Heinrich Accident Ratio

One of the first researchers was H. W. Heinrich (1931) whose accident ratio showed that for every 330 accidents (undesired events) there were 300 accidents that caused no injury, 29 that caused minor injury, and only 1 that caused a serious or major injury. The conclusion was that for every injury-causing accident there were numerous other undesired events (near miss incidents) that had the potential to cause injury (Model 2.1). 

When this research was done in the 1930s, the term near miss incidents was not yet used and these were referred to as accidents (with no injury). These 300 noninjury accidents could be termed near miss incidents if no damage or interruption occurred. This led industrialists to think abont the noninjury accidents and give attention to them. 

MODEL 2.2 The Pearson accident ratio. (From the British Safety Council. 1974/1975 Tye-Pearson theory. With permission.) 

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In 1969, a study of industrial accidents was undertaken by Frank E. Bird, Jr., who was then the Director of Engineering Services for the Insurance Company of North America. He was interested in the accident ratio of 1 major injury to 29 minor injuries to 300 no-injury accidents first discussed in the 1931 book Industrial Accident Prevention by H. W. Heinrich. Since Mr. Heinrich estimated this relationship and stated further that the ratio related to the occurrence of a unit group of 330 accidents of the same kind and involving the same person, Mr. Bird wanted to determine what the actual reporting relationship of accidents was by the entire average population of workers [6]. 

Most people involved with workplace safety are aware of the iceberg theory, the safety triangle, or its correct terminology, the accident ratio. For every recorded injury or loss sitting above the surface, there are many unrecorded near miss incidents submerged below the surface. This was first proposed by H. W. Heinrich in 1931 when he published his 1 29 300 ratios. 

The accident ratio (first discussed by H. W. Heinrich in the 1930s [1931]) has a clear message ... 

Studies of accidents resulting in major or lost time injury, minor injuries, property damage and near misses over the last sixty years have produced a number of accident ratios. The principal objective of these studies was to establish a relationship between near misses and other categories of accident. The various accident ratios produced by Heinrich (1959), Bird (1966), the British Safety Council (1975) and the HSE (1993) are shown in Fig. 4.7 (see p. 114). 

The number of reported near accidents per reported lost-time injury. According to Heinrich, this ratio should be of the order of 300 1. In practice, far lower ratios are acceptable. The total number of recordable incidents (lost-time and first-aid accidents and near accidents) per lost-time injury (TRI/LTI) is a variation of this... 

W. H. Heinrich from America had attempted amore in-depth study on near miss. He investigated more than 5,000 injuries and found that in 330 similar accidents 300 accidents caused no injuries, 29 cases caused minor injuries along with 1 caused serious injury. That is to say, serious injury, minor injury and no injury accident number ratio is 1 29 300, which is the famous Heinrich law, called the accident triangle, as shown in Figure 3. 

At ASSE Professional Development Conferences, always, one or more speakers inform attendees that 90% of accidents are principally caused by unsafe acts of employees. How pitifully unprofessional Heinrich s 88 10 2 ratios were the conventional wisdom years ago. They have been found to be untenable. 

A great many safety practitioners have adopted the premises on which the 88 10 2 ratios are based, and they apply them to this day. Of all the Heinrich concepts, his thoughts pertaining to accident causation, expressed as the 88 10 2 ratios, have had the greatest impact on the practice of safety and have done the most harm. Why harm Because when basing safety efforts on the premise that man failure causes the most accidents, the preventive efforts are directed at the worker rather than on the operating system in which the work is done. 

Heinrich recognized that other studies on accident causation identified both unsafe acts and unsafe conditions as causal factors with almost equal frequency. Those studies produced results different from his 88 10 2 ratios, and Heinrich commented on those differences. For example, he cited the National Safety Council as a resource on such studies (Citation 22). 

Thinking about the changes made in the second and third editions and carried over into the fourth edition, the 300 29 1 ratios present serious conceptual problems. To which types of accidents does In a unit group of 330 accidents of the same kind and occurring to the same person apply Certainly, it does not apply to some commonly cited accident types falling to a lower level, stmck by objects, and so on. Keep this point in mind as you get to understand how Heinrich defined the 300, the 29, and the 1 —discussion of which follows. 

Not only have many safety practitioners used the 300 29 1 ratios in their statistical presentations, but they have also misconstrued what Heinrich intended with respect to the terms major injury, minor injury, and no-injury accidents. In each edition, Heinrich gave nearly identical definitions of the accident categories to which the 300 29 1 ratios apply. This is how the definition reads in the fourth edition. 

While a particular type of unsafe act may be performed many times before a particular type of accident occurs resulting in serious injury, it should not be assumed that such is always the case. Particularly, it is not the case in a very large majority of the incidents resulting in death or serious injury. Also, recall that for Heinrich, a serious injury—the 1 in his 300 29 1 ratios—is any injury that requires more than first aid. 

