fire resistance rating - pan joist floor

huangyhg

fire resistance rating - pan joist floor
i am looking at fire resistance requirements for pan joist floor, using ibc 2000, type 1a construction.  per table 601, for type 1a, structural frame (columns and beams/girders framing into the columns) requires 3 hour, floor construction requires 2 hour.  i am assuming that pan joist top slab thickness therefore can be based on 2 hour, which results in 4.6" minimum thickness per table 719.1(3). the thing that bugs me is that table 719.1(3) shows required slab thicknesses for fire resistance ratings up to 4 hours.  however, table 601 does not require 4 hour for anything.  this makes me wonder if i am missing something.  do you agree with the 2 hour/4.6" top slab thickness for type 1a construction?   
check out our whitepaper library.
you might also be able to get your rating with a thinner top slab and block fillers in the void between the ribs. no metal pans required for this type of construction, just a flat deck.
similar situation - went with 4 3/4" slab thickness.  no questions from local codes or fire marshalls.