A well control system having well controlled fluids distributed through pipes includes valves that are opened by a heat softened valve obstruction element. The translation of a fluid flow obstructing gate in a gate valve is driven by a stem element attached to the gate. Without a mechanical or fluid obstacle, fluid pressure in the distribution pipe above about 2 psi will drive the valve gate to a biased position. This internal pressure displacement of the valve gate also displaces the gate stem. In the present invention, the displacement of gate stems for critical valves from a normal maintenance position to an emergency activation position, is obstructed by a fusible barrier that is secured across the gate stem translation path. In the event of a well fire, at a predetermined temperature of fusion, the barrier element will no longer resist the displacement force imposed by the stem. The internal pipe pressure on the stem will force penetration of the stem through the fusible barrier thereby permitting the valve to open and release fluids into the well for the purpose of plugging uncontrolled well flow and extinguishing the fire.