Emergency Shutdown systems (ESD), which are also called Safety Instrumented Systems (SIS), are used in parallel with control systems to provide higher level of safety. Sensors and actuators of ESD system shall be separated from the control system ones. In a typical process, risks of control loops are evaluated and based on this evaluation a Safety Integrity Level (SIL) will be assigned to each control loop. All equipment in the loop shall have a SIL equal or higher than the loop SIL or shall be arranged in a configuration to provide the required SIL. The SIL of ESD system shall be the highest SIL among the control loops in the process under control. The assigned SIL determines the configuration of the system.