2000 IBC states that (711.3.3)
Membrane penetrations shall comply with Section 711.3.1. Where walls and partitions are required to have a minimum 1-hour fire resistance rating, recessed fixtures shall be installed such that the required fire resistance will not be reduced.
1. Steel electrical boxes that do not exceed 16 square inches in area provided the total of such openings does not exceed 100 Square inches for any 100 square feet of wall area. Outlet boxes on opposite sides of the wall shall be seperated as follows:
1.1 By a horizontal distance of not less than 24";
1.2 By a horizontal distance of not less than the depth of the wall cavity where the cavity is filled with cellulose loose fill or mineral fiber insulation;
1.3 By solid fire blocking in accordance with Section 716.2.1; or
1.4 By other listed materials or methods.
Salt Lake City