What is Allocation of Safety Functions to Protection Layers?
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.
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Technical author
Dil Wetherill
CEO - Method Safety and Security
Dil launched Method Functional Safety in 2013. He now delivers training courses and provide consultancy on all aspects of functional safety.
4 x Recent =Method Functional Safety Function projects
LOPA following earlier HazOp to establish the effectiveness of existing and intended protection layers and safety functions at a hydro electricity facility.
Industry: Water + Waste
Topic: Layer of Protection Analysis (LOPA)
Layer of Protection Analysis for Hydrogen Energy Management System (EMS).
Industry: Other
Topic: Layer of Protection Analysis (LOPA)
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 + Waste
Topic: Layer of Protection Analysis (LOPA)
Project 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 / Cement
Topic: Fault Tree Analysis
