Method Functional Safety

Allocation of Safety Functions to Protection Layers

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.

Safety Functions

What =Method can do for you

  • Experienced study facilitators for HazID, HazOp, LOPA and FTA studies.
  • Independent verification when studies are delivered by others.
  • Training and mentoring support for aspiring HazOp Study Leaders.
  • HazOp Team Members training – either as a standalone training course or as part of our preparation for delivering a particular study.

Support for these activities are provided by =Method Process Safety Ltd.

Most recent projects for Allocation of Safety Functions

Update to earlier LOPA following review by HSE.

Industry: Mining / Metal / Cement
Topic: Layer of Protection Analysis (LOPA)

77 LOPA scenarios were reviewed as part of an ongoing functional safety project.

Industry: Agrochemical
Topic: Layer of Protection Analysis (LOPA)

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
Topic: Layer of Protection Analysis (LOPA)

A Layer of Protection Analysis of a drinks industry demonstration area and laboratory, following an earlier HazOp (P-6164).

Industry: Brewing and Distilling
Topic: Layer of Protection Analysis (LOPA)

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
Topic: Human Factors Risk Assesment (HFRA)

View all of our recent projects here

Functional Safety Consultancy

=Method's specialist, expert consultants support industries across the entire Functional Safety Lifecycle. If you need help please contact us.

Functional Safety Training

=Method delivers training in public venues, In-house and online. See more about how we deliver training here.

Functional Safety Lifecycle

Assessments at key Lifecycle Stages - Functional Safety Management

Planning throughout the Lifecycle - Functional Safety Management

Verification at every Lifecycle Stage - Functional Safety Management
Hazard & Risk Assessment Allocation of Safety Funct's to Protection Layers Safety Requirements Specification Design & Engineering Installation, Commissioning & Validation Operation & Maintenance Modification Decommission
Functional Safety Management
Functional Safety Audit
What is Functional Safety?What is functional safety?
I am new to this, how do i start?What is functional safety?

E: T: 44 (0)1462 713313. W:

LinkedinMethod Functional Safety member of InstMC
subscribe to course updates
Keep up-to-date
Receive our views on the latest industry developments and/or our latest training course dates.

Functional Safety + Process Safety + Cyber Security + Compliance Assessment + Competency Register + Software Solutions = Method Safety and Security

Address: Method Functional Safety Ltd. Method House, Davis Crescent, Hitchin, SG5 3RB
Phone: +44 (0)1462 713313 Email: Website:

Terms and Conditions | Privacy Policy. Registered In England 08453480. VAT No. GB 159 9080 70. Site © Copyright Method Functional Safety Ltd 2024