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ERGONOMICS: Environmental Issues

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Title: ERGONOMICS: Environmental Issues


1
ERGONOMICSEnvironmental Issues
2
Environmental Factors Worksite Considerations
  • The assessment of the working environment needs
    to include
  • The immediate workplace
  • The physical relationship between the work
    situation and the operator
  • Impact of temperature, humidity, altitude, noise,
    illumination and vibration

3
Some Points to Consider
  • What effect, if any, do sub-optimal environmental
    conditions have on the standard of performance of
    the worker? 
  • Is an individuals selective attention and
    concentration disturbed? 
  • Is the operator at risk for injury? 
  • Do environmental disturbances affect the
    emotional state of the worker

4
What seems to be the problem(s)?
  • NOISE
  • VIBRATION
  • LIGHTING
  • AMBIENT CONDITIONS

5
What are some of the key environmental
considerations
?
6
What factors are likely to affect the
performance of the operator
?
7
How would you go about improving the work
site
?
8
Operators PERCEPTION is an important
consideration
  • Active process of looking for meaning in the
    environment in which we live.
  • Involves receiving and interpreting sensory
    information and is unique to each individual.
  • Depends on cultural background, user experience,
    personal disposition and interest in the
    particular task.

9
There are 4 main ENVIRONMENTAL CONSIDERATIONS
  • NOISE
  • VIBRATION
  • LIGHTING
  • AMBIENT CONDITIONS

10
NOISE
11
The Structure of the Ear A review!
  • External ear auricle which collects sound waves
    and transmits them via the external acoustic
    meatus (auditory canal) to the tympanic membrane
    (eardrum).

12
The Structure of the Ear A review!
  • Middle ear made up of the tympanic cavity in the
    temporal bone and contains three auditory
    ossicles (bones) the malleus (hammer), the incus
    (anvil) and the stapes (stirrup).

13
The Structure of the Ear A review!
  • Inner ear this is made up of the bony labyrinth
    which consists of the Cochlea (the main organ of
    hearing), Vestibular Apparatus and the Membranous
    Labyrinth.

14
Creating Sounds The Basics
  • An initial disturbance from a vibrating object
    will force surrounding air molecules to move.
  • Molecules are squeezed closer together then
    pulled apart resulting in compression and
    refraction.
  • Sound is propagated through an elastic medium
    such as air or fluid.
  • Rapid oscillations in air pressure within the
    ear.
  • Sound is thus propagated by a pressure wave
    moving outward from a vibrating body.

15
Sound defined
  • a complex scramble of many
  • frequencies that is highly
  • likely to have a disturbing
  • effect on the listener

16
Loebs (1986) identified 3 distinct but related
meanings of noise
  • 1. Sound which varies randomly in intensity and
    frequency.
  • 2. Sound which interferes with the reception of
    another sound (masking).
  • 3. Sound which the individual does not want to
    hear.

17
Noise leads to two key changes
  • Distraction
  • makes it difficult to maintain concentration
    when there is more than one source of auditory
    information
  • Arousal
  • loud noise is arousing, but whether it has an
    affect on performance is debatable

18
Negative Affects of Noise
  • Damage to hearing
  • Disturbance of sleep
  • Poor performance of required task due to
    increases in muscular tension, accelerated heart
    rate
  • Impaired alertness
  • Increased fatigue, tiredness and irritability
  • Hypertension, Heart Rate

19
Damage to hearing
  • Intensive noise causes a portion of the organ of
    Corti to be separated from the basilar membrane.
  • Metabolic theory suggests the depletion of key
    enzymes and metabolites in the hair cells

20
  • Sound Intensity
  • Is perceived as loudness which is generally
    measured in decibels (dB) 
  • Frequency
  • Pitch of the sound measured in Hertz (Hz)

21
Normal response of the human ear
Note that this is a logarithmic scale
22
Protection against Noise 
  • Design it out before it becomes a factor.
  • Reduce it at source.
  • Insulate sound.
  • Personal ear protection should be worn where
    exposure exceeds 85 db.

23
Two Noise Rating Scales 
24
Actual Sound (Noise Perception Rating Scale)
  • 1. Quiet2. Conscious Awareness3. Loud4. Excessi
    vely Load5. Unbearable

25
Personal Response (Annoyance Scale)
  • 1. Relaxing
  • 2. Not Disturbing
  • 3. Disturbing
  • 4. Annoying
  • 5. Highly Irritating

26
Hearing Sensitive Jobs
http//www2.worksafebc.com/Publications/Multimedia
/Videos.asp?reportid34284
?
27
VIBRATION
28
Vibration
  • Defined simply as a movementwhich a body makes
    about a fixed point (Oborne, 1995).

