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Ergonomics

Ashkan Heydarian

a.heydarian@srbiau.ac.ir

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Course Evaluation

Midterm Exam 3/3

Class activity 2/2

Final Exam 15/15

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Objectives

To be able to:

Understand the ergonomics concepts

Know which products are ergonomics

Design ergonomics products space and ….

upgraded the products or places by ergonomics rules

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References

Biomechanics in Ergonomics ; SHRAWAN KUMAR, Taylor & Francis 1999 , ISBN 0-7484-0704-9

Introduction to Ergonomics ; R.S. Bridger; 2003 by Taylor & Francis, ISBN 0-415-27378

Ergonomics for Beginners, 2nd edition Jan Dul, Erasmus University, The Netherlands and B. A. Weerdmeester, TNO Institute, The Netherlands Taylor & Francis Pbk 0-7484-0825-8

A Guide to Methodology in Ergonomics: Designing for Human Use Neville Stanton and Mark Young, Brunel University, UK Taylor & Francis Pbk 0-7484-0703-0

Fitting the Task to the Human, 5th edition K. Kroemer and E. Grandjean Taylor & Francis Hbk 0-7484-0664-6; Pbk 0-7484-0665-4

Evaluation of Human Work, 2nd edition John Wilson and Nigel Corlett, The University of Nottingham, UK Taylor & Francis Hbk 0-7484-0083-4; Pbk 0-7484-0084-2

Class-notes are NOT sufficient

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Contents

Introduction and concepts

Anatomy, posture and body mechanics

Ergonomics in Biomechanics

Heat and cold

Vision, light and lighting

Hearing, sound, noise and vibration

Displays, controls and virtual environments

ERGONOMICS for REHABILITATION PROFESSIONALS

6Introduction and concepts

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What is Ergonomics?

Ergonomics is the study of the interaction between people and machines and the factors that affect the interaction.

“Ergonomics is an applied science concerned with the design of workplaces, tools, and tasks that match the physiological, anatomical, and psychological characteristics and capabilities of the worker.” Vern Putz-Anderson

“The Goal of ergonomics is to ‘fit the job to the person,’ rather than making the person fit the job.” Ergotech

“If it hurts when you are doing something, don’t do it.” Bill Black

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What is Ergonomics?

A system is a set of elements, the relations between these elements and the boundary around them. Most systems consist of people and machines and perform a function to produce some form of output. Inputs are received in the form of matter, energy and information. For ergonomics, the human is part of the system and must be fully integrated into it at the design stage. Human requirements are therefore system requirements, rather than secondary considerations and can be stated in general terms as requirements for

• Equipment that is usable and safe • Tasks that are compatible with people’s expectations, limitations and training • An environment that is comfortable and appropriate for the task • A system of work organization that recognizes people’s social and economic needs.

9Evolution of Ergonomics

Dates back to Ramazzini 1700’s

Gained significance during WWII for airplane cockpit layout

Progressed slowly until the 80’s and 90’s with the advent of the computer and more efficient workplace design

Now, guidelines are in place and greater use of technology

10Benefits of Ergonomics

Decreased injury risk

Increased productivity

Decreased mistakes/rework

Increased efficiency

Decreased lost work days

Decreased turnover

Improved morale

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12Description of human–machine systems

Human components The human body is part of the physical world and obeys the same physical laws as other animate and inanimate objects. The goal of ergonomics at this level is to optimise the interaction between the body and its physical surroundings.

The effectors The three primary effectors are the hands, the feet and the voice. More generally, the musculoskeletal system and body weight can be regarded as effectors – no purposeful physical activity of the limbs can be carried out without maintenance of the posture of the body and stabilisation of the joints.

13Description of human–machine systems

The senses The senses are the means by which we are made aware of our surroundings. Human beings are often said to have five senses – sight, hearing, touch, taste

Central processes In order to carry out work activities, we require energy and information. Physiological processes provide energy to the working muscles and dissipate waste products.

