Analysis of safety functions and barriers in accidents

A new method for accident investigations is presented. It is based on the concept of safety function, which is defined as a technical or organisational function, a human action or a combination of these, that can reduce the probability and/or consequences of accidents and other unwanted events in a system. An analysis starts with the identification of safety functions related to the event. These are structured; an assessment is then made of whether they worked or not, and finally safety improvements are proposed.The method has been applied to five different incidents, coming from different types of work sites, such as electrical power distribution, a railway, and hospitals. For each case, around 40 safety functions were identified, of which less than half had worked. It was found that technical, organisational and human safety features existed side-by-side. The method supports a consistent analysis of a variety of safety features, and can integrate them into a common format.Each system contained formal and informal elements in parallel, often overlapping. This can be seen as safety redundancy, which makes the safety system less vulnerable to change that supports the preservation of safety. It might be more adequate to describe this as a safety web rather than a distinct set of barriers, and there is also an analogy with the concept of safety resilience.