Answer to Question #1470 Submitted to "Ask the Experts"

Q

I'm thinking about building a shelter attached to my basement with a "baffle" and walls and roof made of 16-inch reinforced concrete. The 16-inch roof would be at ground level. Is this enough protection from a 10 kiloton nuke or dirty bomb? No one can answer whether you need 16 or 24 inches of concrete. Two feet would mean a lot more money and work!

A

There are a few questions to ask yourself before embarking on a project like this: "How likely is it that I'll need to use a shelter?" "How far away do I think a bomb will explode?" "Do I want to protect against a nuclear weapon blast, fallout, or a bomb laced with radioactive materials?" "What level of assurance do I want to have that I will be safe?" "What about filtering air and water?" "How long do I plan to stay in the shelter?" "What's the probability that I'll need to use a shelter in the first place?" The answers to these questions are critical to the design of any shelter.

First, you have to recognize that your shelter will not protect you against a direct hit. So if you are living next door to something that you're certain is a high-priority target, you might want to invest your shelter money into, say, a new house that's a little farther away. You also should be aware that, after any explosion, the greatest risk is from airborne radioactive fallout, so filtering the air into your shelter could be important. Other logistical matters include making sure you can remain safely in your shelter until it's safe to come out (might need a radiation detector to measure radiation levels)—it would be discouraging to die of hunger or thirst while waiting for the air to clear! However, this is perhaps a bit unnecessarily grim. In fact, many people in Hiroshima and Nagasaki were walking around within a few miles of the blasts without much protection at all very shortly after the weapons went off. Some (especially the ones closest to ground zero) became ill, but many did not. Radiation levels from the blast itself drop off rapidly with increasing distance, and fallout is also lower as you move away and/or upwind from any blast. Simply transiting a contaminated area to get to safety will probably not expose you to a harmful amount of radiation, assuming you are far enough from the blast to survive that.

You should also be aware that radiological weapons (such as placing a lot of radioactive cobalt, say, wrapped around a lot of explosive) are more likely to be inconvenient than lethal because dispersing radioactivity over a great area will necessarily reduce the dose rate in any one location, while concentrating the radioactivity in a small area (to try to hurt people) reduces the number of people affected. To be honest with you, my personal plans do not include building a shelter against the possibility of radiological attack. If I find that an attack has taken place and that I've been exposed, my first action would be to put on some sort of mask to filter out radioactive dusts that I could inhale. Next, I'd find out where the attack took place, and I'd try to find out which way the wind was blowing. Then, I'd drive at right angles to the wind direction to get out of the plume as quickly as possible and, after a few miles, I'd turn in the direction of a family member or friend whose home was unaffected. If you do build a shelter, the amount of radiation attenuation given by 16 inches of concrete (compared to 24 inches) is a factor of 2 or so, depending on the composition of the concrete. So the extra inches can make a difference. And, if you build a shelter, please have the design checked out by a professional—it would be a shame to have it cave in on you or collapse after a few years.

A good general reference for this type of information is The Effects of Nuclear Weapons by Samuel Glasstone and Philip Dolan, published in 1977. When you get to the Government Printing Office site, go to "Catalog of US Government Publications" and do a search under Glasstone. The book is unclassified and has a lot of fascinating information. The Federal Emergency Management Agency (FEMA) has a number of documents available on fallout shelters and another source of information is Nuclear War Survival Skills Web site. I also suggest you read Ask the Expert Question/Answer 1141.

Andrew Karam, CHP, PhD