Safety Integrity Level review (SIL assessment)
In most countries the licenses to operate hydrocarbon facilities dictate that the result of process safety studies is incorporated in the design of the process units. These results are implemented as barriers to reduce the risk of a process safety incident. One of these barriers is a Safety Instrumented Function (SIF). The IEC 61511 describes the requirements to evaluate the risk, the methodology to determine the level of required risk reduction and gives requirements and guidelines to select the correct equipment to achieve the risk reduction in the process unit. The IEC 61511 also gives requirements to implement a life cycle management system to ensure that the required risk reduction is maintained throughout the life time of the facility which includes the test regime for the all the equipment related to the SIF and competency of personnel.
A SIL assessment study evaluates consequences (health&safety, economical and environmental), based PEFS (process engineering flowschemes) after a conducted HAZOP, the required level of risk reduction in factors of 10.
- The assessment team consists of personnel from operations, technology, process control and (part time) discipline specialists (fired equipment, rotating equipment and vendors) and a SIL facilitator.
- The timing of the assessment, in case of a project, after a hazop has been conducted and results are incorporated in the PEFS.
- The recording of the assessment is usually done in a client’s database for SIL assessments.
After the SIL level has been established the configuration of equipment is determined (process sensor (transmitter), logic system and final element (e.g. shut-off valve) based on accepted industrial equipment with known failure data.
The SIL database programs available in the market have the ability to calculate the required test frequency of the SIF-loop components, based on the client’s period between two planned shutdowns.
In case a client has an audit system, the SIL audit can be introduced to ensure the requirements of the IEC are auditable and traceable
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