Accidents are caused by multiple interacting factors including human error, equipment failures, and environmental conditions. Major causes of workplace injuries in the US include overexertion, impacts, falls, and exposure to chemicals and extreme temperatures. Legislation like Workers' Compensation aims to provide benefits to injured workers while encouraging safety. Government agencies like OSHA and NIOSH were established to set and enforce safety standards in industries. Accidents result from interactions between human, job, equipment, and environmental factors.

1. Safety, Accidents, and HumanSafety, Accidents, and Human
ErrorError
Human Factors PsychologyHuman Factors Psychology
Dr. SteveDr. Steve

2. Safety and AccidentSafety and Accident
PreventionPrevention
• Accidents caused by multiple factorsAccidents caused by multiple factors
– e.g.,e.g., ““human errorhuman error,,”” equipment failure, improper equipment design,equipment failure, improper equipment design,
environmental factors, or interaction between factorsenvironmental factors, or interaction between factors
• Accident deaths and injury in the U.S.Accident deaths and injury in the U.S.
• 47,000 motor vehicle-related deaths / year47,000 motor vehicle-related deaths / year
• 13,000 deaths due to falls /year13,000 deaths due to falls /year
• 7,000 deaths due to poisoning / year7,000 deaths due to poisoning / year
• Cost of Workplace deaths and injuriesCost of Workplace deaths and injuries
• $48 billion / year$48 billion / year
• $780,000 / victim cost to society$780,000 / victim cost to society
• $420 cost / worker$420 cost / worker
Link to story of Phineas Gage

3. Most Frequent Causes ofMost Frequent Causes of
Workplace Deaths and InjuriesWorkplace Deaths and Injuries
InjuryInjury
OverexertionOverexertion
Impact accidentsImpact accidents
FallsFalls
Bodily reaction to chemicalsBodily reaction to chemicals
CompressionCompression
Motor vehicle accidentsMotor vehicle accidents
Exposure to radiation/causticsExposure to radiation/caustics
Rubbing or abrasionsRubbing or abrasions
Exposure to extreme temperaturesExposure to extreme temperatures
DeathsDeaths
Motor-vehicle relatedMotor-vehicle related
FallsFalls
Electrical currentElectrical current
DrowningDrowning
Fire relatedFire related
Air transport relatedAir transport related
PoisonPoison
Water transport relatedWater transport related
OtherOther

4. Safety LegislationSafety Legislation
• Prior to 1900Prior to 1900’’s employers assumed littles employers assumed little
responsibility for safetyresponsibility for safety
• Companies defended themselves against accidentsCompanies defended themselves against accidents
claiming:claiming:
1.1. Contributory negligence (personContributory negligence (person’’s behaviors behavior
contributed to the accident)contributed to the accident)
2.2. Negligence of fellow employeesNegligence of fellow employees AccidentAccident
3.3. Injured worker was aware of the hazards andInjured worker was aware of the hazards and
knowingly assumed the risksknowingly assumed the risks

5. WorkersWorkers’’ Compensation andCompensation and
LiabilityLiability
• Early laws provided compensation to workers for on-the-jobEarly laws provided compensation to workers for on-the-job
injuries regardless of who was at faultinjuries regardless of who was at fault
– These laws originally thrown out as unconstitutional (passed in 1917)These laws originally thrown out as unconstitutional (passed in 1917)
• Today there are different workersToday there are different workers’’ compensation laws incompensation laws in
each state, with approximately 80% of all workers coveredeach state, with approximately 80% of all workers covered
• To collect workers compensation, injury must:To collect workers compensation, injury must:
1.1. Arise from an accidentArise from an accident
2.2. Arise out of workerArise out of worker’’s employments employment
3.3. Occur during course of employmentOccur during course of employment

