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Chapter 6: Work Environment Design

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Title: Chapter 6: Work Environment Design


1
Chapter 6 Work Environment Design
  • Human Factors IE 5511

2
Chapter 6Work Environment Design
  • Lighting
  • Noise
  • Temperature heat and cold stress
  • Vibration
  • Radiation
  • Shifts to optimize productivity
  • Training in ergonomics and safety

3
The value of a good environment
  • Plants with good working conditions outperform
    those with poor conditions
  • Economic return on investment in better
    conditions is usually significant
  • Improves safety and morale
  • Reduces turn-over, absenteeism
  • Failure to comply results in OSHA fines

OSHA Occupational Safety and Health
Administration
4
Home environmental design
  • Many of the same principles that apply to
    environmental design of the workplace, also apply
    to design of the home.
  • Issues such as lighting, heat, ventilation,
    layout and adequate space for tasks can have
    great impact on the
  • Convenience,
  • Efficiency
  • Feeling in ones home. (Is it a welcoming,
    relaxing haven? Or is it a chaotic, stressful
    pit?)

5
I. Lighting and Illumination
  • Lighting intensity is measured in candalas (cd),
    or lumens, where 1 cd 12.57 lumens.
  • Illuminance is the amount of light shining on an
    object, measured in foot-candles (fc)
  • Illuminance intensity / d2
  • Where d is in feet. Intensity is foot-candles
    (fc) where 1 fc 1 lumen/(ft2).

6
Luminance
  • Luminance is the amount of light reflected from
    an object,
  • It impacts our ability to see objects,
  • It is measured in foot-lamberts (fL)
  • luminance illuminance x reflectance
  • Reflectance is determined by the physical and
    color properties of an object how much light is
    absorbed or thrown back at the viewer?

7
Reflectance
  • Reflectance is the property of a surface which is
    determined by both color and surface finish, and
    expressed as a percentage of light reflected
    (luminance).
  • Luminance is measured by a photometer (pointed at
    surface).
  • Table 6-1 lists reflectances for various colors
    and surfaces.
  • Reflectance is a ration between
  • The measured reflectance of the target surface,
  • The measured reflectance of a standard Kodak
    neutral test card 0.9
  • Reflectance 0.9 x Ltarget / Lstandard

8
Visibility
  • Visibility is the clarity with which a human can
    see an object.
  • There are 3 critical factors in visibility
  • Visual angle
  • Contrast
  • Illuminance

9
Yes, but do I have enough light on my task?
  • The amount of light needed is a function of
  • The nature of the task
  • The worker (age and visual health),
  • The reflectance of the task background.
  • Table 6-2, shows how much light (in fC) is needed
    for different types of tasks.

10
How much light is needed?
  • Table 6-2 will give you a range of lighting
    levels (low, medium, high) suitable for a general
    task category
  • To choose between low, medium and high use table
    6-3.

11
Example Lighting Problem
  • H R Block (tax preparation company) hires
    retired people (60 years old) to prepare taxes
    from January thru April.
  • The task must be done with reasonable speed
    (particularly in April) and high accuracy.
  • The notes people give to their tax preparers
    range from high quality printed receipts, to
    handwritten pencil notes on yellow notebook paper
    (low contrast)
  • Is it sufficient to light the tax preparers desk
    with a single 800 lumen1 incandescent bulb, if
    the bulb is 5 feet above the workers desk, and
    the surroundings are cream colored?

1. Light output (intensity) in lumens or candelas
can often be found on bulb packaging.
12
Example Lighting Problem (cont.)
  • Consider this question in two parts
  • How many fcs are needed?
  • Is a 800 lumen bulb sufficient to provide that
    illuminance, if the light source is 5 ft. from
    the work?

