Subsea Intervention Workover Control Systems Provides the requirements for the design, manufacture, and testing of intervention workover control system (I WOCS) equipment typi cally used in a thru - blowout preventer intervention riser system and an open - water intervention riser system. Some requirements in this document are specific to the execution of end user - defined safety functions. This do cument defines “safety class control functions” used to operate safety cl ass devices. This document provides guidance on the determination of safety class control functions based on the end user - provided safety functions