What is HAZOP? Guide to Hazard and Operability Study

Executive Summary

This is a short guide to HAZOP that explains the concept in an easy to understand language.

HAZOP is an acronym created by combining the words for HAZard and OPerability (Study). It is one of the most popular, non-quantitative Risk Assessment and Process Hazard analysis methods in use today across a wide range of industrial operations, but not limited to, Oil & Gas, Refining, Chemicals, Petrochemicals, Glass, Pulp and Paper, Pharmaceuticals, Food and Beverage, Power Generation and any kind of process industry.Carrying out regular HAZOP studies is considered to be a part of good process safety management.

The only kinds of industries that do not generally use this method for risk analysis, are industries that are into discrete parts manufacturing like Automobile manufacturing and/or assembly, machinery manufacturing, machine tool shops or any kind of assembly operation such as wiring of electronic circuit boards, panels, mobile phones, etc.

However, this technique is even used in places like Mining, Steel Plants and Foundries to identify hazards and mitigate them. It is also used in Electrical Systems, called "Electrical HAZOP" , as well as in software development, but we will not be covering these use cases in this White paper. We will give a brief outline of this technique here.


This technique was first introduced many decades ago at the now defunct Imperial Chemical Industries (ICI) of UK as a part of improving process safety and operability in their plants.  ICI no longer exists today in that form and has morphed into many different entities that have no relation with the original company now. Various parts of the company were hived off, merged and/or have been taken over by companies such as Huntsman and AkzoNobel. However engineers and safety professionals who worked in ICI carried over this to these other companies and it grew in popularity tremendously. It was then also adopted for use in Electrical Networks, used to do risk assessment of the then newly emerging Computer Based Control Systems (DCS, PLC based systems) which was known as Computer / Control HAZOP or CHAZOP for short.

Within a few years, the method became mainstream and widely accepted not only in the UK where it started, but all over the world including in the newly industrializing countries such as India and China. Now one considers it a mainstream de-facto risk analysis technique used in the process industry. Note that the method is not static, it keeps evolving and the latest addition is adding human factors to the list of deviations that are analyzed.

Before we  proceed further, just remember that this is just one of many techniques (out of a bunch of several risk assessment techniques) that engineers and other technical professionals use. Other techniques include FMEA (Failure Modes and Effects Analysis), LOPA (Layer of Protection Analysis), HAZID (Hazard Identification to identify hazards), What-If analysis, Checklists, Quantitative Risk Analysis (QRA) and Risk Matrix.

How to carry out a HAZOP Study

First note that any HAZOP Study has to be carried out by a HAZOP Team led by a team leader, who is also known as a HAZOP Leader or HAZOP Chairman. The other team members are a HAZOP Scribe (also known as HAZOP Secretary) and several HAZOP Professionals, who are subject matter professionals from various departments like Process Engineering, Mechanical, Control & Instrumentation disciplines.  Some other team members may be Health and Safety Professionals and plant operators who know the process well (if it is an existing process). Every team member is involved in the analysis, it is a multidisciplinary effort.

The HAZOP leader starts with dividing the plant or equipment under study into several nodes. For example, a node may be a section of a plant that transports a liquid material from a plant to a storage tank via an inlet pipe, valves, etc. This marked on the P & ID drawing. Then for every node the HAZOP Team starts the analysis for every operation involving the design intent for that node. Hence the operating procedures are also needed as part of the input documentation for the study.  The proceedings are documented by the HAZOP Scribe via a manually created HAZOP template worksheet, or by using a HAZOP Software that documents the study.

The procedure to do this is structured in such as way as to identify the design intent of a particular operation of the node. Then use appropriate guide word to know what deviations are possible from the actual design intent. Then in this node, the original intention is identified which is nothing more than transporting liquid from the plant to the storage tank. Then all possible deviations are analyzed in detail.

Some of these deviations could be potential hazards and hence may result in accidents (for example if there is a reverse flow of liquid from the tank to the plant). To list all the possible deviations that can happen, we use standard guide words such as Low, No, Reverse and so on. These are combined with the principal  process parameter that can cause this deviation (in this case Flow is the process parameter). So we analyze what happens in case of Low flow, No Flow, Reverse Flow and so on. Then for every deviation that we list, we estimate the consequences. For example, a Reverse flow condition may take the liquid back from the storage tank to the plant. Whether this could be a potential hazard or not depends on the consequence that could occurs, only the HAZOP team who are involved in the study can evaluate.

