Safety Security - Is a Physically Separation of the SIS Necessary?

Industrial security is becoming more and more important in the process industry as plant automation systems are being increasingly connected to the office environment and internet. In the meantime, security aspects have also influenced functional safety standards such as IEC 61508 and IEC 61511 (CDV). But there are different targets for safety and security. Safety avoids accidents and damage when a fault occurs and ensures maximum safety for people, processes and the environment. Security protects a machine or plant against unauthorized access by people and against malware, and ensures the availability of the machine or plant. Two questions arise, first, how should security aspects be considered for the Safety Instrumented System (SIS), and second, is a physically separation of the SIS from the Basic Process Control System (BPCS) necessary? The following paper describes SIS security aspects as provided in ISA TR84.00.09, and Industrial Security aspects with additional security layers for the SIS as an integrated approach for SIS & BPCS.