Remote IO Modules, or RIMs, require a Fusion controller or RIM Control Module (RCM) to operate.  The RIM is an extension of the SIL3 safety system, with its on-board safety logic devices directly connected peer-to-peer with the controller via RIM ports.  Though the RIM is powered by its own 24VDC supply, the SIL3 safety system will default to a safe state if a condition arises that breaks the connection between the controller and RIM.  If a RIM is disconnected from the controller, all of its on-board IO cards will be put into a safe state.