Industrial Engineering Knowledge Center: Ergonomics in Human Effort Industrial Engineering

Tuesday, May 24, 2022

Ergonomics in Human Effort Industrial Engineering - Introduction

Chapter 2. OVERVIEW OF ERGONOMICS (Abridged)

OHTA STUDENT MANUAL

Ergonomics Essentials

April 2009

This manual was originally developed by BP and University of Wollongong. The Occupational Hygiene Training Association Ltd would like to acknowledge the contribution of these organisations in funding and developing the material and is grateful for their permission to use and modify it.

Supported by OHTA, IOHA

This work is licensed under a Creative Commons Attribution-No Derivative Works Licence

2.1 GENERAL PRINCIPLES

2.1.1 Definition

The word ‘ergonomics’ is derived from an Ancient Greek word meaning ‘rules’ or ‘study of work’. It is also referred to as ‘human factors (in design)’. Ergonomics is concerned with appropriate design for people - the design of systems, processes, equipment and environments so that tasks and activities required of them are within their limitations but also make the best use of their capabilities. Therefore the focus of the design is on the person or a group of people. This is often termed “user-centred design”. It is applied widely in areas such as aviation and other transport systems, sport, education, public facilities, the home, recreational equipment and facilities and in the workplace generally. In fact, the whole community benefits from ergonomics design. Ergonomics considers the effects of the system and its components on human and system performance.

Ergonomics has three domain areas: Physical ergonomics, Cognitive ergonomics and Organisational ergonomics.

[Industrial engineering has the lead in human effort industrial engineering, engineering the systems and processes so that humans can thrive at work during their entire career span with comfort and health. While productivity is the basic focus, in the case of product, quality is maintained, in the case of machine proper upkeep is maintained and in the case of employees their health, comfort and satisfaction are maintained by industrial engineering. Ergonomics emerged from human science disciplines to develop science and application in the areas identified by industrial engineering.]

2.1.2 History of Ergonomics

Ergonomics in the United Kingdom arose out of World War 2 when scientists were asked to determine the capabilities of the soldier in order to maximise efficiency of the fighting man. In the United States, ergonomics arose out of psychology and cognitive function in the aviation industry and was termed ‘human factors’. Today these terms are used interchangeably.

Ergonomics examines: Societal and Cultural Environment, External Environment – Legislation, Economy, Standards, Organisation Structure & Job Design , Workplace Environment, Workstation, Worker, Output Goods/ Services and Input Orders/ Planning.

2.1.3 Scope of Ergonomics and Systems of Work

Ergonomists and designers take into account a wide range of human factors and consider biological, physical and psychological characteristics as well as the needs of people - how they see, hear, understand, make decisions and take action. They also consider individual differences including those that occur due to age, fitness/health, or disability and how these may alter people’s responses and behaviours.

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Human Characteristics and Capacities Considered in Ergonomics

Anatomy Anthropometry Dimensions of the body (static and dynamic) Biomechanics Application of forces by gravity and muscles

Physiology Work physiology Expenditure of energy Environmental physiology Effects on humans of the physical environment

Psychology Skill psychology Information processing and decision-making Occupational psychology Training, motivation, individual differences, stress

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In order to address ergonomics issues at workplaces, Ergonomists interact and consult with designers, engineers, managers and the end users of any system, the workforce and individual workers.

2.1.4 Aims, Objectives and Benefits of Ergonomics

The overall aim of ergonomics is to promote efficiency and productivity and ensure that the capacities of the human in the system are not exceeded. The word ‘optimum’ is often used in ergonomics and refers to the balancing of the needs of people with real-life limitations such as the availability of solutions, their feasibility and costs. Successful solutions depend on solving the real, rather than the apparent problems. This in turn requires careful observation and analysis.

In terms of cost benefits the advantage of ergonomics changes is that they will make the job faster, easier, safer and enhance productivity. It is important to assess the benefits in the short, medium and long term, as expensive equipment and process changes may take some time to take effect.

2.1.5 Fitting the Job to the Person and Person to the Job, Occupational Ergonomics

At work ergonomics is applied to the design of the workplace and tasks and to work organisation. It is often referred to as occupational ergonomics within the OHS community. As such it aims to promote health, efficiency and wellbeing in employees by designing for safe, satisfying and productive work.

Positive performance factors such as worker comfort, well being, efficiency and productivity are all considered in determining how to achieve an acceptable result. Good ergonomics in the workplace should improve productivity and morale and decrease injuries, sick leave, staff turnover and absenteeism.

When analysing work and how it can be improved from an ergonomics point of view there are five elements that need to be addressed:

1. The worker: the human element of the workplace. Employees have a range of characteristics that need to be considered including physical and cognitive capacities; experience and skills; education and training; age; sex; personality; health; residual disabilities. An individual’s personal needs and aspirations are also considered.

2. Job/task design: what the employee is required to do and what they actually do. It includes job content; work demands; restrictions and time requirements such as deadlines; individual’s control over workload including decision latitude, working with other employees; and responsibilities of the job.

3. Work environment: the buildings, work areas and spaces; lighting, noise, the thermal environment.

4. Equipment design: the hardware of the workplace. It is part of ergonomics that most people recognise and includes electronic and mobile equipment, protective clothing, furniture and tools.

5. Work organisation: the broader context of the organisation and the work and how this affects individuals. It includes patterns of work; peaks and troughs in workload, shiftwork; consultation; inefficiencies or organisational difficulties; rest and work breaks; teamwork; how the work is organised and why; the workplace culture; as well as the broader economic and social influences.

To design better jobs we need to know about the work and how it will be done. We also need to know about the people who will do the work and their capabilities and limitations. Not only do we need to consider physical and cognitive aspects but we also need to take into account individual aspirations and needs - the social component. As work changes over time reviews and modifications are constantly required if systems and people are to work harmoniously and efficiently. No matter how well the workplace is designed it can be undermined by poor job design and work organisation.

2.1.6 Systems of Work: Seeing the Whole Picture

As most people realise, disorders arising from work can have a number of causes and they are not always obvious. Organisations are complex and people are too. For instance we now know that physical disorders may not arise purely from physical stresses.

In order to understand these issues we need to examine the work and its organisation more broadly and understand how various work factors may interact with each other and how personal factors might change the impact of work factors.

In occupational ergonomics, the physical design aspects of work or the ‘hardware’ may be only part of the problem and therefore part of the solution. In some cases it may be a small part. Other factors influence the development of a problem including work organisation and task design, job content, work demands and control over workload, support and training. Usually these aspects require ergonomics to be integrated into the broader work systems.

