Dirty Bombs – Myth versus Fact


There have been a LOT of stories about radiological terrorism in the news lately. We heard that ISIS was surveilling Belgian nuclear power plants, that they killed a nuclear worker to steal his identification, and even that they might be using “nuclear” drones to drop radioactive materials from above upon the unsuspecting. What is often missing in these stories is a realistic – that is, a scientifically informed – discussion about how dangerous attacks such as these might actually be. There is a broad assumption in the press and among the population as a whole that any radiological attack is likely to lead to untold deaths; from radiation sickness in the short term and from radiation-induced cancer over the ensuing decades. As a long-time radiation safety professional, these assumptions are amusing at best, insulting at worst. Not only that, but these assumptions can lead us as a society to make decisions regarding radiological attacks that could be ruinously expensive and disruptive both socially and politically. In this editorial (and hopefully in follow-on pieces) I would like to address some of these concerns to help you sort out what you really need to worry about.

Radiation health effects

The biggest worry about any exposure to radiation is that it’s going to hurt us somehow. We’ve all seen pictures of radiation injuries, children deformed by their parents’ exposure to radiation, not to mention cancer – or worse, if popular culture is to be believed. And the thing is that all of this (well, with the exception of the fictional effects) can happen. What isn’t well-known, though, is that it takes a lot more radiation exposure to cause these problems than most people would believe. For example – while radiation CAN cause birth defects, a single x-ray procedure (even a high-dose procedure such as a CT scan) is almost invariably
incapable of harming a developing baby. Similarly, while radiation can cause cancer, even a dose of radiation high enough to give a person radiation sickness (about 1 Sv or 100 rem) has only a 5% risk of developing a fatal cancer. I acknowledge that this is not trivial – but I also feel obligated to point out that there’s a 95% chance that this exposure will be survived, as well as that any cancer that might result from this exposure won’t show up for at least a few decades. In any event, health effects are certainly something to be concerned about, but they are likely to be far less of a concern than most would believe. And this risk, about 5% per Sievert, is a number to keep in mind.

First, though, let’s back up a little bit and talk about what the radiation actually does to the body. When radiation enters our bodies it can strip electrons off of atoms, creating an ion pair. This ion pair can cause chemical reactions that can produce reactive molecules (free radicals) that can attack and damage the DNA. Our bodies have well over 100 genes that can repair DNA damage – most of the time this damage is repaired without problem; a fraction of the time the damage isn’t repaired at all or is repaired improperly, causing a mutation.


These mutations can be harmful, but the great majority of the time they have no impact at all on the organism. There are a number of reasons for this (a bit too much to discuss here) – but part of the answer is that there are only a few very specific types of mutations that can actually lead to cancer; any other sort of damage simply can’t do so. So these two factors – the fact that our bodies are quite good at repairing DNA damage and the fact that there are only a few specific types of DNA damage that can lead to cancer – help to explain why radiation, while it is a carcinogen, is considered to be a very weak carcinogen. It takes much more radiation to cause cancer than most would believe.

If someone is exposed to a high dose of radiation in a short period of time the major concern is for the acute effects – will they develop, or even die of, radiation sickness over the next few weeks or months?

All of these short-term effects happen only when a person is exposed to a specific dose of radiation. By analogy, think of standing in water. If I’m standing in water up to my ankles, will I drown? Of course not – in fact, I can be standing in water up to my chin and I won’t drown (as long as I don’t fall over). It’s not until it reaches my nose that I’ll succumb. Similarly, I am not going to develop radiation sickness until I get almost 1 Sv (100 rem) of exposure and my chance of death from radiation sickness is virtually non-existent until the dose reaches at least 2-3 Sv (200-300 rem). Without medical treatment, the risk of death is about 50% at a dose of 4-5 Sv; with the best medical treatment then it takes almost 8 Sv (800 rem) to reach a 50% fatality rate. And by the time a person reaches a dose of about 9-10 Sv (900-1000 rem) the fatality rate is 100%.

Dose from a dirty bomb attack

The next question to ask is what level of exposure will people receive in the event of an RDD attack – and the answer might surprise you.

Bombs car inspection

Say a terrorist group steals a high-activity source – 100 TBq (2700 Ci) of cobalt-60 (Co-60) and scatters it across about 1 hectare (about 2.5 acres) of land. The radiation dose rate on this surface will be about 100 mSv/hr (10 rem/hr). The majority of people who are not rescued by the 24-hour point will probably not survive their ordeal – this means that the great majority of people exposed to radiation from this event will not receive a life-endangering radiation dose. Not only that, but a person would have to spend at least 2 hours on this site to have even a 1% risk of developing cancer over the next few decades. Thus, we can see that an attack such as this does not pose a tremendous risk to human health and safety.

The real risks

So – if radiological terrorism isn’t a huge health risk, then what can it do? FukushimaThe biggest impact might well be due to our lack of understanding – people’s exaggerated fears of radiation can easily lead to unnecessary evacuations and needlessly stringent cleanup standards. And – as we saw in Japan, where around 1600 people died while evacuating the areas near to Fukushima (compared to zero predicted deaths due to radiation exposure over the short or long term) – evacuation carries with it some risk. As happened in Japan, an evacuation could well lead to more deaths than would result from staying in place.

With regards to cleanup standards, our fears are going to drive us to cleaning up to levels far
below what would be called for by the actual health risks that contamination would pose. We’ve already seen that it takes much more radiation than most would expect to cause health problems – this means that even apparently frighteningly high levels of contamination pose very little risk. But telling many people that low levels of contamination are harmless is sort of like telling a parent that smoking a single cigarette won’t harm their 5-year old. Even if factually true, there aren’t likely to be any takers.

Thus, the real risks from a radiological attack are likely to not be the health risks, but the risks that ensue from fear and misunderstanding. Because of our worries about health effects we might find ourselves facing the risks of evacuation from a contaminated – but not dangerous – area. And these same fears might lead us to needlessly isolate and deny access to areas that would be safe to enter, not to mention spending tens to hundreds of millions of dollars on years-long cleanup projects that might add little – if any – public health benefits.

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Andrew Karam is a radiation safety expert with 35 years of experience, beginning with 8 years in the US Navy’s Nuclear Power Program that included 4 years on an attack submarine. He has published over two dozen scientific and technical papers and is the author of 16 books and several hundred articles for general audiences. He has worked on issues related to radiological and nuclear terrorism for over 10 years.