Rules on Nuclear Fallout

I have been thinking about posting more information on nuclear fallout so today I will explain the seven – ten rule of nuclear decay.

Assume that a one Megaton Bomb blast occurs and you are sheltered or far enough away to survive the blast.  If fallout of one thousand Rads arrives at your location 1 hour after the blast, you have to be sheltered.  A four hundred and fifty Rad accumulative dose can kill you, so one-half hour of unsheltered exposure can be fatal.  If you have shelter and are using the seven – ten rule you will know that after seven hours the outside rate will drop to 100 Rads per hour.  In another seven times seven hours or forty-nine hours, it will have decayed down to 10 Rads per hour.  Then using the rule of seven times forty-nine hours which equals approximately two weeks it will be down to one Rad per hour.  You need to stay sheltered until it drops to one-half Rad per hour, and that takes about twenty-five days total.

If you are lucky and the Rate is only 10 Rads per hour in your area, then seven hours after the blast it is down to one rad.  Forty-nine hours after the rate is down to one tenth of a Rad and you can leave the shelter.

At this point you may want to review my post on Protection Factors in Nuclear Emergencies.  This will explain how shelter reduce your rates of exposure.

A definition of a Rad (radiation absorbed dose)

The rad is a unit used to measure a quantity called absorbed dose. This relates to the amount of energy actually absorbed in some material, and is used for any type of radiation and any material. One rad is defined as the absorption of 100 ergs per gram of material. The unit rad can be used for any type of radiation, but it does not describe the biological effects of the different radiations.

See also  Nuclear Fallout and (EMP) Electromagnetic Pulse

I will post more on this subject in the future.


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5 thoughts on “Rules on Nuclear Fallout”

  1. Matt in Oklahoma

    Well then i’m probably hosed cause i dont have anyway to filter a month worth of air so exposure is gonna happen. I can mask up but 25 days, whew dunno, spent less than a day in them during training and that was tough trying to operate much less 25 days. MOPP suits dont last that long either and i dont have changeouts. I’m looking at cheaper more availible tyvex but again i gotta have enough to change out cause a folks gotta number 1&2. Guess i could go to rainsuits, stay indoors and hope for the best, sucky plan. Not sure if I have enough fresh water for decon and changeouts on hand though. Proper changeout is hard and remember many a disgruntled NBC NCO.
    Getting old enough that the iodine pills are questionable on effectiveness but i keep a fresh supply for the “kids” cause even survivalist kids have limits as to what they believe or will do LOL. Crazy ole dad
    ahh well if’n i go, reckon i’ve had a good life, but I aint going silently and without the last struggle thats for sure:)

  2. Matt it is not as bad as it sounds, get a copy of Nuclear Warfare Survival Skills by Cresson Kearney. Best book ever written on the subject and tells you how to improvise most of what you need. Air filtration is not that big a deal, the book explains how to handle it, you wont have to mask up unless you leave the shelter.

    1. Matt in Oklahoma

      I’ve read it and several others and i hope they/you are right.
      Based on things i saw stationed in Europe during Chernobyl i’m just not to sure about that. Fallout is a dust. When you dust your house most of what you are dusting came from outside. I see folks putting plastic up, taping windows etc which is good but no matter what you have to filter the air which is where most fail at IMO. We saw alot of changes where we were in things where we were “safe” by standards. The color of fresh eggs yolk was one of the first things we noticed.
      dunno maybe i’m overly sensitive (paranoid) but i didnt get thataway by myself neither

  3. Matt
    Just remember that after the atomic bombs were dropped on Japan they took no protection against radiation and a surprisingly large number of people survived. Admittedly quite a few developed cancers later in life. So my plan is to do the best for the kids and if anyone needs to get exposed it will be me.

  4. Thanks for the post, Howard. Jacqueline Druga has written a fictional book called Dust that was pretty interesting. Barbara Griffin Billig also wrote one: The Nuclear Catastrophe. Billig’s book, written years before Fukushima, has many parallels to the Japanese disaster. My wife, Laura, has written a couple of reviews if you’re interested.

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