BRITISH COLUMBIA INSTITUTE OF TECHNOLOGY
SCHOOL OF HEALTH SCIENCES
OCCUPATIONAL HEALTH AND SAFETY
OCHS 3520
ERGONOMICS
MODULE 11
Physical Environment Issues: An Overview
PREPARED BY:
Stephen Brown, MSc and Anne-Kristina Arnold, MSc, BCPE
DATE:
January, 1995
REVISED BY:
Janet Morrison
DATE:
November, 2011
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 2017 by
British Columbia Institute of Technology
Burnaby, British Columbia
All rights reserved. No part of this module may be reproduced
in any form, without permission in writing from BCIT.
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Table of Contents
Overview .................................................................... 11-1
Learning Objectives ................................................... 11-2
Introduction ................................................................ 11-2
Light ........................................................................... 11-2
Physiology of Vision ............................................ 11-3
Visual Deficiencies .............................................. 11-5
Risk Identification ................................................ 11-5
Risk Assessment ................................................. 11-8
Engineering Controls for Lighting ........................ 11-9
Special Consideration for Inspection Tasks ...... 11-10
Administrative Controls for Lighting ................... 11-11
Noise ........................................................................ 11-11
The Human Ear and Hearing ............................. 11-11
Physiology of Hearing ........................................ 11-11
Risk Identification .............................................. 11-15
Risk Assessment ............................................... 11-16
Risk Control ....................................................... 11-16
Climate ..................................................................... 11-18
Human Temperature Regulation ....................... 11-19
Risk Assessment ............................................... 11-20
Engineering Controls for Climate ....................... 11-20
Administrative Controls for Climate ................... 11-21
Vibration ................................................................... 11-22
The Nature of Vibration ..................................... 11-22
Risk Identification .............................................. 11-23
Risk Assessment ............................................... 11-25
Risk Control ....................................................... 11-26
Administrative Controls for Vibration ................. 11-27
Summary.................................................................. 11-27
Bibliography ............................................................. 11-29
Appendix .................................................................. 11-31
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MODULE 11
Physical Environment
Issues: An Overview
Overview
This module provides a brief overview of the four most common
physical environment issues in the workplace: light, noise, climate,
and vibration.
The physiology of the eye and ear and temperature regulation are
reviewed with particular emphasis on elements which are affected by
workplace design.
Risk factors relating to lighting condition include: size of the target,
contrast, time and illumination, glare, flicker, colour, and shadows. A
light meter can be used to assess illuminance, luminance, and contrast
ratios. Several engineering controls for lighting related to increasing
illumination, reducing glare, and minimizing adaptation can be
applied. Administrative controls are also discussed.
Risk factors relating to noise relate to the intensity and duration of the
noise. Symptoms can include noise-induced hearing loss (NIHL),
increased annoyance, increased blood pressure, fatigue, and blood
levels of epinephrine. Noise is usually measured by a hand-held
sound meter with a frequency analyser. Engineering controls are
presented in the module for controlling at source and controlling
between the worker and the source. Administrative controls are also
presented.
Risk factors for hot and cold environments can be represented by an
equation. Engineering and administrative controls are discussed in the
module for both hot and cold environments.
Whole-body vibration results from standing or sitting on a surface
which is vibrating. Each body part has its own resonance frequency.
Whole-body vibration can result in motion sickness at low
frequencies, increased heart rate, breathing rate, and metabolic rate at
higher frequencies. Visual performance and performance on tracking
tasks will decrease. Vibration is measured by accelerometers and can
be compared to ISO and NIOSH standards. Engineering controls at
the source and between the worker and the source are provided in the
module. Administrative controls are also discussed.
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Learning
Objectives
Once you have successfully completed this module, you will be able
to:

describe how the human eye, ear, and thermoregulatory system
work

outline risk factors for lighting, noise, climate and vibration
which will impact a worker’s physical well-bring and
performance

