Functional Safety in machinery industry

Functional safety in machinery industry is defined in two international standards ISO 13849-1 and IEC 62061.

The standards incorporate safety functions and systems that operate in a high demand mode.

IEC 62061 is derived from the foundational functional safety standard, the IEC 61508 series, and addresses parameters such as Safety-Related Control Systems (SCS), Safety Integrity Level (SIL), Hardware Fault Tolerance (HFT), Safe Failure Fraction (SFF), and Probability of Failure per Hour (PFH).

Conversely, ISO 13849-1 builds upon the initial machinery safety systems standard EN 954-1, addressing parameters such as Safety-Related Parts of Control Systems (SRP/CS), Performance Levels (PL), design architectures with categories, the number of cycles before 10% of components fail dangerously (B10d), Mean Time to Dangerous Failure (MTTFd), and Diagnostic Coverage (DC).

Recently, both standards have undergone significant revisions.

The second edition of IEC 62061 was published in 2021 and has already been harmonized under the Machinery Directive, whereas the fourth edition of ISO 13849-1 was published in 2023 and is still awaiting harmonization.

The standards have become more aligned and now include a range of updates, such as new and more stringent software requirements, enhanced cybersecurity measures, and detailed safety requirement specifications.

Functional Safety in process industry

The international standard IEC 61511 serves as the process industry sector's application of IEC 61508. It focuses on the use of Safety Instrumented Systems (SIS) within the process industry, which operates on low demand mode, and quantifies this with the Probability of Failure on Demand (PFD).

Safety Instrumented Functions, or SIFs, are protective measures implemented within a Safety Instrumented System (SIS). Typically, an SIS comprises multiple SIFs.

The entire standard highlight the importance of Functional Safety Management (FSM) in every project and the implementation of a Safety Life Cycle to ensure that functional safety is achieved for all stakeholders involved, ranging from system integrators and vendors to end users.

The Functional Safety Life Cycle approach begins with hazard identification, typically through HAZOP or HAZID studies, and proceeds with SIL allocation using various techniques such as LOPA, FTA studies, Risk Matrix, or Risk Graph.

The Safety Requirement Specification (SRS) is a crucial document that marks the end of the analysis phase in the safety lifecycle, as well as the beginning of the implementation phase, encompassing the design of the Safety Instrumented System (SIS), which includes both hardware and software, and extends to installation, commissioning, and validation.

The Safety Life Cycle culminates in the operation and maintenance, modification, and decommissioning phases, collectively referred to as the operation phases, which typically fall under the responsibility of the end-users.

Each of these phases can be categorized as "work," which requires verification and assessment. Verification and Functional Safety Assessment (FSA) must be conducted by competent and independent individuals, departments, or even external third parties.

Finally, it is essential to conduct Functional Safety audits at regular intervals to ensure that organizations involved in Functional Safety projects continue to meet the established and defined Functional Safety requirements.