29
Whole Body Vibration (WBV)
  • most commonly associated with motor vehicle
    drivers
  • can occur in a number of different environments

30
Vibration
  • The effects of vibration are often only
    considered in one axis (Z).
  • Need to consider the speed and intensity of the
    vibration.
  • UNIT Hertz (Hz) cycles.s-1

31
Physiological outcomes from vibration frequencies
  • (Hz) Tactile sensation 0.1
    105Giddiness and instability 0.1
    103 Motion sickness 0.2 1Vibrating hand
    tool diseases 75 - 100Major body resonances 3,
    4-7.5, 11Respiration difficulties 4 -
    8Abdominal pain 4 - 14Muscle tone 10 -
    20Lumbosacral pain 7.5 - 20Head
    sensations 9 - 20Disturbances of vision 1 -
    95Speech difficulties 7.5 20Urge to
    defecate urinate 10 20

32
Vibration
  • Resonance occurs when the vibrational frequency
    of an external force matches an organs natural
    frequency
  • Pope et al., (1996) state that spinal resonance
    occurs at 4 - 5 Hz
  • Coerman (1968) reported that vibrations between
    2.5 5 Hz generate strong resonance in the
    vertebrae of the neck and lumbar regions

33
Vibration Terms
  • Daily vibration exposure
  • The 8-hour energy equivalent vibration total
    value for a worker in meters per second squared
    (m/s²), including all hand-arm vibration
    exposures during the day.
  • Partial vibration exposure
  • The contribution of operation i to the daily
    vibration
  • exposure in m/s². The partial vibration exposure
    relates to
  • the daily exposure from an individual tool or
    process, i
  • (where a worker is only exposed to vibration form
    one tool
  • or process then the daily vibration exposure is
    equal to the
  • partial vibration exposure).
  • Exposure limit value
  • A value for a workers daily vibration
    exposure of 5m/s², above which workers should not
    be exposed.
  • Exposure time.
  • The duration per day that a worker is exposure to
    a vibration source.

34
Hand Arm Vibration (HAV)
  • Measurement of vibration is related to
    acceleration (m.s2) of the surface in contact
    with the hand.
  • Depends on the tools used by the operator.
  • Many tools do not provide the operator with an
    indication of the dosage of vibration received.
  • Need exists for detailed analyses of the impacts
    of continuous/repetitive hand arm vibration.

35
The American Conference of Governmental
Industrial Hygienists Threshold Limit Values
Total Daily Exposure Duration (Hours) Maximum Value of Frequency Weighted Acceleration (m.s2) in any Direction
4 to less than 8 hours 4
2 to less than 4 hours 6
1 to less than 2 hours 8
Less than 1 hour 12
Directions of Axes in a 3-D System
36
The effects of vibration on performance
  • Decreased hand steadiness (important for motor
    control).
  • Problems related to sight (for example, blurring
    and fixation difficulties).

37
A vibration standardInternational
Standardization Organizations Guideline (ISO)
2631 Guide for Evaluation of Human Exposure to
Whole Body Vibration
38
Vibration-related Disorders
  • Vascular disorders
  • dead or white finger,
  • Raynaud's phenomenon of occupational origin,
  • vibration-induced white finger.
  • Neurological disorders
  • Carpal Tunnel Syndrome
  • Musculoskeletal disorders

39
Jobs and Hearing
?
40
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41
LIGHTING
42
Vision and the Role of Lighting
  • Problems associated with poor lighting can often
    be solved by low cost interventions and careful
    design consideration.
  • Arrangement of working surfaces, such as
    placement of machines.
  • Placement of work benches for natural lighting.
  • Improved overhead lighting.
  • Changing the paint colour of walls.

43
Why is vision so important in the working
environment?
  • 70 80 of information entering the brain from
    the sensory system is visual

44
Some Lighting Terminology
  • Luminous Flux (lumen) quantity of energy of the
    light emitted per second in all directions.
  • Luminous Intensity ability of a source or
    illuminated surface to emit light.
  • Luminance the amount of light emitted by a
    surface.
  • Illuminance (lux) amount of light falling on a
    surface.

45
Visual Acuity
  • a measure of the resolving qualities of the eye
    (ability to see fine detail).
  • Affected by physiological factors such as
    receptive ability of the visual receptors.
  • Integrity of the nerve pathways to the brain.

