Distractions and interruptions can draw a person’s attention away from a task, impacting on task performance. Distractions and interruptions can be considered Performance Influencing Factors (PIFs) that increase the potential for human failures. If certain other PIFs are present, such as fatigue or time pressure, the adverse impact on human performance may be more likely.

Distractions

These can be described as a process, condition or activity that takes a person’s attention away from a critical task (such as flying an aircraft, driving a vehicle, operating on a patient, or maintaining a safety critical component). Humans have limited mental processing capacity, and multiple stimuli or tasks compete for this limited capacity. If there are simultaneous demands, then attention may be diverted away from the primary task. At this point, a person may be described as being distracted.

Care must be taken in incident investigations not to jump to conclusions of “failed to pay adequate attention”, but to fully explore competing stimuli/tasks and why they were present. Refer to the investigations pages for more details.

Given the potential amount of stimulation that surrounds us, and our limited information processing capacity, it is only natural that we attend to some things and not others. So, our attention to certain things is selective. There is some debate as to how this selection process occurs, where in the process the “filtering” takes place, and how much processing we carry out on any information that is not attended to.

Certain tasks may be more susceptible to distraction: for example, monitoring tasks can be monotonous but require high levels of vigilance, and are therefore vulnerable to distraction when more salient or engaging demands arise.

Note that distraction can be a conscious decision – that is, deciding not to focus on the primary task. For example, on familiar routes in particular, people may see driving as something that can be performed semi-automatically, and the car can become a place where people decide to think about things unrelated to driving. And technology is introducing new forms of distraction for drivers.

There is a relationship between the need for focussed attention and skill levels: for example, when learning to drive we may have to focus on each individual component of the activity, but as we become more experienced, certain tasks become automatic, with less attention or awareness required.

Types of distraction

Research into distracted driving has created two main classifications: distractions within the vehicle (internal) and distractions outside of the vehicle (external). Both of these compete for the driver’s attention.

The US National Highway Transport Safety Administration outlined four different types of distractions in their analysis of drivers, and this framework is useful for other industries:

• Visual distraction, such as looking away from the road, or at infotainment screens.
• Auditory distraction, e.g., notifications from a mobile phone, or listening to music.
• Biomechanical (physical) distraction, e.g., searching for a control to manipulate, or eating/smoking.
• Cognitive (mental) distraction, such as conversations, or being “lost in thought”.

Of course, in a given situation there may be more than one type of distraction involved and there will be interactions between the above categories. Distractions may come from operational activities (i.e., task-related, such as completing a checklist, communicating via radio or addressing an equipment failure) and non-operational activities (such as social conversations not related to the primary task). In aviation, some activities may be defined as head-down tasks (such as programming a navigation system) that can be a source of distraction.

The human factors approach may include designing environments and equipment to reduce unwanted stimuli; to make important information more salient (or pronounced) and to automate certain aspects of a task. It is also beneficial to schedule complex tasks during times when distractions will be less likely.

Interruptions

Interruptions are generally defined as unexpected events that introduce new tasks, preventing a person from attending to the primary task. This may result in conflict, concentrating on an activity at the expense of another (possibly more critical) activity. Like distractions, they can also result from within the immediate workspace (e.g., from a colleague or an alarm) or they may originate from elsewhere (e.g., a telephone or radio call). These may be referred to as “on-task” and “off-task” interruptions.

There has been significant research into the effect (and management) of interruptions on productivity, particularly since the growth of emails, instant messaging and other electronic notifications.

Incidents have occurred in aviation where flight attendants have entered the cockpit during critical phases of the flight, distracting a pilot from key tasks. The “sterile cockpit” rule (dating from 1981) requires that communications or interruptions during the critical flight phases be limited to urgent safety-related matters:

“No flight crewmember may engage in, nor may any pilot in command permit any activity during a critical phase of flight which could distract any flight crewmember from the performance of his or her duties or which could interfere in any way with the proper conduct of those duties”. The term “critical phases of flight” includes: “all ground operations involving taxi, take-off and landing, and all other flight operations below 10,000 feet, except cruise flight”. [U.S. Federal Aviation Regulation (FAR) – Part 121.542].

