Download Vibration

ERGONOMICS:
Environmental
Issues
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
Some Points to Consider
 What effect, if any, do sub-optimal
environmental conditions have on the
standard of performance of the worker?
 Is an individual’s selective attention and
concentration disturbed?
 Is the operator at risk for injury?
 Do environmental disturbances affect the
emotional state of the worker
What seems to be the problem(s)?
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NOISE
VIBRATION
LIGHTING
AMBIENT
CONDITIONS
What are some of the key
environmental considerations
What factors are likely to
affect the performance
of the operator
How would you go
about improving
the work site
Operator’s 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.
There are 4 main
ENVIRONMENTAL CONSIDERATIONS:

NOISE

VIBRATION

LIGHTING

AMBIENT CONDITIONS
NOISE
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).
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).
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.
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.
Sound defined
“a complex scramble of many
frequencies that is highly
likely to have a disturbing
effect on the listener”
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.
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
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
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
Sound Intensity:
Is perceived as loudness which is
generally measured in decibels (dB)
Frequency:
Pitch of the sound measured in Hertz
(Hz)
“Normal” response
of the human ear
Note that this is a
logarithmic scale
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.
Two “Noise”
Rating Scales
Actual Sound
(Noise Perception Rating Scale)
1. Quiet
2. Conscious Awareness
3. Loud
4. Excessively Load
5. Unbearable
Personal Response
(Annoyance Scale)
1.
2.
3.
4.
5.
Relaxing
Not Disturbing
Disturbing
Annoying
Highly Irritating
Hearing Sensitive Jobs
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VIBRATION
Vibration
Defined simply as a movement
which a body makes about a
fixed point (Oborne, 1995).
Whole Body Vibration (WBV)


most commonly associated with motor
vehicle drivers
can occur in a number of different
environments
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
Physiological outcomes from
vibration frequencies:
(Hz)
Tactile sensation
0.1 – 105
Giddiness and instability
0.1 – 103
Motion sickness
0.2 – 1
Vibrating hand tool diseases 75 - 100
Major body resonances
3, 4-7.5, 11
Respiration difficulties
4-8
Abdominal pain
4 - 14
Muscle tone
10 - 20
Lumbosacral pain
7.5 - 20
Head sensations
9 - 20
Disturbances of vision
1 - 95
Speech difficulties
7.5 – 20
Urge to defecate & urinate
10 – 20
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
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.
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.
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
The effects of vibration on
performance:
 Decreased hand steadiness
(important for motor control).
 Problems related to sight (for
example, blurring and fixation
difficulties).
A vibration standard:
International Standardization
Organizations Guideline (ISO)
2631: “Guide for Evaluation
of Human Exposure to
Whole Body Vibration”
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
Jobs and Hearing
LIGHTING
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.
Why is vision so important in
the working environment?
70 – 80% of information
entering the brain from the
sensory system is visual
Some Lighting Terminology

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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.
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.
CHERNCK (1983) considers the
following visual skills important:
a)
b)
c)
d)
e)
f)
g)
h)
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).
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
Good visual acuity depends on
appropriate lighting conditions based on:
 Good illumination
 Sufficient contrast
 Adaptation in the central and
peripheral visual field
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.
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.
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.
Signs of Visual Fatigue:
 Painful irritation and reddening of the
eyelids
 Double vision
 Headaches
 Reduction in the power of
accommodation and convergence
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.
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
Jobs and Vision
Climate/Thermal
Environment
Temperatures
Ventilation
Humidity
Poor
respiratory
function
Dehydration
Reduced work
capacity!!
Assessing Thermal Conditions
Six Factors to assess human
response to thermal conditions:
1.
2.
3.
4.
5.
6.
Air temperature
Radiant temperature
Air velocity
Humidity
Activity of the person
Clothing worn by the person
Cramps
Exhaustion
Stroke
Syncope (fainting)
Rash
Miliaria Profunda – inability to sweat
Work
Work Pace
Climate
Clothing
Heat
Stress
Heat
Strain
Operator
Individual Factors:
Age/Sex
Work Capacity
Health Status
Acclimatization
Criteria:
Health
Comfort
Performance
Heat Balance (homeostasis)
Optimal human internal (core) temperature is around 37°C
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
Maximum Core Temperature


A maximum core temperature of
38°C is often used as a limit for
working environments.
Death will occur in the region of
42°C core temperature.
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
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)
Permissible Heat Exposure Threshold
Limit Values in Degrees C, WBGT
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
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).
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.
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.
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
Heat Production/Loss
D
A
E
B
F
C
Heat Production/Loss
Respiration
Evaporation
(sweat)
Directed
Radiation
Convection
Reflected
Radiation
Conduction
Heat Disorders
Prevention

Slow Moving Fans – increase air circulation

Cooling Jackets

Increased Hydration

Amount and Composition of Clothing

Education about signs and symptoms
Cold Disorders
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
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.
Thermal Sensitive Jobs
Other Environmental
Factors that Affect Work
Air Quality
Indoor environment - inadequate temperature,
humidity, lighting, excessive noise
Indoor air contaminants - chemicals, dusts, moulds
or fungi, bacteria, gases, vapours, odours
Symptoms – Indoor Air Quality

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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
Motion
•Motion-sickness
•Fatigue
•Motion-induced Interruptions