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HAZOP
Hazard and Operability Analysis in the Chemical, Oil and Gas Industry
Introduction
In the chemical industry and the oil and gas sector, process safety is of paramount importance. One of the most widely used methods to identify and control hazards and operational bottlenecks in installations is the HAZOP study (Hazard and Operability Study). HAZOP is a structured risk analysis method that helps to detect potential hazards at an early stage and prevent accidents. In this comprehensive article you will read what HAZOP is , why a HAZOP is necessary , how a HAZOP is performed , supplemented with practical examples and legal/normative requirements (including IEC 61511) around HAZOP.
What is HAZOP?
Definition and purpose:
HAZOP stands for Hazard and Operability study and is a structured and systematic examination of a complex system (usually a process plant) to identify hazards to personnel, equipment or the environment, as well as operability problems that could affect efficiency or operations. It is considered one of the most important methods for hazard identification in process safety. The primary purpose of a HAZOP is to test the (process) design to discover deviations and design errors that might otherwise go unnoticed.
Methodology:
In a HAZOP, the process plant is divided into smaller sections or “nodes”, each of which is assessed separately. A multidisciplinary team of experienced experts performs the analysis during a series of structured meetings. For each node, standardized guidewords are used to examine how process parameters can deviate from the design intent. This stimulates the creativity of the participants to identify potential hazard scenarios and operating problems. The HAZOP method is qualitative in nature and focuses on brainstorming “What could go wrong?” scenarios in an open and critical thinking environment.
History and use:
HAZOP was developed in the 1960s by Imperial Chemical Industries (ICI) and has since become standard practice in process industries worldwide. Originally used in the chemical industry, the method is now widely used in sectors as diverse as refining and petrochemicals, pharmaceuticals and energy. It is now internationally codified in guidelines such as IEC 61882 (HAZOP application) and widely recognised as an essential tool for process safety.
Why is a HAZOP necessary?
Preventing accidents
A HAZOP study is mainly used to identify potential hazards and operational problems before incidents occur. By thoroughly examining a process for deviations, scenarios that lead to unsafe situations can be discovered and addressed in time before they actually cause damage. In this way, HAZOP functions as a proactive measure in risk management: it helps prevent accidents and protects the safety of people, installations and the environment. For example, leaks, explosions or production disruptions can be prevented by systematically analysing the causes and consequences in advance.
Risk management and process safety
HAZOP contributes to the structural reduction of the risk of accidents. It forces teams to think about “conceivable deviations” and worst-case scenarios, which even brings hidden hazards (which can be overlooked in a conventional design process) to light. Studies show that a methodical HAZOP contributes significantly to reducing the chance of incidents and thus guarantees the safety of personnel, the environment and the surrounding community. In addition, it also improves operational excellence : by detecting operability problems, unnecessary downtimes or inefficiencies can be prevented.
Benefits and cost savings
Implementing HAZOP recommendations often results in enhanced safety measures (e.g., additional instrumentation, interlocks, or improved procedures) that increase overall process safety. Although a HAZOP study requires an investment of time and resources, this is far outweighed by the potential costs of an accident (equipment damage, production downtime, injury, environmental damage, legal claims, reputational damage). In other words, prevention is better (and cheaper) than cure . Furthermore, by identifying risks early in the design process, inherently safer design choices can be made, preventing expensive retrofits.
Compliance (compliance with rules)
An important argument for HAZOP is also that it is often mandatory due to regulations and insurance requirements. Insurers, licensing authorities and supervisors (such as OSHA in the US and EU-OSHA in Europe) require companies to perform a thorough Process Hazard Analysis (PHA) to identify, reduce and control hazards in the workplace. The HAZOP method is one of the most widely used and accepted ways to meet this obligation. In the Netherlands, for example, a HAZOP is often performed to comply with the Major Accident Risks Decree (BRZO) and the ARIE scheme for high-risk companies. Worldwide, HAZOP has thus become a de facto standard instrument in the context of process safety management and licensing.
How is a HAZOP performed?
A HAZOP analysis usually goes through five main phases, from preparation to implementation of improvements. First, it is clearly defined what is to be analyzed and by whom . Then comes the actual analysis session, in which the process is critically reviewed step by step using guidewords. Finally, the results are recorded and converted into action points. Below we explain each step step by step:
1 - Preparation (scope & planning):
Clearly define the scope and objectives of the HAZOP study in advance. Define which process (part), which installations and which scenarios fall under the analysis. Collect all necessary process information, such as P&IDs (Piping & Instrumentation Diagrams), process descriptions, flow diagrams, procedures and safety information (MSDS of substances, design data, etc.). Practical planning is also done in this phase: the required resources, timing and location of the HAZOP sessions. Good preparation ensures that the team can work efficiently later on.
