Posted on: January 10, 2013 Posted by: Diane Swarts Comments: 0

The Heinrich (Bird) Safety Triangle of ‘frequency ratios between minor incidents and injuries’, is as false as the truism that ‘unsafe acts cause most accidents’.

Fred A Manuele, author of ‘Henrich Revisted’, pleads for “dislodging two myths from safety practice” in the American Society of Safety Engineers (ASSE) magazine, Professional Safety, October 2011. An extract follows below.

In ‘Standardisation of Error’, Stefansson (1928) makes the case that people are willing to accept as fact what is written or spoken without adequate supporting evidence. When studies show that a supposed fact is not true, dislodging it is difficult because that belief has become deeply embedded in the minds of people, and thereby ‘standardised’.

Stefansson wrote that safety is a professional specialty in which myths have become standardised and deeply embedded. Two myths should be dislodged from the practice of safety: ‘Unsafe acts of workers are the principle causes of occupational accidents’, and ‘Reducing accident frequency will equivalently reduce severe injuries’.

These myths arise from the work of HW Heinrich (1931; 1941; 1950; 1959) in four editions of Industrial Accident Prevention: A Scientific Approach. The incident frequency and severity triangle, or pyramid, was popularised by Frank Bird, and is most often named ‘Bird Triangle’.

Heinrich was a pioneer in the field of accident prevention and must be given his due. Heinrich likely has had more influence than any other individual on the work of occupational safety practitioners.

Attempts were made to locate Heinrich’s research, without success. Dan Petersen, who with Nestor Roos, authored a fifth edition of Industrial Accident Prevention, was asked whether they had located Heinrich’s research. Petersen said that they had to rely on previous editions, and that research data was not available.

With new knowledge about how accidents occur and causal factors, the emphasis is now correctly placed on improving the work system, rather than on worker behavior. Heinrich’s premises are not compatible with current thinking.

Safety psychology

Applied psychology dominates Heinrich’s work with respect to selecting causal factors and is given great importance in safety-related problem resolution.

Heinrich expresses the belief that “psychology in accident prevention is a fundamental of great importance”. His premise is that “psychology lies at the root of sequence of accident causes”. In the fourth edition, Heinrich states that he envisions “the more general acceptance by management of the idea that an industrial psychologist be included as a member of the plant staff as a physician is already so included”.

The focus of applied psychology is on workers: “Safety psychology is as fairly applicable to the employer as to the employee. The initiative and the chief burden of activity in accident prevention rest upon the employer; however the practical field of effort for prevention through psychology is confined to the employee, but through management and supervision.”

The ‘psychology applier’ is supposedly the supervisor. With due respect to managers, supervisors and safety practitioners, it is doubtful that many could knowledgeably apply psychology “as a fundamental of great importance” in their accident prevention efforts.

Heinrich’s Causation Theory, 88:10:2 ratio

Heinrich professes that among the direct and proximate causes of industrial accidents:
• 88% are unsafe acts of persons
• 10% are unsafe mechanical or physical conditions
• 2% are unpreventable.

Heinrich advocates identifying the first proximate and most easily prevented cause in the selection of remedies; “Selection of remedies is based on practical cause-analysis that stops at the selection of the first proximate and most easily prevented cause (such procedure is advocated in this book) and considers psychology when results are not produced by simpler analysis.”

What has been learned subsequently about the complexity of accident causation or that other causal factors may be more significant than the first proximate cause.

For example, the Columbia [space shuttle] Accident Investigation Board (NASA, 2003) notes the need to consider the complexity of incident causation: “Many accident investigations do not go far enough. They identify the technical cause of the accident, and then connect it to a variant of “operator error.” But this is seldom the entire issue. When the determinations of the causal chain are limited to the technical flaw and individual failure, typically the actions taken to prevent a similar event in the future are also limited: fix the technical problem and replace or retrain the individual responsible.

