The myth of the "safety pyramid"

August 5, 2013  |  Best Practices

One of the deeply embedded myths of the safety profession is Herbert William Heinrich's  "safety pyramid." Based on Heinrich's research during the 1930s, he proposed that for every 330 accidents, 300 would result in no injuries, 29 would result in minor injuries and one would result in a major injury.

This theory came to be accepted as the norm for occupational safety for many years, and continues to have a major influence on the ways in which executives and leaders think about it. However, modern methods of examining the causes of accidents prove that the safety pyramid is not a valid tool for injury prevention.

Heinrich believed that unsafe acts of workers were the main causes of occupational accidents. This led to an almost mythical acceptance of the idea that reducing accident frequency would cause a corresponding decrease in the number of severe injuries. But injury statistics from the past 10 years, compiled across many industries, contradicts Heinrich's theory. This data shows that minor injuries have steadily declined, but major injuries have stubbornly remained the same.

Often, companies only look at lost-time injury statistics, which simply show who got hurt and where - but reveal nothing about the underlying causes of these injuries. Two people can have similar injuries, but the causes of them could be completely different. A 2010 study by Behavioral Science Technology (BST) found that serious injuries have different underlying causes than minor ones. In many cases, the causes of a serious incident are much more complicated than that of a minor incident:

"These underlying factors - missing controls, lax procedures, badly designed equipment - create high-risk situations that are likely to lead to a major incident. Thus identifying and addressing these high-risk situations, or 'precursors,' is the key to preventing major accidents. A precursor is any high-risk practice that has not been recognized and corrected. It could, for example, be a safety control that is routinely ignored. In such a case, the company could go for years with very low lost-time injury rates. Then a worker is killed.

To identify and address precursors, companies need not only to examine their procedures, safety observations and audits but also to analyze incident data to distinguish between the small number of incidents that had the potential to be serious and all the rest, which did not."

Current research says that it's often a unique combination of factors that leads to an accident. A case in point was BP's Deepwater Horizon oil platform explosion in 2010. The report prepared by BP personnel following this high-profile accident states, "The team did not identify any single action or inaction that caused this incident. Rather, a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces came together to allow the initiation and escalation of the accident."

This is consistent with the post-accident analyses that several VISTA employees have had to perform during their tenure with mines in the oil sands of northern Alberta. The same exact mine or equipment maintenance procedure was carried out, day after day, thousands of times a year. Nothing bad ever happened. But the one time it did, some small factor was different that led to an unforeseen fatal accident.

Improving the work system - which includes administrative controls, engineered controls and personal protective equipment (PPE) - is the most effective way to improve safety, rather than simply focusing on worker behavior. Training needs to cover all of these bases in order to be effective.

Research sources:

  1. Is safety pyramid a myth? Study suggests new approach to injury prevention - Canadian Occupational Safety, September 8, 2011.
  2. Examining the foundation - Safety & Health Magazine, October 1, 2011.
  3. Reviewing Heinrich: Dislodging Two Myths From the Practice of Safety - Professional Safety, October 2011.


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