5 Ergonomics 5.1 Introduction Ergonomics is a science that includes different branches, such as engineering, anatomy, the'man and machine systems, physiology and psychology. A person having experience in any of these areas will be able to work effectively on the ergonomic aspects related with the different design equipments. Such designed systems, which can be used by the human beings effectively with putting minimum effort and cause the maximum comfort in their use and application fall in category of the Ergonomics Ergonomics is a science which deals with the relationship of man: with machine and his working environment. It takes care of factors governing physical and mental strain that a worker goes through. Ergonomics consists of two Greek words ‘Ergo’ (meaning work), and ‘Nomos* (meaning Natural Laws’), It can also be termed as “Human Engineering’, Ergonomics (or Human Engineering) is defined by I.L.O. (International Labour Organisation) as “the application of human biological sciences in conjunction with engineering sciences to the worker and his’ working Snvironment so as to obtain maximum satisfaction for the worker which, 4 the same time, enhances productivity”. In other words, Ergonomics may be defined as a multidisciplinary Science comprising subjects like anatomy, psychology, physiology, ifa Work Study and Ergonomics sociology, engineering, anthropology, physics, medicine and statistics to ensure that designs of working implements complement the strength and abil their limitations, The task of Ergonomics is to develop such conditions for workers, which are necessary to reduce their physical workload, to “improve their working postures, facilitate instrument handling, and thus improve the quality of labour put in by reducing fatigue, maximising the s of the people working on them and minimise the effects of efficiency of production operators and minimising human errors. Rather than expecting people to adapt to a design that forces them to work in an uncomfortable, stressful or dangerous manner, Ergonomists and human factors specialists seek to understand how a product, workplace or system can be designed to suit the people who need to use it. Ergonomics provides the guiding principles and specifications according to which tools, machines, work procedures and workplaces are designed for safe and efficient use. The efficiency of a machine depends on the ability of the worker to control it effectively and accurately. The fact that workers are able to operate in poorly designed workplaces does not mean that it is the most efficient method of production; workers should be able to operate machines in the least stressful way. Ergonomics aims to create safe, comfortable and productive work spaces suitable to human abilities and limitations taking the individual's body size, strength, skill, speed, sensory abilities (vision, hearing), and even attitudes into consideration. 5.2 History of Development Ergonomics emerged as a scientific discipline in the 1940s as a consequence of the growing realisation that as technical equipments became increasingly complex, not all of the expected benefits could be delivered if people were unable to understand and use the equipment to its full potential Initially, these issues were most evident in the military sector where high demands were placed on the physical and cognitive demands of the human operator, As the technological achievements of World War II were transferred to civilian applications, similar problems of disharmony between the people and equipments were encountered, resulting in poorErgonomics 89 user-performance and an increased risk of human error, The anal: of poor performance, of what came to be known as man-machine systems (now human-machine systems), provided a growing body of evidence which could be linked to difficulties faced by human operators. This motivated the senior academics, and military physiologists and psychologists to further investigate the nature of interaction of people with their equipments and environment. Although the early focus was on work environments, the importance of ergonomics has been increasingly recognised in many spheres, including the design of consumer products, such as cars and computers. In 1949, at a meeting of distinguished physiologists and psychologists at The Admiralty, the term Ergonomics was coined from the Greek roots go and Nomos). Later that year this same body of scientists. together with some like-minded colleagues, formed the Ergonomics Research Society (ERS), which became the first such professional body in the world. In the following sixty-two years, the ERS has evolved to represent the current discipline, both in the United Kingdom and internationally. In 1977 the ERS became the Ergonomics Society (ES) in recognition of the increasing focus on the professional application and practice of Ergonomics that stemmed from the ever-increasing theoretical and research base. The ES became a Registered Charity (number 292401) and a Company limited by guarantee (Company number 1923559) in 1985. As the discipline evolved, some variations in terminology arose in different countries. In the USA the term human factors took on the same Meaning as ergonomics in the UK. Although the two terms have remained synonymous to professionals, popular usage has recently accorded different shades of meaning to them. Consequently, human factors may be considered to imply the cognitive areas of the discipline (perception, Memory, etc.,) whereas ergonomics may be used more specifically {0 refer to the physical aspects (workplace layout, light, heat, noise, &lc.). In 2009, following a vote by the membership and approval from Companies House, the ES was renamed the Institute of Ergonomics and Human Factors (IEHF) to reflect the popular usage of both terms and t0 “mphasise the breadth of the discipline.>>| «3 Work Study ang Ergonomics In 2014, the diseipline’s importance was recognised officially by the award of a Royal Charter to the Institute. This allows us to Confer Chartered status on those members who fulfill certain criteria, Thje includes having a high level of qualification and experience and bein, able to demonstrate continuing professional development. At the end of 2014, the Institute had 294 members who were eligible for Chartered status, with many more about to become so. They are the first such “Chartered Ergonomists and Human Factors Specialists’ in the world. The Charter and its accompanying governing documents were unanimously accepted by the membership at an Extraordinary General Meeting in November. The Institute changed its name once again to the Chartered Institute of Ergonomics & Human Factors. 5.3 Objectives 1. To optimise the integration of man and machine in order to increase productivity with accuracy. It involves the design of: (a) A workplace suitable for the worker (b) Machinery and controls, so as to minimise mental and physical strain on the worker to enable improvement in efficiency (©) A favourable environment for performing the task most effectively (d) Task and work organisation 2. To take care of the factors governing physical and mental strain (“e,, fatigue), so as to get maximum satisfaction for the worker which at the same time would enhance productivity? 