Normal incidents

In 1984, the late sociologist Charles Perrow published the book: Normal Accidents: Living with High-Risk Technologies. In this book, he proposed a theory that accidents were unavoidable in systems that had certain properties, and nuclear power plants had these properties. In such systems, accidents would inevitably occur during the normal course of operations.

You don’t hear much about Perrow’s Normal Accident Theory these days, as it has been superseded by other theories in safety science, such as High Reliability Organizations and Resilience Engineering (although see Hopkins’s 2013 paper Issues in safety science for criticisms of all three theories). But even rejecting the specifics of Perrow’s theory, the idea of a normal accident or incident is a useful one.

An incident is an abnormal event. Because of this, we assume, reasonably, that an incident must have an abnormal cause: something must have gone wrong in order for the incident to have happened. And so we look to find where the abnormal work was, where it was that someone exercised poor judgment that ultimately led to the incident.

But incidents can happen as a result of normal work, when everyone whose actions contributed to the incident was actually exercising reasonable judgment at the time they committed those actions.

This concept, that all actions and decisions that contributed to an incident were reasonable in the moment they were made, is unintuitive. It requires a very different conceptual model of how incidents happen. But, once you adopt this conceptual model, it completely changes the way you understand incidents. You shift from asking “what was the abnormal work?” to “how did this incident happen even though everyone was doing normal work?” And this yields very different insights into how the system actually works, how it is that incidents don’t usually happen due to normal work, and how it is that they occasionally do.