The American Civil Defense Association recently posted a blog post about Radiation Issues reposted from their Journal of Civil Defense after many readers had questions regarding North Korea.
The nuclear threat from North Korea has prompted many callers during the past few weeks, asking about the effects and attenuation of radiation. There is a great deal of misinformation about radiation from fallout. The following old rule of thumb for shelter design still holds true. NBC shelters should have four feet of dirt cover, or three feet of concrete cover to give a minimum PF level of 1,000 from fallout. If a “rainout” should occur, or if the sheltered area is within 1.5 miles of a potential primary target, the shelter will require a minimum of eight to ten feet of cover. Shelter entrances require careful engineering, as most of the radiation exposure will come from these entrance areas.
I recently reviewed a series of articles about Nuclear Weapons Effects, written by Carsten Haaland, of the Oak Ridge national Laboratory. The entire series of articles can be found in our Journal of Civil Defense published in 1990. Some of you may be fortunate enough to still possess these journal articles. I have re-typed, in part, the section on ‘Fallout’ and ‘Rainout’ for this current article.
FALLOUT FROM NUCLEAR DETONATIONS
Carsten M. Haaland, Oak Ridge National Laboratory
What is Fallout?
Fallout is the radioactive dust that comes back to earth as a result of a nuclear explosion at the surface of the earth, or at an altitude low enough for the fireball to engulf solid materials. Fallout dust may look like sand, ash or crystals, depending on the kind of material engulfed by the fireball. If the material engulfed is ordinary earth or sand the fallout will look like sand, but if the engulfed material contains calcium to the extent found in concrete buildings or coral, the fallout may look like ashes. Large dense particles will descend faster than very small particles. For this reason, fallout particles several hundred miles downwind from a nuclear surface burst will be very small, somewhat like particles in atmospheric pollution, and the nuclear radiation from the fallout will be greatly reduced.
The danger of fallout arises from the intense and highly penetrating nuclear radiation emitted from it, which produces a potentially lethal hazard to people in the vicinity unless they have protection. Large areas, covering hundreds to thousands of square miles, depending on the yield and number of surface detonations, can be poisoned with fallout such that radiation from the contaminated area is hazardous or lethal to an unprotected person passing through or dwelling in the area, for periods of days to weeks after the detonations.