Therefore to determine if an optimum solution has been achieved the people who will perform the work (the ‘who’), the nature of the tasks (the ‘what’) and the context in which they are done (the ‘where’, ‘when’ and the ‘how’) need to be considered.

2.1.7 Human Characteristics, Capabilities and Limitations

As outlined above, the human characteristics and capabilities Ergonomists consider are the physical and cognitive capacities of the human at work. These capacities are affected by personal characteristics such as gender, age, pre-existing injury or disability and work organisation factors such as shift work, intensive work cycles and issues such as low morale. We will examine these factors throughout this course.

2.1.8 Human Error

‘Human error’ is a term often used to describe the cause of an accident. Human error has been defined as an inappropriate or undesirable human decision or behaviour that reduces, or has the potential for reducing effectiveness, safety, or system performance. Ergonomics applied to system design will make the system ‘error tolerant’ by considering the cognitive capacity of the human to make decisions in a number of situations. Human error is an unintentional act and is distinguished from a pre-mediated violation of rules and/or procedures by an individual.

Conversely then, ‘human error’ ascribed to accident causation is really indicative of poor design. The ‘failure’ that results from this can be immediate or delayed. (HSE, 2007, p.10.)

In order to make systems ‘error tolerant’, we need to understand why and how people make errors so that we can design the system appropriately.

Active failures are usually made by operators at the front line. These failures have immediate consequences.

Latent failures are made by personnel removed from the ‘front lint’, for example designers and managers. Latent failures are system failures and include poor design of plant, processes and/or procedures (eg: communication, roles, responsibilities, training). These types of failures typically pose a greater risk to health and safety. (HSE, 2007.)

A useful diagram to illustrate the types of human error and violations (Human Failure) can be found in the HSE book: ‘Reducing Error and Influencing Behaviour’, and has been reproduced below.

From this model, it can be seen that human error falls into two main categories, Skill-based errors (slips and lapses) and Mistakes (either rule or knowledge-based).

a) Skill-Based Errors

i) Slips – these types of errors are ones in which the action taken is not as intended and include:

• Performing an action too soon or too late (eg: selecting a button during timed process)

• Leaving out a step or steps in a process

• Performing the action in the wrong direction (eg: turning steering wheel the wrong way when reversing)

• Performing the correct function, but with the incorrect object (eg: using incorrect control lever)

• Carrying out the wrong check on the right item (eg: checking a dial for wrong value)

ii) Lapses – these types of errors are ones in which the action is not taken because the operator forgets or loses their place in the process, or forgets what they had meant to do. Often these errors are due to distractions and interruptions, and lack of systems to monitor work process (eg: checklist).

b) Mistakes

This is a complex form of human error, when an incorrect action is taken under the misapprehension that it is the correct action. These human errors are related to information processing in planning and action, assessing information and making intentions and judging consequences.

i) Rule-based – humans tend to rely on past rules or familiar procedures and will use these in new situations (eg: driving to previous set speed although the speed limit has changed).

ii) Knowledge-based – using past knowledge/analogies to determine planning or problem solving in a new situation, and coming to the incorrect conclusion or action (eg: applying cold climate clothing PPE principles to working in hot climates).

Errors can also be made through inexperience and inadequate training.

c) What Causes Errors?

An individual may be susceptible to making an error due to the influence of numerous organisational and individual factors.

Organisational factors include:

• Inadequate or inappropriate work layout

• Poor physical environment eg noise, heat, humidity, poor lighting or visual distractions

• Inadequate design of equipment including poor ergonomics

• Poor supervision

Individual factors include:

• Inadequate training • Inexperience on a task • Poor knowledge of a task • Inadequate skill level • Low motivation • Attitude and emotional state • Perceptual disabilities • Stress levels • Poor physical condition • Social factors

d) Avoiding Errors

There are three basic ways to decrease human errors:

1. Improve the training received by an individual on a particular task so errors are minimised

2. Reduce the likelihood of a human error by: • Improving the work design and work layout - make improvements that will accommodate human limitations and reduce error provocative situations

• Ensuring early detection of errors and early remedial action eg: installing safeguards and early feedback devices that will alert the individual that an error has occurred and ensure that remedial action is well practiced

3. Reduce the impact of a human error by ensuring that the impact is minimised when things do go wrong

2.1.10 Ageing

One of the biggest features in industry today is that of the rapidly ageing workforce. Ilmarinen (2006) found that the proportion of 50 to 64-year-olds in the workforce will be double in size compared to workers younger than 25 years (35% versus 17%) in the EU15 (the first 15 European countries to join the union) by the year 2025. Additionally his findings illustrate that some countries will experience this by 2010, and that the situation will last for decades to come.

An ageing workforce does have advantages. Older workers tend to be more consistent, careful and conscientious as evidenced by the following: they have no more work absences than other workers, they have fewer accidents and are less inclined to leave their jobs (see section below). They usually have extensive work and life experience which can be used to advantage in most jobs. However, increasing age brings some limitations including some reduced physical and cognitive capacity. The main limitations include:

• Vision and hearing acuity which decrease with increasing age

• Decreased ability to concentrate for long periods on difficult tasks especially in noisy or difficult work environments

• Lowered ability to focus and divide attention and to suppress irrelevant information

• Slower rates of information processing, recalling from memory, speech processing and language production

• Cumulative musculoskeletal wear and tear (sprains and strains) and decreasing physiological capacities leading to a decreased work ability (this appears to be greater in those who have worked in physically demanding jobs)

• Other health problems such as cardiovascular disease, diabetes and digestive disorders

The design of tasks and work organisation need to take these factors into account. Strategies to accommodate older workers might include:

• The reduction of physically heavy work as age increases

• The use of corrective spectacles especially where the tasks are computer based

• Allowing time to learn new tasks and understand new technology

• Designing training programs to assist older workers adapt to new methods and systems. The programs should be based on what older workers already know, ‘learn by doing’ methods. Using older trainers may help overcome difficulties

Generally older workers have considerable knowledge and experience to contribute that is important in decision-making.

They are usually keen to give information and offer suggestions and opinions and they respond well to consultative and participatory processes. These factors need to be considered systematically during job reviews and in long-term planning.

Evidence concerning the influence of age on the shift-working population is not conclusive but it is generally accepted that the ability to tolerate shiftwork declines after 45 years (Harma, 1996).

In summary, a review of the literature regarding occupational accidents showed that:

1. Older workers do not have more accidents at work than younger workers.

2. In an Australian study, the greatest number of traumatic work-related deaths occurred in the age range 20–54 years (about three-quarters); a smaller number of deaths occurred in individuals aged less than 20 years (6%) and those over 65 years (5%).

