Why Do We Use a Dumbass Unit to Measure Explosions?

By Chris Mills on at

There’s been some confusion over the size of yesterday’s explosion in China’s Tianjin province, with some people mistakenly thinking it was the largest non-nuclear explosion of all time. It was not — that honour goes to the Russians — and you can partly blame our stupid system of measurement for the mistake.

An explosion is a release of energy, and would probably best be measured in a unit of energy, like joules. Instead, we measure the size of the explosion based on how many tons of TNT it would take to produce a similarly-sized explosion: when the news talks about a ‘7-tonne’ explosion, it means that seven tonnes of TNT would produce the same magnitude explosion.

This is a bad unit of measurement for a bunch of reasons. It’s arbitrary — why pick TNT over dynamite? — and also misleading: one gram of TNT, or trinitrotoluene, has an explosive energy of somewhere between 2000-6000 joules, depending on the composition and density. To make it more useful as a quasi-scientific unit, that energy level was fixed at 4686 joules per gram, making an arbitrary standard even more so.

Explosions also don’t generate a consistent type of wave: an explosion of a block of TNT, for example, behaves very differently to a fuel-air bomb, which in turn behaves differently to a meteorite impact; yet, all are measured relative to a chemical compound discovered by a German chemist two centuries ago.

Worst of all, the way people say it — as a ‘five-kiloton explosion’ — is confusing and awful, because we already have a unit called the ton. Only, that one isn’t connected to explosives. Let’s come up with a less random and more scientific unit of measurement for explosives instead. And, if we could kill the imperial system while we’re at it, that would be great.

Image: Andrew Kuznetsov/Flickr (cropped)