A HAZOP Terms of Reference (ToR) is a formal agreement between the client or project sponsor and the HAZOP leader that establishes how the HAZOP study will be conducted. A well-defined Terms of Reference aligns expectations from the outset, acts as a clear contractual and protection tool for both the client and the HAZOP leader, and preserves the credibility of the study.
It ensures the HAZOP is conducted in line with recognized good practice and standards such as IEC 61882, while also creating a defensible record that can withstand audits and regulatory scrutiny. In many failed or low-quality HAZOPs, the root cause is not a lack of technical competence, but poorly defined Terms of Reference that allow confusion, scope creep, and misaligned expectations to undermine the study.
HAZOP studies involve multidisciplinary experts, tight schedules, and high stakeholder expectations, which makes a clear Terms of Reference (ToR) critical. Without an agreed ToR, clients may expect unrealistically fast “quick HAZOPs,” the study scope can expand uncontrollably during workshops, design maturity issues may surface halfway through the review, and expectations for reporting and deliverables can differ between stakeholders. A well-defined ToR prevents these problems by aligning expectations upfront and keeping the study focused, efficient, and credible.
Purpose of the HAZOP ToR
The HAZOP ToR serves three core purposes:
- Ensures all participants understand the study goals and process in advance
- Sets clear ground rules for an effective and disciplined workshop
- Acts as a formal agreement between stakeholders on how the HAZOP will be executed
“A HAZOP ToR is not a formality—it is a risk control tool”
Key Components of a HAZOP Terms of Reference (TOR)
- Title and Signatures
- Project Background: a broad description of the facility to be studied.
- Scope and Boundaries: to clearly define the process boundaries, included and excluded systems, interfaces, and applicable P&IDs.
- Objectives of the HAZOP Study: to identify hazards and operability issues, recommend improvements, and thereby reduce safety, environmental, asset, and business risks.
- Methodology: defining the HAZOP type and operating modes, systematically analysing agreed nodes using selected deviations, fully recording causes, consequences, risks, safeguards, and developing clear, well-documented recommendations using agreed recording and review protocols.
- Process safety information
- Hazop Team Composition and Roles
- Schedule and Logistics
- Expected Deliverables and Distribution
1. Title and Signatures
It is good practice to formalize the agreed Terms of Reference by obtaining signatures from the study sponsor or client and prominently displaying them on the front cover of the document, rather than burying them at the end. Signed ToR serve as a clear signal of intent, authority, and commitment, preventing last-minute challenges that can delay or even derail a HAZOP before it begins.
A signed ToR protects the study, the team, and the facilitator, and reinforces the need for disciplined conduct throughout the review highlighting why HAZOP leaders must be proactive, assertive, and prepared to manage both technical issues and human behavior.
2. Project Background
This typically includes a brief description of the facility or process being reviewed, placed within the wider context of overall operations or the project to which it belongs, such as a specific unit within a refinery expansion or a facility within a larger production system. Key factors such as the age, scale, and operating history of the facility—particularly for re-HAZOP studies—as well as the current project status for new builds or modifications, should be outlined. This background allows the HAZOP leader and team to focus appropriately on relevant risks, such as equipment condition and degradation in ageing facilities.
3. Scope and Boundaries
The scope should begin with a clear description of the process or facility to be reviewed, followed by explicit definition of the study boundaries, including battery limits, asset ownership limits, and interfaces with upstream or downstream units. It is essential to clearly list not only the systems and units included in the HAZOP, but also those explicitly excluded, such as shared utilities, storage systems, or vendor packages, to avoid confusion and scope creep.
Once the included and excluded systems are defined, the physical and process boundaries must be clearly identified on the P&IDs, as these points will form the start and end of HAZOP nodes. Wherever possible, boundaries should be based on defined isolation points or battery limits.
The scope definition should conclude with a complete list of all applicable P&IDs, including revision numbers, typically included as an appendix to the ToR. This ensures any newly identified drawings or later revisions are formally treated as scope changes, with their impact on time and effort clearly agreed with the client.
4. Objectives of the HAZOP Study
Clearly defining these objectives ensures the HAZOP delivers meaningful risk reduction and operational improvement rather than a narrow or incomplete assessment. The core objective is to conduct a systematic, line-by-line examination of the process to identify deviations from design intent and to recommend improvements that reduce risk and enhance safe and reliable operation.
The objectives should also explicitly recognize that the HAZOP will address hazards with potential safety, environmental, asset integrity, operability, and business impacts, ensuring that risk is considered in a broad and balanced manner.
Operability is a fundamental element of the study, as poor operability often drives unsafe practices, procedural deviations, workarounds, and unauthorized modifications that can ultimately lead to major process safety incidents.
