NFPA 72 §24.3.14

What it requires

Survivability is not the same thing as circuit class. A system employing relocation or partial evacuation requires Level 2 or Level 3 pathway survivability — typically 2-hour circuit-integrity (CI) cable, a 2-hour rated enclosure, or the alternatives the code allows in a fully sprinklered building. General-evacuation systems have no survivability requirement of their own.