Ergonomics for occupational health

1. 1

2. DEFINITION AND SCOPE
• Definition of Ergonomics is
derived from Greek

Ergo – work



nomos – law


• Hence – Literally translated as
“The laws of work”
• Ergonomics is concerned with the
reduction of stress and physical damage
in the work place 2

3. INTERNATIONAL ERGONOMICS
ASSOCIATION - DEFINITION
• “The scientific discipline concerned
with the process of interaction among
humans and other elements of a
system by way of a profession that
applies theory, principles, data and
methods to design in order to
optimize human well-being and
overall system performance”
3

4. KEY-ELEMENTS FOR HUMAN USAGE

Human capabilities and limitations as they
relate and interface with technology



Hence issues of design standardization and
application are critical



Promotion of human reliability, improved
health & safety of the worker

4

5. PRESENT CONTEXT
• Ergonomics seeks to design equipment,
tools, workstations & tasks to be
compatible with human capabilities and
limitations so as to ensure health, safety,
and well-being and optimum efficiency
• Consequently, this improves &
maintains the operations and
profitability of the organization
Note – It is an evolving or unfolding
science 5

6. OBJECTIVES OF ERGONOMICS
• To decrease individual’s risk of injury
& illness
• To improve health & safety and
workers performance by:

Decreasing worker’s fatigue &
discomfort



Improve quality of worker’s life



Improve quality & productivity, thus less
errors, compensation & operation costs



Enhance employee morale

6

7. ERGONOMICS ARE INTERDISCIPLINARY
• It draws on various fields in human sciences
and technology which include:

Anthropometry (measurement of human body)



Biomechanics



Physiology



Psychology



Mechanical engineering



Industrial design



Industrial management


• It adapts the work environment to fit the worker

8. rather than the other way round 7

9. 8

10. 9

11. ERGONOMIC SYSTEM
• The concept of ergonomics is therefore
based on 3 primary interacting components:
i. Human contact and interaction
with machine or equipment
ii. Machine safety
iii. Environmental hazards such as:
• Height of work benches,
• Equipment layout
• Temp., lighting, ventilation
• Noise, vibrations, radiation
• Shift conditions & psycho-social factors
10

12. ERGONOMIC SYSTEM cont’d
• Tasks are never performed in a
vacuum, and there must therefore be a
complete information flow loop
• It assures safety, comfort &
optimum performance
• It is dynamic, highly interactive &
must be designed to conform to
individual work situations
• It fulfills the demands of ergonomics
11

13. ERGONOMIC HAZARDS

Basic considerations:



Firstly, humans adapt poorly to
machines – tools, machines, work-
places & work procedures – these
have to be designed & developed for
effective, efficient & safe use by man



Secondly, existing tools etc should
be assessed to comply with
ergonomic requirements so as to
assure health, safety & efficiency

12

14. Five factors associated with
human abilities & limitations
1. Anthropometrics (matching people to their
equipment)
2. Biomechanics – study of physical
interaction of workers with machines
etc. Concerned with body
movements by studying biological
systems, anatomy, physiology &
mechanical engineering
3. Human sensory issues – vision,
hearing, smell, taste, balance &
kinesthetic sense (body movement)
13

15. Five factors associated with human
abilities & limitations cont’d
4. Human physiological homeostasis –
physical well-being of the body which
may be affected by:

Thermal conditions of the
environment
Illumination

Barometric pressure

Noise

Vibrations

Toxic substances &

Abnormal shift schedules
14

16. Five factors associated with human
abilities & limitations cont’d
5. Physiological (cognitive) systems – Body
systems are interdependent. Effects in
one may manifest as mental stress or
fatigue leading to poor decision-making
and de-motivation
15

17. ERGONOMIC HAZARD RISK ASSESSMENT
• Risk Assessment: Risk – Probability
of occurrence of injury or damage
• Four elements involved:

The hazard involved



The worker to be harmed



Severity of resultant injury or impact



Probability of injury or ill-health taking
place


• Ergonomics aims at preventing above risks
16

18. ERGONOMIC HAZARD RISK ASSESSMENT

The starting point for an evaluation of ergonomic
factors is an assessment of the workplace



It should address:


Hardware, eg. design and layout of machine
controls, ease of maintenance, and
machinery safety (guarding, interlocks etc)

Software, eg. standard operating procedures and
instructions, manuals, and computer programs

17

19. ERGONOMIC HAZARD RISK ASSESSMENT

Visual workspace, eg. task/display design, display
layout, information load, use of symbols



Organisation, eg. working method, job content
(degree of task variety and personal control), rate
of work, satisfaction, communication, reporting,
surveillance systems, management of conflict, etc



Physical workspace, eg. access, clearance, seating,
work position, reach, storage arrangements,
housekeeping etc.

