LOPA (Layers of Protection Analysis)
A safety report submitted under the Control of Major Accident Hazards Regulations 2015 (COMAH) has to demonstrate that the risks arising from major accident hazards at the establishment are as low as reasonably practicable (ALARP). LOPA is one of the risk assessment methods used to support that demonstration.
Most cases will require a method of risk assessment. HSE guidance recognises several risk assessment techniques using the Line of Defence / Layer of Protection concept and their usefulness in the COMAH context. Several methods (LOPA, TRAM, AVRIM2 and PLANOP) are used for demonstrating ALARP in COMAH safety reports. Of the techniques considered, it is well established that LOPA (Layer of Protection Analysis) is a useful tool in presenting risk assessments for COMAH purposes. (Information contained on this page was sourced from the Health and Safety Executive, you can find out more here).
LOPA allows assurance of safety as it provides:
Detailed, Semi-Quantitative Assessments
LOPA can provide a more detailed, semi-quantitative assessment of the risks and layers of protection associated with hazard scenarios.
Discovers Weaknesses and Strengths
LOPA allows the safety review team an opportunity to discover weaknesses and strengths in the safety systems used to protect employees, the plant, and the public.
Identifies How Safe a Scenario is
LOPA is a means to identify the scenarios that present the most significant risk and determine if the consequences could be reduced by the application of inherently safer design principles.
Identifies the Needs for Safety Instrumented Systems
LOPA can also be used to identify the need for safety instrumented systems (SIS) or other protection layers to improve process safety.
Minimises Safety Risks
Potential risks are minimised which helps to prevent prospective accidents within a business. It is a method of risk assessment and hazard evaluation, particularly pertinent to chemical threats. It is used mainly in the process industries as a risk assessment tool. Every industrial process has a degree of risk associated with running it and this is one of the popular tools to evaluate these risks and ensure that they remain as minimal threat as possible. It may be used in conjunction with other risk assessment tools such as HAZOP and is also used to calculate a target SIL (Safety Integrity Level) for a Safety Instrumented Systems (SIS).
We have many years of expertise and the capabilities required to conduct Layers of Protection Analysis for your business.
Where LOPA is used. Most of our LOPA work is on chemical establishments operating under COMAH, with further work across energy and pharmaceutical plant. See all the sectors we work in.
How we approach it
Much of the value is decided before the workshop starts. We agree the scenario list up front, usually drawn from HAZOP recommendations or an existing risk register, so time in the room goes on scenarios that genuinely need quantifying. We also agree the tolerable risk criteria before we begin. Those criteria belong to you; our job is to apply them consistently and to say so plainly when a result sits close to the line.
In the workshop each candidate protection layer is tested rather than accepted. Is it genuinely independent of the initiating event and of the other layers claimed? Is it effective enough to credit? Can it be audited and proof tested? Layers that fail get no credit, and that is often the most useful output, because it shows where a site believed it had protection it did not have.
Everything is documented so it can be picked up years later by someone who was not there – initiating event frequencies with the data source stated, each layer with its credit and justification, and residual risk set against your criteria. Where a gap remains, the required risk reduction feeds into safety instrumented function design under BS EN 61511, which our functional safety engineers take forward.
What you get
- An agreed scenario list, traceable back to the source hazard study
- The risk criteria and matrix used, recorded as part of the basis
- A facilitated workshop with your process, operations, EC&I and maintenance people
- Initiating event frequencies with the data source stated
- An assessment of each claimed protection layer against independence and effectiveness
- Residual risk calculated per scenario against your tolerable criteria
- Required risk reduction and a target SIL where a safety instrumented function is needed
- A formal report setting out assumptions, calculations and prioritised actions
When clients typically call us
- A HAZOP has raised scenarios where qualitative judgement is no longer enough
- A COMAH safety report is being written or revised and the risk case needs support
- A target SIL is needed before a safety instrumented system can be specified
- A modification or capacity uprate has changed the risk profile of existing plant
- An older study cannot be defended in audit because its assumptions were not recorded
- There is internal disagreement about whether a proposed safeguard is worth the spend
Frequently asked questions
Do we need a HAZOP first?
Normally yes, because the scenarios have to come from somewhere structured. If no recent hazard study exists we can work from a current risk register, but we will usually recommend closing that gap first.
Who should be in the room?
A process engineer, an operations representative who knows how the plant behaves in upset conditions, EC&I and maintenance input on the protective systems, and somebody with authority to accept the criteria applied.
Does a study always end with a new safety instrumented system?
No. Sometimes the existing layers already meet the target, and sometimes a mechanical or procedural change closes the gap more cheaply. Instrumented protection is one option, not the default.
What stops a safeguard being counted as a protection layer?
Most commonly a shared component, utility or operator action that ties it back to the initiating event. Layers that cannot be proof tested, or rely on a response time nobody can evidence, also fall away.
Related: Part of our process safety services. See also HAZOP facilitation and SIL determination and functional safety.
Talk to us about your project. Request a call