Top ten tips for an effective HAZOP (part one)

HAZOP is a key tool in Process Hazard and Risk Assessment and can also form the basis of any IEC 61508 / IEC 61511 Functional Safety Assessment. A HAZOP workshop, however, can be a costly exercise, so it’s clearly important to get ‘bang for your buck’.  So what makes an Effective HAZOP?

Having chaired numerous HAZOPs all over the world and in several different industries, I therefore thought I’d share my thoughts on what makes a good (and not so good!) HAZOP. This list is by no means exhaustive, but captures the key points from my experiences, so here goes:


Like many things in life, preparation is key. If done correctly, the HAZOP can start quickly and progress efficiently; if the prep’ hasn’t been completed to a competent standard, delays are inevitable which could ultimately lead to a HAZOP being rescheduled several months down the line (Think about how difficult it is to schedule a week long meeting with several key personnel!).

To make sure that all the correct documentation (see No. 2), personnel (see No. 3) and logistics (projector, refreshments etc.) are in place, at Engineering Safety Consultants (ESC), we issue a pre-HAZOP Checklist to the HAZOP team prior to the workshop. This is particularly useful when the team are unfamiliar with HAZOPs and similar studies.  Terms of Reference should also be agreed which include the scope, methodology and agreed guide words for the workshop.

From the point of view of the Chair, marking up the nodes and agreeing them with the appropriate process engineer allows the workshop to hit the ground running. If node marking is left until the workshop starts, attendees are likely to become restless and lose interest. Once again: Preparation is key!


Here’s an example of what would typically be required (in no particular order):

  • P&IDs (each HAZOP team member should have their a copy for the workshop)
  • Plot plans
  • Cause and Effect charts
  • Previous Hazard studies (HAZOPs, HAZIDs, LOPAs etc.)
  • Design limits
  • Stream properties (Heat and Material Balance)
  • Materials of construction & Piping specifications
  • Operating procedures (or operating philosophy)
  • Process Description

For existing plants, all documents should reflect the as-built status; for ‘greenfield’ sites, the design documentation should be sufficiently mature to allow an effective HAZOP.

Equally important is legibility! It sounds somewhat obvious, but making sure the documents are of a sufficient size and print quality will make for a far happier and engaged HAZOP team.


Team experience

It is absolutely essential that the HAZOP team, as a whole, provides expertise on the plant under consideration. Actions raised to address gaps in the knowledge of the plant can be troublesome to close out and can delay the objectives of the HAZOP being reached. IChemE[1] recommends that experience within the industry (including process type-specific experience) should average several years per member; we would generally consider this to be the minimum.

Team Composition

A HAZOP workshop team[1] will be made up of the following:


The most important person in the room is not the one supplying the sustenance (although a steady supply of sugary treat does make for a happy team!), but is most likely the Operations Representative. These are the guys operating the plant on a daily basis and will be able to provide invaluable experience on how the plant is operated in the real world. A HAZOP simply cannot function without an experienced Operations Representative.

Team continuity is also important; whilst often difficult to schedule a large group for an extended period of time, it disrupts the workshop when members have to go in and out. An acceptable solution to scheduling issues may be having a core team, then to have experts in certain areas to be called upon where appropriate. “Herding cats” is an expression that often arises when trying to keep a HAZOP team together!

Team Size

The size of the HAZOP team should depend, primarily, on the complexity on the plant under consideration. The minimum number is generally four[1] (with some of the roles listed above combined), but a study team comprising more than around ten members can be counter-productive. An overpopulated HAZOP team is a sure-fire way to lose continuity (as people leave and return to the room) and tempt team-members into side discussions.


Embrace the meeting! Lack of contribution or scepticism about the usefulness of the process can lead to an apathetic atmosphere. Free-flowing ideas and enthusiasm is needed to fulfil the objectives of the HAZOP. The importance of the workshop needs to be realised by all attending; if members of the team allow themselves to be called away to attend to their normal day jobs or accept phone calls during unscheduled breaks (however quietly they manage to do this in the corner of the room), it disrupts the flow of discussion and can make it difficult to continue. If people in the room are allowed unscheduled down-time, voicemails are listened to, emails are checked and team members may start disappearing with echoes of “I’ll be back in five minutes” ringing within the undisciplined room. A strong chair should prevent this, which leads us to…


The main role of the HAZOP chair is to ensure the agreed methodology is used effectively and productively[1]. Whilst experienced in all stages of process hazard studies, the Chair is there to facilitate and make sure the whole team is contributing to the workshop: LISTEN, GUIDE and ENCOURAGE. The Chair may be needed to prompt certain ideas to be discussed, but should not lead the discussion. Equally, they shouldn’t be afraid to challenge the team as appropriate. An experienced chair will encourage an atmosphere of openness and honesty (“there’s no such thing as a stupid question!”), but will know when to call non-relevant conversations to a halt.


ESC is able to offer Hazard and Operability (HAZOP) and Process Hazard Analysis (PHA) studies as part of the risk analysis process detailed in IEC 61508 / 61511 (Phase 1).

ESC can provide:

  • A HAZOP workshop, led by the HAZOP Chair, providing a highly structured and systematic HAZOP study
  • Use of HAZOP guidewords suitable to the requirements and relevance of the HAZOP study
  • Use of ESC’s bespoke software package, PHA Comp, offering both accuracy and consistency throughout the HAZOP / PHA process
  • Facilitation of a robust consensus-based decision-making process within the HAZOP Study team, ensuring the important and relevant points are captured
  • A record of the HAZOP study, through the production of a HAZOP report and/or Actions report, detailing the HAZOP study and any requirements taken away from the HAZOP

We offer HAZOP chairs with approval from (not exhaustive): BP, Shell, Chevron, Maersk Oil, Saudi Aramco, BG Group, SEE and more.

Part 2

My remaining five tips for an Effective HAZOP, plus a bonus tip, are available here
Top ten tips for an effective HAZOP (part two)


[1] Ref. IChemE HAZOP Guide to Best Practice ISBN 978-0-85295-525-3