UL Fire Ratings

[IAAWVU05]

I am on a fire protection project and was wondering what the correlation between the fire ratings were. There seems to be a lot of fire ratings for different things and it seems confusing. For example, why are UL 790 ratings listed as classes (Class A, B, C, etc.. ) for roofing materials, while wall materials have a fire rating in hours. It there a way to correlate a class rating to an hour rating?

 

[IAAWVU05]

Okay, after getting a hold of some sources, it turns out that the fire resistance ratings in hours refer to the structural fire performance, where as the fire spread rating relates to potential fire growth. I have observed that the Class A, B, and C are used with the fire spread rating, but the fire resistance rating will depend on the materials used. I found the UL fire resistance directory, but from what I observe, it lists only the constructed materials in conjunction with each other (masonry + insulation + other stuff constructed in a certain way gives you the fire rating in hours.) From the reference "Fire ratings of Archaic Materials and Assemblies" they list certain materials as having certian fire resistance ratings (i.e. 1-1/4" thick plywood has FR of 30 min) are there any other resources out there that list the fire performance ratings as such?