Thursday, April 19, 2012

18 March 2011 – Humans and risk assessment


As of this morning [18 March 2011], the casualty count in Japan from last Friday’s tsunami stands at 6539.  As another 10,250 persons are still listed as missing, the death toll is almost certain to climb.  These numbers place last week’s event ahead of the 1995 Kobe earthquake in Japan’s annals of lethal disasters.  380,000 people are still in 2200 shelters; 100,000 of them are evacuees from the area surrounding the Fukushima nuclear power plant, where workers are still attempting to bring the situation at stricken reactors and spent-fuel cooling ponds under control.

A few years ago, one of my esteemed colleagues published a paper entitled “Reflections on the Proliferation of Threats”, the core argument of which was that governments display a lamentable tendency to conflate threats driven by human intention with challenges deriving from the often very deadly, but quite insensate, environment in which we live.  One of the chapters of this note, entitled “A sense of proportion”, focussed more closely on a peculiarity of human nature: how very bad we can be at assessing risk.  He offered urban mortality rates as a case in point.  According to a study that had been cited by the IPCC, as a consequence of climate change New York City could be expected to experience an additional 500-1000 deaths due to heat over the period 2000-2050.  This amounts to 10-20 climate-change-related deaths per year for the Big Apple.  Data from the Centres for Disease Control and New York’s own Department of Public Health offer some perspective on that number.  Of the more than 55,000 people who died in NYC in 2006, for example, more than 1000 died from complications from diabetes, more than 1500 from alcohol-related causes, and 1000 in infancy.  100 people die every year in New York in construction accidents - and yet New Yorkers still build buildings.  21,000 die from heart disease, and 13,000 from cancer,(Note A) and yet New Yorkers still eat Big Macs and smoke Marlboros.  Such figures, the paper notes, puts the risk of excess mortality from climate change into appropriate context.(Note B)

I raise the issue of risk assessment in the context of the death toll from last week’s tsunami because of the ongoing drama over events at the Fukushima nuclear power plant and the media-driven frenzy over radiation fears, both in Japan (where at least there is some factual basis for worry, however slender it may be) and elsewhere around the world (where there is no basis whatsoever for the panic).  As I write this, people in Canada and the US are emptying pharmacies of potassium iodide pills, and you can’t get a Geiger counter for love or money.  So let’s take a look at how big the risk really is, shall we?

According to World Nuclear News, the normal annual allowable radiation dose for nuclear power plant workers is 20 millisieverts (mSv) per year; after receiving that much radiation, no further nuclear activities are permitted.  In practice, most workers receive much, much less.  In emergency situations, that limit may be increased 100 mSv.  This is the point at which health effects from exposure become possible.  To make this more clear, below 100 mSv per year, there is no detectable statistical relationship between radiation exposure and human health; above this level, a statistical relationship begins to become apparent.  Due to the scale of the disaster at Fukushima and the importance of controlling the situation, Japan’s Nuclear and Industrial Safety Agency has allowed the maximum exposure for on-site personnel to be increased to 250 mSv.
How bad is that?  Well, as of yesterday, one week into the crisis, this is how bad it was:

·         One Tepco worker working within the reactor building of Fukushima Daiichi unit 3 during “vent work” was taken to hospital after receiving radiation exposure exceeding 100 mSv, a level deemed acceptable in emergency situations by some national nuclear safety regulators.

·         Nine Tepco employees and eight subcontractors suffered facial exposure to low levels of radiation. They did not require hospital treatment.

·         Two policemen were decontaminated after being exposed to radiation.

·         An unspecified number of firemen who were exposed to radiation are under investigation. (Note C)

Yes, you read that right.  One Tepco worker has received a higher than 100 mSv dose.  That’s it.  That’s all.

How about radiation levels?  Well, a couple of days ago the Tokyo office of Denphone has set up a web-enabled real-time radiation monitor showing 4-hour, 24-hour, and 1-week radiation level readings.  Here’s the 1-week chart:
Figure 1 – Denphone Tokyo Realtime radiation monitoring chart; March 17-18 2011

For the past two days the average radiation level at the Denphone office in Tokyo has been below 30 micro-Roentgens per hour; the max has not exceeded 50, and the levels are dropping.  Normal background radiation, by the way, is 23 micro-Roentgens per hour. (Sieverts is the modern unit replacing Roentgen-equivalent-man, or REMs).  If radiation levels were to remain at 30 micro-Roentgens per hour, the annual additional dose a Tokyo resident would receive would be 61 milliRems or .061 Rems.  Since 1 Sievert is 100 Rems, this would be an additional annual dose of 0.61 mSv, or .0016 mSv per day.