3. Older workers generally require longer periods of recuperation from injury due to age-associated physiological changes.

4. Factors that can influence recovery time from injury include the type of workplace hazard exposure, socio-economic factors and possible changes in reporting of minor workplace accidents (older workers may tend not to report minor injuries).

5. Older workers may be at risk of particular types of accidents, specifically sprains and strains of joints such as the shoulder, knee, ankle or back. However, information on exposure to work hazards, taking age into account, is not available.

2.1.11 The Role of the Ergonomist

The role of the Ergonomist is a significant and important one; they have a valuable role to play in assisting industry design appropriate work systems, equipment and human:machine interfaces to promote productivity, efficiency and worker comfort and satisfaction.

Throughout this course we will examine the principles of ergonomics theory, methods and techniques. The course will not turn you into an Ergonomist, but help you see workplace issues with ergonomics in mind and know when a specialist Ergonomist is needed.

2.2 BODY SYSTEM

2.2.1 Body Systems

Simply put, the human body is a complex system of framework (skeleton), moving parts (bones, joints, muscles, ligaments and tendons), energy conversion system (metabolism and physiology), movement control system (nervous system), feedback and decision-making system (senses and brain). From an ergonomics perspective, we need to understand how these systems work, what they are capable of and requirements for optimum function before we can effectively design work systems, equipment and interfaces which rely on their capacity. We will briefly examine these systems in this section.

2.2.2 The Musculoskeletal System

a) Anatomy

The human skeleton performs four main functions, it protects vital organs (brain, heart, lungs); allows movements through its joints; provides framework for upright stature; and contributes to red blood cell production. From an ergonomics perspective, it is the range of movement and types of movements at the joints which are important. These determine the direction and limit of human movements such as reach, important for workstation design.

The skeleton needs ligaments, tendons and muscles to become functional, and together these structures are termed the ‘musculoskeletal system’ and will be the focus of our discussion in this section, as this system is the functional system of human movement

b) Joints

The human skeleton has three main types of joints, synovial joints, hinge joints and ball and socket joints. Each type of joint allows certain movements. Synovial joints can be found in the hands and feet; hinge joints allow movement in one plane only and are found in the elbows and knees (although the forearm can rotate around its long axis due to the movement of bones in the wrist); while the shoulder and hip are ball and socket joints which allow movement in 3 dimensions (though with limits!).

c) Muscle

The muscles produce movement, enable posture and contribute to maintaining body temperature through heat production. Muscles are attached to bone via tendons, and are of two main fibre types: fast twitch or slow twitch. Postural muscles are slow twitch while dynamic muscle is fast twitch. Postural muscles are able to more efficiently sustain a contraction.

Essentially, muscles require oxygen to work efficiently. If they are starved of oxygen, for example by prolonged contraction to sustain a static posture, the muscle will use energy within itself for fuel and form lactic acid which leads to rapid muscle fatigue. This type of contraction is termed an ‘anaerobic’ contraction (without oxygen). An ‘aerobic’ contraction provides adequate supply of oxygen and nutrients to the muscle to work efficiently. Aerobic contractions allow time for muscles to contract and relax to access optimum oxygen, and continue to work.

The muscle contraction is the development of tension in a muscle. However when the muscle ‘contracts’ it does not always shorten. Contraction may be static (no movement) or active (movement). These states are further categorised as:

1. Isometric (static) - the muscle builds up tension but the length remains unchanged. Static muscle work is the most energy efficient but is also the most tiring. Compression of blood vessels and nerves stops nutrients and wastes from muscle activity from being dispersed eg when attempting to lift an immovable object or when an object is held stationary.

2. Concentric (active) - muscle fibres contract to shorten the muscle eg: the biceps muscle bends the elbow and overcomes the resistance of the weight of the arm, the source of the resistance being inertia and the force of gravity.

3. Eccentric (active) - allows for controlled lengthening of the muscle(s) against gravity eg: thigh muscles controlling knee movements while going down stairs.

2.2.3 Posture and Movement

The science of human movement is known as kinesiology and describes motions of the body segments, as well as identifying the muscle actions responsible for the movements.

Posture provides the basis for movement and refers to the angular relationships of the body parts and the distribution of their masses. These elements influence the stability of postures, the loads on the muscles and joints, and how long different body positions can be maintained before fatigue sets in.

Movement and posture is fundamental to human existence. People have evolved through the activity and postures imposed by their living conditions and their need to feed, clothe and look after themselves. As a result, human physical performance is optimum when postures and movements are dynamic and varied.

In general the human body moves and works most efficiently when joints are in the neutral (mid) range and the muscles are around mid length pulling at right angles to the bone. However, movement of joints through their full range each day is necessary to keep the body supple and the joints and muscles working efficiently.

a) Static and Dynamic Postures

The information about muscle contraction is important for ergonomics, as any action/movements in the work process which does not allow the muscle to work aerobically should be avoided. Static muscle work is common in postural muscles of the neck, shoulders, back and buttocks. These stabilise the trunk allowing for more accurate and efficient movement of the limbs. The positioning of the body for optimum movement occurs naturally where the environment allows.

Both types of active muscle work (concentric and eccentric) use more energy but are less tiring than static muscle work.

b) Balance and Movement Control

Balance is the ability to maintain equilibrium in different positions. This changes with the size of the base of support such as the feet, the buttocks in sitting or the whole body in lying and the height of the centre of gravity. Balance is maintained in standing and sitting by continually making minor corrections of position. In general we maintain stable postures by static balancing and unstable postures by dynamic balancing such as in walking.

As the position of a person’s limbs changes sensors in the muscles, tendons and joints relay this information to the brain. This allows a person to know where different parts of their body are in space even when they cannot see them. This feedback mechanism is known as proprioception.

Both the muscle and joint sensors as well as those located in the ear (semicircular canals) are essential for balance and co-ordinated movement.

2.2.4 Biomechanics

The interaction of human movement and posture is called biomechanics and describes the levers and arches of the skeleton, and the forces applied to them by the muscles and gravity.

a) Levers in the Body

A muscle seldom acts alone; most muscle action involves the complex integration of muscle activity to produce whole movements. Most movements employ lever action, the bones acting as levers and the muscles applying force about a fulcrum (joints).

Three types of lever action are employed:

1. First order lever - mechanical advantage is determined by the length of the lever on either side of the fulcrum eg: the see-saw and nodding of the head.

2. Second order lever - a relatively small force (the pull of the arms or the calf muscles respectively) acting through a large distance lifts a large weight through a short distance. This always imparts a mechanical advantage eg: a wheelbarrow or in tip toeing.

