Lesson 219 of IEKC Industrial Engineering FREE ONLINE Course.
Chapter 5. WORKPLACE, JOB & PRODUCT DESIGN (Abridged with Comments)
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
5.1 WORK ENVIRONMENT
5.1.1 Principles of Workplace and Work System Design
5.1.2 Workstation & Equipment Design
5.1.3 Tools
5.1.4 Chairs and Seating
5.1.6 Computers (Visual Display Terminals) & Workstation Design
5.2 INFORMATION, DISPLAYS & CONTROLS
5.2.1 Design Principles For Displays & Controls
5.1 WORK ENVIRONMENT
5.1.1 Principles of Workplace and Work System Design
In ergonomic work system design, the person is the focus, with the aim of optimising human performance and well-being. This ‘work system’ refers to:
“A system comprising one or more workers and work equipment acting together to perform the system function, in the workspace, in the work environment, under the conditions imposed by the work tasks” (ISO 6385)
The general design principles include allowing people postural stability and postural mobility. The most common occupational disorders are musculoskeletal, and these are often as a result of lack of attention in the design to body dimensions and body posture, muscular strength and demands on muscles, and body movements.
The impact of work stress is also considered in design, with the aim of making demands on the worker that facilitate improved system effectiveness without resulting in excess stress and resultant physiological and or psychological impairment. (Refer to Section 2.3, Psychology at work, for more detail.)
Visual discomfort, visual fatigue, and reduced vision are consequences of environments that lack well designed or well controlled lighting. For example luminance that is very high can create glare; high contrasts can contribute to fatigue from the eyes continually readapting; and low luminance reduces the user’s ability to detect detail. (Refer to Section 6.1 for discussion regarding vision and lighting).
To achieve optimal working conditions, the workplace layout and work systems require careful design.
This design process must take into consideration multiple users with different characteristics, including people with special requirements. It must also include the interaction between the user or users and all the components of the work system such as the tasks, equipment, workspaces and the work environment and the movement of people and materials.
Workplace and work systems design (related to human effort) therefore covers more than the individual workspaces and looks at access between workspaces and other functional areas of the organisation eg stores, maintenance, plant room. A workplace may be within a building, a construction site or a mine site; the cab of a vehicle or quite literally ‘out in the field’ in the case of geologists, farmers, surveyors or environmental officers.
The layout of any workplace should consider traffic flow with the view to reducing slips, trips and falls; manual handling risks; traffic accidents involving vehicles e.g., forklifts; emergency and fire escapes.
The main phases of the design process (based on ISO 6385 principles) are:
• Formulation of goals • Analysis and allocation of functions • Design concept • Detailed design • Realisation, implementation and validation • Evaluation
The process of design is iterative, and works best within a multidisciplinary team representing the key stakeholders, users and design professionals.
a) Layout of Workspaces
Workstations and workspaces are the immediate, physical surroundings of the worker.
They can serve a range of different purposes from being the area in which a person works all day to an area that is used by a variety of people for different purposes intermittently. They can be discrete areas such as a computer workstation or part of a larger work area such as a workshop or production area. No matter what they are, workplaces must conform to basic ergonomics principles to accommodate users.
i) Workspace Size
The workspace itself must be of a suitable size. Often this is dictated by external factors that have nothing to do with the people working in the area, the equipment they are using or the activities they are performing.
Within buildings, limitations in space and location may be related to the cost of rent, building availability or a lack of planning. Sometimes functions outgrow spaces: more and more people or equipment are fitted into the same space and arrangements become increasingly ad hoc. Redundant or infrequently used equipment may not be removed or relocated and may be left to clutter the work area. Lighting, temperature control and ventilation may be inappropriate for changed functions and arrangements. In these cases review is needed urgently. However, no matter how adequate they may seem all workspaces need regular reviews to ensure that they are adequate and provide a safe and healthy work area.
In mining and similar industries such as construction and agriculture a person’s workspace may change constantly or may be mobile such as the cabin of a piece of plant or machinery. These may be difficult to control fully due to the requirements of the building, farming or mining process. In these cases the same rules apply – the workspace must be adequate for the workers and the functions that they need to perform.
The longer the worker is in the workspace during a work shift the more critical the design becomes.
One area of concern when considering workspace size is access by maintenance personnel to machinery in a breakdown situation. Environmental conditions in the field may be difficult and these are compounded by difficult and even dangerous access to components and parts of the machine. Heat, cold, excessive moisture, mud, dust, fumes, restricted spaces and difficult access may add to the problems normally experienced in a workshop where mechanical aids and some protection from the elements are available. Under these conditions each task needs to be assessed for ergonomics risks in conjunction with accident and production risks.
ii) Workspace Arrangements
The arrangement of the individual workspace is important especially when the work is stationary and performed in either the sitting or standing position. It depends largely on the type of work being done and the equipment being used. The physical arrangements must permit correct and appropriately supported work posture and unimpeded movements by each worker. The workspace arrangements may have to be modified for each individual if the work is critical.
