In 1931, H.W. Heinrich reported on a study of accidents that he classified according to severity. Heinrich's report showed that for each serious-injury incident, we could expect about 29 minor injuries and 300 near-miss or property-damage incidents. His conclusions are often depicted with a pyramid or triangle indicating a single serious incident at the peak and a broad base of non-injury incidents.

In 1969, the Insurance Company of North America conducted a subsequent and more thoroughly documented study using more than 1.7 million incidents reported by nearly 300 companies in 21 industrial groups. That study revealed a similar pattern with slightly different ratios. For each serious injury, there were 10 minor injuries, 30 property-damage incidents and 600 near-miss incidents that resulted in no injury or property damage.

These relationships may be accurate for large populations and are often used to stress the importance of paying attention to details. The concept is that if the small incidents (near misses and property-damage incidents) continue to occur unabated, that eventually, one of the serious injuries will occur. To a certain degree this may be true. You may have heard someone say that the only difference between a near miss and a serious injury is timing — a matter of seconds or inches. And, certainly it is important for each worker to master the fundamentals of occupational safety to prevent injury and property damage. But there is a risk in limiting the focus to the causes of minor-injury and non-injury incidents.

When applying the ratios of the Heinrich and North American models, it has been suggested that we focus our safety efforts on preventing less-serious events as an indirect means to prevent a single serious event. One should consider the causal relationships. Is it always true that serious injuries are caused by the same factors that cause less-serious incidents? Do the conditions and practices that apply to slip, stumble or back-strain injuries differ from those that apply to falls from elevation, getting caught in machinery, being struck by falling material or electrocution? One must also consider the allocation of resources. How much effort will it take to reduce the base of the pyramid enough to affect the peak?

While the pyramid theory is interesting and important to understand, perhaps we should consider a more direct approach to accident prevention. Through a risk assessment, operators can identify specific work processes and perform a simple evaluation of the associated risk (a function of the likelihood of a potential incident and level of severity of that incident). The conditions and practices associated with the most risk (most likely to result in severe injury) are addressed first. These represent the peak of the pyramid. Those with a remote possibility of a minor injury or property damage (the base) are assigned lower priority and may be addressed individually when the higher priority risks are controlled.

Clearly, some of the same conditions and practices that contribute to minor incidents also contribute to serious incidents. Sometimes the difference is only a matter of inches or seconds. However, consider that the relationship is two-way. The pyramid theorists advise attacking these root causes to affect the peak indirectly. By taking the direct approach, you affect the peaks directly and the base indirectly by controlling the factors that simultaneously affects the potentially serious incidents and the minor incidents. In fact, a thorough analysis of most-serious workplace risks generally reveals at least one basic, fundamental control that applies across the board. Only by addressing the most-serious risks directly can you be confident that the most-serious injuries can be prevented.

Randy K. Logsdon, CMSP, has degrees in education and occupational safety. Comments may be sent to him by e-mail at rlogger@comcast.net