3. Third order lever- a relatively large force (in this case the muscles of the upper arm) acting through a short distance lifts a smaller weight through a large distance. This always leads to a mechanical disadvantage eg pulling up a fishing rod the lower end of which is supported against the thigh or in lifting an object by bending the elbow.

Most levers in the body are third order and as a result the body is very inefficient at generating force. The human body usually works at a large mechanical disadvantage and considerable energy is required to achieve modest output.

However, third order levers give humans some special advantages. These are speed, range and precision of movement.

As a general ergonomics principle, work should never be designed so that it requires strength and precision at the same time. This can place intolerable stresses on muscles and joints especially if it is required for repeated or extended periods during the working day.

2.2.5 Anthropometry

From an ergonomics viewpoint, appropriate design needs to cater for the range of humans at work. To do this, Ergonomists utilise anthropometric data. Anthropometry refers to the dimensions of the human body and how these are measured. It covers the size of people; their height and circumference; their weight and percentage body fat; the length and range of movement of their limbs, head and trunk; and their muscle strength.

Measurements of large numbers of people are needed in any given population to determine ranges, averages and percentiles. Children of different ages, male and female adults and older people all may be included in the population sample depending on how the data may be used.

Measurements are made in two different ways – referred to as static and dynamic anthropometry. The most common measurements are made with the body in rigid standardised positions and this is static anthropometry. Dimensions are linear and are made relative to the body surface eg standing height, length of leg, head circumference. Measurements are standardised using the same methods and postures on different individuals but they allow comparisons between individuals and between population groups. They provide information on the size differences of individuals but they are not functional measurements (that is they are static length measurements).

a) Dynamic Anthropometry

Dynamic or functional anthropometry, in which dimensions are measured with the body in various working positions, is more complex and difficult to perform but it has important applications in the workplace. Measurements are three-dimensional and describe such things as space envelopes in driving cabs, arcs and ranges of movements for the optimum use of controls, and safety clearances.

b) Using Anthropometric Information

In workplace and equipment design, ranges of dimensions are often specified to allow for the short and the tall, the fat and the thin and those who may be differently proportioned to the average. Ranges can include extremes at either end such the 5th percentile in height represents people who are in the shortest 5%, while the 95th percentile represents the tallest 5%.

Often a design needs to suit the majority of the population as far as possible while not accommodating everyone in the extremes of range eg seats in a bus or an aeroplane suit 90% of the population adequately but may be very comfortable for very short or tall or obese people. In these cases static dimensions are used as a guide eg: average (mean) height of the travelling population.

In most dimensions the middle 68% of the population can be accommodated relatively easily with little or no adjustment required.

Ninety-five percent of the population can be accommodated with some flexibility in design or by using adjustments eg desks and chairs. It may be very difficult to achieve a fit for very tall/short or big/small people above 97.5th percentile or below 2.5th percentile.

If it is possible to use equipment lower/higher/wider/narrower than the optimum, variation is limited to one direction - it has a one-way tolerance eg: the height of a door for a tall person, the height of shelf for a small person.

Some design is concerned with static dimensions such as body height (stature), leg length or shoulder width. For instance, thigh length governs the optimum depth of a seat for a particular person while lower leg length dictates the height of the seat.

Where dimensions may not be critical, one dimension, usually stature, may be used as an approximation of other dimensions such as leg length and shoulder width. Using commercially available data tables other static dimensions can be derived. However, this method must be used with care as there are many exceptions to the rule and all the data that are readily available in this form are from the USA or Europe.

• Occupation - workers in active jobs may tend to be physically larger than those in sedentary work. This may be due a selfselection process but is also related to age, diet, health and activity. However sedentary workers tend to have more body fat due to inactivity

• Posture and body position - differences in measurements occur between rigid and slumped postures, and dynamic and static measurements. The rigid, static measurements may provide a starting point for design but the dynamic or more functional postures are more likely to reflect the true situation

2.2.6 Applying Work Physiology: Body Metabolism, Work Capacity and Fatigue

While the musculoskeletal system has capacities and limitations, the Ergonomist also needs to consider the physiological capacity of the human: strength, work capacity, and the result of exceeding these capacities, fatigue.

a) Strength

Strength is affected by a number of factors,

• Gender: While some women are stronger than some men on average men are one third to one half stronger than women. This is due to body size, muscle mass (40 - 45% of body weight in men and 25 - 25% in women), the distribution and percentage of fat, and muscle bulk in the shoulders, abdomen, hips and legs

• Age: Muscle strength peaks are reached in men at about 20 years old and in women a few years earlier. Maximal cardiac efficiency and muscle strength decrease significantly with age. In both sexes maximal aerobic power reaches a peak at the age of 18-20 years followed by a gradual decline

At the age of 65 the mean value of aerobic power is about 70% of what it is for a 25-year-old. The mean value of aerobic power for a 65-year-old man is roughly the same as a 25-year-old woman. The strength of a 65-year-old individual is, on average, 75-80% of that attained at the age of 20-30 years when medical conditions are not a limiting factor. The rate of decline in muscle strength with age is in both sexes greater in the leg and trunk muscles (big muscle groups) than in the strength of the arm muscles. The decline in muscle strength with age is due to a decline in muscle mass

• Training: Muscle strength can be enhanced through training. In a work situation, the training must be highly specific to the movements required by the task, or the training may be ineffective

b) Work Capacity

The capacity of an individual to undertake physical work can be measured directly by examining the individual’s maximal oxygen uptake (ability to take in oxygen in the blood via the lungs), or indirectly by measuring heart rate. Heart rate is a reliable measure of workload and is easily measured in the workplace (as opposed to the oxygen uptake which is measured with special equipment in a laboratory setting).

To maintain a work level all day for a fit, young and healthy person, 25-30% of the maximal aerobic power (oxygen uptake) is usually acceptable. Maximal aerobic power varies markedly between individuals and the important thing is that individuals are measured against their own basic cardio-vascular capacity. However for all people the heavier the work rate the shorter the work periods should be.

Maximal heart rate can be roughly estimated as 220 beats per minute (bpm) minus the individual’s age. For instance for a 40 year old person the maximum heart rate could be expected to be about 180 beats per minute (220-40 bpm).

In most people a heart rate of about 120-130 beats per minute corresponds to a workload of 50 per cent of the individual’s maximal oxygen uptake. These figures would need to be modified for older, less fit or dehydrated workers.

An average heart rate of 110 beats/min for moderate levels of work is generally an acceptable physiological limit for an 8-hr working day for a 20 to 30 year old person. Exceeding these limits, even slightly for some people, may lead to fatigue (tiredness) and general lack of coordination, which may result in errors and injuries.