3. Attempt to minimise the risk of injury, illness, accidents and errors without compromising productivity » To improve the design of machine at the i tial design stage or later whenever the existing product or process is modified (a) Developing most comfortable conditions related to climate, lighting, ventilation and noise level () Reducing the physical workloadErgonomics 1 (c) Improving working postures and reducing efforts of certain movements (a) Making the handling of machine levers and controls easy (c) Increasing safety 5.4 Man-Machine Systems: Design, Characteristics and Classification Human factors are a system concerned with the relationship between human beings and their workplace or work environment and machines. All man-machine systems are produced with some objective in view. This objective is always well defined and the system is designed so as to achieve the objective as successfully as possible. In view of this the operational functions of both the components and constituents, i.e., man and machine should be clearly defined. \There is one another aspect of man-machine system which, though not strictly a part of it, affects the system performance to a great exter or what we call working conditions. 'This is the system environment he proper integration of man and machine, which is beneficial for human operator and enhances the overall system performance, is the primary aim of the Ergonomics discipline. Characteristics of Man-Machine System * The man-machine system consists of man, machine and system environment. * It is essentially artificial in nature and is specifically developed to fulfill some purpose or specific aim. * Ithas specific inputs and outputs which are appropriately balanced. * Itis variable in size and complexity and is dynamic in performance. * Asub-system of man-machine system interacts with and affects the other parts, The man-machine system becomes more efficient when inputs and Out puts are adequately balanced. Vironmental factors or system environment affects system Performance.~ 92 Work Study and Ergonomicg Classification of Man-Machine Systems Depending upon the size and complexity, man-machine systems are of following three typ: 1. Manual Systems They are essentially man-directed systems. These are flexible in nature and small in size. Simple tools and equipments are used, and the efficiency depends upon the human factor. A large variability is possible in a manual system as every worker may select different method to do the same job. nv Mechanical Systems They are more complex and inflexible in nature than the manual ones. The machine component is power-driven, and human activity includes information-processing, decision-making and controlling occasionally the semi-automatic systems; they have components which are well-integrated. This is the feature which renders these systems rather inflexible. An automobile or a machine tool operated by a driver or an operator are good examples of this category. 3. Automatic Systems A complex system in which all operational functions are performed by automatic devices is known as automatic system. Operational functions include sensing information, processing it, making decisions and taking action. It is totally inflexible in nature and cannot be adapted to uses other than that the one for which it has been designed. The human element/component performs the jobs of monitoring, programming the function, maintenaning and up keep of the system, An automatic telephone exchange, a digital computer and an automatic screw of cutting systems. A perfectly machine are good examples of automa reliable automatic system does not exist at present.| — ergonomics 93 55 introduction to Structure of Human Body she sense organs of man make physical contact with their environment. qhrough their senses information is conveyed to the brain, such as the eves. cars and nose. The stimulus has to be strong enough for the senses to detect and become aware of its presence in the environment. The absolute threshold’ marks the difference between being aware and not be different conditions. ¢ aware of a stimulus: this may vary at different times and under - A second threshold, termed as the ‘difference threshold” refers to detectable differences between two stimuli that can be sensed by an individual. People’s senses automatically adapt to various stimuli in different situations, But if the stimulus is constant and familiar the sense organs can become insensitive to it. 5.5.1 Features of Human Body Human body is composed of elements like hydrogen, oxygen, carbon, calcium and phosphorus. These elements reside in trillions of cells and non-cellular components of the body The content, acidity and composition of the water inside and outside of cells is carefully maintained, The main electrolytes in body water outside the cells are sodium and chloride, whereas potassium and other phosphates are found within the cells. Cells The body contains trillions of cells— the fundamental unit of life. At maturity, there are roughly 30-37 trillion cells in the body, an estimate arrived at by totalling the cell numbers of all the organs of the body and cell types, The body is also host to about the same number of non- human cells as well as multicellular organisms which reside in the Sastrointestinal tract and on the skin.Work oa ork Study and Ergonomieg Tissues oon ues, defined as cells, that have a specialised function. The study of t s called histology; the The body consists of four main sists of many different types of sues tissues can be seen with a microscope. types of tissues - lining cells (epithelia), connective tissues, nervous tissues and muscle tissues. Cells that lie on surfaces exposed to the Outside world, or within the gastrointestinal tract (epithelia) or internal cavities (endothelium) are in numerous shapes and forms — from single layers of flat cells, to cells with small beating hair-like cilia in the lungs, to column-like cells that line the stomach. Endothelial cells are cells that line internal cavities including blood vessels and glands. Lining cells regulate what can and can’t pass through them, protect internal structures, and function as sensory surfaces. Organs Organs, structured collection of cells with a specific function, sit within the body. Their examples include heart, lungs and liver. Many organs reside within the cavities inside the body. These cavities include the abdomen and pleura. Circulatory system The circulatory system comprises the heart and blood vessels (arteries, veins and capillaries). The heart propels the circulation of the blood, which serves as a “transportation system” to transfer oxygen, fuel, nutrients, waste products, immune cells and signaling molecules (i.2., hormones) from one part of the body to another. The blood consists of fluid that carries cells in the circulation, including some that move from tissue to blood vessels and ba as well as the spleen and bone marrow. Digestive system ‘The digestive system consists of the mouth including the tongue and teeth, esophagus, stomach, (gastrointestinal tract, small and large intestines, and rectum), as well as the liver, pancreas, gallbladder, and salivaryExgonomics 96 glands. Inconverts food into small, nutritional, non-toxic molecules for jistribution and absorption into the body, d Immune systom The immune system consists of the white blood cells, the thymus, lymph nodes and lymph channels, which are also part of the lymphatic system, The immune system provides a mechanism for the body to distinguish its own cells and tissues from outside cells and substances, and to neutralise or destroy the latter by using spe ed proteins, such as antibodies, cytokines, and toll-like receptors among many others, Eyes Eyes operate like a camera catching (through the pupils) and refracting light (ens) and converting it into a picture (retina to the optic nerve), Eyes are susceptible to hazards, such as flying particles and irritating dusts, chemical o radiation damage and, in cases of inadequate lighting, eyestrain. Protection for the eyes