Process Shutdown : Abnormal operating conditions leading to potential hydrocarbons release shall be controlled by two levels of protection according to ISO 10418 (API RP 14C):
- Primary level of protection
- Secondary level of protection
As far as possible, the two levels of protection shall operate on functionally different basis. Duplication of identical safety devices given different set points shall not be regarded to satisfy the requirement of two levels of protection.
The PSD system shall automatically detect abnormal operation conditions within systems or equipment and initiate actions so that uncontrolled release of hydrocarbons is prevented.
The systems shall be designed to avoid cascading effects due to partial shutdown within PSD, i.e. shutdown signals should trip all affected systems so that a new abnormality is not developed as a result of the initial trip action.
The system philosophy also implies that the fail safe principle shall apply. I.e. components shall move to, or stay in the predetermined safest position upon loss of signal or power.
The degree and extent of a PSD situation will depend on type of abnormality, and may vary from equipment shutdown with minimum effect on the production rate, to a total process shutdown.