Civil Engineering Reference
In-Depth Information
ergonomics to a large multinational corporation. Surprisingly many office workers and
even a top manager were concerned about radiation. May employees used screen filters to
“offset” the radiation.
Many computer terminal workers expressed concern that the exposure to radiation
emitted by CRT screens might lead to the formation of cataracts. Available data indicate
that the threshold dose of X radiation that induces cataracts in humans is between 200
and 500 rad for a single exposure and around 1000 rad for exposure spread over a period
of several months (National Research Council, 1983). In comparison, an operator
exposed to 0.01 mrad/h would absorb less than 1 rad in 40 years of work at a CRT screen.
Likewise, the level of ionizing radiation generally believed to increase significantly the
risk of birth defects is more than 1 rad for acute exposure. In contrast a worker exposed to
CRT screen work would absorb 14 mrad over a period of 9 months. There are indeed
many other items in our daily lives which generate more X radiation than CRTs,
including brick walls and self-illuminating dials on wristwatches.
One remaining concern is the effect of electromagnetic radiation on CRT screen
operators. There is a lack of basic research to prove the effect of electromagnetic
radiation on laboratory animals and organisms in general. However, some research
indicates that railway engineers, who are exposed to a large amount of electromagnetic
radiation from overhead power lines as well as train engines, may have an increased
health risk of leukemia and pituitary cancer (Floderus et al., 1993). It is however unlikely
that CRT screen operators, who experience much lower radiation levels, would be at any
risk.
14.5
REDUCING REFLECTIONS AND GLARE ON CRT
SCREENS
A special problem with CRT screens is that glare and reflections on the screen can make
the text difficult to read. Several national and international ergonomic standards have
proposed guidelines for designing workplaces so as to maximize the visibility of the
screen (ISO, 1998).
As the illumination level in a workplace increases, so will the amount of glare on the
screen. The ideal working environment for screen viewing is a pitch-black room. The
absence of illumination will enhance the screen contrast and make characters very
visible. However, this is not very practical since there are other important tasks which do
require ambient illumination, including communication with coworkers, and the need to
see characters on the keyboard. There are several ways of reducing reflections on a CRT
screen (Table 14.1).
TABLE 14.1
Seven Ways of Reducing Screen
Reflections
Location
Measure
At the source 1. Cover windows partially
2. Place light fixtures strategically
3. Use directional lighting
At the workstation 4. Move the workstation
