Delta Force

Article by Trish Kerin CEng FIChemE

Trish Kerin explains the power of using Delta HAZOP, a new method for revalidating previous HAZOPs

SO, it is that time again. Time to revalidate your risk assessments. These activities come around at least every 5 years, and as usual, we all start doing a good old HAZOP revalidation or redo. But what if there is an alternative that gives you a more in-depth assessment, for less overall effort? Well, here is one I prepared earlier.

In October 2021 the IChemE Safety Centre (ISC) published a guidance document called Effective Revalidation of Risk Assessments: Delta HAZOP. This document introduces a new method to revalidate your previous HAZOPs. This technique was originally developed within ExxonMobil, and after using if for a number of years, Exxon offered the concept to ISC to develop a guidance document. It was certainly a topic of great interest to our members, and resulted in our largest-ever working group of 25 people from four continents! In the last 2 months of 2021 it was downloaded almost 200 times.

ISC guidance document: Downloaded almost 200 times In the last 2 months of 2021

The beauty of Delta HAZOP

We know that traditional HAZOP, when done well, is a robust and thorough analysis of scenarios, and enables the identification of some safeguards. As we keep repeating this process over and over again, we might start to see diminishing returns, as we already addressed all those risks. The beauty of Delta HAZOP is that we focus on the subtle and creeping changes, so we start to see a different risk picture appearing. For example, your design may have made the assumption that a device will activate once a year, but experience shows you that it is actually activating every second month on average. That type of change alters the fundamental assumptions in a risk calculation. These types of issues are more likely to be picked up in a Delta HAZOP as there is more focus on trended data.

The beauty of Delta HAZOP is that we focus on the subtle and creeping changes, so we start to see a different risk picture appearing...That type of change alters the fundamental assumptions in a risk calculation

But there’s more – another key advantage of Delta HAZOPs is that their assessment workshop time is typically less than for a HAZOP. Hence fewer staff hours in a workshop together. While this advantage does not come for free, as there is more preparation time for data collection and preparation, this is typically undertaken by the HAZOP facilitator. Overall, this means it is usually a cheaper process – with the caveat that just because it is cheaper does not mean it is right for all occasions.

What is a Delta HAZOP?

Delta HAZOP is an assessment technique that focuses your review on what has changed (hence Delta), instead of just reassessing with guidewords the same system. Change can occur for many reasons. It might be from a structured and deliberate management of change activity, or it might be from equipment wearing out and operating differently. These more subtle changes are harder to spot via a traditional HAZOP assessment. A Delta HAZOP is designed to focus you in on these changes and look for a changed risk profile because of them. It does not use a guideword approach, but does have some prompting checklists to help you find the right input data.

A Delta HAZOP still follows the basic four stages as defined in IEC61882. You still need a definitions stage where you work through the process of choosing to do a Delta HAZOP, as well as scoping the study and defining the roles and responsibilities. Then you move to the preparation stage. This is where the big difference starts to take shape. While there are many sources of data that are used in a HAZOP, Delta HAZOP requires some additional material. You will spend more time in this stage than you would for a HAZOP preparation, but the payoff is less time in the examination stage. This is because you will perform an analysis of the data trends in this stage to understand the subtle changes and what impact they may be having. Then, in the examination stage, you will again see a difference – there are no guidewords to follow. But there is a checklist to help you consider a range of inputs. This is still done in a workshop environment with a team, and it is vital that experienced operators are present to share their perspective. Lastly, you will complete documentation and follow up. This is similar to a HAZOP – you write the report and manage any actions.

Now that all sounds nice and easy to follow, and it is – once you have decided in stage 1 that a Delta HAZOP is for you.

Should I choose Delta? Some practical tips

Should you choose Delta? This is always going to be an engineering judgement call, but there are a number of items to consider in making that call. In the guidance document we have provided a series of questions to consider when making this decision. The questions are not scored, you may answer yes, no, or maybe to any of them, but the key is to consider the information as a whole in making your decision. These important questions, with some explanation are listed in Table 1.

Table 1: Should you choose Delta? (source: Effective Revalidation of Risk Assessments: Delta HAZOP1)

As you can see, the questions range from the quality of the last HAZOP, to what has changed, including company standards or regulatory needs, to incident history, and management of change activities. Lastly, it is up to each facility to ensure that your local regulator would accept a Delta HAZOP as an alternative to a revalidation or redo HAZOP.

Disclaimer: While Delta HAZOP focuses on changes, it does not negate the need for a thorough management of change process. While many jurisdictions have been accepting this form of analysis, it is up to you to check with your local regulator before substituting a Delta HAZOP for a HAZOP.

Article by Trish Kerin CEng FIChemE

Director - IChemE Safety Centre

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