Work involving use of a computer screen
In the tertiary sector, the ongoing process of modernisation of computer technologies generates constant changes and adjustments to habits, operational procedures and layout of both workplaces and equipment. Operation of a computer which requires regular use of the display screen has become commonplace at a majority of workplaces.
That being so, it is important to consider potential risks associated with the workspaces from the outset when they are designed. The layout of the workspace must be a synthesis of given ergonomic responses to the different work criteria involved and must focus on the overall idea of wellbeing of the operator during the performance of his / her tasks. These different issues will be dealt with in more detail below:•
- organisation of the space as a function of the work performed;
- configuration of the work surface and technical equipment;
- working environment, such as lighting and ambient climate.
Work at a visual display screen is covered by a Grand Ducal regulation published on 4 November 1994 concerning minimum safety and health provisions relating to work at visual display screens. This regulation contains in its annex minimum provisions on which the layout of every workplace using a display screen must be based.
The operator at a workplace using a display screen forms part of a complex work system. It is essential to make sure that his workspace layout, as well as the disposition and configuration of his working tools give him the possibility of varying his working postures to meet his individual needs.
The laxist interpretation of basic ergonomic rules can in fact lead to excessive strains on eyesight and on the muscular and skeletal system of the operator. This phenomenon then gives rise to visual fatigue and muscular contractions, especially at the level of the neck, shoulders and back.
To counteract possible excessive strains, some practical advice is given below:
- rest your eyes by regularly interrupting work at the screen: pauses lasting for just 5 minutes are already very beneficial to the eyes. These pauses may be used to change over to a different type of activity, for instance use of the telephone, looking out through the window or across the office;
- install your computer in such a way that the visual distance between you and the screen is between 50 and 80 cm with the upper edge of the screen not placed above the level of your eyes;
- avoid reflections and dazzle by closing the sun blinds etc. provided for your use on sunny days;
- avoid flashes on your screen by keeping lamps and other electrical appliances some distance away;
- avoid the use of a dark background on your screen. Use of a light background with dark characters is preferable;
- do not use too many colours. Do not use more than 3 different colours on the screen, background colours and characters included;
- make sure to maintain uniform lighting at your workplace.
2. muscular-skeletal system
- leave a space of 10 to 15 cm in front of your keyboard to rest your hands and forearms;
- regularly change your posture and use every opportunity to stand and move around the office;
- avoid tense and non-physiological postures. Do not turn your head sideways towards the screen while using the keyboard placed immediately in front of you; do not unnecessarily place objects in the space available for your legs (for instance waste paper basket, bags etc.);
- make sure that the seat is adjusted to suit your work surface and height;
- make sure that the depth of the space behind your work station is not less than 100 cm
At present, the design of office furniture is increasingly tending to use modular and adjustable elements which allow operators to change their posture within a widely variable range.
The Grand Ducal regulation of 4 November 1994 setting out minimum safety and health requirements for work on visual display units stipulates that:
- the table or work surface must limit reflections to a minimum;
- the size of the work surface must be adequate to allow a flexible arrangement of the screen, keyboard, documents and accessory items.
To implement these criteria for the dimensions of the work surface, a calculation of the net surface will be made depending on the activities of the worker and the office equipment available for the performance of his/her work.
Dimension of the work surface
As a general rule, in order to comply with the provisions of the Grand Ducal regulation the work surface used for work on computer screen must have a minimum width of 160 cm and a minimum depth of 80 cm.
In recent years, flat screens have systematically replaced cathode ray screens which used to take up a great deal of space at the workplace because of their volume and size. In the days of cathode ray tubes, work surface depths of 80 cm were inadequate but today they are perfectly sufficient.
Height of the work surface
A general distinction is made between:
- A fixed work surface
Scientific studies show that a work surface height of 75 cm for an activity in the seated posture is suitable for a great majority of the active population. If we deduct the average 3 cm thickness of a keyboard, the working height for an activity involving the entry of data into a computer is 72 cm. Today work surfaces are adjusted automatically to that height unless specially requested otherwise.
Nowadays every worktable is fitted with a rack and pinion system which permits the height to be adjusted to needs of the user and possible irregularities in the floor level to be compensated when the equipment is installed. The fixed heights of these work surfaces range from 68 cm to 75 cm.
- A vertically adjustable work surface
People used to work standing up. Nowadays, a seated posture is generally adopted. This is only an apparent improvement because the human body is not designed to be seated all day. Employees in the tertiary sector often suffer from muscular and skeletal problems. To remedy those problems it is appropriate to change position from time to time, i.e. to work in a seated, seated-standing or standing posture. The first requirement placed on the work surface is adequate provision for vertical adjustment which should fall within a range of around 65cm to 130 cm.
Surface of the work top
The surface of the work top must be free from reflections. The work top must have a mat finish and colour such that excessive contrasts with different component parts of the work station and its environment are avoided. The work surface must have no sharp edges or projecting angles.
