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Human Error II

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Error probability (EP) also known as Human Error Probability (HEP) ... Error of Omission. typographical errors. Error of Commission. Hitting thumb with the hammer ... – PowerPoint PPT presentation

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Title: Human Error II

1
Human Error II
09/10/99
2
Goals
• Overview of system error
• Review of results and findings

3
System Error
• DEFINITION an action or lack of action that
violates some tolerance limit(s) of the system.
• defined in terms of system requirements and
capabilities.
• Does not imply anything about human. - could be a
system flaw
• Error probability (EP) also known as Human Error
Probability (HEP)
• EP ( of errors)/(total of opportunities for
the error)

09/10/99
4
Reliability
• DEFINITION Probability of a successful outcome
of the system or component
• To evaluate a system it is necessary to know the
goals and purposes of the system.
• Reliability is a probabilistic term.

5
Calculation of Reliability
• R ( of successful operations)/(total
of operations)
• R 1 - EP

6
Basic Error Types (system perspective)
• Unintentional vs. Intentional
• e.g. mistake on a test vs. what speeds most of
us drive.
• Unrecovered vs. Recovered
• Recovered Error with possibility for damage but
no damage e.g., Driving home drunk safely.
• Unrecovered Error where damage could not be
avoided.

7
Human Error Categories
• Error of Omission
• typographical errors
• Error of Commission
• Hitting thumb with the hammer
• Extraneous Act
• reading a different class's assignment in class
• Sequential Error
• E.g., light the fire before opening the damper
• Time Error
• running a red light

8
Where the Error Originates
• Operating error
• Design Error
• Designer does not take into account
human abilities.
• Manufacturing Error
• System is not built according to design.
• Installation and Maintenance Errors
• System is not installed or maintained
correctly.

9
Relative Frequency of Error Types
• Failure to perceive a hazard
• 36
• Underestimate a hazard
• 25
• Failure to respond
• 17
• Ineffective response
• 14

10
Error Analysis
• 1.Describe system goals and functions.
• 2.Describe situation.
• 4.Analyze tasks for where errors are likely.
• 5.Estimate probability of each error.
• 6.Estimate probability error is not corrected.
• 7.Devise means to increase reliability
• 8.Repeat step 4 - 7 in light of changes.

09/10/99
11
Example Human Error Probabilities (HEPs)
• Select wrong control in group of labeled
identical controls

• .003
• Turn control wrong direction under stress
when design violates population norm.

• .5
• Failure to recognize an incorrect status of
item in front of operator

• .01

12
Components in Series
• In a series if any single component fails the
whole system fails e.g., the four tires on a
car.
• Rs R1 R2 ....... Rn
• Examples All components have reliability of
0.90.
• n 1 Rs .90 n 2 Rs .9.9 .81
• n 3 Rs .9.9.9 .73

09/10/99
13
Redundancy and Reliability
• Active Redundancy Failure occurs only when both
fail or (EP1)(EP2)
• Reliability is Rs R1 R2 - R1R2
• E.g., two components have a reliability of 0.90.
• In a series Rs .9.9 .81
• Redundant Rs .9.9-.9.9 .99
• Two redundant components in series
• Rs .99.99 .98

14
Perils of Complexity
• KISS Principle (Keep It Simple Stupid).
• A-10 33 unavailable at any one time.
• F-111D 66 unavailable.
• Apache Helicopter has a similar record to the
F-111D

15
Risk Analysis
• Estimates of safety
• Estimates of probable success
• types of training to use to help operators not to
miss important errors

16
Lessons
• System error analysis different from human error
analysis
• Redundancy increases reliability
• Complex systems tend to be less reliable
• Error and Risk analysis are useful activities

17
Project
• Project description is on the Web
• Check out the requirements
• First deliverable is the project proposal