Functional Safety Assessments: Verifying Your Safety Systems Will Perform as Intended

by Cheryl Garcia | Process Safety Technical Consultant

A functional safety assessment (FSA) is a structured, independent review required by IEC 61508 and IEC 61511 to verify that safety instrumented systems (SIS) and other protection layers meet defined risk reduction requirements. The assessment evaluates whether the safeguards identified during the hazard analysis have been designed, implemented, tested and maintained to perform as intended during operation.

FSAs provide a connection to the entire safety lifecycle, from hazard identification and system design to lifetime operation and maintenance. At the site level, the focus is on confirming that what was defined on paper will hold up during operation.

To maintain objectivity, FSAs are performed by individuals independent of the original design and implementation.

What an FSA Looks Like at the Site Level

The safety lifecycle begins with hazard identification and risk evaluation through HAZOPs and LOPAs. These studies establish risk reduction targets and lead to the development of the Safety Requirement Specifications (SRS, which defines how the SIS and other protection layers are expected to perform.

An FSA evaluates safety instrumented systems (SIS) and other independent protection layers against the requirements defined earlier in the safety lifecycle. That includes confirming the hazard analysis is complete, the required risk reduction is clearly defined, and the system design, installation, and testing activities meet those expectations. It also looks at whether operational practices will support long-term performance once the system is in service.

In many cases, the FSA is primarily a document review, supported by targeted discussions with the project and site teams to resolve specific questions and confirm how the system is intended to perform. Because these assessments are typically performed by third-party reviewers, access to accurate information and the right personnel are critical. The goal is to identify gaps and resolve outstanding issues before the next stage begins.

The Five Stages of an FSA

FSAs are conducted in stages that align with system development and operation phases. Each stage acts as a checkpoint before moving forward, ensuring that requirements are met before the next phase begins.

• FSA 1 – Definition: Confirms that hazard analyses, SIL targets, and SIS system requirements have been developed and documented. This stage depends heavily on complete HAZOP, LOPA, and SRS documentation.
• FSA 2 – Design: Reviews the detailed SIS system design and engineering, including hardware, software, and supporting documentation, to ensure it meets those requirements.
• FSA 3 – Installation and Validation: Verifies that the system has been installed and tested correctly. This often ties into factory and site acceptance testing (FAT/SAT) activities before startup.
• FSA 4 – Pre-Startup Safety Review: Focuses on readiness from an operations standpoint. Training, procedures, and maintenance plans are evaluated to confirm that the system can be supported once it is in service.
• FSA 5 – Operation: A periodic review performed after startup and after any modification to the process to confirm ongoing performance of the safety systems and continued compliance with defined requirements.

Some organizations complete only the first three stages. The latter stages require continued engagement and are sometimes deferred, even though they address how the system performs over time. When organizations choose to stop at the earlier stages, that decision should be clearly defined within internal procedures so that expectations around compliance and lifecycle responsibilities are understood. Often, the site management of change (MOC) procedures will cover the same evaluations as FSA 4/FSA 5.

When an FSA is Needed

An FSA is required when a facility adopts IEC 61511 and determines that SIS functions or other independent protection layers are necessary to reduce process risk. If a hazard analysis shows that basic process controls are not sufficient for risk reduction, additional independent protection layers must be implemented and verified.

The FSA becomes part of the lifecycle, providing verification that each phase from concept through operation meets the standard’s expectations. Without an FSA, it is difficult to demonstrate that identified risks have been adequately addressed or that safeguards will perform as intended.

When a company does not define its own internal standard, IEC 61511 may be treated as recognized and generally accepted good engineering practice (RAGAGEP). In those cases, facilities demonstrate due diligence during regulatory inspections with an FSA.

The FSA is not a one-time check; it is an independent review to confirm that each phase, from initial definition through operation, supports the safety functions and risk reduction that were originally defined.

How Preparation Impacts an FSA

Preparation has a direct impact on how smoothly an FSA progresses. When project information is complete, organized, and accessible, the assessment becomes a focused review, but being unprepared can lengthen the process significantly.

Several factors commonly impact outcomes:

• Availability of key personnel who can answer questions about the system design and safety-related decisions
• Documentation that clearly links hazard analysis to design decisions
• Alignment on project scope and what lifecycle stage is being evaluated
• Timing: allowing each required activity and documentation to be completed before the next stage begins

Common FSA Findings

FSAs often reveal similar issues, especially in fast-moving projects:

• P&IDs that have not been updated to reflect current design
• Missing, incomplete, or inconsistent instrument information
• Incomplete proof test procedures
• Training that are incomplete or not fully documented
• Unresolved action items from earlier project phases

These issues are not unusual and reflect the pace and complexity of most project execution. The FSA provides a structured way to identify and address them before they affect system performance or compliance.

These findings affect both project execution before startup and how the system performs after startup.

Before startup, FSA findings influence both schedule and risk exposure. If a hazard has been identified and the required protection layers are not yet in place, the facility remains exposed to that risk until the system is installed and validated.

After startup, the focus shifts to maintenance and reliability. Safety systems are not always active; they may sit idle until a demand occurs. Without proper maintenance, inspection, and testing programs, there is no assurance these systems will function as intended when needed.

Routine activities such as proof testing and preventive maintenance are critical because they are directly tied to the assumptions made during system design and SIL verification. If those activities are not carried out as defined, the intended risk reduction may not be achieved.

From Assessment to Ongoing Management

Each FSA produces findings and recommendations that must be addressed, and the drawings and specifications must be updated to reflect the current state of the system.
This includes:

• Closing identified gaps
• Updating drawings and specifications
• Aligning maintenance and testing practices
• Documenting training and procedures

Each stage also revisits actions from earlier assessments, such as updating P&IDs, completing proof test procedures, or documenting training. When those actions are not completed, they carry forward into the next phase and can delay approval or require rework before the assessment can be closed. Additionally, incomplete SIS system documentation can delay startup of a new or modified process.

The results of an FSA should be carried forward into ongoing operation and maintenance activities. Teams use that information to update drawings, procedures, and maintenance plans so the system continues to perform as designed.

As systems change, that same information is used to confirm those changes still meet the original safety requirements and provide the intended level of protection.

Putting It All Together

Functional safety assessments connect hazard analysis, system design, implementation, and ongoing operation into a single, traceable lifecycle process. Each stage confirms that the safety systems in place continue to meet the requirements established to reduce risk. When that process is followed consistently, teams have a clear understanding of how their systems are expected to perform and what is required to maintain that performance over time.

For facilities planning a new project or evaluating an existing system, taking the time to prepare for and complete each stage of the FSA process can help identify issues early, avoid rework, reduce risk exposure, and support safe, reliable operation throughout the system lifecycle.

If you are preparing for an upcoming Functional Safety Assessment or need support navigating the safety lifecycle, Hargrove Controls & Automation can assist with activities ranging from hazard analysis and system design through assessment, implementation, and ongoing operation. Contact us today.