A gas-insulated high or medium voltage circuit breaker (100, 200) comprising: a first arcing contact and a second arcing contact, wherein at least one of the two arcing contacts is axially movable including a first and a second state of motion along a switching axis, wherein during a breaking operation, an arc between the first arcing contact and the second arcing contact is formed in an arcing region; a nozzle including a channel directed to the arcing region, for blowing an arc-extinguishing gas to the arcing region during the breaking operation; a diffuser adjacent to the nozzle, for transporting the gas from the arcing region to a region downstream of the diffuser; a buffer volume directly downstream of the diffuser, and an enclosure substantially surrounding the buffer volume circumferentially, wherein the enclosure comprises: an inner enclosure portion and a coaxially arranged outer enclosure portion, a first aperture provided on a surface of the inner enclosure portion and a second aperture provided on a surface of the outer enclosure portion, such that a through opening is provided through the enclosure, characterized in that at least one of the inner portion and the outer portion is movable relative to the other one, wherein in the first state of motion during a breaking operation the through opening is blocked, as to prevent the gas from being released from the buffer volume to a volume outside of the enclosure; and in the second state of motion, the first aperture and the second aperture overlap, such that the overlap of the first aperture and the second aperture provides the through opening for the gas to be partially released from the buffer volume to the volume outside of the enclosure. a first arcing contact and a second arcing contact, wherein at least one of the two arcing contacts is axially movable including a first and a second state of motion along a switching axis, wherein during a breaking operation, an arc between the first arcing contact and the second arcing contact is formed in an arcing region; a nozzle including a channel directed to the arcing region, for blowing an arc-extinguishing gas to the arcing region during the breaking operation; a diffuser adjacent to the nozzle, for transporting the gas from the arcing region to a region downstream of the diffuser; a buffer volume directly downstream of the diffuser, and an enclosure substantially surrounding the buffer volume circumferentially, wherein the enclosure comprises: an inner enclosure portion and a coaxially arranged outer enclosure portion, a first aperture provided on a surface of the inner enclosure portion and a second aperture provided on a surface of the outer enclosure portion, such that a through opening is provided through the enclosure, characterized in that at least one of the inner portion and the outer portion is movable relative to the other one, wherein in the first state of motion during a breaking operation the through opening is blocked, as to prevent the gas from being released from the buffer volume to a volume outside of the enclosure; and in the second state of motion, the first aperture and the second aperture overlap, such that the overlap of the first aperture and the second aperture provides the through opening for the gas to be partially released from the buffer volume to the volume outside of the enclosure. an inner enclosure portion and a coaxially arranged outer enclosure portion, a first aperture provided on a surface of the inner enclosure portion and a second aperture provided on a surface of the outer enclosure portion, such that a through opening is provided through the enclosure, characterized in that at least one of the inner portion and the outer portion is movable relative to the other one, wherein in the first state of motion during a breaking operation the through opening is blocked, as to prevent the gas from being released from the buffer volume to a volume outside of the enclosure; and in the second state of motion, the first aperture and the second aperture overlap, such that the overlap of the first aperture and the second aperture provides the through opening for the gas to be partially released from the buffer volume to the volume outside of the enclosure.