For those who are wondering "What is wrong with these guys?", The Approved Documents are the Brits version of the Building Code. I think there are about 14 classes, some broken down even more basically within class.
"B" is a three part document on fire safety. Their ratings are much like ours, and they also stress that adequate warning and vacating times be figured into the particular structure or construction method fire rating.
We are being somewhat (seemingly) unkind with his post because this is a contractor's forum. And over there, just as here, he dang well BETTER already know what the AD's mean.
He claims to be Chartered (their version of our professional certification) by posting CIOB affiliation. As such, he needs no explanation of Fire Resistance Ratings.