HAZOP Study: How Process Deviations Are Identified Before They Become Major Incidents

Industrial processes involve equipment, chemicals, pressure, temperature, flow, and many other operating conditions. A small change in any of these conditions can sometimes create a serious safety problem. Identifying these changes early is important for preventing fires, explosions, toxic releases, equipment damage, and injuries.

A HAZOP Study is a systematic process safety method used to identify possible hazards and operating problems by examining process deviations. It helps safety teams understand what could go wrong, why it could happen, what the consequences may be, and what safeguards are available.

For industries such as oil and gas, chemicals, pharmaceuticals, power, petrochemicals, and manufacturing, HAZOP can be an important part of process safety management. The Safety Master provides professional process safety support to help organizations identify hazards and improve risk control.

What Is a HAZOP Study?

HAZOP stands for Hazard and Operability Study. It is a structured and team-based technique used to identify potential hazards and operability problems in a process.

During a HAZOP, a team reviews a process step by step. The team considers normal operating conditions and then looks for possible deviations from the intended design.

For example, a process may be designed for a specific flow rate. The team may ask:

• What happens if there is no flow?
• What happens if the flow is too high?
• What happens if the flow is too low?
• What could cause this deviation?
• What would be the consequence?
• Are existing safeguards sufficient?

This systematic approach helps identify problems before they develop into major incidents.

Why Are Process Deviations Important?

A process deviation means that an operating condition is different from what was intended.

Common process parameters include:

• Flow
• Pressure
• Temperature
• Level
• Composition
• Speed
• Time
• Concentration
• Direction

Even a small deviation can create a chain of events.

Example of a Process Deviation

Consider a chemical reactor designed to operate at a controlled temperature.

If the temperature becomes too high:

High temperature → Chemical reaction accelerates → Pressure increases → Equipment may become damaged → Release or fire may occur

A HAZOP helps identify this possible sequence and examines the causes, consequences, and safeguards before an incident happens.

How Does a HAZOP Study Identify Deviations?

HAZOP uses guide words with process parameters to identify possible deviations.

Common guide words include:

• No
• More
• Less
• Reverse
• As well as
• Part of
• Other than

These guide words are combined with process parameters.

Examples of HAZOP Deviations

Parameter	Guide Word	Deviation
Flow	No	No Flow
Flow	More	High Flow
Pressure	More	High Pressure
Pressure	Less	Low Pressure
Temperature	More	High Temperature
Temperature	Less	Low Temperature
Level	More	High Level
Direction	Reverse	Reverse Flow
Composition	Other Than	Wrong Material

The team then investigates each deviation in detail.

Main Steps in a HAZOP Study

1. Select the HAZOP Team

A HAZOP should involve people with different areas of knowledge.

The team may include:

• Process engineers
• Operations personnel
• Instrumentation engineers
• Mechanical engineers
• Electrical engineers
• Safety professionals
• Maintenance personnel
• HAZOP facilitator

Different perspectives help the team identify hazards that one person may overlook.

2. Collect Process Information

Before starting the study, the team reviews relevant technical information.

This may include:

• Process Flow Diagrams (PFDs)
• Piping and Instrumentation Diagrams (P&IDs)
• Equipment specifications
• Operating procedures
• Control philosophy
• Safety systems
• Material information
• Previous incident information
• Process design documents

Accurate information is important for a useful HAZOP.

3. Divide the Process Into Nodes

The process is divided into manageable sections called nodes.

A node may include:

• A pipeline section
• A reactor
• A storage tank
• A pump system
• A heat exchanger
• A process vessel

Each node is studied separately.

4. Define the Design Intent

The team first identifies what the node is supposed to do under normal conditions.

For example:

“Transfer liquid from the storage tank to the reactor at the required flow and pressure.”

The design intent becomes the reference point for identifying deviations.

5. Apply Guide Words

The HAZOP team applies guide words to the process parameters.

For example:

Parameter: Flow
Guide Word: More
Deviation: More Flow

The team then asks why more flow could occur and what could happen as a result.

6. Identify Causes

The team identifies possible causes of each deviation.

For high flow, possible causes could include:

• Control valve failure
• Incorrect valve position
• Instrument failure
• Operator error
• Pump malfunction
• Incorrect process setting

7. Identify Consequences

The team examines what could happen if the deviation occurs.

Possible consequences include:

• Equipment damage
• Product contamination
• Overpressure
• Fire
• Explosion
• Toxic release
• Environmental impact
• Production loss
• Personnel injury

8. Review Existing Safeguards

The team identifies controls already in place.

Safeguards may include:

• Alarms
• Interlocks
• Emergency shutdown systems
• Pressure relief devices
• Automatic control systems
• Detection systems
• Procedures
• Operator monitoring
• Physical protection systems

9. Recommend Additional Actions

If existing safeguards are not sufficient, the team recommends additional actions.

These actions may include:

• Installing additional alarms
• Improving instrumentation
• Adding an interlock
• Modifying operating procedures
• Improving emergency response
• Changing equipment design
• Conducting further risk assessment

HAZOP Study Example

Consider a storage tank receiving a flammable liquid.

Design Intent

The tank should receive the liquid at a controlled flow rate while maintaining a safe operating level.

Deviation: High Level

Possible Causes

• Inlet valve remains open
• Level transmitter fails
• Operator fails to stop filling
• Control system malfunction

Possible Consequences

• Tank overfill
• Liquid release
• Formation of flammable vapors
• Fire or explosion risk
• Environmental contamination

Possible Safeguards

• High-level alarm
• Independent high-high-level shutdown
• Operator monitoring
• Automatic inlet valve closure
• Overfill protection system

Recommended Action

The HAZOP team may recommend reviewing the reliability and testing frequency of the high-level protection system.

