Using Wind Data to Estimate Fallout Risk

People observing the nearby Small Boy test in the NV desert, 1962.
People observing the nearby Small Boy test in the NV desert, 1962.

This is the first part of a three-part article that looks at how to calculate the potential impact on your retreat location of the release of radioactive material somewhere else.  In other words, if a nuclear explosion goes off, or a nuclear power plant has an accident, some distance from you, how will that affect you at your retreat?

After you’ve read this first part, please follow the links on to parts two and three, including some worked examples and links to the resource materials you need to do your own calculations and planning.

Once you have started to zero in on an area for your retreat, you then start considering reasonably local issues such as the potential risk of radiation/fallout from nearby nuclear power plants, in the unlikely event something might go wrong with them, and similarly from any probable nearby targets in the event of nuclear war.

Sometimes you can just simply look at a map showing potential risks and guess as to if you’re safe or not.  You don’t need to do too many calculations to understand that downtown DC is probably at great risk of some type of nuclear event, if/when TSHTF.

Unfortunate, there’s no opposite situation where you can instantly tell by a quick glance at a map that any given area is clearly completely safe.  Plus or minus a hundred miles or so, nowhere in the US is more than 250 miles from either a nuclear power station and/or a possible nuclear target in a high intensity conflict.

Although 50 miles is more than enough distance to survive the immediate heat, blast and radiation effects from a nuclear explosion, the fallout radiation implications can be very different indeed.  As we mentioned in our article about the safety of nuclear power stations. dangerous radiation levels as a result of the Chernobyl disaster occurred in what seemed to be a semi-random manner as far as 300 miles away, and radiation from the Fukushima disaster made it all the way across the Pacific to the US.

Note our italics for the phrase ‘what seemed to be’ – because, of course, there is underlying scientific sense that applies to the observed fallout pattern from Chernobyl.  This article series talks about these issues.

Radiation – A Quick Refresher

We discuss the five most common types of radiation in detail in our article on Radiation and Fallout Risks.  Radiation itself is generally both extremely short-lived and also usually only capable of traveling short distances and easily blocked by most things (quite the opposite of public perception).  There is one notable exception to the easily blocked issue – neutron radiation, which while limited in distance to several miles, can penetrate quite a lot of shielding during the course of its travel.

The initial release of radiation from a nuclear explosion is very intense, but only harmful to people within a few miles of the explosion.

The bigger problem is that as part of the nuclear explosion, some of the radiation released will react with non-radioactive materials, and make them become radioactive in the process – that is, they will then start steadily emitting radiation for some time into the future – maybe only hours, but possibly also days, weeks, years, or even centuries.

The second part of this problem is that the heat and blast of the nuclear explosion will turn whatever these things are into finely powdered dust/sand/dirt type particles and then, via the blast wave, propel them long distances.

These tiny particles of now radioactive dust are what is known as fallout and represent the biggest problem that most people will encounter as a result of a nuclear explosion.

So for us, hopefully having located ourselves safely away from the immediate effects of the initial heat, blast, and radiation burst from the bomb, our concern is to do with the fallout.  As you know, normal dust can go anywhere and get anywhere, and if there is radioactive dust falling in your area, it will have the same ability to spread out and cover surfaces, to hang suspended in the air, to be kicked up into dust clouds when the wind blows, and so on.

Furthermore, while the radiation it releases might be weak, there’s one huge danger, and one more insidious danger.

The big danger – if you ingest the dust – by breathing, or if the dust gets onto food or into water – you then have radioactive substances inside you, where there is no distance and no barrier protecting you and your organs from the full effects of the radioactivity.  Even the weak radiation that can only travel a few inches and be blocked by a sheet of paper is now hitting and harming your internal tissues and organs.

The more insidious danger is that low levels of radiation being emitted from fallout may also be fairly long-lived, and so over a period of months (or years) their effects will start to accumulate and cause problems.

So you really want to avoid being in an area with radioactive fallout.

Three Types of Nuclear Explosion

When evaluating your fallout risk, you need to know whether the initial ‘event’ that creates the radioactive fallout will create a little or a lot of fallout, and whether this fallout will be propelled way up into the jetstream or if it will stay closer to the surface.  The ‘jetstream’ is (are) fast-moving bands of air, situated somewhere between about 22,000 ft and 52,000 ft above the ground, and traveling at speeds of anywhere from about 60 mph up to sometimes in excess of 250 mph.

How do you determine the answers to these questions?  You need to decide if the nuclear blast will most likely be an airblast, a surface blast, or a sub-surface blast.


