To address human factors in workplace safety settings, peoples’ capabilities and limitations must first be understood. The modern working environment is very different from the settings that humans have evolved to deal with. This section examines human characteristics that can lead to difficulties interacting with the working environment. The main factors involved include:
- Attention – the modern workplace can overload human attention with enormous amounts of information far over that’s encountered in the natural world.
- The way in which we learn information can help reduce demands on our attention, but can sometimes create further problems.
- The way in which we learn information can help reduce demands on our attention, but can sometimes create further problems.
- Perception – in order to interact safely with the world, we must correctly perceive it and the dangers it holds.
- Work environments often challenge human perception systems and information can be misinterpreted.
- Work environments often challenge human perception systems and information can be misinterpreted.
- Memory – our capacity for remembering things and the methods we impose upon ourselves to access information often put undue pressure on us.
- Increasing knowledge about a subject or process allows us to retain more information relating to it.
- Increasing knowledge about a subject or process allows us to retain more information relating to it.
- Logical reasoning – failures in reasoning and decision-making can have severe implications for complex systems, such as chemical plants, and for tasks like maintenance and planning.
Here is a detailed explanation of these four (4) main factors in human factors engineering.
Attention
Attention on a task can only be sustained for a fairly short period of time, depending on the specifications of the task. The usual figure cited is around 20 minutes, after which fatigue sets in, and errors are more likely to occur. This is why air traffic controllers must take breaks from their attention-intensive work at regular intervals.
However, there are several other reasons why the attentional system is responsible for errors. These include:
- Information bottleneck – paying attention to a small number of tasks at once is possible. For example, suppose an air traffic controller is focused on handling a particular plane. In that case, it is likely that they will be less attentive to other aspects of safety or other warning signals (although this depends on the nature of the signal).
- Habit forming – if a task is repeated often enough, we can do it without conscious supervision, although this automatization of regular and repetitive behavior can force us into mistakes. In 1979, an Oyster Creek Nuclear Power Plant operator intended to close off two pump discharge valves. Through an attentional slip, he accidentally closed off two other valves as well, and in doing so, closed off all circulation to the reactor core.
The Automatic Warning System installed on all passenger trains in the UK is an example of a system that was not designed with the limitations of human attention in mind. It is a device fitted in the train cab, based on the now obsolete mechanical system of signaling that used to signal either STOP or PROCEED. It sounds a bell when a clear (green) signal is passed and a buzzer when caution or danger is signaled. If the buzzer is not acknowledged by the press of a button, then the train begins to stop automatically. In commuter traffic, most signals will be at the “caution” aspect, and given the frequency of signals (spaced 1km apart), most drivers will face two signals per minute. Given the tendency for the attentional system to automate highly repetitive behavior, many drivers lose focus on the reasons for carrying out this repetitive task and act in reflex whenever the buzzer sounds. The end result is that drivers often hear the buzzer and press the button reflexively without actively thinking about train speed and location.
Source: Davies, D. (2000): Automatic Train Protection for the Railway Network in Britain – A study. RA Eng., London.
Perception
Interpreting the senses – one of the biggest obstacles we face in perceiving the world is that we are forced to interpret the information we sense rather than access it directly. The more visual information available to the perceiver, the less likely it is that errors will be made. Bearing this in mind, systems that include redundant information in their design may cause fewer accidents. An example of this was the change in electrical earth wire color coding in the 1970’s to include not only color, but also a striped pattern.
Signal detection – the more intense a stimulus (such as a light or a noise), the more influential the response elicited (such as brain activity or a physical movement). This has implications for the way danger signals are perceived at work. For instance, the order in which the severity of danger is signaled on UK rail tracks is single red (most dangerous), followed by single yellow, then double yellow, and finally green (no danger). Research suggests there may be some merit in swapping the order of the yellow signals, as the double yellow is more intense and thus more noticeable than the single yellow signal. However, this point must be offset against the fact that the current system provides an automatic mechanical failsafe if a yellow bulb blows and the psychological notion that double yellow serves a valuable role as a countdown to the single.
Memory
Capacity – short-term memory has an extremely limited capacity. People can generally remember no more than seven (7) individual items at a time. This has safety implications in areas such as giving new workers a set of instructions to follow from memory or attempting to remember the correct sequence of procedures within a new task. However, trained individuals can retain larger chunks of information in memory. For example, chess grandmasters can remember the location of more pieces on a chessboard than can a novice because they see the pieces not as single units but as parts of larger conceptual units that form coherent wholes.
Accessibility – even when items are stored in memory, it is sometimes difficult to access them. There has been much research into how recall of information can be improved. For example, research has shown that people are much more likely to remember information in similar conditions to when they encoded it. This was illustrated in a study involving divers who were given lists of words to learn on dry land and underwater. Words learned on the surface were best recalled on the surface, and those learned underwater were best recalled underwater. This has implications for training programs, where albeit under less extremely contrasting situations, staff trained in an office environment may not be able to remember relevant details on the shop floor.
Levels of processing – another way in which information can be more reliably remembered is to learn it at greater depth. For instance, if it is necessary to remember lists of medical symptoms, then it helps to understand more about the conceptual framework behind the list. If only the ‘surface’ features (such as the words on the list) are remembered, then there is a higher chance of information being forgotten.
Sources: Chase, W.G. & Simon, H.A. (1973): Perception in chess. Cognitive Psychology, 4: 55-81.
Tulving, E. (1979): Relation between encoding specificity and levels of processing. In, L.S. Cernak & F.I.M. Craik (Eds.), Levels ofprocessing in human memory. Hillsdale, N.J.:Lawrence Erlbaum.
Logical reasoning
Humans are not very good at thinking logically, but in technological situations, logical procedures are often necessary (for example, troubleshooting a complex system that has broken down). Illogical behavior is a common source of error in industry. During the Three Mile Island incident in 1979, two valves that should have been open were blocked shut. The operators incorrectly deduced that they were, in fact, open by making an illogical assumption about the instrument display panel. The display for the valves in question merely showed that they had been instructed to be opened. In contrast, the operators took this feedback as an indication that they were actually open. Following this, all other signs of impending disaster were misinterpreted concerning the incorrect assumption, and many of the attempts to reduce the danger were counterproductive, resulting in further core damage.
Source: https://www.parliament.uk/globalassets/documents/post/pn156.pdf