• Industrial work place accidents
• 3/100 persons per year
• One accidental death every 51 minutes
• One injury every 19 seconds

Why do accidents happen?

• Is there a theory that explains the causes of accidents?
• To prevent accidents we need to know the causes.
• Six widely used theories for accident causation

• Early theory, not widely held to today
• Two central points
• Injuries caused by the action of preceding factors
• Removal of the central factor negates the action of the preceding factor

• Five factors leading to an accident
• Ancestry & social environment
• Fault of person
• Unsafe act/mechanical or physical hazard
• Accident
• Injury

• Chain of events ultimately caused by human error
• Three factors
• Overload
• Inappropriate response
• Inappropriate activities

• Overload
• Capacity - abilities
• Load
• Environmental factors (e.g noise)
• Internal factors (e.g. personal problems)
• Situational factors (e.g. risk)

• Inappropriate response
• How a person responds given certain conditions
• Incompatibility with workstation

• Inappropriate activities
• Doing a task without training
• Misjudging the degree of risk

• Human factors theory plus
• Ergonomic traps
• Decision to err
• System’s failure

• Overload + Ergonomic traps + Decision to err lead to human error
• System’s failure link
• a causal relationship to management
• establishes management’s role in health and safety

• Causal relationship between environmental factors and disease
• Extended to accidents
• Study causal relationships between environmental factors and the accident

• Predisposition characteristics
• People, perceptions, environment
• Situational characteristics
• Risk assessment, peer pressure, priorities of supervisor, attitude
• Cause or prevent accidents

• System - interacting components intended to meet a common goal
• A change in any component affects the entire system

• Components
• Person
• Machine
• Environment
• Collect information, weigh risks, make decisions

• Stressors cloud judgment
• Job requirements
• Worker’s abilities & limitations
• Benefit if task accomplished
• Loss if task is tried but fails
• Loss if task is not attempted

• In many cases, one theory is not sufficient
• Need to use several models to explore the causes of accidents
• Don’t rely on one theory