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HAZOP: Your Ultimate Guide for Conducting an Effective Risk Assessment


The International Labour Organization estimates there are 340 million occupational accidents and 160 million victims of work-related illnesses every year, globally.

Major workplace accidents and incidents are critical safety issues inherent to business operations. Even one small incident could lead to more serious risk pathways developing.  

That is why the U.S. Occupational Safety and Health Administration requires HAZOP analysis to identify, reduce and manage workplace risk.

HAZOP is a systematic assessment tool used to identify and address potential hazards – mainly in industrial processes – before a dangerous incident occurs. 

In this FAT FINGER article you’ll learn how to conduct HAZOP analysis using five simple steps. This article is structured as follows:

  • What is HAZOP?
  • The benefits of implementing HAZOP
  • How to conduct a HAZOP assessment in five steps

Let’s jump straight to it!

What is HAZOP?


HAZOP is a risk assessment technique commonly referred to as a HaZard OPerability study. It’s a systematic way of identifying hazards in a business process for improved risk management.

“A hazard and operability (HAZOP) study is a systematic brainstorming process of assessing the existence of hazards in equipment and vulnerability of its operation. It is a risk assessment tool that provides information to the management who can make decisions to improve safety and conduct safe operations

Safeopedia, Hazard Operability Study (HAZOP)

HAZOP and its history: The Flixborough disaster and Trevor Kletz

HAZOP originated from the Heavy Organic Chemicals Division of Imperial Chemical Industries (ICI) – a then major British and international chemical company.

In 1963, ICI set out to design a new phenol plant. Potential hazards and operating problems were identified using the then-named critical examination technique,  and the idea of HAZOP was born.

However, the methodology wasn’t a widely adopted risk assessment procedure until 1974 after what was named the Flixborough disaster.

Flixborough is a small town in the UK. An industrial center, home to the chemical plant Nypro Works and was best known for its production of nylon…

…but that was then.

Today, Flixborough is known for the 1974 disaster, where Nypro Works exploded killing 28 men and injuring 105 with raging fires that lasted for ten days. These fires engulfed 200 homes within a six-mile-radius.

What had happened to cause this disaster?

A day before the explosion, operators discovered a six-foot crack in one of the reactors. To keep the plant operational, the cracked reactor was removed, and a quick-fix alternative replacement bypass pipe was put in place. Yet, there was no discussion over the potential hazards of this pipe.

The bypass pipe allowed large amounts of cyclohexane to escape. This coupled with high pressures and temperatures caused the plant to explode.

A broad multidisciplinary review of abnormal operations would have flagged these risks beforehand. If only Nypro Works conducted a thorough risk assessment using HAZOP, the disaster could have been avoided.

The disaster did, however, initiate a drive to promote and improve risk assessment in the chemical industry. One of the leaders pushing this focus on safety was Trevor Asher Kletz.

Kletz became interested in process safety after experiencing firsthand how a process plant works and the hazards present. Kletz got a job at ICI’s research lab. 

When I joined I expected to be spending my life pouring liquids from one test tube into another – but I actually never touched a test tube in the whole time I was there!” he says. “ICI’s research department was far more concerned with solving engineering problems.”

Trevor Asher KletzTrevor Kletz, the father of inherent safety, explains his remarkable career

It wasn’t until after the Flixborough disaster that HAZOP became one of the most widely used risk management techniques in the chemical industry. And it was Kletz who recognized the benefits the approach could deliver, bringing the methodology to the forefront. Kletz became an advocate for HAZOP, using books, papers, and conferences to promote the risk assessment tool. 

Over time, the importance of risk management and the concept of HAZOP spread through the chemical industry. In modern times, HAZOP is used across multiple industries, from food, water, and pharmaceutical industries, to industrial health and safety applications. 

The benefits of implementing HAZOP


HAZOP has revolutionized how industries approach risk assessment, coming as a means of risk control to prevent disasters such as the Flixborough explosion.

The below list details the advantages that come from the implementation of HAZOP. This list has been drawn from the scrutiny and consultation of sources like the Health and Safety Executive (HSE). 

  1. HAZOP explicitly identifies hazards, potential failures, and potential causes of failure, and gives the recommended actions to address these. The analysis is documented and communicated to all relevant parties. 
  2. The HAZOP methodology is extremely useful when confronting hazards that are difficult to quantify. This is because the methodology does not require engineers to explicitly rate or measure the deviation probability of a hazard occurring, the severity of impact, or the ability to detect.
  3. HAZOP takes a multidisciplinary team approach, obtaining viewpoints from a range of disciplines to give a balanced analysis. 
  4. HAZOP is a simple and intuitive means of performing a risk assessment. The approach does not demand considerable technical expertise or technical formulation, and as an approach, is easy to understand.
  5. HAZOP is a proactive risk management strategy, built for detecting problems early to remove the potential of a disaster.

