Ergonomics is defined in wikipedia.org as the study of "designing equipment and devices that fit the human body, its movements, and its cognitive abilities." Research in this field is largely focused on increasing productivity and enhancing occupational health and safety in the workplace.
In the global context, all industries and operations have become very competitive. One of the key words is productivity. There is much emphasis placed in improving productivity. In this context Human Factors or Ergonomics will play a pivotal role. Application of this science assists to ensure the working situations to be in harmony with the activities of the worker.
Prior to the 1980s, ergonomics was hardly known in Sri Lanka. The rapid development process seen in Sri Lanka in early 1980s has been hampered by the political and ethnic unrest. It is widely known that the science of Ergonomics (human factors sciences) contribute immensely to the technology development and can boost the industrialization process in Industrially Developing Countries (IDCs).
Two Swedish experts [including myself] visited Sri Lanka in 1996 to spread the awareness to ergonomics. They carried out ergonomic surveys which revealed that significant mismatches existed between the workers and their work tools as well as work systems. These deficiencies affected adversely the productivity and worker comfort. Deficiencies in occupational health and safety and enormous waste in production are other significant negative factors observed by the experts.
What is Ergonomics?
To explain this multi-disciplinary science, it is best to cite some simple examples under each discipline. To carry out any type of work by a human being in an optimum, safe, profitable and efficient way there are some obvious needs to be satisfied. For example, the environment, the work tools and the job itself must all fit the characteristics of the worker.
Heat is a form of energy. The main sources of heat are environmental heat and body heat. The major source of environmental heat is solar heat. Heat can cause thermal discomfort or thermal stress. There is a misconception among people that the thermal environment depends only on temperature. The factors such as air humidity, air movement, radiant temperature, type of clothing worn and activity performed can all influence the feeling of thermal environment on man.
In a crowded passenger van with the shutters up during rain the passengers started to sweat and it became quite warm. Why? Not due to high temperature but due to factors such as radiant heat given out by the humans (crowded passengers) and the lack of air movement and ventilation.
When building a large concrete walled rectangular factory it is best to face the short walls to the East and West and the long walls facing the North and South. Why? If the long walls face the East and the West, the radiant heat from the sun is absorbed by the large area of the walls which will adversely affect the indoor climate. The inmates will be affected by the radiant heat. This is a common mistake happening in Sri Lanka because of the ignorance of some architects about building orientation and the thermal climate.I walked into an upcountry star-class hotel and experienced thermal discomfort in the restaurant.
The management was clueless why the occupants of the restaurant felt uncomfortable as on one side along the wall there was a row of open large windows. Unfortunately, however, on the opposite wall there was no opening for the air to escape. In other words, there was no cross ventilation. This is another mistake made in many factories, workplaces and houses in Sri Lanka. The lack of adequate cross ventilation which blocks the air coming into the room causes thermal discomfort to inmates.
Light is a form of energy. The two common sources of lighting are natural lighting from the sun and artificial lighting from electrical energy. Lighting is not only illumination (light falling onto a surface). Factors such as luminance (amount of light reflected or emitted from a surface), reflectances (rate of luminance and illuminance at a surface based on material characteristics), glare (imbalance of surface luminances and categorized as disability glare, discomfort glare and reflected glare), contrast (based on luminances of two surfaces, bright and dark colours) and flicker (malfunction of lamps which can cause visual fatigue), are other characteristics of lighting. The above factors influence the vision and lighting in a workplace.
A night driver facing the headlights of an approaching car will be affected by disability glare and his vision will be severely affected.
Visitors to a Managing Director’s room complained that a black curtain that was hung inside the room was causing them stress and a negative feeling. The black curtain was later removed and replaced by a blue curtain which made a remarkable difference in the attitude of the staff.
Noise can be described as unpleasant sound. Sound has a pitch or frequency and loudness or amplitude. Loudness or sound pressure level is measured by a dB or log scale which means that if two machines of sound pressure level 80 dB each are situated close to each other, the total sound pressure level is not 160 dB but 86 dB. The dB linear scale is the actual sound intensity and the dB(A) scale approximates the sensitivity of the human ear. Exposure to noise levels of 85 dB(A) or over for long periods can cause hearing deficiencies. The frequency of the noise expressed in hertz or cycles per second is important to know when measuring deafness in man. The danger of hearing deafness caused by industrial noise is that it is permanent or incurable.
A music teacher who was exposed to high noises of the school band for several years developed signs of deafness at 4 kilohertz. The deafness later spread to other low and high frequencies which made the teacher significantly deaf for life.
