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Cleveland State UniversityWork Zone Safety and Efficiency Transportation Center

Accident Theories

THEORIES OF ACCIDENT

CAUSATION

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You’ve carefully thought out all the angles.

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You’ve done it a thousand times.

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It comes naturally to you.

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You know what you’re doing, it’s what you’ve beentrained to do your whole life.

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Nothing could possibly go wrong, right? Cleveland State University Work Zone Safety and Efficiency Transportation Center

Accident Theories

Cleveland State UniversityWork Zone Safety and Efficiency Transportation Center

Accident Theories

Theories of Accident Causation

There are several major theories concerning accident causation, eachof which has some explanatory and predictive value.1.The domino theory developed by H. W. Heinrich, a safety engineer

and pioneer in the field of industrial accident safety. 2.Human Factors Theory3.Accident/Incident Theory4.Epidemiological Theory5.Systems Theory6.The energy release theory, developed by Dr. William Haddon, Jr.,

of the Insurance Institute for Highway Safety. 7.Behavior TheoryAccident theories guide safety investigations. They describe the

scope of an investigation.

Heinrich's Domino Theory

According to Heinrich, an "accident" is one factor in a sequence that may leadto an injury.

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The factors can be visualized as a series of dominoes standing on edge;when one falls, the linkage required for a chain reaction is completed.

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Cleveland State University Work Zone Safety and Efficiency Transportation Center Each of the factors is dependent on the preceding factor.

Accident Theories

Heinrich’s Dominos – The Process

A personal injury (the final domino) occurs only as a result of anaccident.

An accident occurs only as a result of a personal or mechanicalhazard.

Personal and mechanical hazards exist only through the fault ofcareless persons or poorly designed or improperly maintainedequipment.

Faults of persons are inherited or acquired as a result of their socialenvironment or acquired by ancestry.

The environment is where and how a person was raised andeducated.

.

Cleveland State University Work Zone Safety and Efficiency Transportation Center

Accident Theories

Heinrich’s Domino Theory – Critical Issues

• The factor preceding the accident (the unsafe act or the mechanical or

physical hazard) and it should receive the most attention.

• Heinrich felt that the person responsible at a company for loss control

should be interested in all five factors, but be concerned primarilywith accidents and the proximate causes of those accidents.

• Heinrich also emphasized that accidents, not injuries or property

damage, should be the point of attack.

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An accident is any unplanned, uncontrolled event that couldresult in personal injury or property damage. For example,if a person slips and falls, an injury may or may not result,but an accident has taken place.

Cleveland State University Work Zone Safety and Efficiency Transportation Center

Accident Theories

Cleveland State UniversityWork Zone Safety and Efficiency Transportation Center

Accident Theories

HUMAN FACTORS THEORY

Heinrich posed his model in terms of a single domino leading to an accident.

The premise here is that human errors cause accidents. These errors arecategorized broadly as:

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OVERLOAD

• The work task is beyond the capability of the worker
  1. Includes physical and psychological factors2. Influenced by environmental factors, internal factors, and

situational factors

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INAPPROPRIATE WORKER RESPONSE

• To hazards and safety measures (worker’s fault)- To incompatible work station (management, environment faults) -^

INAPPROPRIATE ACTIVITIES

• Lack of training and misjudgment of risk

But the structure of this theory is still a cause/effect format.

ACCIDENT/INCIDENT THEORY

Extension of human factors theory. Here the following newelements are introduced:•^

Ergonomic traps

• These are incompatible work stations, tools or expectations

(management failure)

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Decision to err

• Unconscious or conscious (personal failure) -^

Systems failure

Cleveland State University Work Zone Safety and Efficiency Transportation Center – Management failure (policy, training, etc.)

Accident Theories

Summary - Traditional Chain-of-Events

Accident Causality Models

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Explain accidents in terms of multiple events,

sequenced

as a

forward chain over time.

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Events linked together by direct relationships (ignore indirectrelationships).

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Events almost always involve component failure, human error, orenergy-related events.

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Causality models form the basis for most safety-engineering andreliability engineering analyses and/or designs.

Cleveland State University Work Zone Safety and Efficiency Transportation Center

Accident Theories

Limitations of Event-Chain Causality Models

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Neglects social and organizational factors

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Does not adequately account for human error– One cannot simply and effectively model human

behavior by decomposing it into individual decisionsand actions. One cannot study human error in isolationfrom:^ 

physical and social context; 

value system in which behaviors takes place; and 

dynamic work process

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Neglects adaptation– Major accidents involve systematic migration of

organizational behavior to higher levels of risk. Cleveland State University Work Zone Safety and Efficiency Transportation Center

Accident Theories

Cleveland State University Work Zone Safety and Efficiency Transportation Center

Accident Theories Civil Engineers areaccustomed to thesetypes of charts – CPMdiagram (aka a PERTchart).

Cleveland State University Work Zone Safety and Efficiency Transportation Center

Accident Theories

Under normal circumstances chances of an accident is low. Rather thanlooking at the environment as being full of hazards and people prone toerrors, system safety assumes harmony (steady state) exists betweenindividuals and the work environment.

Systems Theory Applied to Transportation Engineering Road accidents are seen as failures of the whole traffic system(interaction between the three elements) rather than a failureof the driver.

Driver

Road infrastructure

Vehicle

Cleveland State University Work Zone Safety and Efficiency Transportation Center

Accident Theories

What about weatherconditions?

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The driver is a victim – this assumes the demands that thetraffic system puts on the driver is too complex for thedriver’s limited capacity to process information.

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As a result of this assumption the system must bedesigned to be less complex, which

prevents

errors from

occurring.

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“The energy and barriers perspective”: The system mustalso

reduce

the negative consequences of errors, i.e.,

Cleveland State University Work Zone Safety and Efficiency Transportation Center introduce safety margins that allows the driver to incur anerror without being hurt too seriously.

Accident Theories