How to conduct a HAZOP assessment in five steps


The main objective of HAZOP is to identify potential risks early. This means breaking a system down into sections, and then questioning, dissecting, and discussing each section to consider every possible scenario and every potential deviation from the norm. 

To conduct HAZOP analysis, teams need to be familiar with HAZOP guidewords. The guidewords prompt teams to question all elements of the assessed system.

For instance, typical guidewords for a chemical plant include: Flow, pressure, temperature, level, and reaction. 

For every guideword, the causes and consequences of possible deviations are noted. Questions are posed by the HAZOP team using each guideword, for example:

  • What would happen if [chemical X] was omitted from the mixture?
  • What would happen if too little [chemical X] was added to the mixture?
  • What would happen if too much [chemical X] was added to the mixture?
  • What would happen if a critical component of [chemical X] was omitted?
  • What would happen if [chemical X] was replaced with [chemical Y]?

Provided that you assume that all elements of a system can deviate relative to the expected desire, then it’s unlikely that teams miss risks inherent to a system when using the HAZOP approach. 

Common terms you’ll use when conducting a HAZOP assessment include:

  • Hazard: Is a potential source of harm. Deviations from operational or design intent may constitute or produce a hazard. A single hazard could lead to multiple forms of harm.
  • Harm: Physical injury, damage to health, the property, or the environment. Harm is a consequence of a hazard and can take many forms. 
  • Risk: A combination of the probability of harm and the severity.

For teams new to the HAZOP methodology, it may initially seem overwhelming. However, the approach can be broken down into five simple steps as detailed below.

Step #1: Document your operations

It’s easy to conduct a HAZOP assessment if your operations are documented. 

With FAT FINGER, you can document operations as checklists, procedures, and workflows in seconds. FAT FINGER offers a no-code solution to digitize steps of an operation, giving the full system transparency you need to effectively execute HAZOP. 

For more information about FAT FINGER, watch the video below.

Step #2: Form and assess your HAZOP team 

Assemble your HAZOP team. You’ll need a team of workers with a wide range of expertise, skills, and experience. Remember, a key aspect of the HAZOP approach is that it’s multidisciplinary. 

You’ll also want to make sure your team has the required experience and knowledge. Once more, team members must understand their role and how it fits into the HAZOP process.

Communicate to your team the importance of considering reasonable variations at each point of the system.

Step #3: Create your plan

This is known as the preparation phase of HAZOP. 

Before you create your HAZOP plan, be sure to define the scope of your assessment. That is, what are your study boundaries?


  • Identify and locate supporting data and information. 
  • Identify the audience and users of the study outputs. 
  • Make preparations, e.g. schedule meetings, transcribe proceedings. 

Identify each element of your system to be assessed. It’s a good idea to do this using open discussions among your team. For each system element (e.g. humans, processes, materials), identify the relevant guidewords and note their deviation questions. Document key assumptions you’re making during this process.

To help you create your HAZOP examination plan, follow the below-stepped process:

  • Explain the overall system design. 
  • Select the part of the system to be examined. 
  • Examine and agree on the system design intent. 
  • Identify relevant guidewords to be examined. 

Step #4: Consider variation effects

It’s time to consider the guidewords that were chosen and their deviation effects. Below are the questions you need to ask to do this:

  1. Is the deviation credible?
  2. Have all interpretations of the guideword combinations been applied?
  3. Have all guide words been applied to a selected system element?
  4. Have all relevant system elements been examined?

It’s a good idea to set up a team meeting to document and discuss the above. 

Step #5: Identify hazards or failure points 

Once the potential deviations have been discovered, the team can document their concerns, estimate the impact of a failure at that point, and determine the likelihood of that failure. 

Document the HAZOP process using FAT FINGER

Just as you can use FAT FINGER to document your operations in the system to be assessed, you can also use FAT FINGER’s intuitive process documentation system to write HAZOP as a process as per the five steps detailed above.

You can then use your HAZOP process alongside other risk management techniques for ultimate risk control. You see, although HAZOP provides a powerful means of risk assessment, it only identifies hazards. You also need to adopt a quantified risk assessment process to use in tandem. 

For instance, consider using FATFINGER’s Health and Safety Observation Report Checklist alongside the HAZOP process. 

Also, check out FATFINGER’s risk management, assessment, and health and safety content in the articles below:

With an effective process, risk analysis in the workplace becomes both effective and efficient. By considering changes to normal operations, using a multidisciplinary team, you can avoid disaster. 

Poor operational awareness contributed to the Flixborough explosion, but also many others such as Chernobyl, the BP oil spill, and Texas City Refinery. 

HAZOP gives your a solid foundation to build appropriate safety precautions into your business system. Avoid a disaster and implement HAZOP.