Rhodri Marsden: It's a chance in 21 trillion but that doesn't stop me worrying

Space debris
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A couple of years ago, a Cambridge University professor recommended that children be given probability lessons to help them to assess the concept of risk and make better life choices.

But as the proud owner of an O-level in statistics, I know that studying binomial distribution curves hasn't stopped me catastrophising about unlikely events. After hearing Nasa's statement that there was a one in 3,200 chance of the rapidly descending UARS satellite injuring someone, I immediately imagined 6.5 tons of redundant machinery slamming into my flat as I was doing some light dusting.

Nasa may be trying to raise awareness of space debris, but it's merely given me another potential method of death to ponder while I cross the busy A24 wearing headphones and texting my mate Keith. Hang on, though. It was a one in 3,200 chance of it injuring anybody; the chance of it injuring me alone is one in 21 trillion: much better, but a hard number to quantify. A table of probabilities I found online informed me that I'm far more likely to have my foot sliced off by a lawnmower; this provided some relief, as I don't own a lawnmower.

But expert words of reassurance failed to stop us glancing up nervously to the sky. "Look how much of the earth is covered in water!" said one scientist, clearly forgetting about anyone who might have gone for a refreshing swim. Then we were told that UARS would break up into bits, and we'd be looking at colliding only with a 160kg chunk – but that is still the combined weight of Ant and Dec. And while Nasa would be able to give a better idea of the impact location two hours before it slammed into the planet, that would be only to the nearest 10,000km. Oh.

Only one person has ever been hit by space debris. It bounced harmlessly off her shoulder – but when interviewed yesterday, she advised her fellow humans to "run out of the way". Various plans are afoot to tackle the problem at source, including an Italian spacecraft with robot arms to scoop up the debris (which really should be made into feature -length children's cartoon), but that's too late for UARS. Of course, by the time you read this, it should have landed. If it killed anyone, this will be seen as a spectacularly misjudged piece of comment, unless it's me – in which case consider it my obituary.