6. Goals of worker compensation:Goals of worker compensation:
• Provide income and medical benefits to work-accidentProvide income and medical benefits to work-accident
victims or income to their dependentsvictims or income to their dependents
• Provide a single remedy to reduce court delays, costs, andProvide a single remedy to reduce court delays, costs, and
workloads arising out of perennial-injury litigationworkloads arising out of perennial-injury litigation
• Eliminate payment of fees to lawyers and witnesses asEliminate payment of fees to lawyers and witnesses as
well as time-consuming trials and appealswell as time-consuming trials and appeals
• Encourage employer interest in safety and rehabilitationEncourage employer interest in safety and rehabilitation
• Promote the study of causes of accidentsPromote the study of causes of accidents

7. Establishment of OSHAEstablishment of OSHA
Occupational Safety and Health AdministrationOccupational Safety and Health Administration
(1970)(1970) – OSH– OSH Act set forth by fed government toAct set forth by fed government to
impose safety standards on industryimpose safety standards on industry
– under the U.S. Department of Laborunder the U.S. Department of Labor
– set standards for general and specific industriesset standards for general and specific industries
– companies comply by: keeping records, keeping employeescompanies comply by: keeping records, keeping employees
informed on safety matters, complying with standards forinformed on safety matters, complying with standards for
injury avoidance, etc...injury avoidance, etc...

8. NIOSHNIOSH
• National Institute for Occupational Safety and HealthNational Institute for Occupational Safety and Health
– mainly for research and education functionsmainly for research and education functions
– finds hazardous types of working conditions by reviewing researchfinds hazardous types of working conditions by reviewing research
– human factors professionals use the standards or recommendationshuman factors professionals use the standards or recommendations

9. Product LiabilityProduct Liability
• Suits filed against a company claiming that a product wasSuits filed against a company claiming that a product was
defective and therefore caused injury or deathdefective and therefore caused injury or death
• e.g. McDonalds hot coffee case (overturned by higher court)e.g. McDonalds hot coffee case (overturned by higher court)
• Is the product defective or inherently dangerous?Is the product defective or inherently dangerous?
• e.g. faulty car seat vs. a sharp knifee.g. faulty car seat vs. a sharp knife
• Defective - failed to perform safely as an ordinary userDefective - failed to perform safely as an ordinary user
would expect when it was used in an intended orwould expect when it was used in an intended or
reasonably foreseeable manner, or if the risk inherent inreasonably foreseeable manner, or if the risk inherent in
the design outweighed the benefits of that designthe design outweighed the benefits of that design
– Reasonably foreseeableReasonably foreseeable
– The trade-off between risk and benefitThe trade-off between risk and benefit

10. Factors that cause orFactors that cause or
contribute to accidentscontribute to accidents
• The systems approachThe systems approach- accidents occur because of- accidents occur because of
the interaction between system componentsthe interaction between system components
• Direct causal factors in safetyDirect causal factors in safety
1 the employee performing a taskthe employee performing a task
2 the task itselfthe task itself
3 any equipment directly or indirectly used in the taskany equipment directly or indirectly used in the task
4 other factors - social/psychological & environmentalother factors - social/psychological & environmental

11. Personnel CharacteristicsPersonnel Characteristics
Factors affecting hazard recognition, decisions to actFactors affecting hazard recognition, decisions to act
appropriately, & ability to act appropriatelyappropriately, & ability to act appropriately
• Age & GenderAge & Gender
• younger people have more accidents - ages 15-24,younger people have more accidents - ages 15-24,
mostly young malesmostly young males
• Job ExperienceJob Experience
• 70% of accidents occur within the first 3 years70% of accidents occur within the first 3 years
• Stress, Fatigue, Drugs, & AlcoholStress, Fatigue, Drugs, & Alcohol
• many employers drug testmany employers drug test

12. Job Characteristics/EquipmentJob Characteristics/Equipment
• Job characteristicsJob characteristics – such as high physical– such as high physical
workload, high mental workload, monotony, etc…workload, high mental workload, monotony, etc…
• EquipmentEquipment - where most of the safety analysis is- where most of the safety analysis is
performed. This is due to problems with:performed. This is due to problems with:
• Controls and DisplaysControls and Displays
• e.g. poorly designed, difficult to use, cumulative trauma, etc.e.g. poorly designed, difficult to use, cumulative trauma, etc.
• Electrical HazardsElectrical Hazards
• e.g. occurs when a person is doing repairs and another persone.g. occurs when a person is doing repairs and another person
unknowingly turns the circuit onunknowingly turns the circuit on
• Mechanical HazardsMechanical Hazards
• results in cutting of skin, shearing, crushing, breaking, orresults in cutting of skin, shearing, crushing, breaking, or
strainingstraining
• Pressure and Toxic Substance HazardsPressure and Toxic Substance Hazards
• asphyxiants, irritants, systemic poison, & carcinogensasphyxiants, irritants, systemic poison, & carcinogens

