Human Performance

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Human Performance Safety Predictive Model

• System Safety Human Performance
• One Pilot Model
• Two Pilots (Crew) Model
• Accident prevention - Barriers

Dr Sergey Nesterov. April 2006
2
Changes in attributed cause types for accidents
Technology, equipment
Human performance
Organisation
100
90
?
80
Attributed cause
70
60
50
?
40
30
20
?
10
1960
1965
1970
1975
1980
1985
1990
1995
2000
Erik Hollnagel
3
Systemic accident model
Latent system conditions
Barriers defences
Function failure at the sharp end
Unexpected, unwanted consequence
Function failure at the blunt end
Latent system conditions
Erik Hollnagel
4
Sharp end - blunt end
Factors at local workplace
Morals, social norms
Regulator
Government
Unsafe acts
Management
Company
Blunt end factors are removed in space and time
Sharp end factors work here and now
Erik Holnagell
5
What is an error?
Actual outcomes intended outcomes
Correctly performed actions
Failure detected and recovered
Actual outcomes ? intended outcomes
Failure detected but tolerated
Immediate effects Latent effects
Failure detected but not recovered
Failure not detected
Erik Holnagell
6
Performance deviations
"Knowledge and error flow from the same mental
sources, only success can tell one from the
other."(Mach, 1905)
Actions with a negative outcome.
Human performance is inherently variable!
HUMAN ERROR!
Both types are performance deviations, and may
have the same causes
Work conditions are inherently variable!
Actions with a beneficial outcome.
CREATIVITY, LEARNING
Erik Holnagell
7
Human Reliability Assessment(HRA)

• Human Reliability Assessment (HRA) deals with the
  assessment of human error potential in a system
  and usually occurs within a quantitative risk
  assessment framework.

Human Error Probabilities HEP number of
errors occurred number
of opportunities for error
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HRA techniques fall generally into two categories

• Those that use a database.
• (e.g. THERP, JHEDI, HEART). Use a collection of
  generic error probabilities. These probabilities
  are manipulated by the assessor to fit the
  context-related Performance Shaping Factors(PSF)
  in the scenario being assessed.
• Those that use expert opinions.
• (e.g. APJ, PC, SLIM, IDM) .Uses expert judgments
  of particular scenarios and PSFs to render
  information into HEPs

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Analysis-prediction dilemma
?
Looking back, we acknowledge that accidents
reflect complex coincidences
Looking ahead, accident models are still mostly
linear or sequential.
Erik Hollnagel
10
One Pilot Model

• Generic model for Human Performance and Safety

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Key Questions

• What are Pilot State Safety Relevant Indicators
  (human performance) ?
• How to link safety and human performance
• What is a reasonable predictive model for pilot
  performance and safety?

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Statistical Experiment

• Statistical dynamic modelling of tasks sequence
• Focus on deviations around normal flight
• Focus on cognitive psychological model
• Concept of general task failure probability
• Concept of perceived hazard of task failure
• Concept of human error related temperature
• Concept of flight safety outcome (number of
  errors and errors severity plus aircraft state)

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Simulation Diagram
Number of flight Iterations
Accident 0.001 Major incident 0.4 Minor
incident 1.9
Flight Scenario List of Tasks
Simulator
Pilot State
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Flight Output RecordsInput for Flight Analyser
Task i
Tasks / Errors
S
S
S
F
E
S
S
S
E
E
E
F
F
F
F
Low
Low
Low
Med
High
Med
Med
Perceived Hazard Level
Noise in the Cabin
Flight phases
Takeoff
Time line - Events
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Task Processing Model
Failed Task
Failure
Internal Failed State
Herr 1 Herr 2
Task
Pilot failed to notice
t??
Success
Successful Operation
Pilot noticed error
t????
Herr 1 Herr 3 T Dev Knowledge
t???
Ready for Mitigation
t?
Mitigated? Yes
Temperature
Ok T Dev
Ok
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Human Agent Unique Features

• Internal Error detection state
• Internal Error mitigation state
• Dynamic Pr correction (based on perceived hazard
  level, subjective measure)
• Dynamic stress-temperature related Pr
  correction (objective measure).

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Temperature

• Temperature is a universal mechanism to
  control human performance in the model
• Temperature increase / decrease dynamics. Linear
• Temperature influence on the performance. Non
  linear
• Is Temperature Stress or Anxiety?

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Stress and Performance
Over stimulation Zone
Under stimulation Zone
Optimal Zone
Coping strategy Increase stress intake
Coping strategy Decrease stress intake
IrRational problem solving Exhaustion Illness Low
self esteem
Creativity Rational problem solving Progress Chang
e Satisfaction
Boredom Fatigue Frustration DisSatisfaction
Death from lack of stress
Death from Exstress
Degree of stress
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Stress indices Measure

• Subjective Ratings of how the person feels,
  confidence/anxiety reports
• Behavioural Objective measure of performance
  change on real world tasks
• Psycho-physiological heart beats, muscles
  tensions, galvanic skin response, respiratory
  rate
• Biochemical metabolites of neurotransmitters,
  e.g. serotonin

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Two Pilots Model
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Questions

• What are Crew State Indicators for safety (human
  performance) ?
• Are pilots behaviours independent?
• What is cross check mode for two pilots model?
• Other issues Both task interpretation? What is
  the difference?

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Example Boeing 737-NGStart takeoff procedure
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Crew Task Processing Steps
Human Failure
Crew Failure
Task
Human agent 1
Human agent 2
Crew Success
Crew Success
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Modelling Screen Sample
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Accident prevention
To prevent accidents, we must know
Are there any known or valid indicators for
accident build-up?
Which types of accidents are possible in a system?
What
Which types of accidents are possible in a system?
Are there effective means (barriers, defences) to
guard against accidents?
Where
Where in the system can accidents occur?
What are the mechanisms of an accident?
How
Under which conditions are accidents likely?
When
Erik Hollnagel
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Prevention and protection
Accident
Initiating event, failure mode (Incorrect
action)
Protection (safety barriers) Active barrier
functions that deflect consequences
Protection (boundaries) Passive barrier
functions that minimise consequences
Prevention (control barriers) Active or passive
barrier functions that prevent the initiating
event from occurring.
Erik Hollnagel
27
Barrier system types

• Physical, material
• Obstructions, hindrances, ...
• Functional
• Mechanical (interlocks)
• Logical, spatial, temporal
• Symbolic
• Signs signals
• Procedures
• Interface design
• Immaterial
• Rules, laws, principles
• Ten Commandments, Laws of Robotics

Erik Hollnagel
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Questions ?