Section 704.2 requires that all openings in fire barriers be protected with fire-rated doors or firestopped penetrations. Fire-rated doors must have ratings equal to 75 percent of the barrier rating (minimum 20 minutes). Self-closing mechanisms and smoke seals prevent passage of flames and smoke. Multiple doors in series create additional separation. Through-penetrations must be sealed with materials tested per ASTM E814. Ductwork crossing barriers requires fire dampers that close upon temperature rise.