Theories of Accident Causation OSHE 111, Spring 2016 Instructor: Mr. Chris Kuiper, CSP Phone:

Review: OSH&E Professions Requirements for OSH&E professionals Changing roles of OSH&E professionals Definitions of hazard, accident, and risk Examples of OSH&E disciplines and specialists Importance and Influence of OSH&E professionals Examples of OSH&E certifications

Why We Need to Understand the Theory Understand available approaches to identify, isolate and ultimately remove the factors that contribute to or cause accidents Use to develop a prediction theory of accident causation, although so far none has been universally accepted

Incident Theories Domino Theory Multiple Causation/Factor Theory Energy Transfer Theory Human Factors Theory Behavioral Theory Others

Domino Theory First scientific approach of accident prevention by W.F. Heinrich in 1931 Studied 75,000 industrial accidents –88% of all accidents are caused by unsafe acts of people –10% by unsafe conditions –2% by unavoidable causes (acts of God)

The Domino Theory Studied 75,000 industrial accidents –88% of all accidents are caused by unsafe acts of people –10% by unsafe conditions –2% by unavoidable causes (acts of God)

Newer Version of the Pyramid

The Domino Theory

Sequence of Accident Factors 1.Ancestry and social environment – where and how a person was raised and educated 2.Worker fault – undesirable traits such as carelessness, nervousness, lack of knowledge, etc. 3.Unsafe acts or conditions – caused by careless workers, or poorly designed or improperly maintained equipment 4.Accident – caused by unsafe acts of people or unsafe conditions 5.Injury – caused by accidents

Domino Theory Removal of a single domino in the row would interrupt the sequence of toppling The key domino to be removed is unsafe acts or conditions.

Heinrich’s Axioms of Industrial Safety Injuries result from a series of factors. Accidents only occur as a result of an unsafe act by a person and/or a physical or mechanical hazard. Most accidents are the results of unsafe behaviors by people. Unsafe acts or conditions do not always immediately result in an accident. Reasons people act safely can serve as guidelines for accident prevention.

Heinrich’s Axioms of Industrial Safety Accidents are preventable. Accident prevention techniques are analogous with best quality and production techniques. Management should be responsible for safety. Supervisor is the key person. Accidents have both direct costs and hidden costs.

Multiple Causation Theory Outgrowth of the domino theory For a single accident there may be many contributory factors, causes and sub-causes Certain combinations of those factors give rise to accidents

Multiple Causation Theory Contributory factors can be grouped into the following two categories: –Behavioral: pertaining to the worker, such as improper attitude, lack of knowledge, lack of skills, and inadequate physical and mental condition –Environmental: includes improper guarding of other hazardous work elements, degradation of equipment through use, and unsafe work procedures

Multiple Causation Theory

Multiple Causation Theory Many analytical and statistical methods and techniques available –Fault tree analysis –Factor analysis –Principle component analysis The analyses focus on establishing the relationship between causes and effects.

“Accident Proneness” Theory Little evidence available to affirm If proven true probably very low proportion of accidents Not proven and generally not accepted

Energy Transfer Theory Accidents and injuries involve change of energy Energy source, path and a receiver Theory useful for evaluating energy hazards and controls Strategies can be developed to prevent, limit eliminate energy transfer –Path enclosure –Barrier installation –Energy absorber –Isolator positioning –Exposure limit –PPE

Energy Transfer Theory Energy transfer control at the source can be achieved by: –Source elimination –Changes to design or work station specifications –Preventive maintenance

Energy Types Kinetic –Moving vehicles, wrench falling from a scaffold Chemical –Acid, caustic, toxic chemicals Thermal Electrical Mechanical –Gears, rotating shafts, pulleys Biological –Bacteria and viruses

Energy Types Ionizing radiation –X-ray, nuclear materials Non-ionizing –Laser light, microwave Meteorological Acoustical Pressure –Compressed gas or liquid, pipeline, air compressor Potential –Stored energy, oil pumping unit, conveyor belt

Human Factors Theory

Overload –Environmental factors, including climate, noise, lighting, etc. –Situational factors, including stress, fatigue, etc. –Organizational factors, including structure, culture, policies, etc. Inappropriate response – how person responds to hazard –Identify hazard but do not correct –Remove safeguard –Ignore safety Inappropriate actions – person’s action(s) –Perform tasks without sufficient training –Misjudge tasks, including content, control, etc.

Human Factors Theory Attributes accidents to human error. Different definitions of human error –Hagen & Mays, 1981 –Reason, 1990 –Sanders and McCormick, 1993

Human Error – Hagen & Mays, 1981 Human failure to perform a prescribed act (or conducting a prohibited act) within specified limits of accuracy, sequence, or time Result is damage to equipment and property or disruption of scheduled operations

Human Error – Reason, 1990 Those occasions in which a planned sequence of mental or physical activities fails to achieve its intended outcome without chance intervention (luck?) Swiss Cheese Model of Accident Causation

Reason, J. (1990) Human Error, Cambridge University Press, U.K.

Human Error – Sanders and McCormick, 1993 An inappropriate or undesirable human decision or behavior that reduces, or has the potential to reduce effectiveness, safety, or system performance.

Types of Human Error Slips and lapses –Failure in execution regardless of whether the plan which guided them was adequate to achieve its objective –Person’s actions do not go according to plan Mistake –Deficiency or failure in judgment –The plan itself is inadequate to achieve its objective.

Behavioral Theory Why people behave safely or unsafely and changing behavior to improve safety Focuses on inherent (personality, abilities, etc.) or situational (attention, fatigue, stress) human traits which affect behaviors to cause accidents

Behavioral Theory Old view – Accident Prone –Injuries happen to people who have a genetic predisposition to being injured. –Studies show that removing “accident prone” people DOES NOT lower the overall accident rates. New view – Risk Prone –“Risk proneness” – individual’s tendency to take risks/chances –Behavior can be modified even if risk-taking tendency cannot

Behavior-Based Safety Positive reinforcement in the form of incentives and rewards is used to promote the desired (safe) behaviors and to discourage undesirable (unsafe) behaviors. Does this work in the real world? How well?

Summary Accident causation is very complex and must be understood adequately in order to improve accident prevention No single theory generally or universally accepted Multiple causation is widely applied

Proactive versus Reactive Approach Reactive Accident Investigation Analysis Prevention Proactive Analysis Prevention Accident

Accident Prevention Studying accident causation promotes –Understanding the similarities and differences of various theories –Establishing the structure of accidents Proactive approach vs. reactive approach Engineering, education, and enforcement (3 Es)

Three Es of Safety