GLOSSARY OF TERMS: Safety Instrumented Systems
CFSP: Certified Functional Safety Professional. A personnel competency rating for safety engineers that demonstrates competence in safety lifecycle activities.
DEMAND: A potentially dangerous situation (hazard) caused by initiating event.
FAILURE RATE: The number of failures per unit time for a component or piece of equipment.
FMEDA: Failure Modes Effects and Diagnostics Analysis. A detailed analysis of the different failure modes and diagnostic capability for a piece of equipment.
FUNCTIONAL SAFETY: Freedom from unacceptable risk achieved through the safety lifecycle.
IEC 61508: The IEC standard covering Functional Safety of electrical/electronic/programmable electronic safety-related systems.
IEC 61511: The IEC standard for use of electrical/electronic/programmable electronic safety-related systems in the process industry.
LOPA: Layer of Protection Analysis. A method of analyzing the likelihood (frequency) of a harmful outcome event based on an initiating event frequency and on the probability of failure of a series of independent protection layers capable of preventing the harmful outcome.
PFDAVG: Probability of Failure on Demand average. The probability that a system will fail dangerously, and not be able to perform its safety function when required.
PHA: Process hazards analysis. The process by which the hazards of a process are identified for all reasonably foreseeable circumstances, determining the sequence of events leading to harm, and estimating the likelihood (frequency) and consequence magnitude of the potential harm.
PTC: Proof test coverage. The percentage of dangerous failures that are detected during a manual proof test.
RISK: A measure of the likelihood (frequency) and consequence (severity) of an adverse effect.
SIF: Safety Instrumented Function. A set of equipment intended to reduce the risk due to a specific hazard (a safety loop).
SIL: Safety Integrity Level. A quantitative target for measuring the level of performance needed for safety function to achieve a tolerable risk for a process hazard.
SIL VERIFICATION: The process of calculating the average probability of failure on demand (or the probability of failure per hour) and architectural constraints for a safety function design to see if it meets the required SIL.
These terms were provided by exida, www.exida.com, a certification and research firm specializing in safety critical/high availability automation systems, control system cybersecurity, and alarm management.
