Heinrich’s theory of accident causation

Why Herbert William Heinrich's work should serve as a guideline for planning safety initiatives

Herbert William Heinrich is regarded by some, as the grandfather of modern occupational health and safety.

He was an employee of the engineering and inspection division of an insurance company. Through his employer he collected data from insurance claims and compiled it to form a theory which he outlined in his book Industrial accident prevention: a scientific approach which he published in 1931.

Within this book he outlines a theory that for every incident that causes a major injury or fatality, there are 29 incidents that cause minor injuries and 300 that cause no injuries, which include property damage and near miss incidents.

He provided a graphical representation of his data in a pyramid that is often referred to “Heinrich’s Triangle”, “Heinrich’s Pyramid” or also “Heinrich’s Law”. The Heinrich 300-29-1 Model is illustrated below.

Heinrich believed the wide majority of accidents were a result of unsafe acts of the worker where his research presented this was the case 88 per cent of the time.

There have been other researchers since, firmly placing this percentage as high as 75 per cent. In my own research of a large cleaning company I calculated 65.5 per cent.

Even today there is plenty of research relying on the principle that by reducing the number of near miss incidents, then the overall number of major incidents will decrease as a result. From my point of view, this principle is logical.

Christchurch in New Zealand was struck by a major earthquake in 2011. As a result, a number of reconstruction projects commenced. One research study set about re-iterating the modern relevance of the Heinrich Safety Pyramid.

Again, Heinrich believed worker fatality would not likely have occurred without a consistent foundation of less severe incidents that led up to the fatality. This study found Heinrich’s theory remained relevant to works in construction.

The ratio calculated in that study (by Seaward and Kestle) was different (higher) than the Heinrich ratio at 1-5-20, however, it was noted Heinrich’s data spanned a number of different industries, not just construction.

Further research in this study found that near miss reporting was not always consistent, which was another likely reason the ratios differed.

In interviews in the area, workers were asked if they felt the Heinrich model was a useful visual tool to which most workers and supervisors agreed it was a useful tool.

They commented the pyramid helped bring into perspective how vital it is to accurately report near miss incidents, alongside major and minor incidents.

It was noted that this approach helps provide a better picture of overall safety at a site and initiate toolbox talks on what workers can do to improve site safety.

Some researchers have criticised Heinrich’s theory because of its heavy focus upon worker error rather than the systems the workers operate within.

They propose that accidents have multiple causes and all aspects of an incident must be fully investigated rather than focus solely upon the failure of one piece of equipment or person.

Heinrich’s theories are ingrained in safety education and it is likely that as the reader of this article, you too, have been taught Heinrich’s theory/s during any safety training or courses you have completed.

As such, for many safety professionals, dislodging Heinrich’s theories is a real challenge. Hence it is important that Heinrich’s work should serve as a guideline for planning safety initiatives.

A focus upon the theory must not be the sole focus as this would leave out a range of hazard related issues, system design matters and the element of organisational culture.

Many safety practitioners (including myself) have long held the belief that frequency breeds severity when it comes to incidents.

This belief has morphed into many theories and ideologies in the safety profession, ultimately stemming from the work of Heinrich.

As a result, many safety professionals place major incidents at the top of their pyramid and strive to reduce the frequency of minor incidents and near misses that sit at the bottom of the pyramid.

Personally, I work by this approach in the pursuit of significantly reducing incidents hence reducing public liability and workers compensation premium costs hence making the overall business safer and more efficient.

Regardless, despite all the efforts of safety professionals and leadership models to reduce accident numbers to zero, accidents still occur.

By my calculations in the cleaning industry a high percentage of incidents can be traced back to human error (65.5 per cent).

Still, it is not as simplistic as always targeting one person’s error. Investigations need to run deeper and examine any series of failures, lapses in judgement or supervision, which may have led to failure in the process.

A good understanding of what is going on within a company at all levels is important to effective safety management and an opportunity to improve safety culture.

Whilst it is important to learn from past mistakes, this approach only provides a small view of what is really needed – hence proactive and preventative safety approaches are vital.

The researcher Frank Bird took Heinrich’s model a little further presenting that a pyramid with a ratio of 1-10-30-600 was more likely to occur with 1 reported major injury for every 10 reported minor injuries, 30 incidents resulting in property damage, and 600 near miss incidents.

On a final note, it is also important to note that when there is too heavy a focus upon worker failure as a root incident cause, then management is often let off the hook as a causal factor, hence blaming the worker may sometimes be seen as a path of less resistance.

It is important that an overall approach to incident investigation is taken to provide the best opportunity for incident reduction in the workplace.

Dr Denis Boulais is national safety manager at Broadlex Services 

This article first appeared in INCLEAN Australia magazine 

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