14Description of human–machine systems

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Summary

Ergonomics occupies the ‘no man’s land’ between engineering and medicine, architecture and health and safety, computer science and consumer product design. It is the only scientific subject that focuses specifically on the interaction between people and machines. Historically, ergonomics can be seen to have arisen as a response to the need for rapid design of complex systems. The modern ergonomist has an important role to play as a member of the design team, providing scientific information about humans and ensuring that all aspects of the system are evaluated from the users’ or operators’ point of view. The participatory approach seems to be the best way to ensure that the implementation of ergonomics will be effective.

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Additional note :

Work-Related Musculoskeletal Disorders

(WMSDs)

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Work-Related Musculoskeletal Disorders (WMSDs)

Collective term for painful disorders brought on by acute or cumulative exposure to work activities. WMSDs can affect:- Muscles

- Tendons

- Nerves

- Skeletal Tissue

StrainSprainTendinitisTendinosis MyositisTenosynovitisArthritis

18WMSD are also known as:

Repetitive motion injuries - RMI Repetitive strain injuries - RSI Cumulative trauma disorders - CTD Occupational cervicobrachial disorders - OCBD Overuse syndrome Regional musculoskeletal disorders - RMD Soft tissue disorders Upper extremity cumulative trauma disorders -

UECTD Work related upper limb disorder - WRULD

19Factors to consider when evaluating WMSDs:

the area of the workplace where injury or pain is reported the occupation and job demands of the injured person length of shift worked (eg. night or day) the part of the body injured - examples include: back, neck or

shoulder the nature of the injury - examples include: strain, sprain, or

inflammation the type of accident - examples include: overexertion and

physical stress in lifting the causes/mechanisms of the injury (eg. repetitive

movement, heavy loads)

20What causes WMSDs?

heavy, frequent, or awkward lifting

pushing, pulling or carrying loads

working in awkward postures

hand intensive work

21How do WMSDs occur?

WMSDs do not happen as a result of a single accident or injury.

They develop gradually as a result of repeated trauma.

Excessive stretching of muscles and tendons can cause injuries that only last a short time. But repeated episodes of stretching causing tissue inflammation can lead to long-lasting injury or WMSDs.

22Muscle Injury

A muscle contraction that lasts a long time reduces the blood flow. Consequently, the substances produced by the muscles are not removed fast enough and accumulate.

The accumulation of these substances irritates muscles and causes pain.

The severity of the pain depends on the duration of the muscle contractions and the amount of time between activities for the muscles to get rid of those irritating substances.

23Tendon Injury

Tendons consist of numerous bundles of fibers that attach muscles to bones.

Tendon disorders are related to repetitive or frequent work activities and awkward postures.

Tendonitis

24Nerve Injury Nerves carry signals from the brain to

control activities of muscles. They also carry information about

temperature, pain, and touch from the body to the brain, and control bodily functions such as sweating and salivation.

With repetitive motions and awkward postures, the tissues surrounding nerves become swollen and squeeze or compress nerves.

Compression of a nerve causes muscle weakness, sensations of "pins and needles" and numbness. Dryness of skin and poor circulation to the extremities may also occur. Reynaud’s Phenomenon or “White Finger”

25Nerve Injury• Best known MSD• Compression of

the median nerve at the wrist

• Tunnel made up of nine flexor tendons and one peripheral nerve

• Numbness and tingling on the thumb side of the hand

Carpal Tunnel

Tinel test

Phalen test

26What are the signs and symptoms of work-related injuries?

joint stiffnessmuscle tightnessmuscle “burning”pain through ends of range of motionredness and swelling of the affected areasensations of "pins and needles“numbnessskin colour changesdecreased sweating of the hands

273 Stages of Pain

Stage 1- gradual onset- aching and tiredness of the affected limb occur during the work

shift- disappears with rest (overnight, weekend)- no reduction of work performance

Stage 2- aching and tiredness occur early in the work shift and persist at

night- reduced capacity for repetitive work- rest does not make pain subside

Stage 3- aching, fatigue, and weakness persist at rest- inability to sleep and to perform light duties- medical treatment required

SLR TEST

Acute(7days)o Sub-acute(4 weeks) At risk(>12weeks) Chronic(>6 M) Chronic pain

syndrome(<6 M )

28How can we prevent WMSDs?

