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HAZOP stands for Hazard and Operability Study and is a process by which a new or existing operation, process, policy, or standard is examined to evaluate what types of potential risk may exist to either people or equipment. When done properly, the HAZOP process will identify potential design or process flaws that were not discovered in the past.

The HAZOP process can be used in almost any industry, but it is most common in refining, chemical industries, oil or gas, pharmaceutical, power generation, and other similar places.

This technique is set up in a way to help not just look at the step-by-step processes, but also the intentions and deviations that occur in operation. Identifying all the possible unintended steps that can take place helps expose potential risks. This is unlike most traditional hazard identification processes that only look at what occurs when everything goes per plan.

Guide Words

Part of identifying deviations from the plan is labeling each potential problem with guide words. Each guide word has a set meaning when applied to different nodes, or variations, of the plan. The following is a common set of guide words used in many industries:

HAZOP Guide Words
  • No or Not - This means the complete negation of the intention from the design.
  • More - This means there is a quantitative increase in whatever is being identified.
  • Less - This means there is a quantitative decrease in whatever is being identified.
  • As Well As - This means there is a qualitative modification, or a qualitative increase.
  • Part Of - This means there is a qualitative modification or decrease.
  • Other Than - This means there was a complete substitution.
  • Early - This means something occurred earlier than intended (clock time).
  • Late - This means something occurred later than intended (clock time).
  • Before - This means a step was performed before it should have in the process sequence.
  • After - This means that a step was performed after it should have in the process sequence.

There can be other guide words when appropriate, but this is a common set of words used in almost all industries.

Where Guide Words Are Used

The guide words above are used to describe almost any type of parameter in a process or procedure. Some common parameters that are looked at include flow, pressure, temperature, level, time, agitation, reaction, start-up, shut-down, draining, maintenance, and more.

Assembling a Team

Performing a HAZOP study will require a team of people to accomplish it properly. The ideal team size depends on the process or procedure being evaluated, but should be kept as small as possible without sacrificing necessary talent or knowledge. The most common roles for this team are:

  • Study Leader - This person leads the study and should have experience with HAZOP studies already.
  • Recorder / Scribe - This person documents everything about the study including causes, consequences, actions, deviations, and more.
  • Process Designer - This person provides details about the intent of designs.
  • Operator - This person will operate the process.
  • Specialist - This person provides specialized technological knowledge about the process.
  • Maintainer - This person offers information and details about the maintenance of equipment or other machinery.


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