NATIONAL
INSTITUTE OF INDUSTRIAL ENGINEERING
PGDIE-42
INDUSTRIAL ENGINEERING
Summary of Research Paper on:
Environmental ergonomics: a review of
principles, methods and models
K.C.
Parsons
Department
of Human Sciences, Loughborough University, Loughborough, Leicestershire, LE11
3TU, UK
Received
1 June 2000; accepted 14 July 2000
SUBMITTED BY
JAYANT
PATWARE
ROLL
NO 38
ABSTRACT
A review of the
principles, methods and models used in environmental ergonomics is provided in
terms of the effects of heat and cold, vibration, noise and light on the
health, comfort and performance of people. Environmental ergonomics is an
integral part of the discipline of ergonomics and should be viewed and
practised from that perspective. Humans do not respond to the environment in a
way monotonically related to direct measures of the physical environment. There
are human characteristics which determine human sensitivities and responses.
Practical methods for assessing responses to individual environmental
components are presented as well as responses to &total' environments and
current and proposed International Standards concerned with the ergonomics of
the physical environment.
INTODUCTION
Ergonomics can
be defined as the application of knowledge of human characteristics to the
design of systems. People in systems operate within an environment and
environmental ergonomics is concerned with how they interact with the
environment from the perspective of ergonomics. Although there have been many
studies, over hundreds of years, of human responses to the environment (light,
noise, heat, cold, etc.) and much is known, it is only with the development of
ergonomics as a discipline that the unique features of environmental ergonomics
are beginning to emerge. In principle, environmental ergonomics will encompass
the social, psychological, cultural and organisational environments of systems,
however to date it has been viewed as concerned with the individual components
of the physical environment. Typically, ergonomists have considered the
environment in a mechanistic way in terms such as the lighting or noise survey
rather than as an integral part of ergonomics investigation.
There is a
continuous and dynamic interaction between people and their surroundings that produce
physiological and psychological strain on the person. This can lead to
discomfort, annoyance, subtle and direct affects on performance and productivity,
affects on health and safety, and death. Discomfort in offices can be due to
glare, noisy equipment, draughts, or smells. In the cold people experience
frostbite and die from hypothermia. In the heat they collapse or die from heat
stroke. People exposed to vibrating tools have damage to their hands.
Performance can be dramatically affected by loss of manual dexterity in the
cold, noise interfering with speech communication or work time lost because the
environment is unacceptable or distracting. Accidents can occur due to glare on
displays, missed signals in a warm environment or disorientation due to
exposure to extreme environments.
There are
numerous factors that can make up a working environment. These include noise,
vibration, light, heat and cold, particulates in the air, gases, air pressures,
gravity, etc. The applied ergonomist must consider how these factors, in the
integrated environment, will affect the human occupants. Three effects are
usually considered; those on the health, comfort and performance of the
occupants. The factors of the environment are usually considered separately.
Some attempt at integration of effects can be made. However, there is
insufficient objective knowledge to allow an accurate quantification.
ENVIRANMENTAL
AND HUMAN RESPONSE
Most of the
energy that makes up our environment originally comes as electromagnetic
radiation from the sun. Around 1373Wm~2 (the solar constant) enters the outer
limits of the earth's atmosphere and this arrives on the earth in modified form
where it is transformed from place to place and from one form to another (heat,
mechanical, light, chemical, electrical). The wide diversity of environments to
which people are exposed is therefore defined by that energy which varies in
level, characteristic and form. It is the human condition to interact and
survive in those environments and part of that has been the creation of
&local' optimum environments (e.g. buildings).The human body is not a
passive system that responds to an environmental input in a way that is
monotonically related to the level of the physical stimulus. Any response
depends upon a great number of factors. If viewed in engineering terms the
& transducers' of the body (sensors eyes, ears, etc.) have their own
specification in terms of responses to different types of physical stimuli
(e.g. the eyes have spectral sensitivity characteristics). In addition, the
body does not behave as a passive system; for example, the body responds to a
change in environmental temperature by reacting in a way consistent with
maintaining internal body temperature (e.g. by sweating to lose heat by
evaporation). The body therefore senses the environment with a &transducer'
system that has its own characteristics and it reacts in a dynamic way to
environmental stimuli
ENVIRANMENTAL
ERGONOMICS METHODS
There are four
principal methods of assessing human response to environments. These are: subjective
methods; where those representative of the user population actually report
on the response to the environment; objective measures, where the
occupant's response is directly measured (e.g. body temperature, hearing
ability, performance at a task); behavioural methods; where the
behaviour of a person or group is observed and related to responses to the
environment (e.g. change posture, move away, switch on lights); and modelling
methods. Modelling methods include those where predictions of human
response are made from models that are based on experience of human response in
previously investigated environments (empirical models) or rational models of
human response to environments that attempt to simulate the underlying system
and hence can be used to relate cause and effect.
ENVIRONMENTAL
ERGONOMICS MODELS
Thermal environments and human response
There are six
main factors that should be quantified in order to assess human response to
thermal environments; these are air temperature, radiant temperature, air
velocity, humidity, the activity of the occupants, and the clothing worn by the
occupants. A thermal index integrates these values in a way that will provide a
single value that is related to the effects on the occupants.
