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© De Montfort University, 20011 Ergonomics and EC Directive Howell Istance Department of Computer Science De Montfort University (all illustrations are.

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Presentation on theme: "© De Montfort University, 20011 Ergonomics and EC Directive Howell Istance Department of Computer Science De Montfort University (all illustrations are."— Presentation transcript:

1 © De Montfort University, Ergonomics and EC Directive Howell Istance Department of Computer Science De Montfort University (all illustrations are taken from Safe Office Practice,Safe Office Practice

2 © De Montfort University, Exercise You have all used computer systems. What are the most important things that need to be taken into account in looking after the health and the safety of computer users, i.e. you? What would you put into laws? –Restrictions on what people can do? –Requirements on people to do certain things? Work in pairs or threes and come up with a list of what you would put in a law.

3 © De Montfort University, Ergonomics Fitting work, work-related equipment and workstations around the natural limitations and capabilities of the human, in order to… –To promote efficiency –To reduce risk of occupational strain, accident or injury –To promote comfort and job satisfaction Many application areas – design of computer workstations in offices, design of industrial safety equipment, layout of aircraft cockpits, design of chairs…. Mix of disciplines – physiology, psychology, statistics, anthropometry, environmental engineering

4 © De Montfort University, Anthropometry Think how you might describe –the heights of students in this room –the lower leg lengths (back of kneecap to heel) of UK adults Science of measurement of human bodily dimensions Design to accommodate a known range of body dimensions (95%, not 100%) Knowledge of the variation in different body dimensions enables calculation of, for example…. –range of chair adjustment to accommodate 95% of adults in UK –minimum clearance from floor to underside of desk

5 © De Montfort University, Issues in designing office workplaces Dimensions and adjustability of furniture, desks, chairs, document holders, footrests Design and performance of display screen equipment, VDU, keyboard, mice Layout of equipment, viewing distances and angles, reach distances Design of environment, lighting (in the office and at the desk), temperature, humidity Work organisation, breaks, stress, monotony User’s posture, vision corrections, avoidance of repetitive strain

6 © De Montfort University, Workstation design and layout Poor posture sustained for long periods of time results in fatigue to affected muscle groups Fatigue can result from reduced blood circulation to muscles, as products of muscle work are not removed and consequently build up Design and layout of workstation should enable good posture However, even maintaining a static good posture for extended periods of time will eventually result in fatigue There is a need for regular pauses or breaks in work where the person can get up and move around

7 © De Montfort University, Factors associated with bad layout

8 © De Montfort University, Factors associated with good layout

9 © De Montfort University, Viewing Angles Ideally the centre of the screen should be at right angles to the normal line of sight (which is about 15 o below the horizontal sightline) (rule of thumb) have the the top of the screen level with the eye –If the screen is too high, the neck is bent backwards to afford a comfortable viewing angle –If the screen is too low, the neck is bent forwards to afford a comfortable viewing angle –Both result in postural strain on the neck

10 © De Montfort University, Good location of the screen

11 © De Montfort University, Poor location of the screen

12 © De Montfort University, Requirements of equipment The equipment itself should be designed such it can be used in a way that enables stressors (such as poor posture) to be avoided. Issues here are… –Dimensions (such as keyboard thickness) –Flexibility, ease of and ranges of adjustment (such as screen angle) –Reflectance and colour to prevent it acting as a glare source –Legibility of information –Stability, weight Manufacturers have to ensure that their equipment conforms with any requirements in force at places where they wish to sell their equipment

13 © De Montfort University, Why is keyboard thickness an issue? We want to allow the users forearm to be approximately horizontal when using the keyboard The difference between seat height and elbow height has to accommodate –Thigh thickness (fixed by body size) –Thigh clearance to underside of desk (has to be adequate to enable free movement in and out of the seated position) –Desk thickness (determined by construction/stability requirements) –Keyboard thickness (variable, determined by manufacturers) We need to accommodate the smallest user body sizes in the 95% of the population we are designing for

14 © De Montfort University, Posture determines keyboard thickness Horizontal forearm Adequate space for thighs

15 © De Montfort University, Posture determines keyboard thickness Keyboard has to fit on top of desk and under/up to forearm

16 © De Montfort University, VDU Screen Issues are that (edges of) characters should be well defined and not blurred Otherwise eye constantly tries to bring these into sharp focus, which causes visual fatigue over long periods Contrast between characters and background should be sufficient for adequete legibility Need to avoid large luminance differences between screen and immediate surrounds Better to have dark characters on a light background than vice versa

