Competence and Fatigue on a Two-Person Control Room
A continuous process unit is run from a control room staffed by two operators on 12-hour rotating shifts (two days, two nights, four off). One operator has 18 months' experience; the other is a 30-year veteran due to retire in four months. The unit has 14 manual valves that must be lined up for a grade change, and the procedure is a 9-page document last revised 8 years ago. During the last grade change, a valve was left in the wrong position and the unit ran off-spec for two hours before the lab caught it. The veteran says 'I know the line-up, I don't need the sheet'. The site has no formal task-based competence assessment for grade changes.
1. Analyse the human and organisational factors that contributed to the wrong valve line-up, using the evidence in the scenario.
Read the worked answer
Contributing factors span the individual, the task, and the organisation:
- Procedure quality: A 9-page procedure last revised 8 years ago is likely out of date and hard to use under time pressure. Length alone is a barrier - operators will shortcut a document they cannot follow at the plant.
- Competence asymmetry: An 18-month operator paired with a 30-year veteran creates a dependency. The junior may not challenge the senior, and the senior's 'I know the line-up' removes the written check. Knowledge held in one person's head is a single point of failure, especially with retirement in four months.
- No task-based assessment: Without a formal assessment, there is no evidence either operator can perform the grade change reliably, and no basis for identifying who needs support.
- Fatigue: 12-hour rotating shifts with two nights create fatigue, particularly on the second night. Fatigue degrades vigilance and recall - exactly the skills a manual valve line-up depends on.
- Detection: The lab caught the error after two hours, meaning there was no independent verification (e.g. a second-person check or a post-line-up confirmation) and no early process indication was acted on.
- Normalisation: The veteran's attitude signals a culture where the procedure is optional, which the organisation has tolerated.
These are system factors, not simply 'operator error'.
2. Recommend controls to prevent recurrence, addressing procedure, competence, and fatigue, and explain how you would sequence them.
Read the worked answer
Controls, sequenced by immediacy and strength:
Immediate
- Require a documented line-up check for the next grade change: a signed valve list with a second-person verification of each critical valve, and a post-line-up confirmation against the process indication.
- Brief both operators that the procedure is mandatory; supervisor reinforces this.
Short term
- Rewrite the grade-change procedure as a task-based checklist with valve numbers, positions, and sign-off boxes; validate it by walking the line with an operator.
- Introduce a formal task-based competence assessment for grade changes covering both operators; identify the veteran's knowledge and capture it in the procedure and training material before retirement.
- Add an independent verification step (second operator or supervisor) for critical manual valves.
Fatigue and organisation
- Review the shift pattern against fatigue guidance; consider limiting consecutive night shifts or providing protected rest.
- Review staffing so that grade changes are not performed at the end of a night shift.
Assurance
- Track grade-change errors and near misses; audit compliance with the checklist.
Sequencing rationale: stop the immediate exposure (verification), then fix the weak procedure and competence system, then address the underlying fatigue and staffing drivers. The veteran's retirement is a deadline - knowledge capture must happen now.