Abstract: The existance of fire at or near an oil field wellhead is sensed by a eutectic body which holds a valve system in a cocked position. When the eutectic is melted, the valves are positioned to terminate communication of a hydraulic fluid pressure source with a downhole safety valve and open a bleed conduit connected with the conduit to the downhole valve. A second eutectic body will melt at a different temperature than the first, providing a second position for the valve system which closes the conduit to the downhole valve and atmosphere to give positive isolation from the oil well fluid.