Part 3:
Heinrichs triangle – a traditional framework
When it comes to preventing fatalities and serious injuries in the workplace, one of the most well-known theories is that of Heinrichs Triangle (also known as Birds Triangle or the safety or accident triangle). One of the most significant developments in health and safety in the 20th century, Heinrichs triangle ‘seeks to develop links between fatal accidents, minor accidents and nears misses’.
In the original conception of the triangle (1931), Herbert William Heinrich theorised that for every major injury or fatality there were:
- 29 minor injuries
- 300 non-injury accidents
Over the years the theory has been developed and the triangle amended (such as by Frank E. Bird in 1966) to show the relationship between accident severity and accident frequency. Bird also claimed that most accidents could be prevented through human intervention.
Relating Heinrichs Triangle to SIFs
More recently, there has been criticism levied at Heinrichs triangle. Its focus on the reduction of minor, common hazards could lead to more serious, less likely risks going unnoticed.
As noted by the Campell Institute in ‘Serious Injury and Fatality Prevention: Perspectives and Practices’, “not all non-injury incidents are equal in terms of their potential for resulting in SIF”. Incidents with the potential to become SIFs are fundamentally different in terms of root causes and context and as such, require a different perspective on the traditional triangle model.
Another criticism of the Heinrich Triangle is its focus on the actions of the victim of the incident. This can lead to systemic safety issues being ignored while exonerating the employer of any responsibility. Rather than focus solely on the worker, the Campbell Institutes report recommends designing work processes in a way that mitigates human error and makes safety dependent on the organizations safety management system.
Measuring SIF strategies
To get an understanding of safety performance, many organizations in the US calculate their TRIF/TRIR (Total Recordable Incident Frequency/ Rate). The TRIF/TRIR is an indicator created by OSHA. This is done by using the following formula:
Number of Incidents x 200,000 / total number of hours worked in a year.
In the UK, this metric is known as the Accident Frequency Rate (AFR) and is calculated the same way as TRIF/TRIR. While it is a commonly used metric, a TRIF/TRIR calculation does not tell the full story.
According to the Campbell Institute, since 1993, TRIR in the US has dropped from about 8.5 recordable incidents per 200,000 working hours to less than 3.0 incidents per 200,000 hours in 2016. However, serious injury and fatality incidence rates have plateaued or increased (US National Safety Council).
In the UK, HSE data from 2023/24 indicates that incident reduction has stalled, with accidental deaths rising by 12% since 2021/22.
This indicates that reportable figures are not enough in gaging safety performance, and that organizations require dedicated SIF prevention strategies.