A number of competing demands may make it impossible to have a perfectly arranged workplace or to meet all recommendations simultaneously so the aim is to achieve an optimum overall. In any workspace there needs to be sufficient space for the use and storage of a range of equipment including tools and appliances, lifting aids, components and spare parts, computer-related equipment and supplies, manuals and reference material, personal protective equipment (PPE) and fixed items.
The location and storage of tools, fixtures, equipment and material used at any workstation should be within the reach of the worker and not cause awkward postures during use. In some cases where items are used intermittently it may be preferable to store them away from the workstation. This has two benefits: it allows the employee more space and encourages them to move about from time to time.
b) Workshops and Other Industrial Work Areas
In designing workshops and other industrial work areas, the following factors should be considered:
• Access - hatches, steps/stairs and walkways need to be adequate for the biggest person wearing PPE and carrying equipment such as tools and testing devices.
• Size of the work area - the largest workers should be able to adopt comfortable work postures in the work area and it should also accommodate all the equipment that is required to do the work safely.
• The design and selection of tools and job aids - particularly where access and workspaces are limited may need special attention
• Temperature and other environmental conditions - humidity, heat, cold, fumes, oils and dusts need to be measured and any unwanted effects on the worker must be controlled.
• Visual requirements of the task - need to be assessed and any special requirements must be met especially where workers need to wear protective or prescription eyewear.
• Noise levels – within prescribed guidelines or suitable hearing protection provided. Environmental conditions such as heat and humidity may need to be reassessed if hearing protectors are worn.
• Wearing of PPE – needs consideration in task and workplace design eg hearing and eye protectors, hard hats, cap lamps and batteries, self-rescuers, and gloves.
c) Designing for Maintenance Tasks
There are a number of considerations for maintenance personnel when working on machinery either in a workshop or in the field. Most of these relate to poor access, restricted work spaces especially when large tools needs to be used or PPE must be worn, inadequate tool selection and/or design, heat and cold, poor visibility, noise and environmental pollutants.
In the last few years manufacturers have made significant design changes to plant to reduce both the time required to undertake routine maintenance and the health and safety risks for maintenance personnel.
Ergonomics design and risk assessments are now required for the design, manufacture and registration of plant in some Australian states through the respective OHS legislation. There is a lot of information on body size and strength and this should be used to ensure that workspaces for maintenance personnel are adequate.
The following design issues need to be considered in any workplace and especially in workshops, industrial and construction areas and for maintenance tasks:
i) Design Issues
Workspace • Work areas can accommodate the number of people required to do the job without posing a hazard
• Height and space restrictions are minimised
• There is adequate access and visibility for maintenance and routine checks
• There is an optimum location for operators on or near machinery and equipment while working
• All sized users are considered in the design of the work areas
• The flow of product or components is logical
• Seating areas are sufficient for easy access and correct adjustment
Walkways and stairs • Free, even and uncluttered walkways on and around the machinery and equipment wide enough to be able to walk forward are provided
• Changes in levels of walking surfaces are minimised
• Slip and trips hazards are eliminated (this includes maintaining temporary floors and uneven ground which may be a work area or walkway)
• All holes or depressions where a foot could get stuck or which may pose a trip or a fall hazard are covered or otherwise eliminated
• Well-designed steps, footholds and ladders for access to the machinery and equipment are provided
• Slip-resistant surfaces on all walkways and steps are provided
• Steps have the following characteristics: minimum of 200 mm deep; lowest step maximum of 400 mm off the ground; steps at least two boot widths wide
• Handrails are within reach of the smallest person and comply with the relevant Standards
Plant and machinery • Sharp edges and protruding obstructions are minimised or eliminated
• Pinch points and moving parts that could crush hands, feet, or the body are eliminated
• Fixed and moveable equipment are located with consideration for proximity to the work area, access, use and storage
Supplies and equipment that are handled • All loads (including tools) are stored so that they can be handled close to the body and at about waist height. Avoid deep storage bins; low, deep or high shelves for heavy or awkward items; and ensure that walkways are kept clear
• Designated storage areas for supplies and equipment with adequate, safe access are provided
• Reach distances are minimised or reduced especially for moving and handling loads
• The need for bending especially bending with twisting is minimised
• Minimal work is carried out above the shoulders or below the knees
• There is minimal manual handling of supplies and equipment, most particularly double or multiple handling
Environmental factors • Work areas are lit adequately • Loud noise is controlled at source • Work areas are designed to minimise the use of PPE
5.1.2 Workstation & Equipment Design
Workstation design refers to: “The combination and spatial arrangement of work equipment, surrounded by the work environment under the conditions imposed by the work tasks” (ISO 6385)
Work equipment refers to: “Tools, including hardware and software, machine, vehicles, devices, furniture, installations and other components used in the work system” (ISO 6385)
When designing workstations such as consoles and workbenches, the following factors need to be taken into account in order to accommodate the user:
• Horizontal work area • Working position • Work height (the height at which the hands are working) • Viewing distances and angles • Reach distances • Access and clearance
Each of these factors is outlined below.
