1. 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

2. 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

3. 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?

4. 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

5. Human Error - Classification • Various classification schemes exist • Discrete action classifications • Information processing classifications

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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’

15. 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

16. 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

17. 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)

18. Reducing Accidents -Conclusion • Apply HF principles to design • Provide procedural checklists • Provide training • Provide appropriate & meaningful feedback • Incentive programs • Eliminate/reduce risk through design

19. Reference • Human Factors in Engineering & Design • Saunders M & Mc Cormick E 7th Edition 1992 • Publisher McGraw - Hill