5. HAZOP Methodology
HAZOP methodology includes defining the type of HAZOP to be conducted—continuous, batch, procedural, or a combination—and explicitly identifying all operating modes to be reviewed, such as normal operation, start-up, shutdown, single-train operation, regeneration, or cleaning activities. Where start-up or shutdown are critical, these may be studied as separate stepwise procedures rather than as simple deviations within continuous nodes, as this provides a more robust assessment but requires additional time. The basis for node identification and the selection of guide words and deviations should also be defined to ensure consistency, avoid unnecessary expansion of nodes, and maintain study efficiency.
The methodology section should also explain how causes, consequences, safeguards, and risks will be developed, assessed, and recorded, including the use of any risk ranking or matrix. The ToR should confirm that full recording will be used, ensuring all meaningful discussions, causes, and consequences are captured, rather than recording by exception. It should describe how recommendations will be written, classified, and documented, the tools or software to be used, and the protocol for managing and controlling master P&IDs. Finally, it should outline how requests for additional information will be handled during the study, such as through a managed action or “parking lot” system, to maintain workshop momentum while ensuring unresolved items are properly addressed.
6. Process Safety Information Required and Risk Matrix
A HAZOP requires detailed and reliable Process Safety Information (PSI) to allow the team to properly identify, analyze, and resolve hazardous scenarios. PSI goes well beyond P&IDs and includes all technical data needed to understand process behavior, equipment limits, safeguards, and operator responses. Without adequate PSI, the team cannot credibly assess causes, consequences, or the effectiveness of protection layers, leading to excessive recommendations simply to obtain basic information.
Agreed Risk Matrix is also much necessary for the risk assessment during the hazop study. For this reason, the required PSI must be clearly listed in the Terms of Reference, and the HAZOP should not proceed until the essential documentation is available and reviewed for adequacy.
- Process description and chemistry
- Approved PIDs with latest revision for HAZOP
- Process Flow Diagrams and process operating and design condition
- Material and energy balance
- Facility plot plan/unit layout drawings
- Equipment design conditions
- Control, alarm and trip information
- Pressure relief, flare, vent and de-pressuring information
- Operating procedures and General Operating Manual
- Previous HAZID, HAZOP or LOPA reports
- Changes to design since the last HAZOP
- Previous incident reports
- Material Safety Data Sheets of Chemicals involved
7. HAZOP Team Composition and Roles
The ToR should specify mandatory core roles whose presence is required for the HAZOP to proceed, identify named individuals and their deputies for these roles wherever possible, and define additional non-core roles on a limited or “as-required” basis to control team size. Typically, an effective HAZOP team is kept to around six to eight members to support effective facilitation, while allowing access to specialist expertise, such as vendors or subject-matter experts, only when necessary. By clearly defining roles, responsibilities, and attendance expectations, the ToR helps the HAZOP leader manage team dynamics, ensure continuity, and maintain a focused, productive study. HAZOP core team roles.
- Independent facilitator
- Recorder or scribe
- Process design Engineer
- Plant Operations Engineer
- Mechanical Maintenance Engineer
- Project engineer if necessary
- Instrument Engineer
- Vendor representative if necessary
- Process safety Engineer
8. Schedule and Logistics
The Schedule and Logistics section of the Terms of Reference should clearly define when and where the HAZOP sessions will be conducted, their expected duration, and the overall execution plan, so that time and resource commitments are fully understood by all parties. Unrealistic schedules are a common cause of poor hazard identification. This section defines:
- Workshop dates and duration
- Daily session limits to manage fatigue
- Location or online arrangements
- Logistics such as displays, recording tools, and documentation access
9. Expected, Deliverables, and Follow-Up
The Terms of Reference should clearly define the reporting structure, deliverables, and follow-up arrangements to ensure expectations are aligned from the outset. This includes specifying the format and content of the final HAZOP report, recommendations section, detailing of report main body as well as identifying the primary recipient and intended distribution list. U
- How findings will be recorded
- Recommendation writing standards (clear, standalone actions)
- Final report structure
- Review and approval process
- Action tracking and close-out expectations
The final HAZOP report is the permanent record of the study. Its quality reflects the quality of the ToR.
References:
- The HAZOP Leader’s Handbook by PHIL EAMES
- www.ors-consulting.com
-
HAZOP Guidelines /ehs Tools
Certified Functional Safety Professional (FSP, TÜV SÜD), Certified HAZOP & PHA Leader, LOPA Practitioner, and Specialist in SIL Verification & Functional Safety Lifecycle, with 18 years of professional experience in Plant Operations and Process Safety across Petroleum Refining and Fertilizer Complexes.
