Radiation Exposure Guide: How Much is Too Much?

Radiation Exposure Risk Explained

As Fukushima Daiichi continues to leak radiation, a 30-mile no-fly zone was set up around the reactor site. Residents within 10 km of the nuclear power plant have been evacuated. Residents living between 10 and 30 km of Fukushima Daiichi have been told to stay indoors. Sales of Geiger counters have soared. If you live near Fukushima Daiichi and you bought a Geiger counter, make sure you know how to use it: How to Read a Geiger Counter.

How much radiation exposure is too much? While it's true that we are exposed to radiation all the time, the amount is tiny. Absorbed radiation is measured in millisieverts (mSv). An eight-hour flight exposes you to .085 mSv. A chest x-ray exposes you to 10 mSv.

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Radiation Levels at Fukushima Daiichi are Dangerous

The maximum level of radiation detected at Fukushima Daiichi has been 1,500 mSv (1.5 sieverts), with exposure levels at 400 mSv per hour.

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According to the World Nuclear Association, 1,000 mSv (1 Sv) is the threshold for causing immediate radiation sickness over a short period of exposure, but will not be fatal. Still, that level of radiation is dangerous: those exposed can face illness and health problems later in life.

By comparison, employees killed by the Chernobyl meltdown had radiation doses measuring 6,000 mSv (6 Sv); such a dose is fatal within a month.

Japan's official nuclear monitoring site keeps timing out, probably because it wasn't set up for this much traffic. The Guardian points us to Marian Steinbach's crowdsourced radiation level database. Maggie Koerth-Baker at Boing Boing is also compiling some statistics. Her work is conveying radiation measurements in Rem: 1 Rem = 10 mSv, or 1/100 Sv.

Beware Folk Cures for Radiation Exposure

While there are foods with naturally-occurring iodine, eating them will not serve as a substitute for iodine tablets, which stock the thyroid with inert iodine and crowd out radioactive iodine isotopes.

Banana Equivalent Dose

Someone is going to mention bananas, so we'll get that out of the way. The BED (banana equivalent dose) is a concept of radiation risk assessment based on radiation given off by bananas. Eating one banana per day for a full year will expose you to a cumulative 36 μSv (.036 mSv), which is not anywhere remotely close enough to give you cancer (or turn you into The Hulk). Comparing Fukushima Daiichi to bananas is basically silly, due to the extreme difference in scale.