Glossary
Safety and SIS Terms
Functional safety and hazardous area terms: SIS, SIL, PFDavg, voting, proof testing, LOPA, alarms, zones, gas groups and Ex protection.
31terms
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All Safety and SIS Terms
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TermAlarm ManagementAlarm management is the process of designing, rationalising and maintaining alarms so operators…TermCause and Effect MatrixA cause and effect matrix is a table showing which inputs (causes) trigger which outputs…CCFCommon Cause FailureCommon cause failure is a single cause that makes redundant channels fail together, such as a…DCDiagnostic CoverageDiagnostic coverage is the fraction of dangerous failures that automatic diagnostics detect.EPLEquipment Protection LevelEquipment protection level shows how unlikely equipment is to become an ignition source,…λFailure RateFailure rate is the number of failures per unit time of a device; in safety it is split into…FTAFault Tree AnalysisFault tree analysis is a top down method that models how combinations of basic failures lead to…Ex dFlameproof EnclosureA flameproof enclosure contains any internal explosion and cools escaping gases through flame…
TermGas GroupGas group classifies flammable gases by how easily they ignite and how well flames pass through…HFTHardware Fault ToleranceHardware fault tolerance is the number of hardware faults a subsystem can have while still…TermHazardous Area ZoneA hazardous area zone describes how likely an explosive atmosphere is at a location: Zone 0, 1…TermHAZOPHAZOP is a structured team review that uses guide words to find hazards and operability…IPLIndependent Protection LayerAn independent protection layer is a safeguard that can prevent a hazardous scenario on its own…Ex iIntrinsic SafetyIntrinsic safety is a protection method that limits electrical and thermal energy in a circuit…LOPALayers of Protection AnalysisLayers of protection analysis estimates the frequency of a hazardous event and checks whether…MTBFMean Time Between FailuresMean time between failures is the average operating time between failures of a repairable item.
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FormulaPFDavgPFDavg is the average probability that a safety function fails to act when a demand occurs,…FormulaPFHPFH is the average frequency of dangerous failures per hour, used for safety functions in high…TermProcess Safety TimeProcess safety time is the time from a process fault occurring until the hazardous event…PTCProof Test CoverageProof test coverage is the fraction of dangerous undetected failures that a proof test actually…TIProof Test IntervalProof test interval is the time between periodic tests that reveal dangerous undetected…RRFRisk Reduction FactorRisk reduction factor is how many times a safety function reduces the frequency of a hazardous…SFFSafe Failure FractionSafe failure fraction is the share of all failures that are either safe or dangerous but detected.TermSafe StateSafe state is the process condition a safety function must reach to prevent the hazardous…
TermSafety BypassA safety bypass is a temporary override that stops a trip or alarm from acting, for…SIFSafety Instrumented FunctionA safety instrumented function is one protective action of a SIS, from sensing a hazard to the…SISSafety Instrumented SystemA safety instrumented system is an independent set of sensors, logic solver and final elements…SILSafety Integrity LevelSafety integrity level is a target level of risk reduction for a safety instrumented function,…SRSSafety Requirements SpecificationA safety requirements specification defines what each safety instrumented function must do and…FormulaSpurious TripA spurious trip is an unwanted shutdown caused by a safety system fault rather than a real…MooNVoting ArchitectureVoting architecture describes how many of N redundant channels must act to trip, such as 1oo2…
Frequently Asked Questions
What does the safety and sis glossary cover?
Functional safety and hazardous area terms: SIS, SIL, PFDavg, voting, proof testing, LOPA, alarms, zones, gas groups and Ex protection.
Are the formulas checked?
Yes. Formulas follow the relevant standards such as ISO 5167, and every worked example is calculated and checked.
Other Glossary Sections
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