SIL Safety Manual
D103401X012
ED, ES, ET, EZ, HP, HPA Valves w/ 657/667 Actuator
November 2011
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.