§ 33 Emergency shutdown system
Facilities shall have an emergency shutdown system that can prevent the development of hazard and accident situations and limit the consequences of accidents, cf. Section 7. The system shall be able to perform the intended functions independently of other systems.
The emergency shutdown system shall be designed so that it enters or maintains safe conditions if a fault occurs that can prevent the system from functioning. The emergency shutdown system shall have a simple and clear command structure. The system shall be capable of being activated manually from trigger stations that are in strategic locations on the facility. It shall be possible to manually activate functions from the manned control centre that bring the facility to a safe condition independently of the parts of the system that can be programmed.
Emergency shutdown valves shall be installed that can stop streams of hydrocarbons and chemicals to and from the facility and to and from wells, and which isolate and/or partition the fire areas on the facility.
Section last changed: 01 January 2018
When designing the emergency shutdown system, the standards NS-EN ISO 13702 and NORSOK S-001 should be used.
The requirement to isolate and compartmentalise the fire areas on the facility means, inter alia, that a sufficient number of sectionalising valves shall be installed in the processing facility to ensure that any fire load in the event of a leak in any segment, with reference to the guidelines to Section 30, does not permit uncontrolled spread and/or escalation beyond the area where the leak has occurred. The specific barrier elements that are to have the necessary fire resistance, should be determined on the basis of each specific fire area and relevant barrier functions. In order to determine the heat load per unit of time and the extent of a fire, potential initial leak rates should be used, and account can be taken of systems for depressurisation and drainage where relevant. To make the design robust, leak rates based on conservative assumptions should be used. That is to say, initial rates that result in unfavourable combinations of heat load, fire size and fire duration. NORSOK S-001 Chapter 126.96.36.199 should be used to clarify which fire scenarios should be used as a basis for isolation and compartmentalisation.
The requirement for independence as mentioned in the first subsection, entails that the emergency shutdown system comes in addition to systems for management and control and other safety systems. The emergency shutdown system may have an interface with other systems if it cannot be adversely affected as a consequence of system failures, errors or isolated incidents in these systems.
An unambiguous command structure as mentioned in the second subsection, means that the flow of signals and command hierarchy are clearly stated. When designing the manually activated function as mentioned in the second subsection, the NORSOK S-001 standard Chapter 11.4.1 should be used.
The requirement related to stopping, isolation and partitioning as mentioned in the third subsection, means that the following valves normally will be emergency shutdown valves:
- Subsurface safety valves
- Wing valves and automatic master valves for production or injection wells,
- Valves on the wellhead and christmas tree in connection with gas lifting or chemical injection ,
- Partitioning valves in the processing plant,
- Isolation valves against pipeline systems,
- Partitioning valves in or between the fire areas on the facility.
The requirement related to isolating and partitioning the fire areas on the facility entails, inter alia, that a sufficient number of sectioning valves shall be installed in the processing plant to ensure that any potential fire load from leaks in each and every segment does not make an uncontrolled spread and/or escalation possible out of the area where the leak started. The concrete barrier elements that are to have the necessary fire resistance, should be determined on the basis of each and every fire area and relevant barrier functions. In order to determine the heat load per time unit and the extent of fires, potential initial leak rates that can occur, should be used, and systems for depressurisation and drainage for those cases where it is relevant, can be taken into account. To make the design robust, leak rates based on conservative preconditions should be used; i.e. initial rates that result in unfavourable combinations of heat load, fire size and fire duration.
The number and location of sectioning valves in the processing plant should be determined on the basis of the fire and explosion strategy, cf. Section 5.
For mobile facilities that are not production facilities, and that are registered in a national ship register, DNVGL-OS-A101 Chapter 2, Section 4, with related principles for emergency shutdown in Sections 6, 7 and 8, can be used as an alternative.