The Hazard and Operability Study (HAZOP) is a critical tool used for risk management. The HAZOP technique was developed in the 1960s in the United Kingdom by Imperial Chemical Industries (ICI). Its purpose was to analyze the safety of chemical plants, which later expanded to batch reactions and process plant operational procedures. Now, it has evolved to be an essential methodology used across various sectors.
This article explores the intricacies of HAZOP, highlighting its importance, methodology, and the impact it can have on organizational safety and operability.
Understanding HAZOP: Methodology and Application
HAZOP is a systematic technique for identifying and determining potential hazards and operability problems in processes. The methodology involves a multidisciplinary team thoroughly examining process designs using a set of guide words to probe possible deviations from normal operations. These guide words help uncover hidden risks that might not be evident through conventional analysis methods. HAZOP ensures that even the most subtle risk factors are identified and mitigated by systematically exploring every conceivable deviation. It is a form of risk management to identify, evaluate, and control hazards and risks in complex processes that can cause significant injuries to workers or extensive damage to property and company reputation if not properly processed and handled.
The HAZOP process also promotes collaboration among team members as it requires input from various stakeholders, including engineers, operators, maintenance personnel, and safety professionals. With their help, organizations can leverage their diverse expertise and perspectives to identify potential hazards more effectively. This collaborative approach also fosters better communication among team members and improves overall teamwork within the organization.
A HAZOP study generally follows the following steps:
- Build the HAZOP Team
- Define the scope and divide the whole process into various sections, referred to as nodes
- Select a node
- Identify the deviations using guide words for various parameters
- Brainstorm for identifying the hazard and its consequences
- Apply existing barriers and safeguards to reduce the impact of the hazard
- Brainstorm to provide additional barriers as recommendations
- Assign recommendations to the right person for the action items
- Document the process and communicate to asset-facing employees
HAZOP in Detail
Build a HAZOP Team
This step entails creating a multidisciplinary HAZOP team composed of a team leader and members who can collaborate and provide different perspectives based on their expertise in realizing sources of risks and possible deviations from design. HAZOP team members would be design engineers and personnel familiar with operations, maintenance, process, and safety.
Define Scope and Divide into Nodes
This is the main step in the HAZOP study, which involves defining the study objectives and scope. It sets the foundation for the entire study. The team should plan what they want to achieve through the HAZOP study and outline their goals in detail. It’s important to consider all aspects of safety while defining the objectives and scope of the HAZOP study, whether operational or human safety. It is important to identify the process in operations, be familiar with the Process Flow Diagrams (PFD) and Piping and Instrumentation Diagram (P&ID), and be aware of all the nodes.
PFDs are diagrams that provide an overview of the whole process as a visual representation. P&IDs are drawings that provide a visual representation of interconnected processes, equipment, and controls in the plant.
A HAZOP node refers to a section of a process or system with a defined function and definite boundary. The node needs to be reviewed on a parameter basis to identify any deviation. Material Safety Data Sheets (MSDS) serve as the reference document for choosing the required parameters.
Define Parameters and Guide Words
The next step is to define parameters or safe operating limits during the review of nodes so that deviations can be determined and guide words are selected. Table 1 provides an example.
Parameters | Flow | Level | Pressure | Temp | Viscosity | Impurities | UV Radiation |
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Guide Words |
No | Low | High | High | High | Less | High |
Less | High | Low | Low | Low | More | Low | |
High | Empty | Vacuum | Unexpected | Wrong place | |||
Reverse | Over | ||||||
Misdirected | No | ||||||
As well as |
Using guide words, workplace hazards can be clearly identified since they are deviations beyond acceptable parameters or safe operating limits.
To aid in the identification of deviations, a systematic approach using guide words is applied. Guide words can be positive or negative like “more,” “less,” “no,” “reverse,” “other than,” and many more. By applying these guide words to each parameter, the team can explore all possible scenarios and uncover potential hazards or operability issues systematically in a structured and comprehensive manner.
Hazard Identification and its Consequences
The HAZOP team identifies the process parameters or deviations that need to be analyzed. These parameters include all variables that can affect the process operation, equipment design, or process conditions. Consequences of the process deviations, like what can go wrong or how severe it could be, will be addressed by the HAZOP team. These consequences can vary significantly depending on the specific process or system being analyzed. Some expected consequences are human health and safety-related risks, environmental impact, product quality issues, financial loss, operation loss, reputation damage, etc.