can be achieved either with physica barriers that protect them against foreign objects, ¢.g., safety glasses or by improving workplace and task-design so that they do not have to strain them selves too hard. This can be done by reducing glare and reflections, optimising workplace lighting and viewing object qualities, Such as contrast, colour, size and shape. Scleratic coat (sclera) choroid coat Lens Pupil, Comoa f° -+— Yollow spot is y “SS : \ Ciliary muscle Optic nero Fig. 6.1. Antomoy of a Human Eyo This includes * the design of di inted materials. A small Percent the design of displays and printed 1 willy © Of the population is colour blind, ‘These people are usfa Work Study and Ergonomics men with varying degrees of red/ereen blindness. This can be critica, for certain occupations, and while viewing visual displays involving these colours Ears The car and auditory system are more complicated than most people realise. It consists of the external car, middle ear (separated from the external car by the ear drum), inner car and the central auditory pathways, Sound travels to the ear in waves. These are transmitted via the auricle (visible part) and external auditory canal through the eardrum to small bones in the middle ear that vibrates. From there the vibrations are transmitted to the inner ear and to the sensory cells of the cochlear that respond to particular frequencies or pitches. The cells transform damaged sound waves to nerve impulses that are transmitted to the brain. The cells and hairs can get damaged at times when exposed to loud noise. Auricle (external ear) Vestibule Auditory auditory nerve canal Cochlea Eardrum —_Basilar membrane with sound-sensitive cells Fig, 5.2 Human Ear Different kinds of noise affects hearing in different ways: the higher the pitch the worse the effect is; the clearer the tone the greater the hazard; the higher the intensity the greater the damage; the greater the length of exposure to damaging noise on a daily basis the greater is the risk of hearing loss. (See also Noise). The ears also contain the semicircular canals that are necessary for balance and body orientation.yr egonories 97 skin sheskin isthe largest ( 1-4-2 square meters) visible part of an individual and so iS the body S largest organ. It protects tissues underneath from snysical and chemical damage as well as protect the body from drying jut-and abrupt changes in temperature, The skin contains: « sweat glands that help maintain an even body temperature, and fine blood vessels that assist in temperature control, nutrition and waste Femoval; nerve endings that act as sensory receptors of heat, cold, pain, pressure and touch: sebaceous glands that secrete substances to keep the skin supple and protect it from harmful bacteria. Exposure of the skin to some substances and physical agents, such as the sun, may cause skin irritation, non- allergic contact eczema and burning, Protection of the skin is achieved best through elimination of or isolation from the substances and agents, and less effectively with PPE. Nose The nose transmits sensations of smell and filters as well as alters the temperature of the air that an individual inhales. An individual’s sense of smell adapts quickly to certain smells. However, some of these may tell a worker that there is a problem. Workers may need respiratory protection in environments where unpleasant or obnoxious smells cannot be eliminated. Dangerous, unnecessary and/or unpleasant smells care tequired to be controlled where the sense of smell works as an early detection monitor. Taste Taste buds are on the tongue and respond to the sensations of sweetness, Salti: it ltish, bitterness and sour tastes. 55.2 Stress and Strain the ¢ 01 F Pati ci y related to the. CePt Of fatigue and recovery at human work is closely rela © etgonom:, ; Sonomic concepts of stress and strain.ie Work Study and Ergonomieg ‘ADAPTATION Teaining taigve Fig, 5.3 Stress, Strain and Fatigue Stress implies the sum of all parameters of work in the working system influencing people at work, which are perceived or sensed mainly over the receptor system, or which put demands on the effector system. The parameters of stress result from the work task (muscular work, non- muscular work and task-oriented dimensions and factors) and from the physical, chemical and social conditions under which the work has to be done (noise, climate, illumination, vibration, shift work, etc. situation- oriented dimensions and factors). The intensity/difficulty, the duration and the composition (i.e., the simultaneous and successive distribution of these specific demands) of the stress factors results in combined stress, which all the exogenous effects of a working system exert on the person working. This combined stress can be actively coped with or passively put up with, specifically depending on the behaviour of the engaged person. The active case will involve activities directed towards the efficiency of the working system, while the passive case will induce reactions (voluntary or involuntary), which are mainly concerned with minimising stress. The ely influenced by the individual characteristics and needs of the working person. The main factors of influence are those that determine performance and are related to motivation, and concentration and to disposition, which can be referred to as abilities and skills. relation between the stress and activity is dec The stresses relevant to behaviour, which are manifest in certain activities, cause individually different strains, The strains can be indicated by the reaction of physiological or biochemical indicators (e.g., raising the heart rate) or it can be perceived. Thus, the strains are susceptible to ~yr egorories physical sealing”, which estimates the strain as experienced by 99 ho- im gorking person. In & behavioural approach, the existence of strain ! | Iso be derived from an activity analy: he intensity with which 125 6000 >IT5 <25 Very Heavy 10.0- 12.5 | 4800-6000 150-175 20-25 Heavy 75-10.0 | 3600-4800 | 125-150 15-20 Moderate 50-75 2400-3600 | 100-125 10-15 Light 2.5-5.0 1200 - 2400 60-100 05-10 Very Light <25 <1200 <60 <05 5.6.2 Bio-Mechanics Bio-Mechanics is a discipline that approaches the study of the body as though it were solely a mechanical system: all parts of the body are likened to mechanical structures and are studied as such. The following analogies may, for example, be drawn: * Bones: levers, structural members * Flesh: volumes and masses * Joints: bearing surfaces and articulations * Joint lining : lubricants * Muscles: motors, springs Nerves: feedback control mechanisms * Organs: power supplies Tendons: ropes ay éErgonomics 103 « Tissue: springs alloons. « Body cavitie: The main aim of biomechanics is to study the way the body produces force and generates movement. The di ipline relies primarily on anatomy, elated disciplines are anthropometry (the study of human body measurements), work physiology and kinesiology (the study of the principles of mechanics and anatomy in relation to human movement). While considering the occupational health of the worker, biomechanics helps to understand why some tasks cause injury and ill health. Some relevant types of adverse health effects are muscle strain, joint problems. back problems and fatigue. mathematics and phys Back strains and sprains and more serious problems involving the intervertebral discs are common examples of workplace injuries that can be avoided. These often occur because ofa sudden particular overload, but may also reflect the exertion of excessive forces by the body over many years: such problems may occur suddenly or may take time to develop. An example