Abstract: A fusible safety device for a pressure vessel includes a body of fusible material in the form of a tablet which acts as a leak-proofing gasket and is so arranged as not to be vulnerable to creep movement under normal temperature and pressure. The tablet is seated on a floor in a counterbore which puts the inside of the vessel in communication with atmosphere. The tablet is firmly compressed against the floor by a pressure plate in turn loaded by a sleeve screwing within the counterbore. The gas venting passage through the counterbore consists of a vent bore being the lesser diameter portion of the counterbore, and one or more holes in the pressure plate which are essentially out of axial alignment with the vent bore.