identify assessment tools for lighting, noise, climate, and
vibration

describe engineering and administrative controls for lighting,
noise, climate, and vibration
This module is intended to provide you with an overview of the
impact of the environment on human performance and health and
safety, as there is insufficient space to consider environmental issues
in depth. Other courses in the Occupational Health program address
environmental issues in greater detail.
Introduction
Physical environmental considerations must be taken into account in
any ergonomic investigation because they can dramatically affect a
worker’s health and comfort and performance. The amount of affect
will depend on the personal characteristics of the user as well as
characteristics about the process (the tasks and the way they are
performed).
The four major environmental factors to consider are: lighting, noise,
climate, and vibration.
Light
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As we learned in Module 10, of all of the five senses (vision, hearing,
touch, taste, and smell), vision is the most important. The light which
we see (“visible light”) is only a small portion of the electromagnetic
spectrum (see Figure 11-1). Some types of electromagnetic energy
(such as infrared, ultraviolet, and x-rays) can damage the eyes. In this
module we will not address these forms of electromagnetic energy.
We will only address visible light. Although too little or too much
visible light can not damage the eyes, poor lighting can cause
eyestrain, fatigue, headache, irritability, increased errors, decreased
productivity, and low morale.
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Source: Sanders and McCormick, 1993, p. 512.
Figure 11-1
Physiology of Vision
The eye is approximately spherical, about 25 mm in diameter. A
transparent membrane called the cornea covers the front of the eye.
The cornea protects the eye and provides part of the “refractive
power,” that is, it helps to bend light rays to the retina at the back of
the eye. The coloured part of the eye, the iris, is a circular muscle.
With low light levels, the iris relaxes; this enlarges the pupil, allowing
more light to enter the eye. The opposite happens in bright light.
Behind the pupil lies the lens, the source of the rest of the eye’s
refractive power. The retina is a thin membrane, about the area of a
postage stamp. The retina contains millions of light receptors called
rods and cones. When light strikes these receptors, they produce small
electrical signals, which are transmitted as nerve impulses along
fibres of the optic nerve to the brain, where the signals are processed
and interpreted. See Figure 11-2.
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Source: Vander, Sherman & Lucianno, 1985, p. 68.
Figure 11-2
The human eye: The blood vessels depicted run along the
back of the eye between the retina and the vitreous body.
When one shifts one’s attention from distant objects to close objects,
the little muscles (ciliary muscles) around the lenses change the shape
of the lenses in a way which increases the “refractive power” of the
eyes. This allows the light coming from the near object to focus on
the retinas so that one can see the object clearly. This changing of the
focal length is called “accommodation.” Prolonged viewing of close
objects or frequent changes in focal length fatigue the ciliary muscles.
This can be experienced as eyestrain, and may be accompanied by
headaches, fatigue, and irritability.
Another important visual process is “adaptation.” When one moves
from a bright area to a darker one, it is hard to see at first. With time,
the eyes adapt to the lower levels of illumination by increasing the
size of the pupils and by increased sensitivity of the receptors in the
retinas. A similar, but opposite, adaptation happens when moving
from a dark area to a bright one. In the workplace, conditions which
require repeated adaptation of the eye should be avoided.
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Over-illumination will increase errors and may cause eye strain from
repeated action of the muscles of the pupil.
Visual Deficiencies
Visual deficiencies are common in humans. One study found that
20% of those aged 15 to 30 had visual problems such as near and far
sightedness, color deficiency, or cataracts. The prevalence of
problems rose steadily with age and affected fully 70% of those aged
61 to 70 (Vander et al., 1985). As a result, the following points must
be considered.
1.
Visual information will often be incompletely or inaccurately
perceived.
2.
Ergonomists should plan to present visual information in ways
that make it more difficult to miss (such as using large lettering
and contrasting colours, presenting the information in more than
one way, and perhaps incorporating other cues such as auditory
warning alarms).
3.
Workers should receive periodic (e.g., annual) vision testing,
especially in visually demanding jobs such as quality control
inspection, assembly of small parts, drafting, and video display
terminal (VDT) work.
Risk Identification
The ability to see an object or detect flaws is influenced by a number
of factors.
Size
Generally, larger objects are easier to see; however, it is the “apparent
size” of the object, not its actual size, which matters. A small object
close to the eye occupies a larger portion of the “visual field,” so is
easier to see. This is why precision assembly work (such as watch
repair) is usually best done with the work supported close to the eye
(otherwise, the worker bends the neck and upper back to bring the
head close to the work surface, causing fatigue and pain in the neck
and back muscles). On the other hand, a large object which is far
away (such as a star) may be very difficult to see. The optimal size of
a “target” (object to be seen) is a function of its distance away and the
optimal viewing angle for a task. See Figure 11-3.
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Source: Kroemer, et al., 2001, p. 169.
Figure 11-3
The Subtended Angle
Contrast
Generally, maximizing contrast between an object and its background
makes it easier to see. Thus, books are printed in black ink on white
paper and warning signs feature black lettering on a yellow
background. An exception to this general rule is where the task is to
detect flaws in the color or texture of the object.
Time
The less time which is available for viewing, the harder it is to see an
object. Thus, lettering on highways signs intended for viewing at
100 km/h must be larger than similar directional signs for pedestrians
(e.g., inside an airport or train station).
Illumination
The more light falling on the object, the more light will be reflected
from it, and the easier it will be to see. Thus, for visually demanding
tasks (such as drafting, assembly of small electronic parts, or surgery),
