Incident Ratio studies

There have been many studies which relate the number of major injury incidents to minor injury incidents to property damage incidents to near-misses.

One of the most widely accepted studies was completed by Frank E. Bird Jr. in 1969.  This study involved an analysis of 1,753,498 incidents reported by 297 companies representing 21 industrial groups and 1,750,000 employees.  This study revealed that for every major injury and illness (e.g. death, disability, lost time or medical treatment), there were 9.8 minor injuries and illnesses (e.g. first aid cases).

The study also indicated that there were approximately 30 property damage incidents and 600 near-misses occurring for every major illness and injury.  It is accepted that even though this study relates primarily to injuries, illnesses, property damage accidents and near-misses, many of these events have the potential to produce environmental losses as well.  Therefore the ratio also has significance for environmental incidents.  The results of Bird’s ratio study are represented in Figure 1.

Experience shows that the differences between minor and major incidents are often fortuitous.  In addition, the same “system” failures which cause particular types of incidents (such as injuries) often cause other types of incidents as well (such as environmental spills and property damage incidents).  The 1-10-30-600 relationship indicates a tremendous opportunity to prevent serious and major events if a process exists to identify, investigate and correct the system’s problems associated with minor injuries, illnesses and property damage incidents, as well as near-misses.

Even though the information gained in the Bird study is timeless, there have been other more recent studies which support its findings.  In 1993 the Health and Safety Executive (HSE) group of the British government published the results of one of its studies.  The study was conducted by a team of professionals, including economists, who visited five different locations representing different industry types.   

The relationship of major injury incidents to minor incidents to no-injury incidents was 1 to 7 to 189 (near-miss type incidents were not addressed in this study).  The 1993 ratio study results from the Health and Safety Executive are illustrated in Figure 2.

Other interesting findings of the British research include: 

1. One organisation lost up to 37% of its annual profit due to incident costs. 

2. One organisation lost the equivalent of 8.5% of its product’s total annual revenue due to incident costs. 

3. One organisation lost the equivalent of 5% of its operating budget due to incident costs. 

4. Although there was a wide range of immediate causes for the incidents, there were very common root causes. 

5. A separate analysis of 80% of the incidents showed that over 8% had the potential to have serious or major consequences.

Considering these studies together, it can be seen that there is a fundamental relationship between major incidents, minor incidents, and near-misses.  The exact numbers are not important; rather, the studies tell us that our best results can be achieved by focusing on all events not simply major injuries and illnesses.

Even near-misses and minor incidents should be investigated because they provide valuable information on the causes which lead to major events. They are in effect “free lessons” and, as such, should be taken full advantage of.

As a point of interest, some make the argument that minor incidents tend to occur while people are engaged in routine types of work, whereas more serious incidents occur while people are doing relatively hazardous, non-routine work.   

Therefore, they argue, using incident ratios do not provide much help.  They are missing the point.  The fact remains that incidents occur in such a way that there are many more minor events than serious events.  We must give a significant amount of our attention to the less serious incidents so we can identify the causes of all incidents and correct those causes before serious incidents occur.

In addition, the SHEQ processes should be designed to identify the significant aspects of work that place employees at greatest risk.  

These SHEQ processes should also ensure that the control actions needed to prevent serious incidents are implemented.  Efforts must be focused where they will have the greatest impact.  This is best achieved by analysing the total incident picture, not simply significant incidents.

While ideally it is hoped that work can be done in an environment that is free of incidents, this is neither economically feasible nor practical to achieve.  The only way to guarantee this is to shut down the operation. 

Therefore a practical definition of safety is the “control of accidental losses to an acceptable level”, or “ the minimisation of loss”.  

Our final definition is LOSS, which we define as avoidable harm to people, property, processes or the environment or “the avoidable waste of a resource.”