17 © De Montfort University, Lighting at the workplace Glare is caused by local areas of high luminance relative to the immediate surrounding Causes visual discomfort and possibly poor posture if user adopts a posture to avoid having a glare source in the visual field VDU screens and surroundings can act as glare sources, if these are of high reflectance Areas of high screen luminance can obscure information displayed on the screen. Illumination at the workplace needs to be sufficient to read information on document, but not so high as to cause large luminance differences between screen and documents

18 © De Montfort University, Requirements for lighting Locate screen (and consequently workplace) to avoid areas of high luminance reflected light from windows and light fittings Light fittings should be shielded such that these do not act as glare sources Keep overall lighting levels relatively low to ensure adequate screen legibility, may require local lighting to increase illumination of documents

19 © De Montfort University, Location of workstation and windows

20 © De Montfort University, Low ambient light, higher local light

21 © De Montfort University, User’s vision No evidence that VDU work causes damage but may make existing (uncorrected) vision defects more noticeable Work at VDU normally requires long periods of fixation at close distances, which can rise to visual fatigue Viewing distances to VDU screens are usually further away than normal reading distances to books or hand held paper Viewing a screen through bifocals (using the bottom of the lens) will cause the head to be tilted backwards, giving postural fatigue Existing corrective prescriptions (glasses) may not be suitable for VDU work

22 © De Montfort University, EC Council Directive - 29 th May 1990 ‘EC Council Directive on the minimum safety and health requirements for work with display screen equipment.’ An important piece of EC Law affecting the use of computers across the European Union. Implemented in British Law as the ‘Health and Safety (Display Screen Equipment) Regulations 1992.’ Affected all new workstations put into use after 31 st December Affects all workstations from 31 st December 1996.

23 © De Montfort University, equipment in drivers’ cabs or control cabs for machinery display screen equipment on board a means of transport display screen equipment mainly intended for public operation portable systems not in prolonged use calculators, cash registers or equipment with a small data or measurement display window typewriters. Exclusions…..

24 © De Montfort University, analyse workstations to assess and reduce risks take action to reduce risks identified ensure workstations meet the requirements of the regulations by the necessary dates plan the work activities of users to provide breaks provide eyesight tests for users provide corrective appliances for eyes if required provide training relevant to health and safety issues and workstations provide information to employees about health and safety risks and measures taken to reduce them Employers Obligations

25 © De Montfort University, Schedule: Equipment and Environment Equipment display screen keyboard work desk or work surface work chair Environment space requirements lighting reflections and glare noise heat radiation humidity The “schedule” sets out the minimum requirements for workstations, contained in the annex to (European) Council Directive

26 © De Montfort University, Extracts on equipment… (display screen) “the characters on the screen shall be well defined and clearly formed, of adequate size and with adequate spacing between characters and lines” (display screen) “the image on the screen should be stable, with no flickering or other forms of instability” (display screen) “it shall be possible to use a separate base for the screen or an adjustable table” (keyboard) “..shall be tiltable and separate from the screen so as to allow the operator or user to find a comfortable working position avoiding fatigue in the arms and hands”

27 © De Montfort University, Extracts on environment… (lighting) “any room or task lighting provided shall ensure satisfactory lighting conditions and appropriate contrast between the screen and background environment, taking into account the type of work and the vision requirements of the operator or user” (reflections and glare) “workstations shall be designed that sources of light, such as windows and other openings, transparent or translucid walls, and brightly coloured fixtures or walls cause no direct glare and no distracting reflections on the screen”

28 © De Montfort University, Rather vague…? There are no actual values or data in the Directive to say what is meant by ‘adequate’ or ‘appropriate’ This is intentional… Standards (both national and international) reflect ‘current’ thinking about what is ‘adequate’ and ‘appropriate’ Expert witnesses can provide judgements about ‘adequate’ or ‘appropriate’ in court cases These are used to interpret what is meant by ‘adequate’ or ‘appropriate’ Much easier to update standards than to rewrite/change national legislation

29 © De Montfort University, ISO 9241 International Standards Organisation standard for requirements for work with Visual Display Terminals (VDTs). Covers: –workstation layout, –postural requirements, –human-computer dialogue design, –software aspects of display design, –keyboard requirements, and –user guidance. See full list of sections on p.508 of Preece.

30 © De Montfort University, Summary European and British law now make it obligatory for employers to provide for the health and safety of employees who use display screen equipment. This includes physical aspects of the workstation and its environment and the ergonomics of the software. The International Standards Organisation lays down standards/good practice in ISO 9241, but this is not a legal requirement as it is not cited in the relevant British or European legislation.


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