A thermostatic mixing valve including a cold water bypass passageway controlled by a pressure-operated check valve that opens upon a failure of a hot water supply to the valve for use with safety devices, such as eyewash and drench shower stations. The thermostatic mixing valve allows the continued delivery of cold water upon a failure of a hot water supply. The lack of hot water causes a cold water valve opening to be closed by a thermal motor, which retracts upon the lack of hot water, yet the bypass passageway is adapted to allow cold water to bypass the thermal motor-controlled cold water valve opening and be directed to the outlet of the valve.