A Hazard and Operability (HAZOP) Study is a systematic and structured evaluation of an existing or proposed operation. Its primary objective is to identify and evaluate potential hazards during both the design and operational stages of a process. This study is conducted by a group of engineers with diverse expertise. The team conducts a comprehensive examination of individual segments of a plant, system, or operation, commonly referred to as nodes.
They evaluate the likelihood of any deviations from the intended operation and assess their potential consequences in light of any existing safeguards. The assessment of the impact of identified hazards on safety, assets, and the environment is conducted. The HAZOP methodology is a brainstorming technique that is driven by the use of guidewords. The team members make contributions based on their combined experience and knowledge gained from previous projects.
The HAZOP study procedure documents the hazards that have been identified, refraining from suggesting any solutions unless a clear solution presents itself. Potential resolutions could comprise supplementary measures or functional protocols as deemed essential. The study record functions as a tool for identifying the Health, Safety, and Environment (HSE) concerns that require resolution throughout the project.
The objectives of the HAZOP study are:
- The task at hand involves the identification and assessment of potential hazards and risks that may be linked to process facilities.
- Identify operability and maintenance issues
- Comprehend these perils/challenges and assess their probable outcomes.
- Propose supplementary measures or protocols as deemed essential.
These steps will lead to a better design/ operation of the facility to mitigate the potential hazards identified. Following are the documents required:
- Project and Facility Description
- Facility Layout Drawings
- Process Flow Diagrams
- Piping & Instrumentation Diagrams
- Cause & Effect Matrix
- Hazardous Area Classification Drawings
- The document pertains to the guidelines, operating procedures, and health, safety, and environmental (HSE) philosophies of the company.
- Incident reports
- Facility Risk Register
The HAZOP study proceeds systematically by examining each node of the plant in succession. The Facilitator makes the selection of the node sizes and the route through the plant before the study.The node ought to be explicated in terms of:
- Brief description of the node
- Typical operating and design conditions
Guidewords refer to uncomplicated terms or expressions utilized to specify or measure the purpose and related parameters, with the aim of proposing deviations.
- No, Low/ Less, More/ High, Reverse/ Misdirected, Less/ More
Typical parameters/elements considered for HAZOP Study are as follows
- Flow, Pressure, Temperature, Level, Viscosity
- Composition, Contamination
- Operation, Start-up, Shutdown, Maintenance, Isolation
- Operability & Maintenance Issues
- Instrumentation & Control
Deviation refers to the instances where the process design intent is not followed. The combination of parameters and guidewords in sequence are identified all the deviations (no flow, more temperature etc.). It is possible that there exists a noteworthy degree of overlap among the deviations under consideration, such as the possibility that the absence of flow could produce an effect equivalent to that of increased pressure.
The team will engage in a collaborative process of ideation to identify all plausible factors contributing to the observed deviation. All potential causes should be identified and discussed, as the consequences and actions may be different. Causes are always local or within the node only. If possible, it has been consolidated and limited to the node under discussion.
There exist three primary classifications of causes, ranked in descending order of likelihood:
- Human error
- Equipment failure
- External events
It may be noted that “cause” in worksheet is explicitly worded including one tag. This implies/ includes other corresponding tags for parallel equipment.
The potential consequences for each cause are discussed and assessed within the limits of the information available and the expertise of the team. There may be several consequences involving escalation to other pieces of equipment. All important consequences anywhere in the facility, resulting from the cause are listed out. Worst-case consequences are described assuming that no safeguards are in place or working.
“Safeguards” are the Controls that prevent the cause from occurring, and/ or alert the Operator when deviations occur, and/ or mitigate the consequences of the cause occuring. They include, for example:
- Those systems, engineered designs and written procedures, which are designed to prevent a catastrophic release of hazardous or flammable material.
- Those systems are specifically engineered to identify and provide timely notification subsequent to the onset of a hazardous or combustible substance discharge.
- The aforementioned refers to the set of protocols or documented measures that serve to alleviate the impact of a hazardous or flammable substance discharge.
It is further noted that, positive isolation procedure is followed while handling over any facility for maintenance work such as control valve maintenance, which requires breaking the flange, etc. Once the key safeguards are listed, the team then evaluates the listed Safeguards based on adequacy to eliminate or maintain the potential risks within tolerable limits.
During the HAZOP study session, the study team engaged in a systematic brainstorming process to evaluate the process under review in the scheduled meeting. This was accomplished through the use of a set of Guidewords, which were employed to structure the review. The study team is composed of individuals representing a variety of departments/specialties.
The following procedure is adopted during the HAZOP Study workshop:
- Selecting a Node (i.e. vessel or line) to be assessed;
- Describing the purpose and design of the Node by a Process Engineer or an Operation Representative
- Identifying a potential Deviation that may occur within that Node using a Guideword and Parameter;
- Identifying and evaluating the Causes for the Deviations from the design intent;
- Evaluating the potential Consequences from the Deviations addressed, without considering any Safeguards in place
- Identifying any Safeguards in place in order to prevent the failure scenario from occurring or mitigate the Consequences if it occurs
- Recommendations are raised to mitigate the Consequences further, wherever required.
The recommendations (action items) identified during the HAZOP Study are included in the HAZOP Report and later tracked to closure using the worksheet. Each recommendation suggested by the HAZOP team was proposed to reduce the risk of a hazard scenario to an acceptable level of risk (as determined by the HAZOP team). Should a recommendation not be implemented, the HAZOP Action sheet must identify an alternate action to achieve the required risk reduction or document the basis for reassessing the risks and determining that the risk without the recommendation is within acceptable levels.
It should be noted that the responses to the HAZOP study recommendations should provide a clear audit trail including the reasons for taking or not taking action.