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:-– 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

• 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

• Knowledge based - occur in unique & unfamiliar situations– errors result from inadequate analysis or decision making

Error Classification Schemes

• 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’– 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

• 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