high levels of illumination are required to minimize errors, and
maximize production and worker comfort. Increasing illumination
(for example, by adding more lamps) is often a cost-effective way to
increase productivity. However, increased illumination can also cause
glare.
Glare
Glare can either be direct, such as from a bare overhead light bulb or
the sun shining in through a window, or indirectly reflected from an
object. Either type of glare can reduce the ability to see an object,
thus reducing performance. Both types can also create health and
comfort concerns by causing people to work in awkward postures so
that the object can be seen. Glare in office environments was
discussed in Module 9.
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Flicker
A flickering light can cause eyestrain, even if the flicker rate is so
high that we do not consciously see the light blink on and off.
Discharge lamps (such as sodium, mercury vapor, and fluorescent
bulbs) pulse on and off in phase with the power supply (60 Hz, or
Hertz, meaning 60 cycles per second, in North America). Flicker is
more apparent at high levels of illumination, and some people are
more susceptible. Flicker used to be a problem with VDTs, but
designers have increased flicker rates so that this is rarely a problem
with new computers. The ends of fluorescent bulbs can flicker and
should be shielded. Flickering light can cause a strobe effect, such
that a part which is moving at 60 Hz will appear to be stationary when
illuminated with fluorescent lights. A machinist who tries to reach
through an apparently stationary wheel moving at 60 Hz can be
seriously injured.
Color
The way a coloured object appears depends not only on the amount of
light but also on the color of the light. This is important in retail
merchandising; for example, fresh fruits and vegetables will appear
more “alive” if illuminated by incandescent lamps which have a
warmer reddish-orange tint than the colder bluish-white light of
halogen bulbs. In inspection tasks, light color should be chosen
carefully to minimize distortions or to highlight the defects one is
looking for. Color also has powerful psychological effects. Thus,
hospitals are painted in “healing” pale green or “hygienic” white, and
lounges are designed in dark, warm colors and are dimly illuminated
to promote intimacy. The placement of colors is also important. For
example, the use of red and blue beside each other is problematic
because the eyes focus at different focal lengths for these colors. The
ciliary muscles are, therefore, constantly trying to maintain focus, thus
creating eye fatigue. Module 10 discussed the use of color in the
design of displays.
Shadow
A workplace may be sufficiently illuminated, yet the worker may still
have trouble seeing due to shadows. For example, the labels on stacks
of parts in a warehouse may be shadowed by the shelves. However,
the creation of shadows can be useful in some inspection tasks to
emphasize certain parts of the product thereby helping the worker to
detect flaws.
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Risk Assessment
Lighting measurement and design can be quite complex. Lighting
engineers are the specialists in this field. However, there are a few
simple, lighting measurements which the ergonomist can make with a
hand-held, battery-powered light meter.
The amount of light falling on a surface is called “illumination”
(sometimes called “illuminance”). Tables of recommended
illumination levels for different tasks are available in most basic
ergonomics or industrial hygiene texts (see Table 11-1).
Table 11-1
Source: Sanders and McCormick, 1993.
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Illumination on the work surface can be measured by placing the light
meter at the location of the work with the meter in the horizontal
plane. Ambient illumination is measured by holding the light meter
horizontally at waist level. This measurement is useful to see if there
is enough light for people to safely move around workspaces. Light
reflected from a surface, “luminance,” can also be measured.
Luminance measurements are needed to calculate “contrast ratios,”
that is, the luminance of an object relative to its background. Many
other measurements of light can be taken. The CIBS code for
illuminating engineers in the bibliography is an excellent resource.
Both engineering and administrative controls should be considered
when addressing lighting concerns.
Engineering Controls for Lighting
Increase Illumination
1.
Decrease the distance from the lamps to the work surface. For
example, in a high-ceilinged workshop, mount lamps over
workbenches rather than on the ceiling.
2.
Use openings such as windows and skylights to exploit natural
light. In addition to providing extra illumination, workers usually
strongly prefer natural light. On the other hand, windows present
problems in terms of security, privacy, climate control, and
lighting control. Curtains or shades may be needed to reduce
light or glare on bright days and to prevent light loss after dark.
Supplementary artificial lighting is usually required, especially
on overcast days or at night.
3.
Increase reflectivity of light fixtures, ceiling, and walls in order
to increase the amount of light reflected onto the work surface.
Be careful of glare.
4.
Place groups of lamps on separate switches, so that illumination
can be varied; for example, lamps near windows can be turned
off when there is sufficient sunlight.
5.
Some light should be directed upward to the ceiling to prevent
the “tunnel effect” of a dark ceiling.
Reduce Glare
1.
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Reduce overhead illumination and consider task lighting (a light
source at the workstation) which can be directed toward the parts
of the workstation which require more light.
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2.
Orient workstations so that workers don’t face windows directly.
3.
Install shades or curtains over windows.
4.
Use diffuse rather than concentrated light sources. Use
fluorescent lamps inside translucent covers with an irregular
surface, rather than an uncovered bulb in a polished aluminum
fixture. Translucent parabolic or cube covers create an even,
diffuse illumination.
5.
Use low- to medium-reflectance materials for wall coverings,
floors, and work surfaces. For example, grey or tan fabric wall
panels would be better than plywood painted with glossy white
paint. Similarly, dark red rubber flooring would be better than
white tile.
6.
Use “matte” rather than “glossy” finish on work surfaces.
7.
Reduce contrast between objects and their background.
Minimize Adaptation Problems
For example, on a sunny day, a worker driving a forklift from an
outdoor store yard into a warehouse may be temporarily “blinded.”
Ergonomic control strategies would include:

