Richard Griffiths - Lecture Notes
Ergonomics"Ergonomics (or human factors) is the scientific discipline concerned with interactions among humans and other elements of a system in carrying out a purposeful activity. Ergonomics aims to improve human well-being and overall system performance by optimizing human-system compatibility. Human-system interaction design considerations include physical, cognitive, social, organizational and environmental factors." [International Ergonomics Association]
HistoryEmerged as a discipline during World War II when improving the interaction between human operators and sophisticated military systems was crucial for military success.
After the war, the discipline developed to study and improve human productivity and work physiology in industry.
Subsequently, its scope has been broadened to include other fundamental objectives such as, the provision for safer and healthier working environments, and improvement of the quality of working life.
The discipline of ergonomics has strong links to cognitive science, human-computer interaction, organizational design and management.
LegislationThe well-being of workers and their' health and safety at work is increasingly coming under the regulation of the law. In the UK, the major legislation that is applicable to computer use is the:
- Health and Safety (Display Screen Equipment) Regulations 1992. The regulations lay six main requirements on employers:
For a through review of the issues for employers see the Web site written by Stewart.
- must assess the risks arising from the use of display screen workstations and take steps to reduce any risks identified
- inform users about the results of the assessments, the actions the employer is taking and the users' entitlements under the Regulations
- ensure that new workstations meet minimum ergonomics standards set out in a schedule to the Regulations
- plan display screen work to provide regular breaks or changes of activity
- offer eye tests before display screen use, at regular intervals and if necessary provide special glasses
- provide health and safety training for users before use or whenever the workstation is 'substantially modified'
- Disability Discrimination Act 1995 (c. 50) This requires employers to make modifications to equipment and practices so that disabled workers are not excluded unnecessarily from employment. Finding appropriate modifications may require ergonomic assessment.
Computer ErgonomicsWe are specifically interested in ergonomic insights into the use of computer systems. From the definition above, these should be examined under the headings of:
AnthropometryThis is the measurement of human bodies. Data from this research is obviously vital when physical objects for human use are being designed. The data is specific to different national groups, and varies between genders. An additional complication is that it appears to change over time, each generation being bigger than its parents in many countries.
The notion of anthropometric percentile for particular populations is important. Use System Concepts Ltd's. Height Percentile Calculator to establish your height position with respect to the general population, and read the explanatory notes.
Extensive anthropometric data for children collected as a result of a USA funded research project is given by Reisler.
Examples of anthropometric data that may be used in the design of physical devices are given in the notes by Chignell. The unit of force measurment used is the Newton (N), which is defined as: m*kg*s-2 where m = length in metres, kg = mass in kilogrammes and s = time in seconds.
Musculoskeletal DiscomfortWe are particularly concerned here with the use of computer workstations in office settings, and increasingly in the home were the user may sit for prolonged periods of time, in a relatively fixed position, making constantly repeated small movements of the hands and arms. In certain situations this may result in injury to muscles and ligaments which may be very painful and disabling. Carpel Tunnel Syndrome, one particularly significant injury, is described in detail by Sheehan.
The design and layout of computer workstations is thoroughly described at the Healthy Computing site maintained by IBM.
Eye FatigueEye fatigue is caused when the eyes focus on a near object for a long period. The muscles in the eye have to work harder maintain the near focus, and become fatigued. This can be compounded by excessively bright lighting, causing the iris to contract, which also tires. The factors listed below may play a part in increasing eye fatigue.
They are described fully, together with steps to obviate them by Atencio.
- primary and secondary glare
- excessive lighting
- improper ergonomics
- poor quality or inappropriately adjusted video displays
- uncorrected or improperly corrected vision,
- insufficient or non-existent eye care
The current consensus on the possibility of eye damage by visual display terminals is that they do not cause damage. For comments on on this from an industry group, see the fact sheet prepared by the Electromagnetic Energy Association.