Airblasts are the most common sort, and happily create the least amount of fallout, because the fireball from the blast is mainly above the surface of the ground, and doesn’t impact on as much ‘stuff’ to vaporize and transform into radioactive fallout.  Even more happily, the fallout they do create tends to go up into the upper atmosphere, where it might get caught in the jetstream.

If the fallout gets into the jetstream, this will quickly whisk it away from the site of the blast, and by the time the particles start to drop out of the jetstream again, they may have traveled anywhere from a few hundred miles to many thousands of miles.  The good news is this means the fallout gets dispersed over a very wide area.  The bad news is that while you might not be at risk from a nearby blast, you may get a small amount of fallout from far away blasts (for example the jetstream took fallout all the way from Japan to the US after the Fukushima power plant problem).

Even if the fallout particles from an airblast do not mix into a jetstream, the simple fact of throwing them up a long way means they’ll spread out over a greater area than if they were not thrown up as far to start with.  You can see this for yourself with a simple thought or real experiment.  Take a handful of rice, hold it a couple of inches above the floor, and then drop it.  See where it lands and how it spreads out.  Now, after cleaning up your mess, take a second handful of rice, toss it as far into the air as you can, and see where it lands.  It will be much more spread out, won’t it (good luck with the cleanup!).

Surface Blasts

These are the nastiest of the three types of nuclear explosion.  The initial fireball from the blast is, by definition, right on the ground (or within 100 ft or so of the ground), and will be vaporizing literally tons of material – buildings, dirt, people, anything and everything.  A massive amount of fallout is created.

Much of this fallout does not get thrown as far up into the atmosphere, and will fall back down to earth without reaching the jetstream.

So a surface blast has two severe consequences (compared to an air burst).  The first is the creation of massively more fallout material; the second is that this material is not distributed thinly (and almost safely) over a wide area, but is concentrated in a dense and potentially lethal area, within a few hundred miles of the explosion.

Subsurface Blasts

If the enemy is trying to destroy hardened bunkers, and possibly missile silos, they may use bombs that are designed to penetrate a distance into the ground before exploding.

The best case scenario would be a bomb that traveled so far into the ground before detonating that the earth above it contained the full effects of the blast.  This is what happened most of the time with underground testing of bombs – sure, you’d see the surface rise and blister some, and the shockwave would cause dust to rise from the surface, but it would be non-radioactive dust, and if the calculations were correct, the covering of earth above the bomb would contain the force of the explosion.

However, it is unlikely that missile penetrators would go that deep.  A shallow subsurface blast might actually be even worse than a surface blast, because more of the fireball will interact with material rather than the top half of it less harmfully going upwards into the sky.  A bit deeper and the effects would be similar to a surface explosion, and deeper again and the amount of fallout sent up into the air would start to reduce, as would the height it reaches and therefore the distance it travels.

Nuclear Power Plant Failures

In the case of a nuclear power plant failure, it is likely that the failure will not be akin to a nuclear explosion, but rather it will be some sort of secondary effect caused by runaway heat causing fires and steam buildup (which might possibly then burst through a containment external barrier with explosive force) and the effects of fire and heat and steam releasing radioactive material.

This is most likely to mirror the effects of a surface or subsurface blast, although we again look at the Fukushima event and learn from it – the explosions it experienced sent some radioactive material all the way up into the jetstream.

At the risk of massively oversimplifying, we’re going to say ‘forget about radioactive material that makes it up into the jetstream’; because most of that material goes anywhere and everywhere.  Having happily forgotten about that, we still have to face the remaining reality – ie, that nuclear power plant failures risk releasing potentially large amounts of radioactive fallout type material that will be deposited in the several hundred miles around the plant.

What Type of Blast to Expect

As a quick rule of thumb, attacks on civilian structures will be air bursts because they create the most blast damage over the greatest amount of surface area.

Attacks on hardened (ie military) structures are more likely to be ground or subsurface blasts, because an airburst may not be sufficiently strong to destroy them.  If it is simply an attack on a place with massed troops or equipment, it will probably be an airburst.  Only if the target has unusually strongly constructed buildings will an enemy feel the need to transition from an air burst to a ground burst.  Unusually strongly constructed buildings might include ammunition bunkers (especially if likely to contain nuclear munitions) and some types of airplane protective hangar.

Attacks on bunkers and other underground facilities will definitely be sub-surface.

Continued in Parts Two and Three

Please now click on to the second part of this three-part article series.  Part two explains how the two different types of winds will interact with the fallout and how we can calculate the effect they will have on our retreat location.  The third part then looks at sources and types of wind data you can obtain to work out the impact on your retreat from radiation releases in other places.

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