U is for unsafe acts and conditions

The terms “unsafe acts” and “unsafe (mechanical or physical) conditions” appear in HW Heinrich’s book Industrial Accident Prevention as the central domino in his accident causation sequence. Between the 1941 and 1959 editions, the list of unsafe conditions grew, so that each list had nine items (summarised in the table below).

Image credit: © iStock/koya79

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

Unsafe acts

Unsafe conditions

Operating without clearance or warning Inadequately guarded
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 Unsafely arranged, poor housekeeping, congestion, blocked exits
Taking unsafe position or posture Inadequately lit, sources of glare, etc
Working on moving or dangerous equipment Inadequately ventilated, impure air source, etc
Distracting, teasing, abusing, startling etc Unsafely clothed, no PPE, high heels, etc
Failure to use safe attire or PPE Unsafe processes: mechanical, chemical, electrical, nuclear 




Bridget Leathley is a freelance health and safety consultant, providing risk management support in facilities, retail and office environments.  She delivers face-to-face safety training including IOSH and bespoke courses, and contributes to e-learning courses through evaluations and design work.  She has been writing for health and safety publications since 1996.  


  • One could reasonably argue

    Permalink Submitted by Mike Flannery on 19 September 2017 - 12:51 pm

    One could reasonably argue that all unsafe conditions are created by the unsafe 'act' (or omission) of another, be they operative or Chief Executive Officer via their management team. All unsafe conditions have in the main been created by an unsafe act somewhere in the system. Whilst you can argue percentages, he was right then and is right now and despite the industry's dubious sophistication in relation to causality, the courts appear to support your assertion that unsafe acts and conditions are essentially the bedrock of most accidents. If we dismiss Heinrich's concept of unsafe acts or unsafe conditions because we don't have access to his research material, then we risk throwing the baby out with the bathwater.


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