13
1. How many fcs are needed?
  • Find reflectance of surroundings look in table
    6-1, light cream gives you approximately 75
    reflectance.
  • Look in table 6-3 for a weighting factors based
    on
  • Task characteristic value weight
  • Age of workers, 55 1
  • Reflectance of surroundings, greater than 70
    -1
  • Criticality speed and accuracy, critical 1
  • Total Weight 1 (-1) 1 1
  • Look in table 6-2 to find amount of light needed,
    use weighting factor to pick illuminance value
  • Low -3, -2,
  • Medium -1, 0, 1
  • High 2, 3

14
1. How many fcs are needed?
  • Find reflectance of surroundings look in table
    6-1, light cream gives you approximately 75
    reflectance.
  • Look in table 6-3 for a weighting factors based
    on
  • Task characteristic value weight
  • Age of workers, 55 1
  • Reflectance of surroundings, greater than 70
    -1
  • Criticality speed and accuracy, critical 1
  • Total Weight 1 (-1) 1 1
  • Look in table 6-2 to find amount of light needed,
    use weighting factor to pick illuminance value
  • Low -3, -2,
  • Medium -1, 0, 1 gt weight 1 requires medium
    illumination
  • High 2, 3 need at least 150 fc!

15
2. Is a 800 lumen bulb sufficient?
  • Is a 800 lumen bulb sufficient to provide 150 fc
    on the work surface, if the light source is 5 ft.
    from the work surface?
  • 1 cd 12.57 lumens (see Fig. 6.2)
  • 800 lumens 1 cd/12.57 lumens 63.64 cd
  • Illuminance (fc) intensity/d2
  • 63.64 cd/(5ft)2 2.5 fc
  • .
  • .

16
2. Is a 800 lumen bulb sufficient?
  • Is a 800 lumen bulb sufficient to provide 150 fc
    on the work surface, if the light source is 5 ft.
    from the work surface?
  • 1 cd 12.57 lumens (see Fig. 6.2)
  • so 800 lumens 1 cd/12.57 lumens 63.64 cd
  • Illuminance (fc) intensity/d2
  • 63.64 cd/(5ft)2 2.5 fc
  • This bulb at 5 ft is woefully inadequate! (Ok
    for general lighting in a public area).

17
Improving Visibility
  • One can improve visability in several ways
  • Increase source intensity (increase wattage,
    change to more efficient type florescent,
    halogen)
  • Bring target closer to viewer
  • Bring target closer to light source
  • Increase contrast
  • Increase target size (big print books)
  • Etc.

18
Factors in Visibility
  • Visual angle size of target on retina the angle
    the image takes up on retina.
  • Contrast relative difference in luminance
    (light reflected) for two surfaces,
  • Illuminance amount of light reaching a surface
    (most important)

19
Contrast
  • Contrast relative differences in luminance
    (light reflected) for two surfaces,
  • Contrast can be defined in several ways,
  • A common definition of contrast (unitless)
  • contrast (Lmax Lmin)/Lmax
  • Where L is the luminance of each surface.

20
Glare
  • Any area of excessive brightness, that decreases
    visibility
  • Causes cornea or glasses to scatter light,
  • Causes eyes to have to adjust to extreme bright
    area,
  • Causes
  • Light sources aimed at eyes,
  • Reflectance off or work surfaces
  • Solutions
  • Change to indirect lighting,
  • Change lighting angle, or work surface angle,
  • Use non-glare surfaces,
  • Use polarizing filters on light sources or
    eyewear

21
Other ways of improving visibility Choice of
lighting type
22
Other ways of improving visibility Choice of
lighting angle
23
II. Noise and Hearing
  • Noise Any unwanted sound.
  • Sound is measured in decibels (dB), which measure
    the amplitude of the sound wave.
  • Decibels are measured on a logarithmic scale

24
A-weighted Sound Levels (dBA)
  • A-weighted Sound Levels
  • Measures perceived loudness,
  • Combines both amplitude and frequency of noise.
    (High frequency more annoying and harmful, more
    powerful.)
  • Most widely accepted measure of sound.

25
Hearing Loss
  • OSHA (1970) limits for noise exposure are shown
    in Table 6-6.
  • Duration dBA
  • 8 hours 90
  • 4 hours 95
  • 1 hour 105
  • 15 min 115
  • Risk of hearing loss increases beyond these
    exposures.

26
OSHA Noise Exposure Limits
  • A worker may not be exposed to anything over 90
    dBA for the duration of an 8 hour workday,
  • Nothing over 115 dBA is allowed at all.

