FSOE Written Test key terms

A function implemented by a safety instrumented system that brings the process to a safe state when a defined dangerous condition occurs, specified by its required SIL and its safe state.

An engineered arrangement of sensors, logic solvers, and final elements that executes one or more SIFs. It is a protection layer, not the basic process control system, and is designed to fail toward safety.

A discrete level from 1 to 4 that specifies the required confidence that a safety function achieves its required safety performance, expressed as target failure measures for demand or continuous operation.

The structured sequence of phases from concept through decommissioning that governs how safety functions are specified, designed, verified, operated, and maintained, ensuring traceability and documented evidence at every stage.

The part of overall safety that depends on a system or equipment operating correctly in response to its inputs, achieved through active protective functions rather than through inherent safe design alone.

The management framework that defines required activities, inputs, and outputs for each phase of a safety system's life, from hazard study to decommissioning, with verification and assessment gates between phases.

The planned and systematic set of management activities, responsibilities, and procedures that ensure functional safety objectives are met throughout the lifecycle, including competence, planning, and audit arrangements.

The shared values, attitudes, and behaviours of an organisation that determine how seriously safety is treated in daily decisions, including open reporting of errors and willingness to challenge unsafe practices.

The process of defining the knowledge and skills each safety role requires, assessing individuals against those criteria, recording evidence, and planning development so that only competent people perform safety activities.

An independent review of the safety lifecycle activities and outputs to judge whether functional safety has been achieved to the required level, performed by a person with appropriate independence from the design team.

A potential source of harm, such as a stored energy, a toxic inventory, or a moving machine part, that exists independently of whether any particular failure has occurred.

Physical injury or damage to the health of people, or damage to property or the environment, resulting from a hazard being realised.

The combination of the likelihood of a hazardous event occurring and the severity of the harm it would cause, usually assessed before safeguards (inherent risk) and after safeguards (residual risk).

The principle that risk should be reduced as low as reasonably practicable, meaning further reduction is not required where its cost is grossly disproportionate to the safety benefit gained.

The level of risk accepted in a given context as the maximum that society or an organisation will permit, above which risk reduction is mandatory and below which ALARP considerations apply.

A structured team-based technique that systematically applies guide words to process parameters at each node to identify deviations, their causes, consequences, and existing safeguards.

A semi-quantitative method that estimates the frequency of a hazardous scenario and credits independent protection layers, including SIFs, to determine whether additional risk reduction is needed.

A safeguard that is independent of the initiating cause and of other credited layers, is specific to the scenario, and is audited to a defined performance, so its risk reduction can be counted.

The actions taken to lower the likelihood or severity of harm, achieved through inherently safer design, engineered safeguards, and administrative measures until residual risk meets the tolerability criteria.

The risk remaining after all planned protection layers and safeguards have been credited, which must still be shown to be tolerable and consistent with ALARP.

The ratio of the risk without a safety function to the risk with it, equal to the reciprocal of the average probability of failure on demand for the function.

The document that defines the required safety functions, their SILs, safe states, response times, and the conditions under which each function must act, forming the basis for design and verification.

The early design statement of how each safety function will be allocated to protection layers and systems, including its safety requirements and the assumptions on which allocation depends.

The condition of a process or machine in which risk is acceptably low, which a safety function is designed to reach or maintain when a dangerous condition is detected.

The assignment of safety requirements and integrity targets to specific subsystems, such as sensors, logic solvers, and final elements, so that the combined performance meets the SIF target.

The average probability that a safety function fails to perform its designed function on demand, calculated over the proof-test interval and used as the low-demand integrity measure.

A periodic test that reveals undetected (dangerous) failures in a safety function so that they can be repaired, thereby restoring the achieved integrity assumed in the PFDavg calculation.

A test that moves a final element through part of its travel without fully closing it, detecting some stuck or sluggish failures while the process continues running.

The ability of a hardware architecture to continue performing its safety function in the presence of one or more dangerous faults, expressed as the number of faults it can sustain.

Limits placed on the maximum SIL a subsystem may claim based on its hardware fault tolerance and the proportion of safe failures, independent of the calculated failure rate.

The fraction of all failures of a subsystem that are either safe failures or detected dangerous failures, used together with fault tolerance to determine the maximum achievable SIL.

The proportion of dangerous failures that automatic diagnostics detect, which shortens the time such faults remain undetected and improves the achieved integrity.

A failure of two or more redundant channels from a single shared cause, such as a common power supply, software error, or environmental stress, which undermines redundancy and must be analysed and mitigated.

A modelling parameter representing the fraction of a channel's failure rate that is shared with redundant channels as a common cause, used to quantify dependent failures in reliability calculations.

A channel configuration such as 1-out-of-1, 1-out-of-2, or 2-out-of-3 that determines how many channel agreements are needed to trip, balancing spurious trips against tolerance of dangerous faults.

A design property whereby a component or system moves to its safe state when it loses power, loses signal, or suffers a detected internal failure.

A design convention in which the final element is held energised during normal operation and is released to trip on loss of power, making power loss produce the safe action.

The part of a safety instrumented system that physically acts on the process, such as a shutdown valve or motor contactor, and often dominates the achieved PFDavg.

The ordered set of software activities from requirements through design, coding, verification, and modification, with each phase producing evidence traceable to the safety requirements it implements.

The documented linkage that allows each safety requirement to be followed forward to its implementation and test evidence and backward to its originating hazard or risk assessment.

Confirmation by examination and provision of objective evidence that the outputs of a lifecycle phase meet the requirements specified for that phase, performed before the next phase begins.

Confirmation that the completed safety system meets the safety requirements for its intended use in the actual operating environment, typically through functional testing and commissioning.

Independent third-party assessment confirming that a product or process conforms to a defined functional safety standard, usually evidenced by a certificate with a stated scope and conditions of use.

Evidence that a component has a documented history of satisfactory operation in similar applications, allowing credit for its failure behaviour without full new reliability data.

The formal process for reviewing, approving, implementing, and recording any change to a safety system or its operating context, ensuring that safety integrity is reassessed before the change takes effect.

The final lifecycle phase in which a safety system is permanently taken out of service, with documented justification, removal of hazards, and records retained for the required period.