acmesalesrep says: Worldwide, the average dose rate due to naturally occurring background radiation is about 0.3 µSv/hr (the “per hour” being significant as the sievert is a unit of dose, not dose rate). This can vary significantly depending on local geology, altitude, etc. I don’t know what the normal background rate in Tokyo is—and without that information, this picture is pretty much meaningless.
» We say: You’re right, we should’ve provided that information with the photo. Here’s a piece from AFP that explains the levels: “From Tokyo officials said they had detected 0.809 micro-sievert in the morning and 0.075 four hours later — compared with a normal radiation level of around 0.035. A chest X-ray typically involves a dose of 20 micro-sieverts.” (I double-checked and the levels are “per hour.” AFP just screwed up and didn’t mention that part of the equation.) The fact that it went up is the “minorly” shocking part – and the photo didn’t even show the radiation levels at their peak. But it’s a level so low that officials didn’t seem to think it was dangerous. This chart here shows this in perspective, starting with the X-ray.