Job Design

- mechanization

- job rotation

- work to rest ratios

- job enlargement and enrichment

- team work

Workplace Design and Layout Tools and Equipment Design Worker selection

- training- conditioning- posture

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What are the workplace risk factors for WMSDs?

What are the task risk factors?

Risk Factors

Risk of injury depends upon:

duration of exposure

frequency of exposure

intensity of exposure

combinations of risk factors

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31Just because your job has risk factors, doesn’t mean that you’re going to develop a WMSD. In fact, a little bit of exposure to some risk factors can actually be good for you. Occasionally moving into awkward postures like reaching or bending will help to stretch and exercise your muscles.

Also, if you occasionally do some lifting, especially if you do it properly, it can help to strengthen your muscles. This is the whole point behind exercising.

A constrained posture involving various body segments and joints can increase the risk of injury, even if the loads you are working with are very light.

Constrained postures:

- reduce the ability for muscles to produce force

- reduce the volume inside a joint and cause tissues to rub against each other, or bony structures, leading to injury

- reduce blood flow increasing fatigue and discomfort and can damage nerves and tissue (eg. Carpel tunnel syndrome)

Risk Factors

Constrained postures

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Risk Factors

Repetition

Workers performing highly repetitive tasks are at the highest risk for WMSDs.

Tasks requiring repetitive movements always involve other risk factors for WMSDs such as fixed body position and force.

A job task might require spending only a very small amount of time in a non-neutral posture but the worker may have to complete that same task several times in the course of a shift with this repetition potentially adding to the risk associated with the task.

In addition, repetitive movements of light objects can result in injury caused by the cumulative load on the muscles, joints, and tendons over the course of a shift or a work week.

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Risk Factors

Force The force required to do the task also plays an important role in

the onset of WMSDs.

More force equals more muscular effort and consequently, more time is needed to recover between tasks.

Since in repetitive work, as a rule, there is not sufficient time for recovery, the more forceful movements lead to fatigue much faster.

The amount of force needed to produce fatigue depends on:

- the weight of the tools and objects

- tool placement in relation to the worker's body.

- the shape of the tool

- condition of repair of the tool.

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Press

Pinch(palm)

Pulp PinchLateral Pinch

Finger Press

Grasp

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Images courtesy Canadian Centre for Occupational Health & Safety

http://www.ccohs.ca/oshanswers/diseases/rmirsi.html

Risk Factors

Pace of Work

Pace of work determines the amount of time available for rest and recovery of the body between cycles of a particular task.

The faster the pace, the less time is available and the higher the risk for WMSDs.

When the worker has no control over timing and speed of work because of external factors like assembly line speed or quota and bonus systems, stress levels increase – as do errors.

With higher stress level comes muscle tension causing fatigue and increased risk for WMSDs.

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Risk Factors

Temperature and Environment Temperature and humidity affect the worker performing

repetitive work.

When it is too hot and too humid, the workers tire more quickly and become more susceptible to injury.

Cold temperatures decrease the flexibility of muscles and joints increasing the likelihood of injury.

Noise creates cognitive stress and can negatively impact on work tasks and perceptions of fatigue and discomfort.

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Risk Factors

Vibration Vibration affects tendons, muscles, joints, and nerves.

Workers using vibrating tools may experience numbness of the fingers, loss of touch and grip, and pain.

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Risk Factors

Personal Factors age sex previous trauma job experience morphological

- strength

- aerobic fitness

- anthropometry (body shape)

nutrition

vitamin and mineral deficiency

disease processes- rheumatoid arthritis- diabetes mellitus- renal dialysis- thyroid abnormalities

hormonal factors- diurinal variations- menstruation- oral contraceptives- pregnancy

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40Anatomy, posture and body mechanics