In a spinning mill where the noise level was around 90 dB(A) hearing tests were carried out on a routine basis. It was detected that two workers out of the team of 10 workers after an exposure to the noise for 5 years developed deafness to noises of 4 kilohertz frequency. This is the first stage of deafness which can soon spread to other frequencies.
Human Factors (Anatomical and Physiological)
The machines, work tools and work stations used by man have to fit the body sizes of the user. Body sizes differ between inter individual (different populations or nations) and intra individual (within the same population or nation). In other words an article or machine made to fit people in one population or nation may not fit another population or nation. There are also differences in body proportions between different populations.
During a routine factory inspection I walked into a factory with about 100 knitting machines handled by female labour. I observed that the girls had to raise their upper limbs to operate the machines. In other words the operating levels were higher than the elbow level (which is the comfortable level) of the workers. Naturally the female workers complained of shoulder and upper limb pain. When questioned from the management I was told that the machines were imported and installed on the factory floor without any changes. On further investigation it came to light that the people in the producing country of the machines were taller than Sri Lankans. If, the management knew that operating levels of machines were taller than the elbow level of the female operators, the machines could have been installed sunk in the floor. Unfortunately the management was not aware about the average elbow level of the Sri Lankan female labour.
In Sri Lanka, domestic pantry cupboards, dinner tables, kitchen counters and in general most tables and chairs in offices, work and public places are taller than the average Sri Lankan body sizes. It is presumed that furniture in Sri Lanka has been designed to fit Europeans as the British ruled this country prior to 1948. The ignorance of the furniture manufacturers to make furniture to fit short people (Sri Lankans) is causing much discomfort among the users of tables and chairs in homes, schools, hospitals, offices, factories and public places.
Inappropriately designed chairs used in Sri Lankan factories, offices, homes and public places is causing considerable discomfort and unproductive to the users. There are many ergonomic design features to be satisfied in chairs. The height of the seat surface should be the inner leg height, the back rest should support the low back (not so much the upper back), the seat surface dimensions should accommodate the buttock width and upper leg length of the user, the seat surface should be slightly inclined inwards so that the sitter will not slip out, the back rest should be slightly inclined out to relax the back, etc.
A marketing executive had many customers visiting him in his office. Some visitors were important while others were unproductive but spent much time talking and wasted the precious time of the executive. He kept two similar looking chairs in front of his table. One chair was correctly designed with the chair surface slightly inclined inwards and back support slightly inclined outwards. The productive and important customers were casually directed to this good chair. The other chair was incorrectly designed with the sitting surface with a slight slope downwards and the back rest slightly inclined inwards which made the sitter very uncomfortable after sitting for a while. The unproductive customers were casually directed to the second chair. The design features of the two chairs were not clearly evident to the visitors. However the marketing executive was successful in retaining the good customers and discouraging the bad customers.
The main aim of body mechanics is to study the way the body produces force and generate movements. The common health problems which must be avoided are muscle strain, joint problems, back problems and fatigue. It is important to avoid body postural stress when there is a mechanical loading. The spine and the pelvic support the weight of the body parts above them. The spine consists of four major regions: viz. Cervical spine (above the neck), Thoracic spine (rib box area), Lumbar spine (between rib box and hip bone) and Sacrum (below hip bone). The spinal column is double S shaped. The cervical and lumbar spines are protruded to the front and known as lordosis. The loss of lordosis in the cervical and lumbar regions can occur when bending forwards the neck and the trunk respectively and while adopting a sitting posture. This causes pressure in the cervical and lumbar spines resulting in temporary pain at the start and later permanent pain long term. Sitting long periods every day and working with the body bent posture when lifting a weight or manual handling or standing long periods can all cause fatigue and back problems.
During the early 1970s wearing miniskirts was popular among teenage girls in London. A survey was carried out on back pain or back problems among the teenage girls. The results indicated that back pain was not a problem among teenage girls. In the late 1970s the fashion changed and the style was to wear slacks among teenage girls. The back pain survey was repeated and it was found that a significant number of girls complained of backaches. When picking something from the floor or lifting a weight the girls adopted the easy bent posture when wearing slacks. But for reasons of modesty the girls wearing miniskirts bent their legs and kept their trunks straight when lifting something from the floor or lifting a weight from the floor level.