Assumptions of ‘problem solved’

Putting these corrections in place leads to another mistake: The belief that the problem is solved. Too often, accident investigations blame a failure only on the last step in a complex process, when a more comprehensive understanding of that process could reveal that earlier steps might be equally or even more culpable.

A recent example of the complexity of accident causation appears in this excerpt from the report prepared by BP personnel following the April 20, 2010, Deepwater Horizon explosion in the Gulf of Mexico (BP, 2010): “The team did not identify any single action or inaction that caused this incident. Rather, a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces came together to allow the initiation and escalation of the accident.”

Heinrich does not define his term ‘man failure’. A directly opposite view is expressed by Deming (1986); “The supposition is prevalent throughout the world that there would be no problems in production or service if only our production workers would do their jobs in the way that we taught. Pleasant dreams. Workers are handicapped by the system, and the system belongs to the management.”

Consider Ferry’s (1981) comments; “We cannot argue with the thought that when an operator commits an unsafe act, leading to a mishap, there is an element of human or operator error. We are, however, decades past the place where we once stopped in our search for causes.

“Whenever an act is considered unsafe we must ask why. Why was the unsafe act committed? When this question is answered in depth it will lead us on a trail seldom of the operator’s own conscious choosing.”

‘Human error’ lies above worker level

More recent research warns that;

• It is often not recognised that these errors frequently arise from failures at the management, design or technical expert levels of the company.
• A systems perspective is taken that views error as a natural consequence of a mismatch between human capabilities and demands, and an inappropriate organisational culture. From this perspective, the factors that directly influence error are ultimately controllable by management.
• Almost all major accident investigations in recent years have shown that human error was a significant causal factor at the level of design, operations, maintenance or the management process.
• Consider organisational factors that create preconditions for errors.
• Attitudes toward blame will determine whether an organization develops a blame culture, which attributes error to causes such as lack of motivation or deliberate unsafe behavior.
• Factors such as the degree of participation that is encouraged in an organisation, and the quality of the communication between different levels of management and the workforce, will have a major effect on the safety culture.

Safety professionals should focus on system improvement to attain acceptable risk levels rather than principally on affecting worker behavior.

James Reason reveals management error

James Reason’s (1997) book, Managing the Risks of Organisational Accidents, is a must-read for safety professionals who want an education in ‘human error’ reduction. Reason writes about how the effects of decisions accumulate over time and become the causal factors for incidents resulting in serious injuries or major damage when all the circumstances necessary for the occurrence of a major event fit together.

Focus on decision making above the worker level to prevent major accidents: “Latent conditions, such as poor design, gaps in supervision, undetected manufacturing defects or maintenance failures, unworkable procedures, clumsy automation, shortfalls in training, less than adequate tools and equipment, may be present for many years before they combine with local circumstances and active failures to penetrate the system’s layers of defenses.

“They arise from strategic and other top level decisions made by governments, regulators, manufacturers, designers and organisational managers. The impact of these decisions spreads throughout the organisation, shaping a distinctive corporate culture and creating error-producing factors within the individual workplaces.”

Walton (1986) found that “85% of problems in any operation are within the system and are the responsibly of management, while only 15% lie with workers”.

In 2010, ASSE sponsored the symposium, Rethink Safety: A New View of Human Error and Workplace Safety. Several speakers proposed that the first course of action to prevent human errors is to examine the design of the work system and work methods.

Unfortunately, use of the terms unsafe acts and unsafe conditions focuses attention on workers or conditions, and diverts attention from root causal factors built into an operation.

Chapanis, who was prominent in the field of ergonomics and human factors engineering, wrote “The Error-Provocative Situation,” a chapter in The Measurement of Safety Performance (Tarrants, 1980).

USA Department of Energy (1994) describes the management oversight and risk tree (MORT) as a “comprehensive analytical procedure that provides a disciplined method for determining the systemic causes and contributing factors of accidents.”

Questions raised by MORT are directed at systemic and procedural problems. Assignment of “unsafe act” responsibility to a work-level employee should not be made unless or until the preventive steps of azard analysis, management or supervisory direction, and procedures safety review, are shown adequate.