Humans are
homeotherms-that means that they attempt to maintain their internal (core)
temperature within an optimum range (around 373C). If the body is subjected to
thermal stress then the thermoregulatory system responds by changing its state
in a way which is consistent with maintaining core temperature within this
range. This response of the body has consequences for the health, comfort, and
working efficiency of a person.
Rational indices are derived from
mathematical models that describe the behaviour of the human body in thermal
environments. If the body is to remain at approximately a constant temperature
then, on average, the heat outputs from the body must be equivalent to heat
inputs to the body. This is known as heat balance and a usual starting point
for derivation is the heat balance equation
M=E+R+C+K+S,
Where M is
the energy produced by the metabolic processes of the body and W is the
energy required for physical work; C is the heat loss by convection; R
is the heat loss by radiation; K is the heat loss by conduction; E
is the heat loss by evaporation; and S is the heat stored.
By identifying
the practical ways in which heat is exchanged between the body and its
environment, equations can be derived and values of heat transfer can be
calculated from the parameters measured in the physical environment (air
temperature, humidity, etc.).
Thermal environments- health When the body
becomes &too hot' or &too cold' it reacts in a way that is consistent
with maintaining core temperature at a relatively constant level. When the body
is under heat stress the two main mechanisms for losing heat are controlled by
the anterior hypothalamus. The initial reaction is vasodilatation, where the
peripheral blood vessels dilate and transfer blood, and hence heat, to the
surface of the body where it can be lost to the surrounding environment. If
core temperature continues to rise, sweating occurs and considerable heat loss
by evaporation can occur. If these heat loss mechanisms are insufficient to
maintain heat balance then core temperature rises
Thermal environments-comfort Thermal comfort
can be defined as `that condition of mind which expresses satisfaction with the
thermal environment a (ASHRAE, 1966). The reference to &mind' indicates that
it is essentially a subjective term; however, there has been extensive research
in this area and a number of indices exist which can be used to assess
environments for thermal comfort. Although simple values of air temperature or
globe temperature can be used to provide conditions for comfort in rooms a more
detailed, practical approach is usually taken.
Thermal environments- performance Accurate
predictions of the effects of environments on performance at a specific
&real' task are difficult to make. This is because there are many variables
that relate to specific tasks in specific contexts and all cannot be accounted
for. However, using task analysis, components of tasks can be determined.
General guidance can then often be provided from studies of similar tasks or
studies of similar task components. A simple example would be the division of a
task (or job) into mental and manual components. The effects of a given
environment on similar mental tasks could be derived from previous studies;
similarly for the manual task components. A useful overall prediction can often
then be made
Vibration and human response Vibration can
significantly affect the health, comfort and performance of people,
particularly in vehicles. A full review of the subject is provided in Griffin
(1990). This paper can present only a summary and concentrates on human
responses to the built environment. The study of human response to building
vibration can be divided into two areas: one area is concerned with the effects
of low-frequency (often large displacement) vibration (motion) that would occur
at the top of tall buildings (due to the buildings' response to wind for
example); the other area is concerned with vibration transmitted to buildings
from such things as road traffic, trains, or aircraft passing nearby or the
operation of heavy machinery or blasting operations, etc. This type of
vibration has relatively high-frequency content and can have a different effect
on the building occupants.
Vibration- health There are levels
of vibration that can cause physical damage to the body; for example, those
found in aircraft in severe turbulence, long-term exposure of tractor operators
to vibration, or vibration to the hand from some vibrating tools. It is highly
unlikely that the occupants of buildings would be exposed to vibration levels
that would directly cause physical damage to the body. Methods by which
building vibration can affect health are therefore indirect; causing a loss of
balance in persons, for example, or simply as an additional environmental
stressor that can affect mental health and emotional state. In practice, it is
difficult to provide a model which will predict these effects and subjective,
objective and behavioural methods of investigation are more appropriate.
Vibration-comfort The term
vibration discomfort is used in studies of human response to vibration. However,
this relates more towards the effects of vibration on the occupants of vehicles
and is not appropriate in the context of building vibration. In practice, the
building designer or transport system operator wish to know at what level of
vibration occupants will be disturbed and complain. Whether occupants complain
about an environmental stress is highly context dependent and can be based on
such factors as fear of building collapse or structural damage, the perceived
source of vibration and the attitude of the occupant to the source. Accurate
predictions are therefore difficult to make for individuals, however general
guidance can be provided for populations of occupants.
Vibration- performance Vibration can
have large effects on human performance at simple tasks (e.g. reading, writing,
and drinking) and many studies have shown major effects on manual control and
vision. These effects occur at levels found mainly in vehicles and are unlikely
to occur in buildings. Low frequency vibrations often create large
displacements in tall buildings and can cause loss of orientation and balance
in subjects. However, these effects have yet to be quantified and their effects
on tasks (e.g. typing) cannot be easily predicted.
