|Health and Safety Program Manual|
Increased use of computers in the workplace has caused a corresponding rise in health concerns directly related to their use. The most common health concerns are repetitive strain injuries, general muscle strain and discomfort, as well as eye and vision problems. Workstation design, as well as proper work practices can help to address these concerns. If you have any further concerns or questions please contact Angelo Graham (x6359) at the Safety Office. Also, for office exercise suggestions click here.
The importance of workstation design increases with the amount of time spent at the computer. As a general guide anyone who spends more than two hours a day in front of a Video Display Terminal (VDT) should take special care to ensure the workstation is user friendly.
Ideally the chair, terminal and keyboard height should all be fully adjustable. When this is the case, the chair should be the first piece of furniture adjusted to fit the operator. Once the chair has been properly adjusted it should be used as a reference point for all further adjustments. With the feet firmly planted on the floor and the upper body in a neutral position, the monitor and keyboard position should then be adjusted. Finally additional computer accessories including pointing devices (i.e., mouse) wrist supports and copy holders should be correctly placed. If the work surface height is not adjustable, the chair should be fitted to the workstation and a footrest provided to support the feet if needed. Specific guidelines for these adjustments are outlined in the following sections.
Computer users tend to spend most of their day seated. To provide comfortable support for each particular individual, the following features are important:
Many work surface heights are adjustable, in this case the chair is the first piece of furniture adapted to fit the user. To adjust a chair:
|1. Stand in front of the chair. Adjust the height so that the highest point of the seat is just below the knee cap.|
|2. Sit so that the clearance between the front edge of the seat and the lower part of the legs just fits a clenched fist.|
|3. Adjust the angle and height of the backrest of the chair so that
it supports the hollow in the lower back.
4. Adjust the seat pan tilt to a comfortable position.
A chair should be adjusted many times during the day. This will help to relieve muscle tension in specific muscle groups while loading others.
If the work surface height is not adjustable, position the chair so
that forearms are parallel to the floor, while keying. If necessary, provide a foot rest
to support the legs and reduce strain on the lower back.
The monitor or screen of a computer should be positioned so that the top line of text is slightly below eye level while seated as discussed in the previous section. Distance from the eyes to the screen should be approximately arms length, 45 to 60 cm. Greater distances may contribute to poor posture, if the user leans forward to see the information on the screen.
The monitor should be placed directly in front of the
worker, with a maximum of lateral angle of 30 . Tilting the monitor so that the screen is
vertical is also important as this position may reduce glare. These adjustments to the
monitor help keep the neck in a more neutral position, minimize muscle fatigue and reduce
A computer workstation should accommodate the keyboard on a separate and adjustable surface. The keyboard holder should be long enough to accommodate a pointing device or mouse pad directly beside the keyboard and at the same height. It is important that both the keyboard and the keyboard holder be kept as flat as possible as this places the wrist in a more neutral position minimizing muscle strain.
|The keyboard should be positioned at a height which allows the shoulders to be relaxed, the upper arm relaxed and close to vertical, the lower arm horizontal and the wrist straight.|
The main pointing device used for computer work is the mouse. Shoulder, forearm and wrist discomfort can be significantly reduced if the mouse is used optimally. Tips on proper usage of a mouse include:
|Newer computer furniture makes specific allowances for mouse position. Earlier computer furniture designs may require structural modification to accommodate the mouse (see figure), or the selection of alternate pointing devices.|
Alternatives to a mouse are increasing with the advancement of
technology. Trackballs are a common alternative. They should have a minimum diameter of
7.5 cm. As well, gliding touch pads are available which are activated by the movements of
the finger. Tablet pads (pen like substitutes) are also available. The advantages and
disadvantages of these various input devices have not been well studied, and should be
experimented with before purchase.
Foam pads placed in front of the keyboard known as wrist supports remove sharp, uncomfortable edges.(see figure) These are recommended for frequent VDT users. Wrist supports tend, however, to be misused. Wrists should only be rested on the wrist support during pauses in keying and should not be rested on the wrist support while the user is typing.
|Copy holders are recommended for individuals who perform input tasks from a source document. Copy holders eliminate frequent neck movements caused from looking back and forth between screen and paper, as well as continuous refocusing of the eyes. To maximize the benefits of a copy holder, it should be at the same height as the monitor, and as close to the monitor as possible. (See figure)|
The recommended illuminance at a VDT task area where data entry and retrieval is performed exclusively is 750 lux. Where data entry and retrieval is performed intermittently the recommended lighting level is 500 lux(CSA office standard). These lighting levels can be adjusted for personal preference and may be augmented by task lighting.
Glare is the main lighting concern when working with VDTs. To help minimize glare:
It is generally accepted that VDT use does not create vision problems or worsen existing vision problems. Constant VDT work, however, may contribute to eye fatigue. To reduce eye muscle fatigue frequently look away from the screen and focus on a distant object.
Eye wear may pose some obstacle for VDT users. Bifocal wearers may tilt their head back to view the monitor through the lower portion of their glasses. In this case the monitor should be placed lower than previously recommended. The use of single focus glasses designed specifically for computer use may be the ideal solution for this situation. Consult an optometrist for further guidance in regards to bifocal use.
Contact lens wearers may experience dry eyes when working with a computer. The office environment tends to be drier than normal, and when looking at a monitor people tend to blink less. To reduce these drying effects consciously try to blink more frequently, or use non-medicated eye drops.
Click here for more information
It is recognized that computers, along with many other electrical and electronic devices in our homes and workplaces, emit electromagnetic fields. The health effects of exposure to electromagnetic radiation from sources such as computers are continually under scientific scrutiny.
Various regulatory authorities have established limits for exposure to electromagnetic fields. The University of Waterloo uses these criteria to determine acceptable levels of exposure. The Safety Office has certified testing equipment to test the electromagnetic emissions from computers. Computers tested on campus have all been significantly below these established limits. An information package regarding electromagnetic radiation is available from the Safety Office. If there are additional concerns contact the Radiation Safety Officer (Ian Fraser x6268).
Ergonomic furniture, with proper adjustments may reduce the risk of injury when working with a computer. The risk of injury however, is not entirely eliminated. Work practices can help reduce the risk even further.
This includes proper job design which along with changes in job tasks, should include frequent changes of posture. It is important to stand up, move around, stretch and get away from computing tasks during the work day. Ministry of Labour guidelines recommend five minutes away from the computer every hour. By working with supervisors and managers it should be possible to design a job which incorporates various types of duties and eliminates continuous computer work.
Canadian Centre for Occupational Health and Safety (1989). Ergonomics - A Basic Guide. (Publication No. P88-28E). Hamilton, ON: Author
Canadian Centre for Occupational Health and Safety (1989). Ergonomics for Workplaces with VDTs. (Publication No. P89-22E). Hamilton, ON: Author
Canadian Standards Association (1989). A Guideline on Office Ergonomics. (Publication No. CAN/CSA - Z412-M89). Toronto, ON: Author
Ministry of Labour (1995 draft). Video Display Terminal Workstation
Layout and Lighting. Health & Safety Guidelines.
United States OSHA
|Last Update 25/06/98
This page maintained by Sheila Hurley.