increasing illumination of the area immediately inside the door

installing an awning over the outside of the door to provide a
transition zone of intermediate brightness

ensuring that the area was large and clear of other objects,
people, or vehicles which the driver would have to avoid during
the period of reduced visual performance.
Special Consideration for Inspection
Tasks
Use Side Lighting
Shadows cast by defects make them show up better. A good example
of side lighting is shown in Figure 11-4.
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Source: Sanders & McCormick, 1993.
Figure 11-4
Minimize contrast between the object and the background when
inspecting for color. For example, a worker in a textile mill who
inspects a moving bolt of material for defects in the dye will perform
this job more accurately if the background is the same color as the
material should be, rather than black, white, or some other color.
Administrative Controls for Lighting
Administrative control strategies would include:
Noise
1.
cleaning lamps, light fixtures, and room surfaces to maintain
their reflectivity
2.
replacing lamps when they are worn out (lamp lumen output
decreases significantly as lamps age, even before they burn out)
3.
promoting regular eye exercises when working at visually
intense tasks
The Human Ear and Hearing
After vision, the second most important sense is hearing.
Physiology of Hearing
All sound starts with a pressure wave in the environment. For
example, when a hammer strikes a board, the air in front of the
hammer is compressed. This pressure wave travels like a ripple in a
pond of water. When a pressure wave strikes the ear, it is relayed to
the brain, which interprets the sound.
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Sound waves first reach the auricle, the external part of the ear, then
travel down the air-filled external ear canal. When the pressure wave
strikes the tympanic membrane (“ear drum”), it vibrates like the head
of a drum. The vibration of the tympanic membrane is passed on
through a set of three tiny bones called the ossicles in the fluid-filled
middle ear to the oval window. A narrow, air-filled passage, the
eustachian tube, connects the middle ear and the throat. This allows
for pressure across the middle ear and the throat. This allows for
pressure across the tympanic membrane to be equalized when
atmospheric pressure decreases or increases as in airplane travel or
diving. See Figure 11-5.
Source: Anticaglia, 1973, p. 310.
Figure 11-5
Pathway of Sound Conduction
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The vibration of the oval window creates a pressure wave in the fluid
of the inner ear, and the wave travels up the length of the cochlea, a
small coiled tube. The pressure wave causes certain portions of the
wall of the cochlea to oscillate, or vibrate wildly. Which portion
oscillates depends upon the frequency, or pitch, of the sound which
caused the pressure wave. A structure called the organ of Corti lies
along the length of the cochlea. See Figure 11-6. When the cochlea
wall vibrates, hair cells in that portion of the organ of Corti are
stimulated, which causes them to produce an electrical impulse. This
is conducted as a nerve signal along one of the fibres of the auditory
nerve to a portion of the cortex of the brain, which interprets the
signal as sound.
Source: Anticaglia, 1973, p. 310.
Figure 11-6
Transmission of Vibrations from Drums through Cochlea
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The brain is able to detect the frequency of the sound stimulus based
on the regions of the organ of Corti oscillated. The brain detects the
other dimension of sound, loudness or intensity, as a function of how
many nerve signals it receives. A louder sound will cause a larger
oscillation in the organ of Corti, which will stimulate more hair cells,
and will cause those which are stimulated to emit more impulses per
second.
Hearing Loss
Sounds of sufficient intensity and duration can result in hearing loss,
either temporarily, or permanently. A sound that is of high intensity
and brief duration, such as a cannon blast (175 dB) (dB = decibels;
measure of sound intensity) can permanently damage structures in the
ear. Exposure to lower intensity sounds (< 100 dB) over a period of
hours will cause short-term hearing loss. However, repeated exposure
may cause permanent loss. For a more complete explanation of Noise
Induced Hearing Loss (NIHL) access
http://regulation.healthhandsafetycentre.org on the Internet.
Presenting a person with sounds of different frequencies and intensity
tests hearing ability. The person indicates whether they hear the
sound at each level or not. Usually, the person is initially presented
with a sound of very low intensity, then the intensity is gradually
increased until the person can just detect it. This is called the “hearing
threshold level” (HTL). The results are summarized in a graph called
an audiogram. See Figure 11-7.
Source: Worker’s Compensation Board of BC, 1980.
Figure 11-7
Example of an Audiogram
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The audiogram is a useful aid in diagnosis of hearing deficiencies. In
conductive (or conduction) hearing loss, some element in the
apparatus which conducts sound energy to the oval window is
affected. Conductive hearing loss can result from a number of things,
including:





wax or an insect in the external ear canal
blockage of the eustachian tube
damage to the tympanic membrane, for example by an explosion
or puncture by a sharp object
fluid in the middle ear
damage or disease of the ossicles.
In sensorineural (or nerve) hearing loss, the organ of Corti and/or the
auditory nerve are affected. Chronic (long term) exposure to
excessive noise (especially high-frequency noise) is a main cause of
this form of hearing loss. Noise-induced hearing loss (NIHL)
accounts for about 25% of all workers’ compensation claims in
British Columbia. Another form of sensorineural hearing loss, called
presbycusis, commonly occurs with aging.
Risk Identification
High background noise levels make it harder to hear other sounds,
such as speech, telephone rings, auditory alarms, or dangerous
equipment such as vehicles or overhead cranes. This reduces
efficiency and increases the potential for accidents. The interference
effects of noise occur at lower levels than those which induce NIHL.
The extent of the interference depends upon the strength of the
background noise, as well as the distance over which communication
must take place, voice level (one can compensate for high background
noise by shouting), and the complexity of the message (e.g., simple
messages, such as directing an airplane into a boarding gate at the
terminal, may be transmitted by hand signals).
Excess noise is also a stressor. This occurs at sound levels lower than
those which cause NIHL and shows psychologically as annoyance,
increased fatigue, and irritability. There is also an increase in blood
pressure, blood levels of the hormone epinephrine (adrenaline), blood
clotting rate, and other physiological variables. Prolonged exposure to
excessive noise is associated with increased incidence of coronary
heart disease, migraine headaches, ulcers and other stress-related
disorders.
Finally, some types of noise are more annoying than others:

