ECE 796/896ECE 796/896Human Factor Human Factor EngineeringEngineering

Chapter 20Chapter 20

Human Error, Human Error, Accidents, and SafetyAccidents, and Safety

Human ErrorHuman Error

• Inappropriate or undesirable human decision or behavior the reduces system performances or causes an accident.

• Discrete-action, Information Processing

Error ClassificationsError Classifications

• Discrete Action Classifications:

Errors Of omission, errors of commission, sequence errors, and timing errors.

• Information Processing Classifications:

Execution of procedure: skill-based behavior, rule-based behavior, knowledge-based behavior

Dealing with Human Dealing with Human ErrorError

• Selection: Being able to select the correct employees for the tasks.

• Training: Errors are reduced by proper training. Refreshers are good.

• Design:– Exclusion designs, Prevention designs, and Fail-

Safe designs.

AccidentsAccidents

• A major objective of Human Factors work is Accident reduction/elimination.

• Definition: Unexpected, without cause, mishap …

• Indicators: low degree of expectedness, low degree of avoidability, low degree of intention.

Human Error and Human Error and AccidentsAccidents

• Human error is said to cause a large percentage of accidents.

• What can be other causes ?– Operator Error or Unsafe Conditions– Blame the active operator, legal system

looks at blame/fault, easier to blame the worker than the workplace, forms used point to operator error.

Accident Data AnalysisAccident Data Analysis

• Data Collection: OSHA, MSHA, NSC– Nature of injury, part of body, type of

accident, source of the injury– Data bases exist with frequency data,

trends– Do not provide data that uncover unsafe

situations.

Critical Incident Critical Incident TechniqueTechnique

• Description of observed unsafe acts or near-miss accidents.

• There are more critical Incidents then accidents, there is more data. This data can also show behavior patterns that can be reversed or avoided.

• Problems: selective recall and definition of a near miss

Accident CausationAccident Causation

• Accident Proneness– Some people are more prone to accidents than

others, because of some constitutional characteristics. Changes over time (older have lower rates)

• Job demand vs. worker capability– Share common ground with accident-liability

theories. – Adjustment-to-stress and arousal-alertness

Cont.Cont.

• Psychosocial: Goals-freedom-alertness

If workers are allowed to set reasonably attainable goals then good quality performance follows. Also when morale is high injuries are low.

Factors contributing to Factors contributing to AccidentsAccidents

• Contributing Factors in Accident Causation (CFAC): Emphasis on management and social-psychological factors, recognition of the man-machine system by including categories for each component.

Study of 248 AccidentsStudy of 248 Accidents

• Inadequate SOP: 19%• Error in Recognition: 15%• Error in judgment: 14%• Poor inspection: 12%• Inadequate directives: 10%• Inadequate communications: 10%• Ops error, unskilled Op, other, Maint (20%)

Special Accident Special Accident SituationsSituations

• Stairs: 2 mil injuries, 1000 deaths per year, most occur in the home where they rank number 1 in type of accident.– Most have only one or two steps, poorly

illuminated, the steps have no markings and are colored the same as the levels that they connect, handrails not present.

– Risers 7-4inch, treads 11 inches

Accidental Poisoning of Accidental Poisoning of ChildrenChildren

• 1980 in 3 months, 28,000 children were treated for ingesting hazardous substances.

• 93% happened in the home• 79% child and parent were in different rooms• 89% not closely monitored• 87% parents were engaged in a routine

activity• 59% the substance was left out or was in use• 57% the container had a safety cap

Reducing Accidents by Reducing Accidents by Altering BehaviorAltering Behavior

• Procedural Checklists: std. In aircraft

• Training: stress safe behavior, suitable conditions for practice

• Feedback: after training

• Contingency reinforcement Strategies:– Behavior modification

• Incentive programs:

Perception of RiskPerception of Risk

• Risk,hazard,danger

• Hazard: condition or set of circumstances that has the potential for causing injury or death.

• Risk: The probability of injury or death

• Danger: Risk * Hazard

Evaluation of RiskEvaluation of Risk• Ability to estimate risk. This is hard for people to do well, usually overestimate low risk

and underestimate high risk.

• Relative risk: People are good at estimating this risk type.

• Availability heuristic: higher probabilities to events they can easily remember. News stories bias perceptions of risk.

Risk PerceptionRisk Perception

• Accidents attributed to perceiving risk– Failed to perceive hazard - 36%– Underestimated hazard - 25%– Failed to respond to a hazard - 17%– Responded to hazard, ineffectively - 14%

Altering Hazard & Risk Altering Hazard & Risk PerceptionPerception

• Safety Communications should– Be specific to a particular task and situation– Back up a training program– Give a positive instruction– Be placed close to where the desired action

is to take place– Build on existing attitudes and knowledge– Emphasize non-safety aspects

Altering Hazard & Risk Altering Hazard & Risk PerceptionPerception

• Safety Communications should not– Involve horror– Be negative, can show wrong vs. right way– Be general, most people will think they act

safely.

WarningsWarnings

• Instructions often contain warnings– Approaches to making a product safer

• Design the dangerous feature out of the product.

• Protect with shielding or guarding• Provide adequate warnings and instructions for

proper use and reasonable misuse.

More on WarningsMore on Warnings

• Purposes: 4 principle purposes -1.Inform the users of a hazard or danger.2.Provide users with information regarding the likelihood of injury.3.Inform users of how to reduce the likelihood of injury.4.Remind users of the danger at the time and place where the danger is most encountered.

Cont.Cont.

• Designing: For a warning to change behavior it must be sensed, then received, understood and heeded.

• Sensing: Catch the attention, color,size,shape,graphical design, contrast, lights, etc …

• Receiving: Levels of warning: Danger,warning, caution

• Understanding: Signal word, hazard,consequences, instructions

Effectiveness of Effectiveness of WarningsWarnings

• Warnings placed properly in instruction manuals are effective.

• Warnings on products - ineffective ?

Product LiabilityProduct Liability

• Legal term used to describe an action in which an injured party seeks to recover damages for person injury from a mfg. because the plaintiff believes that the injury resulted from a defective product.

Cont.Cont.

• 1. Negligence: defendant conduct

• 2. Strict liability: tests product quality

• 3. Implied warrantee: product quality

• 4. Express warrantee or misrepresentation: product performance vs. manufactures representation.

Making a CaseMaking a Case

• Established that the product was defective in manufacture or design.

• When is a product defective.

• Product defect is the cause of the injury.

When is a Product When is a Product Defective?Defective?

• Patent-Danger rule: patently obvious danger - later proved poor

• Reasonableness: Product is defective if it presents an unreasonable danger to the user.

• Failed to perform safely as an ordinary user would expect.

• Risks inherent in the design outweighed the benefits of design.

Designing a Reasonably Designing a Reasonably Safe ProductSafe Product

• 1. Delineate the scope of product uses.• 2. Identify the environments within

which the product will be used.• 3. Describe the user population.• 4. Postulate all possible hazards,

including estimates of probability of occurrence and seriousness of resulting harm.

Cont.Cont.• 5. Delineate alternate design features or production

techniques, including warnings and instructions, that can be expected to effectively mitigate or eliminate the hazards.

• 6. Evaluate such alternatives relative to the expected performance standards of the product, including the following:– A. other hazards– B. subsequent usefulness– C. ultimate cost– D. comparison to similar products

• 7. Decide which features to include in the final design.