Stroike of Hilti. Chad does an excellent job explaining the hose stream test, why it is part of the fire test standard and what it is intended to replicate.