In the Kegworth disaster, whilst the pilots were managing an engine fire and diverting to East Midlands airport, their attempts to review events were interrupted by communications with Air Traffic Control and emergency vehicles at the airport.

Are all interruptions bad?

Definitely not. Some interruptions are essential, both during planned work and also if the unexpected happens. Research in aviation has found that the largest category of interruptions came from events that were central to safe flight. Interruptions may provide key information and help us to understand the wider context, provide situation awareness, or cause us to revise our priorities. Therefore, not all of these are disruptive. Tying to eliminate all interruptions would inhibit effective communications.

The impact on human performance

Interruptions can have two main impacts on human performance. Firstly, people may forget what they were doing or about to do. Some researchers have stressed the importance of prospective memory, which is remembering to do something in the future (the act of “remembering to remember“). Secondly, interruptions require switching between two or more tasks, which creates inefficiencies and slows down performance. They do not have to be large or of long duration to have an adverse impact on human performance.

These are both closely related to the topic of situation awareness. Following a distraction or interruption (if this has been recognised!), it may be necessary to re-establish situational awareness by identifying the primary task, assessing at what stage the interruption occurred and then deciding what is necessary to “get back on track”.

Distractions and interruptions break the flow of activities, and safety issues are more likely to arise if this occurs when people are engaged in safety-critical tasks. When an individual’s attention is shifted away from a primary task, there is a potential for error on returning to the primary task. We have limited capacity to manage these in a safe manner. However, it is important to note that not all interruptions lead to human failures or an adverse event.

Here are some ways that distractions and interruptions can have a negative impact on human performance:

• not returning to the original task
• unintentionally omitting key steps when returning to the original task
• purposely taking shortcuts
• a sense of being rushed
• increased feelings of perceived workload
• failing to monitor or interpret key variables
• losing situational awareness.

For both distractions and interruptions, the negative effect may linger once a task has been completed (sometimes called the “hang-over effect”). The time required to resume performance of the primary task following a distraction or interruption is known as “resumption lag”.

Interruptions and “normal work”

In some sectors, interruptions are seen as inevitable and a normal part of doing business. As discussed above, interruptions may happen frequently in many workplaces, but they do not necessarily lead to a human failure or adverse outcome. People are flexible, and are often able to manage interruptions in order to mitigate their impact. There are benefits in understanding why interruptions occur and how people manage these (i.e., understanding normal work).

Managing distractions and interruptions

There are actions that companies can take, relating to the design of workplace and tasks:

• To prevent distractions, consider limiting the number of people in key work areas, such as a control room or cockpit, during critical periods.
• Assign less-critical activities to other people whilst safety-critical tasks are being performed.
• Create clarity around roles and responsibilities: deciding in advance “who will do what” will enable a focus on primary activities.
• Schedule safety-critical tasks and activities during periods that are less prone to distraction and interruption.
• Identify potential sources of disruption and understand their effect on key activities.
• Consider how to limit unnecessary conversations during key activities.
• Defer secondary tasks (e.g. paperwork) to periods of low workload.
• Where possible, design tasks to be conducted sequentially, rather than concurrently.
• Incorporate scenarios that require the management of distractions, interruptions and concurrent tasks into training.

There are also techniques that can be taught for the workforce to practice:

• Following a telephone call or interruption by a colleague or alarm, ask yourself (or the team) two key questions: “Where did we stop?” and “Where are we starting?”.
• There may be opportune moments for interruptions, so carefully time any interruptions based on an appreciation of the work your colleagues are performing.
• Remind team members during pre-start briefings to refrain from interrupting colleagues during critical tasks.
• Raise awareness of the influence of distractions on human performance and the impact on safety-critical work.

Knowledge hub: Distractions and interruptions

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