In a conflagrant episode of Things You Might Not Know, host Tom Scott reveals exactly why fairly regular explosions occur underneath the manhole covers in London. Because he couldn’t prove his theory within an urban environment, he took it out to an open field where Darkstar Pyrotechnics set up comparable conditions to produce 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.