13. The Physical EnvironmentThe Physical Environment
• IlluminationIllumination
• Glare, phototropism, contrastGlare, phototropism, contrast
• Noise and VibrationNoise and Vibration
• affects dexterity, control, and healthaffects dexterity, control, and health
• Temperature and HumidityTemperature and Humidity
• heat exhaustion, inattention, restrictive clothingheat exhaustion, inattention, restrictive clothing
• Fire HazardsFire Hazards
• open flames, electric sparks, & hot surfacesopen flames, electric sparks, & hot surfaces
• Radiation HazardsRadiation Hazards
• Radioactive material - damage to human tissueRadioactive material - damage to human tissue
• FallsFalls
• resulting in injury or death are relatively commonresulting in injury or death are relatively common

14. The Social EnvironmentThe Social Environment
• Human behavior is influenced by social contextHuman behavior is influenced by social context
- Social norms, mgmt practices, morale, training,- Social norms, mgmt practices, morale, training,
incentivesincentives
– e.g. construction workers will not wear safety gear if noe.g. construction workers will not wear safety gear if no
one else isone else is

15. Human ErrorHuman Error
• The Misnomer of Human ErrorThe Misnomer of Human Error – error usually triggered– error usually triggered
by other things (e.g., poor design, management,by other things (e.g., poor design, management,
violations of use and maintenance).violations of use and maintenance).
– Error is the end result of these problemsError is the end result of these problems
– Pilot error blamed on over 70% of airplane accidentsPilot error blamed on over 70% of airplane accidents
– Operator error blamed on over 60% of nuclear power plant accidentsOperator error blamed on over 60% of nuclear power plant accidents
– Doctor/Nurse errors in ICU occur at a rate of 1.7/patient per dayDoctor/Nurse errors in ICU occur at a rate of 1.7/patient per day
• Classifying types of errorClassifying types of error
– errors of omissionerrors of omission - operator fails to perform a procedural step- operator fails to perform a procedural step
– errors of commissionerrors of commission - operator performs extra steps that are- operator performs extra steps that are
incorrect or performs a step incorrectlyincorrect or performs a step incorrectly
Mars Orbiter

16. Taxonomy of Human ErrorTaxonomy of Human Error
InterpretationInterpretation
SituationSituation
AssessmentAssessment
PlanPlan
Intention ofIntention of
ActionAction
ActionAction
ExecutionExecution
Stimulus
Evidence
Memory
MISTAKESMISTAKES SLIPSSLIPS
LAPSES &LAPSES &
MODE ERRORSMODE ERRORS
KnowledgeKnowledge RuleRule

17. Taxonomy of Human ErrorTaxonomy of Human Error
MistakesMistakes
• MistakesMistakes – failure to come up with appropriate– failure to come up with appropriate
solutionsolution
• Takes place at level of perception, memory, or cognitionTakes place at level of perception, memory, or cognition
• Knowledge-based MistakesKnowledge-based Mistakes – wrong solution– wrong solution
because individual did not accurately assess thebecause individual did not accurately assess the
situation.situation.
• Caused by poor heuristics/biases, insufficient info, infoCaused by poor heuristics/biases, insufficient info, info
overloadoverload
• Rule-based MistakesRule-based Mistakes – invoking wrong rule for– invoking wrong rule for
given situationgiven situation
• Often made with confidenceOften made with confidence

