Just reading an article in New Scientist on the harmful effects of radiation. It looks very much as if the common fear of almost any radioactivity is misplaced. We are all exposed to a background radiation level of about 2.5 millisieverts per year. Legal limits run to about 3.5 millisieverts per year. But this seems to be ridiculously low. The clue comes from studies of survivors of the Hiroshima and Nagasaki bombings. A lot of people got hit with very high radiation doses, and their cancer rates were high, as we would expect. But it turns out that everyone who got hit with a single dose of 100 millisieverts or less showed no health problems at all, compared to people from other Japanese cities that were not bombed. The author of the article suggests that 100 millisieverts should be taken as the threshold, below which radiation is harmless, and suggests a new legal maximum of 100 millisieverts per month. By comparison, during radiotherapy for cancer, normal tissue is exposed to 20 sieverts radiation, spread over a period of about 5 weeks. It appears to do no measurable harm. 40 sieverts, focussed on the cancer, kills the cancer tissue. So 100 millisieverts per month would seem to be quite safe. Basically, if we get paranoid about radiation, we should realise that we need a lot more than 40 times the normal background radiation dose, delivered in one hit, to harm us. In this light, the levels of radiation that come to us from nuclear power, are harmless. Even small leaks of radioactive material, as have happened at places like Sellafield, are in fact, totally harmless. Only a major event, such as Chernobyl can harm us. And such events can be prevented with a little care.