RISK5002 Chap.10 Human Reliability and Human Factors
Human Reliability and Human Factors
People are a source of risk, a variable in how techniques are used, and the readers who interpret results, and both ISO 31000 and IEC 31010 require human, organisational and social factors to be considered explicitly.
Human reliability analysis breaks a task into steps with hierarchical task analysis, finds error mechanisms with keywords, identifies performance shaping factors, and estimates error probability by adjusting a nominal rate with multipliers.
This chapter works a medication example from task tree to adjusted probability and a fault-tree check, maps HRA against HAZOP, fault trees, Delphi and Ishikawa diagrams, and examines how automation and AI reshape the person-task-equipment system. The case work concentrates on contributing factors rather than blame.
A depot maintenance example shows how fatigue, rostering, production pressure and a hierarchy that discourages speaking up combine, and a fishbone exercise shows how a team organises causes by category. The quantitative example then turns a task analysis into a number and shows how an independent check, modelled as an AND gate, changes the result, which links this chapter back to fault tree arithmetic.
What this chapter covers
- 01
Human factors in ISO 31000 and IEC 31010
- 02
Hierarchical task analysis
- 03
Error keywords and shaping factors
- 04
Adjusting a nominal error rate
- 05
Ishikawa diagrams for root causes
- 06
Automation and the PTE model
Worked example · free
Find the error-prone step and estimate its probability
- +1Apply the keyword wrong object to the vial-selection sub-step from the task analysis.
- +1Adjusted probability = 0.003 x 3 x 2 = 0.018 per selection.
- +1Expected errors = 200 x 0.018 = 3.6 a week, against 0.6 at the nominal rate.
- +1An independent barcode check missing 10% cuts errors reaching patients to 0.018 x 0.1 = 0.0018 per selection.
Key terms
- Human reliability analysis
- Techniques that judge how a person's actions affect the reliability and safety of a system.
- Performance shaping factor
- A personal, organisational or environmental influence on error probability.
- Hierarchical task analysis
- A breakdown of an activity into steps and sub-steps for error analysis.
- Ishikawa diagram
- A fishbone chart that groups possible causes of an effect into categories.
- Nominal error rate
- The baseline probability of error for a task type before adjustment.
Human Reliability and Human Factors FAQ
How does human reliability analysis estimate an error probability?
It starts from a nominal error rate for the type of task and applies multipliers for behavioural or environmental factors, such as fatigue or time pressure, that raise or lower the probability of failure. The result can feed a fault tree or other logic model.
When is HRA less useful?
HRA works best for routine tasks in well-controlled environments. It is less useful for complex tasks, for actions based on multiple or contradictory information, and for activities without a simple pass or fail, and its numbers rely heavily on expert opinion.
What new risks does automation bring to the person-task-equipment system?
Automation can erode manual skill and situational awareness, encourage complacency and over-trust, add cognitive load from many interfaces, blur accountability when AI errs, introduce biased recommendations, and create systems that are hard to understand or override quickly.
What are performance shaping factors?
Performance shaping factors are influences, arising from the individual, the organisation or the surroundings, that raise or lower the probability of error. Examples include fatigue, time pressure, poor lighting, noise, training and workplace culture. In quantitative human reliability analysis they appear as multipliers applied to a nominal error rate for the task.
Exam move
Pick a routine task you do often, build a three-level task analysis, and apply two error keywords to one step. Practise the nominal rate and multiplier arithmetic, then combine the result with an independent check as an AND gate. For case questions, sort contributing factors into human, organisational, environmental and social groups, and always add a process change that would have caught the risk earlier.
Collect two short incident stories from the news and classify their contributing factors into human, organisational, environmental and social groups, then write the process change that would have exposed each one.
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