In this day and age of measuring radiation in "sieverts" at Fukushima I Nuke Plant, anything that measures in "millisieverts" seems like a low radiation and doesn't even make the news.
Still, TEPCO's latest "survey map" (contamination map) of the plant shows a radiation from bits of concrete at 950 millisievert/hour on the west side of Reactor 3 (in the map, right below the Reactor 3 building). There's also a 550 millisievert/hour concrete block on the west side of Reactor 2, which may have flown from Reactor 3.
Spend 15 to 30 minutes handling these concrete bits, and your maximum radiation dose of 250 millisieverts as a radiation worker at Fukushima I Nuke Plant will be reached. For handling the 950 millisieverts/hr concrete bits, radiation workers in France would exceed their level of 20 millisieverts per year in slightly over a minute. For the US radiation workers, their 50 millisieverts per year would be reached in less than 4 minutes.
(The link to TEPCO's survey maps is posted on the right-hand column of this blog.)
And here's the picture of the 950 millisieverts/hr concrete bits, from TEPCO. "12 mSv/hr" dose shown on the card attached to an orange cone is clearly the air radiation: