FUNCTIONAL SAFETY SERVICES
SAFETY VALIDATION AND
VERIFICATION
Identify hazards early. Strengthen your design before risk becomes operational reality.Confirm your safety instrumented system works. Demonstrate it meets every requirement before startup, and maintain that confidence throughout its operating life.
A Safety Instrumented System that has been correctly specified and designed still needs to be confirmed. Confirmation that each lifecycle phase was completed correctly, that the design achieves the SIL targets defined in the SRS, and that the installed system performs as required before it is depended upon to protect people, plant, and environment.
Validation and verification are the activities that provide that confirmation. They are not a final check at the end of the project. They are structured activities embedded throughout the functional safety lifecycle, each one confirming that the work of a preceding phase meets the requirements set by the phase before it.
When V&V activities are weak, absent, or treated as paperwork formalities, the consequences are predictable. Safety systems are commissioned without confirmed performance, discrepancies between design intent and installed configuration go undetected, and organizations proceed to start up with a safety case that has not been closed. The risk is not abstract. IEC 61511 and decades of process safety incident investigation both point to inadequate verification as a recurring contributor to functional safety failures.
Rigorous, independent validation and verification close that gap. It gives operators, regulators, and management the documented evidence they need to confirm that the safety system will perform when it is demanded.
Verification
Verification answers the question: Have we completed each phase of the safety lifecycle correctly relative to the requirements set in the previous phase? It is a phase-by-phase confirmation activity carried out throughout the project, not just at the end.
Verification checks include:
- Confirming that the SRS correctly and completely captures the requirements derived from HAZOP and SIL determination
- Confirming that the SIS design meets all functional and integrity requirements in the SRS
- Confirming that hardware selections achieve the required SIL, hardware fault tolerance, and systematic capability
- Confirming that software development has followed the required procedures for the applicable SIL
- Confirming that the installed system matches the as-designed configuration before commissioning begins
Validation
Validation answers the question: Does the complete, installed safety system meet the overall safety requirements? It is the confirmation that the SIS, as built and installed, will perform its intended functions under the process conditions and demands it will encounter in operation.
Validation activities include:
- Factory Acceptance Testing (FAT): testing the assembled logic solver configuration against the SRS in a controlled workshop environment before site delivery
- Site Acceptance Testing (SAT): testing the installed SIS, including all field instruments, final elements, and logic solver, after site installation and loop completion
- Functional testing of each Safety Instrumented Function against its SRS requirements, including response time verification, safe state confirmation, and reset logic testing
- Proof test procedure validation: confirming that the developed proof test procedures will achieve the required proof test coverage assumed in the SIL assessment
- Pre-Startup Safety Review (PSSR): the final structured confirmation that all validation activities have been completed, all outstanding actions closed, and the system is ready for live operation
Our validation and verification activities are structured to meet the requirements of:
- IEC 61511-1 Clauses 12 and 14: Verification of the SIS design and validation of the installed SIS against the SRS
- IEC 61508 Part 2 Clause 7: Verification requirements for hardware safety functions
- IEC 61508 Part 3 Clause 7: Verification requirements for software
- ISA 84 (ANSI/ISA-84.00.01): Equivalent requirements for validation and verification in process industry SIS applications
- ISA/IEC 62443: Where cybersecurity requirements intersect with SIS design, particularly for safety systems with networked logic solvers, remote access, or shared OT infrastructure
All validation and verification records are documented to support functional safety assessment, regulatory audit, and the ongoing safety management of the system through its operating life.
Validation and verification activities span the entire functional safety lifecycle. Understanding their scope prevents the common misconception that they are a single end-of-project activity.
- SRS verification: Confirms that the Safety Requirement Specification correctly and completely captures all requirements derived from HAZOP and SIL determination
- Design verification: Confirms that the SIS design, including hardware architecture, component selection, and software specification, meets all SRS requirements
- SIL verification: Confirms through calculation that the proposed architecture achieves the required PFDavg within the proof test interval assumed in the SIS design
- Factory Acceptance Testing: Validates the logic solver configuration against the SRS in a controlled environment before site delivery
- Site Acceptance Testing: Validates the complete installed system, including field devices, wiring, logic solver, and final elements
- Pre-Startup Safety Review: Confirms completion of all validation activities and readiness for live operation
- Periodic proof testing: Ongoing validation during the operating life of the system that safety functions remain capable of performing on demand
We treat validation and verification as integrated lifecycle activities, not isolated tests. That means every V&V activity is planned in advance, executed against defined acceptance criteria, and documented in a way that supports closure and audit.
