Expert: Dan Griffin - 2/12/2008

Question
Dan, I am taking a Fire Codes & Inspections class at a local community college and the following question was posed, but the instructor did not know that answer.  Why is a 20 minute fire rated door allowed in a 1 hour fire wall? The instructor said that IFC and IBC allow a lessor rated door assembly within any fire wall.  For example: 2 hour assembly could have a 90 min door; 1 hour assembly could have a 20 min. door.  Does this sound right? and why is the lessor rated door allowed?  Thanks very much.

Rich Rodewald

Answer
Rich, codes come from so many directions and have so many implications it is amazing we ever get a building built.  Double check your statement about a 20 minute door in a 1 hour wall.  The doors will always be rated for a lower time than the walls.  

There are two distinctions made about fire rating doors - integrity failure and stability failure.  That lower number rates the integrity failure which is deemed to occur when cracks or other openings exist through which flames or hot gases can pass or when flaming occurs on the unexposed face.

Stability Failure, which will match the rating of the wall assembly, is deemed to occur when collapse of the specimen takes place.

I do not have a better explanation or reasoning for this distinction about doors.