18

20. ERGONOMIC HAZARD RISK ASSESSMENT

Physical environment, eg. temperature, noise,
lighting, vibration, substances hazardous to
health, etc.

Individual characteristics, eg. body size
(anthropometry), strength, endurance,
skill, training, motivation, attitude, etc.
NB. For detailed assessments it may be
necessary to involve an ergonomist.
19

21. ERGONOMIC DISORDERS
a) Work-related musculoskeletal
disorders (WMSD)
1. Carpal Tunnel Syndrome (CTS) -
Got through grinding, polishing,
sanding, hammering, forceful grip &
prehensile/extreme flexing &
extension of hands
2. Epicondylitis (tennis elbow) –
Turning screws, small parts assembly,
hammering, repetitive wrist extension
& repetitive grasp
20

22. Work-related musculoskeletal
disorders control
• Expert evaluation is essential in diagnosis of
WMSD taking into account biomechanical,
personal & work organizational factors
• Ergonomics is vital in preventing WMSD by
minimizing cramped positions, twisting,
turning, repeated reaching motions,
mis-alignment of body parts &
manual material handling
21

23. ERGONOMIC DISORDERS cont’d
b) Manual Material Handling
Disorders (MMHD)
• Refers to lifting, lowering, pushing &
dragging of loads without assistance
of mechanical devices
• This traumatizes musculo-
skeletal systems
• It is responsible for cuts,
bruises, hernias & back injuries
22

24. ERGONOMIC DISORDERS cont’d
ILO Guidelines for MMHD (Lifting)
AGE (years) MEN WOMEN
18-20 23 kg 14 kg
20-35 25 kg 15 kg
35-50 21 kg 13 kg
>50 16 kg 10 kg
23

25. MEASURES TO COUNTER MMHD
• Train workers in correct load-
handling procedures
• Avoid turning and twisting when
handling loads – apply feet turn
• Keep load close to body
• Use mechanical assistance
whenever possible
• Design work place to suit tasks
24

26. MEASURES TO COUNTER MMH cont’d

As much as possible design workplace to
push and pull rather than lift & lower



Use hoists, conveyor trolleys etc if possible



Provide ramps instead of stairs



Avoid uneven and slippery under-foots



Consider physical conditions of worker such
as protective clothing and thermal
conditions

25

27. Relationships between work conditions ,
ergonomics and health
Anatomy and Physiology
WORK CONDITIONS HUMAN FACTORS HEALTH HAZARDS
Dimension of seats and Anthropometry Bad posture
Benches • Body dimensions Discomfort
General fatigue
Motion study Anthropometry Bad posture
•Workplace layout •Body dimensions Discomfort
•Work rate •Strength of muscles General fatigue
•Structure of joints Local muscular fatigue
•Functions of muscles (incl. tenosynovitis)
Design of hand tools Anthropometry Local muscle strain
•Body dimensions Local muscular fatigue
•Strength of muscles (incl. tenosynovitis)
•Structure of joints
•Functions of muscles
26

28. Relationships between work conditions
, ergonomics and health
Anatomy and Physiology
WORK CONDITIONS HUMAN FACTORS HEALTH HAZARDS
Design of controls Anthropometry Local muscle strain
- Levers - Body dimensions Local muscular fatigue
- Hand-wheels - Strength of muscles (incl. tenosynovitis)
- Knobs - Structure of joints
- Buttons, etc - Functions of muscles
Mild Manual Handling Kinetic methods based on Injuries
- Strength of muscles -Muscle strain
- Structure of joints - Hernias
- Skeletal damage
- Slipped discs
Heavy manual work Physical fatigue Increased general fatigue
Physiological cost of work
- Oxygen consumption
- increased heart rate
- Raised body temp
27

