After reading these notes you will learn about:- 1. Meaning of Ergonomics 2. Objectives of Ergonomics 3. Ergonomics and Health 4. Manual Handling 5. Industrial Hygiene 6. Guide to Work Area Planning 7. Ergonomic Principles in the Design of Work Systems.
Meaning of Ergonomics:
Ergonomics is the science which deals with the relationship between man and his working environments. It takes care of factors governing the physical and mental strains. Ergonomics consists of words ‘Ergo’ (which means work), and ‘Nomos’ (which means ‘Natural Laws’). This 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 environment so as to obtain maximum satisfaction for the worker which, at the same time, enhances productivity”.
Thus ergonomics is a multi-disciplinary science comprising subjects like anatomy, psychology, physiology, sociology, engineering, anthropology, physics, and medicine.
The task of ergonomics is to develop such conditions for workers, which are necessary to reduce physical workload, to improve working postures, facilitate instrument handling, and thus improves the quality of working life, reduce fatigue, maximise efficiency of production operators and to minimise human errors.
Ergonomics helps to study the effect of working environment on health and safety and in turn on productivity. The workers’ interest in the job to a greater extent depends on how comfortable and safe is the workplace.
Objectives of Ergonomics:
Objective of the study of ergonomics is:
1. To optimise the integration of man and machine in order to increase productivity with accuracy.
It involves in the design of:
(a) A work place suitable for the worker,
(b) Machinery and controls, so as to minimise mental and physical strain on the worker to enable the improvement in efficiency,
(c) A, favourable environment for performing the task most effectively,
(d) Task and work organisation,
2. To take care of the factors governing the physical and mental strain (i.e. fatigue) so as to get maximum satisfaction for the worker which at the same time enhances the productivity.
3. Attempts to minimize the risk of injury, illness, accidents and errors without compromising productivity.
4. To improve the design of machine at the initial design stage or later whenever the existing product or process is modified.
Thus ergonomics helps in:
(a) Developing most comfortable conditions related to climate, lighting, ventilation and noise level;
(b) Reducing the physical work load;
(c) Improving working postures and reducing efforts of certain movements;
(d) Making the handling of machine levers and controls easy;
(e) Increasing safety.
Design of Workplace:
Backaches, necaches, and other muscular strains due to bad seating and incorrect working posture are common in industry, where most of the jobs are performed by the operators either in sitting or standing in a fixed posture for a long duration.
The interaction of the operator with the immediate workspace around him is influenced by many factors such as seat design, the working desk and adjacent machine. These factors are responsible for the position and postures of the users and, hence their efficiency.
(a) location of Tools and Materials:
All tools and materials required must be located within the normal grasp area and as far as possible in front of the worker. This will enable him to travel lesser distances to pick up and put these tools and materials frequently at desired place so as to save time and energy.
For the assembly work, it is advisable to provide such arrangement so that the components can slide along the smooth surface and the worker picks them up. It will greatly reduce the time and effort.
(b) Proper Chairs:
Chairs permitting proper posture for the workers must be provided. This is possible when the worker is working on the work bench (e.g. assembly, fitting and inspection etc.). Performing a job on floor in sitting position or on table in standing position requires more energy.
The height of chair and the work bench must be arranged in such a way so that the worker may not feel any difficulty while working. Their height must be such that the top of bench remains at the height of the elbow of the worker. If possible the height of the bench must be such that worker can work both in sitting and standing positions. Chairs must be provided with foot rests.
(c) Working desk:
All the tools and materials must be located within the normal grasp area and as close in front of the operator as possible. Experiment have shown that a semi-circular table having a radius of 20″ or 50 cm from a point at 4″ or 10 cm back (4″ or 10 cm gives approximately centre line of the operator shoulders and elbow) as shown in Fig. 53.1., allows a most comfortable position.
Working desk must be so designed so that use of both hands can be taken simultaneously.
In the end, “work place layout” helps the analyst in determining the required body and eye motions of operators, safety measures and operational difficulties that may occur at working place.
The posture that a workman needs to adopt to perform the task is an important consideration in the design of workplace. Incorrect posture can cause strain in back, waist, legs and hands. Ergonomic design of the seats include type of seat, seat height, back support, arm support, foot rests etc.
Factors Considered in the Work Place Design:
1. Purpose of operation.
2. Product design-value analysis.
3. Materials related factors, like.
i. space required, quantity of items, size, etc. for raw, finished and scrap materials.
ii. rate of production.
iii. inspection requirement.
