A containment system for internal arc generated gasses includes a compartment having an aperture through a wall thereof. A bus compartment includes an opening through a wall thereof. Arc chamber is in communication with the aperture and the opening. A vent flap member closes the opening and is moveable to an open position to permit gasses to flow through the opening into the arc chamber. Flap structure is associated with the aperture and includes a plurality of interconnected flaps for moving generally simultaneously from an open position, permitting gasses to flow through the aperture into the arc chamber, to a closed position, closing the aperture to prevent gasses from flowing through the aperture. The flap structure includes actuating structure coupled with the interconnected flaps. The vent flap member, when moved to the open position thereof, engages the actuating structure to move the interconnected flaps to the closed position thereof.