a) Horizontal Work Area
These spaces need to include the use of materials and work equipment in the primary and secondary work areas (most frequently and easily accessed) and in the seldom-repeated activities in the tertiary work areas (furthest away).
b) Working Position
A sitting position is generally preferred for fine manipulation, and accurate control work; continuous light manual work; close inspection (visual) work; and where foot controls are regularly used. In sitting there should be enough space between the underside of the work surface and the seat for the legs and to allow movement.
The operator should be seated for constant or repetitive use of foot controls. Where multiple functions are carried out the foot should be used for controls requiring gross movements and the hand for the finer controls eg: driving a vehicle.
e) Reach
Arm and leg reach should be based on the dimensions of the shortest user and taking into consideration the postural, task requirements and working position.
f) Access and Clearance
Space allowances for horizontal and vertical clearances and access to the workstation; access to machines and equipment used by operators and for maintenance personnel must be incorporated into the design of the work stations. These allowances must be based on the dimensions of the largest user.
5.1.3 Tools
Tools are devices designed to extend human physical capabilities of reach, force application and precision movement thereby enhancing performance. Unfortunately they can also be a source of injury when inappropriately used or incorrectly designed.
Forces are generated from the human musculoskeletal system through the tool to the work piece and vice versa. Stresses arising from excessive forces and poor postures are frequently the result of poor tool design or inappropriate use. In some cases if a tool slips, breaks or looses purchase acute injuries can occur.
Tools are grasped in the hands and may be simple or may have controls. Generally mobile equipment is larger and is activated by controls eg: handles, buttons, knobs that have to be gripped, moved or turned by the application of manual or pedal force. These linkages become part of what is called the user interface. In some cases the status of the equipment can be transmitted to the operator through a display of some kind.
a) Handles
Gripping characteristics such as handle shape, palmar or pinch grips, output required eg: power or precision work should be considered. Tools should have handles that have the proper shape, thickness and length to prevent pressure on the soft tissues of the hands and to allow a good firm grasp. They should be free of sharp edges and pinch points.
Insulate contact surfaces to prevent electric shock, burns or the transmission of unwanted vibration. Use low voltage electrical power and double insulation where possible.
b) Forces
The forces required to grip tools during use should be minimal and prevent slippage particularly where gloves are required eg hot, dirty or clean work. The grip surface should be compressible, non-conductive to vibration, heat, cold and electricity. Flanges can be used to stop the hand slipping down the tool or to keep a heavy tool slipping out of the hands when being carried.
If the tool is required to deliver power then it should have a power grip handle design ie: the hand should be capable of gripping the tool with four fingers on one side of the handle and the thumb reaching around the other side locking on the index finger.
Where precision work is being required, the tool should have a handle that allows it to be gripped by the thumb and the first finger, or the thumb and the first and second fingers.
c) Design
All edges and corners of the tool and associated equipment should be rounded off and sharp, protruding elements avoided.
Tools should be designed so that they can be held and used with wrist and hand in the neutral position. Where the task requires large forces or has to be performed over extended periods, the tool should permit the arms and shoulders to be used.
Align the tool’s centre of gravity with the grasping hand so the operator does not have to overcome rotational movement or tool torque.
Ensure that the transmission of noise and vibration is minimised. Guard all moving parts.
d) Type of Operation
Power operated tools should be used instead of muscle power where possible. Using a single finger to operate a power tool is not recommended especially where it is repetitive and/or is required for extended periods. While the majority of the population prefers to use the right hand tools should be designed so that they can be used with either hand.
e) Weight
Tool weight should be minimal. Where tools are heavy counterbalancing devices can reduce the weight. The tool should be easy to set down and pick up.
f) Controls
Detailed advice regarding the design of controls is covered in Section 5.2.4.
g) Mechanical Aids
Job aids need to be well designed for the purpose and readily accessible if they are to be used when they should. For instance lifting aids need to be compact, easy to move and use, stable and safe.
Storage is often a problem and this needs to be considered when purchasing. In some cases moveable lifting aids such as cranes and hoists can be installed overhead thereby overcoming storage problems.
