In a conflagrant episode of Things You Might Not Know, host Tom Scott explains exactly why fairly regular explosions occur underneath the manhole covers in London. Because he couldn’t demonstrate his theory within urban confines, he took it out to an open field where Darkstar Pyrotechnics set up similar conditions to create an explosion of their own.
Every month or so, somewhere in London, a manhole explodes. It’s so common that it doesn’t make the news unless it’s spectacular or someone gets injured. Here’s why, complete with gratuitous pyrotechnics.