Environmental factors such as temperature, humidity, air velocity, noise, vibration and dust need to be considered carefully as these may effect the performance of individuals doing strenuous work. They may decrease the person’s alertness, concentration or physical capacity for work thereby increasing the risks of errors and injuries.

c) Endurance

Efficiency of muscular contraction is necessary to enhance endurance and work capacity. To facilitate this, work tasks should:

• Eliminate unnecessary movements • Use muscles according to their correct function • Make use of body weight and momentum and of gravity • Maintain balance • Vary movements • Vary position and posture • Employ postures allowing maximum torque • Use accessory supports for counterthrust or stability • Provide opportunity for training and practice

Endurance of a given muscular performance varies with the nature and intensity of exertion, the size and structure of the muscles involved, and practice in the task. As noted previously in this section, static effort can be endured for much shorter periods than exertion involving movement. Endurance fails sooner when either rate of work or load is increased, or when degree of contraction of muscles approaches maximum levels. Postural muscles have greater endurance than faster moving muscles, which are designed more for speed of contraction; most muscles have variable amounts of red or pale fibres depending on their main function, movement or support of posture (with red fibres needed for strength and pale fibres for endurance).

Practice increases power and endurance, due largely to better coordination and elimination of unnecessary contraction: the same end is achieved with less effort. Training enhances the speed, strength and stamina of muscle contraction. However, motivation is also of great importance in any activity requiring endurance of muscular effort.

In prolonged static or repetitive muscular exertion, the maintenance of constant speed and load requires a progressive increase in muscle activity ie: more contraction for the same output, both in the muscle group mainly involved and in recruitment of other muscles.

d) Physical Fatigue

If particular movements are carried out continuously it is reasonable to expect all the muscles to tire, both those executing the movement and those stabilising or enhancing the movement. Stabilising (static muscle work) is more fatiguing than muscle contractions that cause movement (active muscle work).

As fatigue can lead to strain the effect of unchanging postures and static muscle work can be equally as damaging as highly repetitive movements. Muscles may tire and become sore to touch and move. Points of weakness such as the muscle/tendon/bone junction at the knee, shoulder or elbow or the tendons over the ankle or the wrist suffer damage and lead to pain.

Dynamic physical work can also lead to problems if it is excessive for the particular individual. Movements in the outer range of the muscle or the joint, heavy lifting, pushing, or pulling (forces that are too high), movements that are prolonged (duration of activity) or repetitive can lead to strain and fatigue and eventually injury. In this respect younger and older, trained and untrained individuals, as well as men and women can vary widely in their capacities. Health and nutrition, previous injuries, lifestyles and natural abilities also play a part in contributing to a person’s capabilities to undertake a specific task.

2.3 PSYCHOLOGY AT WORK

When people work, their output is determined by both their physical and cognitive capacity. Cognitive capacity/behaviour in turn, is affected by intrinsic personal characteristics such as age, experience, training, personality and motivation; as well as extrinsic factors such as work organisation (shift patterns, work loads, morale, etc) and environmental factors which may act as a distracter to the task at hand (eg: excessive noise, poor lighting, etc). Cognitive ergonomics deals with the process of perception, cognition (processing) and action (decision/output).

We will now examine the concepts of perception, motivation, memory, risk perception, work stress and work organisation factors.

2.3.1 Perception and Cognition

Human perception begins with our senses – sight, sound, taste, touch. The information is processed and action taken. Should the information be incompatible with our senses, perception can be altered.

Outlined below is a conceptual drawing of the pathway of human information processing and output/performance. Memory is discussed in the following section.

From an ergonomics perspective, we need to ensure that information is presented to the person at work in the most compatible way so that it can be efficiently processed. This can be achieved in three ways:

1. Not overloading the human with information 2. Not providing too little information or stimulus 3. Not presenting the information too quickly

2.3.2 Memory

Human memory is divided into short and long term components. We are all aware of the vagaries of short term memory! In fact short term memory has a limited capacity – we are able to hold 5 -9 small items in this repository. For the information to move into long term memory, it has to be made more meaningful, otherwise the information is discarded and new information will take its place.

As outlined in the figure below, the pathway of information passes firstly through the short term memory where it is processed, and then either discarded or progressed into long term memory. The pathway to long term memory is not one way, however, as we need information stored in the long term memory, it is called up into the short term memory and processed. A schematic diagram below shows the movement of information into short and long term memory, then either acted upon or discarded.

2.3.3 Decision-making

Once we perceive information, we make a decision to act upon it. A useful model of this decision-making process has been put forward by an Occupational Psychologist, Wickens (2000), who outlines 3 features of decision-making as follows:

Features of Decision-making

• Uncertainty: If a decision has a degree of uncertainty and that uncertainty outcome is disagreeable, unpleasant, or a cost to us, we view the decision as risky.

• Familiarity and Expertise: Making decisions when the outcomes are known and familiar, is an easy and quick decision. When the outcomes are not known, and cues not familiar, the decision is much more difficult.

There is an effect of expertise and training in this type of decisionmaking, whereby an ‘expert’ will make a more rapid decision than a ‘novice’ – though as Wickens points out, accuracy is not guaranteed just because the decision is being made by an expert.

• Time: People may make more ‘risky’ decisions if that decision is a ‘one-off’, such as property purchase, or if the decision can be made, acted upon, and then have additional information before another decision step is taken. An example of this second type would be deciding to treat a serious illness with an unknown outcome. The decision can be taken to deliver initial treatment, have further tests, review decision, elect to proceed, etc.

Conversely, if time is limited, time pressure can have a significant influence on decision-making.

2.3.4 Perception of Risk

Kahneman and Tversky (1984) postulate that humans prefer to make gains rather than losses when making decisions. So, if the consequences of taking a risk are acceptable, this will affect our perception of that risk – that is, by lowering it.

This can be seen in situations where short term gains lead to acceptance and lower perception of risk, for example, driving too fast, not wearing personal protective equipment, or partaking in alcohol and other drugs. In other words, if risk taking is seen to have rewards, then risks seem more acceptable.

In addition to this phenomenon, humans have an inherent view of life that ‘things should be fair’, and ‘what goes around, comes around’, so that should a worker take risks at work and be injured, he or she may be seen to ‘get what they deserved’ and this then lowers the outrage that someone has been injured while working, and this in turn, lowers the perception of risk.

