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Slide 20
InstMC FS2016 V1.3
Nicol Instrument Engineering Limited
HFT – more complicated alternatives
Faults may be excluded, and any exclusions
must be justified and documented.
HFT may be reduced if FVL or LVL
programmable devices not used AND if the
minimum HFT specified results in decreased
of overall process safety. HFT at 0 needs
justified and with evidence.
If not using the rules of IEC 61511; must
follow either route 1H or 2H from IEC 61508.