Height adjustable benches and jigs need to be sufficiently adjustable to accommodate all users and work tasks. Anthropometric tables (ranges of people sizes) are often used to guide designers in this. Adjustments should be easy and quick to make from the working position.
Wheels on mobile equipment should be of sufficient diameter to enable them to be rolled over rough or uneven surfaces without undue force and without the risk of sudden uncontrolled movements.
Maintenance programs must ensure that job aids meet legislative requirements and function as the manufacturer advises.
5.1.4 Chairs and Seating
a) Seated Work and Sitting Postures
Standard work postures recommended in most guides and textbooks are a starting point for seat and work height adjustment. No posture, no matter how good, can be maintained for more than 15-20 minutes before small changes are required. No seat, no matter how comfortable, will allow the user to sit comfortably for more than about an hour at a time without having to move and make significant changes in posture.
Therefore seated work should be mixed with standing and walking. The best way to guarantee that this happens is to design work with a mix of tasks that require employees to get up from a seat and stand and/or walk.
Work at desks and standard-height workbenches require a standard adjustable work chair.
Work at sit/stand workstations may require a higher chair. However, these can be unstable and are not recommended where alternative arrangements are possible. In some cases some work can be done in sitting in one part of the work area and in standing at another part. This may require more space as well as planning.
b) Work Chairs
Designing optimum chairs is an ongoing process with much work still to be done. Nevertheless the basic requirements for a work chair do not change. It should provide adequate support for the user while working, should not place any unnecessary stress on any part of his or her body and should positively encourage optimum posture while allowing for comfort and efficiency and minimum muscle fatigue.
There are three major factors that have to be considered when sitting on a work chair.
1. The posture of the spine and in particular the position of and the pressure within the discs
2. The type and amount of muscle work required to maintain work postures (static and active) and individual fatigue tolerance levels
3. Compression of tissues (blood vessels and nerves) particularly at the back of the thighs and behind the knees
Non-adjustable chairs are used in common areas such as tea or waiting rooms, where people are not required to sit for long periods in the same spot every day, or where chairs may need to be stored from time to time. These should suit most of the population (middle 90%) to a reasonable degree. The seat height should be in the range of 410– 430 mm with a seat depth of no greater than about 360 mm. The seat should have a backrest which is from 80–130 mm above the seat and where practicable (indoors) should have sufficient padding to prevent ‘bottoming out’ (insufficient suspension/cushioning).
Ergonomics considerations for work chair comfort include:
• As a starting position elbows should be level with the work height, forearms horizontal and upper arms hanging freely
• The head should be able to be held erect with the backrest of the seat conforming with the curve of the lumbar spine
• There should be room for the buttocks below the backrest
• There should be adequate space forward for the legs stretched out and for knees and thighs under the bench top or desk
• Chair height should be sufficiently adjustable in relation to work height and lower leg length to accommodate tall and short people
• Feet should be placed flat on the floor to reduce pressure on the soft tissues at the back of the thighs. Very small users may need an adjustable footstool even when the seat height is adjustable
• The backs of the knees should be free from the front edge of the seat so there is no pressure on the soft tissues
These considerations provide a starting point for chair and desk/work bench adjustment. Individual requirements and certain jobs will mean that postures may vary from this but the principles will remain the same.
5.1.6 Computers (Visual Display Terminals) & Workstation Design
a) Computer Tasks
Computers are great tools and are used in most jobs these days. However, problems arise when they become a total job with little variation of tasks, postures or movement throughout the day. As with every sedentary job it is important for people's wellbeing and health to ensure that they undertake a variety of activities during a working day. Where possible, the organisation of the work, including the job content and the furniture designs, should encourage user movement. For example it is recommended to mix computer work with other tasks such as filing, telephoning, meetings etc.
Software design is also important, as described in Section 5.2.5. Flexibility and ease-of-use are often traded off for more features or a higher-powered system that are not utilised by the majority of users. Training and support facilities such as help functions and fully competent colleagues are essential for most users of computer systems. Flexibility and useability of software decrease the need for highly specialised and expensive training, which should be conducted on a need-to-know basis.
Younger people, especially those who may have studied computing or have used a computer at school will have far more confidence with and understanding of computer systems than older people.
People over the age of 60 are likely to be less experienced and less confident users of computers than younger people. Training will need to be organised differently and focussed for older and younger users.
Most users over 45-years-old will need reading spectacles or prescription task spectacles to read the screen as well as any source documents. The size and readability of both the font and display icons will be important for this age group.
b) Computer (VDT) Workstations
There is no one computer workstation design suited to all users, as the design is dependent on the user’s tasks and the inter-relationship between their different tasks. The International Standard relating to VDT workstation layout (ISO 9241-5) recommends that prior to any design work, a thorough task analysis is undertaken. This must include an assessment of the task and subtasks including their frequency, importance, position of visual objects, duration and type of use of any associated equipment.