Now if this is deemed to be a potential hazard, then a suitable mitigation is needed, or better still should be prevented from happening at all. So one could suggest modifications to the piping (e.g. a reverse flow check valve). This is how the Risk of something bad happening is assessed and also prevention & mitigation methods for other potential hazards are listed in the study. The below video will also give you a brief idea of the technique.


HAZOP Software

One can use standard MS-Excel templates to carry out the study, or use (either commercially available or in house developed) documenting software that does the same.

However, note that software per se is not absolutely necessary to do this, it is only a tool that can make the process slightly faster and easier because the software is used only for documenting the findings systematically. If used by a noob or an incompetent person, the best software in the world may well be useless!

Also the persons who are part of the study team should be well versed in the process, as otherwise outsiders cannot judge whether a particular deviation could cause a bad outcome or not. The team should be multidisciplinary because only then can various engineering solutions, of different types such as mechanical devices, electrical devices or process instruments be suggested.

The study when completed, will result in a HAZOP Study Report, that will list out the recommendations suggested by the HAZOP Team. These action items should be implemented as soon as possible to reduce the risk. After implementation the P ID drawing and Standard Operating Procedure is updated to reflect the changes. This is then communicated to the field operators, panel operators, production supervisors, safety officers, HSE managers and all engineering disciplines involved in the plant operation.

HAZOP Competency and HAZOP Certification

When it comes to doing any HAZOP Study, one of the most important questions to be asked is the competency of the persons who do it. Many times companies tend to outsource this to outside agencies. Such agencies can of course do the job, but only if well supported by the plant owner/operator because only they know the intricacies of their process. So outsourcers can be appointed as facilitators/ leaders or scribes or specialists, but the owner operator’s personnel also have to be part of the team for the study to be effective. It is not simply checking a few boxes here and there.

If an unskilled or untrained person carries out such a Study (using the best software or no software), the chances of doing a bad job increase manifold. Doing a bad HAZOP is worse than doing nothing at all because a bad one lulls people into believing that their study is complete (and the recommendations are implemented and the plant is safe and everybody lived happily ever after) when actually the opposite is true.

Hence it is very important that only trained and qualified people should carry out these studies. For example you could take the Abhisam Training course today to build your competency and that of your team as well. The course has an associated exam that can be taken online and a certificate of competency earned alongwith an electronic badge.

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Our  course is the only course on the market that covers everything related to HAZOP including topics such as CHAZOP and human factors. You can view the demo on our Free Trial Courses page to check it out!

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What about Operability Problems?

Lastly though this tool  is well known as a risk assessment technique, it is also useful from an operability studies point of view. Thus it will identify potential operational problems too, such as the response time of a process operator to a process upset, whether manual valves have been installed in hard to access places and so on. However, this should be part of the scope that is given to the team. Spending a little more time on analyzing operability studies in the plant, will be worthwhile as it can significantly affect the human resources deployed in the plant. Think of it as a kind of work study that could optimize resources.

What about Human Factors?

Human Factors have become an important part of the Hazard and Operability Study as they can be the cause of deviations. In order to use these, we use Human HAZOP Guide Words in our analysis. At least one human guide word is added as an additional guide word, to identify hazards due to human errors for every node. This is very well explained in the Abhisam HAZOP Study Online training course, with real life examples, suggested templates and and filled worksheets for the case studies.

Cybersecurity Issues

Of late this has become a factor in many risk assessment studies. In our view one can easily incorporate this in the standard templates while doing a CHAZOP. All the deviations that can happen due to faults in the DCS/SCADA/PLC/SIS could be either due to random hardware faults, systematic (software) faults or malicious attacks. The consequences for these will be similar and can be analysed. The mitigation however will need some expertise in designing fault tolerant systems. The Abhisam ICS Cyber security training and certification course will cover these aspects.

The Abhisam e-course is the only online training course on the market that covers everything  including topics such as CHAZOP and Human Factors HAZOP.

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