27
Noise Dose
  • Noise dose is total exposure to any sound above
    80 dBA during an 8 hour day.
  • D 100 x (C1/T1 C2/T2 Cn/Tn)
  • 100
  • Where D noise dose during an 8 hr day,
  • Ci Hours spent at a given noise level,
  • Ti Hours permitted at noise level (from
    table 6-6).
  • D must be kept below 100 of permissible noise
    dose.

28
Noise Dose Example
  • You are exposed to 3 noise sources during your
    work day.
  • 4 hours at 90 dBA
  • 2 hours at 95 dBA
  • .5 hours at 105 dBA
  • Your total noise dose is
  • D 100 x (4/8 2/4 0.5/1) ?
  • Is your hearing at risk?

29
Noise Dose Example
  • You are exposed to 3 noise sources during your
    work day.
  • 4 hours at 90 dBA
  • 2 hours at 95 dBA
  • .5 hours at 105 dBA
  • Your total noise dose is
  • D 100 x (4/8 2/4 0.5/1) 150
  • Is your hearing at risk? Yes.

30
Noise Control
  • Eliminate noise at its source (best but most
    difficult)
  • Substitute quieter machines (hydraulic for
    pneumatic riveter, electric for gas powered
    mowers)
  • Isolate noise making equipment
  • Rubber feet under equipment
  • Separate room
  • Enclosure
  • Absorb noise (with sound absorbing material on
    ceiling, walls and floor).
  • Use hearing protection on workers

31
Using age-related differences in hearing
  • Mosquito Teen Repellent product which emits a
    very loud, high-pitched tone which teens can hear
    and most people over 30 cannot.
  • Teens have used the Repellents tone as a
    ring-tone on their cell phones so they can send
    messages to their friends in class.
  • You can (try to) listen to the tone at
  • http//www.npr.org/templates/story/story.php?story
    Id5434687
  • http//www.bbc.co.uk/wiltshire/audio/mosquito_soun
    d.mp3

32
III. Temperature heat and cold stress
  • Heat and cold can impact workers
  • Effectiveness
  • Safety (Heat exhaustion)
  • Health
  • Heat can come from
  • The outdoor work environment in summer time
  • (Borax miners in Death Valley)
  • High temperatures of lack of ventilation indoors,
    (Offices in Mechanical Engineering in April, when
    heat is still on)
  • Radiant heat from work
  • (Blast furnace, glass furnace, kitchen oven
    in restaurant Down and Out in Paris and
    London, George Orwell)

33
Heat Stress Measurement
  • Core temperatures inside body should be
  • Normally around 98.6 degrees F
  • Above 100 F performance drops sharply.
  • Above 105 F sweating stops and death may follow.
  • Thermal comfort zone 66 to 79 degrees F.
  • Heat exchange between body and environment
  • S M /- C /- R - E
  • Where
  • M is heat gain from Metabolism
  • C is heat gained or lost from Convection
  • R is heat gained or lost due to Radiant energy
  • E is heat lost through Evaporation of sweat.
  • For thermal neutrality, S should be zero.

34
Heat Stress Measurement
  • Wet Bulb Globe Temperature (WBGT) approximates
    impact of temperature and environment on human
    body
  • Outdoors in the sun
  • WBGT 0.7 NWB 0.2 GT 0.1 DB
  • Indoors or outdoors out of sun
  • WBGT 0.7 NWB 0.2 GT
  • Where
  • NWB natural wet bulb temperature, measure
    of evaporative cooling, (thermometer in wet
    cloth with natural air movement over it)
  • GT globe temperature measure of heat from
    radiation (thermometer in black copper sphere)
  • DB Dry bulb temperature measure of
    ambient air temperature (regular thermometer
    shielded from sun)

35
Heat Stress Management
  • Control environment (indoors)
  • Ventilation (need 300 cubic feet fresh air per
    person, per hour.)
  • Heating, cooling, humidity control
  • Administrative
  • Limit time in hot or cold situations,
  • Provide rest breaks at appropriate intervals in a
    temperature controlled environment.

36
Shift Work
  • Shift work working at times other than daytime
    hours.
  • Helps keep factories, trucking and services
    (fire, police) going 24 hours a day.
  • Problem shift work is hard on the circadian
    rhythms changes in body temperature, heart rate
    and energy level over 24 hours.

