Research Paper on Environmental Ergonomics

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

http://sciencedirect.com

http://knimbus.com/knimbus/user/auth.do