Human Reliability Assessment on Decision Making Task

The Brief

As part of the operating process at a UK Oil Refinery, there is a Hydrofluoric Acid Alkylation Unit (HFA Unit) used in the production of gasoline. Due to the nature of the process, the HFA Unit is designed to be able to dump the Hydrofluoric acid inventory to a safe location, however, this may not always be the most suitable action dependent on plant conditions. Therefore, if the Rapid Action Dump System (RADS) alarm is initiated, the Control Room Operator (CRO) has to decide whether to activate the trip or to abort the trip and respond in a different way. If no action is taken the trip activates automatically after 60 seconds.

The refinery wanted to conduct a safety critical task analysis on the decision-making process associated with this activity and revise their procedure and competence assessment based on the analysis.

  • We discussed the scope of the activity to determine the requirements. Based on this conversation, I advised that a more thorough approach would be to analyse the whole task to cover both the decision-making and the response to both options; abort the RADS alarm or initiate the trip.
  • I facilitated a Human Reliability Assessment for the activity as advised above, including a Hierarchical Task Analysis and Human Error Analysis where a number of recommendations were developed.
  • Rather than writing a wordy procedure, I drafted a simple decision tree which could be easily used by the CROs in the short amount of time available to decide whether to initiate the RADS trip or not.
  • Existing documentation for the training and competence assessment of this activity was reviewed; I updated the competence criteria based on the analysis which was then incorporated into the site’s Competence Management System.

The Outcome

By redefining the scope of the Human Reliability Assessment, the refinery now have a clearly defined approach to initiating the RADS trip and responding to the trip after initiation. Because the likelihood of this trip being initiated was so remote, all the attention had been given to the decision-making process with little definition about what the shift teams would need to do having initiated it. They also now have a clear description of the conditions in which it is not recommended to initiate the trip.

Additionally, the refinery has a visual decision-making tool to support the CROs in the Control Room and a revised competence assessment which is focussed on the safety critical requirements of the task.

Subsequently, I was asked to support the refinery’s programme of safety critical task analysis and all identified tasks on the HFA unit have been completed. We continue to work on this programme in other parts of the refinery.

(This organisation has a policy of not publicly endorsing supplier companies and have asked to remain anonymous)

“Lorraine has acted as a facilitator for task analysis and human reliability analysis for refinery operating and maintenance tasks across a number of different process areas.

She is always professional in her approach and has demonstrated the ability to work well with all levels of the organisation from the senior management to the front-line workers, including various disciplines and specialists. She always ensures that they understand the process and are comfortable with it and consistently gets the best response from those engaged in task analysis. We constantly receive comments on how beneficial attendees have found the sessions and some have actively requested to do further work with Lorraine.”


Technical Authority-Process Safety. A UK Oil Refinery

  • Date
  • Client
  • Category