What Safety Leaders Need to Know about “Nested Interruptions”

Posted by
Lance Roux
on Mar 21, 2017

One of the benefits to safety leaders who have a medical background (and keep dipping that toe into the pool from time to time), is the volume of human factors research that’s being generated by medical professionals.  I would imagine that the aeronautics is much the same, although my experience resides much more squarely in the former than the latter.

The Human Factors and Ergonomics Society does a lot of work in this area, and there’s a lot of applicability in terms of how we design, implement, and maintain programs for operational safety in the occupational environment.  Some of the concepts in current studies and research have obvious impacts on safety leaders in high-hazard high reliability organizations (HROs), and these are the areas where we can learn the most.

Nested Interruptions

Recent research in the journal Human Factors looks at a phenomenon known as nested interruptions (Sasangohar, Donmez, Easty, & Trbovich, 2017).  A nested interruption occurs when tasks are interrupted in succession.  Basically what occurs is a person begins one task and is interrupted to perform a second task when another interruption occurs, and a third task results from the second interruption.  This interruption is considered nested.  These nested interruptions can occur up to the point where the person has multiple tasks/activities in progress and is significantly delayed returning to the original tasks.

Unsurprisingly, the research notes that the participants in the study perform poorly when resuming interrupted activities, especially those which are complex.  A study measuring these effects noted that the nested interruption increased activity error frequency by a factor of 10 (Sasangohaar et al., 2017).

Applicability to Safety Leaders

There are a couple of aspects of this research that are applicable to operational safety that transcend the world of patient safety.  Aviation uses the sterile cockpit concept to minimize interruptions to pilots, which has been related to a number of near misses and aircraft incidents.  As per 14 CFR 121.542 crewmembers of an aircraft, including the command personnel, are not permitted to engage in any other activity other than what is necessary for safe operation of the flight during critical phases e.g. grounds ops, departure/arrival, flight ops below 10,000’.  As aircraft passengers, we know this period as the anxious part of the flight where have to disable and stow electronics.

There are also safety-critical tasks and activities that occur in different phases of work on projects, jobsites, and an organization’s own facilities.  Increasing the odds of an error by a factor of 10 (Sasangohar et al., 2017) translates to an order of increase, not reduction, to risk.

The takeaway for safety leaders is this: create and maintain an environment in which personnel who have safety critical activities are prevented from being interrupted.  As the complexity of the tasks increase, this environment becomes paramount to the prevention of conditions that increase the likelihood of an error.  This can be handled a number of different ways on project sites or work location depending on the availability of resources, using the hierarchy of controls as guidance.

If the organization operates in an environment where interruptions are inevitable and pose a real risk to the safe completion of safety-critical activities, safety leaders can designate a person-in-command for the safety critical activity, leaving the site leadership available to handle interruptions.  Another option is creating a sterile environment, where personnel adopt the culture of understanding roles and responsibilities in critical phases of work and operation.


Legal Information Institute. (n.d.). 14 CFR 121.542 – Flight crewmember duties.  Retrieved from https://www.law.cornell.edu/cfr/text/14/121.542

Sasangohar, F., Donmez, B., Easty, A.C., & Trbovich, P.L. (Jan. 2017). Effects of nested interruptions on task resumption: A laboratory study with intensive care nurses. Human Factors. doi: 10.1177/0018720816689513

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Tags: safety leadership

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