 A SIS is engineered to perform "specific control functions" to failsafe or maintain safe operation of a process when unacceptable or dangerous conditions occur.Safety Instrumented Systems must be independent from all other control systems that control the same equipment in order to ensure SIS functionality is not compromised.SIS is composed of the same types of control elements (including sensors, logic solvers, actuators and other control equipment) as a Basic Process Control System (BPCS).