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Safety Triangle

Last updated: September 27, 2018

What Does Safety Triangle Mean?

The Safety Triangle, also known as the Safety Pyramid, the Heinrich Triangle, and the Bird Triangle, is a theoretical model that describes a stable ratio between workplace incidents of varying degrees of severity.

The traditional ratio given by the Safety Triangle is 1-10-30-600, which denotes one serious injury (resulting in fatality, disability, lost time, or professional medical treatment) for every 10 minor injuries (resulting in first aid), every 30 accidents (resulting in property damage), and every 600 safety incidents.

Safeopedia Explains Safety Triangle

The Safety Triangle operates under the assumption that the vast majority of safety incidents are caused by unsafe acts and that the same behaviors that lead to near-misses also lead to serious injuries. Under this premise, the stability of the Safety Triangle’s ratio implies that reducing the rate of higher-prevalence incidents at the bottom of the triangle (i.e. the “600”) is also the most efficient way to reduce the rate of more severe workplace injuries.

The original “accident pyramid” published by Herbert Heinrich in 1931 purported that in a grouping of 330 similar accidents, one will result in serious injury (fatality, disability, lost time, medical treatment), 29 will result in minor injury (first aid), and 300 will result in no injury.

In 1969, Thomas Bird conducted a follow-up study to Heinrich’s work using a larger, more-randomized sample size (1,753,498 accidents). He found a ratio of one serious injury for every 10 minor injuries, 30 property-damage accidents, and 600 near-miss safety incidents. Due to the rigor of the study, this 1-10-30-600 ratio was accepted as an archetypal ratio in occupational health and safety.

The most-recent major Safety Triangle-type study was undertaken by ConocoPhilips Marine in 2003, and it placed the Safety Triangle within a modern occupational health and safety context. It found that for every single fatality there are at least 30 lost workday cases, 300 recordable injuries, 3,000 near misses (estimated), and 300,000 behaviors not consistent with proper safety procedures (estimated).

The Safety Triangle model’s conception of a stable ratio between accidents of varying severity implies that effective hazard controls and safety training will reduce at-risk behaviors and, in turn, reduce the overall number of severe accidents. The effectiveness of this theory is not universally recognized. Some health and safety professionals view it as a detriment to efforts to effectively deal with high-severity, low-probability safety hazards, and they have pointed out that some U.S. firms with award-winning low injury rates have also suffered some of the most catastrophic incidents in recent memory. These critics argue that a focus on the Safety Triangle may direct too much focus on worker behavior and distract from a necessary consideration of how the worker’s operating environment and the systems within it act as risk factors.



Heinrich Pyramid, Heinrich Triangle, Safety Pyramid, Bird Triangle, Bird’s Triangle, Loss Control Triangle

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