2 - Assembling the HAZOP team
Select and assemble a multidisciplinary team of experts who will perform the HAZOP. This team ideally includes process engineers, process operators, safety experts, maintenance/instrumentation experts, and an independent facilitator (team leader) experienced in HAZOP methodology. Bringing together diverse perspectives is crucial: designers know the design guidelines, operators know how the process works in practice, and safety engineers pay attention to risks and standards. A team member who not involved in the project can be added to provide a fresh, critical perspective. Establish roles in advance (e.g. chair/facilitator, secretary/scribe to accurately document all points discussed).
5 - Follow-up and implementation
A HAZOP is only useful if the identified improvement points are actually followed up . That is why the analysis is followed by an implementation phase: the recommended measures are assessed and scheduled by management and the responsible departments. The HAZOP report serves as a guideline and reference. Often, each action point is assigned to a person or team with a target date. Some actions can be taken up immediately (quick wins), while larger modifications are carried out on a project basis. Also communicate the results of the HAZOP within the organization: operators and technicians must be aware of the new risk insights and measures. By translating the HAZOP findings into improved procedures, training and emergency plans, the safety culture is strengthened.
Finally, after measures have been implemented, it is advisable to re-evaluate the risks and confirm that the intended risk level has been achieved. The HAZOP process is cyclical: during the life of the installation, the HAZOP will be revised in the event of changes or periodically (see below) to ensure continuous safety.
3 - Execution of the HAZOP session (identification of deviations)
During the HAZOP meetings, the team goes through the process node by node (a node is a defined part of the process, for example a pumping system, a reactor, or a pipe section). For each node, the design intent or normal operation is discussed first (e.g. “transporting 100 m³/h solvent from tank A to B at 5 bar and 20°C”).
Next, guide words are systematically applied to relevant process parameters to identify possible deviations to think of. Commonly used guide words are for example None (no/not), More/Higher , Less/Lower , Reversed , Also/As Well , and Different from. These are combined with parameters such as flow, pressure, temperature, level, composition, time, etc. to generate conceivable deviations (e.g. “No Flow”, “Higher Pressure than Design”, “Reverse Flow Direction”).
For each deviation , the team then identifies possible causes (e.g. pump failed, valve stuck closed, temperature gauge defective), consequences (e.g. reactor overheating leading to decomposition, system overpressure with possible explosion, toxic gas emission) and existing safeguards or controls already in place (e.g. pressure relief valve, high alarm, automatic shut-off valve). If a scenario is insufficiently secured, the team assesses the severity and likelihood and generates recommendations to reduce the risk.
This process of deviation → causes → consequences → safeguards → measures is repeated until all possible deviations for that node have been covered, after which one moves on to the next node. This step – the actual HAZOP analysis – is usually the most time-consuming phase and requires focused brainstorming and discussion within the team.
4 - Documentation and recommendations
It is essential to accurately record all findings during the HAZOP session. This is often done in a HAZOP worksheet or spreadsheet with columns for deviation , causes , consequences , existing control measures and recommended actions . The secretary records the information and agreed action points for each scenario discussed. After the sessions, the results are bundled in a HAZOP report .
This report typically includes a summary of the method and scope, the list of team members, the findings tables per node, and a summary of all recommendations with assignment of responsibility and priority. Importantly, in addition to technical measures (such as additional instrumentation or modifications), procedural recommendations can also be made (such as adjustment of work procedures, training, maintenance frequencies, etc.).
Example 2: Oil refinery
An oil refinery performed a HAZOP study on its storage tanks and distillation units. The HAZOP team identified several risks that had previously been underestimated. For example, it turned out that the fire-fighting provisions were inadequate for some scenarios: some tank farms lacked an automatic foam extinguishing system and fire detectors were outdated. In addition, the experts noted that some equipment for pumping and processing highly flammable products was not properly grounded, which posed a risk of ignition. A scenario was also discussed in which a temperature control system in a fractionating column would fail, resulting in potentially dangerous overheating.
Following the HAZOP results, immediate improvements were implemented: modern fire suppression and detection systems were installed, stricter procedures and training for the safe handling of flammable materials were introduced, and all temperature and pressure sensors received additional periodic calibration and testing to prevent failure.
By implementing these actions, the refinery increased its overall safety level and significantly reduced the risk of incidents. This example highlights how HAZOP can help identify and address gaps in existing safety measures before a serious accident occurs.
(NB: In addition to the above examples, HAZOP is routinely applied in many other situations in the chemical, oil and gas industries – from offshore drilling platforms to gas storage and pipelines – each with the aim of systematically identifying hazards and taking appropriate preventive measures.)
Practical examples of
HAZOP studies
A HAZOP delivers concrete improvements in practice. Below we discuss two simplified examples from industry, which illustrate how HAZOP contributes to increased safety and better operability.
