Transcript class 10-2 safety and human error.odp

Human Error
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Definition
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an occasion “… in which a planned sequence of
mental or physical activities fails to achieve its
intended outcome, and when these failures cannot be
attributed to the intervention of some chance agency.”
–
James Reason
Broad Classes of Human Errors
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Planning Failures: Mistakes
• inappropriate plan, misdirected intention
• plan carried out as intended
• e.g., wrong medication prescribed & administered
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Execution Failures
• Slips
– appropriate plan, intention
– part of plan performed incorrectly
– e.g., trocar injury
• Lapses
– appropriate plan, intention
– part of plan omitted
– e.g., forget to remove sponge before closing
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Rasmussen / Reason Model
of Human Performance
Skill-Based
Rule-Based
goal / problem
recognized
Knowledge-Based
consider state info
try to find analogy
yes
familiar
pattern
?
initiate
“automatic”
process with
attentional
checks
problem
resolved
?
yes
no
apply If-Then rule
problem
resolved
?
yes
no
revert to mental
model, analyze
yes
no
found ?
deduce, infer, plan,
execute
no
problem
resolved
?
no
yes
goal achieved
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Reason’s Error Taxonomy
(partial)
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Skill-Based Errors
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Rule-Based Errors
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double-capture slips (distractor capture + strongest schema capture)
omissions (lapses) following interruption
reduced intentionality (prospective memory errors)
first exceptions (strong-but-now-wrong rule)
information overload
wrong rule
Knowledge-Based Errors
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selectivity (salience > importance)
working memory limitations
anchoring / confirmation bias
illusory correlation
problems with complexity
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delayed feedback
serial vs. network causality
thematic vagabonding (flitting from issue to issue)
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Understanding Human Error:
The AORTA (Stage) Model of Human Performance
Attend
attend to one task
attend to several tasks
Remember
Observe
stimuli
see/read
hear
feel (palpate)
detect
discriminate
recognize
perceive
Think
memorize
recall (long-/short-term)
maintain mental model
calculate
decide
solve
develop alternatives
choose alternative
select response
Act
reach
grasp
move/manipulate
speak
walk/run
respond
responses
Environment
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Human Performance Database V 2.5
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Human Error and Accidents

Causes of Adverse Events
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Rarely
• individual incompetence
• lack of due diligence
• bad luck
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Commonly
• Vulnerable Systems*
• Fallible Humans*
* from E.L. Wiener, “Fallible Humans and Vulnerable Systems: Lessons Learned from Aviation,” 1987
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Some Common Human
Fallibilities
Attend
limited attentional resources
attraction to salient but irrelevant cues
inability to focus attention: distraction
inability to divide attention: tunneling
Remember
Observe
Think
Act
responses
stimuli
Environment
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Some Common Human
Fallibilities
Attend
Remember
Observe
stimuli
Think
detection thresholds
limited visual field
sensory impairments
auditory masking
discrimination thresholds
vigilance loss
Act
responses
Environment
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Some Common Human
Fallibilities
Attend
Remember
Observe
stimuli
Think
limited working memory capacity (7 + 2 “chunks”)
limited working memory duration (< 20 sec)
inefficient chunking
verbal/spatial dominance
weak long-term memory associations
Act
responses
Environment
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Some Common Human
Fallibilities
Attend
Remember
Observe
stimuli
Think
Act
anchoring, confirmation bias
recency bias
tendency to treat all sources as equally reliable
bias against absence of cues
asymmetric valuation (gain/loss)
overconfidence
erroneous mental model
responses
Environment
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Some Common Human
Fallibilities
Attend
Remember
Observe
Think
Act
anthropometric limits
neuromuscular limits
strength limits
response time considerations
speed/accuracy tradeoff
stimuli
Environment
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Failure Modes and Effects
Analysis
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A#, Activity / Process / Function
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Contributing Factors
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Potential Failure Mode
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Potential Effects of Failure Mode
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Severity
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Probability
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Nondetectability
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RPN: Risk Priority Number
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Potential Remediations
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Design Requirements
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Fault Tree Analysis (FTA)
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Purpose
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Approach
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(To determine the events and conditions leading up to an adverse event.)
(To determine the probability of an adverse event.)
Identify potential adverse event.
Identify AND/OR combinations of events that lead to the adverse event.
Continue analysis as far as possible/reasonable.
(Determine individual event probabilities and compute probability of adverse event.)
Symbols
E vent
AN D
OR
U n d e v e lo p e d
Event
E x te r n a l
E vent
Fault Tree Aanalysis Example
Slip and fall
(based on Konz & Johnson, Work Design, 7th Ed., Fig. 20.2, p. 383)
Slippery walking
conditions
Distraction
Slippery floor
Low friction
shoes
Wet floor
Highly
waxed floor
Rain
Snow
Spilled
liquid
Slip and fall
FTA Example
Slippery walking
conditions
Distraction
Slippery floor
Low friction
shoes
Wet floor
Highly
waxed floor
Rain
p = 0.1
Snow
p = 0.01
Spilled
liquid
p = 0.01
Slip and fall
FTA Example
Slippery walking
conditions
Distraction
Slippery floor
Simplifying Assumption:
P(A or B) = P(A) + P(B)
(i.e., A and B independent)
Low friction
shoes
Wet floor
Highly
waxed floor
p = 0.12
p = 0.01
Rain
p = 0.1
Snow
p = 0.01
Spilled
liquid
p = 0.01
Slip and fall
FTA Example
Slippery walking
conditions
p = 0.13
Distraction
Slippery floor
Low friction
shoes
p = 0.1
Wet floor
Highly
waxed floor
p = 0.12
p = 0.01
Rain
p = 0.1
Snow
p = 0.01
Spilled
liquid
p = 0.01
Slip and fall
FTA Example
p = 0.23
Slippery walking
conditions
Distraction
p = 0.01
p = 0.13
Slippery floor
Low friction
shoes
p = 0.1
Wet floor
Highly
waxed floor
p = 0.12
p = 0.01
Rain
p = 0.1
Snow
p = 0.01
Spilled
liquid
p = 0.01
p = 0.0023
FTA Example
p = 0.23
Slip and fall
Slippery walking
conditions
Distraction
p = 0.01
p = 0.13
Slippery floor
Low friction
shoes
p = 0.1
Wet floor
Highly
waxed floor
p = 0.12
p = 0.01
Rain
p = 0.1
Snow
p = 0.01
Spilled
liquid
p = 0.01
Hazard Propagation Model of
Occupational Safety
Hazard
(Source)
“Causes:”
Contributing
Factors:
Receiver
Path
Unsafe Conditions
Unsafe Acts
Electrical Hazards
Mechanical Hazards
Pressure & Toxic Substance Hazards
Physical Hazards
Equipment Interfaces
Personnel Characteristics
Social Factors
Human Error
Job Characteristics
Control:
Control At
the Source
Control On
the Path
Control At
the Receiver
Control At the Source Example:
Machine Guarding
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OSHA Machine Guarding Regulations:
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http://www.osha.gov/SLTC/machineguarding/index.html
Machine Guarding Checklist