Layer Of Protection Analysis

Understanding What’s Really Keeping You Safe

LOPA is a deeper layer of risk assessment, focused on what’s protecting your process and whether those protections are truly sufficient.

It’s not about overengineering, it’s about asking: “If something goes wrong, what’s standing between us and a major incident, and is it strong enough?”

Building on high-harm scenarios identified in a HAZOP study (like major injury risks), LOPA applies numerical likelihoods to clarify how an event could occur, what controls are in place, and what could reduce the impact if it happens.

These figures are then compared to pre-agreed ‘acceptable risk’ levels to highlight any gaps, and identify which controls are critical in preventing the outcome.

Key Components Of A LOPA

We usually run LOPAs after a HAZOP, when we already have a solid understanding of the hazardous events that need closer scrutiny - usually those with the potential to cause a major injury, or worse before mitigations are in place. LOPA is where we dig into those events and quantify whether the safeguards in place can reliably reduce the risk to a tolerable level. It’s a critical step in defining Safety Instrumented Functions (SIFs) and determining Safety Integrity Levels (SIL).

01 | Define the Scenario & Consequences

We start by clearly stating the hazardous scenario and what could happen if no protections were in place. This sets the stage for the whole assessment.

We also define the “target risk,” the level of risk your business (or industry) is prepared to tolerate.

02 | Identify The Initiating Events

Initiating events are the things that might set the scenario in motion. These are typically drawn from the HAZOP and could include equipment failure, operator error, or process upsets.

Each event is assigned a frequency based on site data, industry averages, or expert judgement.

03 | Establish The Independent Protection Layers (IPLs)

These are the barriers that catch or stop the hazard before it causes harm, but only if they’re truly independent.

In a LOPA, we test each IPL for its effectiveness, specificity, and reliability. Not every safeguard qualifies.

04 | Add Conditional Modifiers (CMs)

Some factors reduce the likelihood or consequence of a scenario but aren’t engineered systems.

For example, whether people are likely to be present or the probability of ignition in a flammable release. These are factored in as Conditional Modifiers.

05 | Calculate Mitigated Risk

We then crunch the numbers. Initiating frequency x IPL performance x CMs = your final event frequency.

We compare that against the target. If the result is still too risky, we identify what else is needed.

06 | Recommend Further Measures (If Needed)

If a gap remains, we recommend additional actions which could include design changes, automation, alarms, or Safety Instrumented Systems.

The final output is a clear, auditable basis for SIL allocation and functional safety design.

Why LOPA Matters

Where HAZOP explores what could go wrong, LOPA tells you if you’re doing enough about it. It’s a structured, practical way to:

Prioritise where further protection is needed
Justify design decisions and SIL ratings
Identify your Safety Critical Elements (SCEs)
Document a defensible risk basis for high-consequence events

Beyond Box-Ticking

A good LOPA builds understanding across the whole team.

It links your process safety studies to your functional safety strategy and gives clarity on what protection layers are actually doing the heavy lifting.

It’s a team effort, involving design engineers, operators, E&I specialists, and safety professionals, and we’re here to make sure it’s thorough, proportionate, and value-adding.

Built For Your Process

We tailor every LOPA to your site’s specific hazards, systems, and tolerability criteria.

Whether you need help with one scenario or fifty, our experienced facilitators bring structure, independence, and clarity to the process.

If your SIL allocations need verifying or your safety layers need a second look, we’ll help you get it right.

Get In Touch

Need to run a LOPA to support your functional safety or risk assessment process? We’re ready when you are. Drop us a line and we’ll talk through the best approach for your site.

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