Accident / Incident Ratio Studies (F.E Bird Triangle)

The accident triangle, also known as Heinrich's triangle or Bird's triangle, is a theory of industrial accident prevention. It shows a relationship between serious accidents, minor accidents and near misses and proposes that if the number of minor accidents is reduced then there will be a corresponding fall in the number of serious accidents The triangle was first proposed by Herbert William Heinrich in 1931 and has since been updated and expanded upon by other writers, notable Franck E. Bird. It is often shown pictorially as a triangle or pyramid and has been described as a cornerstone of 20th century workplace health and safety philosophy. In recent times, it has come under criticism over the values allocated to each category of accident and for focusing only on the reduction in minor injuries.

There is no shortage of data on incidents such as accidents or near misses. Some researchers have studied the figures in details and concluded that there appears to be a relationship between the numbers of different types of accident.

Most health and safety professionals have come across Bird's triangle, which theories a relationship between the number of near misses and injuries. Alan Field considers whether it is still relevant in controlling accidents.

Accident Triangles - often called Bird's ( or Heinrich's) triangle - are based on a theory of industrial accident prevention and particularly a human factors approach to safety. 

F. E Bird used accident data to produce the following accident triangles. other researchers have produced similar accident ratio triangle:

F.E Birds accident triangle

Heinrichs Pyramid

Further, there is also a Triangle given by 

1. Labor Force Survey 1990
2. Reporting of injuries, Diseases and Dangerous Occurrences Regulations 2013 ( RIDDOR) classifications.  
3. Heinrich's Accident Triangle

the actual figures very between the different accident triangles but the important thing to note is that, for every major incident or fatality, there are many more less serious or near-miss incidents.

Analysis also shows that:

• It is invariable a matter of chance whether a given event results in injury, damage or a near miss, i.e. near misses could so easily become more serious incidents.
• Near-miss/less serious incident data can, therefore, be a useful predictor of accident potential.
• All  events are due to failure to control - so we can learn form even minor incidents.

The data from these triangles has a number of limitations that you need to think about before trying to apply it:

• Not every near miss or minor incident involves risks which could actually have led to a serious incident or fatality.
• Be careful comparing:

            -    Different triangles.

            -    Different definitions ( e.g. lost-time accidents).

            -    Different industries ( with different types of risk).

• Statistical significance - you need a certain amount of representative data for a meaningful comparison between your workplace and industry as a whole.