A Control Systems Hazard and Operability Study (CHAZOP) is a structured risk assessment that identifies hazards, operability issues, and potential failures within industrial control and automation systems. It evaluates Distributed Control Systems (DCS), Programmable Logic Controllers (PLC), Safety Instrumented Systems (SIS), Emergency Shutdown Systems (ESD), Fire & Gas Systems, and SCADA to ensure they operate safely, reliably, and as intended.
At iFluids Engineering, we conduct comprehensive CHAZOP studies to identify control system vulnerabilities, verify automation reliability, assess existing safeguards, and recommend practical engineering improvements that enhance process safety, minimize operational risks, and improve plant performance
What is a CHAZOP Study?
A Control Systems Hazard and Operability Study (CHAZOP) is a systematic engineering review that evaluates the safety, reliability, and performance of industrial control and automation systems. Unlike a conventional HAZOP, which focuses on process equipment and operational deviations, a CHAZOP specifically examines the systems responsible for monitoring, controlling, and protecting industrial processes.
During the study, a multidisciplinary team reviews control logic, instrumentation, communication networks, alarms, shutdown functions, and operator interfaces to identify potential deviations, evaluate their causes and consequences, assess existing safeguards, and recommend practical engineering improvements.
By identifying automation-related risks early, a CHAZOP study helps improve control system reliability, reduce unplanned downtime, strengthen process safety, and support safe, efficient plant operations.
Why is a CHAZOP Study Important?
Industrial control systems are essential for maintaining safe, reliable, and efficient plant operations. Failures in control logic, instrumentation, communication networks, or safety systems can lead to equipment damage, production losses, environmental incidents, or risks to personnel.
A CHAZOP Study helps identify these potential failures before they affect plant operations. By systematically reviewing automation systems and evaluating possible deviations, organizations can strengthen control system reliability, verify existing safeguards, and implement practical improvements that reduce operational risk.
Control system faults may provide incorrect process information, delayed alarms, or inaccurate signals to operators, affecting critical decision-making during abnormal operating conditions. In some situations, failures within the control system may prevent operators from taking timely corrective actions, increasing the likelihood of process upsets or safety incidents.
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PROJECTS DELIVERED ACROSS THE GLOBE
Objectives of a CHAZOP Study
The primary objective of a Control Systems Hazard and Operability Study (CHAZOP) is to identify potential hazards, control system failures, and operability issues that could affect the safe and reliable operation of industrial facilities. The study ensures that automation systems perform their intended functions under both normal and abnormal operating conditions while minimizing risks to personnel, assets, and the environment.
Key Objectives
- Identify hazards and operability issues within industrial control systems.
- Detect single points of failure affecting safety or production.
- Evaluate the reliability of PLC, DCS, SIS, ESD, Fire & Gas, and SCADA systems.
- Verify the effectiveness of alarms, interlocks, and safety shutdown functions.
- Assess existing safeguards and identify protection gaps.
- Recommend engineering improvements to reduce operational risks.
A structured CHAZOP study enables organizations to proactively identify control system vulnerabilities, strengthen safety barriers, and improve the overall reliability and performance of industrial automation systems.
HAZOP vs CHAZOP
Although both HAZOP and CHAZOP use a structured methodology to identify hazards and operability issues, they focus on different aspects of an industrial facility. A HAZOP evaluates process-related hazards, whereas a CHAZOP specifically examines industrial control and automation systems.
| Feature | HAZOP Study | CHAZOP Study |
|---|---|---|
| Primary Focus | Process hazards and operability | Control system hazards and operability |
| Scope | Process equipment and operations | Industrial control and automation systems |
| Systems Evaluated | Piping, vessels, valves, pumps and process equipment | PLC, DCS, SIS, ESD, SCADA, Fire & Gas Systems |
| Objective | Identify process deviations and hazards | Identify automation and control system failures |
| Assessment | Process conditions and equipment | Control logic, communication, instrumentation and safety systems |
| Outcome | Process safety improvements | Control system reliability and safety improvements |
A HAZOP evaluates how the process operates, while a CHAZOP evaluates how the control system manages and protects the process. Together, these studies provide a comprehensive assessment of process safety and automation reliability.