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intermittent noise is more disturbing than continuous noise
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
frequently repeated noise is more irritating than a one-time noise

noises are more bothersome when there is a random variation in
the pitch of the noise

high-frequency noises are more disturbing than low-frequency
noises

a noise with a meaning, such as a baby crying, is more disturbing
than a noise without meaning.
Risk Assessment
Hand-held, battery-powered sound level meters, dosimeters allow
sound to be measured in the workplace. The sound level meter
measures sound pressure in units of decibels.
Some sound level meters also contain frequency analyzers. This
feature allows one to measure the sound pressure level at each of a
number of frequency bands. This analysis is valuable for several
reasons, including:



locating the source of noise in a plant which contains many
machines
locating the more disturbing, high frequency noises
selecting noise reduction strategies.
Personal noise dosimeters are also available. These small devices are
worn by workers and record the total noise to which the worker is
exposed during the work shift. Dosimeters are especially useful where
the worker is exposed to a number of different sounds of differing
duration throughout the workday, such as a maintenance technician
who works throughout a plant rather than in front of a single machine
all day.
Risk Control
Engineering Controls for Noise
Control at the Source
Control at the source is the best solution because it eliminates the
noise altogether:

11-16
changing the process, such as replacing riveting with welding, or
using chemicals to clean parts rather than sandblasting
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
mounting machines on springs (such as used with machines
which shake cans of paint) or rubber pads (such as used with
bench grinders) to isolate the machines from the floor or bench

enclosing noisy machines such as compressors in a box. Layers
of materials of different density (for example, a polystyrene sheet
between two pieces of plywood or sheet metal) provide superior
noise reduction

providing doors which can open or panels which can be removed
to allow access to the machine for servicing, or providing a clear
(e.g., plexiglass) panel to inspect dials during operation of the
machine

allowing ventilation so the machine doesn’t overheat

maintaining machines properly, including lubricating parts,
tightening loose parts, and replacing worn parts.
Control between the Worker and Source
The next best solution is control along the path between the noise
source and the worker:

spraying elastic rubber compound on noisy pipes and heating
ducts

installing partitions to confine sound within an area. Partitions
are more effective at reducing high-frequency sound, as lowfrequency sound waves bend around partitions. “Sandwiches” of
different materials are better than a solid wall.

