WHAT IS HAZOP?
It is a study that identifies hazard and operability problems by investigating how the plant might deviate from the design.
The application of a formal systematic critical examination to the process and engineering intentions of the new facilities to asses the hazard potential of mal-operation or malfunction of individual items of equipment and the consequential effects on the facility as a whole.
WHY WE NEED HAZOP?
- Chemical Industry handling hazardous substances.
- Manufacturing unit with complex reaction(s).
- Deviations may have serious effects.
- Responsible corporate organisation.
- Law abiding company.
- Care for community in and around the unit.
WHERE WE NEED TO APPLY HAZOP?
Limited resources results in method of selection Factors considered;
- Abnormal occurrences, accidents in the past
- Some study has indicated “High Potential Risk”
- Extensive modification have been done
- Statutory requirement
WHEN HAZOP SHOULD BE DONE?
- Ideally to be done when design is firm, before construction & start up.
- Technically can be extended to existing plants to improve operating methods.
WHO SHOULD CARRY OUT HAZOP?
- Normally to be done by multi-disciplinary teams.
Two types of teams,
- a) Technical contribution
- b) Supporting & structuring role
- Should not be too large, ideally 3 to 5 members.
WHO SHOULD CARRY OUT HAZOP?
– Detailed knowledge of process, plant, equipment.
– Technique of guide words generate questions, that need to be answered without resource to further expertise.
- (b) Supporting team,
– Some one to control discussion, called ‘Study leader’.
– Guides systematic questioning.
– Should not be closely associated with the subject, danger of developing blind spots.
HOW TO CARRY OUT HAZOP?
Main steps are,
- Define the purpose, objectives, scope of study.
- Select the team.
- Prepare for the study.
- Carry out the team review.
- Record the results.
Step 1- Define the purpose, objectives, scope:-
- The purpose, objective, scope should be explaned.
- Focus on underlying purpose or reasons.
- Examples of reasons,
– Check the safety of a design.
– Check operating/safety procedures.
– Improve safety of existing facility.
– Verify that instrumentation is adequate.
- Define specific consequence to be considered e.g.
– Loss of equipment/production.
– Public safety/Environmental impact.
- If last one considered, study should focus on
deviations which result in off site hazards.
Step 2- Select the team
- Ideally five persons, one each from one discipline.
- Too large – group approach fails.
- Too small – may lack breadth of knowledge.
- Members to have knowledge of process, equip.
Step 3- Prepare for the study
– Drawings (line diagrams, flow sheets, layouts).
– Operating instructions,logic dia, instr.controls.
– Plant manuals ,equip manuals, history cards.
– Divide the process into sections with activities.
– Start at beginning & progressively downstream.
– Establish study nodes(points where temp/press
have identified design intent).
-Apply guide words at specific study nodes.
-Estimate the team hours (Roughly a vessel with
two inlets & two exits,a vent should take 1.5 hrs
or three hrs for each major piece of equip.
-Each session should not last for more than 3 hrs at a stretch.
Step 4- Cont… Important Terminologies
Study nodes :Location at which process paramete is investigated.
Intention :Defines how plant is expected to operate in absence of deviations.
Guide word :Simple word to qualify intention to guide,stimulate brainstorming
Deviation :Departure from intention discovered by systematic applying guidewords
Cause :Reason why deviation might occur
Consequence :Result of deviation should it occur
Step 4- Cont… GUIDE WORD APPLICATION
Each guide word is applied to the process variable
Guide words Parameter Deviation
No & Flow No flow
More & Pressure High Pressure
As Well As & One phase Two phase
Other Than & Operation Maintenance
Step 4- Continued….
- Deviations with cause, consequence are recorded.
- Two extreme situations,
-A suggested action found for each hazard before
-No search for action until all hazards detected
- If solution is straightforward, decision is easy
- The study may expose gaps of information or knowledge of technical team members.
- Thus it may be necessary to call for specialist.
- Once the section has been examined mark copies.
Step 5- Record results
- Some of the causes may be unrealistic, so derived Consequence will be rejected as not meaningful
- Some of the causes may be trivial hence considered no further.
- Some deviation with both causes that are conceivable & consequences that are potentially hazardous are noted for action.
- The team will make recommendations.
- Some of them require significant changes.
- Clarity needed for responsibility in actions.
- Follow up & ‘Progress chasing’ procedure needed’