46
CHERNCK (1983) considers the following visual
skills important
  • Visual acuity
  • Near point of convergence (i.e. the closest point
    to the person along the median line at which he
    can continue to fixate the target with both
    eyes).
  • Stereopsis (i.e. the perception of
    three-dimensional visual space as a result of
    binocular cues).
  • Fusion (i.e. the integration of two similar
    ocular images into a single precept).
  • Colour Vision
  • Accommodative facility (i.e. the ability to
    change focus efficiently from near to far and
    back again).
  • Eye movement ability (i.e. the ability to follow
    a moving target smoothly, keeping both eyes on
    the target).
  • Visual motor integration (i.e. co-ordination
    between the eyes and the extra-ocular muscles).

47
Other Factors Influencing Performance
  • Depth Perception
  • Contrast Sensitivity
  • Peripheral Awareness
  • Motion Detection
  • Eye Movement
  • Dynamic Visual Acuity
  • Visuo-motor Integration
  • Vestibulo-occular Reflex
  • Reaction Time

48
Good visual acuity depends on appropriate
lighting conditions based on
  • Good illumination
  • Sufficient contrast
  • Adaptation in the central and peripheral visual
    field

49
For visual comfort and good optical performance,
the following criteria apply
  • 1. Balanced arrangements of lights.
  • 2. Suitable level of illumination (lux levels).
  • 3. Avoidance of glare and reflection.

50
Some Lighting Recommendations
  • 1. No source of light should appear in the visual
    field of any worker during operation.
  • 2.  The line from eye to light source should be
    at an angle of more than 30.
  • 3. Lights should be provided with shades.
  • 4. Rather use more lamps of lower power than
    fewer high powered lamps.
  • 5. Reflective colours and materials should be
    avoided.
  • 6. There should be a contrast in colour between
    working surface and working materials.

51
Natural Lighting
  • 1. High windows are more effective than broad
    ones since the light penetrates further into the
    room.
  • 2. Use clear glass as it has a transparency of
    90.
  • 3. Positioning of work benches to avoid looking
    directly into the sun.
  • 4. When working at a VDU windows should be at
    the side of the monitor and lighting should be to
    the left or right and not directly overhead, or
    behind.

52
Signs of Visual Fatigue
  • Painful irritation and reddening of the eyelids
  • Double vision
  • Headaches
  • Reduction in the power of accommodation and
    convergence

53
Flickering Lighting
  • Flickering light may influence basic brainwave
    patterns induce nausea, epileptic seizures.
  • Stroboscopic effect makes rotating or oscillating
    machine parts to appear stationary or moving more
    slowly.

54
RECOMMENDED ILLUMINATIONS
  • Table 10.3 Examples of recommended naturally
    occurring illuminances
  • Area/activity Illuminance on a horizontal
    surface (lux)
  • Clear sky in summer 150 000
  • Overcast sky in summer 16 000
  • Performance of extremely low contrast
    10 000
  • tasks (certain surgical operations)
  • Textile inspection 15 000
  • Office work (writing, reading poor quality
    documents) 1 000
  • Precise assembly work 1 000
  • Office work (without VDUs) 500
  • Office work (data entry) 500
  • Heavy engineering 300
  • Rough assembly work 200
  • Min. illuminance for MMH tasks (NIOSH) 150
  • Rarely visited places where little perception of
    detail is required 50
  • Good street lighting 10
  • Emergency lighting 2
  • Moonlight 0.5

55
Jobs and Vision
?
56
(No Transcript)
57
Climate/Thermal Environment
58
 
Temperatures
Ventilation
Humidity
Poor respiratory function
Dehydration
Reduced work capacity!!
59
Assessing Thermal Conditions
  • Six Factors to assess human response to thermal
    conditions
  • Air temperature
  • Radiant temperature
  • Air velocity
  • Humidity
  • Activity of the person
  • Clothing worn by the person

60
Cramps Exhaustion Stroke Syncope
(fainting) Rash Miliaria Profunda inability to
sweat
Work
Work Pace
Criteria Health Comfort Performance
Heat Stress
Heat Strain
Climate
Operator
Clothing
Individual Factors Age/Sex Work Capacity Health
Status Acclimatization
61
Heat Balance (homeostasis)
Optimal human internal (core) temperature is
around 37C
62
Body under heat stress
  • Two main mechanisms
  • Vasodilation
  • Where the peripheral blood vessels dilate and
    transfer blood (heat) to the surface of the body
    where it can be lost to the surrounding
    environment.
  • Sweating
  • Heat lost by evaporation

63
Maximum Core Temperature
  • A maximum core temperature of 38C is often used
    as a limit for working environments.
  • Death will occur in the region of 42C core
    temperature.

