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Sitting outside a bar at the weekend, I noticed something coming out of my bag that looked and also smelled a lot like a naked flame. Ordinarily, I’d have thought it was my vape, but it couldn’t have been, since that was in my mouth. So I put it down to a mirage created by the clement weather, and thought no more of it until someone much smarter than me said: “Your bag’s on fire.”

It was my remarkable good fortune to be sitting opposite a friend who is a chemistry teacher, and explained what had happened through a laborious sequence of rhetorical questions. What is a spare vape battery made of? What are keys made of? What happens to a lithium battery when you connect something metal to each end? What is the result of closing a circuit inside a handbag? Not only had I set my bag alight; I’d melted my keyring, which for complicated reasons held a plastic portrait of both my nieces circa 2017, and it was yet more bad luck that I was also sitting opposite my sister, who, in fairness, reacted surprisingly well to the sight of her molten children.

Opinion was divided about what to do with the lithium battery once the bag-fire had been extinguished. One person said put it in water; another said do not under any circumstances put it in water. It turned out the first person was joking, which was a risky old game, but luckily the chemistry teacher was still paying attention.

My melted younger niece is an engineering student, and took the long view: it might have been bad in a bar, and it would have been worse in a plane, but in any survival scenario where you were trying to keep warm overnight, one person carrying a powerful battery and a set of keys would be a massive hit, and that person would always be me. Anyone with a magnifying glass trying to harness the majesty of the sun would look like an amateur, and a try-hard with two dry sticks could just forget it. Yet another win for STEM expertise, and also my vaping hobby.

• Zoe Williams is a Guardian columnist