37
Impact of Shift Work on the body
  • Most peoples circadian cycle is 25 hours,
  • Circadian rhythms are set by the sun,
  • People on shift work never truly adjust the sun
    keeps their body set on a day schedule even when
    they have to work at night.
  • Circadian rhythms of shift workers flatten,

38
Health and Accident Rates Associated with Shift
Work
  • Shift workers experience
  • Health problems
  • Disruption in social life.
  • Greater accident rate

39
Circadian Rhythms in environmental and work design
  • Spacecraft living environments designed to have
    24 hour light/dark cycles,
  • The difference between the
  • Mars day (24 hours and 27 minutes) and the
  • Earth day (24 hours)
  • This caused much stress on the operations staff
    at Jet Propulsion Laboratory (JPL) for the Mars
    Rovers
  • Eventually went to daytime-only operations

40
Types of Shifts
  • Three shift system (one shift all the time)
  • Early 8 AM to 4 PM
  • Late 4 PM to 12 Midnight
  • Night 12 Midnight to 8 AM
  • Rapid Rotation shift change every 2 to 3 days
    sleep only disrupted 1/3 of the time.
  • Weekly Rotation shift change every week. (very
    hard on workers never adjust).

41
Types of Shifts
  • Twelve hour shifts (work only 4 days / wk)
  • Day 8 AM 8 PM
  • Night 8 PM 8 AM

42
Guidelines for Shift Work
  • Schedule as few night shifts as possible
  • Avoid shift work for workers over 50
  • Use rapid rotations
  • Use forward rotations (E-L-N)
  • Keep schedule equitable and predictable for all
    workers.

43
Overtime
  • Length of day has a (negative) impact on
    productivity
  • Only 10 increase in productivity for a 25
    increase in hours
  • Scheduling overtime on a regular basis NOT
    recommended!
  • Shortening the work day can actually result in
    increased productivity, fewer rest breaks.

44
Long shifts and safety
  • Medical residents are allowed to spend 24 hour
    shifts working with patients additional time
    beyond that may be spent on paper work
  • How does this impact medical decision making and
    patient safety?

45
Radiation
  • The unit of absorbed radiation dose is the rad,
  • The unit of exposure is the roentgen (R).
  • Tissue at the point of exposure of 1 R, absorbs
    approximately 1 rad.
  • Radiation sickness is caused by doses of 100 rads
    or more.
  • A fatal dose is about 400 rads for 50 of adults,
    1000 rad or more is almost always fatal.
  • The annual dose from background sources is
    between 0.1 0.5 rem/year (100-500 millirem/year)

46
Radiation from Cell Phones
Radiation from cell phones is close to microwave
frequencies. Cell phone frequencies are
non-ionizing.
Non-ionizing radiation, while not necessarily
very dangerous, can heat tissues
47
Sources of Radiation Exposure
Medical dental treatments
Potassium
Nuclear testing and dumping
Visible, ultraviolet and cosmic radiation
Household products orange Fiestaware, lantern
mantels, kitty litter
48
Radon Gas
Radon Gas is naturally occurring. It is the
greatest single source of naturally occurring
background radiation.
Radon is responsible for 20,000 lung cancer
deaths per year in the U.S.
EPA recommended limit 4 pCi/L
49
Background Radiation
Sources
Cosmic rays Radon Granite Etc.
You are always exposed to some level of
naturally occurring background radiation.
U.S. national average 300 millirem/year Franc
e, near Radon Springs 1600 millirem/year Parts
of Brazil 17,500 millirem/year
http//www.yankeerowe.com/images/radiation.jpg
50
Radioactive Products
Marie Curies discovery of radioactive elements
created excitement worldwide. Radioactive
elements were believed to provide energy and
healing powers.
Radioactive medicines
Radioactive skin cream
Radioactive heating pad
Radioactive foods
51
Workplace Radiation
Nuclear power plants
Uranium mining processing
Xray chemo therapy technicians
52
Workplace Radiation
Chernobyl Clean-up
53
Radiation Detection
Badges Passive doseimeters Personal permanent
dose record
Geiger counter
Home radon detectors
Walk-through detector
54
Radiation Protection
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