18. • SlipsSlips – Right intention incorrectly executed (oops!)– Right intention incorrectly executed (oops!)
• Capture errorsCapture errors – similar situation elicits action, which– similar situation elicits action, which
may be wrong inmay be wrong in ““thisthis”” situation. Likely to result when:situation. Likely to result when:
• Intended action is similar to routine behaviorIntended action is similar to routine behavior
• Hitting enter key when software asks,Hitting enter key when software asks, ““sure you want to exitsure you want to exit
without saving?without saving?””
• Either stimulus or response is related to incorrect responseEither stimulus or response is related to incorrect response
• HitHit ““33”” instead ofinstead of ““##”” on phone to hear next message, becauseon phone to hear next message, because
““33”” is what I hit to hear the first messageis what I hit to hear the first message
• Response is relatively automated, not monitored by consciousnessResponse is relatively automated, not monitored by consciousness
• Re-starting your car while the engine is already runningRe-starting your car while the engine is already running
Taxonomy of Human ErrorTaxonomy of Human Error
SlipsSlips

19. • LapsesLapses – failure to carry out an action– failure to carry out an action
• Error of Omission (working memory)Error of Omission (working memory)
• Examples: Forgetting to close gas cap, failure to putExamples: Forgetting to close gas cap, failure to put
safety on before cleaning gun, failure to remove objectssafety on before cleaning gun, failure to remove objects
from surgical patientfrom surgical patient
• Mode ErrorsMode Errors – Making the right response, but– Making the right response, but
while in the wrong mode of operationwhile in the wrong mode of operation
• Examples: leave keyboard in shift mode while trying toExamples: leave keyboard in shift mode while trying to
type a numeral, driving in wrong gear, going wrongtype a numeral, driving in wrong gear, going wrong
direction because display was north-up when thought itdirection because display was north-up when thought it
was nose-upwas nose-up
Taxonomy of Human ErrorTaxonomy of Human Error
Lapses & Mode ErrorsLapses & Mode Errors

20. Human Reliability AnalysisHuman Reliability Analysis
• Human Reliability AnalysisHuman Reliability Analysis –– predict reliability ofpredict reliability of
system in terms of probability of failure or mean timesystem in terms of probability of failure or mean time
between failures (MTBF) when system is designed tobetween failures (MTBF) when system is designed to
work in parallel or serieswork in parallel or series
.9 .9
.9
.9
SeriesSeries
ParallelParallel
Reliability = .9 x .9 = .81Reliability = .9 x .9 = .81
P(failure) = 1 - .81 = .19P(failure) = 1 - .81 = .19
Reliability = 1 – [(1 - .9) (1 - .9)]Reliability = 1 – [(1 - .9) (1 - .9)]
= 1 - .01 = .99= 1 - .01 = .99
P(failure) = 1 - .99 = .01P(failure) = 1 - .99 = .01(see homework)

21. THERP componentsTHERP components
1.1. Human Error ProbabilityHuman Error Probability
• Ratio of errors made to possible errorsRatio of errors made to possible errors
1.1. Event TreeEvent Tree
• Diagram showing sequence of eventsDiagram showing sequence of events
• Probability of success or failure for each componentProbability of success or failure for each component
1.1. Other Moderating FactorsOther Moderating Factors
• May add in multiplier to account for variablesMay add in multiplier to account for variables
such as experience level, time, stress, etc.such as experience level, time, stress, etc.
Technique for Human ErrorTechnique for Human Error
Rate Prediction (THERP)Rate Prediction (THERP)

22. THERP Event TreeTHERP Event Tree
aa AA
baba BaBa
SS
SS
bAbA BABA
FF
SS
FF
SS
FF
FF
SeriesSeries
ParallelParallel
Series:
P[S] = a(ba)
P[F] = 1 – a(ba) = a(Ba) + A(bA) + A(BA)
Parallel:
P[S] = 1 – A(BA) = a(ba) + a(Ba) + A(bA)
P[F] = A(BA)
P(successful task B given A)
P(unsuccessful task B given A)
P(success of task B given a)
P(Unsuccessful task B given a)
P(successful task A) P(unsuccessful task A)
Task A = first task
Task B = second task

