HAZOP Basis

A HAZOP, or HAZard and OPerability analysis, is a structured process hazards analysis technique in which a multi-discipline team performs a systematic study of a process using guide words to discover how deviations from the design intent can occur in equipment, actions, or materials, and whether the consequences of these deviations can result in a hazard.

The results of the HAZOP analysis are the team’s recommendations, which include identification of hazards and the recommendations for changes in design, procedures, etc. to improve the safety of the system. Deviations during normal, startup, shutdown, and maintenance operations are discussed by the team and are included in the HAZOP. A block flow diagram of the HAZOP process is given to the left:

The following terms are used in the HAZOP process and in the HAZOP table (see downloadable example below):

  • Line No. – consists of an “Node/Operation/Item” number and a single letter identifying the specific “Failure Cause” (e.g., 1A, 1B, 2A…).
  • Deviation – a departure from the design intent discovered by systematically applying guide words to process parameters.
  • Failure Cause (guide words used) – simple words such as “high” pressure, “high” temperature, “leak” etc. that are used to modify the design intent and to guide and stimulate the process for identifying process hazards.
  • Failure Cause – the reason why a deviation might occur.
  • Potential Effects – the results of a deviation.
  • Safeguards – engineered systems or administrative controls that prevent the causes or mitigate the consequences of deviations.
  • Hazard Category – an assessment of the hazard risk of the operation. In most analyses, we have used the MIL-STD-882E, “Hazard Risk Assessment Matrix.”
  • Recommendations – recommendations for design changes, procedural changes, or for further study.

Guide words for flow in a chemical process include High Flow, No/Low Flow, Reverse Flow, Misdirected Flow, High Pressure, Low Pressure, High Temperature, Low Temperature, High Contaminants, Leak and Rupture.

For processes utilizing explosives, the guide words include electrical initiation, ESD spark, Impact, Friction, Impingement, Incompatibilities, Explosive shock, Thermal ignition, Propagation, Personnel Injury, Environmental contamination, Equipment damage and Product damage.