Minor incidents and major injuries have different causes

If you manage small incidents effectively, the small incident rate improves, but the major accident rate stays the same, or even slightly increases.

Heinrich’s texts contain contradictions about when a major injury would occur and the relationship between unsafe acts and a major injury. In all editions, reference is made to 330 careless acts or several hundred unsafe acts occurring before a major injury occurs: “Keep in mind that a careless act occurs approximately 300 times before a serious injury results and that there is, therefore, an excellent opportunity to detect and correct unsafe
practices before injury occurs.” Not true.

“Keep in mind that an unsafe act occurs several hundred times before [italics added] a serious injury results”. This is not the case in a large majority of incidents which result in serious injury or fatality.

One of Heinrich’s premises is that “predominant causes of no-injury accidents are, in average cases, identical with the predominant causes of major injuries, and incidentally of minor injuries as well.” This is wrong. It is a myth that must be dislodged from the practice of safety.

Spend on major incident causes

Applying this premise leads to misdirection in resource application and ineffectiveness, particularly with respect to preventing serious injuries. In this author’s experience, many incidents resulting in serious injury are singular and unique events, with multifaceted and complex causal factors, and descriptions of similar incidents are rare in the historical body of incident data.

Furthermore, all hazards do not have equal potential for harm. Some risks are more significant than others. That requires priority setting.

Misinterpretation of Terms

Not only have many safety practitioners used the 300-29-1 ratios in statistical presentations, but many also have misconstrued what Heinrich intended with the terms major injury, minor injury and no-injury accidents.

Some practitioners who cite these ratios in their presentations assume that a “major injury” is a serious injury or a fatality. His major injury is any case that is reported to insurance carriers or to the state compensation commissioner. A minor injury is a scratch, bruise or laceration such as is commonly termed a first-aid case.

A no-injury accident is an unplanned event involving the movement of a person or an object, ray or substance, like slip, fall, flying object, inhalation, having the probability of causing personal injury or property damage.

The great majority of reported or major injuries are not fatalities or fractures or dismemberments; they are not all lost-time cases, and even those that are do not necessarily involve payment of compensation.

When these definitions were developed in the late 1920s, few companies were self-insured for workers’ compensation. On-site medical facilities were rare. Insurance companies typically paid for medical-only claims and for minor and major injuries. According to Heinrich’s definitions, almost all such claims would be considered major injuries.

A safety director recently said that his company sustained one fatality and 30 OSHA days-away-from-work incidents, and, therefore, Heinrich’s progression was validated. Not so. All of the injuries and the fatality would be in the major or lost-time injury category.

Current safety approaches and premises

Current occupational health and safety approaches and premises demonstrate that Heinrich’s premises are not compatible with current knowledge. The most prevalent premises are listed below;

Hazards are the generic base of, and the justification for the existence of, the practice of safety.

Risk is an estimate of the probability of a hazard-related incident or exposure occurring and the severity of harm or damage that could result.

The entirety of purpose of those responsible for safety, regardless of their titles, is to manage their endeavors with respect to hazards so that the risks deriving from those hazards are acceptable.

Risks to which the practice of safety applies derive from hazards. There are no exceptions.

Hazards and risks are most effectively and economically avoided, eliminated or controlled in the design and redesign processes.

The professional practice of safety requires consideration of the two distinct aspects of risk: avoiding, eliminating or reducing the probability of a hazard-related incident or exposure occurring; as well as reducing the severity of harm or damage if an incident or exposure occurs.

Management creates the safety culture, whether positive or negative.

An organisation’s culture, translated into a system of expected behavior, determines management’s commitment or lack of commitment to safety and the level of safety achieved.

Principal evidence of an organization’s culture with respect to occupational risk management is demonstrated through the design decisions that determine the facilities, hardware, equipment, tooling, materials, processes, configuration and layout, work environment and work methods.

Major improvements in safety will be achieved only if a culture change takes place, only if major changes occur in the system of expected behavior.

