What is HAZOP?

HAZOP means Hazard & operability. Hazop is a study that identifies hazard and operability problems by investigating how the plant might deviate from the design. It can also be conducted to improve safety for new or existing projects.

Hazop is defined as the application of a formal systematic critical examination to the process and engineering intentions of the new facilities to assess the hazard potential of mal-operation or malfunction of individual items of equipment and the consequential effects on the facility as a whole.

Hazop is performed by a multidisciplinary expert group and always includes workers familiar with the installation.

Hazop can be conducted to check the designs or operating procedures for a new project or for the existing project. Hazop is complementary to PHA (Preliminary hazard analysis).

Hazop study is carried out to determine deviations from normal operation and operational malfunctions which could lead to uncontrolled events. Each part of the design is analyzed with questions formulated around a number of guide words.

For Hazard & operability study a  team of Mechanical Engineer, Chemical Engineer, R & D Chemist, Production Manager, Project Manager, Instrument/ Electrical Engineers, Civil Engineer, etc. The team should not be too large. The team leader is an experienced specialist from works management or by a specially trained consultant.

The basic concept of the HAZOP study is to take a full description of the process and to question every part of it to discover what deviation from design intention can occur and what the cause & consequence can be. The important features of the study are

1. Design intent
2. Deviation from intent
3. Cause of deviation
4. Consequence of
   • Hazard
   • Operating difficulties

Hazop procedure

• Define objective and scope
• Select the team
• Prepare for the study
• Carry out the examination
• Record the result.

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 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 the breadth of knowledge.
• Members to have knowledge of the process, equip.

Step 3- Prepare for the study

Three steps:

• Obtain necessary data:
  • Drawings (line diagrams, flow sheets, layouts).
  • Operating instructions, logic dia, instr.controls.
  • Plant manuals, equipment manuals, history cards.

• 2 Convert the data
  • 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 guidewords at specific study nodes.
• 3 Arrange for meetings.
  • Estimate the team hours (Roughly a vessel with two inlets & two exits, a vent should take 1.5 hours or three hours for each major piece of equip.
  • Each session should not last for more than 3 hours at a stretch.

Step 4- Carry out the team review

• Study nodes: Location at which process parameter is investigated.
• Intention: Defines how the 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 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 deviations 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.

Hazop guide words:

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 do we need to apply hazop?

Limited resources result in a method of selection. Factors considered;

•  Abnormal occurrences, accidents in the past
•  Some study has indicated “High Potential Risk”.
• Extensive modifications 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,
  • Technical contribution.
  • Supporting & structuring role.
• Should not be too large, ideally 3 to 5 members.

1.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 resource to further expertise.

2.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.

Stages at which HAZOP can be carried out

1. At an early stage of development to decide the site and identify major hazards.
2. At the design freeze stage i.e. when the design is completed and construction is to be started.
3. At the pre-start-up stage i.e. when construction is completed and the operation is to be started.
4. Studies on existing plants.
5. Studies prior to plant modification.
6. Studies prior to taking a plant, out of service.
7. Studies on research facilities.

What to do after finding the hazard?

1. Change in the process (material, recipe, etc.).
2. Change in process conditions (pressure, temperature, flow, etc.).
3. Alteration to the physical design including safety guarding.
4. Change of operating methods.

Difference between Hazop and Hazid

Hazop stands for Hazard & operability whereas hazid stands for hazard identification. Both hazop and hazid are risk analysis tools. Hazid basically used for new projects.

Difference between Hazop and Hazan

Hazan means hazard analysis. In simple terms hazard analysis means the classification of hazards like chemical hazards, mechanical hazards, electrical hazards, fall hazards, etc. HAZAN exercise has to be undertaken by a professional team with expertise in failure mode and effect analysis, fault tree analysis, simulation and modeling, event tree, and consequence analyses.

Related topics:

• What is hazard?
• What is Hazard identification?