.Here is a partial plot of radiation rates at the main gate and other locations around the nuclear plant at Fukushima Daiichi.
Click image for larger versionThe peaks at 12,000 microsieverts/hour corresponds to 1.2 rem per hour. Less than two hour's exposure at this rate would be equivalent to the maximum occupational exposure limit for an entire year (2 rem). A day's exposure would be quite unhealthy. Several days could cause acute radiation sickness.
(The occupational exposure limit for emergencies is 10 rem. This has been increased to 25 rem for Fukushima. After workers reach this limit, they cannot return to the plant.)
Note that these peaks were measured at the main gate -- a long way from the reactors themselves.
CNN is reporting tonight that a radiation exposure rate of 20,000 microsieverts/hour has now been recorded. The highest peak so far. Things don't seem to be getting better.
The original data on the chart is from the plant operator Tokyo Electric Power Company (TEPCO), and was plotted and analyzed by the German organization Gesellschaft fuer Anlangen- und Reaktorsicherheit (GRS) mbH.