Chapter 6: Work Environment Design

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Chapter 6 Work Environment Design

• Overview
• Illumination
• Noise
• Temperature
• Ventilation
• Vibration
• Radiation
• Shift-work and Working Hours
• Safety
• Occupation Safety and Health Administration (OSHA)

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Illumination

• Illuminance an amount of light a
  surface (intensity/d2) ? (fc foot candles d
  from source to surface)
• Luminance an amount of light
• illuminance reflectance
  (fLfoot-lamberts)
• Reflectance 0.9Ltarget/Lstandard
• Visibility the with which the human sees
  something visual angle, contrast, luminance
• For small targets visual angle (arc min) 3438
  h/d
• Contrast (Lmax Lmin)/Lmax
• Light sources efficiency (lumens/w) color
  rendering
• Light distribution of total light output
  emitted above and below the horizontal
• Glare glare happens when eyes receive the
  brightness light
• Color

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?w -2 low -2 5
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Noise

• Characteristic of noise
• Sound velocity c f? (1,100ft/sec in air)
• ? sound wave length (ft), frequency in Hz
• Sound intensity (decibel) Sound pressure
• Frequency (hertz or cycle/sec) human audible
  20-20000Hz
• Sound level L 20 log (Prms/Pref) (dB)
• Prms root-mean-square sound pressure
  (microbars)
• Pref reference sound pressure 0.0002
  microbars
• 2 x10-5 N/m2 (for a young person at 1000Hz)
• Combining noise sources
• LTOT 10log(10L1/10 10L2/10)

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Noise

• Hearing loss nerve deafness due to excess
  exposure to occupational noise.
• Noise dose D 100 x(C1/T1 C2/T2 ) 100
• where D noise dose
• Ci time spent at noise level i
• Ti time permitted at noise level i
• Time adjusted for sound level greater than 90 dB
• T 8/2(L-90)/5
• 8-hour time weighted average sound level (TWA)
• TWA 16.61 x log(D/100) 90 (dB)

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Example

• A worker is exposed to one hour at 80 dBA,
  four hours at 90 dBA, and three hours at 96 dBA.
  The worker is permitted 32 hours for the first
  exposure, 8 hours for the second exposure. The
  total nose dose for this worker is permissible or
  not?

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Solution

• The time is permitted for the third exposure
• T 8/2(96-90)/5 3.48
• The total noise dose
• D 100(1/32 4/8 3/3.48) 139.3 100
• Thus for this worker, the 8-hour noise exposure
  dosage exceeds OSHA requirements

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Noise

• Performance effects some sounds are desirable in
  a work environment (music), should be
  eliminated
• Noise control three ways
• Reduce the noise level at its source best, most
  difficult
• Isolate the noisy equipments
• Install acoustical materials to absorb the noise
• Hearing protection a temporary solution ?
  earplugs, earmuffs (insert-typemuff-type)

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Temperature

• Heat exchanging between human body and
  environment
• S M ? C ? R E
• Where M heat gain from metabolism
• C heat gain or lost due to convection
• R heat gain or lost due to radiation
• E heat lost through evaporation of sweat
• S heat storage of the body (should be 0)
• Heat stress engineering or administrative
  controls ? reduce
• Outdoors with a solar load WBGT 0.7NWB 0.2GT
  0.1DB
• Indoors or outdoors solar load
• WBGT 0.7NWB 0.3GT
• Where NWB natural wet bulb temperature (
  measure of evaporative cooling, using a
  thermometer with a wet wick and natural air
  movement).
• GT Globe temperature ( measure of radiative
  load, using a thermometer in a 6-in-diametr black
  copper sphere)
• DB Dry bulb temperature (basic ambient
  temperature thermometer shielded from radiation)

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The thermal comfort zone
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Recommended heat stress levels
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Cold Stress
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Ventilation, Vibration and Radiation

• Ventilation
• General 8-12 feet
• Local
• Spot
• Vibration
• Radiation

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Guidelines for ventilation requirements for
sedentary workers given the available volume of
room air
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Air velocity vs. distance for fan placement
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Shiftwork and Working Hours

• Three-shift system
• Early (E) 8AM 4PM
• Late-afternoon (L) 4PM 12PM
• Night (N) 12PM 8AM
• Effect of shiftwork
• Sleep pattern
• Social relationship
• Recommendations for shiftwork
• Avoid shiftwork for workers older than 50
• Use rapid rotations as opposed to weekly or
  monthly cycles
• Schedule as few night shifts (3)in succession as
  possible
• Use forward rotation of shifts if possible (E-L-N
  or D-N)
• Limit the total number of working shifts in
  succession to 7 or less
• Include some free weekends, with at least two
  successive full days off
• Schedule rest days after night shifts
• Keep the plans simple, predictable, and equitable
  for all workers

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Shiftwork and Working Hours

• Overtime guidelines for scheduling overtime
• Avoid overtime for heavy manual work
• Reevaluate machine-paced work for appropriate
  rest periods or lowered rates
• For continuous or long periods of overtime,
  rotate the work among several workers, or examine
  alternate shift systems
• In choosing between extending a series of work
  days by one or two hours vs. extending the work
  week by one day, most workers will opt for the
  former, to avoid losing a weekend day with the
  family
• Compressed work week 40h is performed in fewer 5
  days
• Alternative work schedules flextime

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Productivity as a function of working hours
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Safety and OSHA

• Safety
• House keeping
• Personnel protective equipment
• OSHA
• OSHA act
• Workplace inspection
• Citations
• OSHA ergonomics program
• Commitment and Involvement
• Worksite analysis identify existing hazards and
  conditions, and operations and workplaces where
  such hazards may develop
• Incidence rates IR 200,000I/H I number of
  injuries, H work-hours
• Severity rates SR 200,000 LT/H, LT
  number of lost-time days
• Hazard prevention and controls
• Medical management
• Training and education