Heinrich's precursors of unsafe acts and conditions -- social environment and ancestry, and fault of the person -- have been challenged by some as being overly class-conscious, and even racist. Similarly, ideas about causality have become more sophisticated, making the domino theory seem too simplistic. In Heinrich's own words, "each accident was assigned either to the unsafe act of a person or to an unsafe mechanical condition, but in no case were both personal and mechanical causes charged".
The industrial safety pioneer explained that he would assign an accident caused by the use of a badly mushroomed (damaged) chisel as an unsafe act rather than an unsafe condition. His over-simplification and bias towards the unsafe acts cause render as unreliable his view that these were responsible for 88% of accidents, with unsafe conditions accounting for a further 10% (the other 2% were "unpreventable"). Clearly, this rationale is of little use in more sophisticated, modern investigations.
These criticisms of Heinrich's work have led some safety professionals to dismiss all his ideas. But if you read the news of prosecutions in any issue of IOSH Magazine, the role of unsafe acts and unsafe conditions is still apparent: companies allow employees on to unsafe roofs; they provide unsafe ladders. Though we may want to forget about the other dominoes, it is hard to argue that the conditions and acts in the table are seldom part of the network of events contributing to accidents and injury.
A checklist of unsafe acts and unsafe conditions is not a means of attributing blame
A report by the UK Health and Safety Executive on the pitfalls of risk assessment (bit.ly/2vvrRfo) said a "structured, systematic approach" is needed to pinpoint hazards. This should account for "substances, machinery/processes, work organisation, tasks, procedures and the people and circumstances in which the activities take place, including the physical aspects of the plant and/or premises".
The report supports this advice with a case study in which a critical decision was left to local plant management in a predictable emergency rather than fully assessing the situation and determining the best approach in advance. This is an example of an unsafe act being the result of an unnecessarily unsafe condition having been allowed to develop.
One approach to reusing Heinrich's categories would be to work through the hazard identification process twice -- once to see whether all the unsafe conditions that could be created have been considered, and again to consider all the reasonably foreseeable unsafe acts that might need to be mitigated. A checklist of unsafe acts and unsafe conditions is not a means of attributing blame, but an added layer of verification in a "structured, systematic" way of identifying all the reasonably foreseeable hazards.
Heinrich's list of unsafe acts and conditions was developed for the industries he was working with in the middle of the 20th century. Some of these remain relevant, but to reflect 21st century concerns we might want to add some new ones.
Unsafe acts might now include driving or walking while distracted by mobile technology, bullying and harassment, using inappropriate handling techniques, and allocating tasks to staff or contractors without checking their competence. Unsafe conditions could be expanded to take in complex systems instituted without adequate training, stressful environments and unsuitable or missing systems of work.
Heinrich's 1959 list
Operating without clearance or warning
Operating or working at unsafe speed
Unguarded, absence of required guards
Making safety devices inoperative
Defective, sharp, slippery, cracked, etc
Using unsafe equipment, or using equipment unsafely