This tendency can be seen in our daily lives. Most of us drive a car, even though thousands of accidents occur every week and fatalities are not uncommon. Experience on the task of driving leads us to perceive a relatively low level of risk, and past experiences reinforce the “it won’t happen to me” way of thinking (unless you have experienced an accident!) In the workplace this thinking is even more pronounced.

Each time you drive, there is a small risk for each trip. Over a lifetime this risk increases with the increased exposure. Over a lifetime of driving, the risk of accident is calculated to be 30-50% and is dependent upon age, gender, geographic location, trip frequency and duration, drugs/alcohol, etc (Evans, 1991). Risk is difficult to measure in these situations.

Real risk is determined by the magnitude of loss if a mishap occurs (severity) and the probability that the accident or loss will actually happen (frequency). Humans’ perception of risk is generally much lower than actual risk.

Evidence of this in the workplace is the low levels or reluctance to wear personal protective equipment, or to follow safe work procedures which take longer than other methods and in the eyes of the worker provide the same results.

Sandman et al (1994) investigated factors influencing perceived risk, and found that lower risk is perceived when

• Exposure is voluntary • Hazard is familiar • Hazard is forgettable • Hazard is cumulative • Collective statistics are presented • Hazard is understood • Hazard is controllable • Hazard affects everyone • Hazard is preventable • Hazard is consequential

The following factors were found to increase risk perception:

• Exposure is mandatory • Hazard is unusual • Hazard is memorable • Hazard is catastrophic • Individual statistics are presented • Hazard is unknown • Hazard is uncontrollable • Hazard effects vulnerable people • Hazard is only reducible, and cannot be eliminated • Hazard is inconsequential

From looking at these factors, we can see that the more we know about risk the less threatening it appears, and that personalising experiences leads to increased perceptions of risk as people can identify with personal stories, and these affect them emotionally. Typically, the hazards we choose to be exposed to are perceived as less risky than those we are forced to go through.

For example, skiing, driving, working are usually seen as less risk than earthquakes, pollution, and exposure to certain food additives. If you are in a situation where you are feeling ‘trapped’, for example, unable to leave a job due to factors such as income for repayments, etc you are more likely to perceive high levels of risk than those who feel they are free to leave their job.

Balancing this process of risk perception, there is a concept of Risk Compensation, that is, that people will adjust behaviours to compensate for changes in perceived risk. This controversial area of research states that the lower the risk perception, the more and greater the risks that will be taken. This could be seen by workers wearing PPE feeling safer, and therefore behave more recklessly. Scott Geller, well known writer on human behaviour and safety, believes that risk compensation is a real phenomenon (eg: Geller 2001).

To investigate this, Geller ran a study with go-carts. Subjects were told to drive go-carts quickly but only at a speed they felt comfortable with. The 56 subjects were either buckled up or unbuckled in the first of 2 phases of driving trials. They then switched conditions for half the subjects so that there was no longer a seat belt for those previously buckled up and available for the group who previously did not have a seat belt. He found that people did feel less safe the 2nd time around when no belt was available BUT no change in driving speeds occurred despite the unease that people felt. Later a study by Jansson (1994) showed in a real situation that habitual “hardcore” non users of seat belts drove much more hazardously when asked to wear seat-belts.

It is Geller’s contention that the implications for this is that some people will take extra risks when wearing PPE or some safeguards have been put in place. Also some will only follow safe practices when supervised. Worse still, some people may exercise their freedom by deliberately doing unsafe things.

Accordingly, interventions should focus on lowering the level of risk people are willing to tolerate.

The implications of risk compensation is that OHS excellence cannot be achieved through top-down rules and enforcement; some people will only follow rules when they are supervised, and others may like to ‘make a stand’ and deliberately not follow the rules because they feel too controlled.

2.3.5 Signal Detection Theory

Humans learn about their world by detecting changes within it. Effective operation of a process or work system requires signals to the operator informing them of the state of the system and indicating when action is required of the operator. This topic is relevant to the design of displays on equipment and should be considered with the work design and control design section.

On a simple level, the operator needs to be able to detect whether or not a signal is present. Should there be a serious overheating within a production line, for example, the operator should easily be able to detect and understand the problem in order to make a decision and deal with the issue with an appropriate response. This concept is known as signal detection – that is the signal is present or it is not.

The workplace, however, is not usually this straight forward. A control room may have multiple displays: meters, readouts, visual and auditory alarms etc.

This processing of information can be applied readily to the control room, and also judgement tasks such as reading an x-ray to view a fracture (which require careful professional judgement based on knowledge and experience). The signal detection model was developed by Green and Swets, in 1966.

To schematically represent this, a 2 by 2 Matrix is used as shown below. The operator determines whether or not a signal is present, and as a result of these choices, the categories of response are ‘hit’, ‘false alarm’, ‘miss’ or ‘correct rejection.’ In the ideal world, with clear signals, all the responses would be a ‘hit’. However, given that the signal is not always clear and/or not always detected, the conventional method of considering the likelihood of each outcome is to consider the probability. For example if 100 signals were present, there would be 25 hits, and 75 misses, or a 25% chance of getting the right outcome.

The probability of outcome is affected by the response bias of the operator – more misses or more false alarms. This can be due to the individual or the circumstances. For example, if the outcome of missing a signal is very serious (as in medical diagnosis from a scan), then the operator is more likely to say a signal is present (‘false alarm’); or if an operator is fearful of shutting down a process line due to the costs, they are more likely to ‘miss’ the signal.

Incorrect outcomes can also be due to the signal itself – not obvious (see section on vision and hearing), ‘drowned out’ by other ‘noise’ in the environment such as other alarms, screens, lights, etc.; or a result of inadequate training or skill of the operator.

These are known as operator ‘sensitivity’ and can be improved to promote correct outcomes/response decisions.

Three main strategies can be implemented to overcome this sensitivity:

1. Reducing the unnecessary ‘noise’ in the environment – distractors, excessive information.

2. Increasing the strength of the signal itself, eg: using audio and visual cues.

3. Presenting relevant information simply and with good design.

2.3.6 Vigilance

Many work environments require ongoing monitoring of equipment and/or process. This watching over of operations is termed ‘vigilance’ and of course in many workplaces can be carried out over various shifts, and with the operator working different shift patterns.