using sound-absorbing materials to absorb sound, such as:
►
►
►
►
►
►
►
►

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acoustic ceiling tiles
resilient floor surfaces
hanging baffles
plants
carpet
wood
wall hangings
drapes.
enclosing workers in a remote-control room, as in a sawmill or
pulp mill.
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Administrative Controls for Noise
If controlling at the source or along the path does not reduce the noise
enough, workers can be protected by spending part of the day
working in a less noisy environment so that total daily noise exposure
is not excessive.
Protect workers with personal hearing protectors. There are two main
types of hearing protection: plugs and muffs. Plugs, made of rubber,
foam, or wax, fit directly into the ear canal. Muffs are rubber or
plastic cups, which completely encompass the external ears.
Plugs are simple to use, less expensive, and more comfortable than
muffs in hot or damp conditions. However, plugs provide less
protection than some muffs and must be properly inserted to provide
maximum protection. Also, plugs are not as visible as muffs, thus it is
harder to determine if a worker is wearing them.
Muffs can provide better protection than plugs (depending upon the
type of muff) and are easier to fit. However, hard hats, glasses, and
beards make it more difficult to get the necessary tight seal between
the muff and the head. Muffs are more durable and replacement parts
are available. Sometimes neither muffs nor plugs alone will provide
the required level of protection from noise. In this case, it may be
appropriate to use plugs and muffs in combination.
Read: Human Factors in Engineering and Design by Sanders and
McCormick, pp. 613–618.
Climate
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Exposure to high ambient temperature, humidity, and/or radiant
energy is common in some industries (for example, metal foundries,
firefighting, and working outdoors in the summer). Sometimes
additional hazards such as open fires and molten metal make
protective clothing mandatory, impairing heat loss from the body.
Furthermore, the work itself may be rather vigorous, generating
substantial amounts of metabolic heat. The combined heat stress from
metabolic heat production, ambient conditions, and protective
clothing may exceed the maximum heat loss capability of the body.
At the other extreme, some workers must perform in cold climates.
For example, meat cutters who work in refrigerated rooms,
commercial fishers, and divers working underwater are all at risk of
cold stress.
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Human Temperature Regulation
Humans regulate body temperature within quite narrow limits. This
regulation is provided by a combination of behavioral and
physiological mechanisms. Behaviorally, we can add or remove
clothing, fan ourselves, huddle before a fire, or rest in the shade.
Physiologically, when we are hot, muscles around blood vessels close
to the skin automatically relax, increasing blood flow to the skin.
Sweat secretion also increases. When sweat evaporates, it cools the
skin. On the other hand, when we are cold, skin blood flow decreases,
preserving heat in the body’s “core,” often at the expense of the
extremities such as fingers, toes, and ears. Cold also stimulates
increased muscle tension and shivering, both of which generate more
internal heat.
Risk Factors
In the heat, the increased flow of blood to the skin reduces the blood
available to working muscles. This reduces capacity for physical
work. Performance on complex cognitive and perceptual-motor tasks
is also reduced in the heat. Sweating causes a loss of body fluids.
Unless these fluids are replaced, dehydration will result. Mild
dehydration reduces work performance, while more extreme
dehydration can cause heat illness and death.
When the body is cold, strength and endurance decrease, thus
decreasing physical work capacity. If the hands are numb, decreased
tactile sensitivity and manual dexterity will impair performance on
manual tasks, especially where stability or precision of movement is
required. As body temperature drops, cognitive (mental) function also
slows and decision-making errors increase.
When we feel comfortable our heat storage (S) is in balance. Heat
loss is primarily accomplished through evaporation (E) of
perspiration. Heat is added by working harder or faster generating
more metabolic heat (M). Heat loss or gain can be accomplished
through radiative heat (R) (sitting by a fire) or convective heat (C)
(holding onto a hot coffee cup). Thus the equation:
S=M–E±R±C
describes the human response to a thermal environment.
However, it is not just the air temperature which determines the
effects of heat or cold. High air speed usually increases the rate of
heat loss from exposed skin and clothing. A cold winter day can be
quite comfortable if there is no wind, but a “wind chill factor” can
make the same temperature miserable.
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The humidity, or amount of water vapour in the air, also influences
climatic effects. When the air is dry, water evaporates readily from
the skin (and with each breath we exhale from the lungs). Under these
conditions, dehydration is a potential risk, even if the air is cold.
Conversely, sweat evaporates poorly in high humidity and the body
can overheat. Thus, tree planting in the interior of British Columbia
can be tolerable at 30°C (86°F), while the same temperature in a
humid mine shaft is debilitating. The term “relative humidity” (RH)
expresses how much moisture the air holds as a percentage of its
maximum capacity for moisture at that temperature.
The effects of climate also depend upon the nature of the work.
Cooler temperature and/or higher air velocities favour heavy physical
work, while sedentary office workers prefer warmer temperature and
find air velocities greater than 0.2 metres per second to create an
uncomfortable draft. There are also individual and cultural
differences in comfort level. Some people prefer a cooler room than
others. Europeans, for example, generally prefer a room to be several
degrees cooler than do North Americans.
Risk Assessment
The dry bulb thermometer is the thermometer with which people are
most familiar. The mercury-containing bulb at the bottom of the
thermometer is exposed to air. The dry bulb temperature (Tdb) is thus
a measure of air temperature.
There are three types of thermometers that provide different
information about climate.
1.
The dry bulb thermometer, a common mercury-containing bulb,
measures air temperature.
2.
The wet bulb thermometer can be used to determine relative
humidity by comparing the wet bulb temperature to the dry bulb
temperature.
3.
The globe thermometer provides a measure of radiant energy.
An anemometer measures air velocity.
Engineering Controls for Climate
For Hot Environments
Increase the distance between the worker and the heat source; for
example, use a long-handled ladle when pouring molten metal.
