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