A gas segregator barrier is for quenching, segregating and controllably directing ionized gases discharged from a pair of spaced-apart circuit breakers double-branch mounted within a panelboard assembly. The spaced-apart circuit breakers include corresponding pairs of opposing poles, and a housing with exhaust vent openings for discharging ionized gases developed from an electrical fault. The gas segregator barrier includes at least substantially parallel segregator fins divided into first and second portions by a transverse dividing member. Baffles in the transverse dividing member quench the ionized gases and provide fluid communication between exhaust channels formed between the segregator fins of the first portion, and gas ducts disposed between the segregator fins of the second portion. The gas ducts include one or more lateral members structured to controllably direct the discharged ionized gases.