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Install panels to shield workers from radiant energy. Aluminum is a
good material, as it has a high reflectivity and doesn’t corrode.
Provide spaces between the bottom of panels and the floor to allow
for air movement. If the operator must see beyond the panel, use
coated glass or a screen of chains. Chains are also useful where parts
must move, such as a conveyor belt entering and leaving an oven.
Increase ambient air velocity with fans.
Decrease humidity by installing dehumidifiers. However, this tends to
be an expensive solution.
Install air conditioners.
Wear as few clothes as feasible, unless Tdb is greater than 35°C or
radiant heat is a problem, in which case, wear protective garments,
such as those worn by foundry workers and firefighters. Aluminized
mylar reflects radiant energy very effectively, but even light coloured
cloth helps. Be aware that sometimes protective garments increase
demands for heat loss because of the weight of the suit and because
the suit blocks heat loss through skin.
For extreme heat conditions, special suits are available which cool the
worker by circulating air or water inside the suit, or which have
pockets for packets of dry ice or regular ice. Dry ice removes heat
more effectively, but ice made from water is less expensive and can
be re-frozen. Alternatively, the worker can inhale cooled gas provided
either by lines to an overhead gas cylinder or by a portable breathing
apparatus.
For Cold Environments
Install auxiliary heaters, such as radiant space heaters, under work
benches or in guard shacks.
Redirect cooling vents away from the worker.
Administrative Controls for Climate
For Hot Environments
Reduce work rate, which reduces heat production by the body.
Promote rest breaks. Ideally, these breaks should be in a cool
environment, such as an air-conditioned control room. Where
feasible, remove protective clothing during the rest breaks.
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Replace lost fluids and electrolytes (“salts”). Drink small quantities
frequently, for example, 250 ml (8 ounces) every 10 to 15 minutes.
Electrolyte supplements may be necessary if sweating is prolonged,
but salt tablets are rarely indicated, as they are usually much too
concentrated. It is better to mix salt in fluids or to salt food.
Acclimatize; that is, prepare workers for hot climates by progressively
increasing exposure, or by working in the heat for a couple of hours a
day for a week before going to a hot climate. Acclimatized workers
sweat more and their sweat is more dilute (contains fewer “salts”).
Thus, they can evaporate more heat from the skin than nonacclimatized people. However, they will need to drink more fluids to
replace the greater volume of sweat lost.
For Cold Environments
In the cold, wear thicker clothing. Layers of clothing are better than a
single thick garment, as layers can be removed or added as needed.
This is especially useful when performing heavy work in the cold.
Because the insulated value of most materials is dramatically reduced
when they are damp, remove and replace damp clothing.
Protect hands with gloves or mittens. Where more finger dexterity is
required (such as operating a cash register, baiting hooks, or pulling a
rifle trigger), partial gloves which leave the finger tips exposed may
be appropriate.
Drink warm beverages periodically. Warm the hands around the cup.
Sweetened hot beverages provide extra energy for the increased
metabolism needed to stay warm.
Provide rewarming facilities where workers can take shelter from the
elements on breaks.
Read: Human Factors in Engineering and Design by Sanders and
McCormick, pp. 574–585.
Vibration
The Nature of Vibration
There are two main types of vibration: segmental (also called handarm) and whole-body. The first type is dealt with in Modules 5 and 6
on cumulative trauma disorders. This module covers whole body
vibration, so when we say “vibration” in this module, we mean
whole-body vibration. Workers get whole-body vibration by standing
or sitting on a surface that is vibrating.
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Vibration is described in terms of the amount (expressed as
acceleration and displacement), frequency (how many times per
second the vibration occurs), and the direction it occurs in (X, Y, or
Z axis). If all else is equal, the higher the vibration acceleration, the
greater the effect on the exposed worker. However, different parts of
the human body are sensitive to different vibration frequencies. For
example, the eyeballs vibrate most at 60 Hz, while the spine, pelvis,
heart, kidneys, and most other internal organs are most sensitive to
vibration frequencies of 3 to 10 Hz. A particular concern occurs when
the vibration which the worker is exposed to creates “resonance.”
Resonance increases the displacement of the object above that of the
original vibration. It occurs at different frequencies for different
objects. See Figure 11-8.
Source: Fernandez, 1998.
Figure 11-8
Model reflecting different resonance
frequencies for various parts of the body
The magnitude of vibration also depends upon the stiffness and
damping within the system. In the human body, stiffness is provided
by the elasticity of ligaments and the tension in muscles. Damping
occurs due to friction in the fluids around the muscles, ligaments, etc.
and due to pads between bones in the spine (intervertebral discs) and
the knee joint (“cartilages”). Thus, the human body has more
damping when standing than when sitting because some of the
vibration applied to the feet of the standing worker is dissipated in the
legs and never reaches the spine, head, or internal organs.
Risk Identification
Whole-body vibration with a peak magnitude below
0.01 ms-2 is hardly felt, while acceleration of 10 ms-2 or higher are
considered hazardous (Kroemer et al., 2001). At low frequencies
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(< 1 Hz), vibration causes “motion sickness.” This is a particular
problem for workers on ocean oil platforms. At higher frequencies,
increases in heart rate, breathing rate, and metabolic rate are typical.
Increased muscle tension has the benefit of damping the vibration.
However, prolonged vibration exposure can cause fatigue of these
muscles, removing their protective effect. Visual performance is
decreased because the vibrating eyeballs blur vision. Tracking tasks
are also affected by whole body vibration. Vibrations between 6 to
10 Hz in the upper body are problematic (Kroemer et al., 2001). As
the duration of vibration is increased, people experience first
discomfort, then pain, then alarm; further increases in intensity
become intolerable. Long-term effects of vibration include damage to
the spine and intervertebral discs, low back pain, and damage to
internal organs.
Vehicle drivers are at special risk because of prolonged whole-body
vibration exposure. Rough roads increase the impact on heavy
equipment operators and drivers of off-road logging and mining
trucks. Drivers of delivery trucks who unload their own trucks have
the additional stresses of manual material handling; vibration-fatigued
