Hazard Studies: Lighting the way to Safe Processes

It was once the case that industry developed by ‘trial and error.’  A process plant would be built, started-up and all the operating problems and safety incidents would appear. Sometimes the plant would never operate as intended and be deemed a failure. Sometimes the incidents would kill or maim operators or cause environmental damage harming the health of residents. 

In the early 1960s chemical engineers in the UK’s petrochemical industry developed a new way to study the design of a chemical process plant, revealing the operating problems and safety threats in advance and allowing for their avoidance or management. This method developed to become what is now known all around the world as Hazard and Operability Study (‘HAZOP’ for short). 

HAZOP works through a multi-disciplinary team who meet to study the plant design in a systematic, consistent, and rigorous way. The process equipment and pipework are split-up into simple ‘nodes.’  The team then discusses every conceivable way in which a range of different ‘deviations’ from the intent of the design can occur in that node, along with the consequences of each of these deviations. The deviations considered are prompted by systematic application of relevant ‘guide words.’  For example, in a pipe, deviations including high temperature, low temperature, high flow, low flow, no flow, reverse flow, high pressure and low pressure are all often credible and may have many different consequences. The provisions in the design to deal with the potential deviations are considered and any gaps between the proposed design and the goal of a design that will prove safe and effective are identified for further consideration. 

Awareness of the HAZOP technique grew through the 1970s, with conference papers and the publication of books. Further, chemical engineers developed a suite of other study techniques applied throughout the lifetime (or ‘lifecycle’) of the plant, from selection of the concept (‘optioneering’) to decommissioning of the plant. 

By the 1980s HAZOP was a routine part of designing oil, gas, and chemical plants in several countries. HAZOP is applied prospectively to new designs, and intermittently during plant life to account for changes and new options becoming available. HAZOP has also been applied retrospectively to many plants, as its value in exploring the individual susceptibility of a plant is difficult to mimic by any other technique. Chemical plants designs are often similar, but very rarely identical, even when implementing the same process in the same organisation. Over the years since HAZOP became a well-defined and published technique, it has been further refined and developed, has spread almost worldwide, and is now applied to a very wide range of process industries. 

This structured approach to identifying safety and operability issues has given us the ability to proactively make process plants safe and reliable, rather than waiting for incidents inevitably to occur before reacting. Countless lives have been saved.  

References:

Crawley, F & Tyler, B, HAZOP: Guide to Best Practice (3rd Edition), Institution of Chemical Engineers, 2015

R. Ellis-Knowlton, A Manual of Hazard & Operability Studies: The Creative Identification of Deviations and Disturbances, Chemetics International Company, 1992

Lawley, HG, Operability Studies and Hazard Analysis, Chemical Engineering Progress, 1974

Kletz, TA, HAZOP and HAZAN, Identifying and Assessing Process Industry Hazards (4th Edition), Institution of Chemical Engineers, 1999

Kletz, TA, Hazop – past and future, Reliability Engineering and System Safety, 1997