Functional Safety (IEC 61508)

What is Functional Safety?

Functional safety is the part of overall plant safety that depends on the correct functioning of control and safety systems. The IEC 61508 standard defines the framework for designing, implementing and maintaining electrical, electronic and programmable electronic (E/E/PE) systems that perform safety functions.

A key concept is the Safety Integrity Level (SIL), which defines the required reliability of a safety function on a scale from SIL 1 (lowest) to SIL 4 (highest). Determining the required SIL is based on risk analysis - assessing the probability and consequences of a hazardous event.

IEC 61508 is the parent standard from which sector-specific standards derive: IEC 61511 for process industries, IEC 62061 for machinery, ISO 26262 for automotive. These standards specify requirements for the entire safety system lifecycle - from concept and design through operation and decommissioning.

Why does it matter?

Cybersecurity and functional safety are inextricably linked. An attack on a SIS or safety controller could prevent proper response to a physical hazard - as demonstrated by the TRITON/TRISIS attack on Triconex controllers in 2017. The IEC 62443 standard addresses cybersecurity for automation systems, but effective protection requires collaboration between safety and security teams.

Related topics

• SIS
• IEC 62443
• OT security