Functional safety glossary
Plain-language definitions of the concepts, measures, documents, and roles used in functional safety programs. Select a term for its complete reference entry.
Concept
CENELEC Rail Standards
The European rail safety standard family: EN 50126 (RAMS), EN 50128 (software), and EN 50129 (system safety cases).
Functional Safety
The part of overall safety that depends on a system or equipment operating correctly in response to its inputs, including safe management of faults and failures.
FuSa
The common industry abbreviation for functional safety, used heavily in automotive and semiconductor development.
Hierarchy of Risk Reduction
The ISO 12100 ordering of protective measures: inherently safe design first, then safeguarding, then information for use.
ODD (Operational Design Domain)
The specific operating conditions under which an autonomous system is designed to function safely.
RAMS
Reliability, Availability, Maintainability and Safety: the combined dependability discipline for railway systems under EN 50126.
Reliability Engineering
The discipline of predicting, measuring, and improving how long systems operate without failure, quantified through failure rates, MTBF, and related measures.
Safety Function
A function implemented by a safety-related system intended to achieve or maintain a safe state for a specific hazardous event.
Safety-Critical System
A system whose failure or malfunction can result in death, serious injury, significant property or environmental damage.
SOTIF
Safety Of The Intended Functionality: absence of unreasonable risk from functional insufficiencies or foreseeable misuse, per ISO 21448.
V-Model
A development lifecycle model whose left side decomposes requirements into design and whose right side integrates and verifies, with each verification stage paired against the design stage at the same level.
Measure
ASIL
Automotive Safety Integrity Level (A to D) under ISO 26262, derived from severity, exposure, and controllability.
MTTFd
Mean Time To dangerous Failure: a channel-level reliability measure used in ISO 13849 PL determination.
Performance Level (PL)
A discrete level (PL a to PL e) used by ISO 13849 to specify the ability of safety-related parts of control systems to perform a safety function.
PFH
Probability of dangerous Failure per Hour: the random hardware failure metric for high-demand and continuous-mode safety functions.
SIL (Safety Integrity Level)
A discrete level (SIL 1 to SIL 4) specifying the required risk reduction and dependability of a safety function under IEC 61508 and its sector standards.
Artifact
Fault Tree Analysis
A top-down deductive analysis tracing an undesired top event to combinations of lower-level faults using boolean logic.
FMEA
Failure Modes and Effects Analysis: a bottom-up method cataloging how components fail and what effects those failures produce.
FMEDA
Failure Modes, Effects and Diagnostic Analysis: quantitative failure analysis producing safe/dangerous failure rates and diagnostic coverage.
Functional Safety Plan
The program-level plan defining safety lifecycle activities, responsibilities, independence, and evidence for a specific development.
Functional Safety Requirements
The requirements specifying what safety functions must do and how dependably, decomposed from top-level safety goals down to technical, hardware, and software safety requirements.
HARA
Hazard Analysis and Risk Assessment: the concept-phase activity and resulting document that identifies hazards and derives safety goals and integrity targets.
Safety Case
A structured argument, supported by a body of evidence, that a system is acceptably safe for a specific application in a specific environment.
Activity
Functional Safety Assessment (FSA)
The independent investigation and judgement, required by IEC 61508 and its sector standards, of whether functional safety has actually been achieved by a safety-related system.
Functional Safety Audit
An examination of whether the safety lifecycle processes required by the standards and the safety plan were actually followed, as distinct from judging the safety achieved by the product.
Functional Safety Testing
The testing that demonstrates safety functions behave as specified, including under fault conditions, with rigor and coverage scaled to the integrity level.
Hazard Analysis
The umbrella term for systematic techniques that identify how a system can cause harm and evaluate the resulting risk, from early preliminary analyses to detailed causal studies.
Risk Assessment
The systematic process of hazard identification, risk estimation, and risk evaluation defined for machinery by ISO 12100.
Verification and Validation (V&V)
Verification confirms work products meet their requirements; validation confirms the system meets its intended use.
System
AMR (Autonomous Mobile Robot)
A mobile robot that navigates using onboard sensing without fixed paths, covered by ANSI/A3 R15.08 and ISO 3691-4.
ATO (Automatic Train Operation)
Automation of train driving functions, graded GoA 1 through GoA 4 (unattended operation).
CBTC
Communications-Based Train Control: continuous, high-resolution train control using radio communication, per IEEE 1474.
Collaborative Robot
A robot system designed for direct human interaction within a shared workspace, per ISO 10218 and ISO/TS 15066.
PTC (Positive Train Control)
US-mandated train control systems that prevent train-to-train collisions, overspeed derailments, and incursions into work zones.
Process
CE Marking
The manufacturer's declaration that a product meets applicable EU directives, including the Machinery Directive and its harmonized standards.
Functional Safety Certification
Third-party confirmation by a certification body that a product, process, or person meets the requirements of a functional safety standard, within a defined scope.
Safety Management System (SMS)
The organizational structure, processes, and procedures that govern how safety is planned, executed, and assured across programs.
Job title
Functional Safety Consultant
An external specialist engaged to supply functional safety expertise: gap analyses, hazard analyses, safety planning, certification preparation, or fractional safety roles.
Functional Safety Engineer
An engineer who specifies, analyzes, implements, or assesses safety functions and safety lifecycle work products.
Safety Manager
The role accountable for planning and steering a program's safety activities, evidence, and certification path.