ofa problem that develops over time is “seamstress’s finger”. A recent description describes the hands of a woman who, after 28 years of work ina clothing factory, as well as sewing in her spare time, developed hardened thickened skin and an inability to flex her fingers (Poole 1993). (Specifically, she suffered from a flexion deformity of the right index rominent Heberden’s nodes on the index finger and thumb of allosity on the right middle finger due films of her hands showed fing the right hand, and a prominent ¢; to constant friction from the scissors.) X-ray severe degenerative changes in the outermost joints of her right index and middle fingers, with loss of joint space, articular sclerosis (hardening of tissue), osteophytes (bony growths at the joint) and bone cysts. Inspection at the workplace showed that these problems were due to repeated hyperextension (bending up) of the outermost finger joint. Mechanical overload and restriction in blood flow (visible as a whitening of the finger) would be maximal across these joints. These problems rtion ina site other than the signing tasks to avoid develop in response to repeated muscle muscle. Biomechanics helps to suggest ways of deof Work Study and Ergonomicg these types of injuries or of improving poorly designed tasks. Remedieg for these particular problems are to redesign the scissors and to alter the sewing tasks to remove the need for the actions performed. 5.6.3 Types of Movements of Body Members Exion: movement in the sagittal plane that decreases the angle of the joint and brings two bones closer together Extension: opposite of flexion; movement in the sagittal plane that increases the angle of the joint or distance between two bones or parts of the body Hyperextension: extension greater than 180 degrees Rotation: movement of a bone around its longitudinal axis Abduction: moving a limb away in the frontal plane from the median plane of the body. spreading the fingers apart Adduction: opposite of abduction; movement of a limb toward the body midline Circumduction: a combination of all the movements, commonly seen in ball and socket joints where the proximal end of the limb is stationary while the distal end moves ina circle Dorsiflexion: lifting the foot so the superior surface approaches the shin, standing on the heels Plantar flexion: pointing the toes Inversion: turning the sole of the foot medially Eversion: turning the sole of the foot laterally Supination: forearm rotation laterally so that the palm is facing anteriorly and the radius and ulna are parallel Pronation: forearm rotation medially so that the palm faces posteriorly and the ulna and radius are crossed Opposition: touching the thumb to other fingers,= Ergonomics 108 5.6.4 Strength and Endurance Muscular strength and endurance are (wo important parts of your body's ability to move. lift things and do day-to-day activities. Muscular strength js the amount of force you can put out or the amount of weight you can Iift, Muscular endurance is how many times you can move that weight without getting exhausted (very tired). Muscular strength and endurance are important for many reasons: « Increase your ability to do activities like opening doors, lifting boxes or chopping wood without getting tired. Reduce the risk of injury. « Help you keep a healthy body weight. Lead to healthier, stronger muscles and bones. « Improve confidence and how you feel about yourself. * Give you a sense of accomplishment. « Allow you to add new and different activities to your exercise programme. « Improving muscular strength and endurance «© There are many ways to improve muscular strength and endurance. A gym or fitness centre is a good place to go if you're interested in doing resistance training (also called strength training, weight training or weight lifting). This involves working a muscle or group of muscles against resistance to increase strength and power. 5.6.5 Speed of Movements overriding objective, shared by 1a feasible objective for ity was determined In immediate postwar industry the ergonomics, was greater productivity. This was ergonomics because so much industrial productiv directly by the physical effort of the workers involved, like speed of assembly, rate of lifting and movement determined the extent of output. Gradually, mechanical power replaced human muscle pow More power,Work Study and Ergonomics 106 dis to more accidents on the simple principle that an accident «< the consequence of power in the wrong place at the wrong time. When oe one a faster, the potential for accidents is further increased, ane heconvern of industry and the airy of ergonomics gradually shifted from productivity to safety. This occurred in the 1960s and early 1979s, ‘About and after this time, much of manufacturing industry shifted from batch production to flow and process production. The role of the operator shifted correspondingly from direct participation to monitoring and inspection, This resulted in a lower frequency of accidents because the operator was more remote from the scene of action, but sometimes in a greater severity of accidents because of the speed and power inherent however. lea in the process. 5.7 Anthropometry Anthropometry is a fundamental branch of physical anthropology. It represents the quantitative aspect. A wide system of theories and practice is devoted to define methods and variables to relate the aims in different fields of application. In the fields of occupational health, safety and ergonomics anthropometric systems are mainly concerned with the body build, composition and constitution, and with the dimensions of the human body’s interrelation to workplace dimensions, machines, the industrial environment and clothing. Anthropometric Variables An anthropometric variable is a measurable characteristic of the body that can be defined, standardised and referred to a unit of measurement. Linear variables are generally defined by landmarks that can be precisely traced on the body. Landmarks are generally of two types: skeletal anatomical, which maybe found and traced by feeling bony prominences through the skin, and virtual landmarks that are simply found as maximum or minimum distances using the branches of a caliper. Anthropometric variables have both genetic and environmental components and may — be used to define individual and population variability, The choice ofErgonomics 107 variables must be related to the specific research purpose and standardi: with other research in the same field, as the number of variables i in the literature Is extremely large, up to 2,200 have been described for the human body. ’ ghts, distances from landmarks with subject standing or seated in standardised posture: diameters, such as distances between bilateral landmarks: Jengths, such as distances between two different landmarks; curved s, namely ares, such as distances on the body surface between Anthropometric variables are mainly linear measures, such as heii measure: two landmarks; and girths, such as closed all-around measures on body surfaces. generally positioned at least at one landmark or at a defined height. Other variables may require special methods and instruments. For instance. skinfold thickness is measured by means of special constant pressure calipers. Volumes are measured by calculation or by immersion in water. To obtain full jnformation on body surface characteristics, 2 computer matrix of surface points may be plotted using biostereo metric techniques. 