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Instructor: Vincent Duffy, Ph.D.Instructor: Vincent Duffy, Ph.D.

Associate Professor of IE/ABEAssociate Professor of IE/ABE

Lecture 20 – Safety DesignLecture 20 – Safety Design

Tues. April 10, 2007 Tues. April 10, 2007

IE 486 Work Analysis & Design IIIE 486 Work Analysis & Design II

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

• Ch.14 in Wickens text – Introduction to Safety and Accident

Prevention– Safety Legislation– Factors that contribute to accidents– Human Error & Approaches to Hazard Control– Safety Analysis for Products and Equipment

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Introduction to Safety and Introduction to Safety and Accident PreventionAccident Prevention

• Accidents are the leading cause of death of young people (under age 44).– 47000 in motor vehicles– 13000 from falls– 7000 from poisoning

• In 1993, 10000 deaths in the workplace alone.• Overexertion, impact accidents, falls

• Accidents are costly – safety is an economic issue– Workplace accidents alone are estimated to cost

$48B per year.

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Safety LegislationSafety Legislation• It is commonly recognized that during the

1800s, workers performed under unsafe and unhealthful conditions.– OSHA – established in 1970

• Monitors safety in the workplace, however, it is understaffed.

– NIOSH – National Institute of Occupational Safety and Health

• Typically performs research that may later be integrated into OSHA standards

• These days, most change with regard to safety is due to litigation – eg. Product liability lawsuits.

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Factors that contribute to accidentsFactors that contribute to accidents

Task components Age – younger have more accidents, Ability, experience, drugs, alcohol, gender, stress Alertness, fatigue, motivation, accident proneness

Job Arousal, fatigue, physical and mental workload, work-

rest cycles, shifts, shift rotation, pacing, ergonomic hazards, procedures

Equipment & tools Controls & displays, electrical, mechanical and thermal

hazards, pressure hazards, toxic substances, explosives and other component failures

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Factors that contribute to accidentsFactors that contribute to accidents

Physical Environment Illumination, noise, vibration, temperature,

humidity, airborne pollutants, fire hazards, radiation hazards, falls

Social/psychological environment Management practices, social norms, training,

incentives

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Model of causal factors in occupational Model of causal factors in occupational injury – Fig 14.1injury – Fig 14.1 Management or

design error creating certain conditions in the…

Work system Includes employee

characteristics, job characteristics, equipment & tools, physical environment, social environment

Natural factors, hazards, operator error

Leading to accident or injury

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Human errorHuman error

Errors of omission Leaving out a step

Errors of commission Doing a step incorrectly or adding a step

Slips Intend to step on rung of ladder, but miss Intend to save file, but save incorrectly and lose

itHow to reduce human error?

One of three waysSelection, training, or system design

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Human errorHuman error It is also important to identify potentials for human

error Some techniques such as THERP

Technique for human error prediction provide guidelines for an analyst to identify errors that might occur at each point in a task analysis Assign probabilities to each error

Other such methods exist Some may suggest the psychological mechanism that

caused the error, others rely on the skills/rules/knowledge based model To explain behavior in relation to Rasmussen’s Information

processing model. So far, none are comprehensive and they tend to

rely on the ability of the person using the method (not very repeatable)

It is suggested that more than one method be used

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Approaches to Hazard ControlApproaches to Hazard ControlRisk = hazard severity * likelihood

Severity – catastrophic, critical, marginal, negligible

Frequency – frequent, probable, occasional, remote, improbable

Reducing hazards can be focused on Source, path, person, administrative controls

Source – eg. ‘Design out’Path – eg. ‘safeguard’

Keep worker from entering a hazardous area Wear protective equipment

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Table 14.3 Hazard MatrixTable 14.3 Hazard Matrix

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Approaches to Hazard ControlApproaches to Hazard Control Person – eg. ‘Warning’ or ‘training’

These include attempts to change the behavior that may be hazardous

Eg. Warning: don’t place hands near pinchpoints on machine.

Administrative – eg. ‘legislation’ Other examples include shift rotation, mandatory rest

breaks, sanctions for incorrect and risky behavior These are typically not as effective as ‘design out’ (or source

solutions).

How to identify possible methods of hazard reduction? – read a lot, know/study how people will use the product.

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Safety Analysis for Products and EquipmentSafety Analysis for Products and Equipment

Three alternatives: 1. Designers can consider safety during initial

design Identifying potential hazards of a product, tool or

piece of equipment when it is first designed. 2. Facilities or systems can be evaluated

‘proactively’ to identify hazards to control them ‘before’ accidents occur.

3. Facilities and systems can be evaluated in a ‘reactive’ manner by evaluating actual accidents to fix the hazards that caused them.

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Safety Analysis for Products and EquipmentSafety Analysis for Products and EquipmentOne such method suggests

Breaking the system or product into sub-components Then analyzing the sub-components or sub

assemblies for potential ‘failure’ And then evaluating potential ‘effects’ of each failure

This the failure mode and effects analysis (FMEA) This is sort of ‘bottom-up’ approach

A top-down approach could be the ‘fault-tree analysis From incident or undesirable event to possible

causes

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Bottom up - Considering each failure Bottom up - Considering each failure & analyzing what can lead to it& analyzing what can lead to it

• Failure Mode, Effects & Criticality Analysis

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QOTDQOTD

1. FMECA is a

a. bottom up approach to safety analysisb. top down approach c. top down to analysis of work designs that use automationd. all of the abovee. none of the above