The Standard also reminds the designer to consider the location and use of the hands, and to include an assessment of posture, reach distance, device manipulation and the complexity of the movements.
In summary, the computer (VDT) workstation should be carefully designed to take account of:
• Users – their age, physical characteristics such as height, their education and training, and their experience
• Type of computer equipment used – its age, special features, and general design
• Users' tasks
c) Chairs and Desks
These should accommodate the range of height and sizes of users. Ideally the desk and chair should be height adjustable, with the chair having a properly shaped and padded adjustable back support.
Alternatively, if cost is a problem, different height chairs with an adjustable footstool or foot rail may be a solution. Most importantly, users should be given instruction on how to adjust the workstation for themselves and why it is important. Refer to Section 5.1.4 for further information regarding chairs and seating.
d) Computer Equipment
i) Screen Image
Characters, figures and other aspects of the display should be easily read. A black-on-white image is easier to read than the reverse. The use of colours should not diminish the clarity of the image or the information. The information display should not be compromised by additional material on the screen which is not used regularly eg: toolbars, rulers.
Larger screens may improve image clarity but need longer focal lengths (↑ distance to focus on image) than the average sized screen and therefore up to 50% more desk depth. Older users will have difficulty with smaller fonts and less contrast.
ii) Keyboard
This should be:
• Detached from the screen
• Thin - not > 30 mm at home row of keys on QWERTY keyboard (starting ASDF)
• Matt finish
• Dished keys
• Clear, etched figures on keys
• Firm travel and end-feel of keys
iii) Mouse
The mouse should:
• Have adequate resistance to movement but sufficiently sensitive for fine control
• Be shaped appropriately
• Be large enough to be easily grasped by the hand
• Have firm travel and end-feel of keys
• Have adjustable resistance
iv) Screen
The screen should be adjustable in height, angle (vertical axis), tilt (horizontal axis) and distance from the operator (larger screens need up to 50% more space).
v) Document Holders
These should be made available for source material. There are various designs for different types of work and documents. Some work better than others. If source documents are a standard shape and size a raised and tilted surface of any kind may be suitable. Books and special items may need particular designs that are available commercially.
e) The Visual Environment
The visual environment should be carefully designed. Lighting, either natural or artificial should create no glare, bright spots or annoying reflections in the visual field of the computer user. Reflections from the screen must be avoided. If possible computers should be positioned away from windows. If this is not possible the terminal should be at right angles to the window. Curtains and/or blinds are necessary to reduce glare from windows.
Generally speaking lighting levels should be lower than is normal for artificially lit rooms. Usually 300-500 lux (measure of light falling on a surface) is recommended as optimum if source documents or reference material are to be read easily.
Similarly, light fittings should be at right angles to the screen and to either side of the user. One-centimetre ‘egg crate’ light filters (specific design) reduce glare by shielding direct light from the side of lights. Refer to Section 6.1 for further advice regarding illumination and lighting.
f) Assessing Computer (VDT) Workstations
There are many checklists that assist the user to assess the above points. The best ones do not provide specific measurements and dimensions but rather encourage and assist the assessor to understand the user’s task demands and to identify any workstation design or layout issues that are restricting the user’s ability to perform their work comfortably, safely and efficiently.
It is important to remember that one cannot complete a workstation assessment without a specific user and without some knowledge of their tasks. For example one workstation design may suit a large, left- handed data entry operator working from small papers, but be a poor design for a person of different stature, different handedness and performing different tasks that require reference to multiple items of information presented in a variety of different formats.
One recommended assessment checklist is available online from the Cornell University Human Factors Group, at: http://ergo.human.cornell.edu/CUVDTChecklist.html
This checklist is appended for your reference. Other recommended and easily accessible tools are: HSE VDU Workstation checklist (2003), HSE, UK http://www.hse.gov.uk.msd/campaigns/vduchecklist.pdf
A Guide to Health & Safety in the Office (2006), WorkSafe Victoria, Australia http://www.workcover.vic.gov.au/wps/wcm/resources/file/ebcb9c435c88 1f7/officewise.pdf
5.2 INFORMATION, DISPLAYS & CONTROLS
5.2.1 Design Principles For Displays & Controls
Work often requires the use of human-machine interaction, where:
• The machine displays information to the operator
• The operator use control actuators to affect the machine (switches various functions of machine on and off)
• The machine in turn provides feedback to the operator
To ensure accurate and efficient use of the machine, and as required under International Standards, both the control actuators and the displays must be designed with consideration of issues such as:
• Suitability for the task – including function allocation, complexity, grouping, identification, operational relationship
• Self descriptiveness – including information availability
• Controllability - including redundancy, accessibility, movement space
• Conformity with user expectations – including compatibility with learning and practice and with consistency
• Error tolerances – including error correction, error handling time
• Suitability for individualisation and learning – including flexibility
(Principles above as listed in IS EN 894-1: 1997)
A description and examples of the application of these principles follows.