4. Equipment related factors, like
ii. Utility, service requirements.
iii. Auxiliary equipment.
iv. Number of machines, and space required.
v. Nature of process.
vi. Noise, pollution, vibration, safety hazards etc.
5. Material handling methods.
6. Space related factors; like
ii. Ceiling height required.
iii. Space utilisation.
7. Operated related factors:
i. Sitting or standing.
ii. Level of comfort.
iii. Movement required.
iv. Number of operators.
v. Supervision requirement.
8. Working Conditions:
i. Noise, lighting, heating and Ventilation.
ii. Dust, Vibration, window location.
9. Method related factors:
i. Direction of flow.
ii. Floor levels.
iii. location of items.
iv. Material movement.
v. Safety requirement.
vi. Operation sequence.
vii. Tools and material locations.
viii. Production rate.
ix. Auxiliary services.
Design of Machinery and Controls:
Most machines today are reasonably well designed for optimum performance, but the capacity of the worker assigned to the machine is generally different. This may result in a job taking longer to complete and the risk of errors increases.
To prevent this, user and machinery must be looked as a combined unit. Thus the ergonomics must be involved in fitting the tool and the machine to the worker by designing it accordingly.
When a worker operates or uses a machine, instrument or tool, it is essential that man- machine must be considered as a single working unit from the design points of view, as explained above.
Machine must be so designed so that worker can use both hands and foot simultaneously for operating it and all the levers, pedals, instruments, hand wheels, knobs and buttons must be located within the normal grasp at a suitable height and in front of the operator. Foot pedals must be provided with suitably returning springs. Care must be taken to avoid eye, muscular and mental strain.
Fatigue may further be reduced if proper use of jigs or fixtures, stops or guides is taken.
The size of the driver’s cab and the placement of gearshift and brake pedals etc. are generally designed to suit common man, resulting transportation operator, if he is a taller or shorter than average, readily succumb to fatigue, through straining to reach the brakes, gears, and other controls. Therefore, modifications to suit the size of the users will result in significant improvement in health and also reduction in accident rates. Generally adjustable chairs Eire therefore provided.
Design and layout of display panels and instrument should be such, so that it enable accurate observations. Design and location of various manual controls, knobs, levers, wheels etc. should not cause excessive physical and mental strain to the worker. All controls should move in one direction for one kind of action e.g. acceleration or retardation, energise or de-energise.
Work Environment Design:
Physical and psycho-social aspects of the work environment are crucial factors which affect comfort of worker and his performance. The physical factors at the workplace include lighting, ventilation, noise and temperature.
Psychosocial aspects are concerned with motivational work environment, these includes working hours, rest pauses, shift systems, health and safety along-with other factors.
Task and Work Organisation Design:
(A) Task Design:
Task design is based on the nature of job and the design of equipment, machinery and tools in accordance with the ergonomic concepts. This ensures that jobs are within the physical and mental capacities of workers.
Efforts be made to include the job with a mixture of repetitive and non-repetitive work during which recovery from the effects of the former is possible. The task should be designed in such a way that muscles are not required to be used repetitively in a forceful manner.
(B) Work Organization:
Measures such as reducing work rate in paced operations, reducing shift lengths, and provisions for extra rest breaks have proved of greater help. Lifting of heavy objects presents a high risk of overexertion, injuries and cumulative damage to soft tissues around the spine.
Ergonomics and Health:
Ergonomics is helpful in both the prevention of occupational diseases and promotion of health. Studies have suggested that many of the occupational diseases are connected to poor design of tools, machines, work place and work environment.
To prevent cumulative/repetitive strain injuries, variety of health problems including visual fatigue, ergonomics play an important role to increase work efficiency and productivity.
Poor workplace layout and design are major factors contributing to workplace injuries as well as increasing the risk of sprain and strain injuries and occupational overuse injuries. It also make it difficult to deal with emergency situations.
If poor workplace design means you have to work near noisy equipment or in areas where you may be exposed to hazardous substances, this can increase the risk of hearing loss and of chemical related health problems.
Factors which need to be considered when assessing Workplace design and layout are:
(i) Are desks, benches and chairs suitable for the people using them and for the tasks they are performing? Poorly designed chairs which cannot be adjusted for height and to support your lower back can cause back pain. Desks which are not ergonomically designed to acomodate a range of heights can also cause discomfort and increase the risk of injuries.
(ii) Are passages and exits kept clear at all times? Accidents can be caused by poor housekeeping.
(iii) Is equipment with dangerous moving parts properly guarded?
(iv) Are items which are manually, lifted and carried are stored and worked on at a suitable height? Well-designed storage areas and work areas can significantly reduce the amount of bending, twisting and lifting that you need to do to carry out your tasks.
