A Hazard and Operability (HAZOP) study, highly regarded as the most widely adopted process hazard analysis (PHA) method globally, is recognized and accepted by regulatory bodies in the United States for its effectiveness in enhancing safety and operability within industrial settings. Particularly in California, USA, known for its very stringent process safety regulations, HAZOP study is integral to ensuring federal and state compliance.

Central to the HAZOP methodology is its unique approach to identifying deviations from an intended design by applying specific guide words like “No,” “More,” and “Less” to different aspects of the design intent, such as flow, temperature, and pressure. This occurs within defined segments of the process known as nodes. During HAZOP, a multidisciplinary team collaboratively brainstorms potential causes for each deviation at these nodes, mapping out the resulting sequence of events. This includes pinpointing safeguards in place and assessing the possible consequences, with each sequence forming a distinct scenario.

The primary aim of a HAZOP is to systematically uncover potential hazards rather than provide a quantitative risk analysis. The result is typically a compilation of concerns and actionable recommendations rather than a detailed frequency or occurrence analysis. Applicable throughout a process’s lifecycle—from design to maintenance—and adaptable to both continuous and batch processes, HAZOP requires a skilled facilitator to lead the process.

This facilitator, supported by a scribe, ensures that the analysis remains focused and comprehensive, leveraging structured discussions to enhance the safety and operability of the system, thus affirming HAZOP’s invaluable role in process safety management.

Let’s explore the meaning of HAZOP in greater detail and clarify how it differs from the often-confused term: HAZID (Hazard Identification).


Risk, in its essence, is defined as the potential for an event to lead to an unwanted outcome, quantified by the likelihood of the event and the severity of its consequences. This dual aspect of risk—probability and impact—makes it a pivotal focus in the field of risk management. Risk identification and assessment form the core activities in managing risk, aiming to pinpoint potential threats and evaluate their implications thoroughly.

HIRA is a broad term encompassing these activities, ensuring that risks to employees, the public, or the environment are consistently managed within an organization’s tolerance levels. The process of HIRA involves addressing critical questions about what can go wrong (Hazard), the severity of potential outcomes (Consequences), and the frequency of such events (Likelihood). By determining the necessary depth of analysis to inform decision-making, HIRA helps balance between insufficient examination, which can lead to poor decisions, and excessive analysis, which can waste resources.

Within the spectrum of tools available for HIRA, Hazard Identification (HAZID) and Hazard and Operability Study (HAZOP) are prominent techniques used to identify and assess risks. HAZID focuses on the early identification of potential hazards through structured brainstorming among experts, making it crucial for preemptive risk management.

On the other hand, HAZOP provides a more granular analysis by examining process deviations that could lead to operational hazards. This method employs a systematic approach, using guide words like “No,” “More,” and “Less” to explore potential deviations from intended operations, thus enabling teams to identify hazards, assess operability issues, and recommend preventive measures.

Both HAZID and HAZOP are integral to ensuring that safety and operational integrity are maintained through detailed scrutiny of processes and systems, highlighting the importance of comprehensive risk analysis in industrial settings.

In a chemical plant processing highly hazardous chemicals, such as a unit handling chlorine gas, HAZID and HAZOP are vital for ensuring safety and operational integrity. HAZID is a proactive process used to identify potential hazards early in the project life cycle or during operational changes.

For example, during a HAZID session for the chlorine gas unit, subject matter experts might systematically brainstorm and document potential hazards, such as chlorine gas leaks stemming from equipment failure or operational errors. They would analyze scenarios like the failure of gasket seals under high pressure, identifying such risks before they manifest.

Following HAZID, a HAZOP study provides a more detailed and systematic examination of the same unit by focusing on potential deviations from the design or operational intentions. By applying guide words such as “No” for no flow conditions (which might suggest blockages) or “More” for increased pressure (leading to overpressure scenarios), the HAZOP process allows a team to delve deeper into each identified scenario.

The team would discuss these deviations and their possible consequences, like toxic releases. Then, they will propose appropriate corrective actions, such as the installation of more robust monitoring systems or improved safety valve specifications. This structured approach ensures that both immediate and long-term hazards are addressed, enhancing the safety and reliability of operations within the chemical plant.

