One of the more frightening scenarios that civil defence teams worry about is the possibility that a bomb contaminated with radioactive material would be detonated in a heavily populated area.
Various research teams have considered this problem and come to similar conclusions–that the actual threat to human health from such a device is low. Some even claim that terror groups must have come to a similar conclusion which is why we’ve not been on the receiving end of such an attack. The panic such a device would cause is another questions.
Today Theodore Liolios from a private institution called the Hellenic Arms Control Center in Thessaloniki in Greece, goes through the figures.
He says the most likely material to be used in such an attack is Cesium-137, widely used throughout the developed and developing world as a source for medical therapies.
The unstated implication is that it would be relatively easy to get hold of this stuff from a poorly guarded hospital. Exactly this happened in Goiania in Brazil when an abandoned hospital was broken into and its supply of cesium-137 distributed around the surrounding neighbourhoods. The incident left 200 people contaminated. Four of them died.
But a dirty bomb would not be nearly as lethal. The trouble with them (from a terrorist’s point of view, at least) is that distributing radioactive material over a large area dramatically reduces the exposure that people receive. Particularly when most could be warned to stay indoors or be evacuated (unlike the Goiania incident in which most people were unaware they were contaminated).
Liolios calculates that anybody within a 300 metre range of a dirty bomb would increase their lifetime risk of cancer mortality by about 1.5 per cent. And then only if they were unable to take shelter or leave the area. That’s about 280 people given the kind of densities you expect in metropolitan areas.
And he goes on to say that it is reasonable to assume that a cesium-137 dirty bomb would not increase the cancer mortality risk for the entire city by a statistically significant amount.
But the terror such a device might cause is another question. Liolios reckons that current radiation safety standards would mean the evacuation of some 78 square kilometres around ground zero. That would affect some 78,000 people, cost $7.8m per day to evacuate and some $78m to decontaminate.
That seems a tad conservative but however it is calculated, it may turn out to be chickenfeed compared to the chaos caused by panic, which may well result in more deaths than the bomb itself could claim. How to calculate the effect of that?
Ref: arxiv.org/abs/0902.3789: The Effects of Using Cesium-137 Teletherapy Sources as a Radiological Weapon