Abstract: A safety release pipe cap for emergency venting of fluids under excessive temperatures by melting out a replaceable portion. In one embodiment the replaceable portion is arranged to yield under excessive pressure differentials on its opposed faces. The cap is employed on tanks. A threaded ferrule is provided with a flange overlying the end of a pipe with which it is threadingly engaged to clamp the periphery of a separable disk of thermally fusible material against the pipe end. When the disk is of a yieldable plastic it functions as a seal gasket on the pipe end and will yield under pressure differentials to provide a visual indication of such differentials by material and wall thickness characteristics as well as the geometry of the disk. Temperature fusing can be controlled by these characteristics and particularly the melting temperature of the plastic.