Looking at Early Accident Models for Safety Management at Work

By RRC

Accident models, used to evaluate how accidents happen, didn’t just appear by, well, accident. Health and safety experts have gained insights over the years as to how accidents happen, and these insights have helped to evolve current thinking about health and safety. Let’s take a look at some early models, which, although they’ve been replaced by more complex models, still have value in helping you understand that accidents are the result of a series of events.

In 1931, an American safety expert named HW Heinrich proposed a simple model for accident causation. He saw accidents as resulting from a simple sequence of events, with 88 per cent caused by the unsafe acts of people, 10 per cent by unsafe conditions and 2 per cent by ‘acts of God’.

Heinrich proposed a ‘five-factor accident sequence’ in which each factor leads to the next, much like toppling dominoes lined up in a row. This creates a nice simple model for accident prevention, because all you have to do is remove one domino (or factor) to prevent the final outcome of damage or injury.

Heinrich’s five-factor accident sequence consisted of the following factors:

  1. Ancestry and social environment

  2. Employee fault

  3. Unsafe act, together with mechanical and physical hazard

  4. Accident

  5. Damage or injury

Factors 1 and 2 are rather quaint and probably politically incorrect these days, since 1 is described further as ‘recklessness, stubbornness, greed and other undesirable traits of character’ and 2 includes ‘violent temper, nervousness, excitability’ – but this was back in 1931! However, this linear causal chain does provide you with a way to track back to the underlying factors that have led to a given accident, helping you to look for clues about its causes and how it may have been prevented.

F Bird and G Loftus (both safety researchers) extended Heinrich’s theory in the 1970s, replacing ‘the reckless employee with the violent temper’ with ‘lack of control by management’. This approach is more enlightened and in tune with current thinking on managerial responsibility for risk control.

Modern theories recognise that many accidents don’t have a single cause but instead have multiple causes, and each of these causes has multiple root causes. However, early theories on accident causation can offer an initial perspective for considering how accidents may be caused.