Abstract: A retaining device is described. The retaining device has a retaining barrier, wherein the retaining barrier has a support frame including at least three arms. The support frame is adapted to assume a non-operating closed configuration and an operating radial configuration. In the operating radial configuration, each arm is oriented along a respective radial direction; in the non-operating closed configuration, at least a first arm is oriented along the same radial direction of the operating radial configuration and the remaining second arms are oriented along a direction substantially parallel to said radial direction of said at least one first arm.