HAZOP

1. HAZOP

2. Hazard and Operability Studies – Overview • Originated as a hazard identification technique for process plants – developed by ICI in mid 1960s • also commonly applied in petrochemical, nuclear and food processing industries • Described as a system of imaginative anticipation of hazards • Differs from Functional Failure Analysis in 4 key ways: • always a team activity • concentrates on deviations in flows between components • uses well-defined guide words to steer analysis • considers both plausible causes and possible consequences of deviations

3. HAZOP – technical approach • In the process industries, HAZOP is normally applied once the piping and instrumentation (P&I) diagram has been produced • Scope of study explicitly extends to cover unusual circumstances such as startup, shutdown and plant maintenance • Scope of study does not include making detailed design changes, although recommendations and follow-up questions should be produced • As with FHA, results are recorded in a tabular format • No reason why HAZOP cannot be applied to any system in which flows can be identified – including information flow in software

4. HAZOP procedure

5. Leader planning and preparation act as chairman for meeting sign off documentation ensure follow-up work is completed Recorder participant in study (?) document the analysis Designer(s), process / project engineers understand and explain the plant design answer questions about the plant and process User(s) may be site representative, operator, maintenance crew supply information about the context in which the system will be used, e.g. site facilities ask questions, and help decide which issues affect safety Expert(s) key function is to explore ask questions suggest deviations / causes / effects need good knowledge of process chemistry, or experience of similar plant HAZOP Team Members 1 • Team may recruit extra members (technical specialists) if required

6. HAZOP Team Members 2 • Team may recruit additional members when required • Typically to answer specific questions, e.g. • control engineer • mechanical engineer • occupational health / hygienist • environmental specialists • Different teams often appropriate for different stages of the lifecycle, but continuity (e.g. same leader) usually recommended

7. HAZOP – guide words Physical properties  Temperature  Flow rate  Pressure  Reaction rate  Viscosity

8. HAZOP – guide words 2 Guide word “Other Than” has many interpretations • this word particularly is often defined specifically for particular study • examples include • plant operation phases • startup, shutdown, maintenance, sampling and inspection • instrumentation • control philosophy, location of instruments, alarms and trips • failure of plant services • cooling water, fuels, power supplies • other external factors • weather • spare / non-installed / portable equipment • safety • fire and leak detection, emergency planning

9. HAZOP example – a bit of P&I

10. HAZOP example – output

11. Hazard Study Phasing 1

12. Hazard Study Phasing 2 • 1 - Concept Study • PHI, checklist, materials and reagents study, first outline HAZOP • 2 - Process Flow Study • HAZOP • 3 - Detailed Design (P&I) Study • HAZOP • 4 - Detailed Design (Physical) Study • HAZOP update, Sneak, Fault Trees, FMEA • 5 - Audit of installed plant against design • Checklist, review of HAZOP actions, inspections • 6 - Audit / review of process • Final review of evidence, completeness of HAZOP actions

13. HAZOP – Pros and Cons Advantages • very methodical. Use of guide words can give confidence in completeness of analysis. • has both inductive and deductive phases • team conclusions may carry more weight than those reached by individual analysts Disadvantages • can produce lots of output. Structure is only obtained by reference back to P&I diagrams • team approach is expensive – must be shown to be cost-effective

14. ICI Experience • More operability problems than hazards are usually found • though difference is smaller with existing plants • Number of post-commissioning modifications to plant is reduced • Time to achieve intended production rates is reduced • For major plant, cost is typically about 1% of design cost • 0.1 - 0.2% of total plant cost