Fisher ET - Manual (Page 2)

ED, ET, EZ, HP, HPA Valves w/ 657/667 Actuator
SIL Safety Manual
July 2010
2
Terms and Abbreviations
Safety: Freedom from unacceptable risk of harm.
Functional Safety: The ability of a system to carry
out the actions necessary to achieve or to maintain a
defined safe state for the equipment / machinery /
plant / apparatus under control of the system.
Basic Safety: The equipment must be designed and
manufactured such that it protects against risk of
injury to persons by electrical shock and other
hazards and against resulting fire and explosion.
The protection must be effective under all conditions
of the nominal operation and under single fault
condition.
Safety Assessment: The investigation to arrive at a
judgment - based on the facts - of the safety
achieved by safety-related systems.
Fail-Safe State: State where valve actuator is
de-energized and spring is extended.
Fail Safe: Failure that causes the valve to go to the
defined fail-safe state without a demand from the
process.
Fail Dangerous: Failure that does not respond to a
demand from the process (i.e. being unable to go to
the defined fail-safe state).
Fail Dangerous Undetected: Failure that is
dangerous and that is not being diagnosed by
automatic stroke testing.
Fail Dangerous Detected: Failure that is dangerous
but is detected by automatic stroke testing.
Fail Annunciation Undetected: Failure that does
not cause a false trip or prevent the safety function
but does cause loss of an automatic diagnostic and
is not detected by another diagnostic.
Fail Annunciation Detected: Failure that does not
cause a false trip or prevent the safety function but
does cause loss of an automatic diagnostic or false
diagnostic indication.
Fail No Effect: Failure of a component that is part of
the safety function but that has no effect on the
safety function.
Low Demand Mode: Mode, where the frequency of
demands for operation made on a safety-related
system is no greater than twice the proof test
frequency.
Acronyms
FMEDA: Failure Modes, Effects and Diagnostic
Analysis
HFT: Hardware Fault Tolerance
MOC: Management of Change. These are specific
procedures often done when performing any work
activities in compliance with government regulatory
authorities.
PFD
AVG
: Average Probability of Failure on Demand
SFF: Safe Failure Fraction, the fraction of the overall
failure rate of a device that results in either a safe
fault or a diagnosed unsafe fault.
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, discrete level (one out of
a possible four) for specifying the safety integrity
requirements of the safety functions to be allocated
to the E/E/PE safety-related systems where Safety
Integrity Level 4 has the highest level of safety
integrity and Safety Integrity Level 1 has the lowest.
SIS: Safety Instrumented System – Implementation
of one or more Safety Instrumented Functions. A
SIS is composed of any combination of sensor(s),
logic solver(s), and final element(s).