The HAZOP Experience Gap We Don’t Always Recognise

It is widely accepted that the effectiveness of a HAZOP depends on the experience of the people in the room. What is less often examined is the type of experience those people bring, and how it influences the outcome of the study.

In design HAZOPs, the balance is usually well aligned. Some of the participants are typically drawn from engineering teams with deep experience in design and consultancy environments. They understand the system architecture, the design philosophy, and the assumptions that underpin key decisions. Engineers and operators from the operating company provide a balance with how things are expected to work in the real world.

This creates a strong foundation for discussion. Deviations can be assessed not only in terms of what might happen, but in the context of why the system was designed to behave in a certain way.

Revalidation HAZOPs present a different challenge. By the time a system is revisited, the original designers are rarely available. The study team is instead mainly composed of engineers from the operating company. These individuals bring valuable insight into how the plant has performed in practice, including its operational constraints, the changes implemented, maintenance history, and previous incidents. Their experience is grounded in observed performance, which can lead to a more pragmatic view of risk.

However, their exposure to the original design intent is often limited. This creates a gap that is not always immediately visible.

Design engineers and operations engineers develop different skill sets over time. Design engineers are accustomed to sizing systems for the worst case and this experience gives them the ability to quickly understand if a scenario is potentially hazardous or not. They are trained to ask what could happen under abnormal conditions and have then done the calculations to determine if there is a problem, building their experience for future scenarios.

Operations engineers rarely get this experience as it is increasingly outsourced.

In a revalidation HAZOP, this can manifest in several ways. There may be a tendency to discount or not even identify scenarios that have not been observed in practice. Alternatively, there may be a lack of confidence in assessing how a deviation will develop. This can add time to workshops, with the potential for more recommendations to be recorded or for hazards to be missed.

This is particularly evident in process engineering.

An experienced, design-focused, process engineer can often assess these situations quickly. For example, they can calculate in their head if a pressure drop will exceed a line’s MDMT limit and often they can estimate if a missed relief valve sizing case is less than a known case. These are skills developed through repeated exposure to design problems, rather than operational experience alone.

Importantly, this is not about technical capability or intelligence.

A design perspective is not inherently more correct than an operations viewpoint. HAZOPs deliberately include participants from a range of backgrounds. The challenge arises when one dominates the discussion. The fact that a scenario has not occurred previously can begin to carry more weight than whether it remains technically credible. Additionally, design engineers are experienced in what can go wrong, whereas operations engineers are experienced in what has gone wrong. Each brings knowledge of different hazards and both are valuable.

This is one of the reasons independent process engineering input can be so valuable during revalidation studies. The role of this professional is not to override the operating team, but to complement it.

Done well, this creates a far more productive discussion that identifies more credible hazards. It often saves time, as their experience calculating and investigating upset design cases allows dead ends to be identified quickly. There is no need for a formal recommendation to calculate if a PSV’s tailpipe has the right MDMT when the independent process engineer has already done a conservative calculation in their head.

Revalidation HAZOPs are intended to spot the hazards that others have missed. It has been suggested that a good HAZOP will identify 80% of the hazards in a process, meaning that the revalidation study is looking for the remaining 20%. Additionally, they serve to identify hazards from creeping changes, such as declining pressure, changes in composition or the cumulative effects of multiple MOCs. These can be hard for inexperienced people to identify. I’ve found that experienced process design engineers are both excellent ‘spotters’ of missed hazards while also preventing unnecessary recommendations and their associated workload.

Ultimately, a HAZOP is not just about having experienced individuals. It is about having the right combination of experience.

When that balance is achieved, the discussion becomes more robust, more efficient, and often more insightful. When it is not, the study may still proceed with the right engineering disciplines seemingly represented, and usually at a cheaper price, but the quality of the outcomes can be compromised in ways that are not immediately obvious.