A duct member, comprising: a tubular wall defining a passageway between an upstream end portion and a downstream end portion of the tubular wall; a damper adapted to be sealed within the passageway; an opening in the tubular wall between the upstream end portion and the downstream end portion, adapted to allow access for positioning the damper within the passageway, and; a closure member, adapted to sealingly close the opening, wherein the closure member comprises at least two fasteners (108, 110) adapted to fasten the closure member to the tubular wall; characterised in that: the closure member is a detachable closure member adapted to detach from the tubular wall; wherein the damper is mounted on the detachable closure member and is adapted to sealingly engage with an inner surface of the tubular wall and an inner surface of the detachable closure member to seal the passageway when the detachable closure member is in a closed position; wherein the duct member comprises a saddle portion matingly engageable with the tubular wall at a location opposite the opening, and adapted to lockably cooperate with the fasteners (108, 110) of the detachable closure member; and wherein the saddle portion has first and second ends, each of the first and second ends having a respective flange portion (118, 120) adapted to engage with one of the first and second fasteners (108, 110) respectively. a tubular wall defining a passageway between an upstream end portion and a downstream end portion of the tubular wall; a damper adapted to be sealed within the passageway; an opening in the tubular wall between the upstream end portion and the downstream end portion, adapted to allow access for positioning the damper within the passageway, and; a closure member, adapted to sealingly close the opening, wherein the closure member comprises at least two fasteners (108, 110) adapted to fasten the closure member to the tubular wall; characterised in that: the closure member is a detachable closure member adapted to detach from the tubular wall; wherein the damper is mounted on the detachable closure member and is adapted to sealingly engage with an inner surface of the tubular wall and an inner surface of the detachable closure member to seal the passageway when the detachable closure member is in a closed position; wherein the duct member comprises a saddle portion matingly engageable with the tubular wall at a location opposite the opening, and adapted to lockably cooperate with the fasteners (108, 110) of the detachable closure member; and wherein the saddle portion has first and second ends, each of the first and second ends having a respective flange portion (118, 120) adapted to engage with one of the first and second fasteners (108, 110) respectively. the closure member is a detachable closure member adapted to detach from the tubular wall; wherein the damper is mounted on the detachable closure member and is adapted to sealingly engage with an inner surface of the tubular wall and an inner surface of the detachable closure member to seal the passageway when the detachable closure member is in a closed position; wherein the duct member comprises a saddle portion matingly engageable with the tubular wall at a location opposite the opening, and adapted to lockably cooperate with the fasteners (108, 110) of the detachable closure member; and wherein the saddle portion has first and second ends, each of the first and second ends having a respective flange portion (118, 120) adapted to engage with one of the first and second fasteners (108, 110) respectively.