Downhole safety valve:

A downhole device that isolates wellbore pressure and fluids in the event of an emergency or catastrophic failure of surface equipment.

The control systems associated with safety valves are generally set in a fail-safe mode, such that any interruption or malfunction of the system will result in the safety valve closing to render the well safe.

Downhole safety valves are fitted in almost all wells and are typically subject to rigorous local or regional legislative requirements.