Scope of a CHAZOP Study
- Distributed Control Systems (DCS)
- Programmable Logic Controllers (PLC)
- Safety Instrumented Systems (SIS)
- Emergency Shutdown Systems (ESD)
- Fire & Gas Detection Systems
- SCADA Systems
- Human Machine Interfaces (HMI)
- Instrumentation and Field Devices
- Control Loops and Process Signals
- Alarm Management Systems
- Industrial Communication Networks
- Control Logic and Software Configuration
- Input/Output (I/O) Modules
- UPS and Power Supply Systems
- Operator Workstations
- Network Infrastructure
The study also evaluates communication interfaces, control strategies, system redundancy, alarm management, and automation architecture to identify single points of failure, incorrect control logic, communication issues, instrumentation faults, and other automation-related risks that may affect personnel safety, environmental protection, asset integrity, or production continuity.
CHAZOP Methodology for Identifying Hazards Within Each Study Node
A Control Systems Hazard and Operability Study (CHAZOP) follows a systematic and structured methodology to identify hazards, operability issues, and potential failures within industrial control and automation systems. The study is conducted by a multidisciplinary team comprising process engineers, control and instrumentation engineers, automation specialists, operations personnel, maintenance engineers, and safety professionals.
The control system is divided into logical study nodes, and each node is reviewed using predefined guidewords to identify deviations, evaluate their causes and consequences, assess existing safeguards, and recommend practical engineering improvements.
1. Define the Study Scope
Establish the objectives, study boundaries, and control systems included in the assessment.
2. Divide the System into Study Nodes
Break the control system into logical sections such as PLCs, DCS controllers, SIS, ESD systems, communication networks, or instrument loops.
3. Apply Guidewords
Systematically apply guidewords to identify deviations from the intended design or operation.
4. Identify Possible Causes
Determine credible causes such as hardware failures, software errors, communication failures, incorrect configurations, power interruptions, or human errors.
5. Assess Consequences
Evaluate the potential impact of each deviation on personnel safety, plant operations, equipment, production, and the environment.
6. Review Existing Safeguards
Assess the effectiveness of alarms, shutdown systems, engineering controls, operating procedures, and system redundancies.
7. Recommend Risk Reduction Measures
Where existing safeguards are inadequate, recommend practical engineering improvements to reduce operational risks.
8. Risk Ranking and Documentation
Assign risk rankings based on the likelihood and severity of each identified deviation, and document all findings in the final CHAZOP report.
CHAZOP Guidewords
Guidewords are predefined keywords used during a CHAZOP study to systematically identify deviations from the intended operation of industrial control systems. They help the study team evaluate potential failures, discuss their impact, and recommend suitable engineering improvements.
| Guideword | Meaning |
|---|---|
| No | Complete absence of the intended function or signal |
| More | Higher value or greater magnitude than intended |
| Less | Lower value than expected |
| Reverse | Opposite action or incorrect direction |
| Early | Action occurs earlier than intended |
| Late | Action occurs later than intended |
| Incorrect | Wrong signal, command, or data |
| Delayed | Response occurs later than expected |
| Frozen | Signal remains unchanged despite changing process conditions |
| Corrupted | Invalid or damaged communication or data |
| Intermittent | Function operates inconsistently |
| Failed | Complete hardware, software, or communication failure |
Required Documents for a CHAZOP Study
A successful CHAZOP study requires key engineering documents to evaluate control system architecture, instrumentation, safety functions, and automation logic effectively.
| Required Document | Purpose |
|---|---|
| System Architecture Diagram | Reviews the overall control system configuration |
| P&ID / PFD | Reviews process flow and instrumentation |
| Control & Shutdown Philosophy | Verifies control and shutdown strategies |
| Instrumentation Design Basis | Reviews instrumentation specifications |
| Alarm & Trip Schedule | Assesses alarm and trip settings |
| Functional Design Specifications | Reviews hardware and software logic |
| I/O List & Loop Diagrams | Verifies signals and control loops |
| Network Architecture Diagram | Assesses communication reliability |
| UPS & Power Supply Diagrams | Reviews power redundancy |
| Earthing & Grounding Layout | Verifies grounding arrangements |
| Control Room Layout | Evaluates operator interfaces |
Providing complete documentation before the workshop improves the efficiency, accuracy, and quality of the CHAZOP study.
CHAZOP Deliverables
Upon completion of the study, iFluids Engineering provides a comprehensive CHAZOP report that documents identified hazards, risk assessments, engineering recommendations, and actions to improve the safety and reliability of industrial control systems.
