How much risk is OK?

U.S. Military Combined Forces Medical Responses Exercise 2002Earlier this week I was lucky enough to be asked to join a 1-day workshop on some legal aspects of responding to a radiological emergency, hosted by the National Association of County and City Health Officials (NACCHO – pronounced “natch-o” in case you’re wondering). There were a number of questions we discussed but much of it came down to if or when the government has the authority to detain people who are contaminated or to decontaminate them against their wishes. There were a number of aspects to this discussion – enough for a couple postings. But an over-arching question concerned some of the terms that were used – in particular, what does the law mean when it uses terms like “risk,” “danger,” or “significant?”

Let’s take one example – there was general agreement that it could be acceptable to hold a person (or a group of people) for decontamination if they were to pose a substantial risk to public health. But who makes this determination and what do they base it on?

Consider the possibility of a health physicist being asked to give testimony to a judge in favor of detaining a person (or people) covered with radioactive contamination. One way to approach this would be to point out that, according to the Linear No Threshold hypothesis of radiation dose-response, every added bit of radiation exposure adds risk. Thus, letting a contaminated person walk the streets adds to the risk of every person encountered, even if only a little bit. But given that there is incremental risk, why not err on the side of caution and simply hold all of those who are contaminated until they’re cleaned off? After all, who could object to a shower and a change of clothes? On the other hand, who has the right to force someone to disrobe (and throw away their clothing) and shower before heading home? The bottom line is that we have to balance the risk to society versus individual rights – in a society that already accepts the risks of driving, eating fast food, and so forth.

On the other hand, I can also argue that the Nuclear Regulatory Commission has already answered this question, although somewhat indirectly. Consider nuclear medicine patients who, after being injected with radioactivity, are often sent home. The NRC seems to have decided that nuclear medicine patients do not pose a substantial risk to public health – if so, then how can we justify detaining someone who has less radioactivity on their clothing and skin than a nuclear medicine patient carries within their body?

The problem is the fuzziness of the operative words. Take risk for example – I’m sitting in a chair right now typing away and I’m at risk. The people in the apartment above mine could fall through the floor, a truck could careen into my apartment, we could have a fire in my building – any of a number of things could happen to me as I sit here typing away and all of them are pretty unlikely. So I’m at risk – the question is how substantial that risk is. In my case the risk of sitting in front of a computer is pretty low – maybe a single chance in many millions that ill will befall me. So do we need to take protective measures to protect me against the chance that a truck might drive into my living room? Actually, we have to some extent. Building codes help to protect me against the risk of structural collapse and traffic laws help to protect me from stray trucks – not perfectly, of course, because buildings still collapse and trucks still run off-course. But the residual risks are low enough that I’m not too concerned. So yes – I am at risk from any number of things, but those risks are not substantial enough for me (or most people) to worry about. Similarly, the NRC has decided that the risk posed by nuclear medicine patients is not substantial enough to worry about.

I guess that brings up the question of what constitutes a substantial risk. Probably most of us would agree that a 10% risk of death would be far too high, and even a 1% risk would also be a bit on the high side for most of us (even though that’s about the risk we face from driving). Similarly, I’m guessing that most of us would agree that it doesn’t make much sense to spend money to mitigate a risk of one in a billion. And many would even consider one chance in a million to be too skimpy to warrant a huge investment to prevent. So somewhere between one chance in a million and one chance in a thousand is where society starts to consider a risk to be “substantial” enough to warrant taking preventative measures.

So – do we confine people who are contaminated after a radiological accident or not? Do they pose a substantial threat to public health?

From my perspective as a scientist it’s hard to give a unique and unambiguous answer to this question because what I consider to be “substantial” might horrify some and leave others blasé. But give me a solid target to aim at – a number that can be calculated or measured – and I’m on much firmer ground. For example, the NRC guidance on nuclear medicine patients is based on keeping radiation dose to members of the public lower than 100 mrem – give me a number like that and I can tell you what level of contamination will produce that dose; anything lower than that level would be acceptable and anyone with higher levels of contamination would need to be held for decon. But lacking a number – giving me fuzzy words like “substantial” and “danger” – takes away my tools as a scientist and makes it harder to answer objectively.

So let’s recap a little bit. The fundamental question is whether or not the government can (or should) detain contaminated people after a radiological event. But before we can make that decision we have to decide when it’s acceptable to deprive someone – even briefly – of their liberty. This would seem acceptable only if the risk to society (in this case, public health) is high enough to warrant the detention. But since so many people have different subjective views of what constitutes a “substantial risk” it might be better to develop a numerical standard – such as the NRC’s standard for releasing nuclear medicine patients.

So – to wrap this up, I should also note that there are no existing standards to help address this problem. So the first step might be to ask an advisory body to develop a numerical recommendation: In the aftermath of a radiological emergency, at what point – at what dose to the public – do we restrict people for the overall good of society? Once we have a recommended standard to hang our hat on the rest could fairly easily fall into place.

2 Responses to “How much risk is OK?”

  1. William Lorenzen March 18, 2013 at 12:17 PM #

    The analogy to Nuclear Medicine has some validity as far as the “creation” of a number that could be assigned to an “acceptable” risk however what is missing from the discussion is the nature of the contamination and its imposing risk. Nuclear Medicine is conducted with short half-life nuclides that are injected into a patient and thus the transfer and subsequent exposure to other is minimal. With a dirty bomb there would be external contamination of a long-lived isotope on clothing that could result in the material becoming airborne and inhaled by people. If the material were an alpha emitter like Americium 241 the health (and risk) consequences could be substantial.

    • Dr. Y April 14, 2013 at 7:34 PM #

      Sorry to be late replying to your comments – you’ve got a great point about nuclear medicine and the nature of the nuclides. I agree that it’s not a completely accurate comparison – contaminated people from an RDD attack versus nuclear medicine patients – but it’s at least a starting point. And it should be possible to develop guidelines that take into account the difference between external gamma exposure from a nuke med patient versus the internal dose from inhaling airborne alpha from a contaminated person.

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