Layers of Protection Analysis (LOPA)

Layers of Protection Analysis

What is LOPA?

Layers of Protection Analysis (LOPA) is a technique for process safety analysis and risk evaluation, aimed at assessing scenarios with significant consequences across various processes. By examining the potential for hazard occurrence, the chance of safeguard failure, and the severity of potential outcomes identified through hazard identification efforts, LOPA is crucial for determining whether the risks associated with high-consequence situations are aligned with a company's tolerance for risk.

The concept that sits behind LOPA is the recognition that there will always be some level of risk in the high hazard industries and that there is not infinite resource available. The technique therefore challenges operating companies to understand "how safe do we need to be?" and "have we achieved this?" LOPA can also feed into other assessments such as COMAH Risk Assessment, Quantified Risk Assessment (QRA), Occupied Buildings Risk Assessment (OBRA) and Safety Integrity Level (SIL) requirements.

Our facilitators have worked with the LOPA process for decades, across all industry sectors, and can assist you with the following:

Guidance on whether to use LOPA or other techniques.
Screening hazard studies to identify scenarios requiring LOPA.
Independent Facilitation of your Layers of Protection Analysis studies.
Peer review of your studies.
Guidance on setting risk tolerability.
Training, coaching and mentoring your staff.
Linking LOPA studies to other process safety assessments.
Developing your procedures to enable you to conduct your own studies.

Require Assistance?

If you require assistance in performing LOPA then please get in touch today to discuss your requirements.

Layers of Protection Analysis - Key Concepts

Layers of protection analysis (LOPA) showing alarms, instrumented systems and mechanical protection

The study works on the principal that there should be multiple layers of protection which stand between a process upset and a hazardous event. LOPA assesses these layers and challenges

Are there enough layers?

Are the layers reliable enough?

Independent protection layers must be independent, auditable and effective.

One key concept is that of independent protection layers (IPL's). To qualify as an IPL the protection must be.

Independent - of the initiating cause and other IPL's.

Effective - it actually protects against the given scenario.

Auditable - we can prove it.

LOPA used as a part of SIL determination to understand the safety integrity level requirements (SIL)

The study can be used for SIL Determination of a safety instrumented function. When used for this purpose we aim to understand.

What is the target risk?

What is the measured risk WITHOUT the safety instrumented function?

What is the "risk gap" that the safety instrumented function needs to cover?

LOPA Methodology

Step 1 - Scenario Identification

Obtain an initiating event related to a potential hazard from a process hazard analysis study such as HAZID or HAZOP.

Step 2 - Determine the consequences.

Analyse the potential consequences if the scenario unfolds, including harm to people and, if required, environmental harm.

Step 3 - Risk Tolerance

For the given outcome, what level of risk are we willing to tolerate.

Step 4 - Initiating Event Frequency

Identify how often (times per year) that the initiating event will occur.

Step 5 - Identify the independent protection layers (IPL).

Using the rules of independent, auditable and effective, identify relevant Independent Protection Layers along with their probabilities of failure upon demand (PFD).

Step 6 - Identify the conditional modifiers.

The risk might be reduced by conditional modifiers - e.g. probabilities of ignition, harm, presence. Identify these along with relevant probabilities.

Step 7 - Risk Calculation

By multiplying the relevant initiating event frequencies along with probabilities of IPL failure and conditional modifiers, the risk is calculated as number of events / year.

Step 8 - Consider what more can be done.

Compare the target risk with the measured risk to establish if a gap exists. Use the outputs to understand if additional layers of protection are required.

Layers of Protection Analysis (LOPA)