23. 1.1. Task DesignTask Design – design tasks with working memory– design tasks with working memory
capacity in mindcapacity in mind
2.2. Equipment DesignEquipment Design
a)a) Minimize perceptual confusionsMinimize perceptual confusions – ease of– ease of
discriminationdiscrimination
• Ex: airplane controls that feel like what they do (flaps, wheels)Ex: airplane controls that feel like what they do (flaps, wheels)
a)a) Make consequences of action visible –Make consequences of action visible – immediateimmediate
feedbackfeedback
• Ex: preview window in some software programsEx: preview window in some software programs
a)a) Lockouts –Lockouts – design to prevent wrong actionsdesign to prevent wrong actions
• Ex: car that will not let you lock door from outside without keyEx: car that will not let you lock door from outside without key
a)a) RemindersReminders – compensate for memory failures– compensate for memory failures
• Ex: ATM reminds you to take your cardEx: ATM reminds you to take your card
Error Prevention /Error Prevention /
RemediationRemediation

24. 3.3. TrainingTraining – provide opportunity for mistakes in– provide opportunity for mistakes in
training, so can learn from themtraining, so can learn from them
• Ex: SimulationEx: Simulation
4.4. Assists and RulesAssists and Rules – checklists to follow– checklists to follow
• Ex: Pilot pre-flight checklistEx: Pilot pre-flight checklist
4.4. Error-tolerant systemsError-tolerant systems – system allows for error– system allows for error
correction or takes over when operator makescorrection or takes over when operator makes
serious errorserious error
• Ex: Undo buttonEx: Undo button
Error Prevention /Error Prevention /
Remediation (continued)Remediation (continued)

25. Approaches to Hazard ControlApproaches to Hazard Control
• Optimization standpointOptimization standpoint - the most critical or- the most critical or
““high-riskhigh-risk”” hazards should receive top priorityhazards should receive top priority
• e.g. MIL-STD-882B categories of hazard (matrix combinese.g. MIL-STD-882B categories of hazard (matrix combines
frequency and severity categories)frequency and severity categories)
FrequencyFrequency CatastrophicCatastrophic CriticalCritical MarginalMarginal NegligibleNegligible
FrequentFrequent 11 33 77 1313
ProbableProbable 22 55 99 1616
OccasionalOccasional 44 66 1111 1818
RemoteRemote 88 1010 1414 1919
ImprobableImprobable 1212 1515 1717 2020
SeveritySeverity
1 = Highest priority, 20 = Lowest priority

26. Hazard Control PriorityHazard Control Priority
Reduce Hazards by:Reduce Hazards by:
1.1. SourceSource – designing out a hazard– designing out a hazard
• Baby items too large to swallowBaby items too large to swallow
1.1. PathPath – barrier or safeguard– barrier or safeguard
• Guard on back of lawnmower to protect toesGuard on back of lawnmower to protect toes
1.1. PersonPerson – change behavior with training or warnings– change behavior with training or warnings
• Warning: fan blades can turn on while engine is offWarning: fan blades can turn on while engine is off
1.1. Administrative controlsAdministrative controls – rules mandating behavior– rules mandating behavior
• Must wear safety beltsMust wear safety belts

27. Safety AnalysisSafety Analysis
Sequence for identifying potential hazards andSequence for identifying potential hazards and
recommendations for hazard reduction:recommendations for hazard reduction: (Weinstein et al. 1978)(Weinstein et al. 1978)
– Task AnalysisTask Analysis – How will product be used?– How will product be used?
– Environment AnalysisEnvironment Analysis – Where will product be used?– Where will product be used?
– User AnalysisUser Analysis – Who will use product?– Who will use product?
– Hazard IdentificationHazard Identification – What is likelihood of hazard with product?– What is likelihood of hazard with product?
– Generate Methods for Hazard ControlGenerate Methods for Hazard Control – What might eliminate– What might eliminate
hazards?hazards?
– Evaluate AlternativesEvaluate Alternatives – How will alternative designs affect product– How will alternative designs affect product
performance?performance?
– Select Hazard ControlSelect Hazard Control – Given alternatives, what is best design to– Given alternatives, what is best design to
minimize hazards?minimize hazards?