This example shows how HAZOP can identify a potential incident scenario before it becomes a real event.

Common HAZOP Guide Words

No

Indicates the complete absence of the intended action or parameter.

Example: No Flow

More

Indicates an increase in the process parameter.

Example: More Pressure

Less

Indicates a decrease in the process parameter.

Example: Less Temperature

Reverse

Indicates that the process occurs in the opposite direction.

Example: Reverse Flow

As Well As

Indicates the presence of something additional to the intended condition.

Example: Liquid plus unwanted gas

Part Of

Indicates that only part of the intended material or activity is present.

Other Than

Indicates a different material, condition, or operation from what was intended.

Benefits of Conducting a HAZOP Study

A properly conducted HAZOP can provide several benefits.

Early Hazard Identification

It helps organizations identify potential problems before they lead to incidents.

Better Process Understanding

The discussion helps engineers and operators understand how different process conditions can interact.

Improved Safeguards

HAZOP can identify gaps in alarms, interlocks, procedures, and other protection systems.

Reduced Incident Risk

Identifying and controlling hazardous deviations can reduce the likelihood and severity of major incidents.

Better Safety Decisions

The findings provide useful information for further risk assessments and safety improvements.

Support for Process Safety Management

HAZOP findings can contribute to a broader process safety management system.

When Should a HAZOP Study Be Conducted?

HAZOP is commonly conducted during the design and development of a new process. However, it can also be useful for existing facilities.

A HAZOP may be considered:

• During new plant design
• Before commissioning
• Before major modifications
• During Management of Change (MOC)
• After significant process changes
• During periodic process safety reviews
• When serious process hazards are identified
• When previous incidents indicate the need for review

HAZOP and Management of Change

Changes to equipment, processes, chemicals, control systems, or operating conditions can introduce new hazards.

A HAZOP can support the Management of Change (MOC) process by examining how a proposed change may affect existing hazards and safeguards.

For example, changing a pump capacity may affect:

• Flow rate
• Pressure
• Equipment loading
• Control systems
• Relief systems
• Downstream equipment

A structured review helps ensure that safety implications are considered before the change is implemented.

Common Mistakes During a HAZOP

Incomplete Process Information

Using outdated P&IDs or incorrect process information can reduce the quality of the study.

Poor Team Participation

HAZOP works best when team members actively contribute their technical knowledge.

Focusing Only on Obvious Hazards

The team should consider both common and less obvious deviations.

Weak Action Recommendations

Actions should be clear, practical, and assigned to responsible persons.

Ignoring Human Factors

Operator errors, maintenance activities, procedures, and communication issues can contribute to process deviations and should be considered.

How to Make a HAZOP More Effective

Use an Experienced Facilitator

A skilled facilitator keeps the discussion structured and ensures that relevant deviations are properly reviewed.

Use Updated Documents

The study should use the latest approved process and engineering documents.

Include Different Disciplines

A multidisciplinary team can provide a broader understanding of process risks.

Record Findings Clearly

Each deviation should be documented with its causes, consequences, safeguards, and recommendations.

Follow Up on Actions

HAZOP is not complete simply because the workshop is finished. Recommended actions should be tracked until they are properly addressed.

Role of The Safety Master in HAZOP and Process Safety

The Safety Master supports organizations with process safety and risk management services designed to identify hazards and strengthen safety systems.

Professional HAZOP support can help organizations:

• Identify process deviations
• Evaluate potential consequences
• Review existing safeguards
• Identify safety gaps
• Recommend risk reduction measures
• Support process safety studies
• Improve operational safety
• Strengthen overall risk management

A systematic HAZOP Study can help organizations move from reactive incident management toward proactive hazard prevention.

Conclusion

Major industrial incidents often develop through a combination of smaller failures, process deviations, and inadequate safeguards. Identifying these conditions before they become serious is an important part of process safety.

A HAZOP Study provides a structured way to examine process deviations, identify their causes and consequences, review existing safeguards, and recommend improvements.

When conducted by a competent multidisciplinary team and followed by proper action tracking, HAZOP can become a valuable tool for preventing fires, explosions, toxic releases, equipment failures, and other major incidents. The Safety Master can support organizations in strengthening their process safety and hazard identification practices.

Frequently Asked Questions (FAQs)

Q-What is a HAZOP Study?

A HAZOP Study is a systematic and team-based process safety technique used to identify hazards and operability problems by examining deviations from the intended design.

Q-What does HAZOP stand for?

HAZOP stands for Hazard and Operability Study.

Q-What are the main elements of HAZOP?

The main elements include design intent, guide words, deviations, causes, consequences, safeguards, and recommendations.

Q-What are common HAZOP guide words?

Common guide words include No, More, Less, Reverse, As Well As, Part Of, and Other Than.

Q-Why is HAZOP important for process industries?

HAZOP helps identify hazardous process deviations before they can develop into serious incidents. It can also help improve safeguards and operating procedures.

Q-Who should participate in a HAZOP?

A HAZOP team commonly includes a facilitator, process engineer, operations representative, instrumentation engineer, mechanical engineer, safety professional, and other relevant specialists.

Q-Can HAZOP be used for existing plants?

Yes. HAZOP can be used for existing facilities, particularly when significant process changes or modifications are planned or when a safety review is required.

Q-Is HAZOP part of risk assessment?

HAZOP is a hazard identification and risk analysis technique. Its findings can be used as an important input to broader process safety and risk assessment activities.

Q-How does HAZOP help prevent major incidents?

It identifies deviations, their possible causes and consequences, and evaluates whether existing safeguards are adequate. Additional risk controls can then be recommended where necessary.