While it is a bit of a mouthful, “Allocation of Safety Functions to Protection Layers” describes reasonably well the objective of this task – which is to work out how much risk reduction is to be delivered by the various protection layers.
The SISSafety Instrumented System is just one of the protection layers identified. This task is often referred to as “SIL Determination” – while it is true that the SILSafety Integrity Level of any SIFSafety Instrumented Function ’s is found through this process, this label is not used by IEC 61511 and it doesn’t reflect how important the other protection layers (like relief valves) can be in delivering the required risk reduction to achieve tolerable risks.
As with H&RA, IEC 61511 doesn’t provide detailed guidance on which technique should be used for Allocation of Safety Functions to Protection Layers – since many different techniques are available and some are more suited to particular applications and industries than others. But it does require that this activity is subject to the full force of Functional Safety Management.
Support for these activities are provided by =Method Process Safety Ltd.
Project to undertake a Layer of Protection Analysis (LOPA) for three scenarios related to the overfill of the gasoline tanks at an oil Terminal.
Industry: Water + WasteProject to model a LOPA scenario using a Fault Tree Analysis methodology. The analysis modelled the relationship between the initiating causes, protection layers and consequence identified within the LOPA scenario.
Industry: Mining / Metal / CementProject to carry out a Human Factors Analysis to establish Human Error Rate (HER) to be used in an updated Layer of Protection Analysis (LOPA) of a Galvanising Line. The specific technique used to determine the HER is known as HEART (Human Error Assessment and Reduction Technique).
Industry: Mining / Metal / CementA project to deliver a Human Factors Analysis (HFA) of selected pipeline receipt tasks at a pipeline terminal. The purpose of this study was to evaluate the appropriateness of the use of the (industry standard) figure of 0.01 applied to human reliability or probability of failure within a recent LOPA Report. Through application of the HEART+ (Human Error Assessment and Reduction Technique) a study on the Human Factors (HF) aspects associated with the pipeline receipts tasks was undertaken. This provided a figure for human error; the assessed nominal likelihood of failure, which could then be directly used in the LOPA study in place of the generic data previously used.
Industry: Oil and Gas OnshoreLayer of Protection Analysis (LOPA) study fora distillery expansion project.
Industry: Brewing and DistillingE: support@methodfs.com. T: 44 (0)1462 713313. W: www.methodfs.com