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Hazard and Operability Study (HAZOP)

By: Tabitha Mishra
| Last updated: August 21, 2017

What Does Hazard and Operability Study (HAZOP) Mean?

A hazard and operability (HAZOP) study is a process hazard analysis (PHA) method for assessing hazards and vulnerabilities in complex processes. It provides employers, safety professionals, and engineers with vital information to help them mitigate potential risks or implement response plans in the event of a foreseeable malfunction.

HAZOP studies are mainly used in the oil and gas, chemical, pharmaceutical, and nuclear industries.

Safeopedia Explains Hazard and Operability Study (HAZOP)

HAZOP studies are performed by a team of experts, including specialists in operations, maintenance, engineering, instrumentation, and process design. The team size depends on the complexity of the processes being evaluated.

What are Hazard and Operability?

  • A hazard is any object or operation that could possibly cause an accident or accidental release of toxic, flammable, or explosive materials that could injure humans, damage property, or harm the natural environment.
  • Operability is the functionality that could lead to a violation of environmental, health, or safety regulations or a negative impact on profitability in the event of a mishap.

The Purpose of a HAZOP Study

HAZOP studies are undertaken to identify and rectify engineering and design issues that may have been overlooked. It involves breaking complex processes into smaller, less complex sections (called “nodes”) and reviewing them individually. The HAZOP team then applies labels known as guidewords to the nodes to identify potential deviations from the process and sets to work finding a solution to those deviations.

A HAZOP Guide Words table showing examples of guide words that a HAZOP team may use to label process deviations.Source: Creative Safety Supply

A HAZOP study helps the organization:

  • Address probable hazards in business operations
  • Study past incidents that could have had catastrophic consequences
  • Improve safety in the workplace
  • Increase sampling and testing frequency
  • Address human factors
  • Address the consequences of failed control measures
  • Relieve budget pressures by preventing costly system failures
  • Improve communication between all stakeholders involved in the project


Hazard Identification (HAZID) studies and HAZOP studies have similarities that go beyond their names. Both are risk analysis tools used in the workplace. They can also complement each other - a HAZOP study can be conducted following a HAZID study to identify further risks.

Each is a different approach and serves a different purpose, however. Some of the basic distinguishing features include:

  • HAZOP identifies abnormalities in the work environment and pinpoints their root causes. HAZID is a general risk analysis tool that alerts management to threats and hazards as early in the process as possible.
  • A HAZOP study is well documented and used as part of a Quantitative Risk Assessment (QRA). A HAZID study, on the other hand, can be done at the unit level with little documentation and is conducted by simplifying all processes in a worksite for detailed analysis.

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