Some precautions should be taken when lifting or carrying weights to prevent any damage to the spine. For example heavy weights should not be manually lifted or carried. A weight should be lifted with the trunk straight, bent knees and keeping the weight as close as possible to the body.I was invited to visit a wall tile factory in Sri Lanka to make a presentation about ergonomics to the senior executives. A quick walk through and survey of the workplace was carried out prior to the talk. It was observed during the survey that a team of 10 workers inspected for flaws and cracks in the wall tiles sent along a conveyor belt. The workers stood along the belt which was situated higher than the elbow level of the workers. The workers rejected with their hands the tiles that were defective. Observing the fatigue felt by the workers as they worked standing throughout the day in an uncomfortable posture with their operating level being uncomfortable as they worked raising their elbows, I casually informed the management as follows: Provide 10 tall chairs to the workers to bring their operating level to that of the elbow level and provide foot-rests in the tall chairs. Three months later I received a telephone call from the management that although my advice was given casually, the management provided the workers with the tall chairs and foot-rests. The manager said that the productivity of the workers increased significantly and when calculated for one year the cost benefit was sizable. The workers complaints were also significantly reduced too by this change. A simple and a cheap change giving a big profit to the company.
Work Physiology and Muscular Work
In spite of the advances in technology and the automated industry there still remains much physical activity and manual tasks that are performed in workplaces. Physiology is the study of how the body and its parts function. Therefore knowledge of work physiology helps in the optimum design of manual work and to control negative physiological implications experienced at work.
Muscle: Human movement is brought about by the muscular system which is distributed throughout the body. Longer the muscle the more work can it perform. The contractual forces of muscle fibres together give strength to the whole muscle. Muscle strength depends on many factors such as (a) Posture (b) Sex, - at same age female’s muscle strength is lower than male (c) Age - greatest at late 20s and early 30s (d) Body Size - proportional to the transverse sectional area of muscle. Any muscular activity requires energy.
Energy Production: Energy is required for various kinds of biological work. The food taken by man contains energy in the form of chemical energy. The food mixes with oxygen breathed in through the lungs and the chemical energy is converted to work energy, heat and waste products. The above process is known as metabolism. Producing work energy depends on the amount of oxygen uptake and therefore the heart rate is directly proportional to the work energy. Energy consumption is depended on the food as well as oxygen uptake and therefore it has its capacities and limitations. The capacities can be developed through various kinds of physical exercises and to control limitations rest pauses are needed to recover. An individual’s highest capacity to work is his maximum oxygen uptake.
A man was digging the garden and excavating a pit. He was working at a higher capacity almost close to his maximum oxygen uptake. After about 20 minutes he felt extremely tired and exhausted and he rested for nearly half an hour before he could start to work again. Later he did some lighter work e.g. weeding. He could work for nearly one hour without feeling very tired. Again he rested but after just five minutes he recovered sufficiently enough to start work again.
The WORK-REST regime has to be so designed according to the severity of the work and the capacity to do physical work of the individual. Similar physiological principles apply when an individual is engaged in muscular work.
A steady supply of oxygen is needed to do muscular work. A waste product e.g. Carbon Dioxide formed during metabolism is carried by the red blood cells and excreted via lungs. In the absence of oxygen a waste product called lactic acid remains in the muscle which causes muscular pain.
A man was asked to hold a weight of one kg on his palm with the hand outstretched for five minutes. Another man was asked to turn a wheel holding the handle on the wheel. Both jobs had similar energy expenditure. The first man holding the weight complained of a pain in the arm after three minutes and it became unbearable after five minutes. But the man turning the wheel continued to turn the wheel without any complaint. The first man was actually doing static work without any movement and the blood vessels to the muscles were compressed and blocked. In other words the supply of oxygen to the muscles was blocked and could not wash away the waste products causing accumulation of lactic acid which caused the pain. The second man turning the wheel did dynamic work. There was a steady supply of oxygen to the muscles which washed away the waste products. Hence he could continue the work without any pain or fatigue.
Human Factors (Psychological Aspects of Work)
There is wider implications and influence to design from psychological characteristics of man. Some important psychological characteristics are: the capacity and limitations of perception and processing of information, decision making, the mental work load and overload, performance of vigilant tasks, boredom and psychological aspects of control and display design. Modern work is carried out more by machines than by man, more automotive than manual, use more artificial intelligence than man’s intelligence, more sedentary than moving.
Information Processing: Information enters through the senses as a result of physical stimulus impinging on the sense organs. Perception is the identification of the stimulus and influenced by individual factors such as personality, mood, expectation, level of training and its retention. Perception is achieved by the use of memory. With the use of long term memory, working memory, attention, decision and response selection are made. The response execution (in the form of physical activity) in the information processing model will result in a feedback.
What must be avoided in the information processing model are perceptual load (too much of information), mental load (stressful decision making) and physical load (heavy physical activity).
