Transcript Human Factors & Errors

Human Factors & Errors
• Key objectives of HF is to design systems that
– people can use
– increase efficiency and performance
– minimise the risks of errors
• Will define and consider the nature of error
• Consider the implications for systems design
Definition of Human Error
• …is an inappropriate or undesirable human
decision or behaviour that reduces or has the
potential for reducing the
– effectiveness
– safety
– system performance
Human Error
• Tendency to view error at the operator level
• Other people involved in the design and
operation of the system can make errors
• Should therefore consider the entire system
• What might each approach reveal?
Human error
• 1st blame only the individual
• 2nd identify other factors. Eg:–
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badly designed or faulty equipment
poor management practices
inaccurate or incomplete procedures
inadequate or inappropriate training
Human Error - Classification
• Various classification schemes exist
• Discrete action classifications
• Information processing classifications
Discrete Action Classifications
• One of the simplest (Swain & Guttman
1983)
• Errors of omission - forget to do something
• Errors of commission - doing the task
incorrectly
• Sequence errors - out of order
• Timing errors - too slow - too fast - too late
Information Processing
Classifications
• Rouse & Rouse (1983) propose one scheme
• This scheme follows the information
processing assumed to occur when humans
operate and control systems such as:– an aircraft
– a ship
– a power plant
Information Processing Scheme
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Operator observes the state of the system
Formulates a hypothesis
Chooses a goal
Selects a procedure to achieve desired goal
Executes the procedure
Specific categories of errors can occur at
each stage - eg incorrect interpretation of
state of the system
Alternative Classification
• Rasmussen (1982) identifies 13 types of
error 9 (See fig 20.1 in exercise book)
• Errors depend on the type of behaviour
involved
– skill based
– rule based
– knowledge-based
Error Classification
• Skill based
– controlled by sub-conscious behavior and
stored patterns of behavior
– errors usually errors of execution
• Rule based
– applies to familiar situations - stored rules are
applied
– errors involve recognising the salient features
of the situation
Error Classification Schemes
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No scheme particularly useful
Partly because human error is complex
Schemes do not capture that complexity
Often the full facts are not available
Dealing with Human Error
• Human error is inevitable
• Consequences and likelihood can be
reduced by:– better recruitment & selection
– training
– better design of equipment procedures & work
environment
Dealing with Human Error (cont)
• Three generic design approaches for dealing with
human error:– Exclusion designs - impossible to make the
error - Example?
– Prevention designs - difficult but not impossible
- Example?
– Fail-safe designs - reduces the consequences
but not the possibility - Example?
• Designing to reduce error is often the most cost
effective
Human Error and Accidents
• A key objective of HF is to reduce accidents
and improve safety
• Difficult to define ‘accident’
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without apparent reason
mishap
unexpected
chance
‘act of God’
Human error and Accidents
• what % of errors is caused by human error?
• Depends on several factors
• Which perspective do we take ? The broad or the
narrow?
• May wish to consider other factors - was it an
unsafe act or unsafe conditions - Eg The
Singapore Airlines crash
• Often it is the narrow perspective which is applied
- blame the operator - Eg The pilot
Blame the Operator
• Shealey 91979) suggests several reasons for this
– it is human nature to apportion blame at someone else
– legal system is geared to apportioning blame
– easier for management to blame the worker than other
aspects
– it is in the interests of the company to blame the worker
rather than admit deficiencies in their procedures
product or system
• Studies of accidents (Shanders & Shaw 1988) reveal that
in no case was human error the only factor
• They proposed a model of contributing factors in accident
causation - CFAC
Sanders & Shaws’ CFAC
• Factors are broad & encompass most factors found
in other models
• Their model includes and emphasises
– management social and psychological factors
• Human factors variables are recognised in the
categories
– physical environment
– equipment design
– work itself (refer to model diagram in exercise
book)
Reducing Accidents -Conclusion
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Apply HF principles to design
Provide procedural checklists
Provide training
Provide appropriate & meaningful feedback
Incentive programs
Eliminate/reduce risk through design
Reference
• Human Factors in Engineering & Design
• Saunders M & Mc Cormick E 7th Edition
1992
• Publisher McGraw - Hill