Typical Deliverables
- Executive Summary
- Study Scope & Methodology
- Guideword Analysis Worksheets
- Identified Deviations
- Causes & Consequences
- Existing Safeguards
- Risk Ranking
- Engineering Recommendations
- Action Register
- Final CHAZOP Study Report
CHAZOP findings are documented using structured worksheets and, where applicable, software tools such as PHA-Pro to ensure accurate recording, action tracking, and comprehensive reporting.
Risk Assessment & Risk Matrix
Risk assessment is a fundamental part of every CHAZOP study. Each identified deviation is evaluated by considering its likelihood of occurrence, potential consequences, and the effectiveness of existing safeguards. This structured approach enables organizations to prioritize engineering improvements and reduce risks to an acceptable level.
Risk Assessment Process
Each identified deviation is assessed based on:
- Likelihood of occurrence
- Severity of consequences
- Existing safeguards
- Residual risk
- Recommended mitigation measures
The final risk ranking helps prioritize corrective actions and supports informed engineering decisions.
Safety Risk Tolerability Criteria
| Risk Category | Control Regime |
|---|---|
| Unacceptable | The risk is intolerable. Immediate corrective action is required before operation. |
| ALARP (As Low As Reasonably Practicable) | The risk is tolerable only after implementing practical risk reduction measures. |
| Acceptable | The risk is adequately controlled through existing safeguards and routine monitoring. |
A Sample Guidelines for assessing Hazard Severity is described below
Guidelines for Assessing “Hazard Severity”
The CHAZOP meeting discussions are recorded in a Sample CHAZOP worksheet as shown below
Guideline for Assessing Likelihood of Occurrence
| Category | Likelihood | Typical Frequency |
|---|---|---|
| A | Very Unlikely | Less than 10⁻⁵ per year |
| B | Unlikely | Between 10⁻⁵ and 10⁻⁴ per year |
| C | Possible | Between 10⁻⁴ and 10⁻³ per year |
| D | Likely | Between 10⁻³ and 10⁻² per year |
| E | Frequent | Greater than 10⁻² per year |
During the workshop, each identified deviation is documented in a CHAZOP worksheet together with its guideword, causes, consequences, existing safeguards, risk ranking, recommendations, and assigned responsibility. This structured documentation ensures that all identified risks are tracked, reviewed, and effectively managed throughout the project lifecycle.
Why Choose iFluids Engineering?
iFluids Engineering provides comprehensive CHAZOP studies to help organizations identify control system hazards, improve automation reliability, and strengthen process safety. Our multidisciplinary team delivers practical, risk-based solutions tailored to the unique requirements of each project.
Why Clients Choose Us
- Experienced Process Safety & Automation Engineers
- Expertise in PLC, DCS, SIS, ESD, SCADA & Fire & Gas Systems
- Structured CHAZOP Methodology
- Comprehensive Hazard Identification & Risk Assessment
- Practical Engineering Recommendations
- Compliance with International Engineering Standards
- Detailed Technical Reports
- Timely Project Delivery
- End-to-End Engineering Support
Need a CHAZOP Study for Your Facility?
Whether you’re designing a new facility, upgrading automation systems, or improving process safety, iFluids Engineering delivers structured CHAZOP studies to identify control system hazards, strengthen safety, and improve operational reliability.
Contact our process safety experts today to discuss your CHAZOP study requirements and receive a tailored solution for your facility.
Frequently Asked Questions
A CHAZOP (Control Systems Hazard and Operability Study) is a structured risk assessment that identifies hazards, operability issues, and potential failures in industrial control and automation systems to improve safety and reliability.
The purpose of a CHAZOP study is to identify control system risks, evaluate existing safeguards, and recommend engineering improvements that enhance process safety, reduce operational risks, and improve system reliability.
A HAZOP study focuses on process hazards and operational deviations, while a CHAZOP study evaluates hazards and failures within industrial control and automation systems such as PLC, DCS, SIS, ESD, and SCADA.
A CHAZOP study is typically conducted during detailed engineering, before plant commissioning, after major control system modifications, or when upgrading automation systems.
A CHAZOP study evaluates systems including DCS, PLC, SIS, ESD, Fire & Gas Systems, SCADA, HMI, communication networks, instrumentation, and control logic.