29. Relationships between work conditions ,
ergonomics and health
Anatomy and Physiology
WORK CONDITIONS HUMAN FACTORS HEALTH HAZARDS
Uncontrolled Physiological cost of work Thermal discomfort
- Air temp. - Subjective feelings Heat stress and disorders
- Radiant heat -Increased heart rate Cold stress and disorders
- Humidity - Raised body temp
- Air movement - Increased temp
regulating mechanism
Vibrations Raynaud’s phenomenon
Cold (disorder of blood vessels
and nerves caused by
vibrations of fingers from
hand tools and surfaces
Flying Ear anatomy Ear damage
Diving Gases in blood Bends
Caisson work Anoxia
Oxygen poisoning
28

30. Relationships between work conditions ,
ergonomics and health
Anatomy and Physiology
WORK CONDITIONS HUMAN FACTORS HEALTH HAZARDS
Noise Hearing Deafness
Auditory discomfort
Design of indicators Sensory and perceptual Increased accidents
-Dials abilities – especially Raised stress
- Warning lights etc visual
- Design of controls -Loss of natural
- Levers directions
- Buttons etc
Design of Visual abilities Accidents
-Labels - Sensory Stress
- Notices - Perceptual
- Posters Mental abilities
-Learning
- Thinking
29

31. Relationships between work conditions ,
ergonomics and health
Anatomy and Physiology
WORK CONDITIONS HUMAN FACTORS HEALTH HAZARDS
Lighting Visual abilities Accidents
- Quantity -Sensory Stress
- Distribution - Perceptual Visual fatigue
- Glare Mental abilities Visual discomfort
Colour – environment -Learning Depression
- Colour coding - Thinking
Inspections and fine Visual abilities Boredom
assembly (arrangement): -Sensory Stress
-Lighting - Perceptual Visual fatigue
- Contrasts Vigilance
-- colours
- Movements
Job design Sensory and perceptual Boredom, stress
- Duties Mental abilities, accidents
motivation
Human relations Personalities Stress, neuroses
30

32. POSTURES AT WORK

A person’s posture at work—the
mutual organization of the trunk, head
and extremities—can be analysed and
understood from several points of view



Postures aim at advancing the work; thus,
they have a finality which influences their
nature, their time relation and their cost
(physiological or otherwise) to the person in
question.

31

33. POSTURES AT WORK

Musculoskeletal load is a necessary element in
body functions and indispensable in well-being



From the standpoint of the design of the work,
the question is to find the optimal balance
between the necessary and the excessive



Postures have interested researchers and
practitioners for at least the following reasons:

32

34. POSTURES AT WORK

A posture is the source of musculoskeletal load



Posture is closely related to balance and
stability. Loss of balance is a common
immediate cause of work accidents



Posture is a source of information on the events
taking place at work. Observing posture may be
intentional or unconscious



Posture is the basis of skilled movements and

visual observation
33

35. 34

36. 35

37. Too high hand positions/forward bending may contribute to static (repetetive)
load
36

38. 37

39. 38

40. International standards

The International Labour Organization
published a Recommendation in 1967 on
maximum loads to be handled



The NIOSH lifting guidelines (NIOSH 1981)The
guidelines derive weight limits for loads using the
location of the load—a postural element—as a
basis



In the International Organization for
Standardization as well as in the European
Community, ergonomics standards and directives

exist which contain matters relating to postural
elements (CEN 1990 and 1991)
39

41. Biomechanics

Biomechanics is a discipline that approaches the study
of the body as though it were solely a mechanical
system: all parts of the body are likened to mechanical
structures and are studied as such



The following analogies may, for example, be drawn:


bones: levers, structural members

flesh: volumes and masses

joints: bearing surfaces and articulations

joint linings: lubricants

40

42. Biomechanics

muscles: motors, springs



nerves: feedback control mechanisms



organs: power supplies



tendons: ropes



tissue: springs



body cavities: balloons

41

43. Biomechanics

The main aim of biomechanics is to study the way
the body produces force and generates movement



The discipline relies primarily on anatomy,
mathematics and physics; related disciplines are
anthropometry (the study of human body
measurements), work physiology and kinesiology
(the study of the principles of mechanics and
anatomy in relation to human movement)