To put that into perspective, consider the following:

·         sleeping next to another human for 8 hrs: .0005 mSv.  So the additional annual dose rate would be the same as sleeping next to 3 humans for 8 hours per day.

·         a mammogram is 3 mSv

·         a chest CT scan is 6-18 mSv

·         cosmic radiation at sea level is .24 mSv/year

·         terrestrial radiation (from the ground) is .28 mSv/year

·         radiation from the granite in the US Capitol Building: .85 mSv/year

·         airline crew on New York - Tokyo runs accumulate an additional 9 mSv/year

·         smoking 1.5 packs of cigarettes per day: 18-65 mSv per year

In other words, someone who smokes a pack and a half a day will receive up to 100 times more excess radiation per year than the folks in Tokyo are absorbing at present.  To say nothing of the further dangers of smoking, of course.

Radiation is a complicated phenomenon and is present in so much of the world around us that we never think about it.  For example, the dose from eating a banana is .0001 mSv.  So if you eat a banana a day, you’re voluntarily absorbing more radiation every year than you would get from 7 dental X-rays.(Note D)

How about North America?  Are we in any danger?  Well, there’s a network of radiation detectors in the US (and you can join it, if you want to, and if you can buy a real-time web-enabled Geiger counter, which at present you can’t because the companies that make them are sold out).  Geiger counters measure radiation in counts-per-minute (CPM) of alpha and beta particles.  The normal background level is 25-75 CPM.  Here’s the US as of 7:04 EST this morning:

Figure 2 – Realtime radiation results for the continental US as of 0404 PST, 18 March 2011

The numbers on the West Coast are revealing; 16-34 CPM, low on the normal range for background radiation. (2004 is the patent date)  Why is Denver so high, you ask?  Probably because of its altitude; there’s less atmosphere to block cosmic radiation.

So I’d reflect before popping too many potassium iodide pills.  They work by filling your thyroid gland with non-radioactive iodine so that it can’t absorb highly radioactive iodine-131 - but the potential radiation from Fukushima, if any ever gets here, won’t be in the form of I-131 anyway.  Which sort of makes you wonder why US Surgeon General Regina Benjamin told people to stock up on them...but that’s a problem for another day.

Bottom line, there has been no significant radiation from the Fukushima disaster to reach North America.  Additional radiation levels in Tokyo are two orders of magnitude lower than the radiation to which the average Japanese is exposed from cigarette smoking.  And even in the heart of the crisis, at the Fukushima power plant itself, there has to date only been one individual exposed to more than 100 mSv of radiation - and he absorbed less than he would if he were a 3-pack-a-day man.  Could it get worse?  Yes, of course it could.  But so far it hasn’t.  A meltdown, partial or complete, is possible.  “Chernobyl” (let alone “The China Syndrome”) is not.

Earlier this morning, Japan rated the Fukushima situation as “equivalent to 3-Mile Island”, which - as Greenpeace, the Union of Concerned Scientists, CNN and other media outlets keep reminding us - was the “worst nuclear accident in US history”.(Note E)  There were no deaths or injuries either at the plant or in the local community as a result of the 3-Mile Island partial meltdown.(Note F)  As “worst accidents” go, that’s not so bad - especially when you consider that, according to the CDC mortality data reported in Peter’s paper, it is statistically probable that 131 Americans will die in traffic accidents, and 34 in gun

Over the past week, the only death at the Fukushima power plant was a crane operator who succumbed to injuries received in the initial earthquake.  Meanwhile, 25 of the 100,000 people evacuated from the Fukushima area have died in the shelters to which they were moved.  Sometimes the cure is worse than the disease.  Idiotic headlines comparing Fukushima to Chernobyl or evoking the dreaded “China Syndrome” aren’t helpful, and they distract scarce recovery efforts from the real problems.  And, depressingly, they show how bad people continue to be at assessing probabilities, costs and risks. 

Now, to go buy a LottoMax ticket!



A) See Peter Archambault, Reflections on the Proliferation of Threats, DRDC CORA TN 2009-020, June 2009, 9-10.
B) The study predicting excess heat-related mortality (Kalkstein and Greene, 1997) assumed that the IPCC model predictions for future temperature regimes were accurate and that temperatures would continue to rise.  The average global temperature has in fact fallen since Kalkstein and Greene published their study.
D) This is because bananas, as we all know, are a major source of potassium, and potassium-40 is a highly radioactive isotope.  Crates of bananas regularly set off radiation detectors at US ports and customs facilities.  By the way, if radiations cares you, then stay the hell away from Brazil Nuts; pound for pound, they’re about 30 times as radioactive as bananas.
E) []
F) [].