Toolbox: HAZOP Studies

HAZOP is an abbreviation for 'Hazard and Operability' and is a formalised approach to identifying hazards and problems in Process Plants which can prevent efficient operation. HAZOP studies provide a forum for people to use their experience and skills to assess ways in which hazards or operating problems might arise.

A systematic approach, considering each line, mode of operation, and type of hazard in turn, minimizes the chance of overlooking a problem. The technique has been used extensively in the process industries, primarily as a tool in the design phase of a plant or plant upgrade.

Existing plants, in particular those that have been extensively debottlenecked or modified, may have deviated from original design intent and safety concepts. A HAZOP study will assist in reviewing such changes.

Approach

The timing of a HAZOP is critical to maximising the benefit. Inevitably, a HAZOP will result in design changes. Time is required to implement these changes, so the optimum time for a HAZOP is at the start of detail design - with completed Process Flow Diagrams (PFD's).

It thus can provide a valuable tool in project scheduling - to fix a 'Design Freeze' milestone. Process changes after this time must be agreed as essential to the operation, in order to minimise cost impact. If an existing plant is being studied, an essential first step is to bring the PFD's up to date, and confirm current operating practices.

A HAZOP is carried out by a team. This team varies slightly for the above cases, but representatives from the Design, Process, Operating and Maintenance groups are all required. Specialist in instrumentation and control areas, and vendor representatives, will also be of value.

An independent chairman, skilled in the HAZOP technique, is necessary to keep the team following the procedure. Ideally the chairman is not closely involved with the design or operation of the process plant, in order to ensure objectivity. The chairman will prompt discussion where necessary, whilst leaving team members to arrive at solutions. If no immediate solutions are forthcoming, the problem is noted for subsequent action outside the meeting.

Benefits

• Utilisation of combined experience of staff in a constructive way.
• Early interaction between design and 'end user' personnel.
• Confirmation of plant 'fitness for purpose'- non essential equipment and piping is avoided at design stage.
• Establishment of a milestone which permits detail design proceed unhindered.
• Proven benefits in reducing commissioning and start up delays.