To sum up, Heinrich s attempt at developing a method to discover the total costs of accidents was noteworthy. But, the 4-to-l ratio cannot... 

Heinrich s 88 10 2 ratios indicate that among the direct and proximate accident causes, 88% are unsafe acts, 10% are unsafe mechanical or physical conditions, and 2% are unpreventable. 

In the 1930s, Heinrich smdied the relative role of unsafe acts and unsafe conditions. He concluded that 88% of cases involved unsafe acts, 10% involved unsafe conditions and 2% had no preventable cause. A different study in the 1960s by the State of Pennsylvania found both unsafe acts and unsafe conditions were causes for nearly every accident studied. The ratio between the two causes is irrelevant. Any ratio does not provide a suitable strategy when analyzing hazards and accident prevention. Preventing accidents must consider both as well as the surrounding circumstances. 

In the above extract, the italics are Heinrich s. The phrase and involving the same person was not a part of the supporting statements for the ratios in the second edition of Industrial Accident Prevention. No explanation is given for adding the phrase in the third and fourth editions. 

The ratios apply to accidents both of the same kind and involving the same person. Think about it. The premise lacks plausibility on its face. Consider this example. A worker reports to a construction job, takes the hoist to the tenth floor, and within minutes backs into an unguarded floor opening and falls to his death. For how many types of accidents occurring to the same person will the odds be 10 out of 11 that no injury occurs (Heinrich makes it clear in his fourth edition of Industrial Accident Prevention that the ratios pertain to accidents, and not unsafe acts.)... 

Heinrich s (1950) premises with respect to what had become broadly known as his 300-29-1 ratios varied from the first, to the second, to the third edition of his book Industrial Accident Prevention. This is what appeared in the third and fourth editions ... 

The data collection and analytical methods used by Heinrich to develop the 88-10-2 ratios are unsupportable. Heinrich s premise that unsafe acts are the primary causes of occupational accidents cannot be sustained. The myth represented by those ratios must be dislodged from the practice of safety and actively refuted by safety professionals. 

Heinrich s conclusion with respect to the ratios of incidents that result in no injuries, minor injuries, and major injuries was the base on which educators taught (and still teach), and many safety practitioners came to believe that reducing accident frequency will achieve equivalent reduction in injury severity. The following statement appears in all four editions of Heinrich s text ... 

In the second edition, similar was added to the citation above so that it reads Analysis proves that for every mishap, there are many other similar accidents in industry. .(H-12). Heinrich s study resulting in the 88-10-2 ratios was made in the late 1920s. Both the relationship of a study made then to the work world as it now exists and the methods used in producing it are questionable and unknown. 

Within a chart displaying the 300-29-1 ratios in the first edition, Heinrich writes The total of 330 accidents all have the same cause. Note that cause is singular (H-13). This statement, that all 330 incidents have the same cause, challenges credulity. Also, note that the sentence in quotations in this paragraph appears only in the first edition. It does not appear in later editions (H-14). 

H. W. Heinrich is the author of Industrial Accident Prevention A Scientific Approach. His presentation on the indirect-to-direct cost ratio... 

More than 80 years ago, H. W. Heinrich suggested that one should focus on the accident rather than the injury. He was the first to propose a ratio existed between injuries and accidents that produced no injuries. 

A simple but powerful example of this is a case described in H.W. Heinrich s 1931 book. Industrial Accident Prevention. The adverse outcome or injury was that a mill employee fractured his kneecap because he slipped and fell on a wet floor. It had, however, for more than six years been the practice to wet down too great an area of floor space at one time and to delay unnecessarily the process of wiping up. Slipping on the part of one or more employees was therefore a daily occurrence, although usually without serious consequences. (The ratio of no-injury slips to the injury was 1,800 1.) Since Heinrich does not relate what happened after the accident, it is anybody s guess whether the established practice of floor cleaning was changed. 

Heinrich s work was the forerunner of the widely held philosophy that proactive safety was centered in the three Es — engineering, education, and enforcemenf —a viewpoint that has lasted nearly four decades. The idea that 85% of accidents were caused by imsafe acts and only 15% by hazardous conditions resulted in nearly universal adherence in safety management circles and the emphasis appeared appropriate (Petersen 1989). This observation was subsequently vahdated by other organizations, although with different numerical ratios (e.g., DuPont). 

Used in industrial safety as a method for illustrating the progressive effects of lower level incidents on the upper level incidents, typically as a series of ratios. Safety is controlled by monitoring the lowest levels which are viewed as near misses for the next level up. see Heinrich et al (1980). Hubbard and Neil (1986) reported from a UK case study that they had 1 major accident for every 32 minor accidents. Typically, this data is not kept by contractors. 

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