Principles of Ergonomics

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Principles of Ergonomics

• TM 655
• SDSMT
• Summer 2008

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Assignment

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

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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

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Ergo concepts come from . . .

• Engineering concepts
• physics
• psychology
• anthropometry
• anatomy
• physiology
• kinesiology

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Ergo requires skills in . . .

• Teamwork
• problem solving
• innovative thinking
• communications
• economic accountability
• desire to help people

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Why Address Ergonomics?

• Regulatory reasons
• Humanitarian reasons
• Good business practice

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Cost Categories Forgotten?

• Lost productivity
• medical plan
• absenteeism
• reduced quality / service
• employee turnover
• training

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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!

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Cost Accounting

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

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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
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Physical Temporal Risk Factors

• Force
• Posture
• Temperature
• Vibration

• Repetitions
• Sustained
• Shift Length
• Work / Rest Ratio
• Lack of Rest

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Vibration

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

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Thermal Considerations

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

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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

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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

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Psychosocial Risk Factors

• Organizational climate culture
• Job attitude job satisfaction
• Personality traits
• Personal problems
• marital problems
• death of loved ones
• financial problems

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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.

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People are Different

• Go to the presentation titled, People are
  Different

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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

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People Have Limitations

• Size
• Strength
• Range of Motion
• Vision
• Hearing

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People Have Predictable Reactions

• Spatial Compatibility
• Complexity

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To Err is Human

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

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Cognitive Errors

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

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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.

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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.

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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.

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10 Physical Principles
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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!!

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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.

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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)

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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.

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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.

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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

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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)

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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

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Tool Balancer
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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.

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Repetition Guidelines

• Damaging wrist motion
• 1000 per hour maximum
• 2000 maximum per 8 hour shift

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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

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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.

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9. Provide Mobility and Change of Posture

• Even a great posture needs a break
• Sit-Stand Workstations
• Micro-Break Concept

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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

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10 Cognitive Principles
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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.

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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

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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.

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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)

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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.

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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. [phone]

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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

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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

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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.

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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.