(1) Accident causation model originally postulated by HW Heinrich which states that an injury at work is invariably the result of an accident which is the consequence of an unsafe act or condition generated by the fault of some person. Faults of person are in turn described as the result of genetic and social factors. If these are represented by 5 dominoes standing on end the 'inevitable' causal chain can be demonstrated. Modern approaches now tend to favour multi causality theory rather then the narrow causal path of the domino theory. (2) Heinrich's model was updated by Frank Bird who replaced the term unsafe acts and conditions with substandard acts and conditions. 'Faults of person' was altered to job factors and personal factors and the initiating domino (genetic and social) was given the label 'management system failures'. Bird also added the attribute of chance to the result by adding categories of damage and near miss accidents at the result end. See: Multi Causality Theory