The Grand Ducal regulation of 4 November 1994 setting out minimum safety and health provisions for work at visual display screens stipulates that the office chair must
- be stable;
- allow the user freedom of movement;
- assure a comfortable position for the user;
- be vertically adjustable;
- have a back rest with adjustable height and angle.
Apart from these elementary characteristics, some additional features can add ergonomic value to an office chair:
- the 5 branch pedestal should be fitted with castors suited to the quality of the floor covering so as to permit free movement of the chair;
- the back rest should be fitted with a vertically adjustable lumbar support;
- the upper line of the chair backrest should correspond to the middle of the shoulder of its user;
- if armrests are provided, their height, width and direction must be adjustable; the seat front should be padded and curved;
- the depth of the seat should be adjustable;
- the seat should be fitted with a synchronous adjustment system;
- the individual settings of the seat must be explained to its user.
Persons of small height who use a fixed work surface or a work surface with limited vertical adjustment possibilities often find it hard to adopt a correct position for the legs and feet. They cannot touch the floor while keeping the thigh and leg at a right angle. In such cases, a footrest must be provided.
A footrest adapted to the working system must have the following characteristics:
- height adjustable to 11 cm above the floor;
- inclination of the platform between 5° and 15°;
- minimum width 45 cm
- minimum depth 35 cm;
- non-slip surface.
Nowadays, the visual display screen is an integral part of the working equipment. It must be directional and inclinable to suit the user. Cathode ray screens are being systematically replaced by flat liquid crystal screens. Available firstly in a single colour and in small sizes these were used for pocket calculators and watches because of their low power consumption. Nowadays, they enable colours to be displayed in dimensions which may exceed a diagonal width of 1 metre. They have replaced cathode ray tubes for most applications except for very high definition when the colour range must be precise and faithful, and also in difficult environments.
Liquid crystal displays have several advantages over cathode ray screens:
- absence of radiation although the electrical magnetic fields emitted by cathode ray screens are minimal and present no danger to the health of their users;
- LCD screens have the advantage that they emit practically no electro-magnetic waves;
- they are less cumbersome ;
- they emit less heat, which makes their use a very attractive proposition, especially in landscaped offices.
The choice of the screen location in relation to the position of its user plays a vital role in the ergonomic layout of the workplace. The following criteria must be respected:
- the screen must be placed in the central line of sight in front of the operator;
- the location of the screen will be chosen in such a way that it is positioned between two rows of lighting;
- the axis of the operator’s sight must be parallel to the windows;
- the distance between the operator’s eyes and the screen must be 50 cm to 80 cm;
- the first readable line of the screen must not be above the height of the operator’s eyes. As the physiological line of sight is directed slightly downwards, the orientation of the screen must follow the movement to avoid placing any unnecessary strain on the eyes.
Keyboard and mouse
The keyboard and mouse are the principal data input peripherals. The law stipulates that the workplace using the visual display screen must be fitted with a mobile keyboard which is separate from the screen. This enables at one and the same time the distance of vision to be adjusted to assure visual comfort, while the location of the keyboard can be altered to suit the working procedures.
The space in front of the keyboard must be sufficient to rest the hands when no writing is being performed.
The keyboard must be angled.
The keyboard symbols must be easy to read and free from reflections.
The typing posture at the keyboard must create the least possible stress.
It is important to inform the users that they can adjust a number of parameters themselves, such as the size of the characters, contrast, clarity, background colours…
The use of colours in software should preferably be kept to a minimum. Some colours are incompatible: because of different wavelengths, they are perceived in relief mode.
Do not forget that good training is worth its weight in gold in information technology and will enable users to save a great deal of time.
The working tools must be located at positions which are freely accessible within the radius of the forearm and in the logical direction of their use (for example, telephone positioned on the right).
Depending on the work to be done, the tools will be laid out differently. For example, for straightforward data input work it is easier to place the document on a document holder arranged to one side of the screen.
Breaks must be used to stand up and walk for a few steps to relax the static muscles. It is also important to look up towards the horizon to change the accommodation of the eyes and to open the windows to let more oxygen into the room.
As far as prevention is concerned, a visit to the occupational physician will enable eyesight problems that may have been undetected previously to be diagnosed or unsuitable spectacles replaced.
Office lighting is a vital feature of good ergonomics: low luminance lamps, adequate lighting intensity, secondary lamps, non-reflective furniture, blinds in front of the windows … are all factors which facilitate work at a visual display screen.
The office temperature should ideally be around 20°C. Relative humidity should be in the region of 40%, but that figure is seldom reached because air conditioned air is generally drier.
The quality of the air has been substantially improved since smoking in offices has been prohibited. Tobacco is the No. 1 indoor pollutant. Photocopiers and printers must also be placed elsewhere for the same reason.