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Principles of Ergonomics

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Title: Principles of Ergonomics


1
Principles of Ergonomics
  • TM 655
  • SDSMT
  • Summer 2008

2
Assignment
  • MacLeod, Chapter Two
  • Gabriel, Chapter Two
  • Case Examples I and II

3
What is Ergonomics?
  • Laws of Work
  • the science and art of fitting the job to the
    employee to
  • minimize injuries
  • improve productivity quality
  • The Dual Goals

4
Ergo concepts come from . . .
  • Engineering concepts
  • physics
  • psychology
  • anthropometry
  • anatomy
  • physiology
  • kinesiology

5
Ergo requires skills in . . .
  • Teamwork
  • problem solving
  • innovative thinking
  • communications
  • economic accountability
  • desire to help people

6
Why Address Ergonomics?
  • Regulatory reasons
  • Humanitarian reasons
  • Good business practice

7
Cost Categories Forgotten?
  • Lost productivity
  • medical plan
  • absenteeism
  • reduced quality / service
  • employee turnover
  • training

8
Why?
  • Median days away from work for carpal tunnel
    syndrome was 30 days (94 BLS)
  • A single CTD could reach 50,000
  • But, we dont need to justify based on claim
    costs
  • Because ergonomics is good business!

9
Cost Accounting
  • Account for safety injury costs by department
    or unit
  • Coordinate Workers Compensation costs and
    Medical costs

10
The Risk Factor Model
Lack of Rest
Work/Rest Ratio
Shift Length
Environment
Sustained
Repetition
Occupational
Vibration
Non-Occupational
Temperature
Posture
Physical Temporal Risk Factors
Force
Personal
Psychosocial
Compounding Risk Factors
11
Physical Temporal Risk Factors
  • Force
  • Posture
  • Temperature
  • Vibration
  • Repetitions
  • Sustained
  • Shift Length
  • Work / Rest Ratio
  • Lack of Rest

12
Vibration
  • Identify sources
  • Eliminate or isolate if possible
  • Dampening
  • better tool design
  • handle coatings
  • dampening gloves

13
Thermal Considerations
  • Avoid cold exposure to extremities
  • especially fingers
  • Consider special gloves
  • Consider localized heating

14
Non-Occupational Activities
  • Hobbies
  • gardening, knitting, sewing, musical instruments,
    etc.
  • Sports
  • jogging, softball, rock climbing, golf, racquet
    sports, etc.
  • Miscellaneous
  • household chores, carrying children, driving cars
  • Sleep

15
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16
Personal Risk Factors
  • Aerobic capacity
  • age
  • alcoholism
  • body build
  • diabetes
  • flexibility
  • gender
  • gout
  • hypertension
  • medical history
  • menopause
  • Nutrition
  • obesity
  • oral contraceptives
  • posture
  • pregnancy
  • prior history of injury
  • renal disease
  • rheumatoid arthritis
  • smoking
  • stature
  • strength

17
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18
Psychosocial Risk Factors
  • Organizational climate culture
  • Job attitude job satisfaction
  • Personality traits
  • Personal problems
  • marital problems
  • death of loved ones
  • financial problems

19
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20
Basic Factors for the Design of Products
Workplaces
  • People are different.
  • People have limitations.
  • People have certain expectations and predictable
    responses to given situations.
  • If you ignore these factors, the consequences
    will be costly financially and in terms of human
    discomfort and performance.

21
People are Different
  • Go to the presentation titled, People are
    Different

22
People are Different
  • Commonly the workplace is designed for a One
    size fits all
  • This approach ends up fitting only a small
    portion of the working population
  • The workforce is aging
  • More experience, but . . .
  • Less strength, poorer vision, less range of motion

23
People Have Limitations
  • Size
  • Strength
  • Range of Motion
  • Vision
  • Hearing

24
People Have Predictable Reactions
  • Spatial Compatibility
  • Complexity

25
To Err is Human
  • Human errors may be due to lack of ergonomics in
    design.
  • With good ergonomics in design, errors can be
    reduced.

26
Cognitive Errors
  1. Perception Errors
  2. Decision Errors
  3. Action Errors

27
1. Perception Errors
  • The person did not grasp the needed information
    for any number of reasons.
  • The signal or message was not clear.
  • There were other distracting signals.
  • The person was not trained in the meaning of the
    information.

28
2. Decision Errors
  • The person did not respond to the signal or
    information
  • Other decisions had to be made quickly and the
    person decided the signal was not important or a
    priority.
  • The person judged the situation incorrectly.

29
3. Action Errors
  • The person reacted, but activated the wrong
    control or activated the correct control
    improperly.
  • Controls were not laid out as expected.
  • Controls did not operate as expected.
  • Inadvertently activated a control when there was
    not signal or decision made.

30
10 Physical Principles
31
1. Keep Everything in Easy Reach
  • Long reaches can strain the body and make work
    more difficult, plus waste time.
  • Keep frequently used items (knobs, switches,
    tools, parts, etc.) within easy reach.
  • Reduce overall dimensions of work surface.
  • Tilt work surfaces upward.
  • Make cutouts to allow closer access.
  • Use Lazy Susans. Suspend tools in mid-air.
  • DESIGN FOR THE SMALLEST PERSONS!!

32
2. Work at Proper Heights
  • Mismatches between worker heights and work
    heights leads to awkward/contorted postures and
    contributes to fatigue, discomfort and possibly
    injury and lower productivity.
  • Work is generally done at elbow height.
  • Heavier work a bit lower.
  • Lighter work a bit higher.
  • Consider visual demands and lighting.

