Smog a bigger risk in Japan than nuclear radiation

People are often irrational when it comes to assessing risks.

As a science teacher, part of my job is performing risk assessments, so this is fairly well-trodden territory for me. Non-science staff often assume that the most hazardous activities are those involving chemicals. After all, isn't it dangerous dealing with acids and bases?

Actually no – the most dangerous piece of apparatus turns out to be the tripod we use to hold items up while we heat them. Most of our injuries are burns inflicted by someone attempting to pick up a hot tripod!

Why, then, do we miss that one and concentrate our efforts on the chemicals? I think it's because for many people chemicals are an unknown quantity, whereas the dangers of picking up a red-hot piece of metal are well known and understood to everyone. Somehow, a familiar danger seems to be less frightening; therefore we tend to ignore it, even when the statistics would lead us in a different direction.

Similarly, most people assume getting on a plane is dangerous; in reality, the most dangerous part of your next journey by plane will be crossing the road at the airport! Again, because that's a risk we face every day we tend to ignore it, assuming that the comparatively exotic activity of flying inside a pressurized metal tube is the more hazardous; in fact, the reverse is true.

A stark demonstration of this fact has been very evident over recent months as we have watched the unfolding of events at the Fukushima Daichi nuclear power plant. In the midst of the massive death and destruction of the largest tsunami in many years, perhaps on record, media attention has been on a serious but comparatively minor situation at a nuclear reactor.

Yes, you heard me – comparatively minor. Despite the media circus and the frenzy of doom-and-gloom on every television station, the vaunted radiation didn't cause one death or serious injury. In short, in the midst of incredible disaster, media focused on one thing that really wasn't that big a deal.

The problem was that magic word "meltdown." Most journalists had little or no understanding of what that actually meant; the only experience that was remotely similar was the Chernobyl disaster of 1986. And since it was the same word, the assumption was that the event would be the same.

The meltdown was the unfamiliar danger. Because of a lack of understanding, it was assumed that this was a big deal. In reality, the simple force of a vast wall of sea water smashing its way inland – and then out to sea again – was a much bigger problem. But the familiar danger was ignored in favour of the exotic danger, even though the danger of radiation was never all that great.

There was recently a report of 138,000 Bq of radioactive Caesium per square metre being detected in a Tokyo park. Panic ensued, perhaps not surprisingly. The trouble is that this enormous number doesn't tell you the full story. You should know that there is a 4,400Bq source of radiation reading this article right now – that's the level of radioactivity caused by radioactive Potassium in your body!

138,000 Bq is not as high as you may think. The trick is to understand that the relevant number isn't the actual amount of radioactive substance present, but the dose of radiation it would deliver to humans nearby. In this case the dose works out to about 3 microsieverts per hour, which is tiny. For perspective, there is radiation everywhere (we call it "background" radiation), and that level equates to 10 microsieverts every single day. So if someone stood on that spot all day, they might receive six days worth of radiation in 24 hours; the increased risk from this level is immeasurably small.

By contrast, smog in the air in Tokyo is a major risk factor, and it won't surprise you to know that it's a known cause of cancer. What may surprise you is to discover that the risk posed by radiation contaminating the ground around the stricken nuclear reactors in Fukushima is sufficiently small that if we were to move the population from the polluted air of Tokyo and settle them in the radiation - contaminated (but comparatively smog-free) region, we'd expect to see a net DECREASE in the cancer rate.

This irrationality is a real danger. We know that climate change poses a large threat to us, not just in Australia but throughout the world; yet we irrationally oppose nuclear energy when the numbers tell us that it is safer even than Solar energy. At the same time we ignore the well-known but much greater dangers of coal-fired power stations, both for now and for the future.