The chain is both a tool and a symbol that is familiar to one and all. The dictionary contains basic definitions of what a chain is and then follows with many pairings of words such as chain armor, chain feed, chain reaction, etc. This reflects the fact that chains are used in a variety of applications throughout the world. Concepts of chains are also used in metaphors such as chained to a desk, chained to the past, chains of oppression, and many others. Various analogies that are commonly used include chains of stores, chain letters, and chains of episodes. Almost inseparable from any thinking involving a chain is the notion that a chain will fail at its weakest link. When dealing with a broken physical chain, examination of the failure will indeed reveal that one link failed completely (although more than one link may show impending failure), and that the point of failure surely must have been the weakest link. Most of us learn this outlook early on in our lives, and carry the thought through to many of the basic views we have of how the world works.

In the safety profession, we frequently use a chain analogy in describing incidents or accidents and their causation. This most commonly takes the form of relating an incident to a chain of events. Within this chain of events, we look for the weak link as a means of identifying what went wrong and allowed the incident to occur. We then very often go further and identify a specific human error that was made, and the person who made it. That person, and/or what they did or didn't do, is thought of as a weak link in the sense of a "performance" chain. Prospective corrective actions to prevent recurrences usually center on strengthening this weak link. This approach is so fundamental to widely accepted problem solving techniques that few people look for or see any flaw in it. But there are in fact major problems with applying the chain analogy in this manner. These problems fall into three significant categories and present substantial obstacles to improvement of incident prevention. Learning to rethink the chain of events analogy presents quite a challenge to some of our basic concepts of how things work, but also presents real opportunities to make big improvements. The chain analogy is in fact a useful map if we take on some new thinking to avoid using it incorrectly.

The three main problems that the traditional thinking about the chain of events analogy can lead to are:

  1. The very notion of a chain invokes an image of a linear sequence and can lead to a failure to acknowledge the multivariable nature of outcomes in systems where people are involved. That is to say that there are in fact many different possible paths to an incident. A consequence of ignoring multivariable outcomes is the incorrect notion that any one change or interruption in "the chain" will prevent an incident. In reality, this wishful thinking is seldom the case.

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