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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.
  • 3.Describe tasks and jobs.
  • 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
  • If your group has not started meeting about the
    project you have a problem.
  • Tomorrows lecture is a review for the midterm
    exam

18
Tutorial/Exam
The midterm exam will be held during this weeks
tutorial, But in a different location (WW 111)
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