Functional Safety Lifecycle
Where high hazard plants are operated it is important to ensure that risks are managed and maintained to an agreed tolerability criteria. For safety-instrumented systems, industry has largely adopted the approach taken in IEC 61511 as best practice to manage and maintain their systems from concept to decommissioning to achieve the agreed tolerable criteria.
Phase 1 Hazard and Risk Assessment
To systematically review a process, with a competent team, to identify the potential causes and consequences that may lead to hazard scenarios and the safeguards, which can prevent, mitigate, or interrupt the event sequence and the ultimate consequence. Typical techniques adopted for this phase include HAZOP, HAZID and FMEA.Phase 1 Learn more
Allocation of safety functions to protection layers
To review those safeguards, which are electrical / electronic or programmable electronic functions and to determine for each function the associated safety or environmental integrity level against an agreed tolerability criteria determined by an Organisations HSEQ department. Typical techniques adopted for this phase include LOPA, Risk Graph, Risk Matrix and Fault tree.Phase 2 Learn more
Safety Requirements Specification (SRS) for the Safety-Instrumented Function (SIF)
The SRS captures the integrity and functionality requirements for each safety-instrumented function identified during phase 1 and 2. As the safety lifecycle progresses the SRS is populated with all of the necessary data to design, install, commission and maintain the safety-instrumented function to the agreed safety integrity level. The SRS forms the basis of the Validation, inspection and testing of the system, it must be maintained throughout the lifecycle for as long as the SIF is required.Phase 3 Learn more
Stage 1 Assessment:
Conducted after the completion of phase 1, 2 and 3 although the SRS may only be partially developed at this stage. A Stage 1 Assessment can offer early identification of potential inconsistencies and discrepancies within and between the requirements of phases 1, 2 and 3 prior to the onset of detailed design.
Design and engineering of Safety-Instrumented System
The SRS is the basis of the design in terms of functionality and integrity requirements, combined with the detailed requirements of clauses 11 and 12. This phase enables competent engineers to design the SIF to meet the defined requirements and is achieved by appropriate selection of components, system architecture and verification.Phase 4 Learn more
Stage 2 Assessment:
Conducted after Phase 4 completion and prior to installation and commissioning activities. A Stage 2 Assessment can offer identification of potential inconsistencies and discrepancies within and between the requirements of phases 1, 2, 3 and 4 prior to the onset installation and commissioning activities.
Installation, commissioning and validation
The SIF must be installed, by competent persons, as per the design pack and commissioned ready for final validation against the SRS. Systematic failures are often introduced during installation and can impact the achieved integrity level, it is therefore important that competent persons are used to install and verify the SIF. The SIF must be validated, through inspection and testing, that after installation and commissioning the SIF achieves the requirements as stated in the SRS to be considered fit-for-purpose.Phase 5 Learn more
Stage 3 Assessment:
Conducted after Phase 5 but prior to hazards being introduced to the process. This assessment is identified in IEC61511 as MANDATORY and should include the requirements from Stages 1 and 2 should they not have been completed. A Stage 3 Assessment provides an engineering judgement from a person independent of the project or organisation (where applicable) that the SIF identified has achieved the functional safety and integrity required.
Operation and maintenance
The SIF must be operated, managed, inspected and tested to ensure that the designed functional safety is maintained for the life of the SIF. This is best achieved through the application of a functional safety management procedure, which includes the maintenance and testing requirements from vendor safety manuals. The training and assessment of persons who interact with the safety system is required to provide assurance that they are competent to operate and maintain the SIF.Phase 6 Learn more
Stage 4 Assessment:
Conducted after gaining operating and maintenance experience with the SIF (having conducted the required proof tests). The purpose of a Stage 4 Assessment is to verify that the assumptions made in the SRS are valid after gaining operating experience. The assessment also verifies that the operators / persons testing and maintaining the SIF are aware of its purpose, function, operation, testing and maintenance requirements. The Stage 4 Assessment should be carried out periodically throughout the operational life of the SIF.
Modification to a SIF or a process must be appropriately planned, reviewed and approved prior to making the change to ensure that the required integrity is maintained despite of any changes made. This review should include an assessment to determine the impact on functional safety and where in the safety lifecycle the review should commence so that it is appropriately re-assessed.Phase 7 Learn more
Stage 5 Assessment:
Conducted prior to decommissioning or reintroduction of the hazard after modification of the SIF or process. This Stage of assessment should ensure that functional safety is maintained prior to the removal or post modification of the SIF. Dependant on the Impact Analysis (Clause 17 & 18) a return to an earlier Stage Assessment may be required.
Decommissioning of a SIF must be appropriately planned, reviewed and approved prior to it being decommissioned. To ensure that the required functional safety remains in place during decommissioning it is important, that until the hazard is removed, suitable means of protection is assigned. Consideration must be also given where the SIF has been utilised as a safeguard for other safety systems that its removal does not negatively impact the functional safety in other areas.Phase 8 Learn more
Verification demonstrates by review, analysis and/or testing that the required outputs for a lifecycle phase have been achieved. It is a check that every lifecycle phase’s outputs are consistent with the products, standards, objectives of the associate clauses, current engineering best practices and information used as inputs to that phase.Phase 9 Learn more
Management of functional safety and Functional safety assessment and auditing
This is the means by which an organisation utilises systematic approaches to manage its SIF. This will include the use of Functional Safety Management Procedures and checklists, which will outline how the organisation will accomplish the requirements of the IEC61511 lifecycle and manage the competency of the persons who will interact with the SIF at any stage of the lifecycle. It will also identify how the system will be audited and assessed to ensure continuing compliance with organisational requirements. A competent person or team should assess the SIF to determine by engineering judgement that it achieves the functional and integrity requirements as defined in the SRS and complies with the objectives of the IEC 61511 lifecycle.Phase 10 Learn more
Safety life-cycle structure and planning
The Functional Safety Plan and procedures will differ depending on the organisational requirements but should always be structured and planned to include the technical and managerial activities required to maintain functional safety through out the lifecycle of the SIF.Phase 11 Learn more
IEC 61511 Compliance
To comply with IEC 61511 it is necessary to demonstrate how an organisation complies with each of the clauses within the standard, generally termed the safety lifecycle. This compliance is best demonstrated through the use of templates and checklists, which ProSalus has available for each of the life-cycle phases. Combined with our consultants’ knowledge and experience of lifecycle phases’ requirements we assist our clients in meeting current best practice.