The ones that are not absorbed by the screen are usually at very low or undetectable levels.

Higher levels of X-rays can be produced when the VDT unit is faultily constructed, improperly maintained or worn out.

Chronic exposure to even low level sources of X-ray radiation can cause the body to age prematurely as well as causing changes in the immune system, genetic damage and cancer.

If you are working on an older machine, especially those built before 1970 or one where the picture tube is breaking down, make sure your company checks the amount of X-rays being emitted or if necessary, hire a reputable company to do it for you, at least once a year. Do not use the computer at all if the picture tube image collapses and fails to fill the entire picture area.

The use of lead aprons, which protect against X-ray radiation, is not recommended. Wearing a lead apron can cause postural problems. In addition, The Canadian Center for Occupational Health and Safety (CCOHS) advised that "if a pregnant women wears a heavy lead apron, this could be dangerous for the fetus because of the additional pressure exerted on the abdomen."

Ultraviolet, Infrared And Visible Light

Overexposure to infrared light (IR) can result in skin and eye burns and over the long-term cause cataracts. Most tests indicate that IR from VDT's are about one-tenth of the standard allowed.

Ultraviolet (UV) radiation and visible light (VL) are also given off from the screen. But measurements of UV and VL are well below the recommended maximum exposures set for North America.

Rarely, in one in 5,000 or 10,000 people (adults or children), pulsating visible light from the screen may trigger an epileptic seizure.

At present, it seems that these three forms of radiation do not pose any major health risk.

Electrostatic Charges

A large static electric field can build-up in front of a screen and is loaded with positive ions. This can be detected by a build up of dust on your VDT screen, glasses, synthetic clothes, carpeting and chair coverings. These high static fields can cause charged air pollutants to be attracted to the face and eyes of the operator. Itching and rashes on the face, neck and cheeks as well as eye irritation can result. The depletion of negative ions in the body caused by these high static fields in turn produces biochemical changes in the body. These changes can cause symptoms of fatigue, headaches, nausea, dizziness, muscular aches and anxiety.

Dr. Alan Hedge recently led a Cornell University research team that surveyed more than 4,400 workers in 27 buildings about job satisfaction, stress, VDT use and work environment. Air quality tests were normal. However, the team found that there was a direct correlation between workers' complaints and the concentration of mineral fibres in dust samples taken from computer screens.(VDT NEWS Sept/Oct/92) As a result, Dr. Hedge concluded that complaints of sick building syndrome may have more to do with VDT use than with indoor air quality.

What About Children

Children's systems are more susceptible to the effect of electromagnetic radiation. In addition, children often work on cheap computers that are poorly shielded and sit too close to them. They are also exposed to ELF radiation from sitting too close to TV sets and video games.

Several studies have linked an increase in childhood leukemia to proximity of high voltage power line or community distribution lines, both of which emit ELF radiation. VDT's also emit ELF waves as well other forms of radiation. But, fortunately, there is not the continuous exposure that occurs with power lines.

Most recently, after the September 1992 release of two major studies, the Swedish government formally announced that from now on it "will act on the assumption that there is a connection between exposure to power frequency magnetic lines and cancer, in particular, childhood cancer (Microwave News, Sept/Oct/92)." The Swedish government is planning to limit exposure to magnetic fields from new power lines, but no decision has been made on how to handle exposure from existing power lines in Sweden.