The other important aspects in psychology are:
- The concept of vigilance (human observers state of alertness to tasks demanding efficient detection and processing of signals)
- Design of Displays and Controls
An electrically operated elevator was used to raise and lower goods from the upper floor of the raw material store. The controller of the elevator had three switches one for raising, one for lowering and the other one for stopping the elevator. The three switches were placed horizontally on the control box (showing the up down positions by means of small arrows). Workers sometimes got confused in selecting the correct button. New workers often use the incorrect button.
Solution: The up and down switches were proposed to orient vertically. The result was that the workers easily and naturally selected the correct button.
Ergonomic considerations are supreme in the design process. To design to fit the user, which is the concept of ergonomics, the design should be user centered. The design has to be based on physical and mental characteristics of the human user, which in other words the final design, and which should have the best possible match with the human use. The ergonomic demands in any design have the following purposes.
- Efficient performance of the job
- Not suffer work-related injuries
- Increase speed of performance
- Achieve higher customer satisfaction
All workstations, environments, machines, products, hand tools, furniture, etc used by man have to be ergonomically designed.
Several years ago in the US a passenger plane crashed on a mountain and all passengers died. Subsequent investigation along with the information taken from the black box revealed that the pilot judged that the altitude at which the plane was flying was 10,000 feet whereas the actual altitude was 1000 feet. The altimeter in the cockpit of the plane was installed at the knee level of the pilot. The inappropriate viewing angle and the distance of the altimeter from the pilot’s eye obviously caused the error made in the pilot’s judgement of the altitude.
Note: Important dials such as the altimeter of an aero plane have to be installed at a point which is easy for the pilot to read e.g. at the eye level, and at the shortest clear viewing distance from the eye. After this air accident the design of the cockpit has been changed to avoid such obvious errors in design.
Prolonged working with bent wrist can lead to serious medical problems, thus Ergonomics aspects should thoroughly be considered during hand tool design. As ergonomics promotes natural postures, maximum efforts should be taken to design the handle such a way that the wrist will remain at its natural posture during usage of the hand tool.
Safety and Ergonomics
Occupational accidents are said to be one of the most public health problems today. The traditional approach adopted in accident prevention is to identify the cause and effect “after” an accident or a near miss and to train individuals on safety procedures based on “after event” information. In spite of the legal enforcements on prevention of occupational accidents and the methods used in industry based on accident research, there still occur industrial catastrophes where thousands have died in one accident. Therefore an integrated or ergonomic approach has been adopted based on human limitations when designing equipment and procedures with the objective of reducing human error. Many accidents occur due to errors in design or training.
Blame and punishment have not had a significant effect on reduction of accidents. Good housekeeping which provides a positive feedback is a new strategy to control accidents. Good housekeeping is order and tidiness and a cheap and a sure method to reduce accidents.
A shipyard in Finland once had a long history of industrial accidents. A long term study using the method of good housekeeping reduced accidents by nearly 70%. A very optimistic estimate was 25%.
Tsunami in Sri Lanka
In 2004 the eastern coastal belt of Sri Lanka was devastated by the sea water caused by a severe earthquake in the Indian Ocean near Sumatra. This catastrophe which got the name Tsunami came as a shock as Sri Lanka has never experienced such a severe tsunami before. This is a clear example of a tragedy occurring without warning and no precautions have been taken to soften its effect and control the damages. After the event Sri Lanka has now taken preventive measures like giving warning signals and precautionary measures in constructing buildings near the sea. Ergonomic measures were introduced after the event.
The above examples discussed under different disciplines in Ergonomics are simple and cheap to implement. The examples are easy to understand and provide the basic knowledge in ergonomics for beginners. There are also sophisticated and expensive application methods in ergonomics. However significant cost benefits can be obtained from many Ergonomic applications including technology transfer problems. Ergonomic principles can be used to prevent or control many chronic issues and industrial disputes at workplaces. Designing to fit the human characteristics of the users of workstations and products, considering the limitations and capacities of users, contribute immensely in increasing productivity and safety at work. All Ergonomic solutions must however be cost beneficial.
(An international consultant in the field of Ergonomics, Professor Abeysekera formerly worked for the Sri Lankan government specialising in Occupation Health and Safety issues before emigrating to Sweden in 1984. He is currently an Ergonomic Consultant for Work Science Academy of Sweden, and, since September 2011, has been affiliated to the Work Science Academy, Sri Lanka Branch, where he consults on Ergonomics issues in industry and academia. He can be reached via 011 2232492 or firstname.lastname@example.org).