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.
Update to earlier LOPA following review by HSE.Industry: Mining / Metal / Cement
77 LOPA scenarios were reviewed as part of an ongoing functional safety project.Industry: Agrochemical
A LOPA “Layer of Protection Analysis” study for three events relating to a hydro-power system: flood gates opened not in accordance with procedures, flood gates not opened when required and insufficient flow. The purpose of the LOPA study was to establish the effectiveness of existing and intended protection layers and safety functions. The LOPA study considered four scenarios derived from the three events and identified a set of actions where there were uncertainties in quantifying the initiating causes and frequency modifiers.Industry: Power
A Layer of Protection Analysis of a drinks industry demonstration area and laboratory, following an earlier HazOp (P-6164).Industry: Brewing and Distilling
A human factors risk assessment was carried out on a number of manual tasks carried out on site on a regular basis. The outcome of this gave a more realistic human failure rate for each of the tasks to be used in the subsequent LOPA updates.Industry: Brewing and Distilling
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