Reliability /Safety Index Page


This page provides outline information and links to information on HAZOP studies and their purpose.

Hazops Introduction

The implementation Hazard and Operability Studies are completed at an early stage in the design project to ensure that if the plant is operated away from the design intent there are no unacceptable safety or the Operability consequences. Hazops were initially 'invented' by ICI in the United Kingdom.   Through the general exchange of ideas and personnel, the system was then adopted by the petroleum industry, which has a potential for major disasters.   A number of industries now use this system including the water industry , the nuclear industry, the food industry to note just a few. The procedures used are most conveniently applied to the chemical industry but, with only minor modifications can be applied to any industry.

Hazops Team

A hazop study is generally completed by a team which includes the designers, safety representatives and a number of members with expertise in a range of related fields.   The team should also include individuals who have knowledge of operating similar equipment and plant.

Information presented to for HAZOP Study

The design process generally includes a number of HAZOP studies (HAZOP 1, 2 3)

The first (HAZOP 1) study would be based on the design specification and the resulting process flow diagrams / block diagrams.

The second (HAZOP 2) study would be based on the design specification and the more detailed Engineeering Flow Diagram / Mechanical Flow diagrams.

The later HAZOP studies would be based on actual Production and Operating document

Key Words

The HAZOP study is based on the use of Primary and Secondary Keywords

Primary Keywords which focus attention upon a particular aspect of the design intent or an associated process condition or parameter.

Secondary Keywords which, when combined with a primary keyword, suggest possible deviations.

Typical Primary Keywords

Flow TemperaturePressure

Typical Secondary Keywords

No LessMore
HAZOP methodology

The Hazop study process involves applying in a systematic way all relevant keyword combinations to the plant in question in an effort to uncover potential problems.   Each flow sheet is reviewed on a line by line, item by item basis.   The results are recorded systematically in tabular form.   Relevent Headings for the table are provided below:

DeviationCauseConsquence SafeguardsAction

  • The deviation may be, for instance, High level.
  • The cause would be considered and may include various causes for the high level including valve jammed open, level instrument failed, control failure.etc etc.
  • The consequence of the high level would have to be identified.. This may include vessel overflow, vessel vent blockage, uncontrolled fluid transfer to unacceptable route etc.
  • Existing safeguards which prevent or mitigate the problem are identified.
  • If the consequence is negative and the safeguards are insufficient then an action is registered.  This is placed on the relevant members of the team to provide a solution to the problem.

On completion of the HAZOP review activity a detailed list of HAZOP table is produced and actions are identified.  The actions are completed and are circulated and accepted by the full team or the actions are reviewed at a follow-up meeting.

Links providing relevant information
  1. HAZARD & OPERABILITY STUDIES (1 of 2) ... Notes on HAZOP studies and relevant software
  2. Note on Hazard and Operability Studies ...Royal Society of Chemistry Paper
  3. The HAZOP (Hazard and Operability) Method ...A relevant ACUSAFE Paper

Reliability /Safety Index Page

Please Send Comments to Roy Beardmore