The Basic Concept of HAZOP

Understanding the concept of HAZOP requires familiarity with specific terminologies that are central to its methodology:

  • Design Intent: Specifies the expected operation of a process or component
  • Guide Words: Simple terms used to challenge the design intent and stimulate creative thinking to identify potential deviations. Commonly used guide words include:
    • No, Not, None: Indicates a complete negation of the intended function
    • More of: Suggests a quantitative increase in any relevant parameter
    • Less of: Indicates a quantitative decrease
    • As well as: Points to a qualitative increase
    • Part of: Suggests a qualitative decrease
    • Reverse: The logical opposite of the intended function
    • Other than: Signifies a complete substitution
  • Deviations: Variations from the design intent identified through the systematic use of guide words
  • Causes: The underlying reasons why deviations might occur
  • Consequences: The potential outcomes or results if deviations occur
  • Safeguards: Measures implemented to prevent causes, mitigate consequences, and control actions. These include installing alarms to signal when systems may be getting out of control and defining actions to regain control.

For example, a HAZOP study is conducted employing the guide word “No” to assess the functioning of a valve within a chemical processing system. If “No” is applied to the valve operation, it suggests a scenario where the valve fails to open or close when activated. This deviation from the design intent could be caused by several factors, such as electrical failures, mechanical jams, or a breakdown in the actuator mechanism.

The consequences of this failure mode might include an inability to control the flow of hazardous chemicals, potentially leading to overpressure situations, environmental contamination, or process inefficiency. To mitigate these risks, safeguards such as regular maintenance checks, the installation of a backup power supply for the valve, or the implementation of a secondary manual override system could be crucial. Additionally, installing an alarm system that alerts operators to nonoperation can help in taking swift corrective actions, thereby enhancing system safety and reliability.

Steps in the HAZOP Study Process

Stage 1 – Project Initiation Phase

The initiation begins with scope and requirement confirmation, where the project coordinator collaborates closely with the client to gather essential information, encompassing all facets from process to structural details. This foundational step ensures all project requirements are clearly understood and agreed upon.

Following this, a thorough review of project information is conducted by the project lead in collaboration with key stakeholders. This review confirms the project scope, requirements, and schedule, ensuring all parties are aligned with the client’s expectations.

Along with this step is assembling the HAZOP team. In California and other parts of the USA, the team is led by a HAZOP facilitator. Typically comprising less than 10 members, a HAZOP team draws from a diverse pool of disciplines, including design, process engineering, operations, maintenance, and process safety, with at least one member specifically trained in HAZOP methodologies.

The inclusion of specialized roles, such as a control systems engineer and a package vendor, enhances the breadth and depth of the analysis by integrating comprehensive process knowledge and diverse perspectives. The facilitator’s role is critical, often necessitating professional certifications to adeptly manage complex technical issues and team dynamics.

This ensures the study is conducted thoroughly and effectively, with a scribe playing a key supportive role in documenting the findings accurately, whether they are the facilitator themselves or a separate individual proficient in HAZOP recording software. Together, a well-assembled team and knowledgeable facilitator are fundamental to the thorough identification and mitigation of potential risks in the HAZOP study.

To officially start the project, a kick-off meeting is scheduled. Conducted by the facilitator or sometimes the project lead, this meeting establishes the project’s timeline, identifies critical milestones, and outlines dependencies, setting a clear path forward.

Stage 2 – Preparation Phase

During the preparation phase, the Saltegra project engineer thoroughly performs an initial assessment of the required Process Safety Information (PSI), like Process Flow Diagrams (PFDs) and Piping and Instrumentation Diagrams (P&IDs).

This involves defining the nodes for HAZOP examination and highlighting relevant sections of the PFDs and P&IDs to guide the upcoming sessions. “Noding” is defined as the segmentation of the process into manageable sections or nodes for detailed analysis. Nodes typically represent specific parts of the process, such as pipe sections, vessels, or even steps in a procedure, facilitating a detailed and targeted review.

Following noding, the preparation phase involves meticulously populating the HAZOP worksheets. These worksheets are based on the detailed PFDs and P&IDs that outline each node. The documentation must highlight all pertinent process information, which is then pre-populated into HAZOP-specific software, like PHA-Pro, to streamline the subsequent analysis.

Additionally, to make the session phase more efficient, a process known as pre-causing is implemented. This involves identifying potential causes of deviations before the actual sessions begin, thereby enhancing the focus and productivity of the HAZOP discussions.