(v) Chemicals should be stored safely in areas located near suitable safety equipment. These should be in areas where there is adequate ventilation.
Manual handling means a range of activities including lifting, lowering, pushing, pulling, carrying, moving, holding or restraining an object. It also covers activities which require the use of force or effort such as pulling a lever or operating power tools.
It has been estimated that about a third of all work injuries occur during manual handling and most or them cause back injury. A risk situation arise when tasks are poorly designed or where handling involves awkward or constrained postures.
Following are the some examples of actions that may cause manual handling injuries:
(i) Work involving sudden, jerky or hard to control movements or which causes discomfort and pain.
(ii) Work involving too much bending, reaching or twisting.
(iii) Work where a long time is spent holding the same posture or position.
(iv) Work that is fast and repetitious.
(v) Heavy weights to be lifted and carried manually.
(vi) Work where force is needed to carry out a task.
(vii) The loads to be handled below your mid-thigh or above your shoulder.
Some of the solutions to deal with such problems are:
Redesign the task or work area to make it safer, by:
i. Modifying the object (shape, size or weight);
ii. Modifying the work area or work station layout;
iii. Eliminating unnecessary handling;
iv. Ensuring that all heavy objects are at waist level where they can be handled comfortably.
v. Reducing the amount of bending, lifting, twisting, reaching and holding required to carry out a task.
vi. Modifying the task by using tools such as levers, hooks hoists, trolleys or by team lifting.
vii. Providing the training and information about safe working practices.
In order to neutralise the effect of wrong postures for long periods during working, it is advisable to perform stretching exercises for neck, back, shoulders, upper body, full body etc. While stretching care should be taken that, move slowly and hold stretches for 5-10 seconds. Right type of exercise(s) can be selected and practiced under the guidance of experts.
Some Practical Solutions:
In order to reduce chances of “Overuse Injuries” some of the following solutions are suggested:
(i) Reorganise the work so that you can mix repetitive and non-repetitive activities.
(ii) Frequent short breaks should be introduced, if the job assigned to the worker cannot be varied or rotated. In such a case simple and gentle exercises performed at the workstation can reduce muscle tension.
(iii) Economically designed furniture is available which can be adjusted to suit employees of different sizes.
(iv) The work area may be rearranged so that materials, equipment, tools and controls can be easily reached without stretching or twisting.
(v) Hand tools for repetitive tasks should be of comfortable size, shape and weight, well- balanced with a comfortable grip and do not need more than reasonable force to operate.
Industrial hygiene is the science of anticipating, recognising, evaluating and controlling workplace conditions that may cause workers’ injury or illness. In short, we can say that industrial hygiene is the science of dealing with job hazards.
Industrial hygienists use environmental monitoring and analytical methods to detect the extent of worker exposure and employ engineering work practice controls, and other methods to control potential health hazards.
Industrial hygienists analyse, identify, and measure workplace hazards or stressors that can cause sickness, impaired health, or significant discomfort in workers through chemical, physical, ergonomic, or biological exposures.
Industrial hygienist determine about the jobs and workstations which are the sources of the potential problems by using the worksite analysis. During the worksite analysis he measures and identifies exposures, problem tasks and risks.
The industrial hygienist inspects, researches, or analyses as to how the particular chemicals or physical hazards at that worksite effect worker’s health. If a situation is found to be hazardous to health, industrial hygienist recommends the appropriate corrective actions.
Industrial hygienist in addition to engineering controls, recognises work practice controls which are the primary means of reducing employee exposure to occupational hazards.
Work practice controls include:
(i) Following proper procedures that minimise exposures while operating production and control equipment;
(ii) Inspecting and maintaining process and control equipment on a regular basis;
(iii) Implementing good house-keeping procedures;
(iv) Providing good supervision;
(v) Mandating that smoking and drinking in regulated areas be prohibited
Major Job Risks (Hazards):
1. Air Contamination:
The most common particulate contaminants include dusts, fumes, mists, aerosols, and fibres. These are commonly classified as either particulate or gas or vapour contaminants.
2. Chemical Hazards:
Harmful chemical compounds are in the form of solids, liquids, gases, mists, dusts, fumes, and vapours, and exert toxic effects by inhalation, absorption (through direct contact with the skin), or ingestion (eating or drinking).
3. Biological Hazards:
These include bacteria, viruses, fungi and other living organisms that can cause acute and chronic infections by entering the body either directly or through breaks in the skin.
4. Physical Hazards:
These include noise, vibration, illumination, temperature and excessive levels of radiation.