42

44. Biomechanics

In considering the occupational health of
the worker, biomechanics helps to
understand why some tasks cause injury and
ill health



Some relevant types of adverse health effect
are muscle strain, joint problems, back
problems and fatigue

43

45. Biomechanics

Back strains and sprains and more serious
problems involving the intervertebral discs
are common examples of workplace injuries
that can be avoided



These often occur because of a sudden
particular overload, but may also reflect the
exertion of excessive forces by the body over
many years: problems may occur suddenly

or may take time to develop
44

46. Biomechanics

An example of a problem that develops over time is


“seamstress’s finger”. A recent description describes
the hands of a woman who, after 28 years of work in a
clothing factory, as well as sewing in her spare time,
developed hardened thickened skin and an inability
to flex her fingers (Poole 1993). (Specifically, she
suffered from a flexion deformity of the right index
finger, prominent Heberden’s nodes on the index
finger and thumb of the right hand, and a prominent
callosity on the right middle finger due to constant
friction from the scissors) bone cysts.
45

47. Biomechanics

X-ray films of her hands showed severe degenerative
changes in the outermost joints of her right index and
middle fingers, with loss of joint space, articular sclerosis
(hardening of tissue), osteophytes (bony growths at the
joint) and Inspection at the workplace showed that these
problems were due to repeated hyperextension (bending
up) of the outermost finger joint. Mechanical overload and
restriction in blood flow (visible as a whitening of the
finger) would be maximal across these joints. These
problems developed in response to repeated muscle
exertion in a site other than the muscle.

46

48. Biomechanics

Biomechanics helps to suggest ways of designing
tasks to avoid these types of injuries or of
improving poorly designed tasks



Remedies for these particular problems are to
redesign the scissors and to alter the sewing tasks
to remove the need for the actions performed

47

49. Biomechanics

Two important principles of biomechanics are:


Muscles come in pairs. Muscles can only
contract, so for any joint there must be one
muscle (or muscle group) to move it one way
and a corresponding muscle (or muscle group)
to move it in the opposite direction

Muscles contract most efficiently when the
muscle pair is in relaxed balance
48

50. 49

51. Biomechanics
Applications

The following are some examples illustrating
the application of biomechanics.


The optimum diameter of tool
handles
The use of pliers

Screwdriving
50

52. Manual Material Handling

The term manual handling includes lifting,
lowering, pushing, pulling, carrying, moving,
holding and restraining, and encompasses a large
part of the activities of working life.



Biomechanics has obvious direct relevance to
manual handling work, since muscles must move to
carry out tasks.

51

53. Manual Material Handling

The question is: how much physical work
can people be reasonably expected to do?



The answer depends on the circumstances;



there are really three questions that need to
be asked.



Each one has an answer that is based on
scientifically researched criteria:

52

54. Manual Material Handling
1. How much can be handled without damage to the
body (in the form, for example, of muscle strain,
disc injury or joint problems)? This is called the
biomechanical criterion.
2. How much can be handled without overexerting the
lungs (breathing hard to the point of panting)? This is
called the physiological criterion.
3. How much do people feel able to handle comfortably?
This is called the psychophysical criterion.
53

55. Manual Material Handling

Many factors determine the extent of the
load placed on the body by a manual
handling task. All of them suggest
opportunities for control



Posture and Movements


The load

56. 
Organization and
environment
Personal
factors
54

57. Manual Material Handling

It should be noted that 23 kg is the maximum weight
that NIOSH recommends for lifting



This has been reduced from 40 kg after observation of
many people doing many lifting tasks has revealed that
the average distance from the body of the start of the
lift is 25 cm, not the 15 cm assumed in an earlier version
of the equation (NIOSH 1981)

55

58. Manual Material Handling
Estimating Spinal Compression Imposed by
the Task

Computer software is available to estimate the spinal
compression produced by a manual handling task



The 2D and 3D Static Strength Prediction Programs
from the University of Michigan (“Backsoft”)
estimate spinal compression.

56

59. Manual Material Handling

The inputs required to the program are:


the posture in which the handling activity is
performed

the force exerted

the direction of the force exertion

the percentile of the population under study
57

60. THANK YOU