What characterizes safety instrumented systems (SIS)?

Safety instrumented systems (SIS) are designed to maintain safe operation by effectively reducing risks associated with hazardous processes. These systems are integral to industrial operations, particularly in environments where there is a potential for accidents or unsafe conditions. They function by implementing specific safety functions that can automatically bring the process to a safe state in the event of a fault or abnormal situation.

The focus of an SIS is on risk management; it assesses potential hazards and implements preventive measures to mitigate these risks. By doing so, SIS contribute directly to the safety of personnel, the environment, and equipment, aligning with the principles of functional safety as outlined in industry standards such as IEC 61508 and IEC 61511.

In contrast, systems that do not take action or require human intervention do not effectively fulfill the purpose of a safety instrumented system, which is to provide automated responses to dangerous conditions without relying on human decision-making. This automation is key in scenarios where quick action is necessary to avert disaster. Additionally, focusing solely on optimizing production rates does not align with the primary functions of safety critical systems, which prioritize safety over production efficiency.