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’