Here is what I said:
Hey. Calm down. Have a seat. I just want to talk to you to help you calm down. There are a lot of things to be concerned about, but there is no reason to get crazy about this 750 RADS thing you hear. There are people out there throwing these numbers around, moving decimal points three ways to one side or another, not realizing they are doing it, mistaking millicuries for curies, Rads for millirems, sieverts for grays, and so on. Look. Don't get crazed. When someone tells you that 750 Rads are going to contaminate an area, it is nonsensical. The units are wrong. It is like telling someone they need a kilometer of flour to bake a loaf of bread. It is nonsensical and irresponsible, because it is scaring the crap out of people.
Here's the thing. A Rad measures the amount of absorbed radiation on something. Not the amount of radiation, but the amount of energy transferred to something, typically human flesh. (note, you may hear someone refer to rads and rems...for the purposes of human flesh and discussion, they both mean about the same thing...so we will just stick to "rads" because that is what you hear out there a lot) Basically, a Rad measures EXPOSURE to radiation.
If you hear someone mention curies, millicuries or megacuries, that is an amount of decays of an isotope in a given amount of time. When you know what the isotope is, and you know how much energy or what kind of energy is given off when that particular isotope decays, then you have an idea how much radiation there will be.
When you know THAT, then you can figure out how much exposure human flesh will get in a given amount of time when exposed to certain levels of that radiation, and that exposure is measured in Rads.
Now. Here is the thing. EVERYONE gets exposure to radiation, and when your tissue absorbs that radiation, you get exposed to a certain amount of rads of radiation. We ALL get exposed. The average annual exposure to the average person living on this planet is 310 millirem. That is very, very small. That is .31 Rads, spread out over a year. Think of it as eating a cup of salt. Would it be bad for you if you took a cup of salt, mixed it in a glass of water and drank it in one minute? You bet it would be bad. But if you eat that cup of salt over the period of a year, you would probably be fine, but if you eat that much all the time, you will probably have cumulative problems from it, right? Radiation is the same. If you get it spread out over time, it isn't that bad, your body fixes it, but a fair amount over time might have cumulative effects.
I worked in nuclear medicine for 15 years, and I was allowed to have up to 5 rads (that is 5,000 mrad, but we refer to it as mrem or a millirem) a year of exposure to my body. I could have a lot more than that to my hands, which I probably did. But I was allowed to get up to 50 Rads (that's 50,000 mrad!!!!) over the course of a year to my hands because you don't have much in your hands that can be damaged by radiation. I am still here. And I worked with people who handled radiation at much higher levels than I did, and they are in their eighties now, without a problem.
The have a measurement they use called the "LD50/30" dose. It means, the amount of radiation (Rads) that a person can get at one time, all in one shot, that will give you a 50% probability of being dead in 30 days. That amount of radiation is about 600 Rads, more or less.
The 750 Rads came from some graphic that was posted a few hours after the emergency began. I have no idea who created it but I did see it; they had, like a weather map, charted the projected “fallout zones,” assuming a giant plume of big, uniform areas that managed to catch the Jet Stream and dump uniformly hot particulates on every square inch of the West Coast. The first thing that occurred to me was how no plume model I’ve ever seen for a reactor accident would support anything remotely like that kind of absolute, cartoon-like continuity of emission strength over thousands of miles. Ridiculous.