Safety, Accidents, and Safety, Accidents, and Human ErrorHuman Error

Human Factors PsychologyHuman Factors Psychology

Dr. SteveDr. Steve

Safety and Accident Safety and Accident PreventionPrevention

• Accidents caused by multiple factorsAccidents caused by multiple factors– e.g., “e.g., “human errorhuman error,” equipment failure, improper equipment ,” equipment failure, improper equipment

design, environmental factors, or interaction between factorsdesign, environmental 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

Most Frequent Causes of Most Frequent Causes of Workplace Deaths and Workplace Deaths and

InjuriesInjuries

InjuryInjuryOverexertionOverexertion

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 Exposure to extreme temperaturestemperatures

DeathsDeathsMotor-vehicle relatedMotor-vehicle related

FallsFalls

Electrical currentElectrical current

DrowningDrowning

Fire relatedFire related

Air transport relatedAir transport related

PoisonPoison

Water transport relatedWater transport related

OtherOther

Safety LegislationSafety Legislation• Prior to 1900’s employers assumed little Prior to 1900’s employers assumed little

responsibility for safetyresponsibility for safety• Companies defended themselves against Companies defended themselves against

accidents claiming:accidents claiming:1.1. Contributory negligence (person’s behavior Contributory negligence (person’s behavior

contributed to the accident)contributed to the accident)

2.2. Negligence of fellow employees Negligence of fellow employees AccidentAccident

3.3. Injured worker was aware of the hazards and Injured worker was aware of the hazards and knowingly assumed the risksknowingly assumed the risks

Workers’ Compensation Workers’ Compensation and Liabilityand Liability

• Early laws provided compensation to workers for Early laws provided compensation to workers for on-the-job injuries regardless of who was at faulton-the-job injuries regardless of who was at fault

– These laws originally thrown out as unconstitutional (passed in These laws originally thrown out as unconstitutional (passed in 1917)1917)

• Today there are different workers’ compensation Today there are different workers’ compensation laws in each state, with approximately 80% of all laws in each state, with approximately 80% of all workers covered 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 worker’s employmentArise out of worker’s employment

3.3. Occur during course of employmentOccur during course of employment

Goals of worker Goals of worker compensation:compensation:

• Provide income and medical benefits to work-Provide income and medical benefits to work-accident victims or income to their dependentsaccident victims or income to their dependents

• Provide a single remedy to reduce court delays, Provide a single remedy to reduce court delays, costs, and workloads arising out of perennial-injury costs, and workloads arising out of perennial-injury litigationlitigation

• Eliminate payment of fees to lawyers and witnesses Eliminate payment of fees to lawyers and witnesses as well as time-consuming trials and appealsas well as time-consuming trials and appeals

• Encourage employer interest in safety and Encourage employer interest in safety and rehabilitationrehabilitation

• Promote the study of causes of accidentsPromote the study of causes of accidents

Establishment of OSHA Establishment of OSHA

Occupational Safety and Health Occupational Safety and Health AdministrationAdministration (1970) (1970) – OSH– OSH Act set forth by Act set forth by fed government to impose safety standards on fed government to impose safety standards on industryindustry– 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 companies comply by: keeping records, keeping

employees informed on safety matters, complying employees informed on safety matters, complying with standards for injury avoidance, etc...with standards for injury avoidance, etc...

NIOSHNIOSH• National Institute for Occupational Safety and National Institute for Occupational Safety and

HealthHealth– mainly for research and education functionsmainly for research and education functions– finds hazardous types of working conditions by reviewing finds hazardous types of working conditions by reviewing

researchresearch– human factors professionals use the standards or human factors professionals use the standards or

recommendationsrecommendations

Product LiabilityProduct Liability• Suits filed against a company claiming that a product Suits filed against a company claiming that a product

was defective and therefore caused injury or deathwas defective 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 user Defective - failed to perform safely as an ordinary user would expect when it was used in an intended or would expect when it was used in an intended or reasonably foreseeable manner, or if the risk inherent in reasonably 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

Factors that cause or Factors that cause or contribute to accidentscontribute to accidents

• The systems approachThe systems approach- accidents occur - accidents occur because of the interaction between system because of the interaction between system componentscomponents

• Direct causal factors in safetyDirect causal factors in safety1 the employee performing a taskthe employee performing a task2 the task itselfthe task itself3 any equipment directly or indirectly used in the taskany equipment directly or indirectly used in the task4 other factors - social/psychological & environmentalother factors - social/psychological & environmental

Personnel CharacteristicsPersonnel Characteristics

Factors affecting hazard recognition, decisions Factors affecting hazard recognition, decisions to act appropriately, & ability to act to act appropriately, & ability to act appropriatelyappropriately• Age & GenderAge & Gender

• younger people have more accidents - ages younger people have more accidents - ages 15-24, mostly young males15-24, mostly 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

Job Job Characteristics/EquipmentCharacteristics/Equipment

• Job characteristicsJob characteristics – such as high physical – such as high physical workload, high mental workload, monotony, etc…workload, high mental workload, monotony, etc…

