There is a vigorous debate within the industrial refrigeration industry surrounding whether or not the use of hazard and operability methodology, referred to as HAZOP, should be considered the industry standard for hazard reviews and process hazard analyses. While there are advocates for and against employing HAZOP methodology, Stephanie Smith, senior engineer II with Risk Management Professionals Inc., said her research and experience show that the benefits generally outweigh the costs.

Smith made the comments while speaking during the IIAR 2021 Natural Refrigeration Conference & Expo virtual meeting. The Center Chemical Process Safety defines the purpose of a HAZOP Study as to “carefully review a process or operation in a systematic fashion to determine whether deviations from the design or operational intent can lead to undesirable consequences.”

Smith said HAZOP produces more comprehensive hazard reviews and process hazard analyses than other, more common methodologies, and provides more information specific to the location of system vulnerabilities, which may also result in focused recommendations that are specific and straightforward to address.

Other methodologies include what-if/checklists, failure mode and effect analysis (FMEA), and fault tree analysis. Smith said what-if/checklists tend to be more flexible, qualitative, and more general in evaluating hazards while HAZOP is more systematic, qualitative and identifies specific causes and failures. FMEA is about single-failure modes, is more qualitative, and is specific for equipment failure leading to an incident rather than human involvement. Fault tree analysis is even more advanced and specific and focuses on incidents for deriving causes and is more quantitative.

Currently, HAZOP and what-if/ checklists are the most used methodologies in the industrial refrigeration industry and what-if/checklists can be used in conjunction with HAZOP. When conducting a HAZOP study, the first step is to gather information. Smith said it is important to have good and updated piping and instrumentation diagrams (P&IDs), process safety information, and the team’s input on operations and maintenance procedures implemented at the facility.

“Essentially when we do a HAZOP, we break the P&IDs down into nodes. The system is broken down into smaller nodes for the study. Then we look at parameters. What process parameters do we evaluate? We also look at guide words, which provide guidance on deviation from normal operations,” Smith said.

In her technical paper on HAZOP, Smith wrote that guide words are used to lead the team through their discussions. Teams can develop scenarios under each set of guide words, examine the consequences of each scenario, discuss and document deviations from normal operating conditions, rank the severity of the consequence and identify safeguards. They can then rank the anticipated frequency accounting for the safeguards, develop recommendations to lower risk, if necessary, and then repeat for all scenarios and nodes.

The challenges of using the HAZOP methodology are multifold, but they can largely be mitigated by a facilitator who is experienced and conversant in the methodology. Smith said the facilitator’s primary role is to guide the team to its own conclusions. Sometimes the conclusion is obvious, sometimes it can take hours or days of discussion and investigation to unearth.

Probably the most difficult role for a facilitator is to be a mediator for the methodology, ensuring that all team members understand the “rules” and appropriately address the agreed-upon hazard scenarios. Common struggles include trouble assessing severity without safeguards, identifying hazards outside the node/ scenario, disagreements between the design intent and actual function of the system, and recommendations lacking the specificity needed for the study. The facilitator must also understand the risk ranking methodology.

Smith said HAZOP studies can take more time than other methodologies, but that’s to be expected for a more critical examination that requires additional time for discussing results. Even still, Smith said the benefits of HAZOP far outweigh the challenges, and they can be enhanced by a facilitator who can lead the HAZOP team to a full understanding of the study itself and the resulting conversations. Plus, the more complex, quantitative methodology lends additional power to the study in that an ultimate consequence can be narrowed down to specific failures in the system without much additional effort. Ultimately, this information is more valuable than that provided by the most common methodologies used to evaluate ammonia processes, she explained.

The HAZOP methodology is systematic when it comes to discussing hazards, as it requires the team to identify each piece of equipment and each valve in the system, which makes the evaluation specific and thorough. Other methodologies generalize the brainstorming of hazards, which can lead the team to misjudge or even overlook hazards, Smith said.