64
Body under cold stress
  • Two main mechanisms
  • Vasoconstriction
  • Peripheral blood vessels constrict to reduce the
    flow of blood to the body surface that reduces
    heat loss.
  • Shivering

65
Psychological Responses to Poor Ambient
Conditions
  • Less Severe
  • Decreased Concentration
  • Decreased Response Time
  • More Severe
  • Mental confusion
  • Unconsciousness
  • Death due to Ventricular Fibrillation (heart
    failure)

66
Permissible Heat Exposure Threshold Limit Values
in Degrees C, WBGT
Workload Workload Workload Workload
Work/Rest (per hour) Light Moderate Heavy
Continuous 30.0 26.7 25.0
75 / 25 30.6 28.0 25.9
50 / 50 31.4 29.4 27.9
25 / 75 32.2 31.1 30.0
67
Wet Bulb Temperature (WBT)
  • Temperature associated with moisture content of
    the air. WBT is taken by surrounding the
    thermometer with a wet wick and measuring the
    reading as the water evaporates. WBT readings
    are typically lower than dry-bulb temperatures.
  • With high relative humidity, little evaporative
    cooling occurs, and the reading is similar to
    that of a dry-bulb thermometer.
  • On a dry day, significant evaporation occurs from
    the wetted bulb, which maximized the differences
    between the two thermometer readings (air
    velocity is obviously a factor).

68
Dry Bulb Temperature (DBT)
  • Temperature we measure with a standard
    thermometer that has no water surface on it.
    When people refer to temperature of the air they
    are usually referring to this.

69
Relative Humidity (RH)
  • How saturated the air is with water vapor. The
    amount of moisture air can hold increases a the
    dry bulb temperature increases. When referring
    to the relative humidity it is important to
    define the dry bulb temperature of the air as
    well.

70
Methods of Heat Loss
  • Convection
  • Air flows along the skin
  • Heat transferred from skin to air
  • Conduction
  • Heat transferred by touch
  • i.e. working in water, handling cold products,
    etc.
  • Evaporation
  • i.e. sweating.
  • Respiration
  • Both convective and evaporative heat loss
  • Occurs from the lungs by respiration as inspired
    air

71
Heat Production/Loss
72
Heat Production/Loss
73
Heat Disorders
?
74
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75
Prevention
  • Slow Moving Fans increase air circulation
  • Cooling Jackets
  • Increased Hydration
  • Amount and Composition of Clothing
  • Education about signs and symptoms

76
Cold Disorders
?
77
Cold-related Disorders
  • Frost-nip versus Frostbite
  • With frost nip, there is freezing of the
    superficial tissues commonly diagnosed by a
    blanching of fingers, noses, ears, etc. Frost
    bite is significantly more serious. There we find
    freezing of the deep tissues resulting in the
    formation of ice crystals.
  • Hypothermia
  • Trench Foot and Immersion Foot
  • conditions that present much like frost bite
    however, they occur at temperatures above
    freezing when the foot is continuously immersed
    in water

78
Prevention
  • Apply skin moisturizer to the face, hands, and
    any other body part that may be exposed to the
    cold.
  • Dress warmly, wear dry clothing, and stay out of
    the wind. Wear a face mask for extra protection.
    Wear heavy mittens instead of gloves in freezing
    cold weather.
  • Be extremely careful when pumping gas into your
    car if the temperature is below freezing.
    Gasoline on exposed skin evaporates very quickly,
    lowers the temperature of the skin, and makes it
    more susceptible to frostbite.
  • When you exercise in below-freezing temperatures,
    wear layers of clothing. The innermost garment
    must be nonabsorbent and loosely woven.
  • Go inside, if possible, when you feel too cold.
    Remember that fatigue, lack of oxygen in high
    elevations, and consumption of alcohol may cause
    you to disregard discomfort and cold.
  • Avoid smoking or drinking before venturing out
    into extreme cold. Tobacco decreases circulation
    by constricting blood vessels, and alcohol
    interferes with the body's ability to regulate
    temperature.

79
Thermal Sensitive Jobs
?
80
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81
Other Environmental Factors that Affect Work
?
82
Air Quality
  • Indoor environment - inadequate temperature,
    humidity, lighting, excessive noise
  • Indoor air contaminants - chemicals, dusts,
    moulds or fungi, bacteria, gases, vapours, odours

83
Symptoms Indoor Air Quality
  • dryness and irritation of the eyes, nose, throat,
    and skin,
  • headache,
  • fatigue,
  • shortness of breath,
  • hypersensitivity and allergies,
  • sinus congestion,
  • coughing and sneezing,
  • dizziness, and/or
  • nausea

84
Motion
  • Motion-sickness
  • Fatigue
  • Motion-induced Interruptions
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