The facilities regulations § 34

§ 34 Process safety system

Facilities outfitted with or attached to process facilities, shall have a process safety system. The system shall be able to perform the intended functions independently of other systems.
The process safety system shall be designed such that it enters or maintains a safe condition if a fault occurs that can prevent the system from functioning.
The process safety system shall be designed with two independent levels of safety to protect equipment.
Section last changed: 01 January 2011

The requirement for independence as mentioned in the first subsection, entails that the process safety system is in addition to systems for management and control and other safety systems. The process safety system can have an interface with other systems if it is not adversely affected as a consequence of system failures, errors or isolated incidents in these systems.
The ISO 10418 standard, in combination with NORSOK P-002, should be used for design of process safety systems. Auxiliary facilities containing flammable fluids should also be secured in accordance with the methods described in these standards. Overpressure protection should be designed in accordance with API Standard 520/NS-EN ISO 4126 and API Standard 521.
The requirement for two independent safety levels as mentioned in the third subsection, entails that the process safety levels shall be protected against dependent errors, so that an isolated error does not lead to the failure of both safety levels.
Process safety interlocks implemented in software should not be overridable.