5.2.2 Information & Displays
Ergonomics is concerned with all aspects of communication but most importantly it has contributed substantially to our understanding of displayed and oral information (machines communicating to people). It has also developed some basic principles for communication systems.
In all jobs the communication of information is important. In some jobs it is critical. Depending on its nature and how essential it is to communicate precisely and quickly there are a range of methods that can be used. The objectives of a communication system are:
• Detectability -- the intended receiver can sense the signal • Recognisability -- the intended receiver can tell what the signal is • Intelligibility -- the intended receiver can tell what the signal means • Conspicuousness -- signal is attention-getting
a) Visual Displays
Of the display types, the use of visual displays is most common for the transfer of information.
Simultaneous perception of a large amount of information by humans is best achieved through the eyes and the form in which it is presented must be suited to as many people as possible. Therefore visual information displays should be clear, concise and precise. There should be no doubt about what information is being communicated to the user. In order to achieve this, a range of design rules applies.
Displayed characters may be illuminated such as on a computer screen or on a flat surface such as on the page of book. For legibility consider size, shape, spacing and contrast. In continuous text lower case letters are preferable to upper case.
Capitals should be reserved for the first letter in a sentence, and for headings, titles, abbreviations and proper nouns. Use a familiar typeface, plain and without ornamentation. Use proportional spacing for letters and do not right justify as the spaces become disproportionate to the words, making it harder to read.
Apart from the design of the display its location is critical. For information to be read and interpreted correctly it must be in the user’s line of vision, it should not have reflective surfaces or be able to be degraded by high levels of light. The more critical the information the more it must be easily seen and interpreted.
If analogue displays are used (dials and pointers) to indicate levels or speed for instance be sure that increments are sufficient to be able to be detected and they are not subject to parallax error (whereby a change in observer’s position leads to a perceived change in measurement display).
Displays should be readable from the user’s position without them having to use awkward postures or movements. This is particularly important when information is critical. All information necessary to the normal functioning of the machine, equipment or system needs to be displayed in a readily interpretable form.
The design of information displays and instruments should enhance the operator’s capacity to determine the state of the machine accurately, easily and when it is needed. The aim is to minimise errors, operator fatigue and wear and tear on machinery.
b) Auditory Displays
Using auditory displays requires variation in the sound using different intensity, frequency, duration, timbre, or in the duration of intervals between specific sounds. The use of an auditory display may alert the user and precede a forthcoming visual display, and in emergency situations both an auditory and visual display may be used simultaneously.
The use of auditory displays is indicated in the following work situations:
• The operator’s vision is already occupied • The information requires immediate actions • The message is simple and short • The work is undertaken in the dark or with limited vision; or • When the operator must move within the workplace
Auditory displays allow communication with an operator even when they may be occupied with other tasks.
When designing auditory displays consideration must be given to the operator’s ability to detect, identify and interpret the sound.
c) Tactile Displays
These displays use the state of a surface, and the contours or relief of objects to convey information. The operator then applies touch or pressure to interpret the information. Tactile displays tend to supplement rather than replace other displays, except in cases where workers have a sensory impairment such as blindness.
As with other display types, the display must be easy for the operator to detect, identify and interpret. For example if gloved hands are used on the display the display should have exaggerated features for easier detection, and displays of different shapes should be sufficiently different from each other for easier discrimination.
d) Quantitative & Qualitative Information Displays
As Stevenson (1999) outlines, information displays can present the same data in different ways, and this is dependent on the level of detail required and the speed at which it must be understood. Consider what type of instrument display is best suited to the data, without adding any unnecessary complexity.
For example digital or analogue displays or a combination of the two may be used where a quantitative measure such as a specific temperature or pressure must be interpreted.
Where detailed quantitative data is not required, a representational display is well suited to providing rapidly understood advice, such as a change in status of the machine or system. For example this display may simply show zones to represent normal operation, an impending problem, and danger. Alternatively, a system of warning lights with or without an auditory signal may be used.
5.2.3 Danger and Information Signals
The phrase ‘danger signals’ range from emergency signals where people should leave the danger zone immediately, or take urgent action for rescue or protection, to warning signals where people should take preventative or preparatory actions.
