HAZOP Technique — What It Is and How It Works

The Hazard and Operability (HAZOP) Study is a well-established technique used to systematically evaluate potential hazards and operational issues in industrial processes. Originally developed in the 1960s by Imperial Chemical Industries (ICI), HAZOP has become a standard method for risk assessment in industries dealing with hazardous materials and complex systems.

Key points

• Systematic and structured: Follows a structured approach using guide words to explore deviations
• Team-based approach: Involves experts from various disciplines
• Qualitative risk assessment: Identifies hazards and operability issues rather than quantifying risk
• Process-oriented: Best suited for industrial processes and system designs
• Focuses on deviations: Uses guide words like "More," "Less," "Reverse," and "No" to explore potential failures

The key question is: for every process parameter in your system, have you systematically explored what happens when it deviates from design intent?

Benefits and limitations

Benefits

• Identifies both safety hazards and operability issues
• Encourages cross-functional collaboration
• Enhances process safety and regulatory compliance
• Improves system understanding by systematically analysing deviations
• Helps in identifying potential failure modes early in the design phase

Limitations

• Time-consuming and resource-intensive
• Heavily reliant on the expertise of the team
• Does not provide quantitative risk assessment
• May not effectively capture all possible hazards if guide words are applied incorrectly

Introduction

The technique relies on breaking down a process into manageable sections (nodes) and analysing potential deviations using predefined guide words. These deviations help uncover hazardous conditions and operability problems that could lead to accidents, system failures, or inefficiencies.

How HAZOP works

1. Process breakdown into parts/nodes

The system or process under analysis is divided into functional sections called parts. Each part represents a segment of the process where a specific operation occurs, such as a reactor, a heat exchanger, or a storage tank.

2. Application of guide words

Guide words are applied systematically to process parameters (e.g. flow, temperature, pressure, level) to explore possible deviations.

Guide Word	Meaning	Example Deviation	Potential Hazard
No / Not	Complete absence of the intended function	No flow in a pipe	Blockage or pump failure
More	Higher than expected parameter value	Excessive pressure	Over-pressurisation leading to explosion
Less	Lower than expected parameter value	Insufficient cooling	Overheating causing thermal runaway
As well as	Presence of an unintended element	Contaminants in a process stream	Product quality degradation
Reverse	Opposite of the intended action	Reverse flow in a pipeline	Cross-contamination or pump damage
Other than	A completely different event occurs	Wrong material in a tank	Safety or quality hazard

3. Identifying causes and consequences

For each deviation identified, the team investigates:

• Possible causes (e.g. equipment failure, human error, design flaw)
• Potential consequences (e.g. fire, explosion, product loss, environmental impact)

4. Safeguard analysis

Existing safeguards such as alarms, relief valves, interlocks, and operator interventions are evaluated for their effectiveness in preventing or mitigating hazards.

5. Recommendations for improvement

If safeguards are inadequate, the team proposes additional control measures such as design modifications, procedural changes, or enhanced monitoring systems.

Real-world applications of HAZOP

Chemical processing plants

• Used to identify risks in reactor operations, piping systems, and storage tanks
• Helps prevent dangerous chemical reactions, over-pressurisation, and leakages

Oil and gas industry

• Applied in refineries, offshore platforms, and LNG facilities to assess pipeline flow deviations, pressure build-ups, and equipment malfunctions
• Ensures compliance with safety regulations such as OSHA and API standards

Pharmaceutical manufacturing

• Ensures that deviations in ingredient mixing, sterilisation, and packaging do not lead to quality or safety issues

Water treatment plants

• Evaluates risks in filtration, chemical dosing, and distribution systems to prevent contamination

Step-by-step guide to conducting a HAZOP study

Step 1: Define the scope and objectives

• Determine which system, process, or facility will be analysed
• Set objectives based on regulatory requirements, safety goals, or design reviews

Step 2: Assemble a multidisciplinary team

A HAZOP study team typically includes:

• Chairperson (Facilitator): Ensures the study follows the methodology
• Process Engineers: Provide technical details about the system
• Operators: Offer practical insights into daily operations
• Safety Experts: Assess risks and safeguards
• Instrumentation & Control Engineers: Evaluate automation and interlocks

Step 3: Break the system into parts/nodes

• Divide the process into logical sections (called parts/nodes) such as equipment, piping, or control loops
• Use Piping and Instrumentation Diagrams (P&IDs) to define parts clearly

Step 4: Apply guide words to identify deviations

• Select a process parameter (e.g. pressure, temperature, flow)
• Apply a guide word (e.g. "More" → More Pressure)
• Identify potential causes and consequences of the deviation

Step 5: Assess existing safeguards

• List safety measures (e.g. alarms, relief valves, operating procedures)
• Evaluate if safeguards effectively prevent or mitigate the hazard

Step 6: Recommend improvements

• Propose additional safety measures, process changes, or training
• Document findings in a HAZOP worksheet for review and implementation

Step 7: Review and follow-up

• Present findings to management for decision-making
• Implement approved recommendations and verify effectiveness through audits or follow-up reviews

Further reading

• IEC 61882:2016 — International standard for HAZOP methodology
• CCPS Guidelines for Hazard Evaluation Procedures — Center for Chemical Process Safety
• OSHA Process Safety Management (PSM) Standard (29 CFR 1910.119) — Regulatory framework for hazardous processes
• Complement HAZOP with the HAZID technique to find hazards from outside the process

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