As I remember from my Building Practices class in college, fire blocking is used to stop the chimney effect of a fire when it's burning inside a wall, preventing or slowing the fire until help can arrive. They used to figure a 2 x 4 would take about an hour to burn through, giving the fire dept. time to do their job. In my area blocking was generally only required for exterior walls. Your stand alone office may not need to go this far, but it never hurts, as you are the one to benefit, and it would be a shame to lose a building over the cost of a 2 x 4 and some labor.
