Systems model of construction accident causation

The current approach to safety focuses on prescribing and enforcing "defenses;" that is, physical and procedural barriers that reduce the workers' exposure to hazards. Under this perspective, accidents occur because the prescribed defenses are violated due to lack of safety knowledge and/or commitment. This perspective has a limited view of accident causality, as it ignores the work system factors and their interactions that generate the hazardous situations and shape the work behaviors. Understanding and addressing these causal factors that lead to accidents is necessary to develop effective accident prevention strategies. This paper presents a new accident causation model of the factors affecting the likelihood of accidents during a construction activity. The model takes a systems view of accidents-it focuses on how the characteristics of the production system generate hazardous situations and shape the work behaviors, and analyzes the conditions that trigger the release of the hazards. The model is based on descriptive rather than prescriptive models of work behaviors-it takes into account the actual production behaviors, as opposed to the normative behaviors and procedures that workers "should" follow. The model identifies the critical role of task unpredictability in generating unexpected hazardous situations, and acknowledges the inevitability of exposures and errors. The model identifies the need for two accident prevention strategies: (1) reliable production planning to reduce task unpredictability, and (2) error management to increase the workers' ability to avoid, trap, and mitigate errors. The new causation model contributes to safety research by increasing understanding of the production system factors that affect the frequency of accident. The practical benefit of the model is that it provides practitioners with strategies to reduce the likelihood of accidents.