HSE Risk Management Services Pvt. Ltd.SCO-30, Second floor near V.R Mall, TDI Business Centre Sector 118, TDI City, Mohali, Punjab-140501Mail id:yashpal@hse-rms.comContact No.:9012200076, 9012100076, 8288088030Website: www.hse-rms.comHSE Risk Management Services Pvt. Ltd.SCO-30, Second floor near V.R Mall, TDI Business Centre Sector 118, TDI City, Mohali, Punjab-140501Mail id:yashpal@hse-rms.comContact No.:9012200076, 9012100076, 8288088030Website: www.hse-rms.comHSE Risk Management Services Pvt. Ltd.SCO-30, Second floor near V.R Mall, TDI Business Centre Sector 118, TDI City, Mohali, Punjab-140501Mail id:yashpal@hse-rms.comContact No.:9012200076, 9012100076, 8288088030Website: www.hse-rms.comHSE Risk Management Services Pvt. Ltd.SCO-30, Second floor near V.R Mall, TDI Business Centre Sector 118, TDI City, Mohali, Punjab-140501Mail id:yashpal@hse-rms.comContact No.:9012200076, 9012100076, 8288088030Website: www.hse-rms.com

Client: M/s ___ Title: METHODOLOGY FOR CONTROL SYSTEM HAZARD & OPERABILITY STUDY (C-HAZOP)
20/01/2026	A	Draft	SS	YSG	YSG
Date	Rev	Remarks / Revision Summary	Prepared	Checked	Approved
			HSE RMSPL
REVISION RECORDS

DISCLAIMER

HSE Risk Management Services Private Limited accepts no liability or responsibility whatsoever for it in respect of any use of or reliance upon this Methodology by any third party.

Copying this Methodology without the permission of HSE Risk Management Services Private Limited is not permitted.

OBJECTIVE

The objective of the Control System Hazard and Operability Study (C-HAZOP) is to systematically identify, assess, and document hazards and operability issues arising from failures or malfunctions of control systems, including hardware, software, communication networks, power supplies, and human–machine interfaces.

The study aims to ensure that control system failures do not lead to unacceptable risks to personnel, environment, assets, or plant operability, and that adequate safeguards and recommendations are defined where necessary .

SCOPE

The scope of the C-HAZOP includes:

• Basic Process Control Systems (BPCS / DCS)
• PLC-based control systems and package PLCs
• Control system hardware (processors, I/O cards, cabinets, power supplies)
• Control and safety-related software and configuration
• Communication networks, data highways, gateways, and interfaces
• Operator interfaces (HMI, workstations)
• Power supply arrangements including UPS
• Interfaces between control systems and field devices up to I/O termination points

C-HAZOP is applied primarily to projects involving new control systems, major upgrades, significant modifications, or new system interfaces, and is generally performed after HAZOP and before SIL determination .

Reference/ International Standards & Guidelines for C-HAZOP

• Introduction to CHAZOP: Assessing the Risks of Control System Failure, xSeriCon Limited, Rev. 0.1
• IEC 61882:2016 – HAZOP Study (Core Standard)
• IEC 61511 / IEC 61508 – Functional Safety
• ISO 17776 – Offshore & Process Hazard Identification
• CCPS (AIChE) Guidelines
• ISO 12100 – Safety of Machinery (for PLC-controlled systems)

ORDER OF PRECENDENCE

• As per Client Guidelines
• National & International reference books.

Proposed Methodology

1. Introduction
2. C-HAZOP follows a structured, workshop-based approach similar to conventional HAZOP, but focused on control system functionality rather than process nodes.
   1. Methodology
3. Definition of Functional AreasThe control system is divided into functional areas (e.g., DCS, networks, power supply, remote I/O, <br>Human–Machine Interface (HMI)), analogous to nodes in a HAZOP.
4. Form the C-HAZOP Team

Minimum Team Composition

• C-HAZOP Leader (trained)
• Process Engineer
• Control / Automation Engineer
• Operations representative
• Instrumentation Engineer
• Safety / HSE Engineer
• Maintenance (optional but useful)
• Identification of Safety-Related SignalsAll I/O signals are reviewed to determine whether they perform safety-related or protective functions.<br>
• Application of Guidewords / Failure ClassesC-HAZOP guidewords such as <br>LOSS, RANGE, MIXTURE, VERSION, SECURITY, along with time-related guidewords (early, late, before, after), are applied to each functional area and communication channel.
• Deviation and Failure AnalysisCredible control system failures (hardware, software, communications, power, human factors, security) are identified using a structured “What-If” approach.<br>
• Consequence IdentificationReasonable worst-case consequences are identified, with reference to the HAZOP study to ensure consistency of impact assessment.<br>
• Safeguard IdentificationExisting safeguards within the control system and the process are identified, ensuring that assumed independence from failures is validated.<br>
• Risk Evaluation and RecommendationsWhere risks are judged potentially unacceptable or uncertain, recommendations for design changes, additional safeguards, or further studies (e.g. LOPA) are generated.<br>

C-HAZOP may be performed as a two-stage process:

• Preliminary C-HAZOP – integrated with conventional HAZOP for early design decisions
• Detailed C-HAZOP – applied to high-risk, complex, or unusual systems where detailed design is available.
  1. Documents Requirement

Essential documents include:

1. Control Philosophy
2. P&IDs (latest approved)
3. Cause & Effect diagrams
4. Logic diagrams / narratives
5. Interlock lists
6. Alarm list / alarm philosophy
7. Shutdown & start-up procedures
8. Network architecture (for advanced C-HAZOP)

1. Project Deliverables

Table 1:C-HAZOP Study

Sr. No.	Document Deliverable
	Executive Summary
	Document Review
	Submission of terms of reference
	C-HAZOP Methodology
	C-HAZOP Worksheet
	Marked-up control system architecture and network diagrams
	List of identified control system hazards and operability issues
	Identified critical single points of failure
	Register of safeguards and assumptions
	Action list with recommendations, responsibilities, and priorities
	Inputs to LOPA and SIL determination studies, where applicable
	Participant Attendance sheet

1. Fundamental Assumption

The C-HAZOP Methodology is based on the following assumption:

• A completed and approved HAZOP study is available
• Control system design information is sufficiently mature for the study stage
• Control system failures are considered as initiating causes, not consequences
• Only single, credible root-cause failures are considered unless justified otherwise
• Operator response is considered only where clearly defined and supported by alarms and procedures
  1. Exclusions
     • Detailed software code reviews
     • Quantitative reliability or availability calculations
     • Mechanical integrity assessment of field equipment
     • Cybersecurity penetration testing (only conceptual security risks are considered)
     • Failure scenarios with no credible impact on process safety or operability

1. Software to be used
2. PHA Pro version 8.19 software.
3. Standard spreadsheet-based HAZOP/C-HAZOP worksheets (e.g. Excel) provided by the client