5.8 Design of Seat and Workplace pressure in the back isto be ina standing ou need to sit. While sittin: seat. Some weight is also Where the weight is position. The best way to reduce the main However, there are times when y part of the body weight is transferred to the transferred to the floor, back rest, and armrests. transferred is the key to a good seat design. When the proper areas are not supported, sitting in a seat all day ure on the back causing pain. The lumbar (bottom to be supported to decrease disc presst that inclines backwards and has a lumbar sup} excessive low back pressures. The combination on the lower back is to have @ backrest inclination of 120 de! 4 lumbar support of 5 cm. The 120 degrees inclination means the angle between the seat; and the backrest should be 120 degrees. The lumbar support of 5 cm means the chair backrest supports the lumbar by sticking can put unwanted presst five vertebrate in the spine) needs re, Providing both a seat back port is critical to prevent which minimises pressure grees and~ Work Study ang Ergonomieg 108 t Sem inthe lower back area, One drawback in creating an open oe out Sc One’S body ning inwarg be found in air creates the Open body angle eping the spine in alignmeny ask. The benefit of this position is sle remains 90 degrees or wider angle by moving the backrest backwards is that it takes away from the tasking position, which ty ically involves lea towards a desk or table. One solution to this problem can the kneeling chair. A proper kneeling ch by lowering the angle of the lower body, and the sitter properly positioned to t that if one leans inward, the body an; Viewing Distance 50cm y, 4 —_l! 7 — Viewing Angie T ——_ h of kneeling chairs iding a horizontal seating surface with an ancillary knee pad. This design Wholly defeats the purpose of the chair. Ina proper kneeling chair, some of the weight bears on the shins, not the knees, but the Primary function of the shin rests (kneerests) is ‘0 keep one from falling forward out Of the chair. Most of the weight remains on the buttocks. Another Way to keep the body from falling forward is with a saddle seat, This type of seat is generally seen in some Sit-stand stools, which seek to emulate the riding or saddle position of horseback rider, the first “job” involving extended periods of sitting. Another way to reduce lumbar dise pressure is to use armrests, They force of your body not entirely on the seat and s by prov: help by putting theErgonomics 109 tack rest, but by putting some of this pressure on the armrests as well armrests need t© be adjustable in height to ensure that the shoulders are not ov erstressed. 5.8.1 Steps in the Workplace Design inthe workstation design and implementation process, there is always an initial need to inform the users, and to organise the Project so as to allow their full participation. This would increase the chance of full employee acceptance of the final results. A treatment of this goal is not within the scope of the present treatise which concentrates on the problem of arriving at an optimal solution for the physical design of the workstation, but the designing process nonetheless allows the integration of such a goal. In this process, the following steps should always be considered: * Collection of user-specific demands * Prioritising demands « Transfer of demands into (a) technical specifications, and (b) specifications in user terms iterative development of the workstation’s physical layout * Physical implementation * Trial period of production * Full production * Evaluation and identification of resting problems. The focus here is on steps one to five. Many times, only a subset of all these steps is actually included in while designing workstations. There “te Various reasons for this. If the workstation is of a standard design, Such as in some Visual Display Unit (VDU) working situations, some Steps may duly be excluded, However, in most cases the exclusion of Some of the Steps listed would lead to a lower quality of workstation than “hat can be considered acceptable, This may be the ease when financial Srtime constrai . ints are too severe, or when there is a sheer neglect of things due to th ¢ lack of knowledge or insight at the management level. | | | | |r _. | 110 Work Study and Ean 8 5.8.2 Other Workplace Risk Factors The risk factors addressed by industrial ergonomics are a partial fj 5 ‘ , metal Vise hazards present in a work-setting, Others include: of Job stress * Job invariability * Cognitive demands © Work organisation © Workload + Working hours (shift work, overtime) * Displays and control panels © Slip and falls ¢ Fire * Electrical exposures * Chemical exposures * Biological exposures * lonising radiation * Radiofrequency/microwave radiation * Professionals such as industrial hygienists, human factors analysts, safety engineers, occupational medicine physicians, and occupational nurses evaluate and control these other risks. The ergonomist must recognise the skills and capabilities of these individuals, A close Working relationship among these is essential for preparing an almost perfect workplace where prime considerations are health and sagely. Certain features at of the work-setting have been associated with injury. These are called physical risk factors and include the following: Posture: Posture is the position that a body takes while performing work activities. Awkward postures are associated with increased risks of injury. It is generally considered that the more a joint deviates from its neutral (natural) position, the greater is the risk of injury. Posture issues are caused by work methods (bending and twisting to pick up a box;ergoro® a singe wrist ase PAF) oF workplhedimension (extended ending the ota xtende ten prin part roma bin ata high ection kneeling inthe ’ rage plane because of confined space while handling lug . egage). tures have been associated with injury. For exampl y. For example. specific pos! « Wrist . Flexion/extension (bending up and down) Ulnar/radial deviation (side bending) Shoulder ‘Abduction/fiexion (upper arm positioned out to the side or above shoulder level) Hands at or above shoulder height « Neck (cervical spine) Flexion/extension or bending the neck forward and to the back « Side bending as when holding a telephone receiver on the shoulder Low back « Bending at the waist, twisting Force: Task forces can be viewed as the effect of an exertion on intemal body tissues (e.g., compression on a spinal dise from lifting, tension within a muscle/tendon unit from a pinch grasp), or the physical features associated with an object(s) external to the body (e.g., weight ofa box, pressure required to activate a tool, pressure necessary to Snap two pieces together). Generally, the greater is the force, the higher is the degree of risk. High force has been associated with the risk of injury at the shoulder/neck (Berg et al.), the low back (Herrin et al.), and the arm/ wristhand (Silver stein et al). It is important to note that the relationship between foree and degree of injury risk is modified by other work risk factors, such as posture, acceleration/velocity, repetition, and duration. errelationship of force with st Better analysis tools recognise the int ; is eG the sk factors relative to overall task risk. Five aon force-tlaed oe tisk conditions have been extensively studied by researcher an nomists, They are not “rudimentary” risk factors: Rather, they ® Wor en sok factors with "kplace conditions that present a combination of risk fa cooWork Stud 112 Y and Ergonomicg force being a significant component. Their common appearance in the force as mil " workplace and strong association with injury prompts their introduction workplace 4 here. Static Ex generally means the performance of a task from one postural position for an extended duration. The condition is a