5. Ergonomic Hazards:
These include excessive vibration, noise, eye strain, repetitive motions, repetitive shocks over prolonged period of time, heavy lifting problems, and improperly designed tools or work areas. Ergonomic hazards are avoided primarily by the effective design of a job or jobsite and better designed tools or equipment.
By adopting thorough worksite analyses, employers can set up procedures to correct or control ergonomic hazards, teaching correct work practices, employing proper administrative controls (e.g. shifting workers among several different tasks, and increasing rest breaks,) and providing and mandating personal protective equipment.
Evaluating working conditions from an ergonomics standpoint involves looking at the total physiological and psychological demands of the job. Benefits of a well-designed ergonomic work environment include increased efficiency, fewer accidents, lower operating costs, and more effective use of personnel.
1. Plan for tools, gauges and materials.
2. Use gravity, where possible.
3. Plan the position for each tool, and gauge.
4. Plan for delivery of material directly at the point of use.
5. Plan for prompt removal of materials from work place.
6. Provide adequate provision for planned scrap removal.
7. Plan for proper height relationship between material supply, use, and disposal.
8. Eliminate intermediate handling.
9. Place material on pallets etc. and move it along with them.
10. Use the same container throughout the system to avoid frequent changes.
11. Plan each work place in proper relationship with adjacent operations/work places.
12. Use proper containers to prevent damage of materials.
13. Plan for minimum walking.
14. Plan for judicial manual, gravity, and equipment handling.
Ergonomic Principles in the Design of Work Systems:
The work system comprises a combination of people and work equipment acting together in the work process to perform the work task at the workplace in the work environment under the conditions imposed by the work task.
Various ergonomic principles which should be considered during design of various work systems are given here-under:
1. Design of Workspace and Work Equipment in Relation to Body Dimensions:
(a) Working height should be adopted to the body dimensions of the operator and to the kind of work performed.
(b) Seat and working desk should be designed as a unit to achieve the preferred body posture.
(c) Sufficient space should be provided for body movements.
(d) Controls should be within functional reach
(e) Grips and handles should suit the structure of the hand
2. Design in Relation to the Body Posture:
(а) Design of work should be such that it avoid unnecessary or excessive strain in muscles, joints and respiratory and circulatory systems.
(b) The operator should be able to alternate between sitting and standing.
(c) If high muscle is to be exerted, the chain of force through the body should be kept short and simple by allowing suitable body posture and providing appropriate body support.
(d) Body postures should not cause work fatigue from prolonged static muscular tension.
3. Design in Relation to the Muscular Strength:
(a) Strength requirements should be within physiological desirable limits.
(b) Maintenance of prolonged static tension in the same muscle should be avoided.
4. Design in Relation to Body Movement:
(a) Body movements should be in harmony with each other.
(b) A good balance should be established among body movement. Motion should be preferred to prolonged immobility.
(c) Movements with great accuracy requirements should not entail exertion of considerable muscular strength.
(d) Execution and sequencing of movements should be facilitated by guiding devices.
5. Design of Signals, Displays and Controls:
(a) Signals and displays should be selected, designed and laid out in a manner compatible with the characteristics of human perception.
(b) Controls shall be selected, designed and laid out in such a way as to be compatible with the movement of that part of the body by which they are operated.
(c) Control movement, equipment response and display information should be mutually compatible.
(d) Where controls are numerous they should be laid out so as to ensure safe, unambiguous and quick operation.
(e) Critical control should be safeguarded against inadvertent operations.
6. Design of the Work Environment:
(a) The work environment should be designed and maintained so that physical, chemical, biological conditions have no adverse effect on people, but serve to ensure their health, as well as their capacity and readiness to work.
Work environment should include adequate work space, air renewable, emission of pollutants, appliances consuming oxygen, thermal conditions, air temperature, air humidity, air velocity, thermal radiation, intensity of physical work involved, illumination, absence of glare and undesirable reflections, noise, distribution of working hours, vibrations, exposure to dangerous materials.
7. Design of the Work Process:
(a) The design of the work process should safe guard workers’ health and safety, promote their well-being, and facilitate task performance, in particular by avoiding overloading and under loading. Overloading produce fatigue, while under loading results in monotony which diminishes vigilance.
(b) The physical and psychological stresses exerted depend not only on factors considered above but also on the content and repetitiveness of operations and on the workers control over the work process.
(c) While designing the work process, particular attention should be paid to the following:
(i) Variations in vigilance and work capacity over day and night,
(ii) Differences in work capacity among operators, and changes with the age.
(iii) Individual development.