A warning is a message that is intended to provide information concerning a possible unpleasant or negative consequence of either an action or a nonaction. Warnings can be provided in several ways:
• Verbal speech - warnings given by co-workers or supervisors
• Auditory non-verbal signals -- the timer on the stove sounding that food is cooked
• Visual signals -- traffic lights
• Signs, labels or symbols -- a traffic stop sign or a warning label on a hazardous substance or the non-smoking symbol
The type of warnings given will depend largely upon the situation and for whom the warning is intended. For example, an auditory non-verbal signal would be lost in a noisy work environment.
Organisations should consider what type of warning would be suitable to use in a particular circumstance and ensure that the warning is appropriately designed. For example, when using written signs to convey a warning message, the type of language used in the message should be taken into account- use short statements in plain language with symbols where appropriate. Colour/s of the sign, the typeface and the suitable placement of the sign in the workplace need also to be considered.
Where the operator might be in a fixed position the visibility or audibility of warning signals need careful attention.
With visual danger signals, the discrimination between signals requires the use of different characteristics such as colour of the signal light, location, relative position of lights, and temporal pattern.
Colour-blindness needs to be considered where red/green combinations might be used for danger and operational status.
With auditory danger and information signals, the sound can be made to have different characteristics to indicate different situations. For example quick pulsed bursts or alternating pitches indicate danger, short sounds indicate caution, while a prolonged sound following danger signal indicates normal conditions or all clear.
Further detail regarding auditory and visual danger and information signals is provided in the relevant Standards.
The following summary outlines characteristics of signals as recommended by the International Standard for the system of auditory and visual danger and information signals (ISO 11429: 1996).
a) Safety Signs and Labels
The primary objective of safety signs is to warn or caution. The device should be noticeable, recognisable and understandable. They may fall into specific classifications of warning or caution signals or signs; or hazard advisory or instructional. They need to meet the following criteria:
• Conspicuousness – the sign should stand out and be located where most people would look
• Emphasis – words or symbols should imply danger. Words such as ‘danger’, ‘hazard’, ‘caution’ and ‘warning’ are suitable. Symbols should be standardised and immediately indicate the nature of the hazard
• Legibility – when words and messages are used the size and style of letters and contrast with them and the background need to be sufficient to be read. A border separates the message from the background.
• Simplicity – use as few words as possible; keep information short and simple; tell the observer what to do or what not to do; avoid acronyms or abbreviations
• Intelligibility – say exactly what the hazard is and what might happen if the warning is ignored.
• Visibility – make sure that the sign is visible under all expected viewing conditions
• Permanence – devices and sign materials need to be resistant to aging, wear, soil, vandalism and deterioration due to sunlight or cleaning.
• Standardisation – use standard signs and symbols where they already exist. If local, long-term usage is likely to be better understood this might be acceptable.
However, consider interpretation by visitors and newcomers. Wherever possible ergonomics principles should apply.
5.2.4 Controls
Controls provide a method for workers to change the status and operations of a machine. The control actuator may be operated by light touch on a button, grasping and moving a lever, turning a dial, using a foot on a pedal, or other means.
Any controls should be within the reach of the worker when operating the equipment. The forces required to engage the controls should be within the worker's capabilities but not so light as to be inadvertently activated or difficult to control speed or force. The direction of movement of the controls should be consistent with the expected outcome eg moving the control lever forward moves the equipment forward. Ensure that weight-holding is separate from the force, guidance and control functions.
a) Layout
Specific considerations in the design of controls should include the following:
• Laid out and designed for easy and safe operation, and to prevent confusion over allocation of control functions or direction of operation. When operators are moving from machine to machine with similar functions controls should be standardised for position, function and operation as far as practicable
• Organised into primary and secondary groups
• Arranged so that similar functions are together (dissociate if confusion is likely) and position with sufficient space between controls to prevent unintentional operation
• Backlit with a dimmer switch for easier identification at night
• There are safeguards against accidental or inadvertent operation for critical controls eg locate out of easy reach; separate; or use guards, recessing, collars or an opening cover
b) Shape and Size
Each control should be readily distinguished by its location, type, shape, feel.
The size, shape, colour and location of knobs and switches and other controls must be matched to usage and their importance.
Size should accommodate large feet (pedals) or small/large hands and account for the need to wear protective clothing like gloves or safety shoes.
c) Movement, Effort, Resistance and Feedback
Movement of controls should produce a consistent and expected effect. Control force and function need to comply with conventions. Recommended control motions should be observed. For example pushing a control forward will elevate forklift tines and pulling back will lower tines; pushing to left will lead to movement to left.
Optimum force should be required to activate control and movements should be consistent with the natural movements of the arms or legs. Angle of push or pull should be designed for optimum control and movement. Control type should be selected to provide the most appropriate movement or activation control eg: levers for the application of force and speed, smaller controls for fine control and accuracy.