combination of force, posture, Although defined in a variety of ways, static exertion and duration. The degree of risk is in proportion to the combination of the magnitude of the external resistance, awkwardness of the posture, and duration. Grip: A grip is the conformity of the hand to an object accompanied by the application of exertion usually to manipulate the object. Hence, itis a combination of a force with a posture. Grips are applied to tools, parts, and other physical objects in the work-setting during task performance. To generate a specific force, a pinch grip requires a much greater muscle exertion than a power grip (object in the palm of the hand). Hence, a pinch grip has a greater likelihood of creating injury. The relationship between the size of the hand and the size of the object also influences risk of injury. Grant et al. found reduced physical exertion when the handle was one cm less than the subjects” grip-diameter. Contact Trauma Two types of contact trauma are: (a) Local mechanical stress generated from sustained contact between the body and an external object, such as the forearm against the edge of a counter, (b) Local mechanical stress generated from shock impact, such as using the hand to strike an object. The degree of injury risk is in proportion to the magnitude of force, duration of contact, and sharpne: s of external object. Gloves Depending on material, gloves may affect the grip force generated bY a or fr : 5 . . in 4 worker for a given level of muscular exertion. To achieve a cetta :Ergonomics 193 grip force while wearing gloves, a worker may need to generate muscular exertion than when not wearing gloves, Greate associated with increased risk of injury, greater r force is Bulky Clothes Bulky clothes, used to protect the worker from cold or other physical elements, may increase the muscle effort required to perform tasks, Velocity Angular velocity/angular acceleration are the speed of body-part motion and the rate of change of speed of body-part motion, respectively. Marras and Schoenmarklin found a mean wrist flexion/extension acceleration of 490 deg/sec sec in low risk jobs and acceleration of 820 deg/sec in high risk jobs. Marras et al. associated trunk lateral velocity and trunk- twisting velocity with medium and high-risk occupationally-related low back disorder. Repetition Repetition is the time quantification of a similar exertion performed during a task. A warehouse worker may lift and place on the floor three boxes per minute; an assembly worker may produce 20 units per hour. Repetitive motion has been associated with injury and worker discomfort. Generally, the greater is the number of repetitions, the higher is the degree of risk. However, the relationship between repetition and degree of injury risk is modified by other risk factors, such as force, posture, duration, and recovery time. No specific repetition threshold value (cycles/unit of time, movements/unit of time) is associated with injury. Duration Duration is the time quantification of exposure to a risk factor. Duration can be viewed as the minutes or hours per day the worker is exposed to 4 risk, Duration also can be viewed as the years of exposure to a risk factor or a job characterised by a risk factor. In general, the greater is the duration of exposure to a risk factor, the greater is the degree of risk.Work Study and Ergonomics 114 Recovery time Recovery time is the time quantified for rest, performance of low stress ecoven) : aus or performance of an activity that allows a strained body area a y ed discomfort, and rest to rest. Short work pauses have reduced per periods between exertions have reduced performance decrement. The recovery time needed to reduce the risk of injury increases as the duration of risk factor increases. Specific minimum recovery times for risk factors have not been established. Heavy dynamic exertion The cardiovascular system provides oxygen and metabolites to muscle tissues. Some tasks require long-term/repetitive muscle contractions such as walking great distances, heavy-carrying, and repeat-lifting. As physical activity increases, muscles demand more oxygen and metabolites. The body responds by increasing the breathing rate and heart rate. When muscle demand for metabolites cannot be met (metabolic energy expenditure rate exceeds the body’s energy producing and lactic acid removal rate) physical fatigue occurs. When this happens in a specific area of the body (e.g., shoulder muscle from repeat or long-term shoulder abduction), it is termed localized fatigue and is characterised by tired/sore muscles. When this happens to the body in general (from long-term heavy-carrying/lifting/climbing stairs), it is termed whole body fatigue and may produce a cardiovascular accident. Also, high heat from the environment can cause an increase in heart rate through body cooling mechanisms. Therefore, for a given task, metabolic stress can be influenced by environmental heat. Segmental vibration (Hand-Arm vibration) Vibration applied to the hand can cause a vascular insufficiency of the hands/fingers (Raynaud’s disease or vibration white finger). Also, it ean interfere with sensory receptor feedback leading to increased hand-griP force to hold the tool. Further, a strong association has been reported between carpal tunnel syndrome and segmental vibration.Ergonomics a §.9 Visual Display Design There are three basic types of visual displays: (a) The check display indi exists (for example tes whether or not a given condition 8 green light indicates normal function). (8) The qualitative display indicates the status ofa changing variable or its approximate value, or its trend of change (for example, a pointer moves within a “normal” range). (c) The quantitative display shows exact information that must be ascertained (for example, to finda location ona map, to read text or to draw on a computer monitor), or it may indicate an exact numerical value that must be read by the operator (for example, a time or a temperature). Design guidelines for visual displays are: (a) Arrange displays in such a way that the operator can locate and identify them easily without unnecessary searching. (This usually means that the displays should be in or near the medial plane of the operator. either below or at eye height.) (6) Group displays can be arranged functionally or sequentially so that the operator can use them easily. (c) Make sure that all displays are properly illuminated, coded and labelled according to their function. (d) Use lights, often coloured, to indicate the status of a system (such as ON or OFF) or to alert the operator that the system, or a subsystem is inoperative and that special action must be taken, Common meanings of light colours are: Flashing red indicates an emergency condition that requires immediate action. An emergency signal is most effective when it combines sounds with a flashing red light. 