Human error is an important concept in ergonomics but it is mainly referred to in context. It is a possible answer to the questions: "What caused the accident?" or "How did it break?" That doesn't mean that the vase broke because of human error. But when you are evaluating a mishap from a piece of equipment or a system then the cause may be human error. It may also be incorrect installation or a manufacturing defect or a slew of other possibilities.
There's an old episode of I Love Lucy where Lucy gets a job working on an assembly line boxing candies. The line is moving too fast for her to keep up and madcap comic romps ensure. The break down in the system was not mechanical but human error.
Human error is typically called into being during an accident or mishap investigation such as a car crash, house fire or a problem with a consumer product leading to a recall. Usually it is associated with a negative happening. In industrial operations something called an unintended consequence may occur. This may not necessarily be bad, just unexplained. And investigation may conclude that the equipment or system design is fine but the human component messed up.
The legend of Ivory soap is an example of positive unintended consequences due to human error. Back in the late 1800's Proctor and Gamble were manufacturing their new White Soap with hope to compete in the fine soap market. One day a line worker left the soap mixing machine on while he went to lunch. When he got back from lunch the soap was extra frothy having incorporated more air than normal into it. They sent the mixture down the line and turned it into bars of soap. Soon Proctor and Gamble were inundated with requests for the soap that floats. They investigated, found the human error, and incorporated it into their product Ivory soap which is still selling well over a century later. (Note-recent research by proctor and Gamble suggests that the soap was actually invented by one of their chemists but the legendary example still illustrates the human error point)
From a design perspective the engineer or designer produces a piece of equipment or a system with intentions to function in a certain way. When it doesn't function that way (it breaks, catches on fire, messes up its output or is befallen of some other mishap) they try to find the root cause.
Typically the cause can be identified as a:
- design deficiency - when the mechanical, electrical or other components of the design has a problem that caused the mishap
- equipment malfunction - when the machine operated incorrectly
- manufacturing defect - when the material or assembly has an issue that causes it to fail
- environmental hazard - when an outside factor such as the weather causes the hazardous condition
- human error - when a person did something wrong
If we look at watching TV as a system we can give examples for all of these types of errors that would lead to the TV not working. If there is not a power button on the set itself it is a design deficiency. If the channel scanner can't pick up the channels because of a software glitch it is a malfunction. If the screen won't light up because of a short it is a manufacturing defect. If the set gets struck by lightning it is an environmental hazard. If you lose the remote in the couch cushions it is human error.
"That's all well and good," you say, "But what constitutes human error?" I am glad you asked. To better analyze the mishap and better understand the human error we have to quantify it. Human error is more specific than just making a mistake.
Human error includes:
- Failing to perform or omitting a task
- Performing the task incorrectly
- Performing an extra or non-required task
- Performing tasks out of sequence
- Failing to perform the task within the time limit associated with it
- Failing to respond adequately to a contingency
To continue with our TV example if you omit pressing the power button the TV won't come on and it's human error. If you press power on the remote with it facing backwards you've performed the task incorrectly. Pressing the power button twice is an extra task and no TV. If you try to turn it on before you plug it in you're going out of sequence. If you have an old plasma TV and you move it laying down, if you turn it on without letting it sit upright for a while to redistribute the gasses you can actually blow it up by going out of sequence. If you don't pay your cable bill on time you've failed to act within the allotted time and, again, no TV. Furthermore, if you don't tackle the cable guy we he comes to disconnect it you've failed to react adequately to a contingency.
Human error may be identified as the cause when the root cause is actually something else on the list. If a switch malfunctions when the operator uses it that is not human error it is a malfunction. While there are some things that contribute to human error, design deficiencies are often misdiagnosed as human errors as well. There is an ongoing debate between ergonomic centered designers and engineering minded designers about human error and design deficiency. On one side is the belief that almost all human error is related to design deficiency because a good design should take into account human behavior and design out those possibilities while on the other side they believe people make mistakes and no matter what you give them they will find a way to break them.