Controls should provide feedback so that operator knows at all times what his/her input is accomplishing. They should have distinct resistance gradients at critical control positions.
Static friction should be minimised (resistance to control movement initiation) as use of excessive force may cause overshoot and correction may be required.
Sensitivity of adjustment controls should be related to the degree of control required especially if they are heavy. Excessive force should not be required for small increases. For instance small movements should not produce large unwanted increases eg: volume control.
d) Labelling and Identification
The purpose and location of all controls must be clear. Controls should be marked with etched labels or permanent paint of contrasting colour ie white on black or black on white.
Lighted switches can provide quick identification and feedback on condition and function.
e) Remote Control Devices
Special attention needs to be paid to the design of remote control devices and there are many aspects where incorrect design could cause disastrous consequences. The design of the control, the environment the operator is working in and physical load of remote control on operator are examples and factors to consider.
f) Compatibility When Combining Displays and Controls
Where the design of controls and displays does not take into account the user’s knowledge, habits or capacity there will be a lack of compatibility. For example a common problem is confusing placement of controls to the displays, such as dials equally spaced along the front of a domestic cooktop, where the cooktop has 4 hotplates arranged in a square. The different spatial arrangement and grouping of the controls and the displays can result in user error.
With experience in operating tools and machines people develop knowledge and expectations about the movement of mechanical objects - such as the way pointers move over scales and dials. Bridger (2003) explains that where the movement on a display is inconsistent with a population’s assumptions, the message may not be understood.
For example a common belief or ‘population stereotype’ that applies to many controls is that clockwise movement refers to an increase or the passage of time, while anticlockwise refers to the reverse.
Even after learning and practice of a new or different movement, people can revert to their stereotypical behaviour and this is particularly the case in times of stress or haste. In Europe the issue of stereotypical behaviour can be a problem when people used to driving on the left hand side of the road and in right hand drive cars (such as drivers from the UK) are faced with the opposite situation, and at times of stress or in emergency situations the likelihood of error with the driving task increases.
5.2.5 Principles of Software Ergonomics
Software ergonomics refers to the interface and interaction between the human and machine in terms of the software. The ergonomic design of software aims to enhance the user’s ability to operate applications effectively, efficiently and with satisfaction. Consideration must be given to the user characteristics, the tasks to be performed and the environment in which the system will be used.
The International Standard relating to ‘Human-centred design processes for interactive system’ (ISO 13407: 1999) identifies and outlines the following key principles of software ergonomics:
• “Appropriate allocation of function between user and system, based on an appreciation of human capabilities and demands of the task
• Active involvement of users in order to enhance the new system and its acceptance
• Iteration of design systems to entail the feedback of users following their use of early design systems (ie: allow user feedback to inform ongoing modification of design systems)
• Multi-disciplinary design team to allow a collaborative process which benefits from the active involvement of various parties, each of whom have insights and expertise to share”
In order to apply these principles, a number of design activities with the focus on the user or human must be undertaken. This user-centred approach requires the following activities are undertaken:
• “Understand and specify the context of use • Specify the user and organisational requirements • Produce designs and prototypes • Carry out user-based assessment”
The design must focus on the usability of the software, and so have regard for human sensory physiology, perception and motivation, cognition and communication, following the principles of:
• “Suitability for the task • Self descriptiveness • Controllability • Conformity with user expectations • Error tolerance • Suitability for individualisation • Suitability for learning”
(from ISO 14915-1:2002)
To enhance usability, the software should be easy for the user to adapt to their experience and knowledge, with information displayed in a format suited to the task and the user. The system should also provide feedback on performance.
International Standards provide detailed guidance regarding the ergonomics issues relating to software design, including design of information technology, multimedia user interfaces, software engineering etc. (Refer to ISO 13407: 1999 and ISO 14915 – 1:2002.)
Additional Materials
ERGONOMIC WORK SYSTEM DESIGN USING KANSEI ENGINEERING APPROACH
April 2020, SINERGI 24(2):109
DOI:10.22441/sinergi.2020.2.004
Authors: Hari Purnomo, Vitri Lestari, Alex Kisanjani
https://www.researchgate.net/publication/341010789_ERGONOMIC_WORK_SYSTEM_DESIGN_USING_KANSEI_ENGINEERING_APPROACH
Work place and process optimization for improved productivity
Vinayak Shete
Warehouse Solution Design | FMS MBA Exec | Part time writer
May 31, 2018
https://www.linkedin.com/pulse/work-place-process-optimization-improved-productivity-vinayak-shete/
More results are there for Ergonomics of Work System Design in Google search. To be included.
Ud. 14.11.2023
Pub. 9.11.2021
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