While performing the vigilance task, the worker detects signals over a period of their shift and the signals are sporadic and unpredictable. For example, monitoring coal mining process, x-raying luggage at an airport, or checking for faults in manufacturing process. The operator is required to sustain an adequate level of vigilance – the vigilance level. Research has demonstrated that this vigilance level declines sharply during the first 30 minutes of the task, and this decline is known as vigilance decrement.

a) Types of Vigilance Tasks

Vigilance can be considered in a number of ways. It can be a task which is a

• ‘Free response’ whereby the event occurs indiscriminately and non-events are not defined (eg: gas plant monitor where the process is continuously monitored)

• ‘Inspection’ task where events occur at regular times

• ‘Successive’ task in which the operator must remember a standard and compare data with that standard (eg: fruit grading)

• ‘Simultaneous’ in which the operator would have the different grades of fruit in front of them and be able to make direct comparisons each time

• ‘Sensory’ in which the signal requiring detection is a change in visual or auditory levels

• ‘Cognitive’ in which the change will be in cognitive demand, such as proof reading a document

These different vigilance demands result in different outcomes for the vigilance task. Despite a great deal of laboratory experiments on vigilance, there is limited reliable cross-over to the workplace due to the complexity of task demands. However, there are a number of strategies that organisations can put in place to enhance vigilance performance, and these are outlined below (after Chengalur et al., 2004, p.282).

Promote signal detection by:

• Provide good training and ensure familiarity with the signals

• Use simultaneous presentation of signals (eg: auditory and visual)

• Ensure the signal ‘stands out’ from background noise

• Make the signal dynamic

• Provide 2 operators for monitoring; allow them to communicate freely

• Provide 10 minutes of rest or alternate activity for every 30 minutes of monitoring

• Provide feedback for action taken as result of the signal

• Install ‘artificial signals’ that require a response, and provide feedback on these

• Provide refresher training

• Vary the environmental stimulation inversely to the task stimulation

• Avoid overloading or underloading the signal detection and action taken

• Not using artificial signals that do not require a response

• Require operator to report all signals, even those in doubt

b) Improvement Strategies

Devising goals to be met by employees and rewarding them for meeting these goals are one way in which employers can motivate employees. In order for motivational strategies to succeed in the workplace employers must recognise that each employee will have different individual needs and goals. Thus types of organisational rewards that motivate one employee to perform well may not necessarily motivate all employees eg: monetary, or time off in-lieu.

Employees must be included in the decision-making process regarding goal setting and have the ability to provide comment on the types of rewards that are proposed by management.

The organisation needs to ensure that:

• Goals to be achieved contain an element of challenge for the employee

• Goals are attainable

• Feedback mechanisms are in place so that employees are provided with information regarding their performance

• Any organisational rewards offered are linked to objective employee performance achievements and that these rewards are individualised.

• Group goals do not have unwanted outcomes such as peer pressure that leads to overloading of slower or physically weaker workers

2.3.7 Motivation and Behaviour

Motivation in the workplace refers to as an individual’s intention or willingness to perform a task to achieve a goal or reward that will satisfy them. Each individual experiences differing amounts and types of motivation and considers different rewards or incentives as being attractive.

Some individuals are intrinsically motivated ie: performing and completing a task and the resulting feeling of accomplishment is its own reward. Others are extrinsically motivated and prefer their rewards to come from external sources in the form of bonuses, promotions and/or praise.

2.3.8 Work ‘Stress’ – Causes, Preventative and Protective Measures

Individuals can experience stress when demands exceed their ability to cope. These demands can be personal or work-related or both. Stress can have negative effects on an individual’s work performance, health and wellbeing. It can occur in the workplace when individuals experience:

• A lack of control over workloads or overly demanding workloads and schedules

• A lack of social support in the workplace, either through supervisors or peers

• A lack of clear direction from supervisors or management

• A lack of information regarding the individual’s role in the organisation

• A lack of career opportunities or job security

• Conflict with other individuals within or external to the organisation

• Physical work environment problems with extremes in temperature, noise, vibration or exposure to hazardous substances

• Violence or aggression from fellow employees or clients or as the result of events such as armed hold-ups

a) The Signs of Stress

Individuals who are experiencing stress may have psychological symptoms such as increased feelings of anxiety, depression, aggression or confusion. They may have physical symptoms such as increased blood pressure, heart rate and muscle tension and headaches. They may also be prone to habits such as smoking or drinking alcohol, show signs of irritability, perform poorly at work and have a high rate of absenteeism.

b) Overcoming Occupational Stress

Identifying the real causes of stress amongst individuals may take time and may need mediation skills to resolve (such as counselling). In some cases discussions and a general willingness to listen will be all that is required. In general solutions to the problem of occupational stress can involve both alterations to the work environment itself and/or attempts to improve an individual’s ability to manage stressful situations. Stress management training can be beneficial and may include development of coping techniques to deal with stress such as muscle relaxation, meditation and time management skills.

Organisations should try to identify why individuals may be feeling stressed. They should then structure an appropriate response that will address the stressor or stressors – stress related problems could have several causes. All interventions should be developed in consultation with the individual involved, trialled and then evaluated.

2.3.9 Work Organisation – Shift Work and Overtime

Work organisation refers to the broader context in which the work is done – the culture and the way the workplace functions as a whole. It encompasses management styles, organisation of work groups, responsibilities and accountabilities. It is influenced by the type of industry or business in which it operates; its history and culture; peaks and troughs in demand for services or products; whether or not there is shiftwork, extended hours or flexitime; and profitability. The extent and type of trade union involvement and the need to meet externally determined standards also influence how a workplace is organised and managed.

Ultimately work organisation affects all parts of the workplace and probably has the greatest influence on ergonomics, occupational health and safety (OHS) practices and the development of high quality, satisfying work. Given this the application of ergonomics in the workplace needs to be understood in an organisational and social context.

a) Flexible Work Hours

The traditional 9am to 5pm eight-hour-day is no longer the primary work schedule available to many employees. With the introduction of flexible work schedules many individuals have the opportunity to use flexitime arrangements, time-in-lieu, 4-day weeks and other such arrangements.

There can be benefits for both the organisation and the individual in using flexible work schedules.

BENEFITS OF FLEXIBLE WORK SCHEDULES

For the Organisation: The opportunity to extend services and operating times

Increased attractiveness of working conditions for potential employees

For the Individual: The opportunity to balance the demands of private and working lives

Any changes in the pattern of work in an organisation should be developed in consultation with employees.

b) Peaks and Troughs in Workloads

One major source of excessive work demands on individuals is the seasonal or cyclical nature of some types of work. Mining, manufacturing and service industries all have problems balancing increased workloads and worker capacity from time to time. Where these peaks and troughs can be anticipated they can be planned for and adjustments can be made. Where they are unexpected careful scheduling is needed. Excessive overtime and unpaid extended work hours can be harmful to health, safety and productivity. These workloads need to be managed at an acceptable level.

c) Shiftwork and Extended Hours

Shiftwork involves working outside what are considered to be ‘normal’ working hours, generally between 7am and 6pm. As a rule of thumb the 40-hour week (comprising five 8-hour workdays with two days break) is the ‘gold standard’. The more work hours deviate from this regular pattern the more strategies may be needed to overcome the effects of excessive fatigue and sleep disturbances. An increasing number of workers are performing shiftwork and many suffer adverse effects from it.

d) Problems Associated with Shiftwork

Most of the health and safety problems associated with shiftwork arise from the working of irregular hours, often at times that are in conflict with the individual’s internal biological rhythms. The body’s circadian rhythm is normally set for activity during the daytime and for rest and relaxation at night. Disruptions to the body’s circadian rhythm are most evident when an individual is required to work night shifts (between 11pm and 6am) and many people experience sleep problems during the day.

