The validation of three Human Reliability Quantification techniques THERP, HEART, and JHEDI

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The validation of three Human Reliability
Quantification techniques-THERP, HEART, and JHEDI

• Written by Barry Kirwan
• Presented by Alena VanWinkle

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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.

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3 Basic Functions of Human Reliability Assessment

• The identification of human errors
• The prediction of their likelihood
• The reduction of their likelihood if required

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Why Validate an HRA?

• If HRAs could identify performance problems and
  also improve performance during the prediction
  process this would be a powerful tool used in
  solving human performance problems!

HRA purports to be able to do both things.
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Kirwans series of papers, in this presentation,
is concerned primarily with the valid prediction
of the likelihood or probability of human errors
(known as quantification) in the form of
H.E.P.Human Error Probabilities HEP
number of errors occurred
number of opportunities for error

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The Central Tenet of HRA
Is that the HEP estimation process must be
reasonably accurate or at least conservative.
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If the HEP is not accurate, or is optimistic
Risk may be under-estimated, Or the wrong errors
highlighted for reduction
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The validation of HRA techniques relies
implicitly on the collection of real HEP data.
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CORE-DATA
(Computerized Operators Reliability and Error
Data Base)

• Is one such collection of real HEP data that can
  be utilized for validation purposes.

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If an HRA technique is found valid by its author.

• It must be validated accurate and reliable by
  many different assessors on different occasions.

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While there are several HRAs

• There has been very few validations

However there has been three critical reviews!
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Human Reliability Assessors guide.
Kirwan et al, 1988

• Swains Review

Author of THERP 1989

• HRA Review by ACSNI

Advisory Committee for the Safety of Nuclear
Installations, 1991
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In all three reviews it was clear

• There is insufficient validations of techniques
  to draw firm conclusions on the techniques
  predictive accuracy and consistency.

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HRA techniques fall generally into two categories

• Those that use a database.
• (e.g. THERP, JHEDI, HEART)
• Those that use expert opinions.
• (e.g. APJ, PC, SLIM, IDM)

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Data based HRAs

• 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.
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Quasi-data-base HEPs are then formed.

• Via the assessors manipulation and interrogations
  of real incident data and expert judgments.

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Expert based HRAs

• Uses expert judgments of particular scenarios and
  PSFs to render information into HEPs

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Part 1
Technique Descriptions Validation Issues
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THERP

• Technique for Human Error Rate Prediction

Swain and Guttmann, 1983
This Technique uses a database of error
probabilities modified by the assessor using PSF
and other considerations.
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HEART

• Human Error Assessment and Reduction Technique

Williams, 198619881992
This Technique is based on the ergonomics
literature, and uses a set of basic error
probabilities modified by the assessor
using structured PSF considerations.
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JHEDI

• Justification of Human Error Data Information

Kirwan, 19901994
This Technique starts from a set of basic error
descriptors and empirically derived error
probabilities, and uses a set of PSF questions (
answered by the assessor) to determine the HEP.
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This study as a whole is attempting to answer
three major Validation questions
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• What is the degree of accuracy and precision
• of the three techniques?

• Is the HRA technique usable by everyone or
• only by seasoned HRA practitioners?

• Do these techniques lead to the reliable
• identification of effective error reduction
• mechanisms?

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The way in which these questions are addressed in
the study, and the answers to them, are
dealtwith in the following presentations!
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Congratulations You made it through The first
part.