• Equipment Equipment - 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 e.g. occurs when a person is doing repairs and another person unknowingly turns the circuit onperson unknowingly turns the circuit on

• Mechanical HazardsMechanical Hazards• results in cutting of skin, shearing, crushing, breaking, or results 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

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

The Social EnvironmentThe Social Environment

• Human behavior is influenced by social Human behavior is influenced by social contextcontext- Social norms, mgmt practices, morale, training, - Social norms, mgmt practices, morale, training,

incentivesincentives– e.g. construction workers will not wear safety e.g. construction workers will not wear safety

gear if no one else isgear if no one else is

Human ErrorHuman Error• The Misnomer of Human Error The Misnomer of Human Error – error usually – error usually

triggered by other things (e.g., poor design, triggered by other things (e.g., poor design, management, violations of use and maintenance). management, 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 Operator error blamed on over 60% of nuclear power plant

accidentsaccidents– 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

Taxonomy of Human ErrorTaxonomy of Human Error

InterpretationInterpretation

Situation Situation AssessmentAssessment

PlanPlan

Intention ofIntention ofActionAction

Action Action ExecutionExecution

StimulusEvidence

Memory

MISTAKESMISTAKES SLIPSSLIPS

LAPSES &LAPSES &MODE ERRORSMODE ERRORS

KnowledgeKnowledge RuleRule

Taxonomy of Human ErrorTaxonomy of Human ErrorMistakesMistakes

• MistakesMistakes – failure to come up with – failure to come up with appropriate solutionappropriate solution• Takes place at level of perception, memory, or Takes place at level of perception, memory, or

cognitioncognition• Knowledge-based MistakesKnowledge-based Mistakes – wrong solution – wrong solution

because individual did not accurately assess because individual did not accurately assess the situation.the situation.• Caused by poor heuristics/biases, insufficient Caused by poor heuristics/biases, insufficient

info, info overloadinfo, info overload• Rule-based MistakesRule-based Mistakes – invoking wrong rule – invoking wrong rule

for given situationfor given situation• Often made with confidenceOften made with confidence

• SlipsSlips – Right intention incorrectly executed – Right intention incorrectly executed (oops!)(oops!)• Capture errorsCapture errors – similar situation elicits action, which – similar situation elicits action, which

may be wrong in “this” situation. Likely to result when:may be wrong in “this” situation. Likely to result when:• Intended action is similar to routine behaviorIntended action is similar to routine behavior

• Hitting enter key when software asks, “sure you want to Hitting enter key when software asks, “sure you want to exit without saving?”exit without saving?”

• Either stimulus or response is related to incorrect responseEither stimulus or response is related to incorrect response• Hit “3” instead of “#” on phone to hear next message, Hit “3” instead of “#” on phone to hear next message,

because “3” is what I hit to hear the first messagebecause “3” is what I hit to hear the first message• Response is relatively automated, not monitored by Response is relatively automated, not monitored by

consciousnessconsciousness• 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 ErrorSlipsSlips

• 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 Examples: Forgetting to close gas cap, failure to

put safety on before cleaning gun, failure to put safety on before cleaning gun, failure to remove objects from surgical patientremove objects from surgical patient

• Mode ErrorsMode Errors – Making the right response, – Making the right response, but while in the wrong mode of operationbut while in the wrong mode of operation• Examples: leave keyboard in shift mode while Examples: leave keyboard in shift mode while

trying to type a numeral, driving in wrong gear, trying to type a numeral, driving in wrong gear, going wrong direction because display was north-going wrong direction because display was north-up when thought it was nose-upup when thought it was nose-up

Taxonomy of Human ErrorTaxonomy of Human ErrorLapses & Mode ErrorsLapses & Mode Errors

Human Reliability AnalysisHuman Reliability Analysis• Human Reliability AnalysisHuman Reliability Analysis – – predict predict

reliability of system in terms of probability of reliability of system in terms of probability of failure or mean time between failures (MTBF) failure or mean time between failures (MTBF) when system is designed to work in parallel or when system is designed to work in parallel or seriesseries

.9 .9

.9

.9

SeriesSeriesParallelParallel

Reliability = .9 x .9 = .81Reliability = .9 x .9 = .81P(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)

THERP componentsTHERP components

1.1. Human Error ProbabilityHuman Error Probability• Ratio of errors made to possible errorsRatio of errors made to possible errors

2.2. Event TreeEvent Tree• Diagram showing sequence of eventsDiagram showing sequence of events

• Probability of success or failure for each Probability of success or failure for each componentcomponent

3.3. Other Moderating FactorsOther Moderating Factors• May add in multiplier to account for variables May add in multiplier to account for variables

such as experience level, time, stress, etc.such as experience level, time, stress, etc.

