Human Factors &
System Safety
Mark-Alexander Sujan
Human Reliability Ltd.
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• Is not a property of individual components
• but of their interaction in specific contexts
• and includes the people working with technological components
• as well as their social interaction
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The individual view:
Incidents are mainly due to individual failings
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Cause:
“ Human error —maintenance staff failed to use procedures (violation), therefore critical action omitted.”
Corrective Actions:
– “Maintenance personnel to be disciplined.”
– “Directive to be issued regarding the importance of using procedures.”
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Individual View of Human Error 1: incidents are caused by failure to follow rules
• Causes • Solutions :
–Negligence
–Lack of commitment
–Improve motivation
–Improve commitment
–Failures to follow rules or procedures
–Write a new rule or procedure to prevent the error
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Individual View of Human Error 2: incidents are caused by lack of competence
• Cause
–Lack of capability
–Accident proneness
–Inadequate skill
–Loss of skill
• Solution
–Selection
–Selection / ‘Weeding out’
–More training (more of the same?)
–Refresher training

All of these solutions focus on Individual Causes
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The systems view:
Human error is mainly due to deficiencies in the system which create the pre conditions for error

Why did the maintenance staff fail to use the procedures?
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• There were frequent distractions
• The maintenance staff were working under pressure on several pieces of equipment at once
• Responsibilities were not defined
• Maintenance operators had too many roles
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Why Were the Procedures
Not Used ?
• There was a large amount of irrelevant paperwork
• Operators did not participate in procedures development (therefore did not ‘own’ them)
• Procedures generally regarded as inaccurate and impractical (If followed to the letter job could not be done within time constraints)
• Using procedures regarded as only necessary for novices
• Under time pressure maintenance staff did not usually bother to look at procedures
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Assessing the context:
Maintenance Activity (simplified)
Factors affecting errors in maintenance activity
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Suitability of tools and equipment
Technical competence
Time Stress
Features of the activity
Quality of procedures
Degree of complexity
Isolated steps
Similarity to other activities
Stability of activity method
Accessibility of components
Design of system for maintainability
Component design
Access to parts
Amount of removal

Error potential analysis
Evaluating the Error Potential
Score for Violations
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Violations
Strongly disagree
Disagree Neutral Agree
Strongly agree
Following the procedure makes the task more time consuming
Following the procedure makes the task more difficult
The task is carried out under time pressure
0
0
0
2
2
2
4
4
4
6
6
6
8
8
8
Violations EPS = 2 + 2 + 0 = 4

• Dependability of the HW/SW System is meaningful only with respect to the context – including humans !!
• Systems factors may make incidents inevitable
• The operator is often held responsible for deficiencies in systems
• Interventions should address the systems factors that provoke error
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