If in Pripyat, exercise caution when entering buildings—the ground around entrances to, and inside buildings will generally be littered with broken glass, concrete and debris. Be sure to take care inside buildings as the flooring can be be somewhat uneven and sometimes unstable. Watch your footing—a decent pair of shoes/boots would be a good idea.
The levels of radiation on guided tours are relatively small; radiation levels in most places are less than those of being in an aircraft flying at 30,000 feet. The main danger is not in the radiation itself, but in particles of radioactive materials that may remain on your clothes or items.
A lethal dose of radiation is in the range of 3 to 5 sieverts 300 to 500 roentgens when administered within an hour. Levels on the tour reportedly range from 0.15 to several microsieverts per hour 15 to several hundred microroentgens an hour. A microsievert is one-millionth of a sievert.
Example: On a six-hour trip arranged in October 2008 the total dose was 4 microsieverts according to the meter 400 microroentgens. This was less than the total dose of the connecting two-hour flight, which was 6 microsieverts 600 microroentgens. Radiation levels by the power plant were 1.7 microsieverts per hour 170 microroentgens per hour and they varied between 0.4 and 9.5 microsieverts per hour 40-950 microroentgens per hour in the Pripyat amusement park. Thus, risks are pretty much non-existent as long as you don't get yourself contaminated.
Stay on roads, the radiation levels on areas covered by vegetation are significantly higher. Even more important, the risk for contamination when walking amongst vegetation is higher because it is more difficult to avoid touching or inhaling anything. Radiation ends when you leave the place, but you don't want radioactive elements inside your body. Follow common sense if you are on your own; if you see an area marked with a radiation sign, the meaning is clear: DON'T GO THERE.
The International Council on Radiation Protection has a recommended annual limit of 50 millisieverts 5 rem uniform irradiation of the whole body for nuclear plant workers.
Clinical effects are seen at 750-2000 millisieverts 75-200 rem when administered in a short time scale.
Since the levels are microsieverts 10^-6 the exposure level is very low. But it is still possible to be in contact with some very hot surfaces, so caution should be stressed.Note: One rem is equal to 1.07 R roentgen, or 0.01 sieverts or 10 millisieverts.
