The wartime military nuclear occupation types use a rule of thumb for calculating personnel radiation exposure called the FIT forever rule. This rule essentially states:
The total radiation exposure, if you stayed in the radiation area forever equals five times the intensity of the radiation at the time of entering the radiation area times the time since the nuclear detonation.
I have a quibble with this with the definition of time since detonation. In reality, all that stuff that goes up (people, bridges, grocery stores, etc) takes a while to come back down. In fact, a significant level of injure and death is caused by people staring up at the mushroom crowd, only to be hit be rocks, cars, and other hard objects. Think Tornados. We will talk about this in Part 4. The definition of time you should use is H+1 or H+2, depending on the size of the bomb. The real definition will be based on the disaster broadcasters that will give you the time of maximum radiation in your area. That would be H-max. If you dont have H-max then use one of the other Hs.
The FIT forever calculation is used as follows:
Given example -- H occurs at 9:00 am 0n 9/11/12.
Hmax occurs at 10:30am on 9/11/12
The intensity at Hmax is about 3000 rads/hour
If you can stay under good cover, essentially radiati0n free until
T = 5:30pm 9/11/12
After 7 hours, or at 5:30, the radiation level will be about 300Rads/hour
You would recieve: 5 x 300 Rads/hour x 7 Hours
or 10,500 Rads if you stayed forever, enough to bring you to room temperature.
If you re-entered the shielded area at 12:30 am on 9/12/12,
and stayed forever, you would avoid 5 x 30 Rads/hour x 14 hours or 2,100 Rads
To continue, if you had stayed shielded until 6:30 on 9/12/12, you would accumulate a radiation dose of 5 x 3 Rads/hour x 21 hours or 315 Rads for the rest of your life. This is quite survivable, assuming you limit radiation input later in your life. As further example: If you stayed under cover for a day and a half, you would have a lifetime exposure in that area of less than 5 Rads, which brings you into the peace time radiation worker exposure ranges. Calculate it yourself. If you can, you pass.