28. Hazard IdentificationHazard Identification
Methods for identifying potential hazards:Methods for identifying potential hazards:
• Preliminary Hazards AnalysisPreliminary Hazards Analysis
• simplest methodsimplest method
• Development of a list of the most obvious hazardsDevelopment of a list of the most obvious hazards
• Failure Modes and Effects Criticality Analysis (FMECA)Failure Modes and Effects Criticality Analysis (FMECA)
• Breaking down of physical system into subassembliesBreaking down of physical system into subassemblies
• Each subassembly is broken down further and each component isEach subassembly is broken down further and each component is
analyzedanalyzed
• Effect of each componentEffect of each component’’s failure on other components is estimateds failure on other components is estimated
• Fault Tree AnalysisFault Tree Analysis
• Top-down processTop-down process
• Works from incident to possible causesWorks from incident to possible causes

29. Accident InvestigationAccident Investigation
Fact-FindingFact-Finding (OSHA recommendations)(OSHA recommendations)
• Interview witnesses as soon after accident as possibleInterview witnesses as soon after accident as possible
• Inspect accident site before changes occurInspect accident site before changes occur
• Take photos/sketches of sceneTake photos/sketches of scene
• Record all pertinent data on mapsRecord all pertinent data on maps
• Get copies of all reportsGet copies of all reports
• Obtain documents containing normal operatingObtain documents containing normal operating
procedures/ maintenance charts, reported abnormalitiesprocedures/ maintenance charts, reported abnormalities
• Keep complete accurate notes in bound notebookKeep complete accurate notes in bound notebook
• Record pre-accident conditions, accident sequence, post-Record pre-accident conditions, accident sequence, post-
accident conditionsaccident conditions
• Document location of victims, witnesses, machinery,Document location of victims, witnesses, machinery,
energy sources, and hazardous materialsenergy sources, and hazardous materials
Click on picture to link to
story of 3 Mile Island

30. Accident InvestigationAccident Investigation
Levels of CausesLevels of Causes
Management Safety Policy & Decisions
Personal Factors
Environmental factors
Unsafe Act Unsafe
Condition
Unplanned Release of Energy
And/or
Hazardous Material
ACCIDENT
Personal Injury
Property Damage
BASIC
CAUSES
INDIRECT
CAUSES
(SYMPTOMS)
DIRECT
CAUSES

31. Safety ProgramsSafety Programs
1.1. Identify risks to the companyIdentify risks to the company
 identify hazards, hazard controls, accidentidentify hazards, hazard controls, accident
frequency, & company losses due tofrequency, & company losses due to
accidents/incident claimsaccidents/incident claims
2.2. Implement safety programs, includes:Implement safety programs, includes:
 management involvement, accident investigation,management involvement, accident investigation,
recommendations for equipment, safety rules,recommendations for equipment, safety rules,
personal protective equipment, employee training,personal protective equipment, employee training,
safety promotionsafety promotion
3.3. Measuring program effectivenessMeasuring program effectiveness
 evaluated by assessing changes in safety behaviors,evaluated by assessing changes in safety behaviors,
accident/incident rates, number of injuries or death,accident/incident rates, number of injuries or death,
and number of days off due to injuryand number of days off due to injury

32. Risk-Taking and WarningsRisk-Taking and Warnings
• Risk-Taking as a Decision ProcessRisk-Taking as a Decision Process
• People must know a hazard exists, know whatPeople must know a hazard exists, know what
actions are available, & know the consequences ofactions are available, & know the consequences of
the safe behavior vs. alternative behaviorsthe safe behavior vs. alternative behaviors
• Written Warnings and Warning LabelsWritten Warnings and Warning Labels
• Accurately convey the hazards of a productAccurately convey the hazards of a product
• Should include a signal word, info pertaining to theShould include a signal word, info pertaining to the
hazard, consequences, & necessary behaviorhazard, consequences, & necessary behavior
• DangerDanger: Immediate hazard likely results in severe injury: Immediate hazard likely results in severe injury
• WarningWarning: Hazard could result in injury: Hazard could result in injury
• CautionCaution: Hazard or unsafe use my result in minor injury: Hazard or unsafe use my result in minor injury