33
3. Work in Good Postures
  • Corollary to 2. Working in good postures
    increases comfort and productivity.
  • Understand the concept of the neutral posture for
    wrists, elbows, shoulders, head/neck, and spine.
  • Adjustable height angle workstations (p 46)
  • Store items in the POWER ZONE (knuckle height to
    elbow height)
  • Pistol grip vs. inline tools (see next slide)

34
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35
4. Reduce Excessive Forces
  • Anything that can be done to minimize the
    exertion required to perform a task.
  • Needlessly excessive forces load the muscles
    creating fatigue and potential injury.
  • Example Ford truck assembly wiring connectors.
    Commonly found forces as high as 75 lbs. Reduced
    many forces to as low as 2 lbs.

36
4 Continued . . .
  • Hand Grasping Forces
  • Power grips are better than pinch grips.
  • Tool grips can be too large and too small
  • Two-handed tools are better than one-handed tools
  • Arm Push/Pull Forces
  • Use mechanical assists and power tools to your
    advantage
  • Use of jigs / fixtures are better than static
    grips.

37
4. Continued . . .
  • Loads on lower back
  • Utilize the power zone when lifting
  • Knuckle to elbow height close in.
  • Pushing is better than lifting / carrying.
    Pushing is better than pulling.
  • Larger diameter wheels are better
  • Maintain wheels
  • Keep floor clean

38
Force Guidelines
  • Pinch grip maximum 8 lbs
  • Power grip maximum 25 lbs
  • Push maximum 24 lbs
  • Pull maximum 18 lbs
  • Static force exertion maximum of 60 s
  • Lifting (see NIOSH Lifting Guide)

39
5. Minimize Fatigue
  • Overloading human capabilities can lead to
    injuries, accidents, poor quality, lost
    productivity.
  • Avoid static muscle loading
  • Restricts blood flow, oxygen, lactic acid
  • Better tool handles, Tool Balancers

40
Tool Balancer
41
6. Reduce Excessive Repetition
  • The number of repeated motions produces wear and
    tear on the body.
  • Use machines for repetitive tasks.
  • Design for motion efficiency and efficient
    workstation layout.
  • Eliminate double handling.

42
Repetition Guidelines
  • Damaging wrist motion
  • 1000 per hour maximum
  • 2000 maximum per 8 hour shift

43
7. Provide Clearance and Access
  • Provide space to both get the task done and have
    easy access to everything needed.
  • Provide adequate clearance for head, arms, torso,
    knees, feet.
  • Keep largest and smallest workers in mind during
    design.
  • Design for the range.
  • Use adjustable workstation

44
8. Minimize Contact Stress
  • Direct pressure or contact stress can disrupt
    blood flow and nerve function.
  • Remember stress is is the force distributed over
    a given area.
  • Reduce the force
  • Increase the contact area
  • Avoid sharp edges on work surfaces and tools.

45
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46
9. Provide Mobility and Change of Posture
  • Even a great posture needs a break
  • Sit-Stand Workstations
  • Micro-Break Concept

47
10. Maintain a Comfortable Environment
  • The work environment can directly and indirectly
    affect worker comfort, but also quality and
    productivity.
  • There are standards for appropriate
  • Lighting
  • Temperature/humidity
  • Noise
  • Vibration

48
10 Cognitive Principles
49
1. Standardize
  • Many errors are caused because there is
    inconsistency in how information is displayed and
    how controls work.
  • To prevent mistakes, a general rule is to insure
    that similar devices work the same way agreeing
    on a standard.

50
2. Use Stereotypes
  • A commonly held expectation of what people think
    is supposed to happen when they recognize a
    signal or activate a control.
  • Examples
  • Moving a lever forward to increase speed
  • Rotating a knob clockwise to make a pointer turn
    to the right or make it increase
  • Using red to mean stop or danger

51
3. Link Actions with Perceptions
  • Ideally there should be a strong relationships
    between the perception of the need to take an
    action and the action itself a compatibility
    between a display of information and a control.
  • Good design means configuring things so that it
    is self-evident what one is supposed to do.

52
4. Simplify Presentation of Information
  • Sometimes too much information is provided in too
    complex a fashion.
  • Good designs provide simplified displays.
  • Visual images (photos, icons, signs) can be
    better than words.
  • Example The acceptability of universal road
    signs (deer crossing)

53
5. Present Information at the Appropriate Level
of Detail
  • Find out what the user needs to know and deliver
    at that level of detail not too detailed and
    not too simple.
  • Computer software pop-up help vs. on-line help
    vs. a hardcopy users manual.

54
6. Present Clear Images
  • Make images
  • Visible
  • Size, contrast
  • Distinguishable
  • Separate from other signals
  • Fire alarm bell vs. class bell
  • Interpretable
  • 1 vs. l
  • 6053946067 vs. (605) 394-6067

55
7. Use Redundancies
  • Provide the same information in more than one
    way.
  • Zip code is redundant with street, city,
    state
  • Police car has flashing lights and sirens
  • Stop sign has three redundancies red,
    octagon, STOP

56
8. Use Patterns
  • Information presented in visual patterns can be
    understood more quickly and accurately.
  • Graphs are usually better than tables of data.
  • Normal control settings

57
9. Provide Variable Stimuli
  • Humans detect a novel stimuli more readily than a
    constant one.
  • Flashing lights are more noticeable than
    unchanging lights.
  • Wavering or unusual sirens are more noticeable
    than constant ones.
  • In training sessions, use a variety of techniques
    of presenting information.

58
10. Provide Instantaneous Feedback
  • Provide timely feedback to the user on the course
    of action taken.
  • Repeating a phone number during a conversation
    insures success.
  • Computer keys have an audible or tactile click to
    indicate successful use.
  • Lack of feedback leaves uncertainty and could
    lead to further errors.
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