Abstract: Liquefied gas tank that is easy to machine and quick to operate and bag for sealing cable ducts incorporating said tank. The tank is provided with breaking means for inflating sealed compartments composed of a main pipe (1) closed on one side, an outlet pipe (4) inserted on the other side of the main tube through a first end (6) and closed on the distal end thereof, wherein the outlet pipe is provided with a narrowing (5) that defines a breaking point and an internal orifice (8) that extends from the first end of the outlet pipe to the narrowing (5) towards the distal end, and wherein the size of the narrowing (5), the size of the orifice (8) and the length of the outlet pipe (4) are determined such that a force applied on a lever of between 19N and 80N will break the outlet pipe (4) at the breaking point (5), releasing the gas through the orifice (8).