HAZARD & OPERABILITY STUDY (HAZOP)

WHAT IS HAZOP?

It is a study that identifies hazard and operability problems by investigating how the plant might deviate from the design.

Definition of HAZOP:-

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 organization.
• Law abiding company.
• Care for the community in and around the unit.

WHERE did WE need TO APPLY HAZOP?

Limited resources result in the 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 the design is firm, before construction & startup.
• 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,

1. a) Technical contribution
2. b) Supporting & structuring role

Should not be too large, ideally 3 to 5 members.

WHO SHOULD CARRY OUT HAZOP?

(a)Technical team

• Chemical,Mechanical,Instrument,Electrical.
• Detailed knowledge of process, plant, equipment.
• The technique of guide words generate questions,    that need to be answered without recourse to further expertise.

1. (b) Supporting team,

• Someone 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 the 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, the scope should be explained.
• Focus on underlying purpose or reasons.
• Examples of reasons,

• Check the safety of a design.
• Check operating/safety procedures.
• Improve the safety of the existing facility.
• Verify that instrumentation is adequate.

• Define specific consequence to be considered e.g.
• Loss of equipment/production.
• Liability.
• Public safety/Environmental impact.
• If the last one considered, the 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 the breadth of knowledge.
• Members to have knowledge of the process, equip.

Step 3- Prepare for the study

Three steps:

–  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 the 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 parameter is investigated.

Intention: Defines how the plant is expected to operate in the 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, the consequence is recorded.
• Two extreme situations,

-A suggested action found for each hazard before

-No search for action until all hazards detected

• If the solution is straightforward, the decision is easy
• The study may expose gaps in information or knowledge of technical team members.
• Thus it may be necessary to call for a 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 is 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’

Also, read this:

Safety Audit Report

Emergency Response Plan

Scaffolding