5.9.1 Factors Influencing Visual Display Effectiveness Physical Location The positioning of a visual display is of key importance in determining Us effectiveness, The ‘textbook’ example of the “user-interface” may Conjure up an image of an individual setting in front of a computer= ay Work Study and Ergonomics sereen, Under these circumstances, the optimised location of it shoutg not present itself'asa major problem. However, location ofa display that is out of the main field of view or requires head or body movements, illustrates the problem of the wide variety of physical locations that display can have, Information about the way visual acuity drops off ag an object's retinal location moves from the fovea to the periphery ean be based upon the relative importance of the information used to site displ conveyed, the size of the informational content and the time course of the signal. In the present context, the assumption can be made that the physical location of the display is optimised for the purpose for which it is required. If a user has to make frequent references to the current time, the positioning of the clock within his/her normal field of view would be self-evident. For a user who makes infrequent use of the current time a more peripheral location can be used. Display Arrangements The example of clock used above is not an appropriate one when it comes to thinking about the arrangement of multiple displays. In many advanced applications, itis likely that a number of displays will need to be grouped in close proximity to one another. This will be the case with motor car or aircraft instruments, etc. Similarly, items appearing on a computer screen for a set of tasks should all fall into the general field of view of the user. At the same time, they will need to be clearly distinguishable from one another. Examination of some display configurations may lead o the belief that such arrangements are governed largely by random assignments or aesthetics. It is, however, possible to collect hard data on the optimal arrangement of a set of displays (or indeed controls). Items of primary importance should be placed in the central field of view, while those of less importance must be on the periphery. Importance should be decided by an analysis of the tasks or by expert-rating. Lighting Conditions The extent to which the display is usable will depend upon the extent to which there is sufficient light falling on or emitted by the display.Ergonomics u7 in the case of warning lights and computer displays, they have fight sources within themselves, and although adjustments may be made for sprightness’, there should be no problem over viewing them. even in a darkened room. Supplementary lighting may be required for other displays. There is usually background lighting for car instruments, which in tum can be adjusted for brightness, but for many displays, the natural or artificial light within the workspace is what will determine whether they can be viewed or not. As well as providing sufficient light for effective display, light sources can in turn give rise to problems. Variability in lighting from external sources may produce reflections when instruments are covered in glass. Contrast between the display and the external environment are also important. Dashboard instruments remain legible by night and day. Internal lighting must be sufficient to negate the reduction of visual acuity in low light conditions at the same time as preserving adaptation or the ‘night vision’ required to drive in the dark. Bright lights may also cause problems. Static versus Dynamic Displays Another obvious manner in which displays can differ from one another is the extent to which they function purely as a static source. typically in the case of notices, signs, labels and instructions and the extent to which they represent dynamically changing features, typically called parameters. Analogue clocks display dynamic changes though it may be difficult to see the hands moving. Other displays associated with processes and changing states are much more dynamic in nature. Sometimes the changes are discrete as in the changing indication of how many miles/kilometers 4 car has travelled. Sometimes they are continuous in the way that the speedometer needle moves up and down in relation to changing speed. The complexity of a modern aircraft cockpit reflects the number of Parameters that are being simultaneously measured and displayed for the Pilot's attention. An important consideration with these complex displays 's the limit on the number of items that humans can simultaneously Process (cognitive psychologist have traditionally referred to this limit 4S the “attentional-bottleneck’).we 118 Work Study and Ergonomics 5.10 Environmental Risk Factors Heat Stress Heat stress is the total heat load the body must accommodate. It ig generated externally from environment temperature and internally from human metabolism. that can be life threatening or result in irreversible damage. Less serious xeessive heat can cause heat stroke, a condition conditions associated with excessive heat include heat exhaustion, heat cramps and heat-related disorders (e.g., dehydration, electrolyte imbalance, loss of physical/mental work capacity). : Cold Stress Cold stress is the exposure of the body to cold such that there isa lowering of the deep core temperature, Systemic symptoms that a worker can present when exposed to cold include shivering, clouded consciousness, extreme pain, dilated pupils, and ventricular fibrillation. Cold can also reduce hand-grip strength and coordination, As mentioned earlier in the section on Force, bulky clothes and gloves used to protect the worker from cold exposure can increase the muscle effort required to perform tasks. Whole Body Vibration Exposure of the whole body to vibration (usually through the feet/ buttocks when riding in a vehicle) has some support as a risk for injury. Boshuizen found the prevalence of reported back pain to be approximately 10 percent higher in tractor drivers than in workers not exposed to vibration, and the prevalence of back pain increased with vibration dose. Dupuis reported that operators of earth-moving machines with at least 10 years of exposure to the whole body vibration showed lumbar spine morphological changes earlier and more frequently than the non- exposed people. Lighting With industrialisation, the trend regarding lighting has been to provide a higher lighting level. This has proven hazardous within certainErgonomics 0 a s, such as in offices in which problems with glare and eye symptoms have been associated with levels above 1000 lux as suggested by Grandjean. Barreiros and Carnide found differences in val functions over the course of a workday among Video Display Terminal (VDT) operators and money changers who worked in badly lighted environments, The current recommended trend in office lighting is to have low background lighting (from 300 to 700 lux) coupled with non-glare task lighting which can be controlled with a rheostat. This is consistent with Yearout and Konz’s findings of operator preference regarding lighting. Work that requires high visual acuity and contrast sensitivity needs high levels of illumination, Fine and delicate work should be illuminated at 1,000 to 10,000 lux. Noise Noise means unwanted sound. In an industrial setting, it may be continuous or intermittent and present in various ways (bang of a rifle, clatter of a pneumatic wrench and whirl of an electric motor).Exposure to noise can lead to temporary or even permanent deafness, tinnitus, Paracusis, or speech misperception. The louder the noise and greater its duration, the higher is the risk to hearing. Also, noise well below thresholds that cause hearing loss may interfere with the ability of some People to concentrate. Air Quality The next element of the work environment, which has impact on employee Productivity, is air quality. Poor air quality can raise a negative impact ©n employees’ health in the form of respiratory problems, headaches, and fatigue, which in the long period would reduce productivity. The 4ir quality contains four factors and that are: temperature, humidity, Ventilation, and cleanliness. High Temperature Levels Ployee lethargy and tiredness as a result of increased body temperature dec : Tease the possible efficiency.4 120 Work Study and Ergon, orig Low Temperature Levels Low Temperate Levels deerease the efficieney due to cooler body eg and shivering. High Humidity This in itself may not be a direct problem, but it does increase our susceptibility to high temperature levels as evaporation of body sweat is impeded. Low Humidity Levels have intolerable effect on our ability to breathe and swallow without discomfort as our mouths and noses can become dry due to an increased evel of evaporation in the surrounding environment. A comfortable work environment of a building or room in which workers can do their work properly should be clean, have proper range of temperature, enough ventilation, and adequate humidity. Too little humidity level may cause magnetic tapes and disks to stick during processing operations, whereas too much humidity produces condensation on the electronic parts of the equipment and causes short circuiting. Ventilation Ventilation is important to control the dust, fumes, gases, aerosols, climate and thermal comfort factors. Exposure to different types of dust can result in fibrosis of the lung, allergic reactions and asthma attacks. 