Plant Hazard Analysis and Safety Instrumentation Systems

8.0. Functional Safety and Safety Integrity Level

So far, short discussions have been presented on SISs. Naturally, one important question comes to mind; what is safety? According to IEC 61508, safety is the freedom from unacceptable risk (3.1.8). This is overall of physical injury or damage to health of people directly or indirectly as a result of damage of property or to the environment. Then; what is functional safety? Functional safety is a part of overall safety, responsible for correct operation of system or equipment in response to input changes including safety management taking into account the possibility of human error and/or system/equipment or hardware failure and environmental changes. Functional safeties usually stand for the equipment ...