According to the International Basic Safety Standards an accident is “any
unintended event, including operating errors, equipment failures or other mishaps, the
consequences or potential consequences of which are not negligible from the point of
view of protection or safety” .
A radiological accident is defined as an unforeseen event involving overexposure
or contamination of persons and/or the environment by radioactive material.
Exposure may have actually occurred or only be suspected. This distinction is important
because experience has shown that it is safer and less costly to put an accident
plan into operation when an accident is suspected, rather than wait until its occurrence
is established. Although infrequent compared to conventional accident situations,
occurrences over the past five decades have provided sufficient data to develop
guidelines for medical management of radiation casualties.
Although the March 1979 incident at Three Mile Island in the United States of
America created tremendous public concern, it caused no radiation injuries. Because
of the integrity of the containment vessel, and in spite of a fuel meltdown, the contamination
outside the reactor building and the release of radioiodine were negligible.
By contrast, the major nuclear and radiological accidents at Chernobyl, Ukraine, and
Goiânia, Brazil, have provided important information for the diagnosis, monitoring
and treatment of radiation injuries. The explosion of vapour in April 1986 at the
Chernobyl nuclear power plant, which had no containment vessel, resulted in the hospitalization
of 237 patients identified as having been overexposed. Of these,134 developed acute radiation syndrome (ARS); 28 of these patients eventually died
of ARS associated with extensive radiation burns .