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HAZOPs 101: The Basics of HAZOPs

Industrial manufacturing facilities rely on sound process safety management to reduce human, environmental and economic risk. These facilities are highly regulated to prevent accidents involving the releases of toxic, reactive, flammable, or explosive chemicals. HAZOPs are a critical tool for process safety management.


What are HAZOPs? A Hazard and Operability study (HAZOP) is a structured process safety analysis (PHA) methodology to evaluate and prioritize potential hazards for a manufacturing facility.

In a HAZOP, a multi-disciplinary team will brainstorm scenarios to identify potential hazards. For each hazard, the team identifies and analyzes trigger events, consequences, and current safeguards. The team then recommends further safeguards to reduce risk if these risks exceed the company’s risk profile.

In identifying & prioritizing risks, HAZOPs rely on qualitative assessments. To supplement this approach, HAZOPs may pair with a subsequent layer of protection analysis (LOPA) which uses a semi-quantitative analysis to compare a scenario’s probability and consequence severity against a company’s risk tolerance.

High Level HAZOP Process | Source: iFluids

Why are HAZOPs important? In short, they’re required! HAZOPs are an industry best practice and very often a requirement under regulatory agencies such as US OSHA Process Safety Management (PSM), US EPA Risk Management Plant (RMP), or UK Control of Major Accident Hazards (COMAH).

When are HAZOPs performed? Plants perform HAZOPs for two different reasons. The first occasion is when a complex change occurs within the facility (e.g., a new project, new process, major process modification, etc.). These changes typically involve multiple disciplines and may add additional risk to the plant.

The second occasion is for periodic review of the plant’s existing operations. To maintain compliance with OSHA’s PSM, HAZOPs should occur over a plant or area every 5 years. While this may seem excessive, small (seemingly inconsequential) changes over time may “creep” into new unintended hazards. There is also a chance that previous teams may have missed a scenario.

How are HAZOPs performed? HAZOPs are run with a cross-functional team and led by a facilitator. For a refinery, this could include an operator, operations supervisor, maintenance, engineering support, and other specialists.


In the first stage of HAZOP, the team begins its preparation by defining the scope, the team, and the schedule. In this stage, the team breaks down the overall HAZOP scope into nodes by highlighting them on P&IDs for that plant. The highlighted P&IDs serve as the main guiding document for the HAZOP. Defining the nodes is not an exact science and will generally depend on the team's experience, the complexity of the process under review, and the judgment of the facilitator. During this step, the team also brings together other supporting documentation.

Discussion and Analysis

The team will then start with the first node in the process and define the process design and intent of the study node. To structure the analysis, the team will select a set of process parameters that apply to the node like flow, temperature, or pressure and pair it with a guideword to understand the implications.

Example HAZOP guide words and process parameters | Source Citizendium HAZOP

For example, a team may evaluate deviations from the standard process that might occur from “MORE” (guideword) “PRESSURE” (parameter). This evaluation would include:

  • Identifying the cause of the deviation (e.g., a downstream valve is closed)

  • Identifying the consequence of the deviation (e.g., a vessel over-pressures)

  • Assessing the risk based on severity and likelihood (e.g., moderate severity, with occasional likelihood)

  • Identifying any existing safeguards in the facility design and modifying the risk ranking (e.g., a relief valve is in place so we can reduce the severity and likelihood to small severity with remote likelihood)

  • Identifying any recommendations for preventing and reducing unacceptable, unmitigated risk

Risk Ranking Matrix | Source Citizendium HAZOP

The team repeats this process for each guideword and parameter combination for the node. The exercise is repeated for each study node and each P&ID until completed.

Post Analysis

Throughout the discussion & analysis period, the scribe meticulously records the analysis into a template to maintain

documentation. That documentation is stored in a database and used as a communication tool.

The HAZOP records may be presented to gain buy-in on recommendations and are used to create action items and feed the plant’s MOC process.


As you can see, HAZOPs are an involved, thoughtful, cross-functional activity in the plant. But they do not always go swimmingly. Stay tuned for our upcoming blog on the pain points of HAZOP and how new technologies can improve process safety management.


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