People interact with machines via interfaces. Although the interface is not the task, its design is a representation of the task. The interface is the platform for task performance. If users' conceptions of the interface are compatible with their conceptions of the task, then the interface will be 'transparent' to the user when the task is performed and the need to master secondary tasks associated with the operation of interface will be minimised, even if the task itself is difficult. Human errors resulting in accidents and injuries always take place in the context of a task, embedded in an organised system of work. Badly designed systems invite users to make errors and then do nothing to prevent the error from having disastrous consequences. Well-designed systems make it unlikely that users will make errors in the first place. When errors do occur, they block, ignore or feed back to users the errors that they make; and when they do fail, they either
A new born baby died in a hospital intensive care unit after a member of staff had entered a decimal point in the wrong place in a drug prescription… The (decimal) point had been written-up in the wrong place and so the baby received too much of a particular drug.
(The Times, 11 October 2000)
|• Failsafe: revert to a state that is non-threatening or dangerous.|
|• Failsoft: slowly cease to function, giving plenty of indication that something is wrong and plenty of time for it to be put right.|
|• Unusual or inconsistent operation. Users may assume that if they know how to use one type of infusion pump, they know how to use all types. Problems occur when different makes have different control logic. Good practice standardises the procedures for operating different types of products to enhance positive transfer of learning. Dixon (1991) demonstrated that even if there is a large conceptual|