2 Various vapours, gases and aerosols have the ability to cause respiratory and skin damage. Extreme heat can reduce the concentration of the worket and demotivate him, and may also cause a number of heat-related issues. Extreme heat can also reduce tolerance to chemical and noise exposut® and increase the risk of heart attacks. Afier the temperature level in an office has been set-up proper! Suiting to the favourable level of humidity, the air in the office still i i ich it can inerease the temperature, WP needs to be circulated, otherwis it can in turn may cause discomfort. Air circulation is also essential as |Yr ics 424 gore workers’ from inhaling inadequate air. Moreover, smoking must evel! aera sar re spibited in the office. Some small offices still use electric fans to pr a PA gre that the air is circulated well m make . . . sjecleanfiness is also becoming one of the prime considerations for management. Due to technological advances, many devices developed to clean the air, These devices free the air from the oftiee t have been germs, dusty and dirt. Office Furniture itice furniture comprises desks, chairs, the filing system, shelves, drawers, ete. All these components have a specific role to play in the proper functioning of any office and the productivity improvement of the employees. One of the most important aspect to be considered while buying office furniture is to ensure whether it is Ergonomic or not. Ergonomics of office furniture is important because an employee has to work with them for the entire time that he is in office; if they are uncomfortable and not user-friendly, employees’ working style and performance get hampered considerably, which in turn affect the overall productivity of the organization concerned. Non-ergonomic office furniture can also lead to health problems of employees, which well again have an adverse effect on the productivity. Ergonomic office furniture ensures that each employee gets comfortable with the things around him, like desks, chairs, computer alignment and even environmental factors. If all factors surrounding the employee are ergonomically suitable, he/she will be comfortable tnd remain motivated to give his best. These days’ organisations Consult, and even employ ergonomic experts to advice people on how to Prove their office ergonomics to make it a better wore-palee. Having ene office furniture reduces the chances of any risk injury. They in the el in such a manner that reduce the possibility of any accidents treater Place, Office furniture like desks can be designed e give the computer ay and adequate support to the elbows while bs base Should also be ne positioning of the eomputer monitor and the mot lequate, so that the user does not have to strain his vision >ts Work Study and Ergonomics J stretch himseli/herself uncomfortably to reach them. Proper to view and sation tremendously in increasing its office furniture helps the organi productivity, and at the same time in taking care of its employees* health, Vibration Vibration is the oscillatory motion of various bodies. All bodies with mass elements and elasticity are capable of vibration; hence, most including the human body experience vibration machines and structures to some degree, Two different categories of vibration are distinguished in literature, Free vibration takes place when the system oscillates due to the action of internal forces only. Forced vibration is caused by the action of external forces. If the frequency of excitation coincides with the natural frequency of the system, resonance occurs. The result is large oscillations within the structure of creating potentially harmful or example, the potential effect of resonance is the shattering stress. of a crystal glass, when opera singer sings at the natural frequency of the crystal. Energy dissipation leads to friction and other resistances, damping occurs in all structures. The Effects of Vibration on Human Body Vibrations affect human body in many different ways. The response to a vibration exposure is primarily dependent on the frequency, amplitude, and duration of exposure. Other factors may include the direction of vibration input, location and mass of different body segments, level of fatigue and the presence of external support. The human response to n be both mechanical and psychological. Mechanical damage y are caused by resonance within vibration ca to human tissues can also occur as the: ess reactions also occur from arily frequently related. From point of view of exposure, the low frequency range of vibration is the most interesting. Exposure to vertical vibrations in the 5-10 Hz range various organ systems. Psychological st vibrations; however, they are not ne gene Hz in the head-nee! ly causes resonance in the thoracic-abdominal system, at 20-30 houlder system, and at 60-90 Hz in the eyeball. When vibrations are attenuated in the body, its energy is absorbed by the tissues and organs. The muscles are also important in this respect-Ergonomics 123 Vibration leads to both voluntary and involuntary contractions of muscles. and can cause local muscle fatigue, particularly when the vibration is at the resonant-frequency level. Furthermore. it may cause reflex contractions, which will reduce motor performance capabilities. The amount of mechanical energy transmitted due to vibrations depends on the body position and muscle contractions. In a standing subject, the first resonance occurs at the hip. shoulder, and head at about SHz. With sitting subjects, resonance occurs at the shoulders and to some degree at the head at 5 Hz. Furthermore, a significant resonance oceans from shoulder to head occurs at about 30 Hz. Based on psychological studies, observations indicate that the general state of consciousness is influenced by vibrations. Low frequency vibrations 1-2 Hz with moderate intensities induce sleep. Unspecific psychological stress reactions have also been noted (Guignard & Von Gierke), as well as degraded visual and motor effects on functional performance. Some symptoms of vibration exposure at low frequencies are given in Table |, along with the frequency ranges at which the symptoms are most predominant. Table 5.2 Symptoms caused by Whole-Body Vibration and the Frequency Range at which They Usually Occur (Adapted from Rasmussen, 1982). ‘Symptoms Frequency (Hz) | General feeling of discomfort a | Head symptoms eae | Lower Jaw symptoms ss | Inffuence on speech eed “Lump in throat” 2:16 Chest Pain Bal Abdominal pain ci) Fregment Urge to urinate uae Increased muscle tone {Influence on breathing movements Muscle contractions =