How do scientists determine when your health is at risk due to the
amount of radiation in the air? First they measure the amounts and
translate those measurements into levels that they know have caused
biological harm in the past. They have learned from longitudinal
studies of people in the paths of Hiroshima, Chernobyl, Three Mile
Island, and many smaller-scale, but serious, incidents of radiation
exposure. Here is a look at the basic radiation measuring scheme and
how other variables can affect biological dangers from radiation.