Safety Instrumented Systems Definitions

λS : Rate of Safe failures (1/t)

λD : Rate of Dangerous failures (1/t)

λSd : Rate of Safe failures, detected (1/t)

λSu : Rate of Safe failures, undetected (1/t)

λDd : Rate of Dangerous failures, detected

(1/t)λDd : Rate of Dangerous failures, undetected (1/t)

λDd : Rate of Dangerous detected failures (1/t)

λDu : Rate of Dangerous undetected failures (1/t)

ESD : Emergency Shut Down

Fault-Tolerant : A SIS or part of a SIS is considered as being fault-tolerant, if it continues to perform its safety functions in spite of the presence of one (or more) dangerous failures.

FMEA : Failure Mode Effect Analysis

FSM : Functional Safety Management

HIP§S : High Integrity (Pressure) Protection System

IEC : International Electrotechnical Commission

IEC 61508 : Functional safety of electrical/electronic / programmable electronic safety-related systems

IEC 61511 : Functional safety- Safety instrumented systems for the process industry sector

PFDAVG : Average Probability of Failure on Demand

PLC : Programmable Logic Solver

SFF : Safe Failure Fraction: SFF = (λS+λDd)/(λS+λDd+λDu)

SIF : Safety Instrumented Function

SIL : Safety Integrity Level

SIS : Safety Instrumented System

SRS : Safety Requirements Specification

TMR : Triple Modular Redundant