HAZOP (Hazard and Operability) Study: A brief introduction

HAZOP (Hazard and Operability) Study: A brief introduction

Full form of HAZOP is Hazard and Operability Study. This is a comprehensive multi-disciplinary team exercise to critically review (Study) the piping design (Layout/ Routing/Placement of branches/inline instrumentation items/ equipments etc.) with respect to Hazardous and Operational considerations and requirements.

A Hazard and Operability (HAZOP) study is a structured and systematic examination of a planned or existing process or operation in order to identify and evaluate problems that may represent risks to personnel or equipment, or prevent efficient operation.

The HAZOP technique was initially developed to analyse chemical process systems, but has later been extended to other types of systems and also to complex operations and to software systems.

A HAZOP is a qualitative technique based on guide-words and is carried out by a multi-disciplinary team (HAZOP team) during a set of meetings.

HAZOP is now a mandatory activity. It is a qualitative, experience intensive exercise as of now. It is in the form of deviation analysis. After the process design, the steady state specifications of each stream in the flow sheet are known. The HAZOP team exhaustively asks itself questions as to what will happen if this specification deviated on the positive or negative side of the expected steady state value. It debates the possible causes and consequences of each such eventuality. Anything which appears to them as likely to lead to hazardous situations is debated further and possible means of avoiding the same or raising alarm if it happens so that remedial action can be taken etc. are recommended. This may lead to recommendation of additional instrumentation on lines and equipment, Hi-Lo alarms and trips etc. may be required to be provided.

The idea of HAZOP is to foresee hazardous situation and take measures and abundant precaution to avoid them and increase process safety.

This is a structured analysis, conducted after the design review, to ensure the design is suitable for all the intended operating conditions and complies with the HSE requirements. This process is also to ensure that the fundamentals of the design are thoroughly explained, understood, and examined.


The benefit of the HAZOP is that early identification and assessment of the critical hazards provides essential input to project development decisions.  This leads to a safer and more cost effective design with a minimum cost of change penalty.

Key Documents required:

  • PFD / PFS’s (Process Flow Diagram/ Process Flow Schemes)
  • P&ID / PEFS’s (Piping & Instrument Diagrams/ Process Engineering Flow Schemes)
  • Basis of Design
  • Operating, Control and safeguarding philosophy
  • Plot plans & Hazardous area classification drawings
  • Cause & Effect diagrams

Team Composition:

  • Chairman (independent)
  • Lead engineers from Process, Instrumentation & Control (both from Design team and Client/ End user)
  • Operations engineer (from Client/ End user)
  • Lead engineers from Mechanical/Piping, Pipeline, HSE and Electrical as required. (Both from Design team and Client/ End user)


The HAZOP study should preferably be carried out as early in the design phase as possible – to have influence on the design. On the other hand; to carry out a HAZOP we need a rather complete design. As a compromise, the HAZOP is usually carried out as a final check when the detailed design has been completed.

A HAZOP study may also be conducted on an existing facility to identify modifications that should be implemented to reduce risk and operability problems.

Typically HAZOP in EPC design companies are performed 3 to 4 weeks after the Design review meeting, once the design review points are incorporated in the key documents.

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