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Wind.

Right. Most of the radiologicals that have been released with the steam have very short half lives so the radiation levels drop rapidly (relatively speaking).

I would point out that the dangerous stuff that is there is iodine(-131 IIRC) with a half life of 8 days and since it can give you thyroid cancer it is not "safe" until it virtually is gone at 80 days; and cesium-137 with a half life of 30 years, a gram of which can kill you.