Before the first guide word is applied, many factors can influence the effectiveness of the study. These include the maturity of the design, clarity of scope, quality of process information, team competence, node selection and the time allocated.
A skilled HAZOP Leader can challenge assumptions and steer the discussion. However, even the best leader can not compensate for missing P&IDs, unclear design intent or maybe an incomplete team.
Is HAZOP the right technique?
HAZOP is a systematic and multidisciplinary approach to identify hazards and operability problems caused by deviations from the design intent. It works best when the design is sufficiently developed to allow meaningful examination, but changes can still be made without too much cost.
At an early stage of a project, a HAZID, Preliminary Hazard Analysis or What-If review may be more appropriate. A detailed HAZOP on an immature design can lead to assumptions, duplicated discussions and findings that date very quickly.
So a responsible leader would say, “Is the design really ready for HAZOP, or are we just trying to meet a project milestone?”
Establish a clear Terms of Reference (ToR)
The study objectives and boundaries should be agreed in advance of the workshop. The Terms of Reference shall include:
- The aim and scope of the study.
- Physical and procedural boundaries.
- Consideration of operating modes.
- Interfaces, exclusions, and assumptions.
- The risk ranking methodology.
- Required documents, deliverables and reporting arrangements.
- Roles and responsibilities of the team.
If this agreement is not reached, one participant may expect a design review and another a detailed risk assessment.
Confirm design and information readiness
As I always said, “Before talking about the safety of the process, you should understand the process very clearly”.
Drawings shall be current and controlled. The design intent for each node should clearly state the expected flow, composition, pressure, temperature, operating limits, control philosophy and relevant safeguards.
The information pack may contain:
- P&IDs & PFDs.
- Process descriptions and design data.
- Material and energy balance.
- Equipment and instrument data sheets.
- Cause-and-effect diagrams.
- Information on alarm, trip and relief systems.
- Operating, start-up and shut-down procedures.
- Designs and hazardous material information.
- Existing plant data, incidents and MOC records from previous studies.
Select the right team
HAZOP relies on structured creativity. Its strength is the combination of different perspectives. The study team may consist of process engineering, operations, maintenance, instrumentation, mechanical engineering, process safety and relevant vendors or specialists.
The choice should be made on the basis of competence and practical knowledge, not simply on job titles. The experienced operator may recognise a situation not shown on the drawing. A maintenance representative may discover isolation problems. An instrument engineer may discover that two apparent safeguards have the same sensor or final element.
The scribe, i.e. study recorder, also has a critical role. A discussion in technical terms which is vague or incomplete may be discounted as strong.
Prepare the nodes in advance
Large nodes can mask important differences in conditions and safeguards. Too small nodes create repetition and obscure interactions between systems.
Before the workshop, the following should be considered:
- Mark the proposed nodes on the P&IDs.
- Set their boundaries.
- Write node descriptions and design intents.
- Identify the relevant operating modes and interfaces.
Batch and procedural studies may need to follow process steps, sequence, timing and operator actions, rather than the traditional equipment-based nodes.
Allow enough time
HAZOP study is a demanding process. The team is required to identify plausible causes, trace consequences, evaluate safeguards, assess risk and decide whether or not action is required.
The study schedule must take into account:
- Number and complexity of nodes.
- Complexity of the process and control systems.
- Design maturity and quality of information.
- Team experience.
- Operating modes and procedural matters.
- Recording level and risk ranking needed.
Counting P&IDs has not proven to be the best option to scope HAZOP Studies well. Two drawings can represent completely different levels of complexity.
Prepare the workshop environment
The team should be able to see the P&ID and worksheet clearly, communicate easily and participate without avoidable disruption. The leader should be able to confirm that the room, software, displays, remote connections, file backups and breaks are properly arranged.
The software may be pre-populated with node details, drawing references and worksheet headings, but causes, consequences and recommendations should never be predetermined.
Final readiness check
Before starting, confirm that:
- HAZOP is the appropriate method.
- Scope and objectives are agreed.
- The design is sufficiently mature.
- Current process safety information is available.
- Nodes and design intents are prepared.
- The necessary disciplines are represented.
- Adequate time has been allocated.
- Recording and logistical arrangements are ready and suitable.
When preparation is strong, the team can concentrate on the questions that matter:
What could deviate? Why could it happen? What would the consequences be? What preventive or mitigating measures are available? And what further action is required?
“A successful HAZOP Study does not begin with the first guide word, but with proper preparation”