Ergonomic Computer Workstation Design
KeyboardsThe standard keyboard is not the only possibility for data input! In fact, it was designed to be deliberately inefficient, to prevent problems with the original mechanics of typewriters. All sorts of variations, with all sorts of claims for their improved use are available. For details of ergonomic input devices (keyboards, mice, etc.) view this LookSmart page.
LightingLevels of lighting must be appropriate to the task. Fine detailed work is best carried out in bright light, as visual acuity is improved. However, this can result in eye fatigue (see section above). This can also result in glare in the environment.
In situations where light levels can vary markedly, e.g., in an aircraft cockpit, acclimatization of the eye to a new light level will take time, and the brightness of displays will need to be adjusted to retain their visibility.
Electromagnetic EmissionsSmall quantities of these are generated by the cathode-ray tubes (CRT) used in most visual display terminals. The output of this radiation is restricted by national health and safety legislation, and the residual level is generally believed to be harmless. For brief comments on this from an industry group, see the fact sheet prepared by the Electromagnetic Energy Association.
With the increasing introduction of non CRT displays, (liquid-crystal displays, etc.) electromagnetic emissions will be reduced considerably.
Ozone EmissionsElectrical equipment in operation may cause oxygen in the air to change into its ozone form. Ozone is actually a poison which in small quantities acts as an irritant. People with breathing related illnesses may be particularly susceptible to its effects. The xerographic process used by photocopiers and laser printers produces considerable quantities of ozone. Fortunately, it naturally breaks down rapidly, but can still cause problems in a confined and ill ventilated space. Filters are fitted to these devices to minimize its release, but precautions should still be taken over the siting of photocopiers and laser printers.
NoiseWhilst most computer workstations are relatively quiet in operation, spinning disk drives and cooling fans can produce a background level of white noise which can be problematic, particularly if a number of computers are sited in the same room.
Printers also have become much quieter, but where dot-matrix or other impact printers are used, care over their siting should be exercised, and if they must be in the same room as people, silencing covers should be used.
HeatThe power consumption of computers continues to fall, but the heat output from VDUs is still appreciable, typically of the order of 300 Watts. (Put your hand on top of the VDU you are using right now to check this.) Human beings are estimated to emit approximately 100 Watts heat energy, so a VDU counts for approximately three people. Where considerable numbers of VDUs are co-located, air conditioning may be necessary to retain comfortable working temperatures for the users.
ReferencesAtencio, Rosemarie Eyestrain: The Number One Complaint of Computer Users Computers in Libraries Volume 16, Number 8 • Sept. 1996 http://www.eng.newcastle.edu.au/~akingsland/study-areas/Communication/Electronic/General-info/CiLMag/ATENCIO.HTM
Chignell, Mark Anthropometry http://anarch.ie.utoronto.ca/courses/mie343/lectures/anthropometry/index.html Design to Fit Body Posture http://anarch.ie.utoronto.ca/courses/mie343/lectures/design/index.html University of Toronto.
Disability Discrimination Act 1995 (c. 50) http://188.8.131.52/acts/acts1995/1995050.htm
Electromagnetic Energy Association Fact Sheet Three: Visual Display Terminals http://www.elecenergy.com/vdt.htm
IBM Healthy Computing http://www.pc.ibm.com/ww/healthycomputing/
International Ergonomics Association http://www-iea.me.tut.fi
Ressler, Sandy AnthroKids - Anthropometric Data of Children http://www.itl.nist.gov/iaui/ovrt/projects/anthrokids/ National Institute of Standards and Technology, Information Technology Laboratory
Sheehan, Mark Avoiding carpal tunnel syndrome: A guide for computer keyboard users University Computing Times, July-August 1990, pages 17-19. http://www.indiana.edu/~ucsstaff/cts.html
Stewart, Tom An Employer's Guide to the Display Screen Regulations System Concepts Ltd http://www.system-concepts.com/stds/hse_index.html
This page is maintained by Richard Griffiths and does not necessarily reflect the official position of the University of Brighton.