Recommendations and Action Items
Recommendations play a crucial part in the HAZOP study. They are the ultimate output generated by experienced team members. These recommendations help create a clear set of instructions that will mitigate or reduce the risks associated with the identified deviations.
The team should prioritize the recommendations based on the impact on health and safety, environment, and production needs. Each recommendation should be assigned to a specific individual for implementation and follow-up. With a well-defined set of instructions in hand, the organization can take steps toward implementing them promptly while monitoring progress.
The Strategic Importance of HAZOP
The implementation of HAZOP goes beyond mere regulatory compliance. It acts as a strategic tool that enhances the safety culture within an organization. By identifying potential issues early in the design phase, HAZOP helps prevent accidents, reduces downtime, and ensures the seamless operation of processes. The insights gained from HAZOP studies can lead to the development of robust safety protocols and emergency response strategies, thereby fostering a proactive approach to risk management. In today's competitive landscape, such foresight can be a significant differentiator, enhancing both operational reliability and corporate reputation.
HAZOP in Action
A HAZOP study is widely used in various industries, including, but not limited to, oil and gas, manufacturing, and pharmaceuticals. This method effectively identifies hazards and associated risks. Usually, a HAZOP study is carried out during the design phase of a project to ensure smooth operations.
In the manufacturing industry, HAZOP studies evaluate the hazards and safety risks at the equipment level during the design and operations stages. By identifying potential deviations in process operations or machine performance during the early stages, manufacturers can take necessary steps to minimize or mitigate the hazards and improve overall safety.
The pharmaceutical industry is another area where HAZOP studies are utilized. These studies are useful in identifying the possible hazards and their associated risks in the development stage of new drugs or medicine. Pharmaceutical companies can ensure that their products are safe to use by patients across different demographics by identifying these factors early through a systematic approach during HAZOP studies.
Case Study
The Incident
In 2005, a hydrocarbon vapor cloud ignited and violently exploded at the isomerization process unit at a large Gulf Coast refinery, resulting in fatalities.
A series of explosions and fires occurred during startup after scheduled maintenance of an isomerization (ISOM) unit that converted low-octane feeds into higher-octane components blended with regular gasoline. During startup, a hydrocarbon vapor cloud was released accidentally from a fractionating column and ignited. All of the fatalities occurred in temporary porta cabins used by contract workers supporting turnaround work. These trailers were too close to process units that handled highly hazardous materials.
The Cause
The accident occurred when operators started up a tower called a raffinate splitter. The tower and associated piping were over-filled, which led the flammable liquid to flow into a blowdown drum. The blowdown drum vented to the atmosphere through a tall stack. The blowdown drum filled with flammable liquid released the liquid into the atmosphere. A large flammable vapor cloud developed and drifted underneath the trailers housing the contract workers. A vehicle near the affected area was running, which probably provided the ignition source for the flammable cloud. The complete incident report of events that led to the explosion can be found in the referenced document [1].
Gaps in Process Safety
Multiple causes led to the incident, however, HAZOP could have played a crucial role in avoiding this incident.
- Tower level indicator, alarm, and control valve malfunctions
- HAZOP can help in analyzing the risk associated with the worst credible scenario for high-level fractionator tower
- On the day of the incident, an unsafe blowdown drum vented highly flammable material to the atmosphere
- The blowdown drum vent was not connected to the flare. A HAZOP study identifies scenarios where unsafe venting can occur and provides recommendations to mitigate these scenarios.
- Failure to adequately evaluate the safety and health impact of a catastrophic blast on temporary trailers located near the ISOM unit
- HAZOP identifies, evaluates, and reduces the impact of catastrophic scenarios by proactive strategies to mitigate these scenarios.
- No automated emergency shutdown system was established
- HAZOP identifies the Safety Integrated Systems as in case of emergency
Conclusion: Embracing HAZOP for a Safer Future
As industries continue to evolve, the complexity of processes and the potential for unforeseen hazards increase. Embracing HAZOP as a fundamental component of risk management strategies is not just prudent, but it is also essential. By fostering a culture of safety and proactive risk identification, organizations can safeguard their operations, protect their workforce, and achieve sustainable success. The versatility and effectiveness of HAZOP in diverse industrial contexts reaffirm its value as a universal safety tool.
References
- Gurung, K., Jayadeep, L, Siwek, J., et al, “Texas City Refinery Explosion – safety out of focus,” University of Bradford, UK, Institution of Chemical Engineers, Loss Prevention Bulletin 275, October 2020.
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