Safety models and accident models
What are the main factors that allow systems to operate safety?


Heinrich’s domino model A safety model is a set of beliefs or hypotheses (often implicit) about the features and conditions that contribute to the safety of a system. An accident model is a set of beliefs on the way in which accidents and incidents occur in a system and the causal factors that make them possible. The mental models concerning safety are important because they impact system design, operational decisions and behaviours.

We analyze a few accident models and safety models to understand the implicit assumptions underlying the models:

  • H. Heinrich’s domino model of accident causation
  • H. Heinrich’s and F. Bird’s safety triangle, the companion safety model
  • epidemiological accident models such as J. Reason’s famous Swiss cheese model
  • the bow-tie model of accident causation and the role of barriers
  • a loss of control safety model
  • J. Rasmussen’s drift into failure model

This submodule is a part of the hazard analysis module.

Course material

Safety models and accident models

Lecture slides (PDF)

Assessing risk controls using bow-ties

Lecture slides (PDF)