V&V Planning
We develop a validation and verification plan that identifies every V&V activity required across the safety lifecycle, the acceptance criteria for each activity, the evidence to be generated, and the responsible parties. Planning at the start prevents gaps and ensures that no lifecycle phase advances without its verification being completed.
Design and SIL Verification
We conduct a structured review of the SIS design against the SRS, confirming that all functional and integrity requirements have been addressed. We perform or review SIL verification calculations, checking PFDavg against the SIL target for each SIF and confirming that proof test interval assumptions are consistent with achievable field practices.
FAT and SAT Execution
We develop and execute Factory Acceptance Test and Site Acceptance Test procedures against the SRS. Each test case is linked to a specific SRS requirement. Test results are documented with pass or fail status, deviations are recorded and tracked to closure, and a final test record is produced that supports the safety case.
PSSR and Lifecycle Handoff
We conduct a Pre-Startup Safety Review that confirms all V&V activities have been completed, all outstanding actions closed, and the system is ready for live operation. We produce the final validation report and ensure the documentation package is structured for use in functional safety assessment, regulatory submission, and ongoing operational management.
SIL verification is one of the most technically demanding parts of the V&V process. It involves calculating the average probability of failure on demand (PFDavg) for each Safety Instrumented Function using the failure rates of the selected components, the redundancy configuration, the proof test interval, and the assumed proof test coverage.
- PFDavg for SIF: Confirms that PFDavg for the complete SIF (sensor subsystem, logic solver, final element subsystem) is within the target SIL range.
- Hardware fault tolerance: Hardware fault tolerance of each subsystem meets the minimum requirement for the applicable SIL under IEC 61511 Table 5 or IEC 61508 Table 2.
- Safe Failure Fraction (SFF): SFF of each subsystem meets the requirements for the architecture type and SIL.
- Proof test interval: Proof test interval is achievable in practice and consistent with the coverage assumed in the calculation.
- Common cause failure: Common cause failure contribution has been assessed and is within acceptable limits.
Where SIL verification calculations show that the proposed architecture does not achieve the required SIL, we identify the specific contributors and recommend targeted design changes, proof test interval adjustments, or component substitutions that close the gap with minimum design impact.
- Documented evidence that each SIF performs correctly and achieves its SIL target before the system enters live service
- Confidence that every lifecycle phase was completed correctly, with a traceable record from hazard identification through to the commissioned system
- Reduced risk of post-startup failures, non-conformances, and unplanned shutdowns caused by discrepancies between design intent and installed configuration
- A complete, audit-ready V&V record that supports functional safety assessment, regulatory submissions, and management of change during operation
- Proof test procedures validated for coverage, giving operations teams a testing regime that actually maintains SIL achievement through the operating life of the system
- Clear evidence of due diligence for operators, insurers, and regulators who require confirmation that safety systems have been properly tested before startup
- Validation and verification plan covering all V&V activities, acceptance criteria, evidence requirements, and responsible parties
- Design verification report confirming SIS design compliance with the SRS
- SIL verification calculations for each SIF with PFDavg results, architecture assessment, and SIL achievement confirmation
- FAT procedures and test records with individual test case results and deviation log
- SAT procedures and test records for the installed system
- PSSR report confirming readiness for live operation and closure of all outstanding V&V actions
- Final validation report with consolidated evidence and a summary of the safety case status at the point of startup
Safety systems in modern industrial environments present validation and verification challenges that go beyond traditional SIS testing. Logic solvers communicate over OT networks, configuration is managed digitally, remote diagnostics capabilities introduce new attack surfaces, and software-intensive safety functions require validation approaches that account for both functional and cybersecurity requirements.
- Integrated functional safety and OT/ICS security perspective: we validate not just that the SIF functions correctly, but that the architecture supporting it is appropriately protected against threats that could compromise its integrity
- Structured, traceable test procedures linked directly to SRS requirements, so every test case has a clear purpose and every result has a documented basis.
- Independent V&V capability: where objectivity is required for regulatory submissions or FSA preparation, we provide assessment and verification independent of the design team.
- SIL verification expertise covering complex architectures, voted configurations, partial stroke testing, and proof test optimization
- Deep operational experience across high-consequence sectors, including oil and gas, energy, pharmaceuticals, and process manufacturing
- We do more than run tests and produce records. We help teams understand what their safety system has demonstrated, where gaps remain, and how to close them before the system is placed in service.
Ready to Plan Your Safety Validation and Verification Activities?
Reach out to our functional safety team. We will review your SRS and SIS design documentation, identify the V&V activities required, and develop a plan that fits your project schedule and regulatory obligations.