Engineers Journal / Chemical

HAZOP is not the only answer – it depends on the question

Tuesday 5 May 2015

Author: Denis Connon, chartered engineer, process safety consultant, PM Group HAZOP (hazard and operability study) has long served as the default go-to solution when analysing process hazard risk across many industry sectors and, while it offers many significant benefits, it is just one of a number of choices available within the process hazard analysis (PHA) toolbox. Why use a hammer to crack a nut, if you happen to own a nutcracker? A hammer is the right tool for many jobs, but sometimes it is better to keep it simple and just use a nutcracker. Likewise, HAZOP is the right option for many process risk analysis scenarios, but not for all. Picking the most appropriate option has the potential to deliver major time and cost savings for an organisation, depending on the type of project involved and where you are in the delivery lifecycle. Another reason companies often defer to HAZOP is to ensure that they are compliant with national and international laws and regulations. What many of them do not realise, however, is that they will be equally compliant using any one of the many other PHA options available. There is no legal or regulatory obligation to use HAZOP over any other PHA methodology, as all are approved by the likes of the Health & Safety Authority (HSA), the UK Health and Safety Executive (HSE), the European Process Safety Centre (EPSC) and the Centre for Chemical Process Safety (CCPS). With this in mind, there is a strong case to argue that the time is right for a sea change in approach at corporate level where all PHA options are taken into consideration before committing to a particular hazard risk analysis methodology. So, what exactly is HAZOP and what are the other options in the PHA toolbox? Well, HAZOP is a structured analysis of an operation, process or system design where a multi-disciplinary team closely examines each stage of the design to identify potential deviations from the intended outcome. This is done using a set of guidewords in combination with the parameters of the system in question. Where a potential hazard or operability problem is identified, the team decides what action should be taken and also prepares a written report to that effect. HAZOP was developed in the aftermath of World War Two by the British chemical company Imperial Chemical Industries for use in the chemicals manufacturing sector. This was at a time of great change in the industry, as new methodologies and technologies were being introduced. It quickly became established as a hazard risk analysis 'standard' across a wide range of processing industries, a position it still holds today.

Other PHA options

But there are other options in the PHA toolbox, each of which have their own advantages. These include:

Checklists – a carefully-compiled list of protective measures, procedures, materials properties and recommended good practice parameters. Checklists are suited to most stages of a project lifecycle;
Relative Ranking (RR) – more effective in the initial stages or in expansion or modification scenarios, RR is a structured analysis tool whereby the potential hazards for each element of the process are numerically graded in order of risk;
What-if/What-if Checklists – effective throughout an entire project lifecycle. These involve a brainstorming process through which team members ask questions, voice concerns and proffer solutions to potential hazards;
Fault Tree Analysis (FTA) – a top-down analysis that assesses the cause and effect of potential risks and what actions need to be taken along the way to avoid an accident or malfunction;
Event Tree Analysis (ETA) – a bottom-up approach that focuses on how particular responses to potential issues or live events can contribute to either a positive or negative outcome;
Failure Modes and Effects Analysis (FMEA) – assesses each individual plant item and how their failure can impact on overall system operability;
Layer of Protection Analysis (LOPA) – uses an accident scenario to assess the effectiveness of the various layers of protection that are in place throughout a system;
Process Hazard Review (PHR) – provides a strategic overview of all plant processes and employee system expertise.

With a range range of PHA options available, the next consideration is where and when to use them. This is largely dependant on the type of project involved, what stage it is at and the expertise of the personnel involved. As mentioned, FTA, ETA, FMEA, LOPA and PHR are best suited to scenarios where the initial concept design is already in place. RR is mainly used in the research and development and pilot plant operation phases, while Checklists and What-if/What-if Checklists are effective throughout almost the entire project lifecycle. Ideally HAZOP should only be used once all detailed design work has been completed. However, given its default status as the go-to PHA option, choosing HAZOP without regard to project status is a common mistake many organisations make and one that can add significantly to delivery costs. HAZOP is frequently used earlier in the design to ensure that nothing major is missed. In these instances, a HAZOP is carried out on a system rather than a node basis. HAZOP is effective at this system level, but other tools such as Process Safety Screening, or hazard identification (HAZID) may be just as effective and less resource intensive. The other PHA tools should be considered, rather than reaching for HAZOP as the default tool. Another factor to consider when choosing a PHA methodology is that HAZOP is extremely resource-intensive compared to other options. Normally, it involves a team of eight personnel and can take up to six weeks to complete a full analysis. This equates to approximately 240 man-days, which is a significant outlay for any organisation. However, by using, for example, a Checklist or one of the other options, the job can be completed in three to five days with a much smaller team, thereby creating sizeable time and cost savings on the project. Even if a team of eight is used, the analysis can be completed in 24-40 man-days – which means savings of 80% or more can easily be achieved.

Replicated design

There are other instances where it simply does not make sense to use HAZOP. Chief among these is where the design is being replicated from an earlier project. In such cases, most of the risks are known and a less arbitrary option such as a Checklist would be equally effective, particularly if the project is rated as low risk. However, HAZOP may be deemed appropriate in replicated design cases where the hazard potential is high, although Checklist or What-if/What-if Checklists may serve just as well. As we can see, each of the options in the PHA toolbox offers its own unique benefits. Some are more costly and time consuming to implement than others, but all are based on industry best practice and are fully compliant with relevant national and international legislation and regulations. Therefore, when it comes to choosing a PHA solution, it should not be a case of 'one size fits all', followed by immediate deferral to HAZOP. There may be a better answer. Denis Connon, process safety consultant with PM Group, is a chartered engineer with an MSc in process systems engineering. He has 20 years’ experience advising leading pharmaceutical, food and energy clients in Ireland and internationally on safety issues such as HAZOPS, ATEX, Seveso and Root Cause Analysis. Connon is a chartered member of IOSH and IChemE, and is a registered safety professional.