During a night shift, an individual’s circadian rhythm is at a low and, when combined with fatigue, performance is generally reduced. Poor performance can affect both safety and productivity on the job.

Health-related problems that have been associated with working irregular hours include gastrointestinal problems resulting from irregular diet and eating habits, an increased risk of stomach ulcers, cardiovascular problems and nervous complaints. Shiftwork also imposes restrictions on social and home life.

Individual differences can play a factor in a worker’s adjustment to shiftwork and for a few individuals working irregular hours poses few if any problems.

e) Minimising OHS Problems

It is important to minimise any OHS problems that are associated with shiftwork by:

• Reducing consecutive night shifts where possible, with a maximum of three 8-hour or two 12-hour night shifts a week

• Rapidly rotating shift rosters, with shift changes every two to three days. These are preferable to slow rotating rosters

• Forward rotating rosters (day-afternoon-night) are preferable to backward rotating rosters (night-afternoon-day) as they cause the least disruption to the body’s circadian rhythm

• The adoption of compressed work weeks. These have benefited shift workers in some workplaces

• Identification of individual coping strategies. These lessen some of the adverse effects of shiftwork experienced by many workers. Examples of these strategies include physical exercise regimes prior to sleep periods

f) Importance of Uninterrupted Sleep

A problem for many shiftworkers, especially those with young families, is getting enough uninterrupted sleep during the day after working a night shift.

Shiftworkers should try and ensure that:

• Unwanted noise is controlled eg: unplugging the telephone and restricting noisy activities in the home such as vacuuming

• The bedroom is free from direct sunlight through the use of curtains or blinds

• Heavy foodstuffs and alcohol are avoided before sleep

• A regular sleep routine is established

g) Advantages of Shiftwork

For some individuals there are advantages to performing shiftwork as workers do not need to commute to work during peak travel times. Commuting time to and from work can be reduced and shift workers are able to pursue hobbies and other interests and undertake family commitments during daylight hours, although this may be at the expense of sleep.

h) Compressed Work Weeks

One alternative to the traditional shiftwork pattern is the adoption of compressed work weeks. These involve the use of a set block of shifts of increased length, usually of 10-12 hours duration, offset by a reduced number of work days and with blocks of three to four days rest.

Compressed work weeks can be useful to the individual as they contain shorter blocks of shifts, fewer successive night shifts, and increased blocks of free time including weekends.

Conversely, compressed work weeks involve additional working time per shift, possibly leading to fatigue that could affect performance.

Extended work hours may also adversely affect an individual’s health and recovery may be prolonged for a worker after completing a block of 10 or 12-hour shifts.

The adoption of compressed work weeks has benefited shiftworkers in some industries through increasing their recreation time, improving the quality and duration of sleep and through improving their physical health and wellbeing. However, this is not always the case. Each workplace and workforce is unique and will require shift rosters that suit their particular requirements.

2.3.10 Rest and Work Breaks

Everybody needs to rest for some part of any 24-hour period. How much rest is needed and what form it takes varies widely between individuals and will depend on the intensity of activity in the preceding hours.

Sixteen hours in a 24-hour cycle is the normal period of wakefulness for humans. Beyond this point the body’s processes increasingly promote sleep. If work is continued beyond 16 hours substantial performance impairment is observed particularly with respect to attention lapses.

The following is a guide to the average amount of sleep required by individuals. However, some people can do with less, others may need more:

• No less than 5.5 hrs sleep in each 24 hours

• No less than 49 hrs sleep in each week

• No less than 210 hrs sleep in each month ie: No less than an average 7.5 hrs sleep per day

Work by its nature is tiring. During a work day most people need to take regular rest breaks in order to complete eight hours of work without excessive fatigue and the increased risk of injury or illness.

a) Work Pauses

Work pauses are additional, spontaneous breaks not incorporated into the job structure but taken by all individuals in the course of a day. They are not the normal fixed breaks in a working day such as lunch but may be breaks between tasks or a change in routine. They are essential because they delay the onset of fatigue by allowing the body to recover from physical or mental work.

b) Work Breaks

If intensive physical and/or mental work constitutes a significant part of a person’s workload during the day it may be necessary to for them to take breaks in addition to the normal lunch and personal breaks.

There is no easy way to determine how long breaks should be to ward off the effects of fatigue at work, even for someone who is undertaking specific tasks. Therefore many work systems now incorporate set breaks to allow for mental and physical recovery. These are usually about 5-10 minutes within each hour for moderately demanding work.

In general the length and type of break will depend on how hard the work is, the age and fitness of the worker and environmental conditions such as heat and humidity. Too short a break may lead to progressive or cumulative fatigue. (See also Fatigue in Section 2.2.6.)

Employees are usually best placed to determine for themselves when a break should be taken and how long it should be. However, workers often have to be encouraged to pause from work even when they are tired and they must be actively discouraged from accumulating breaks.

As work demands sometimes do not allow this to happen, care must be taken not to impose too demanding a work schedule with insufficient breaks. Consultation with employees who do the work should be undertaken before fixed work-rest schedules are finalised. Ongoing monitoring should be carried out to ensure that the breaks are appropriate. (See also Repetitive Work in Section 4.2.)

To estimate reasonable rest allowances in physical work it is necessary to examine the load and work rate against the number of hours the work is carried out during a work shift. There are guidelines on rest allowances for jobs such as heavy, physical work involving manual handling and work where safety is critical eg: airline pilots. However, care is needed when using these guidelines as risks arising from fatigue may be underestimated. As a general rule, the number and duration of rest allowances must increase as the load and/or the intensity of work increases.

Exercises may be useful in reducing the damaging effects of repetitive or sedentary tasks or work in fixed or awkward postures. However they need careful planning and supervision.

Additional Materials

https://www.iloencyclopaedia.org/part-iv-66769/ergonomics-52353

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From the above link

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