A Safety Shutdown System shall be independent of and in addition to other systems and equipment used for normal operation, control and monitoring, and shall act as a safety barrier in case of malfunction or maloperation of these systems and equipment.
The Safety Shutdown System is logically divided into three main levels of shutdown:
- Process Shutdown (PSD)
- Emergency Shutdown (ESD)
- Abandon Platform Shutdown (APS)
Basic system philosophy is that a shutdown on a certain level shall never initiate shutdowns on higher levels, but shall always include shutdowns on lower levels.