Noise-human response The human ear
detects sound pressure changes in the air and transmits a signal, which is
related to the sound pressure changes, to the brain where it is perceived as
sound. The signal which is &perceived' by the person is not directly
proportional to the sound pressure stimulus which first entered the ear. There
is a human perception transfer function. For a given sound pressure level, for
example, a single frequency noise (pure tone) at one frequency may sound
&louder' than a pure tone sound at a different frequency even though they
are at the same physical sound pressure levels. The relative effect of sound
frequency on loudness (for example) has been quantified in experimentation and
&equal loudness contours ' have been produced. Based on &equal loudness
(annoyance, noisiness, etc.) contours' weighting functions have been proposed
which approximate the average perceived response of a population.
Noise-health Noise can have
direct and indirect effects on workers health. Long-term exposure to noise
causes noise-induced hearing loss. This is due to damage to sensors in the
inner ear. The effect is in terms of reduced sensitivity to certain frequencies
of noise. Reduced sensitivity occurs initially, usually in the region of 4 kHz
and, as the condition becomes more severe, sensitivity is further reduced and
this occurs over a broader frequency band. A practical approach to assessing
the noise health hazard is to use the index dB(A) L%2 (Burns and
Robinson, 1970). Limiting values of around 85}90 dB(A) L%2 have been proposed
for 8 h exposure in industrial environments.
Noise-comfort The term comfort
is not usually used when assessing the effects of noise on the occupants of
buildings. In practice, annoyance levels are the most useful criterion,
although loudness, perceived noisiness, and nuisance are also terms used. There
are many indices that can be used to provide a value that is related to ratings
of the terms described and no one index is generally used. However dB(A) L%2
is a widely used index. A simple practical approach to assessing noise in
offices, for example, would be to measure the noise throughout the office and
take the average dB(A) value. If a more detailed analysis is required then the
noise could be analysed in the frequency domain that would also help identify
the causes of the noise.
Noise-performance The effects of
noise on human physical and mental performance can be divided into effects on
non-auditory task performance and effects on auditory task performance (e.g.
interference with speech communication, etc.). The effects of noise on
non-auditory task performance have been inconclusive, different studies
indicating that noise reduces task performance, has no effect on task
performance or increases task performance. No obvious general predictions can
therefore be made. A major consideration appears to be the level of arousal of
persons as compared with that required for optimum performance at tasks.
Performance at vigilance tasks, for example, can be improved by increasing
noise levels, hence increasing arousal to an optimum level. In practical
application the variation in results has not been sufficiently explained to
allow accurate predictions of the effects of noise on the performance of the
occupants of buildings. Some general predictions can be made, however, based on
models of human response to noise and previous laboratory and field
investigations.
Light and human response Light is that
part of the electromagnetic spectrum that is detected by the human eye. The eye
is, however, not equally sensitive to all wavelengths of light and there is a
human perception transfer function. This function depends upon the level of
light present. A consequence of the dynamic response of the eye to a change in
light level is that when there is a wide range of luminance within a visual
field, glare can occur. This depends upon the luminance of a source compared
with its background and its position within the angle of sight of the observer.
Using these variables a glare constant can be calculated for a single glare
source and, if integrated over the visual field, this provides a glare index.
It is important to note that there are large individual differences in human
response to light. In addition, defects occur in the visual system (colour
defects, myopia, etc.).
Light-health Excessive
exposure to light can cause direct effects on health. Ultra violet, infrared,
and visible radiation can cause health problems in the eye. In addition, this
radiation can also damage skin. In addition to these direct effects on health,
eyestrain can be caused by inadequate lighting conditions. Too little or too
much light, veiling rejections, disability, and discomfort glare and flicker
can all cause eyestrain (Boyce, 1981). This can cause irritation in the eyes, a
breakdown of vision and headaches, indigestion, giddiness, etc.
Light-comfort Light can cause
discomfort to the occupants of an environment as well as positive sensations
such as pleasure and emotional sensations (cold, warm, etc.). Human response to
light is a very complex subject and, despite a great deal of research, accurate
predictions of subjective impressions are still difficult to make. However,
this area of human response to the environment has employed sophisticated
psychophysical scaling techniques (e.g. multidimensional scaling) and it may be
possible in the future to provide more accurate models of subjective
impressions of lighting environments.
Light-performance Although light
can affect human performance at general tasks, glare can cause a distraction
effect; for example, the main effects of light are on visual performance.
Visual performance is related to a combination of the efficiency of the eye in
receiving and conditioning light and the interpretation of what is seen by the
person. While training can influence workers' interpretation of what is seen,
in practice lighting guidelines are required to provide the desired visual
performance at particular tasks.
CONCLUSION
It is clear from
the above discussions that there has been a great deal of work on the effects
of light, noise, vibration, and thermal environments on the health, comfort,
and working efficiency of the occupants of buildings. Models exist which can
provide realistic predictions of the effects or probable effects of components
of environments. In addition, general guidance on interactive effects and the
effects of total environments can be provided. The effects of &total'
environments include `2the sum of the physiological, psychological and social
sensations experienced by people in or around buildings which follow from their
use of the buildings. Models of these &integrated effects are not available
and buildings should also still be evaluated using subjective (and also
possibly objective) methods.
REFERENCES