While human errors may occur at the worker level, preconditions for the commission of such errors may derive from decisions made with respect to the workplace and work methods at the management, design, engineering or technical expert levels of an organization.

Greater progress can be obtained with respect to safety by focusing on system improvement to achieve acceptable risk levels, rather than through modifying worker behavior.
A large proportion of problems in an operation are systemic, deriving from the workplace and work methods created by management, and can be resolved only by management. Responsibility for only a relatively small remainder lies with the worker.

While employees should be trained and empowered up to their capabilities and encouraged to make contributions with respect to hazard identification and analysis, and risk elimination or control, they should not be expected to do what they cannot do.

Accidents usually result from multiple and interacting causal factors that may have organizational, cultural, technical or operational systems origins.

If accident investigations do not relate to actual causal factors, corrective actions taken will be misdirected and ineffective.

Causal factors for low-probability/high-consequence events are rarely represented in the analytical data on incidents that occur frequently, and the uniqueness of serious injury potential must be adequately addressed. However, accidents that occur frequently may be predictors of severity potential if a high energy source was present.

Health and safety consultants should correct managers

As knowledge has evolved about how accidents occur and their causal factors, the emphasis is now properly placed on improving the work system, rather than on worker behavior.

Safety professionals who reference Heinrich premises as fact, says, “It is borderline unethical on their part.”

Heinrich’s premises have become truisms.

Safety practice recommendations

Safety professionals should ensure that the Heinrich misconceptions discussed in this article are discarded by the profession. To achieve this, each safety professional should:

• Stop using or promoting the premises that unsafe acts are the primary causes of accidents and that focusing on reducing accident frequency will equivalently reduce injury severity.

• Actively dispel these premises in presentations, writings and discussions.

• Politely but firmly refute allegations by others who continue to promote the validity of these premises.

• Apply current methods that look beyond Heinrich’s myths to determine true causal factors of accidents.

For the full article, visit under Professional Safety, 2011 October.

• Fred A Manuele, PE, CSP, is president of Hazards Limited, and former Marsh & McLennan where MD, and manager of M&M Protection Consultants. His books include Management: Focusing on Z10 and Serious Injury Prevention, On the Practice of Safety, Innovations in Safety Management: Addressing Career Knowledge Needs, and Heinrich Revisited: Truisms or Myths. He is a professional member of ASSE Northeastern Illinois Chapter, an ASSE Fellow, and former board member of ASSE, NSC and BCSP.

PHOTO; One of WH Heinrich’s popular but outdated safety management books.

Comment from practitioners

Comment by editor SHEQafrica; As much as Heinrich, Bird and many popular health and safety consulting services have popularised their conclusions to the point of truisms, they are now shown to be based on, and constructed of truisms. The truth does not sell well, and selling safety is ever at risk of sliding into truism and platitude to stay in business.

Health and safety officials, consultants, trainers and auditors are invited to comment on this report, or any report on, by typing into the Comment window that follows each report. Longer comments, letters, articles or research results could be sent to

Safety management and case study references

BP (2010 Sept 8). Deepwater Horizon accident investigation report, Houston, TX;

Center for Chemical Process Safety (CCPS) (1994). Guidelines for preventing human error in process safety. New York:

Columbia Accident Investigation Board, 2003; Columbia accident investigation report, Washington, DC: NASA; www

Deming, WE 1986; Out of the crisis. Cambridge,
MA: Center for Advanced Engineering Study, Massachusetts Institute of Technology.

Det Norske Veritas (DNV) Consulting, 2004; Leading indicators for major accident hazards: An invitation to industry partners. Houston, TX

Ferry, TS (1981). Modern accident investigation and analysis: An executive guide. New York: John Wiley & Sons.

Reason, J. (1997). Managing the risks of organizational accidents. London: Ashgate

Stefansson, V. (1928). The standardization of error. London: K. Paul, Trench, Trubner & Co

Tarrants, W.E. (1980). The measurement of safety performance. New York: Garland


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