HAZOP study

The Hazard and Operability (HAZOP) study is the most widely used Process Hazard Analysis (PHA) technique in the petrochemical, pharmaceutical, food, oil and gas, nuclear, and other process industries worldwide.

The HAZOP method is used during the design phase of a new work process or project, for significant process changes, and for periodic evaluation of existing operations.

The U.S. Occupational Safety and Health Administration (OSHA) and the European Standard NEN-EN-IEC-61882 are typically used for this purpose. International regulatory authorities recognize HAZOP as an acceptable method for risk assessment.

Routine HAZOP studies

Routine HAZOP studies are conducted on:
New facilities where the design is virtually finalized and documented.
Existing installations as part of a periodic risk analysis or a change management process.

Preparation of a HAZOP report to improve safety and mitigate the consequences of hazards:

• System Identification
• Defining guiding principles and process parameters
• Identifying causes
• Identifying consequences
• Identifying safety measures
• Formulating recommendations

HAZOP Process

Step 1: System Identification
Step 1 in a HAZOP study is to select a system or component for which deviations from design values will be assessed. This could be a heat exchanger, a vessel, or a tank; in fact, it could be any system or piece of equipment on which a HAZOP study can be performed.

Step 2: Keywords and process parameters
Step 2 involves identifying each process parameter relevant to the operation of the equipment in question. Based on the process parameter, keywords can be used to systematically consider all abnormal operating scenarios.

The keywords must be systematically linked to the process parameter to analyze whether the scenario is possible. The keywords that may be included in the HAZOP study are:

Parameter	Keyword	Definition
Flow	More Less Reverse No Other than As well as Misdirected	Quantitative Increase Quantitative decrease, includes no flow Reverse/ opposite direction Complete negation of the Design intent Complete substitution Qualitative modification/ increase
Pressure	More Less No	More than normal operating Less than normal operating Vacuum
Temperature	More Less	More than normal Less than normal
Level	More Less	More than normal Less than normal
Composition	Change Contamination	Corrosive Contamination Out of specifications
Others	Start-up/ Shutdown Maintenance Corrosion Utilities Failure Vent/Drain Safety	Leakage or release to atmosphere Deviations related to mentioned conditions

HAZOP Checklist

A HAZOP checklist is a tool to identify potential hazards in a system. It is a systematic approach to examining the process and detecting any deviations from the intended design or operation. The HAZOP team assesses the severity and probability of each deviation and makes recommendations to eliminate these hazards.

No or None	Complete Negation (Failure of a Function)
More	Quantitative Increase
Less	Quantitative decrease
Reverse	Opposite of the design Intent
Part of	Qualitative decrease
AS well as	Qualitative Increase
Other than	Complete Substitution
Early/later	Relative to a clock
Before/ After	Relating to an order/a sequence
Too long/ Too late	Considering a required time
Too short/ Too soon	Considering a required time

How is a HAZOP study managed?

A brainstorming session is held with the multidisciplinary team, led by the HAZOP chairperson and a note-taker. During the session, safeguards are identified for each node and deviation, after which preventive measures and recommendations are noted.

HAZOP Input Documents

The following input documents are required for the HAZOP team:

• PDFs (Process Diagrams)
• PIDs (Process and Instrumentation Diagrams) for process and utilities
• HSE Risk Matrix and Response Diagram
• Thermal and Mass Balances
• Floor plans or general equipment layouts and elevation drawings
• Material Specifications and Selection Charts
• Cause and Effect Diagrams
• Process Design Basis
• Process Operation and Control Philosophy
• Operations and Maintenance Manual

Knowledge and summary.. The team conducting the HAZOP study has a good understanding of plant operations. In principle, therefore, a field survey is not strictly necessary, as all required information can be obtained through interviews with operational personnel. By interviewing the operators for a few hours during their workday, relevant information can be obtained for compiling a hazard list. This list is subsequently categorized based on frequency and severity using checklists.

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