How do you select the appropriate nodes and parameters for a HAZOP Study?
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Before you start a HAZOP Study, you need to define the scope and objectives of the analysis. This will help you to focus on the relevant aspects of the process or system, and avoid wasting time and resources on irrelevant or redundant nodes and parameters. The scope and objectives should be clear, specific, measurable, achievable, realistic, and time-bound. They should also align with the project requirements, regulations, standards, and best practices.
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The scope is relatively easy in the project phases however it is when we get to a change on the system that the scope can be tricky. What I think about when setting the scope: - Is there any upstream or downstream system which is significantly impacted by the change? We may include these drawings in the pack or even in the node definition. - Is there already a good understanding of the system (that is a quality HAZOP is already in place)? If not then the scope of the node may need to be extended. - Is there any other factors which may influence scope? For example wanting to engage an external stakeholder in the HAZOP.
A node is a discrete part of the process or system that has a defined function or purpose. It can be a physical component, such as a vessel, a pipe, a valve, or a pump, or a logical component, such as a control loop, a process step, or a phase change. You should identify the nodes by using the available information sources, such as process flow diagrams, piping and instrumentation diagrams, layout drawings, operating manuals, and expert knowledge. You should also consider the boundaries and interfaces of the nodes, and how they interact with each other and with the environment.
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Identify the nodes is a critical pre-work for a successful HazOp session. The tip I usually provide is to start defining the node from the "design intent" of the system subject to analysis, identify the input and output at the delivery point and run along the line of the service - including all sub routes - up to closing the loop. This is not an error proof advice, but it's a good way of visualizing the nodes and their belonging devices.
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In addition to the basic methodology of following the ‘intended’ flow path, consider also what can happen if fluids flow in other possible pathways (often overlooked by designers). Another effective methodology is to consider nodes which align in terms of the isolatable sections used in the QRA or to break these down into smaller nodes where necessary. Conversely for complex or specialist systems it may be necessary to use larger nodes to encompass the correct functions and modes of operation of the system e.g. compressor recycle loops, batch operations, well systems, specialist processes, etc
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Agree Jerry. I always like to end and start a node on a valve. This makes it easier to ensure we are not duplicating causes in different nodes.
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Node selection in a HAZOP study is based on several factors: Process Complexity: Break down the process into manageable sections, with each section representing a node. Criticality: Prioritize nodes based on critical equipment or process steps that are essential for product quality or safety. Safety Concerns: Identify nodes associated with known safety hazards, such as handling hazardous chemicals or high-pressure operations. Operational Impact: Select nodes that have a significant impact on process operability, such as control loops for maintaining stability and product quality. Stakeholder Input: Consider feedback from process engineers, operators, and safety professionals to identify areas of concern or priority.
A parameter is a variable or characteristic that affects or influences the function or performance of a node. It can be a physical property, such as temperature, pressure, flow rate, level, or composition, or a functional property, such as speed, frequency, voltage, or current. You should select the parameters that are relevant and significant for each node, based on the scope and objectives of the HAZOP Study. You should also use a consistent and comprehensive set of parameters for the whole process or system, and avoid overlapping or missing parameters.
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Consider also what constitutes a hazard in the context of the organisation, scope/basis and purpose of the review and the risk dimensions to be considered (e.g. safety, environment, loss prevention, reputation, risk to public etc) to determine relevant parameters for use in the review to achieve the desired objectives
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parameters for a HAZOP study are selected by considering: Process Variables: Identify relevant variables such as temperature, pressure, flow rate, etc. Guide Words: Choose parameters applicable to guide words used during analysis (e.g., more, less, no). Criticality: Prioritize parameters critical to safety, quality, and performance. Regulatory Compliance: Include parameters relevant to regulatory requirements. Industry Standards: Refer to standards for guidance on parameter selection. Stakeholder Input: Gather insights from process experts and operators. Historical Data: Analyze past incidents to identify relevant parameters. Resource Constraints: Consider available time, budget, and expertise.
A guide word is a word or phrase that modifies a parameter to create a deviation from the normal or expected condition of a node. It can be a qualitative term, such as no, more, less, reverse, or other than, or a quantitative term, such as high, low, positive, negative, or zero. You should apply the guide words to each parameter of each node, using a standard and systematic approach, such as a matrix or a checklist. You should also use the guide words that are appropriate and meaningful for the type and nature of the parameter.
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Guide words serve as essential prompts during a HAZOP study by: Stimulating creativity and critical thinking. Providing a systematic approach to exploring potential deviations. Encouraging collaboration among team members. Helping identify root causes of deviations. Facilitating documentation of study results. Ensuring consistency in the analysis process. By effectively utilizing guide words, the HAZOP team can comprehensively identify and mitigate potential hazards and operability issues within the process, ultimately enhancing safety and reliability.
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The selection of the relevant guidewords will also depend on the nature of the review and to some extent the capabilities of the team in the context. For procedural reviews, consider for example : step missing, too early, too late, out of sequence, ineffective, duration and so on. Specialists may be able to conceptualise ‘other’ hazards but some teams may need a consistent and comprehensive set of guidewords to be used throughout.
A deviation is a potential scenario that results from applying a guide word to a parameter of a node. It can be a deviation from the design intention, the operating specification, the safety requirement, or the quality standard. You should evaluate the deviations by considering their causes, consequences, safeguards, and recommendations. You should also use a risk matrix or a similar tool to rank the deviations according to their likelihood and severity, and prioritize the ones that need further action or improvement.
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In general, consider causes ONLY within the node, although consequences may occur elsewhere. In large, complex Hazops there is inevitably a need for cross-referencing and it is helpful to do this consistently. Where the adequacy of safeguards is unclear, disputed or not immediately apparent to the team, this should be explicitly clear in the action to require further detailed assessment and remediation.
The last step of selecting the appropriate nodes and parameters for a HAZOP Study is to document the results of the analysis. You should record the nodes, parameters, guide words, deviations, evaluations, and actions in a structured and consistent format, such as a HAZOP worksheet or a software tool. You should also review and verify the results with the relevant stakeholders, such as the project team, the client, the regulator, and the operator, and ensure that they are accurate, complete, and clear.
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Keeping consistent as Jerry said is crucial. I have seen recordings where it says refer to Node 29 in Node 54. Then I go to Node 29 and it says go to Node 54. Therefore this hazard has never been matured. Keeping the causes within the Node and consequences anywhere helps ensure that the system is examined thoroughly and this is clearly documented. We should also copy consequences from other places rather than referring so as to ensure that all the initiating events for a specific consequence are identified if it is taken forward to LOPA.
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Good luck with all of the recommendations, getting actions raised, tracked and properly closed out, reverting to the independent facilitator to confirm the Hazop intent has been met properly and to confirm that the action item can reasonably be closed out. This is the hardest part of the process and is seldom completed, checked and documented comprehensively - but it ought to be.
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Selecting nodes and parameters for a HAZOP study involves identifying critical components and potential hazards. In subsea engineering, nodes might include wellheads, pipelines, and control systems, with parameters such as pressure and temperature. For offshore wind power, nodes could be turbines and substation equipment, with parameters like wind speed and voltage levels. Grid code compliance studies focus on nodes like transformers and switchgear, considering parameters related to power flow and voltage stability. In manufacturing, nodes may be machinery and processes, with parameters like temperature and pressure. The selection process ensures comprehensive risk assessment across various project phases.