1. HUMAN ERROR
AND HUMAN PERFORMANCE

2. HUMAN ERROR AS A SOURCE OF RISK
There are three major causes of risk:
Hardware failures
Human error
Natural disasters
So far, we’ve analyzed only hardware failures
However, over time, hardware has become more reliable:
And technology is getting more powerful and complex
So, human error is now a larger share of the total risk 2

3. HUMAN ERROR AS A SOURCE OF RISK
Moreover, studies of major accidents show similarities in the types of human errors that are involved:
“Random error…is not the issue”
Situations can predispose people to make errors
Bley (2002) identifies the following predisposing factors:
“Operation outside designer’s intention”
“Resulting physical regime not well understood”
“Operators refuse to believe or recognize…evidence”
“Prepared plans are not applicable or helpful”
Links and Notes: Bley, D. (2002). “New Methods for Human Reliability Analysis,” Environmental Management and Health, Vol. 13, No. 3, pp , 3

4. EXAMPLE Historically, Chernobyl considered inapplicable to U.S.:
No containment
Graphite moderator
Bley (2002) identified common operational issues:
Three Mile Island
Chernobyl
Work-around
Intentional circumvention
Lack of understanding of implications
Lack of understanding in unusual situation
Continued refusal to believe implications of instruments
Continued refusal to believe instruments, field reports
Links and Notes: Bley, D. (2002). “New Methods for Human Reliability Analysis,” Environmental Management and Health, Vol. 13, pp , 4

5. BASIC TYPES OF BEHAVIOR
Skill-based (automatic, reflexive):
Playing an instrument
Driving a car
Rule-based:
Following a pre-specified rule or procedure
Knowledge-based:
Reasoning from one’s basic knowledge
Links and Notes:
Rasmussen, J. (1986). Information Processing and Human-Machine Interaction: An Approach to Cognitive Engineering, Elsevier Science Ltd., New York, NY. 5

6. BASIC TYPES OF BEHAVIOR
Over time, nuclear power has become more rule-based:
And less knowledge-based
Three Mile Island showed that operators may not find the right answer in a timely manner from basic knowledge
However, we may now be overly rule-based:
Leading to loss of broader “situational awareness” 6

7. ERRORS ASSOCIATED WITH BEHAVIOR TYPES
Skill-based errors:
Slips and lapses (driving home instead of to store)
Rule-based mistakes:
Misapplication of good rules
Application of bad rules
Knowledge-based mistakes:
Misdiagnosis (e.g., due to instrument errors)
Insufficient or incorrect domain knowledge
Time pressure (e.g., on a calculus exam)
Links and Notes: Reason, J. (1990). Human Error, Cambridge University Press, New York, NY, 7

8. ERRORS ASSOCIATED WITH BEHAVIOR TYPES
Some designs are much better than others:
Easy to recognize
Difficult to recognize
However, with skill-based (reflexive) behavior:
Someone who is used to the poor design may be prone to errors when using the “better” design
Especially under time pressure or emergencies 8

9. ERRORS OF OMISSION AND COMMISSION
Necessary action is not taken
Errors of commission:
Undesirable action is taken
Historically considered impossible to analyze 9

10. ERRORS OF COMMISSION
However, Macwan and Mosleh (1994) argued that most errors of commission are in principle predictable:
Intentional skips (task viewed as unnecessary)
Short cuts (taking the path of least resistance)
Misdiagnosis (resulting in a sequence of errors)
Delayed actions (e.g., due to conflicting goals)
Links and Notes:
Macwan, A., and A. Mosleh (1994). “A Methodology for Modeling Operator Errors of Commission in Probabilistic Risk Assessment,” Reliability Engineering and System Safety, Vol. 45, pp 10

11. FACTORS PREDISPOSING TO ERROR
Because most serious errors have complex causes:
Bley (2002) refers to unsafe actions, not errors
Action may not have seemed like an error at the time
Predisposing factors:
Plant conditions (work-around, circumvention)
Performance shaping factors (fatigue, poor training)
Error mechanisms (Thompson et al., 1997):
“Not inherently bad behaviors but…allow humans to perform skilled and speedy operations”
Links and Notes: Thompson, C. M., et al. (1997). “The Application of ATHEANA: A Technique for Human Error Analysis,” 11

12. HUMAN BEHAVIORAL TECHNOLOGY
People do what they’ve done before
People do what they see others do
People don’t do what they can’t do
Behavior is a function of consequence
Behavior is a function of structure
Behavior is elicited by antecedents
Experience makes an antecedent out of an item
Reinforcement increases frequency
Reinforcement works until it saturates
Punishment decreases frequency
Punishment elicits only its avoidance
Null consequences are punishment for functional behavior
Null consequences are reinforcement for dysfunctional behavior
Links and Notes: Corcoran, W. R. (1999, 2004). The Firebird Forum, Vol. 2 (No. 5) and Vol. 7 (No.11), available on request from 12