Stage 3 – Session Phase

In the session phase, an expert facilitator leads the project team through the actual HAZOP study, utilizing a series of structured and detailed sessions. A typical session agenda begins with team member introductions, an overview of the process, a discussion of the session schedule, the establishment of study ground rules, a discussion of the team member’s responsibilities, and a brief introduction to risk management principles specific to HAZOP.

Following this ceremony, the facilitator leads the team through each node systematically. This involves reviewing the design intent and philosophy of each node, applying guide words to identify potential hazards and operability issues, and assessing existing safeguards. If issues are identified, the team undertakes formal risk ranking to prioritize high-risk areas and suggest modifications to the design or operation to mitigate these risks.

All discussions, findings, and recommendations are meticulously documented in the HAZOP worksheets, ensuring a comprehensive record of the session’s outcomes and action points. This methodical approach ensures every aspect of the process is scrutinized, fostering a thorough understanding and management of risks.

The facilitator uses their expertise to steer discussions, ensuring all potential hazards, their causes, and consequences are thoroughly explored. In California and other parts of the USA, the flexibility of Hazard and Operability (HAZOP) study session formats—ranging from in-person to virtual—allows for adaptive and responsive engagement strategies that can accommodate various project needs and stakeholder locations.

The duration of these sessions is influenced by various factors, such as the size and complexity of the process, the detailed nature of the nodes, and the overall purpose, scope, and objectives of the study. Team dynamics also play significant roles in the efficiency of the sessions. Of course, it would be helpful if the members of the team had attended HAZOP training in the USA and were equipped with the necessary skills and experience.

Stage 4 – Post-Documentation and Close-Out Phase

The final stages of a HAZOP study are crucial for translating the detailed analyses conducted during the sessions into actionable recommendations and comprehensive documentation. As each scenario is identified and dissected during the study sessions, it is meticulously recorded using specialized software like PHA Pro.

These worksheets are essential not only for immediate reference and checking by the facilitator and team members but also serve as a basis for quality control reviews, generation of action items, and subsequent reviews by external parties such as regulators and third-party auditors. They also play a crucial role in revalidating studies when required.

Upon completion of the sessions, Saltegra’s project engineer compiles all findings and recommendations into draft deliverables, including detailed HAZOP worksheets and a comprehensive final report. This documentation undergoes a rigorous internal review to ensure accuracy and completeness. Once vetted internally, these documents are presented to the client for feedback.

This collaborative review process allows the incorporation of client insights and any additional data that may become available post-session, ensuring that all aspects of the study are thorough and reflect the most current information. The finalized documents, including recommended actions for risk reduction – whether enhancing existing safeguards or introducing new ones – are then systematically prepared for implementation by the client. Typically based on risk assessments using matrices or layers of protection analysis, these recommendations are designed to reduce risks to tolerable levels.

The project is formally closed out with the electronic submission of all final deliverables to the client, ensuring a seamless transfer of crucial safety information and facilitating the practical application of the study’s outcomes to enhance process safety.


Conducting successful HAZOP studies within your company begins with the careful selection of your team, guided by a skilled HAZOP facilitator in the USA. The diversity and expertise of the team are paramount; hence, it’s essential to include individuals from various disciplines, such as process engineering, operations, maintenance, and safety, each bringing a unique perspective to the table. Ensure at least one member is well-trained in HAZOP methodologies. The inclusion of members with varied expertise not only enhances the depth of the analysis but also aids in covering all aspects of the process being studied.

Once the team is set, defining a realistic timeline for the HAZOP study is crucial. This includes setting reasonable deadlines for each phase of the process, from preparation to close-out, ensuring that the study does not rush through critical analysis or drag on unnecessarily.

During the HAZOP sessions, meticulous documentation is key. Every scenario, discussion, and decision should be recorded in detail. This not only helps maintain a clear record of the study but also ensures that actionable insights are captured and can be referred back to during the implementation of recommendations.

By adhering to these practices – meticulous team selection, setting reasonable deadlines, and thorough documentation – your company can significantly enhance the effectiveness and efficiency of HAZOP studies, leading to safer and more reliable process operations.

With Saltegra’s extensive experience in conducting Hazard and Operability (HAZOP) studies not only in California but also across the USA, we have refined the steps in the HAZOP study process to perfection. This expertise is our secret sauce in successfully safeguarding people and the environment against chemical safety incidents, consistently leading to successful projects and enhanced safety outcomes.