Example 1: Chemical plant
An extensive HAZOP study was conducted in a chemical production unit. The analysis revealed several potential hazards. For example, certain areas appeared to have insufficient ventilation, which could lead to the accumulation of flammable or toxic vapours. The participants also discovered unsafe situations due to incorrect handling of hazardous chemicals – for example, incompatible chemicals were mistakenly stored next to each other – and pointed out the risk of failed overpressure protection in high-pressure systems (e.g. if a safety valve were to get stuck).
For each of these findings, the team made specific recommendations. They recommended installing additional or improved ventilation systems at critical locations, implementing stricter procedures for the storage and handling of hazardous materials (so that incompatible materials are strictly separated), and increasing periodic inspection and maintenance of pressure relief valves.
By implementing these measures, the company dramatically reduced the risk of dangerous incidents and significantly improved the overall safety of the plant.
Norms and standards (IEC 61511)
In the field of international standards, HAZOP is also anchored. The global HAZOP methodology is defined in the IEC 61882 guideline, while the functional safety standard IEC 61511 (applied in the process industry) prescribes the application of PHAs such as HAZOP as part of the safety life cycle. IEC 61511 defines the Safety Life Cycle for Safety Instrumented Systems (SIS) – this is the life cycle of analysis, design, implementation and management of safety instrumented systems. In this life cycle, the initial risk analysis (Hazard and Risk Assessment) is the very first step.
According to IEC 61511, a HAZOP or similar study must be carried out already in the design phase of an installation based on early P&IDs and process designs.
This ensures that all significant hazards and scenarios are identified before the protection system is designed – after all, no action can be taken against a hazard that has not been recognised.
The results of the HAZOP then form the input for determining the necessary additional safety measures. For example, based on the identified scenarios, the required Safety Instrumented Functions (SIF) are determined and, using methods such as risk graphs or LOPA, the Safety Integrity Level (SIL) each function must have is assessed.
In other words, HAZOP does not quantify the risk itself, but exposes the hazards which are then analysed according to IEC 61511 to determine the required level of protection (e.g. SIL 1, 2, 3 or 4).
Legal and normative requirements (incl. IEC 61511)
International regulations
HAZOP is not only a best practice, but in many cases also a requirement of legislation and regulations. In the United States, the OSHA Process Safety Management (PSM) regulation requires companies to perform a thorough Process Hazard Analysis for hazardous processes, with HAZOP as a method being used very often. In the European Union, the Seveso III Directive (Decree on Major Accident Risks in the Netherlands) requires that major accident risks be systematically identified and analyzed – a requirement that is usually met by means of HAZOP studies.
In short, for high-hazard industries, a HAZOP or equivalent risk assessment is usually a mandatory step to obtain and maintain a permit to operate installations. Also, internal company guidelines and insurers often require periodic review of HAZOPs, for example every five years, to ensure that the risk assessment remains up-to-date throughout the life of the installation.
IEC 61511 also requires that the HAZOP remains up-to-date throughout the project and operational phase. Any changes to the design or process must be assessed for their impact on the HAZOP findings using Management of Change (MOC) procedures.
Before a new installation is put into operation, a Pre-Startup Safety Review (PSSR) is often carried out, in which the HAZOP recommendations are checked off and the study is revised if necessary.
During the operational phase, the HAZOP should be reviewed periodically (e.g. every 5 years, as also required by OSHA PSM) to verify that risk management is still adequate and that any changes in process, organization or knowledge have been taken into account.
This cyclical nature of HAZOP ensures continuous improvement and assurance of process safety throughout the entire life cycle of the installation.
Conclusion
HAZOP has proven to be an indispensable tool for process safety in the chemical, oil and gas industries. It provides a structured method to proactively identify hazards and operability issues that would otherwise remain unnoticed. By taking a multidisciplinary critical look at “what can go wrong?” in each step of a process, HAZOP helps companies to prevent accidents , ensure the safety of people and the environment, and increase operational reliability . In addition, performing HAZOP studies is often necessary to comply with legal obligations and industry standards (such as IEC 61511) in the field of risk management and functional safety.
In summary, a HAZOP does not only provide a list of potential hazards, but above all an action plan to reduce risks to an acceptable level. Implementation of the recommendations leads to safer and more efficient processes. For organizations in the (petro)chemical and energy sectors, HAZOP should therefore be an integral part of the design and operational management process. By properly applying and regularly repeating HAZOP, one invests in a culture of continuous improvements in safety – which ultimately protects human lives, prevents environmental incidents and ensures continuity of production. A well-executed HAZOP study is therefore not just a paper exercise , but a valuable investment in the sustainable and safe operation of every process installation.
HAZOP, process safety, risk management, Hazard and Operability, IEC 61511, chemical industry, oil and gas industry, process hazard analysis, SIL, LOPA, process safety management.
