I was asked a few weeks back about connections; when something is attached to a structural member that is or has to be fireproofed.
We can think of each connection as a “thermal short circuit”, meaning a clip, a piece of steel, or some kind of metal framing that is connected to the structural frame of the building thus creating a path of heat transfer, presumably high heat from a fire, thereby short circuiting the fire protection which may cause premature failure of the steel.
Depending on the size, shape, and configuration of the short circuit determines how it is handled. A small penetration, such as a roof fastener (screw) that penetrates the fireproofing on a roof deck, according to Underwriter’s Laboratories Inc, must be covered with at least 1/2” of fire resistive material.
If we have a large (large being defined as having a W/D ratio of .38 or greater) seismic brace stabilizing a masonry wall, or something similar, the rule in this condition is that the attachment must be sprayed with the same material and thickness 12” away from that protected member or to it full length if the attachment less than 12”.
In between, we have thermal short circuits larger than the point of a screw, but smaller than a .38 W/D, typically a length of thin gauge framing stabilizing a drywall partition. Without the minimum .38 W/D, the accepted position is that the metal attachment, be it track or stud, only has to be fireproofed to the same thickness as the structural member.
Extending the fireproofing away from that member is meaningless by size definition and therefore is not necessary.