muscles are more vulnerable to strain during lifting and carrying.
There are many uncertainties about the detrimental effects of whole
body vibration; however, there are standards that have been published
that describe acceptable exposures to vibration (ISO 2631).
Figure 11-9 is part of the ISO standard.
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Source: Kroemer, et al., p. 266.
Figure 11-9
Risk Assessment
Vibration is measured with accelerometers. The accelerometers are
applied to the worker’s body or to some part of the vibration source.
Whole-body vibration exposure to vehicle drivers can be measured
with a seat pan accelerometer, a flat pad about the shape and size of a
dinner plate which rests on the seat. The accelerometers are
connected to amplifiers (and often to a set of filters to measure the
vibration of certain frequencies) and a display meter.
Battery-powered, hand-held instruments are available for field
research.
The effects of whole-body vibration on humans are measured in the
laboratory by having subjects sit or stand on a platform which is made
to vibrate by a powerful motor. Mostly such experiments have been
done by aerospace research laboratories for military applications
(such as the effects of blurring of vision on jet fighter pilots and the
effects on the spine of armoured vehicle drivers). Typically, young,
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fit, male military personnel are exposed to short-term intense
vibrations. It is often hard to apply the results of these studies to
industry, where effects are mostly due to long-term, low-grade
vibration and where workers may be older and less fit.
Risk Control
Engineering Controls for Vibration
Vibration can be controlled at the source, between the source and the
person, or at the person. As with noise, the first line of defence is to
reduce the vibrations which are produced.
Control at the Source
Maintain equipment in good repair.
Maintain roads in good repair. Potholes and “washboard” increase
vehicle vibration.
Designers of equipment can “tune” systems (by adjusting their mass
and/or stiffness) so that the vibrations they produce are not in the
range of frequencies that human organs absorb.
Control between the Worker and Source
Add damping. Shock absorbers dampen the vibration transmitted
from the object to the user.
Provide flexible connectors for electrical piping and ducting. This
dissipates vibration at the connector rather than passing it on through
the piping to the worker.
Anchor enclosures (such as sound-insulating boxes around machines)
to the floor, not to the machine. Otherwise, the panels of the
enclosure will vibrate.
Use panels made of sandwiches of different materials (such as rubber
between two sheets of metal) or spray asphalt-based polymers over
vibrating surfaces. Such materials in the engine compartment isolate
passengers from road and engine noise and from vibration.
Good vehicle design will reduce the operator’s exposure to vibration.
For example, adequate visibility from the cab and pedals and controls
placed within the comfortable reach of the driver will minimize
twisting and straining and, therefore, unnecessary muscle tension,
thereby reducing the transmission of vibrations.
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Administrative Controls for Vibration
Keep vehicles tires properly inflated, as air in the tires dampens to
vibration due to rough road surfaces.
Maintain equipment. Lubricate bearings, tighten nuts and belts,
replace worn bushings, gaskets, shock absorbers, etc. Remember,
noise and vibration are related. Vibration causes sound; reducing the
noise a machine makes will usually also reduce the vibration.
Assume proper seated posture. A rolled towel placed behind the low
back supports the natural curve of the spine and reduces fatigue of
low back muscles. Move the seat close to the steering wheel, so that
the knees are above the hips, putting the pelvis and low back into the
correct position.
Reduce speed on rough roads.
Allow workers to take breaks or to spend part of their day working at
a task with less vibration (job rotation).
Train workers about the signs and symptoms of vibration-induced
disorders, risk identification, assessment, and possible solutions.
Read: Human Factors in Engineering and Design by Sanders and
McCormick, pp. 627–632.
Summary
This module has provided an overview of four physical environment
issues which commonly have an impact on the workplace: light,
noise, climate, and vibration. For each issue, risk factors have been
identified, assessment techniques discussed, and control strategies
have been outlined. The material in this module is important for
understanding the impact of the physical environment on the
workplace system and should be understood at the level of detail
provided in the module. More detailed information about these issues
are provided in other Occupational Health and Safety courses at BCIT
and can be explored in the bibliography provided at the end of the
module.
Now go to online Self Test 11.
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Bibliography
Anticaglia, J.R. (1973). The physiology of hearing, in The industrial
environment — Its evaluation and control. NIOSH.
Fernandez, J.E., & Marley, R.J. (1998). Applied occupational
ergonomics. Dubuque, IA: Kendall/Hunter.
International Organization for Standardization. (1985).
ISO 2631-1:1997. Mechanical vibration and shock: Evaluation
of human exposure to whole-body vibration.
Geneva, Switzerland: ISO.
Kroemer, K.H.E., Kroemer, H.B., & Kroemer-Elbert, K.E. (2001).
Ergonomics: How to design for ease and efficiency. (2nd ed.).
Upper Saddle River, NJ: Prentice Hall.
Sanders, M.S., & McCormick, E.J. (1993). Human factors in
engineering and design (7th ed.). New York: McGraw-Hill.
Vander, A.J., Sherman, J.H., & Lucianno, D.S. (1985). Human
physiology: The mechanics of body function. New York, NY:
McGraw-Hill.
Worker’s Compensation Board of BC. (1980). Industrial audiometry:
How and why? Richmond, BC: WCB.
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Appendix
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WPC #33128.DOC
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Chapter 18: Noise
by
M.S Sanders and E.J. McCormick
in
Human Factors in Engineering and Design
pp. 613–618
1993
© This material has been copied under licence from Access Copyright.
Resale or further copying of this material is strictly prohibited.
WPC #33128.DOC
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Chapter 17: Climate
by
M.S. Sanders and E.J. McCormick
in
Human Factors in Engineering and Design
pp. 574–585'
1993
© This material has been copied under licence from Access Copyright.
Resale or further copying of this material is strictly prohibited.
WPC #33128.DOC
07/17
Chapter 19: Motion
by
M.S. Sanders and E.J. McCormick
in
Human Factors in Engineering and Design
pp. 627–634
1993
© This material has been copied under licence from Access Copyright.
Resale or further copying of this material is strictly prohibited.
WPC #33128.DOC
07/17