Technique for Human Technique for Human Error Rate Prediction Error Rate Prediction

(THERP)(THERP)

THERP Event TreeTHERP Event Tree

aa AA

b\ab\a B\aB\a

SSSS

b\Ab\A B\AB\A

FFSS

FFSS

FFFF

SeriesSeriesParallelParallel

Series:P[S] = a(b\a)P[F] = 1 – a(b\a) = a(B\a) + A(b\A) + A(B\A)Parallel:P[S] = 1 – A(B\A) = a(b\a) + a(B\a) + A(b\A)P[F] = A(B\A)

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

1.1. Task Design Task Design – design tasks with working – design tasks with working memory capacity in mindmemory capacity in mind

2.2. Equipment Design Equipment Design a)a) Minimize perceptual confusions Minimize perceptual confusions – ease of – ease of

discriminationdiscrimination• Ex: airplane controls that feel like what they do (flaps, Ex: airplane controls that feel like what they do (flaps,

wheels)wheels)

b)b) Make consequences of action visible – Make consequences of action visible – immediate immediate feedbackfeedback

• Ex: preview window in some software programsEx: preview window in some software programs

c)c) 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

d)d) Reminders Reminders – 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

3.3. TrainingTraining – provide opportunity for – provide opportunity for mistakes in training, so can learn from mistakes in training, so can learn from themthem

• 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

5.5. Error-tolerant systemsError-tolerant systems – system allows for – system allows for error correction or takes over when error correction or takes over when operator makes serious erroroperator makes serious error

• Ex: Undo buttonEx: Undo button

Error Prevention / Error Prevention / Remediation (continued)Remediation (continued)

Approaches to Hazard Approaches to Hazard ControlControl

• Optimization standpoint Optimization standpoint - the most critical or - the most critical or “high-risk” hazards should receive top “high-risk” hazards should receive top prioritypriority• e.g. MIL-STD-882B categories of hazard (matrix combines e.g. MIL-STD-882B categories of hazard (matrix combines

frequency and severity categories)frequency and severity categories)

FrequencFrequencyy

CatastrophCatastrophicic

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

Hazard Control PriorityHazard Control PriorityReduce 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

2.2. PathPath – barrier or safeguard – barrier or safeguard• Guard on back of lawnmower to protect toesGuard on back of lawnmower to protect toes

3.3. PersonPerson – change behavior with training or – change behavior with training or warningswarnings• Warning: fan blades can turn on while engine is offWarning: fan blades can turn on while engine is off

4.4. Administrative controlsAdministrative controls – rules mandating – rules mandating behaviorbehavior• Must wear safety beltsMust wear safety belts

Safety AnalysisSafety Analysis

Sequence for identifying potential hazards and Sequence for identifying potential hazards and recommendations for hazard reduction: recommendations for hazard reduction: (Weinstein et al. (Weinstein et al. 1978)1978)

1.1. Task AnalysisTask Analysis – How will product be used? – How will product be used?2.2. Environment AnalysisEnvironment Analysis – Where will product be used? – Where will product be used?3.3. User AnalysisUser Analysis – Who will use product? – Who will use product?4.4. Hazard IdentificationHazard Identification – What is likelihood of hazard with – What is likelihood of hazard with

product?product?5.5. Generate Methods for Hazard ControlGenerate Methods for Hazard Control – What might – What might

eliminate hazards?eliminate hazards?6.6. Evaluate AlternativesEvaluate Alternatives – How will alternative designs affect – How will alternative designs affect

product performance?product performance?7.7. Select Hazard ControlSelect Hazard Control – Given alternatives, what is best – Given alternatives, what is best

design to minimize hazards?design to minimize hazards?

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 is Each subassembly is broken down further and each component is

analyzedanalyzed• Effect of each component’s failure on other components is Effect of each component’s failure on other components is

estimatedestimated

• Fault Tree AnalysisFault Tree Analysis• Top-down processTop-down process• Works from incident to possible causesWorks from incident to possible causes

Accident InvestigationAccident Investigation

Fact-Finding Fact-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 operating Obtain documents containing normal operating

procedures/ maintenance charts, reported procedures/ maintenance charts, reported abnormalitiesabnormalities

• Keep complete accurate notes in bound notebookKeep complete accurate notes in bound notebook• Record pre-accident conditions, accident sequence, Record pre-accident conditions, accident sequence,

post-accident conditionspost-accident 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

Accident InvestigationAccident InvestigationLevels of CausesLevels of Causes

Management Safety Policy & DecisionsPersonal Factors

Environmental factors

Unsafe Act Unsafe Condition

Unplanned Release of EnergyAnd/or

Hazardous Material

ACCIDENTPersonal Injury

Property Damage

BASICCAUSES

INDIRECTCAUSES(SYMPTOMS)

DIRECTCAUSES

Safety ProgramsSafety Programs

1.1. Identify risks to the companyIdentify risks to the company identify hazards, hazard controls, accident frequency, identify hazards, hazard controls, accident frequency,

& company losses due to accidents/incident claims& company losses due to accidents/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

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 what People must know a hazard exists, know what

actions are available, & know the consequences of actions 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 product Accurately convey the hazards of a product • Should include a signal word, info pertaining to the Should 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